Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2018	Feb. 08, 2019	Jun. 30, 2018
Document and Entity Information
Entity Registrant Name	Editas Medicine, Inc.
Entity Central Index Key	0001650664
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 1,631,271,034.00
Entity Common Stock, Shares Outstanding		49,092,251
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 134,776	$ 146,630
Marketable securities	234,179	182,509
Accounts receivable	30	679
Prepaid expenses and other current assets	5,791	2,381
Total current assets	374,776	332,199
Property and equipment, net	40,232	39,442
Restricted cash and other non-current assets	5,378	1,619
Total assets	420,386	373,260
Current liabilities:
Accounts payable	5,327	4,020
Accrued expenses	12,813	11,049
Notes payable		7,500
Deferred revenue, current	15,712	13,238
Other current liabilities	2,048	900
Total current liabilities	35,900	36,707
Deferred revenue, net of current portion	115,614	94,725
Construction financing lease obligation, net of current portion	32,417	33,431
Other non-current liabilities	293	317
Total liabilities	184,224	165,180
Commitments and contingencies (see note 8)
Stockholders’ equity
Preferred stock, $0.0001 par value per share: 5,000,000 shares authorized; no shares issued or outstanding
Common stock, $0.0001 par value per share: 195,000,000 shares authorized; 49,028,907 and 45,025,448 shares issued, and 48,758,951 and 44,507,960 shares outstanding at December 31, 2018 and December 31, 2017, respectively	5	4
Additional paid-in capital	652,464	514,002
Accumulated other comprehensive loss	(29)	(76)
Accumulated deficit	(416,278)	(305,850)
Total stockholders’ equity	236,162	208,080
Total liabilities and stockholders’ equity	$ 420,386	$ 373,260

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Consolidated Balance Sheets
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	195,000,000	195,000,000
Common stock, shares issued	49,028,907	45,025,448
Common stock, shares outstanding	48,758,951	44,507,960

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Operations
Collaboration and other research and development revenues	$ 31,937	$ 13,728	$ 6,053
Revenue type	us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Operating expenses:
Research and development	$ 90,654	$ 83,159	$ 56,979
General and administrative	55,010	50,502	46,262
Total operating expenses	145,664	133,661	103,241
Operating loss	(113,727)	(119,933)	(97,188)
Other income (expense), net
Other income (expense), net	328	587	(57)
Interest income (expense), net	3,445	(978)	62
Total other income (expense), net	3,773	(391)	5
Net loss	(109,954)	(120,324)	(97,183)
Accretion of redeemable convertible preferred stock to redemption value			(47)
Net loss attributable to common stockholders	$ (109,954)	$ (120,324)	$ (97,230)
Net loss per share attributable to common stockholders, basic and diluted	$ (2.33)	$ (2.98)	$ (3.02)
Weighted-average common shares outstanding, basic and diluted	47,097,735	40,323,631	32,219,717

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidated Statements of Comprehensive Loss
Net Loss	$ (109,954)	$ (120,324)	$ (97,183)
Other comprehensive loss:
Unrealized loss on marketable securities	47	(76)
Comprehensive loss	$ (109,907)	$ (120,400)	$ (97,183)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Redeemable Convertible Preferred Stock.	Common Stock. Initial Public Offering	Common Stock. 2017 March Offering	Common Stock. 2017 December Offering	Common Stock. January 2018 ATM Offering	Common Stock. November 2018 ATM Offering	Common Stock.	Additional Paid-In Capital Initial Public Offering	Additional Paid-In Capital 2017 March Offering	Additional Paid-In Capital 2017 December Offering	Additional Paid-In Capital January 2018 ATM Offering	Additional Paid-In Capital November 2018 ATM Offering	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	Initial Public Offering	2017 March Offering	2017 December Offering	January 2018 ATM Offering	November 2018 ATM Offering	Total
Balance, beginning of period at Dec. 31, 2015	$ 199,915
Balance, beginning of period (in shares) at Dec. 31, 2015	64,817,359
Statements of Redeemable Convertible Preferred Stock
Accretion of redeemable convertible preferred stock to redemption value	$ 47																				$ 47
Conversion of redeemable convertible preferred stock into common stock upon closing of the initial public offering	$ (199,962)
Conversion of redeemable convertible preferred stock into common stock upon closing of the initial public offering (in shares)	(64,817,359)
Balance, beginning of period at Dec. 31, 2015													$ 5,234	$ (88,348)							(83,114)
Balance, beginning of period (in shares) at Dec. 31, 2015							3,233,638
Statement of Stockholders' Equity (Deficit)
Accretion of redeemable convertible preferred stock to redemption value													(47)								(47)
Conversion of redeemable convertible preferred stock into common stock upon closing of the initial public offering							$ 3						199,954	5							199,962
Conversion of redeemable convertible preferred stock into common stock upon closing of the initial public offering (in shares)							24,929,709
Conversion of preferred stock warrant to common stock warrant upon closing of initial public offering													376								376
Issuance of common stock from public offering, net of issuance costs		$ 1						$ 97,487								$ 97,488
Issuance of common stock from public offering, net of issuance costs (in shares)		6,785,000
Exercise of common stock warrant (in shares)							19,271
Exercise of stock options													233								233
Exercise of stock options (in shares)							58,915
Vesting of restricted common stock and common stock subject to repurchase													11								11
Vesting of restricted common stock and common stock subject to repurchase (in shares)							431,018
Vesting of founder shares													8,315								8,315
Vesting of founder shares (in shares)							360,580
Stock-based compensation expense													8,566								8,566
Net loss														(97,183)							(97,183)
Balance, end of period at Dec. 31, 2016							$ 4						320,129	(185,526)							134,607
Balance, end of period (in shares) at Dec. 31, 2016							35,818,131
Statement of Stockholders' Equity (Deficit)
Issuance of common stock from public offering, net of issuance costs									$ 96,685	$ 57,223							$ 96,685	$ 57,223
Issuance of common stock from public offering, net of issuance costs (in shares)			4,600,000	2,265,500
Issuance of common stock for repayment of notes payable													14,823								14,823
Issuance of common stock for repayment of notes payable (in shares)							750,617
Exercise of stock options													1,768								1,768
Exercise of stock options (in shares)							272,210
Vesting of restricted common stock and common stock subject to repurchase													4,096								4,096
Vesting of restricted common stock and common stock subject to repurchase (in shares)							561,118
Vesting of founder shares													3,989								3,989
Vesting of founder shares (in shares)							240,384
Stock-based compensation expense													15,289								15,289
Unrealized losses on marketable securities															$ (76)						(76)
Net loss														(120,324)							(120,324)
Balance, end of period at Dec. 31, 2017							$ 4						514,002	(305,850)	(76)						208,080
Balance, end of period (in shares) at Dec. 31, 2017							44,507,960
Statement of Stockholders' Equity (Deficit)
Issuance of common stock from public offering, net of issuance costs					$ 1						$ 48,493	$ 28,387							$ 48,494	$ 28,387
Issuance of common stock from public offering, net of issuance costs (in shares)					1,429,205	1,107,000
Issuance of common stock for repayment of notes payable													22,030								22,030
Issuance of common stock for repayment of notes payable (in shares)							636,526
Issuance of common stock for asset purchase agreement													1,942								1,942
Issuance of common stock for asset purchase agreement (in shares)							56,099
Exercise of stock options													10,328								10,328
Exercise of stock options (in shares)							749,294
Vesting of restricted common stock and common stock subject to repurchase													4								4
Vesting of restricted common stock and common stock subject to repurchase (in shares)							174,595
Vesting of founder shares													2,418								2,418
Vesting of founder shares (in shares)							72,000
Stock-based compensation expense													24,180								24,180
Purchase of common stock under benefits plans													680								680
Purchase of common stock under benefits plans (in shares)							26,272
Unrealized losses on marketable securities															47						47
Net loss														(109,954)							(109,954)
Balance, end of period at Dec. 31, 2018							$ 5						$ 652,464	(416,278)	$ (29)						236,162
Balance, end of period (in shares) at Dec. 31, 2018							48,758,951
Statement of Stockholders' Equity (Deficit)
Cumulative Effect of New Accounting Principle in Period of Adoption														$ (474)							$ (474)

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flow from operating activities
Net loss	$ (109,954)	$ (120,324)	$ (97,183)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	26,598	23,364	16,881
Depreciation	3,254	2,683	1,202
Non-cash research and development expenses	14,442	14,500	10,000
Re-measurement of warrant to purchase redeemable securities			87
Non-cash investment in equity securities	(3,667)
Other non-cash items, net	(3,268)	(300)	869
Changes in operating assets and liabilities:
Accounts receivable	649	(591)	931
Prepaid expenses and other current assets	(3,410)	(596)	(1,306)
Other non-current assets	(92)	2	2,246
Accounts payable	1,780	(1,515)	3,251
Accrued expenses	4,042	(8,334)	11,841
Deferred revenue	22,889	81,707	935
Other current and non-current liabilities	1,030	(13)
Net cash used in operating activities	(45,707)	(9,417)	(50,246)
Cash flow from investing activities
Purchases of property and equipment	(4,754)	(2,059)	(3,493)
Proceeds from the sale of equipment	37	15	20
Purchases of marketable securities	(459,370)	(375,266)
Proceeds from maturities of marketable securities	411,000	193,500
Net cash used in investing activities	(53,087)	(183,810)	(3,473)
Cash flow from financing activities
Proceeds from offering of common stock, net of issuance costs	76,789	154,143	97,488
Proceeds from exercise of stock options	10,328	1,755	233
Payments on construction financing lease obligation	(857)	(764)	(560)
Issuances of common stock under benefit plans	680
Payments of notes payable		(600)
Net cash provided by financing activities	86,940	154,534	97,161
Net increase (decrease) in cash, cash equivalents, and restricted cash	(11,854)	(38,693)	43,442
Cash, cash equivalents, and restricted cash, beginning of period	148,249	186,942	143,500
Cash, cash equivalents, and restricted cash, end of period	136,395	148,249	186,942
Supplemental disclosure of cash and non-cash activities:
Accretion of redeemable convertible preferred stock to redemption value			47
Fixed asset additions included in accounts payable and accrued expenses	659	623	130
Reclassification of warrants to additional paid in capital			376
Conversion of preferred stock to common stock upon closing of the initial public offering			199,962
Reclassification of liability for common stock subject to repurchase	4	11	$ 11
Offering expenses included in accounts payable and accrued expenses	92	235
Issuance of common stock for repayment of notes payable	22,030	$ 14,823
Issuance of common stock for asset acquisition	$ 1,942

Nature of Business	12 Months Ended
Nature of Business	Dec. 31, 2018
Nature of Business
Nature of Business	1. Nature of Business Editas Medicine, Inc. (the “Company”) is a clinical stage company dedicated to treating patients with genetically addressable diseases. The Company was incorporated in the state of Delaware in September 2013. Its principal offices are in Cambridge, Massachusetts. Since its inception, the Company has devoted substantially all of its efforts to business planning, research and development, recruiting management and technical staff, and raising capital. The Company has primarily financed its operations through various equity and debt financings, including the initial public offering of its common stock (the “IPO”), its follow-on public offerings of its common stock in March 2017 and December 2017, its at-the-market offerings of its common stock in January 2018 and November 2018, and private placements of preferred stock, payments received under a research collaboration with Juno Therapeutics, Inc., a Celgene company that is a wholly-owned subsidiary of Celgene Corporation (“Juno Therapeutics”), and from payments received under a strategic alliance and option agreement with Allergan Pharmaceuticals International Limited (“Allergan”). The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any drug product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and ability to transition from pilot-scale manufacturing to large-scale production of products. Liquidity In February 2016, the Company completed its IPO and received aggregate net proceeds of approximately $97.5 million. In March 2017, the Company completed a follow-on offering and received net proceeds of approximately $96.7 million (the “2017 March Offering”). In December 2017, the Company completed another follow-on offering and received net proceeds of approximately $57.2 million (the “2017 December Offering”). The Company completed at-the-market offerings in January 2018, receiving net proceeds of approximately $48.5 million (the “January 2018 ATM Offering”), and an at-the-market offering November 2018, receiving net proceeds of approximately $28.4 million (the “November 2018 ATM Offering”). The Company has incurred annual net operating losses in every year since its inception. The Company expects that its existing cash, cash equivalents, and marketable securities at December 31, 2018 and anticipated interest income will enable it to fund its operating expenses and capital expenditure requirements for at least the next 24 months following the date of this Annual Report on Form 10-K. The Company had an accumulated deficit of $416.3 million at December 31, 2018, and will require substantial additional capital to fund its operations. The Company has never generated any product revenue. There can be no assurance that the Company will be able to obtain additional debt or equity financing or generate product revenue or revenues from collaborative partners, on terms acceptable to the Company, on a timely basis or at all. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial condition.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of significant accounting policies

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of Editas Medicine, Inc. and its wholly owned subsidiary, Editas Securities Corporation, which is a Delaware subsidiary created to buy, sell and hold securities. All intercompany transactions and balances have been eliminated.

Basis of Presentation

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Reclassification

Certain prior period amounts have been reclassified for consistency with the current period presentation. These reclassifications had no effect on previously reported results of operations.

Use of Estimates

The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to revenue recognition, accrued expenses, stock-based compensation expense and deferred tax valuation allowances. The Company bases its estimates on historical experience and other market-specific or relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.

Fair Value of Financial Instruments

ASC Topic 820, Fair Value Measurement (“ASC 820”), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances.

ASC 820 identifies fair value as the exchange price representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three‑tier fair value hierarchy that distinguishes between the following:

Level 1 – Quoted market prices in active markets for identical assets or liabilities.

Level 2 – Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates, and yield curves.

Level 3 – Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use.

To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

The carrying amounts reflected in the consolidated balance sheets for cash and cash equivalents, restricted cash, marketable securities, accounts receivable, prepaid expenses and other current assets, accounts payable, accrued expenses, and other current liabilities approximate their fair values, due to their short‑term nature. The Company believes that the carrying value of the notes payable approximates their fair value based on Level 3 inputs including a quoted rate.

Cash, Cash Equivalents, and Restricted Cash

The Company considers all highly liquid investments purchased with original maturities of 90 days or less at acquisition to be cash equivalents. Cash and cash equivalents include cash held in banks and amounts held in money market funds and U.S. government-backed securities.

The Company had restricted cash of $1.6 million held in the form of money market accounts as collateral for the Company’s construction financing lease obligation as of December 31, 2018, 2017 and 2016.

The following table presents cash, cash equivalents, and restricted cash as reported on the consolidated balance sheets that equal the total amounts on the consolidated statements of cash flows (in thousands):


	Year Ended
	As of December 31,
	2018		2017		2016
Cash and cash equivalents	$	134,776	$	146,630	$	185,323
Restricted cash included in "Restricted cash and other non-current assets"		1,619		1,619		1,619
Total	$	136,395	$	148,249	$	186,942

Marketable Securities

The Company classifies marketable securities with a remaining maturity when purchased of greater than three months and less than one year from the balance sheet date as current. Marketable securities with a remaining maturity date greater than one year are classified as non-current. The Company classifies all of its marketable securities as available-for-sale securities. Available-for-sale securities are carried at fair value with the unrealized gains and losses included in other comprehensive loss as a component of stockholders’ equity (deficit) until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the of the underlying security. Realized gains and losses are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary.” To determine whether an impairment is other-than-temporary, the Company considers whether it has the ability and intent to hold the investment until a market price recovery and considers whether evidence indicating the cost of the investment is recoverable outweighs evidence to the contrary. The Company does not intend to sell the investments and it is not likely that the Company will be required to sell the investments before recovery of their amortized cost bases, which may be maturity.

Accounts Receivable

The Company makes judgments as to its ability to collect outstanding receivables and provides an allowance for receivables when collection becomes doubtful. Provisions are made based upon a specific review of all significant outstanding invoices and the overall quality and age of those invoices not specifically reviewed. The Company's receivables primarily relate to amounts reimbursed under its collaboration agreement with Juno Therapeutics. The Company believes that credit risks associated with its collaborations partner is not significant. To date, the Company has not had any write-offs of bad debt, and the Company did not have an allowance for doubtful accounts as of December 31, 2018 and 2017.

Property and Equipment

Property and equipment consists of computers, laboratory equipment, furniture and office equipment, and leasehold improvements and is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred, while costs of major additions and betterments are capitalized. Depreciation is calculated over the estimated useful lives of the assets using the straight‑line method. The Company capitalizes laboratory equipment used for research and development if it has alternative future use in research and development or otherwise.


Asset:		Estimated Useful life
Lab equipment		5 years
Computer equipment and software		3 years
Furniture and equipment		5 years
Leasehold improvements		Shorter of useful life or remaining lease term
Building		30 years

The Company records certain estimated costs incurred and reported by a landlord as an asset and corresponding financing lease obligation on the consolidated balance sheets. See Note 8, “Commitments and contingencies,” for additional information.

Impairment of Long‑lived Assets

The Company evaluates long‑lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book values of the assets exceed their fair value. The Company has not recognized any impairment losses from inception through December 31, 2018.

Revenue Recognition

To date, the Company has primarily earned revenue under the collaboration and license agreement with Juno Therapeutics and the strategic alliance with Allergan.

The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”), effective January 1, 2018. The Company enters into collaboration agreements and certain other agreements that are within the scope of ASC 606, under which the Company licenses, may license or grants an option to license rights to certain of the Company’s product candidates and performs research and development services in connection with such arrangements. The terms of these arrangements typically include payment of one or more of the following: non-refundable, up-front fees; reimbursement of research and development costs; development, clinical, regulatory and commercial sales milestone payments, and royalties on net sales of licensed products.

Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer.

The promised goods or services in the Company’s arrangements typically consist of a license, or option to license, rights to the Company’s intellectual property or research and development services. The Company provides options to additional items in such arrangements, which are accounted for as separate contracts when the customer elects to exercise such options, unless the option provides a material right to the customer. Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer and are considered distinct when (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised good or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on its own or whether the required expertise is readily available and whether the goods or services are integral or dependent to other goods or services in the contract.

The Company estimates the transaction price based on the amount expected to be received for transferring the promised goods or services in the contract. The consideration may include fixed consideration or variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of potential payment and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected value method to estimate the amount expected to be received based on which method best predicts the amount expected to be received. The amount of variable consideration that is included in the transaction price may be constrained and is included in the transaction price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period.

The Company’s contracts often include development and regulatory milestone payments that are as assessed under the most likely amount method and constrained if it is probable that a significant revenue reversal would occur. Milestone payments that are not within the Company’s control or the licensee’s control, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. At the end of each reporting period, the Company re-evaluates the probability of achievement of such development and clinical milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect collaboration and other research and development revenues in the period of adjustment.

For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of the Company’s collaboration or strategic alliance arrangements.

The Company allocates the transaction price based on the estimated standalone selling price. The Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the stand-alone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated are consistent with the amounts the Company would expect to receive for the satisfaction of each performance obligation.

The consideration allocated to each performance obligation is recognized as revenue when control is transferred for the related goods or services. For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

The Company receives payments from its customers based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional.

Prior to ASC 606 Adoption

Revenue for the years ended December 31, 2017 and 2016 were recognized in accordance with ASC Topic 605, Revenue Recognition (“ASC 605”). Accordingly, revenue was recognized for each unit of accounting when all of the following criteria are met:

Persuasive evidence of an arrangement exists;

Delivery has occurred or services have been rendered;

The seller’s price to the buyer is fixed or determinable; and

Collectability is reasonably assured.

Amounts received prior to satisfying the revenue recognition criteria were recorded as deferred revenue. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified in current liabilities. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion.

The Company evaluated multiple‑element arrangements based on the guidance in ASC Topic 605‑25, Revenue Recognition Multiple‑Element Arrangements (“ASC 605‑25”). Pursuant to the guidance in ASC 605‑25, the Company evaluated multiple‑element arrangements to determine (1) the deliverables included in the arrangement and (2) whether the individual deliverables represented separate units of accounting or whether they must be accounted for as a combined unit of accounting. This evaluation involved subjective determinations and required the Company to make judgments about the individual deliverables and whether such deliverables were separable from the other aspects of the contractual relationship. Deliverables were considered separate units of accounting provided that the delivered item had value to the customer on a standalone basis and, if the arrangement included a general right of return relative to the delivered item, delivery or performance of the undelivered item is considered probable and substantially in the Company’s control. In assessing whether an item had standalone value, the Company considered factors such as the research, development, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considered whether the collaboration partner can use a deliverable for its intended purpose without the receipt of the remaining deliverable, whether the value of the deliverable is dependent on the undelivered item and whether there are other vendors that can provide the undelivered items.

Options were considered substantive if, at the inception of the arrangement, the Company was at risk as to whether the collaboration partner will choose to exercise the option. Factors that the Company considered in evaluating whether an option is substantive include the cost to exercise the option, the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option and the likelihood the option will be exercised. When an option was considered substantive, the Company does not consider the option or item underlying the option to be a deliverable at the inception of the arrangement and the associated option fees are not included in allocable consideration, assuming the option is not priced at a significant and incremental discount. Conversely, when an option is not considered substantive, the Company would consider the option, including other deliverables contingent upon the exercise of the option, to be a deliverable at the inception of the arrangement and a corresponding amount would be included in allocable arrangement consideration. In addition, if the price of the option includes a significant incremental discount, the discount would be included as a deliverable at the inception of the arrangement.

The consideration received under the arrangement that is fixed or determinable was then allocated among the separate units of accounting using the relative selling price method. The Company determined the estimated selling price for units of accounting within each arrangement using vendor‑specific objective evidence (“VSOE”) of selling price, if available, third‑party evidence (“TPE”) of selling price if VSOE is not available, or best estimate of selling price (“BESP”) if neither VSOE nor TPE is available. Determining the BESP for a unit of accounting required significant judgment. In developing the BESP for a unit of accounting, the Company considered applicable market conditions and relevant entity‑specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validated the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP had a significant effect on the allocation of arrangement consideration between multiple units of accounting.

The Company recognized arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 are satisfied for that particular unit of accounting. In the event that a deliverable does not represent a separate unit of accounting, the Company recognized revenue from the combined unit of accounting over the Company’s contractual or estimated performance period for the undelivered elements, which is typically the term of the Company’s research and development obligations. If there is no discernible pattern of performance or objectively measurable performance measures do not exist, then the Company recognized revenue under the arrangement on a straight‑line basis over the period the Company is expected to complete its performance obligations. Conversely, if the pattern of performance in which the service is provided to the customer can be determined and objectively measurable performance measures exist, then the Company recognized revenue under the arrangement using the proportional performance method. Revenue recognized is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the straight‑line method or proportional performance method, as applicable, as of the period ending date.

At the inception of an arrangement that includes milestone payments, the Company evaluated whether each milestone was substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether: (1) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from its performance to achieve the milestone, (2) the consideration relates solely to past performance and (3) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone and the level of effort and investment required to achieve the particular milestone in making this assessment. There was considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. Milestones that are not considered substantive were recognized as earned if there are no remaining performance obligations or over the remaining period of performance, assuming all other revenue recognition criteria are met.

Research and Development Expenses

Research and development expenses are charged to expense as incurred in performing research and development activities. The costs include employee‑related expenses including salaries, benefits, and stock‑based compensation expense, costs of funding research performed by third parties that conduct research and development and preclinical and clinical activities on the Company’s behalf, the cost of purchasing lab supplies and non‑capital equipment used in preclinical and clinical activities and in manufacturing preclinical and clinical study materials, consultant fees, facility costs including rent, depreciation, and maintenance expenses, and fees for acquiring and maintaining licenses under third party licensing agreements, including any sublicensing or success payments made to the Company’s licensors. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the Company’s estimate, the accrual or prepaid is adjusted accordingly. The Company defers and capitalizes non-refundable advance payments made by the Company for research and development activities until the related goods are received or the related services are performed. In circumstances where amounts have been paid in excess of costs incurred, the Company records a prepaid expense.

Patent Costs

The Company expenses patent and patent application costs and related legal costs for the prosecution and maintenance of such patents and patent applications, including patents and patent applications the Company in-licenses, as incurred and classifies such costs as general and administrative expenses in the accompanying consolidated statements of operations.

Construction Financing Lease Obligation

Beginning in 2016, the Company began recording certain estimated construction costs incurred and reported to the Company by a landlord as an asset and corresponding construction financing lease obligation on the Company’s consolidated balance sheets because the Company was deemed to be the owner of the building during the construction period for accounting purposes. In each reporting period, the landlord estimated and reported to the Company the costs incurred to date and provided supporting invoices for the Company to review. The Company periodically met with the landlord and its construction manager to review the estimates and observe construction progress prior to recording such amounts. Construction was completed in October 2016 and the Company considered the requirements for sale-leaseback accounting treatment, which included an evaluation of whether all risks of ownership had transferred back to the landlord as evidenced by a lack of continuing involvement in the lease property. The Company determined that the arrangement did not qualify for sale lease-back accounting treatment, the building asset will remain on the Company’s consolidated balance sheet at its historical cost, and such asset would be depreciated over its estimated useful life of thirty years.

Operating Lease Obligations

Operating lease obligations represent future minimum lease payments under the Company’s non-cancelable operating leases. The minimum lease payments exclude the Company’s share of the facility operating expenses and other costs that are reimbursable to the landlord under the leases. The Company enters into contracts in the normal course of business with contract research organizations and other vendors to assist in the performance of its research and development activities and other services and products for operating purposes. These contracts generally provide for termination on notice, and therefore are cancelable contracts and not included in the table of contractual obligations and commitments.

Stock‑based Compensation Expense

The Company accounts for stock-based compensation awards in accordance with ASC Topic 718, Compensation—Stock Compensation (“ASC 718”). ASC 718 requires all share-based payments to employees, including grants of employee stock options, to be recognized as expense in the consolidated statements of operations based on their grant date fair values. For stock options granted to employees and to members of the Company’s board of directors for their services on the board of directors, the Company estimates the grant date fair value of each option award using the Black-Scholes option-pricing model. For stock options subject to service-based vesting conditions, the Company recognizes stock-based compensation expense equal to the grant date fair value of stock options on a straight-line basis over the requisite service period.

Share-based payments issued to non-employees are initially recorded at their fair values, and are revalued at each reporting date and as the equity instruments vest and are recognized as expense over the related service period in accordance with the provisions of ASC Topic 505-50, Equity-Based Payments to Non-Employees.

The Black‑Scholes option pricing model requires the input of certain subjective assumptions, including (1) the expected stock price volatility, (2) the calculation of expected term of the award, (3) the risk‑free interest rate, and (4) the expected dividend yield. Because there had been no public market for the Company’s common stock prior to the IPO, there was a lack of company‑specific historical and implied volatility data. Accordingly, the Company bases its estimates of expected volatility on the historical volatility of a group of similar companies that are publicly traded. The Company calculates historical volatility based on a period of time commensurate with the expected term. The Company computes expected volatility based on the historical volatility of a representative group of companies with similar characteristics to the Company, including their stages of product development and focus on the life science industry. The Company uses the simplified method as prescribed by the Securities and Exchange Commission’s Staff Accounting Bulletin No. 107, Share‑Based Payment, to calculate the expected term for options granted to employees as the Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. For options granted to non‑employees, the Company utilizes the contractual term of the arrangement as the basis for the expected term. The Company determines the risk‑free interest rate based on a treasury instrument whose term is consistent with the expected term of the stock options. The Company uses an assumed dividend yield of zero as the Company has never paid dividends and does not have current plans to pay any dividends on common stock. If factors change or different assumptions are used, the Company’s stock-based compensation expense could be materially different in the future.

Income taxes

Income taxes are recorded in accordance with ASC Topic 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial reporting and the tax reporting basis of assets and liabilities and are measured using the enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. The Company provides a valuation allowance against net deferred tax assets unless, based upon the weight of available evidence, it is more likely than not that the deferred tax assets will be realized.

The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognized the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances.

Other Income (Expense), Net

For the years ended December 31, 2018 and 2017, other income (expense), net consists primarily of interest income earned on cash equivalents and marketable securities, interest expense on the construction financing lease obligation and promissory notes, rental income from the Company’s former subtenant, interest income, accretion of discounts, and amortization of premiums associated with marketable securities.

Prior to 2017, other income (expense), net consisted primarily of interest income earned on cash equivalents and government grant income, net of re-measurement losses associated with changes in the fair value of the Company’s liability for a warrant to purchase preferred stock. Upon the completion of the IPO, the outstanding warrant to purchase preferred stock converted into a warrant to purchase common stock and the Company reclassified the fair value of the warrant to additional paid-in capital. As a result, there were no further remeasurement gains or losses associated with the warrant after the first quarter of 2016.

Comprehensive Loss

Comprehensive loss is comprised of net loss and other comprehensive income or loss. Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. Comprehensive loss currently consists of net loss and changes in unrealized losses on marketable securities.

Corporate Equity Securities

The Company records investments in privately issued corporate equity securities that do not have readily determinable fair values at cost and adjusts for changes in observable prices minus impairment. Each reporting period the Company adjusts the carrying value of these investments if it observes that additional shares have been issued in an orderly transaction between market participants resulting in a price increase or decrease per share. Additionally, each reporting period the Company reviews these investments for impairment considering all available information to conclude whether an impairment exists. Changes in measurement for all corporate equity investments are recognized in “Other income (expense), net.”

Concentrations of Credit Risk and Off‑Balance Sheet Risk

The Company has no financial instruments with off‑balance sheet risk such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Financial instruments that potentially subject the Company to a concentration of credit risk are cash, cash equivalents, marketable securities and accounts receivable. The Company’s cash, cash equivalents and marketable securities are held in accounts at a financial institution that may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. Accounts receivable primarily consist of amounts due under the collaboration agreement with Juno Therapeutics for which the Company does not obtain collateral. As of December 31, 2018, substantially all of the Company’s revenue to date has been generated from the strategic alliance with Allergan and the collaboration with Juno Therapeutics.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s Chief Executive Officer, view the Company’s operations and manage the Company’s business as a single operating segment, which is the business of developing and commercializing genome editing technology.

Recent Accounting Pronouncements - Adopted

In October 2016, the FASB issued ASU No. 2016-18, Restricted Cash (“ASU 2016-18”), which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents, and restricted cash or restricted cash equivalents. Therefore, amounts described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 was effective for fiscal years beginning after December 15, 2017, and interim periods within those years. The guidance is effective on a retrospective basis. The Company adopted this guidance as of October 1, 2017. The Company reclassified restricted cash in the statements of cash flows to be included in the cash and cash equivalents balance. The reclassification was not material to the periods presented. The following table presents cash, cash equivalents and restricted cash as reported on the consolidated balance sheets that equal the total amounts on the consolidated statements of cash flows (in thousands):


	Year Ended
	As of December 31,
	2018		2017		2016
Cash and cash equivalents	$	134,776	$	146,630	$	185,323
Restricted cash included in "Restricted cash and other non-current assets"		1,619		1,619		1,619
Total	$	136,395	$	148,249	$	186,942

In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, which supersedes the revenue recognition requirements in FASB ASC Topic 605, Revenue Recognition, and most industry-specific guidance. The Company adopted the new standard effective January 1, 2018 using the modified retrospective approach. As part of the adoption, the Company reviewed all contracts that were not yet completed as of the date of initial application in determining the cumulative-effect impact related to the adoption of ASC 606. The adoption of ASC 606 resulted in the changes to (i) the allocation of arrangement consideration, including the determination of estimated selling price and the allocation of variable consideration to specific performance obligations for the Company’s collaboration agreement with Juno Therapeutics, and (ii) the application of proportional performance as a measure of progress on service related deliverables for the Company’s strategic alliance with Allergan.

Effective January 1, 2018, the Company’s adoption of ASC 606 resulted in increases of $0.5 million in deferred revenue and accumulated deficit, which was primarily due to an adjustment for two milestone payments previously earned that will now be recognized over time, partially offset by acceleration of proportional performance revenue.

The following table presents changes in the Company’s deferred revenue balance as of January 1, 2018 resulting from adoption of ASC 606 (in thousands):


	Balance at December 31, 2017		Adjustments		Balance at January 1, 2018
Contract liabilities:
Deferred revenue	$	(107,963)	$	(474)	$	(108,437)

As of December 31, 2018, the Company’s accounts receivable and contract liabilities were primarily related to the Company’s collaboration with Juno Therapeutics and strategic alliance Allergan. The following table presents changes in the Company’s accounts receivable and contract liabilities for the year ended December 31, 2018 (in thousands):


For the year ended December 31, 2018	Balance at December 31, 2017		Additions		Deductions		Balance at December 31, 2018
Accounts receivable	$	679	$	1,189	$	(1,838)	$	30
Contract liabilities:
Deferred revenue	$	(107,963)	$	(31,497)	$	8,134	$	(131,326)

During the three months and year ended December 31, 2018, the Company recognized revenue as a result of the following (in thousands):


		Three Months Ended		Year Ended
Revenue recognized in the period from:	December 31, 2018
Amounts included in deferred revenue at the beginning of the period	$	1,417	$	5,874
Performance obligations satisfied in previous periods	$	4,645	$	5,956

For additional information regarding revenue recognition from contracts with customers, refer to Note 9.

The Company has included the following financial statement line items for comparability purposes as of and for the three months and year ended December 31, 2018 (in thousands, except per share data):


		Three Months Ended December 31, 2018
	As reported under Topic 606		Balances without adoption of ASC 606		Effect of Change
Collaboration and other research and development revenues	$	6,119	$	5,060	$	1,059
Operating loss	$	(26,253)	$	(27,312)	$	1,059
Net loss attributable to common stockholders	$	(25,054)	$	(26,113)	$	1,059
Net loss per share attributable to common stockholders, basic and diluted	$	(0.52)	$	(0.54)	$	0.02


		Year Ended December 31, 2018
	As reported under Topic 606		Balances without adoption of ASC 606		Effect of Change
Collaboration and other research and development revenues	$	31,937	$	33,993	$	(2,056)
Operating loss	$	(113,727)	$	(111,671)	$	(2,056)
Net loss attributable to common stockholders	$	(109,954)	$	(107,898)	$	(2,056)
Net loss per share attributable to common stockholders, basic and diluted	$	(2.33)	$	(2.29)	$	(0.04)


		As of December 31, 2018
	As reported under Topic 606		Balances without adoption of ASC 606		Effect of Change
Deferred revenue, current	$	(15,712)	$	(17,552)	$	1,840
Deferred revenue, net of current portion	$	(115,614)	$	(111,466)	$	(4,148)
Accumulated deficit	$	(416,278)	$	(414,222)	$	(2,056)

In 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities (“ASU 2016-01”). ASU 2016-01 amended guidance related to the recording of financial assets and liabilities. Under the amended guidance, equity investments that are not accounted for under the equity method or those that result in the consolidation of an investee, are to be measured at fair value with changes in fair value recognized in net income (loss). An entity has the option to measure equity investments without readily determinable fair values at cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transaction for the identical or similar investments. The amended guidance became effective January 1, 2018. As of December 31, 2018, the Company held an equity investment in Beam Therapeutics Inc. (“Beam”), a privately held company, that it accounted for under the cost method. The equity investment does not have a readily determinable fair value. The Company measured the investment at cost adjusted for impairment or observable price changes. During the year ended December 31, 2018, the Company did not adjust the value of the Company’s investment in Beam as a result of impairment or based on observable price changes.

Recent Accounting Pronouncements – Issued But Not Yet Adopted

In February 2016, the FASB issued ASU 2016-02, Leases (“ASC 842”), which applies to all leases and will require lessees to record most leases on the balance sheet, but recognize expense in a manner similar to the current standard, was codified as ASC 842, Leases, and amended through subsequent ASUs. ASC 842 is effective for fiscal years beginning after December 15, 2018 and interim periods within those years. Entities are required to use a modified retrospective approach of adoption. The Company will recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption, for which comparative periods will be presented in accordance with the previous guidance in ASC 840, Leases. The Company has elected, in transition, to apply the package of practical expedients which allows the Company not to reassess whether existing contracts are or contain leases, the classification of existing leases, and whether initial direct costs qualify for capitalization. Additionally, the Company expects to elect the package of practical expedients to: i) not recognize lease assets and lease liabilities for leases with a term of 12 months of less; and ii) not separate the non-lease components from the associated lease components for leases of real estate and, instead, account for each non-lease component and associated lease component as a single component. The Company is evaluating the effect of this guidance on the Company’s consolidated financial statements and disclosures, which includes, but is not limited to, the impact on the lease of its corporate headquarters in Cambridge, Massachusetts, and its laboratory space in Boulder, Colorado. The Company currently expects to derecognize the existing asset and liabilities on the consolidated balance sheet resulting from the build-to-suit lease arrangement at the Company’s corporate headquarters in Cambridge, Massachusetts, which did not meet the criteria for “sale-leaseback” treatment at the time construction was completed. Also, the Company is in the process of updating its systems, policies and internal controls over financial reporting in anticipation of adopting these standards.

In June 2018, the FASB issued ASU No. 2018-07, Compensation - Stock Compensation: Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”) to simplify the accounting for share-based payments to non-employees by aligning it with the accounting for share-based payments to employees, with certain exceptions. The new guidance expands the scope of ASC 718, Compensation – Stock Compensation, to include share-based payments granted to non-employees in exchange for goods or services used or consumed in an entity’s own operations and supersedes the guidance in ASC Topic 505-50, Equity-Based Payments to Non-Employees. The guidance is effective for public business entities in annual periods beginning after December 15, 2018 and interim periods within those years. Early adoption is permitted. The Company is currently evaluating the effect of this guidance on the Company’s consolidated financial statements and disclosures.

In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which modifies certain disclosure requirements on fair value measurements. The amendments regarding changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements and the narrative description of measurement uncertainty are required to be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments are required to be applied retrospectively to all periods presented upon their effective date. ASU 2018-13 is effective for fiscal years beginning after December 15, 2019 and interim periods within those years. The Company does not anticipate a material impact to disclosures as a result of the adoption of ASU 2018-13.

Cash Equivalents, Marketable Securities and Corporate Equity Securities

12 Months Ended

Dec. 31, 2018

Cash Equivalents, Marketable Securities and Corporate Equity Securities

Cash Equivalents, Marketable Securities and Corporate Equity Securities

3. Cash Equivalents, Marketable Securities and Corporate Equity Securities

Cash equivalents, marketable securities and corporate equity securities consisted of the following at December 31, 2018 (in thousands):


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
December 31, 2018	Cost		Gains		Losses		Value
Cash equivalents and marketable securities:
Money market funds	$	130,049	$	—	$	—	$	130,049
U.S. Treasuries		208,754		—		(24)		208,730
Government agency securities		29,940		—		(5)		29,935
Equity securities included in other non-current assets:
Corporate equity securities		3,667		—		—		3,667
Total	$	372,410	$	—	$	(29)	$	372,381

Cash equivalents and marketable securities consisted of the following at December 31, 2017 (in thousands):


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
December 31, 2017	Cost		Gains		Losses		Value
Cash equivalents and marketable securities:
Money market funds	$	134,635	$	—	$	—	$	134,635
U.S. Treasuries		135,601		—		(47)		135,554
Government agency securities		58,979		—		(29)		58,950
Total cash equivalents and marketable securities	$	329,215	$	—	$	(76)	$	329,139

At December 31, 2018, the Company held 38 securities that were in an unrealized loss position. The aggregate fair value of securities held by the Company in an unrealized loss position for less than 12 months at December 31, 2018 was $210.7 million, and there were no securities held by the Company in an unrealized loss position for more than 12 months. As of December 31, 2018, the Company did not intend to sell, and would not be more likely than not required to sell, the securities in an unrealized loss position before recovery of their amortized cost bases. Furthermore, the Company has determined that there was no material change in the credit risk of these securities. As a result, the Company determined it did not hold any securities with any other-than-temporary impairment as of December 31, 2018.

There were no realized gains or losses on available-for-sale securities during the years ended December 31, 2018 or 2017.

Fair Value Measurements

12 Months Ended

Dec. 31, 2018

Fair Value Measurements

Fair Value Measurements

4. Fair Value Measurements

Assets measured at fair value on a recurring basis as of December 31, 2018 are as follows (in thousands):


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	December 31,		Identical Assets		Inputs		Inputs
Financial Assets	2018		(Level 1)		(Level 2)		(Level 3)
Cash equivalents:
Money market funds	$	130,049	$	130,049	$	—	$	—
U.S. Treasuries		4,487		4,487		—		—
Marketable securities:
U.S. Treasuries		204,243		204,243		—		—
Government agency securities		29,935		29,935		—		—
Restricted cash and other non-current assets:
Corporate equity securities		3,667		—		3,667		—
Money market funds		1,619		1,619		—		—
Total financial assets	$	374,000	$	370,333	$	3,667	$	—

Assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 are as follows (in thousands):


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	December 31,		Identical Assets		Inputs		Inputs
Financial Assets	2017		(Level 1)		(Level 2)		(Level 3)
Cash and cash equivalents:
Money market funds	$	134,635	$	134,635	$	—	$	—
U.S. Treasuries		11,995		11,995		—		—
Marketable securities:
U.S. Treasuries		123,559		123,559		—		—
Government agency securities		58,950		58,950		—		—
Money market funds, included in restricted cash		1,619		1,619		—		—
Total financial assets	$	330,758	$	330,758	$	—	$	—

There were no transfers between fair value measurement levels during the years ended December 31, 2018 or 2017.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Prepaid Expenses and Other Current Assets

12 Months Ended

Dec. 31, 2018

Prepaid Expenses and Other Current Assets

Prepaid Expenses and Other Current Assets

5. Prepaid Expenses and Other Current Assets

Prepaid expense and other current assets consisted of the following (in thousands):


	As of
	December 31,
	2018		2017
Prepaid expenses	$	2,918	$	1,864
Other		2,873		517
Total	$	5,791	$	2,381

Property and Equipment, Net

12 Months Ended

Dec. 31, 2018

Property and Equipment, Net

Property and Equipment, Net

6. Property and Equipment, Net

Property and equipment, net consisted of the following (in thousands):


	As of
	December 31,
	2018		2017
Building	$	35,167	$	35,167
Laboratory equipment		10,892		7,415
Computer equipment		733		550
Leasehold improvements		289		177
Furniture and office equipment		166		96
Software		118		95
Total property and equipment		47,365		43,500
Less: accumulated depreciation		(7,133)		(4,058)
Property and equipment, net	$	40,232	$	39,442

The Company recorded $3.3 million, $2.7 million and $1.2 million in depreciation expense during the years ended December 31, 2018, 2017 and 2016, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2018

Accrued Expenses

Accrued Expenses

7. Accrued Expenses

Accrued expenses consisted of the following (in thousands):


	As of
	December 31,
	2018		2017
Employee related expenses	$	5,201	$	3,708
Sublicensing and success payment expenses		3,750		2,000
Intellectual property and patent related fees		1,939		2,370
Process and platform development expenses		1,044		2,301
Professional service expenses		475		487
Other expenses		404		183
Total	$	12,813	$	11,049

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies

Commitments and Contingencies

8. Commitments and Contingencies

Hurley Street Lease

In February 2016, the Company entered into a lease agreement for 59,783 square feet of office and laboratory space located on Hurley Street in Cambridge, Massachusetts. The term of the lease began on October 1, 2016. In connection with the lease and as a security deposit, the Company deposited with the landlord a letter of credit in the amount of approximately $1.6 million. Subject to the terms of the lease and certain reduction requirements specified therein, the $1.6 million security deposit may decrease over time. The letter of credit, which is collateralized by the Company with cash held in a money market account, is recorded in restricted cash and other non-current assets in the accompanying consolidated balance sheets as of December 31, 2018 and December 31, 2017.

In connection with this lease, the landlord provided a tenant improvement allowance for costs associated with the design, engineering, and construction of tenant improvements for the leased facility. For accounting purposes, the Company was deemed the owner of the building during the construction period due to the fact that the Company was involved in the construction project, including having responsibilities for cost overruns for planned tenant improvements that did not qualify as “normal tenant improvements” under the lease accounting guidance. Throughout the construction period, the Company recorded the project construction costs incurred as an asset, along with a corresponding construction financing lease obligation, on its balance sheet for the total amount of the project costs incurred whether funded by the Company or the landlord.

Construction was completed in October 2016, and the Company considered the requirements for sale-leaseback accounting treatment, which included an evaluation of whether all risks of ownership had transferred back to the landlord, as evidenced by a lack of continuing involvement in the leased property. The Company determined that the arrangement did not qualify for sale-leaseback accounting treatment, the building asset would remain on the Company’s balance sheet at its historical cost, and such asset would be depreciated over its estimated useful life of 30 years.

The Company bifurcates its future lease payments pursuant to the Hurley Street lease into (i) a portion that is allocated to the building and (ii) a portion that is allocated to the land on which the building is located, which is recorded as rental expense. Although the Company did not begin making lease payments pursuant to the Hurley Street lease until November 2016, the portion of the lease obligation allocated to the land is treated for accounting purposes as an operating lease that commenced upon execution of the Hurley Street lease in February 2016.

The lease will continue until October 2023. The Company has the option to extend the lease for an additional five year term at market-based rates. The Company began using this space as its headquarters in October 2016 and rental payments for this property began in November 2016. The base rent is subject to increases over the term of the lease. The non-cancelable minimum annual lease payments, excluding the Company’s share of the facility operating expenses and other costs that are reimbursable to the landlord under the lease, consist of the following (in thousands):


Year ended December 31,	11 Hurley Street Lease
2019		4,155
2020		4,257
2021		4,362
2022		4,470
2023 (partial year)		3,802
2024 and thereafter		-
Total minimum lease payments	$	21,046

Rent expense of approximately $1.8 million, $1.2 million and $2.5 million was incurred during the years ended December 31, 2018, 2017 and 2016, respectively.

The Company subleased approximately 10,000 square feet of the Hurley Street premises pursuant to a sublease, which commenced in February 2017 and terminated in June 2018.

Licensor Expense Reimbursement

The Company is obligated to reimburse The Broad Institute, Inc. (“Broad”) and the President and Fellows of Harvard College (“Harvard”) for expenses incurred by each of them associated with the prosecution and maintenance of the patent rights that the Company licenses from them pursuant to the license agreement by and among the Company, Broad and Harvard, including the interference and opposition proceedings involving patents licensed to the Company under the license agreement, and other license agreements between the Company and Broad. As such, the Company anticipates that it has a substantial commitment in connection with these proceedings until such time as these proceedings have been resolved, but the amount of such commitment is not determinable. The Company incurred an aggregate of $14.2 million, $18.2 million and $23.1 million in expense during the years ended December 31, 2018, 2017 and 2016, respectively, for such reimbursement.

Success Payments

In 2016, the Company entered into patent license agreements with each of The General Hospital Corporation, d/b/a Massachusetts General Hospital (“MGH”), and Broad (collectively, the “2016 License Agreements”). Pursuant to the terms of the 2016 License Agreements, the Company is required to make certain success payments to MGH, Broad and Wageningen University (“Wageningen” and such payments, collectively, the “Success Payments”), payable in cash or, at the Company’s election, common stock in the case of MGH or, in the case of Broad and Wageningen, promissory notes payable in cash or, at the Company’s election subject to certain conditions, common stock of the Company. The Success Payments are payable, if and when, the Company’s market capitalization reaches specified thresholds for a specific period of time or upon a sale of the Company for consideration in excess of those thresholds, as discussed more fully in Note 9 (collectively, the “Payment Conditions”).

The Success Payments were accounted for under the provisions of FASB ASC, Topic 505-50, Equity-Based Payments to Non-Employees. The Company has the right to terminate any of the 2016 License Agreements at will upon written notice. Absent any of the Payment Conditions being achieved prior to termination, the Company would not be obligated to pay any Success Payments. As such, the Company will recognize the expense and liability associated with each Success Payment upon achievement of the associated Payment Conditions, if ever. The Company records this expense as a research and development expense in its consolidated statements of operations.

The Company triggered the first Success Payment under one of the 2016 License Agreements during the first quarter of 2017 when the Company’s market capitalization reached $750.0 million. In March 2017, the Company issued promissory notes for an aggregate principal amount of $5.0 million to Broad and Wageningen and the Company settled such notes in August 2017.

The Company triggered another Success Payment under one of the 2016 License Agreements during the fourth quarter of 2017 when the Company’s market capitalization reached $1.0 billion. In December 2017, the Company issued promissory notes for an aggregate principal amount of $7.5 million to Broad and settled such notes in January 2018.

The Company triggered a Success Payment under the MGH license agreement during the fourth quarter of 2017 when the Company’s market capitalization reached $1.0 billion. The Company accrued $2.0 million relating to the such Success Payment owed to MGH which is included in accrued expense on the consolidated balance sheet for the year ended December 31, 2017. In January 2018, the Company settled this liability through the issuance of 80,000 shares of its common stock to MGH.

The Success Payments issued to Broad and Wageningen are discussed more fully within the Notes Payable section below.

Research Funding Payments

In June 2018, the Company entered into a sponsored research agreement (the “Sponsored Research Agreement”) with Broad, which is described more fully in Note 9. Pursuant to the terms of the Sponsored Research Agreement, the Company is required to make certain research funding payments to Broad, payable by promissory note, cash or common stock. Under the Sponsored Research Agreement, the Company is obligated to make payments of research funding to Broad in the event the Company’s market capitalization reaches specified thresholds ranging from a mid-nine digit dollar amount to a low-eleven digit dollar amount (“Market Cap Research Funding”) or a Company sale for consideration ranging from a mid-nine digit dollar amount to a low-eleven digit dollar amount (“Company Sale Research Funding” and, collectively with the Market Cap Research Funding, the “Research Funding Payments”). In connection with entering into the Sponsored Research Agreement, the Company confirmed that the first two Research Funding Payments of $5.0 million and $7.5 million were due and payable to Broad (the “Initial Research Payments”). In June 2018, the Company issued promissory notes for an aggregate principal balance of $12.5 million to Broad, which were settled by the issuance of shares of common stock, and are described more fully in the Notes Payable section.

The Research Funding Payments were accounted for under the provisions of FASB ASC, Topic 505-50, Equity-Based Payments to Non-Employees. Other than the Initial Research Payments, the Company is not required to make additional Research Funding Payments if the Company, whether directly or through its affiliates or sublicensees, is not researching, developing, or commercializing products based on or incorporating inventions developed under the Sponsored Research Agreement and exclusively licensed to the Company from Broad or based on or incorporating CRISPR technology owned, co-owned, or controlled by Broad and otherwise licensed to the Company, subject to certain exclusions. As such, the Company will recognize the expenses and liability associated with each Research Funding Payment upon achievement of the associated Research Funding Payment conditions, if ever. The Company records this expense as a research and development expense in its consolidated statements of operations.

Notes Payable

In December 2016, in connection with the Company’s entry into the Cpf1 license agreement with Broad (the “Cpf1 License Agreement”), one of the 2016 License Agreements, the Company issued promissory notes in an aggregate principal amount of $10.0 million to Broad and Wageningen (the “Initial Notes”). Outstanding principal and accrued interest on the Initial Notes were due and payable on the earlier of December 2017 or a specified period of time following a Company sale or change of control event. The Initial Notes accrued interest at a rate of 4.8% per annum. The Company fully settled the outstanding principal and accrued interest on the Initial Notes by paying $0.2 million in cash to Wageningen in August 2017 and issuing 108,104 shares and 371,166 shares of common stock to Broad in August 2017 and September 2017, respectively.

In March 2017, a $5.0 million Success Payment under the Cpf1 License Agreement became due upon the market capitalization of the Company’s common stock reaching $750 million. The Company issued a promissory note to each of Broad and Wageningen in an aggregate original principal amount of $5.0 million (collectively, the “March Success Payment Notes”). Outstanding principal and accrued interest on the March Success Payment Notes were due and payable in August 2017. The March Success Payment Notes were subject to the same interest and terms as the Initial Notes, other than the maturity date. The Company settled the outstanding principal and accrued interest on the March Success Payment Notes in August 2017 by paying $0.4 million in cash to Wageningen and issuing 271,347 shares of common stock to Broad in August 2017. In September 2017, Wageningen designated Broad as the recipient of any future promissory notes that are owed to Wageningen pursuant to the Cpf1 License Agreement.

In December 2017, $7.5 million in Success Payments under the Cpf1 License Agreement and the Cas9-II license agreement with Broad (the “Cas9-II License Agreement”), one of the 2016 License Agreements, became due upon the Company’s market capitalization reaching $1.0 billion. The Company issued promissory notes to Broad in an aggregate original principal amount of $7.5 million (collectively, the “December Success Payment Notes”). Outstanding principal and accrued interest on the December Success Payment Notes were due and payable in May 2018. The December Success Payment Notes were subject to the same interest and terms as the Initial Notes, other than the maturity date. The Company fully settled the outstanding principal and accrued interest on the December Success Payment Notes by issuing 225,909 shares of common stock to Broad in January 2018.

In June 2018, in connection with the Company’s entry into the Sponsored Research Agreement and the trigger of the Initial Research Payments, the Company issued promissory notes in an aggregate principal amount of $12.5 million to Broad (the “Initial Research Notes”) bearing interest at a rate of 4.8% annum, except with respect to $7.5 million of the principal, which would not start accruing interest until November 2018. The Company fully settled the outstanding principal and accrued interest on the Initial Research Notes by issuing 330,617 shares of common stock to Broad in June 2018.

Litigation

The Company is not a party to any litigation and did not have contingency reserves established for any litigation liabilities as of December 31, 2018 or 2017.

Significant Agreements	12 Months Ended
Significant Agreements	Dec. 31, 2018
Significant Agreements.
Significant Agreements	9. Significant Agreements Juno Therapeutics Collaboration Agreement Summary of Agreement In May 2015, the Company entered into a collaboration and license agreement (the “Collaboration Agreement”) with Juno Therapeutics and in May 2018 the Company and Juno Therapeutics entered into an amended and restated collaboration and license agreement (the Collaboration Agreement, as amended and restated, the “Amended Collaboration Agreement”). The collaboration is focused on the research and development of engineered T cells with chimeric antigen receptors (“CARs”) and T cell receptors (“TCRs”) that have been genetically modified to recognize and kill other cells. Pursuant to the Collaboration Agreement, the parties were pursuing the research and development of CAR and TCR engineered T cell products utilizing the Company’s genome editing technologies with Juno Therapeutics’ CAR and TCR technologies across three research areas, which was increased to four research areas under the Amended Collaboration Agreement. The collaborative program of research to be undertaken by the parties pursuant to the Amended Collaboration Agreement will be conducted in accordance with a mutually agreed upon research plan which outlines each party’s research and development responsibilities across the four research areas. The Company’s research and development responsibilities under the research plan are related to generating genome editing reagents that modify gene targets selected by Juno Therapeutics. Juno Therapeutics is responsible for evaluating and selecting for further research and development CAR and TCR engineered T cell products modified with the Company’s genome editing reagents. Except with respect to the Company’s obligations under the mutually agreed upon research plan, Juno Therapeutics has sole responsibility, at its own cost, for the worldwide research, development, manufacturing and commercialization of products within each of the four research areas for the diagnosis, treatment or prevention of any cancer in humans through the use of engineered T cells, excluding the diagnosis, treatment or prevention of medullary cystic kidney disease 1 (the “Exclusive Field”). The initial term of the research program commenced on May 26, 2015 and continues for five years ending on May 26, 2020 (the “Initial Research Program Term”). Juno Therapeutics may extend the Initial Research Program Term for up to two additional one year periods upon the payment of extension fees for each one year extension period, assuming the Company has agreed to the extension request(s) (together, the initial term and any extension period(s) are referred to as the “Research Program Term”). The Research Program Term and the optional extensions were not changed by the Amended Collaboration Agreement. Under the terms of the Collaboration Agreement, the Company granted to Juno Therapeutics during the Research Program Term a nonexclusive, worldwide, royalty free, non-sublicensable license under certain of the intellectual property controlled by the Company solely for the purpose of conducting the following activities required under the specified research under the Collaboration Agreement: (i) conduct activities assigned to Juno Therapeutics under the research plan, (ii) conduct activities assigned to the Company under the research plan that the Company fails or refuses to conduct in a timely manner, (iii) research, evaluate and conduct preclinical testing and development of certain engineered T cells relating to the three research areas that were originally the subject of the arrangement and (iv) evaluate the data developed in the conduct of activities under the research plan. Pursuant to the terms of the Amended Collaboration Agreement, the license rights granted to Juno Therapeutics were expanded to include, during the Research Program Term, a nonexclusive, worldwide, royalty free, non-sublicensable license under certain of the intellectual property controlled by the Company to: (i) research, evaluate and conduct preclinical testing and development of certain engineered T cells relating to the fourth research area and (ii) research, develop and use certain research tools (together, the initial research license granted per the terms of the Collaboration Agreement and the incremental research license granted per the terms of the Amended Collaboration Agreement, the “Research License”). As it relates to two of the three research areas that were originally the subject of the arrangement, under the terms of the Collaboration Agreement, the Company granted to Juno Therapeutics an exclusive, milestone and royalty bearing, sublicensable license under certain of the intellectual property controlled by the Company to research, develop, make and have made, use, offer for sale, sell, import and export selected CAR and TCR engineered T cell products in the Exclusive Field on a worldwide basis, specifically as it relates to certain targets selected by Juno Therapeutics pursuant to the research program. Furthermore, as it relates to the same two research areas, under the terms of the Collaboration Agreement, the Company granted to Juno Therapeutics a non-exclusive, milestone and royalty bearing, sublicensable license under certain of the intellectual property controlled by the Company to use genome editing reagents generated under the research program that are used in the creation of certain CAR or TCR engineered T cell products on which Juno Therapeutics has filed an investigational new drug (“IND”) application in the Exclusive Field for the treatment or prevention of a cancer in humans to research, develop, make and have made, use, offer for sale, sell, import and export those CAR or TCR engineered T cell products in all fields outside of the Exclusive Field (the “Non Exclusive Field”) on a worldwide basis, specifically as it relates to certain targets selected by Juno Therapeutics pursuant to the research program (together, the license in the Exclusive Field and the license in the Non Exclusive Field are referred to as the “Development and Commercialization License” for each particular research area). Additionally, as it relates to the third research area that was originally the subject of the arrangement, under the terms of the Collaboration Agreement, the Company granted to Juno Therapeutics a milestone and royalty bearing, sublicensable license under certain of the intellectual property controlled by the Company to research, develop, make and have made, use, offer for sale, sell, import or export selected CAR and TCR engineered T cell products that utilize the genome editing reagents generated under the research program associated with those CAR and TCR engineered T cell products in the Exclusive Field on a worldwide basis, specifically as it relates to certain products selected by Juno Therapeutics pursuant to the research program. The license associated with the third research area is exclusive as it relates to CAR or TCR engineered T cell products directed to certain targets as selected by Juno Therapeutics, but is otherwise non-exclusive (referred to as the “Development and Commercialization License” for the third research area). Pursuant to the terms of the Amended Collaboration Agreement, as it relates to the fourth area of research that was added to the collaboration, the Company granted to Juno Therapeutics a milestone and royalty bearing, sublicensable license under certain of the intellectual property controlled by the Company to research, develop, make and have made, use, offer for sale, sell, import or export selected CAR and TCR engineered T cell products that utilize the genome editing reagents generated under the research program associated with those CAR and TCR engineered T cell products in the Exclusive Field on a worldwide basis, specifically as it relates to certain products selected by Juno Therapeutics pursuant to the research program. The license associated with the fourth research area is exclusive as it relates to CAR or TCR engineered T cell products directed to certain targets as selected by Juno Therapeutics, but is otherwise non-exclusive (referred to as the “Development and Commercialization License” for the fourth research area). The Amended Collaboration Agreement is being managed on an overall basis by a project leader from each of the Company and Juno Therapeutics. The project leaders serve as the contact point between the parties with respect to the research program and are primarily responsible for facilitating the flow of information, interaction, and collaboration between the parties. In addition, the research and development activities under the Amended Collaboration Agreement during the Research Program Term are governed by a joint research committee (“JRC”) formed by an equal number of representatives from the Company and Juno Therapeutics. The JRC oversees, reviews and recommends the direction of the research program. Among other responsibilities, the JRC monitors and reports research progress and ensures open and frequent exchange between the parties regarding research program activities. The Amended Collaboration Agreement did not alter the governance provisions in the Collaboration Agreement. Under the terms of the Collaboration Agreement, the Company received a $25.0 million up front, non-refundable, non-creditable cash payment. In connection with the entry into the Amended Collaboration Agreement, the Company received an additional $5.0 million up-front, non-refundable, non-creditable cash payment. Moreover, the Company became entitled to receive two $2.5 million milestones related to technical progress in one of the research areas upon the execution of the Amended Collaboration Agreement. In addition, Juno Therapeutics is obligated to pay to the Company an aggregate of up to $22.0 million in research and development funding over the Initial Research Program Term across the four research areas consisting primarily of funding for up to a specified maximum number of full time equivalents personnel each year over the Initial Research Program Term across four research areas. Consistent with the terms of the Collaboration Agreement, under the terms of the Amended Collaboration Agreement, there is no incremental compensation due to the Company with respect to the Development and Commercialization License granted to Juno Therapeutics associated with the first target or product, as applicable, designated by Juno Therapeutics within each of the four research areas. However, for two of the three research areas that were originally the subject of the arrangement, Juno Therapeutics continues to have the option to purchase up to three additional Development and Commercialization Licenses associated with other gene targets for an additional fee of approximately $2.5 million per target. In addition, Juno Therapeutics is required to make certain milestone payments to the Company upon the achievement of specified development, regulatory and commercial events. More specifically, for the first product to achieve the associated event in each of the three research areas that were originally the subject of the arrangement, the Company is eligible to receive up to $77.5 million in development milestone payments and up to $80.0 million in regulatory milestone payments, while the Company is eligible to receive up to $80.0 million in development milestone payments and up to $80.0 million in regulatory milestone payments for the first product to achieve the associated event in the fourth area of research that was added to the collaboration. In addition, the Company is eligible to receive additional development and regulatory milestone payments for subsequent products developed within each of the four research areas. Moreover, the Company is eligible for up to $75.0 million in commercial milestone payments associated with aggregate sales of all products within each of the four research areas. Development milestone payments are generally triggered upon the achievement of certain specified development criteria or upon initiation of a defined phase of clinical research for a product candidate. Regulatory milestone payments are triggered upon approval to market a product candidate by the United States Food and Drug Administration (“FDA”) or other global regulatory authorities. Commercial milestone payments are triggered when an approved pharmaceutical product reaches certain defined levels of net sales by the licensee. The milestone payments and related triggering events associated with the three research areas that were originally the subject of the Collaboration Agreement were not modified in the Amended Collaboration Agreement. In addition, to the extent any of the product candidates covered by the licenses conveyed to Juno Therapeutics under the Amended Collaboration Agreement are commercialized, the Company would be entitled to receive tiered royalty payments of low double digits based on a percentage of net sales. Similar to the milestones, pursuant to the Amended Collaboration Agreement, the Company is eligible to receive an independent royalty stream associated with the fourth area of research that was added to the collaboration. Royalty payments are subject to certain reductions, including for any royalty payments required to be made by Juno Therapeutics related to a third party’s intellectual property rights, subject to an aggregate minimum floor. Royalties are due on a licensed product by licensed product and country by country basis from the date of the first commercial sale of each product in a country until the later of: (i) the tenth anniversary of the first commercial sale of such licensed product in such country and (ii) the expiration date in such country of the last to expire valid claim within the licensed intellectual property covering the manufacture, use or sale of such licensed product in such country. The Company achieved $2.5 million development milestones under the Collaboration Agreement resulting from technical progress in a research program in each of May 2016 and July 2017 (the “July 2017 Juno Milestone Payment”). The Company achieved two additional $2.5 million development milestones under the Amended Collaboration Agreement resulting from technical progress in a research program in May 2018. Due to the uncertainty of pharmaceutical development and the high historical failure rates generally associated with drug development, no additional milestone or royalty payments may ever be received from Juno Therapeutics. As of December 31, 2018, the next potential milestone payment that the Company may be entitled to receive under the Amended Collaboration Agreement is a milestone payment of $2.5 million for the achievement of certain development criteria. There are no cancellation, termination or refund provisions in the Amended Collaboration Agreement that contain material financial consequences to the Company. Unless earlier terminated, the Amended Collaboration Agreement will continue in full force and effect, on a licensed product by licensed product and country by country basis until the date no further payments are due to the Company from Juno Therapeutics. Either party may terminate the Amended Collaboration Agreement if the other party has materially breached or defaulted in the performance of any of its material obligations and such breach or default continues after the specified cure period. Either party may terminate the Amended Collaboration Agreement in the event of the commencement of any proceeding in or for bankruptcy, insolvency, dissolution or winding up by or against the other party that is not dismissed or otherwise disposed of within a specified time period. Juno Therapeutics may terminate the Amended Collaboration Agreement for convenience upon not less than six months prior written notice to the Company. The Company may terminate the Amended Collaboration Agreement in the event that Juno Therapeutics brings, assumes, or participates in, or knowingly, willfully or recklessly assists in bringing a dispute or challenge against the Company related to its intellectual property. Termination of the Amended Collaboration Agreement for any reason does not release either party from any liability which, at the time of such termination, has already accrued to the other party or which is attributable to a period prior to such termination nor preclude either party from pursuing any rights and remedies it may have under the agreement or at law or in equity with respect to any breach of the Amended Collaboration Agreement. If Juno Therapeutics terminates the Amended Collaboration Agreement as a result of the Company’s uncured material breach or default, then: (i) the licenses and rights conveyed to Juno Therapeutics will continue as set forth in the agreement, (ii) Juno Therapeutics’ obligations related to milestones and royalties will continue as set forth in the agreement and (iii) Juno Therapeutics’ rights to prosecute, maintain and enforce certain intellectual property rights will continue as set forth in the agreement. If Juno Therapeutics terminates the Amended Collaboration Agreement for convenience or if the Company terminates the Amended Collaboration Agreement as a result of Juno Therapeutics’ uncured material breach or default, then the licenses conveyed to Juno Therapeutics will terminate. The Amended Collaboration Agreement did not modify the termination provisions in the Collaboration Agreement. Accounting Analysis The Company evaluated the Amended Collaboration Agreement in accordance with the provisions of ASC 606. The Company has accounted for the amendment resulting from the Amended Collaboration Agreement as a modification to the original contract and not as a separate contract. The Company combined the Amended Collaboration Agreement with the Collaboration Agreement because the scope of the arrangement did not solely increase due to the addition of distinct promised goods or services with pricing that reflects the associated standalone selling prices. For the remaining goods and services that are distinct from the goods and services that were transferred on or before the date of the effectiveness of the Amended Collaboration Agreement, the Company has accounted for the modification on a prospective basis as if it were a termination of the existing contract and the creation of a new contract. Conversely, the remaining goods and services that are not distinct from the goods and services that were transferred on or before the date of the effectiveness of the Amended Collaboration Agreement were deemed to form part of a single performance obligation that is partially satisfied so they have been accounted for as part of the existing contract for which an adjustment was recorded on a cumulative catch-up basis at the date of the modification. The Company has identified the following performance obligations under the combined arrangement: (i) Research License and the related research and development services during the Initial Research Program Term (the “Research License and Related Services”), (ii) four material rights related to the first Development and Commercialization Licenses related to each of the four research areas (each, a “First Development and Commercialization License Material Right”) and (iii) six material rights related to the option to purchase up to three additional Development and Commercialization Licenses for two of the research areas (each, an “Additional Development and Commercialization License Material Right”). Upon exercise of the option to obtain a Development and Commercialization License under any of the four research areas, the Company will provide Juno Therapeutics with a license covering the further development and potential commercialization of the underlying target or product, as applicable. The Company has determined that the ability to obtain Development and Commercialization Licenses under the arrangement represents a material right because Juno Therapeutics is entitled to incremental licenses for additional consideration that represents a significant discount from amounts that would otherwise be offered for the related goods to comparable customers outside of the contract. The Company has concluded that the Research License is not distinct from the research and development services during the Initial Research Program Term as Juno Therapeutics cannot obtain the benefit of the Research License without the Company performing the research and development services. The services incorporate proprietary technology, unique skills and specialized expertise, particularly as it relates to genome editing technology that is not available in the marketplace. As a result, the Research License, inclusive of the incremental license granted in connection with the Amended Collaboration Agreement, has been combined with the research and development services into a bundled performance obligation. The Company has concluded that the First Development and Commercialization License Material Rights for each respective research area and the Additional Development and Commercialization License Material Rights for the two research areas to which they relate are each a separate performance obligation. These material rights, of which there are ten in total, are distinct from the other performance obligations in the arrangement as they are options in the contract that are not required for Juno Therapeutics to obtain the benefit of the other promised goods and services in the arrangement. Accordingly, in accounting for the modification resulting from the Amended Collaboration Agreement, the Research License and Related Services performance obligation was treated as part of the existing contract, whereas the material right performance obligations were treated as a termination of the existing contract and the creation of a new contract. As of December 31, 2018, the total transaction price associated with the remaining consideration based on the Amended Collaboration Agreement was determined to be $40.7 million, consisting of: (i) $25.0 million upfront non-refundable, non-creditable cash payment associated with the Collaboration Agreement, (ii) $5.0 million upfront non-refundable, non-creditable cash payment associated with the Amended Collaboration Agreement, (iii) $2.9 million of remaining research and development funding, (iv) $2.7 million of milestone payments received by the Company under the Collaboration Agreement that were not yet recognized as revenue and (v) $5.0 million of milestone payments associated with the execution of the Amended Collaboration Agreement. The research and development funding is being paid by Juno Therapeutics to the Company based on the number of the Company’s full time equivalents of its personnel conducting the research under the Amended Collaboration Agreement. The Company utilizes the most likely amount method to determine the amount of research and development funding to be received. The Company also utilizes the most likely amount method to estimate any development and regulatory milestone payments to be received. As of December 31, 2018, the only milestones that were included in the transaction price were milestones that had been contractually earned and received. The remaining milestones were fully constrained due to the significant uncertainties surrounding such payments. The Company considers the stage of development and the risks associated with the remaining development required to achieve the milestone, as well as whether the achievement of the milestone is outside the control of the Company or Juno Therapeutics. The outstanding milestone payments were fully constrained as of December 31, 2018, as a result of the uncertainty whether any of the milestones will be achieved. The Company has determined that any commercial milestones and sales-based royalties will be recognized when the related sales occur as they were determined to relate predominantly to the license(s) to be granted and therefore have also been excluded from the transaction price. The Company reevaluates the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur. Through the date of the Amended Collaboration Agreement, the Company had recognized approximately $12.3 million of revenue associated with the Research License and Related Services which was excluded from the modification date transaction price. The transaction price was allocated to the performance obligations based on the relative estimated standalone selling prices of each performance obligation or, in the case of certain variable consideration, to one or more performance obligations. The estimated standalone selling price for the Research License and Related Services is primarily based on the nature of the services to be performed and estimates of the associated effort and costs of the services, adjusted for a reasonable profit margin that would be expected to be realized under similar contracts. The Company developed the estimated standalone selling price for the material rights based on the difference between the value of the license granted and any additional consideration to be received upon exercise of the underlying option, adjusted for the probability of exercise. The value of the license granted was determined based on the probability-weighted present value of expected future cash flows associated with each license related to each specific research area. In developing such estimate, the Company also considered applicable market conditions and relevant entity-specific factors, including those factors contemplated in negotiating the agreement, probability of success and the time needed to commercialize a product candidate pursuant to the associated license. The transaction price allocated to each performance obligation as of December 31, 2018 was as follows: (i) Research License and Related Services: $10.7 million, (ii) First Development and Commercialization License Material Right related to the first research area: $3.6 million, (iii) First Development and Commercialization License Material Right related to the second research area: $6.0 million, (iv) First Development and Commercialization License Material Right related to the third research area: $0.1 million, (v) First Development and Commercialization License Material Right related to the fourth research area: $18.3 million, (vi) the first Additional Development and Commercialization License Material Right for the first research area: $0.3 million, (vii) the second Additional Development and Commercialization License Material Right for the first research area: $0.2 million, (viii) the third Additional Development and Commercialization License Material Right for the first research area: $0.1 million, (ix) the first Additional Development and Commercialization License Material Right for the second research area: $0.8 million, (x) the second Additional Development and Commercialization License Material Right for the second research area: $0.5 million, and (xi) the third Additional Development and Commercialization License Material Right for the second research area: $0.3 million. The Company recognizes revenue related to amounts allocated to the Research License and Related Services as the underlying services are performed using a proportional performance model. The Company measures proportional performance based on full time employee hours relative to projected full time employee hours to complete the research services which best reflects the progress towards satisfaction of the performance obligation. Revenue related to each of the material rights will be recognized upon the earlier of when the respective options are exercised and the Company transfers control of the related license or when the respective options lapse. The rights to be conveyed to Juno Therapeutics pursuant to each of the Development and Commercialization Licenses extend exclusively to an individual target or product, as applicable; therefore, control is deemed to be transferred upon the designation by Juno Therapeutics of the specific target or product, as applicable, whereupon the license becomes effective upon Juno Therapeutics exercising their option. None of the options associated with the material rights had been exercised or had lapsed as of December 31, 2018. During the years ended December 31, 2018 and 2017, the Company recognized revenue under the Collaboration Agreement and the Amended Collaboration Agreement totaling approximately $6.4 million and $4.9 million, respectively. Included in the revenue recognized during the year ended December 31, 2018 is approximately $3.0 million of additional revenue related to a cumulative catch-up adjustment associated with the Amended Collaboration Agreement. Included in the revenue recognized during the year ended December 31, 2017 is $2.5 million related to the July 2017 Juno Milestone Payment. No revenue had been recognized through the date of the Amended Collaboration Agreement for the material rights performance obligations and there were no cumulative catch-up adjustments recorded for such performance obligations as a result of the Amended Collaboration Agreement. Amounts allocated to each of the material rights will be recognized as revenue prospectively when the material right has been exercised or when the respective option has lapsed. The revenue is classified as collaboration and other research and development revenues in the accompanying consolidated statements of operations. As of December 31, 2018 and 2017, there was approximately $32.0 million and $26.4 million of deferred revenue, respectively, related to the Amended Collaboration Agreement and the Collaboration Agreement, respectively, of which $29.2 million and $26.4 million were classified as long-term, respectively, in the accompanying consolidated balance sheets. In addition, as of December 31, 2017, the Company had recorded accounts receivable of $0.5 million related to reimbursable research and development costs under the Collaboration Agreement for activities performed during the fourth quarter of 2017. There was no receivable balance as of December 31, 2018. During the year ended December 31, 2018, the Company paid $1.7 million in sublicense fees that were owed to certain of the Company’s licensors in connection with the Amended Collaboration Agreement, which the Company recorded as research and development expenses during such period. During the year ended December 31, 2017, the Company paid $0.5 million in sublicense fees that were owed to certain of the Company’s licensors in connection with the July 2017 Juno Milestone Payment, which the Company recorded as research and development expenses during such period. Allergan Pharmaceuticals Strategic Alliance and Option Agreement Summary of Agreement In March 2017, the Company entered into a Strategic Alliance and Option Agreement with Allergan to discover, develop, and commercialize new gene editing medicines for a range of ocular disorders (the “Allergan Agreement”). Over a seven-year research term, Allergan will have an exclusive option to exclusively license from the Company up to five collaboration development programs for the treatment of ocular disorders (each a “CDP”), including the Company’s Leber congenital amaurosis 10 program (the “LCA10 Program”). Under the Allergan Agreement, the Company will use commercially reasonable efforts to develop at least five CDPs and deliver preclinical results and data meeting specified criteria with respect to each CDP (each, an “Option Package” and such criteria, the “Option Package Criteria”) to Allergan. The list of proposed targets that may be subject to a CDP may be amended from time to time by mutual agreement of the Company and Allergan. The Company is responsible for the preparation and delivery of a written development plan for each particular CDP setting forth the discovery and research activities to be conducted which is subject to the approval of the alliance steering committee that was formed under the Allergan Agreement, comprised of three members from each of the Company and Allergan (the “Steering Committee”). The Company will maintain primary responsibility for the development efforts under each CDP. The Company is responsible for all research and development costs prior to the achievement of the Option Package Criteria. Allergan will have the ability for a defined period of time (“Initial Option Period”) to exercise an option (each, an “Option”) to obtain a worldwide right and license to the Company’s background intellectual property and the Company’s interest in the CDP intellectual property to develop, commercialize, make, have made, use, offer for sale, sell, and import any gene editing therapy product that results from such CDP during the term of the Allergan Agreement (a “Licensed Product”) in any category of human diseases and conditions other than the diagnosis, treatment or prevention of any cancer in humans through the use of engineered T-cells and subject to specified other limitations. Allergan has the option to extend the Initial Option Period and require the Company to perform additional research and development services, subject to the payment of additional consideration. After exercise of an Option with respect to a CDP, with the exception of any CDP’s where the Company has exercised its profit-sharing option, Allergan will be responsible for all development, manufacturing, and commercialization activities in connection with licensed products arising from such CDP, other than with respect to the LCA10 Program, if LCA10 is designated as a CDP. In July 2018, Allergan exercised its Option with respect to the LCA10 Program. In connection with such exercise, Allergan paid the Company $15.0 million (the “LCA10 Option Exercise Payment”). Following such exercise, the Company exercised its Profit-Share Election with respect to the LCA10 Program. Following such election, the LCA10 Program became subject to a Profit-Sharing Arrangement and, as of December 31, 2018, the parties have not yet entered into a separate profit-sharing agreement with respect to the Profit-Sharing Arrangement. The initial term of the Allergan Agreement commenced on March 14, 2017 and continues for seven years ending on March 14, 2024 (the “Research Term”). If the Company has not delivered an Option Package, which includes the results and data from the CDP, for five CDPs that satisfy the Option Package Criteria, then the Research Term will automatically extend by one-year increments until such obligation is satisfied, up to a maximum of ten years from March 2017. The activities under the Allergan Agreement during the Research Term will be governed by the Steering Committee. The Steering Committee will review and monitor the direction of the development plan, evaluate and determine which targets are selected to become CDP, establish the Option Package Criteria for each CDP and evaluate the achievement of such criteria as well as oversee the development and commercialization activities after Allergan has licensed a CDP. Under the terms of the Allergan Agreement, the Company received a $90.0 million up front, non-refundable, non-creditable cash payment (the “Allergan Upfront”) related to the Company’s research and development costs for Option Packages for at least five CDPs and for reimbursement of the Company’s past out of pocket costs with respect to the prosecution and defense of patents that it owns and in-licenses. Allergan has the option to purchase at least five development and commercialization licenses associated CDP that have satisfied the Option Package Criteria. The option exercise fee during the Initial Option Period is $15.0 million per CDP. If Allergan elects to extend the Initial Option Period, Allergan is required to pay an additional fee of $5.0 million to extend the option, at which point the Company is required to perform additional research services. If Allergan elects to exercise its option to a development and commercialization license after extending the Initial Option Period, Allergan must pay the Company the option exercise fee of $22.5 million, plus specified costs incurred by the Company in connection with the additional development work. Following the exercise by Allergan of an Option with respect to a CDP, Allergan would be required to make certain milestone payments to the Company upon the achievement of specified development, product approval and launch and commercial events, on a CDP by CDP basis. On a CDP by CDP basis, for the first product in the first field to achieve the associated event, the Company is eligible to receive up to an aggregate of $42.0 million for development milestone payments and $75.0 million for product approval and launch milestone payments, in each case, for an indication in the field per CDP. In addition, the Company is eligible to receive additional development and product approval and launch milestone payments for subsequent products developed within two additional fields. The Company is also eligible for up to $90.0 million in sales milestone payments on a CDP by CDP basis, associated with aggregate worldwide sales. Certain product approval milestones are subject to certain reductions under specified circumstances, including for payments required to be made by Allergan to obtain certain third party intellectual property rights. In December 2018, the Company received a $25.0 million payment from Allergan in connection with the acceptance of the IND for EDIT-101, the Company’s experimental therapeutic generated under the LCA10 Program (the “EDIT-101 Milestone Payment”). With respect to the LCA10 Program, and up to one other CDP of the Company’s choosing, following the exercise by Allergan of its Option to such programs the Company will have the right to elect to participate in a profit-sharing arrangement with Allergan in the United States, on terms mutually agreed by the Company and Allergan and subject to a right of Allergan to reject such election under certain circumstances, under which the Company and Allergan would share equally in net profits and losses on specific terms to be agreed between the Company and Allergan, in lieu of Allergan paying royalties on net sales of any applicable Licensed Products in the United States, and in such event Allergan’s milestone payment obligations would be reduced, with the Company being eligible to receive development and product approval and launch milestone payments up to a low nine-digit amount in the aggregate and further sales milestone payments up to a high-eight digit amount in the aggregate, subject to reduction under certain circumstances (such right, the “Profit-Share Election,” and such arrangement, a “Profit-Sharing Arrangement”). If the Company elects to participate in a Profit-Sharing Arrangement, which it has for the LCA10 Program, the Company is obligated to reimburse Allergan for half of the United States development costs incurred by Allergan with respect to the applicable CDP, and Allergan will retain control of all development and commercialization activities for the applicable Licensed Products. In addition, to the extent there is any Licensed Product, the Company would be entitled to receive tiered royalty payments of high single digits based on a percentage of net sales of such Licensed Product, subject to certain reductions under specified circumstances, and the Company will remain obligated to pay all license fees, milestone payments, and royalties due to its upstream licensors based on Allergan’s exercise of its license rights with respect to Licensed Products. However, if a Licensed Product is subject to a Profit-Sharing Arrangement the royalties will only be paid on ex-U.S. net sales. Royalties are due on a Licensed Product by Licensed Product and country by country basis from the date of the first commercial sale of each Licensed Product in a country until the later of: (i) the tenth anniversary of the first commercial sale of such Licensed Product in such country, (ii) the expiration date in such country of the last to expire valid claim within the licensed intellectual property covering the manufacture, use or sale of such Licensed Product in such country and (iii) the expiration of an exclusive legal right granted by the regulatory authority in such country to market and sell such Licensed Product. Unless earlier terminated, the Allergan Agreement will terminate upon (i) the expiration of the Research Term, if Allergan does not exercise an Option, (ii) on a Licensed Product-by-Licensed Product and country-by-country basis, on the date of the expiration of all payment obligations under the Allergan Agreement with respect to such Licensed Product in such country or (iii) in its entirety upon the expiration of all payment obligations with respect to the last Licensed Product in all countries, unless terminated earlier due to the early termination provisions. Either party may terminate the Allergan Agreement if the other party has materially breached or defaulted in the performance of any of its material obligations and such breach or default continues after the specified cure period. During the Research Term, Allergan will have the right to terminate the Allergan Agreement on a CDP by CDP basis in the event of a change in control of the Company or for all CDPs, provided that Allergan will not have any right to exercise an Option for any CDPs following such termination. After the exercise of an Option, Allergan will have the right, at its sole discretion, to terminate the Allergan Agreement, on a CDP by CDP basis, upon 90 days’ written notice. The Company may terminate the Allergan Agreement in the event that Allergan brings, assumes, or participates in, or knowingly, willfully or recklessly assists in bringing a dispute or challenge against the Company related to its intellectual property. Lastly, Allergan may terminate the Allergan Agreement with respect to a CDP if a safety concern, as specified in the Allergan Agreement, arises. Termination of the Allergan Agreement for any reason will not release either party from any liability which, at the time of such termination, has already accrued to the other party or which is attributable to a period prior to such termination. In addition, termination of the Allergan Agreement will not preclude either party from pursuing any rights and remedies it may have under the agreement or at law or in equity with respect to any breach of the Allergan Agreement. If Allergan terminates the Allergan Agreement as a result of the Company’s uncured material breach or default, then: (i) the licenses and rights conveyed to Allergan will continue as set forth in the agreement for any CDP Allergan has already licensed and (ii) Allergan’s obligations related to milestones and royalties will continue as set forth in the agreement. If the Allergan Agreement is terminated for any other reason, then the options and licenses conveyed to Allergan under the agreement will terminate. Accounting Analysis Under the Allergan Agreement, the Company has identified a single performance obligation that includes (i) the research and development services during the Research Term (the “Allergan R&D Services”), and (ii) Steering Committee services during the Research Term (the “ASC Services”). The Company has concluded that the Allergan R&D Services is not distinct from the ASC Services during the Research Term. The Steering Committee provides oversight and management of the overall Allergan Agreement, and the members of the Steering Committee from the Company have specialized industry knowledge, particularly as it relates to genome editing technology. The Steering Committee is meant to facilitate the early stage research being performed and coordinate the activities of both the Company and Allergan. Further, the Steering Committee services are critical to the selection of a CDP, the ongoing evaluation of a CDP and the development and evaluation of the Option Package Criteria. Accordingly, the Company’s participation on the Steering Committee is essential to Allergan receiving value from the Allergan R&D Services and as such, the ASC Services along with the Allergan R&D Services are considered one performance obligation (the “CDP Services”). In addition, the Company has concluded that the option to purchase five development and commercialization licenses is considered a marketing offer as the options did not provide any discounts or other rights that would be considered a material right in the arrangement. As of January 1, 2018, the date of the initial application of ASC 606 by the Company, the total transaction price was determined to be $90.0 million, consisting solely of the upfront non-refundable, non-creditable cash payment. The Company also utilized the most likely amount method to estimate any development and regulatory milestone payments to be received. As of January 1, 2018, there were no milestones included in the transaction price. The milestones were fully constrained due to the significant uncertainties surrounding such payments. The Company considered the stage of development and the risks associated with the remaining development required to achieve the milestone, as well as whether the achievement of the milestone is outside the control of the Company or Allergan. Upon achievement of the EDIT-101 Milestone Payment, $25.0 million was added to the transaction price in November 2018. As of December 31, 2018, the total transaction price is $115.0 million. The remaining milestone payments were fully constrained, as a result of the uncertainty whether any of the milestones would be achieved, as of December 31, 2018. The Company has determined that any commercial milestones and sales-based royalties will be recognized when the related sales occur and therefore have also been excluded from the transaction price. The Company will re-evaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur. The Company will recognize revenue related to the CDP Services as the underlying services are performed using a proportional performance model. The Company measures proportional performance based on full time employee hours relative to projected full time employee hours to complete the research service. During the year ended December 31, 2018, the Company recognized revenue under the Allergan Agreement of approximately $21.5 million, which includes $15.0 million related to the LCA10 Option Exercise Payment. During the year ended December 31, 2017, the Company recognized revenue under the Allergan Agreement of approximately $8.8 million. The LCA10 Option Exercise Payment was recognized upon the grant to Allergan of the right to use intellectual property associated with the development and commercialization license for LCA10 and final decision making authority with respect to the LCA10 Program. As of December 31, 2018 and 2017, there was $99.2 million and $81.2 million of deferred revenue related to the Allergan Agreement, respectively, of which $86.4 million and $68.3 million is classified as long-term on the consolidated balance sheet, respectively. As part of the Profit-Sharing Arrangement, the Company and Allergan will equally split U.S. profits and losses for the LCA10 Program in the United States and will co-develop the LCA10 Program in the United States. The Company accounts for the Profit-Sharing Arrangement with respect to the LCA10 Program within the scope of ASC Topic 808, Collaborative Arrangements, given that both the Company and Allergan are active participants in future research and development activities and both parties are exposed to significant risks and rewards dependent on the commercial success of such activities. During the year ended December 31, 2018, the Company and Allergan incurred $5.9 million in expense associated with the LCA10 Program after the option exercise, of which the Company recognized $1.7 million in contra research and development expenses during such period. The reimbursement of $2.3 million is classified as prepaid expenses and other current assets and the liability of $0.6 million in expenses owed to Allergan is classified as other current liabilities in the consolidated balance sheet as of December 31, 2018. During the year ended December 31, 2018, the Company incurred $6.0 million in sublicense fees owed to certain of the Company’s licensors in connection with the LCA10 Option Exercise Payment and EDIT-101 Milestone Payment, which the Company recorded as research and development expenses during such period, of which $3.8 million were accrued in the consolidated balance sheet as of December 31, 2018. During the year ended December 31, 2017, the Company paid $14.1 million in sublicense fees that were owed to certain of the Company’s licensors in connection with the Allergan Upfront, which the Company recorded as research and development expenses during such period. Broad Sponsored Research Agreement Summary of Agreement The Sponsored Research Agreement provides for Broad to conduct research useful or relevant to genome editing in the field of genomic medicines for the prevention or treatment of human disease with funding from the Company. Under the Sponsored Research Agreement, Broad granted to the Company an exclusive right of first negotiation for licenses from Broad with respect to patentable inventions developed by Broad in the course of the sponsored research, subject to certain limitations and retained rights (“Sponsored Invention Licenses”). Under the Sponsored Research Agreement, the Company is obligated to make Market Cap Research Funding payments in the event the Company’s market capitalization reaches specified thresholds ranging from a mid-nine digit dollar amount to a low-eleven digit dollar amount or Company Sale Research Funding payments in the event of a Company sale for consideration ranging from a mid-nine digit dollar amount to a low-eleven digit dollar amount. In connection with entering into the Sponsored Research Agreement, the Company confirmed that the first two research payments of $5.0 million and $7.5 million, respectively, were due and payable to Broad. In connection with the Initial Research Payments, the Company issued promissory notes to Broad that it settled in common stock in June 2018 as discussed more fully in Note 8. The $12.5 million in research funding expense was recorded to research and development expenses during the year ended December 31, 2018. Other than the Initial Research Payments, the Company is not required to make additional Research Funding Payments if the Company, whether directly or through its affiliates or sublicensees, is not researching, developing, or commercializing products based on or incorporating inventions exclusively licensed to the Company from Broad under Sponsored Invention Licenses or based on or incorporating CRISPR technology owned, co-owned, or controlled by Broad and otherwise licensed to the Company, subject to certain exclusions (an “Applicable Product” and such exemption from payment, the “Funding Exemption”). In the event that the Company, whether directly or through its affiliates or sublicensees, later resumes research, development, or commercialization of an Applicable Product within a specified period of time, any Research Funding Payment that was not paid to Broad as a result of the Funding Exemption shall become payable. Under the Sponsored Research Agreement, the Company is obligated to pay up to $125.0 million to Broad in Research Funding, inclusive of the Initial Research Payments, and in no event shall the aggregate amount of all Research Funding Payments exceed such amount. Unless the Company has undergone a change in control, Market Cap Research Funding is payable by the Company in cash, common stock, or in the form of promissory notes, which may be settled in shares of common stock at the election of the Company, as discussed more fully in Note 8. Following a change in control of the Company, Company Sale Research Funding is required to be made in cash. The Sponsored Research Agreement is terminable by each party upon the occurrence of specified bankruptcy events of the other party and otherwise will continue in effect until the later of the expenditure of all Research Funding Payments by Broad and such time as the Company has no further rights of first negotiation for Sponsored Invention Licenses, unless otherwise mutually agreed between the parties. Beam Therapeutics License Agreement Summary of Agreement In May 2018, the Company entered into a license agreement with Beam (the “Beam License Agreement”). Beam is a biotechnology company focused on developing precision genetic medicines using technology that converts a single nucleobase into a different nucleobase (“Base Editing”). Pursuant to the Beam License Agreement, the Company granted to Beam licenses and options to acquire licenses to certain intellectual property rights owned or controlled by the Company, for specified uses. More specifically, the Company granted to Beam a worldwide, exclusive (subject to certain exceptions), sublicensable (subject to certain conditions), license under certain intellectual property controlled by the Company for the use of Base Editing therapies for the treatment of any field of human diseases and conditions, subject to certain exceptions (the “Beam Field,” and the licenses granted or to be granted under the Beam License Agreement, the “Beam Development and Commercialization License”). Additionally, the Company granted to Beam a royalty-free, non-exclusive license under certain intellectual property owned or controlled by the Company to perform research activities in the Beam Field (the “Beam Research License”). The Company provided Beam with an exclusive option to obtain a Beam Development and Commercialization License to three additional groups of intellectual property owned or controlled by the Company, on a group by group basis, during the specified option period, subject to certain exceptions. Pursuant to the Beam License Agreement, Beam will use commercially reasonable efforts to develop a product that includes the rights licensed to Beam within a specified period of time and to commercialize any such product that have received regulatory approval in certain specified countries. As consideration for the license and option rights granted to Beam, the Company received a nominal one-time, non-refundable, non-creditable upfront cash payment. The Company also received non-cash consideration, consisting of a low to mid-single digit million number of shares of Beam Series A-1 and A-2 preferred stock, having an aggregate fair value of approximately $3.6 million. The Company is eligible to receive additional consideration if Beam elects to exercise its option to obtain a Beam Development and Commercialization License to the three categories of intellectual property underlying the Research License, for a fee ranging from a mid-teen million dollar amount to a low to mid-eight digit dollar amount per group, depending on the timing of the option exercise. Additionally, Beam is required to reimburse the Company for certain payments the Company may be obligated to make under the Company’s existing license agreements related to the intellectual property being licensed to Beam, including (i) development, regulatory and commercial milestone payments and certain sublicense income payments due as a result of the Beam License Agreement and (ii) a percentage of the annual maintenance fees and patent fees due to certain of the Company’s licensors. In addition, to the extent any products are commercialized under a Beam Development and Commercialization License, the Company would be entitled to receive royalty payments equivalent to the royalties that would be due from the Company to any applicable licensors of the Company related to the sales of such licensed products, plus an additional low single-digit percentage royalty. Additionally, if Beam exercises its right to obtain a Beam Development and Commercialization License to one of the categories of optioned intellectual property comprising Company-owned intellectual property and any related licensed products that are commercialized, the Company would be entitled to tiered low single-digit royalty payments related to sales of such licensed products. The license rights and option rights granted to Beam are subject to the terms and conditions of the underlying license agreements that the Company is a party to and under which the Company licensed rights or option rights to Beam and the termination of such in-licenses, as applicable. Unless earlier terminated by either party pursuant to the terms of the agreement, the Beam License Agreement will continue in full force and effect and will expire on a licensed product-by-licensed product and country-by-country basis upon the expiration of the royalty term with respect to such licensed product in such country. Beam has the right, at its sole discretion, at any time to terminate the Beam License Agreement in its entirety or on a group-by-group of intellectual property basis, upon ninety days written notice to the Company. Upon termination of the Beam License Agreement, all rights and licenses granted by the Company to Beam (including the rights to exercise options and obtain such licenses) will immediately terminate and patents within a group of patents will no longer be deemed licensed patents. Expiration or termination of the Beam License Agreement for any reason does not release either party of any obligation or liability which had accrued or which is attributable to a period prior to such expiration or termination. Accounting Analysis The Company has identified the following performance obligations (i) the Beam Development and Commercialization License and (ii) the Beam Research License. In addition, the Company has concluded the option to obtain additional Beam Development and Commercialization Licenses to up to three additional groups of patents in the future is considered a marketing offer as the options did not provide any discounts or other rights that would be considered a material right in the arrangement. As of December 31, 2018, the total transaction price at the inception of the arrangement was determined to be approximately $3.8 million, consisting of the upfront cash payment and non-cash consideration related to the shares of Beam preferred stock. The Company determined the fair value based on the price paid by other unrelated investors for such shares. The consideration associated with the exercise of the option(s) will be accounted for if and when Beam elects to purchase the additional licenses. The other forms of consideration, including the development and regulatory milestone reimbursement, the sublicense income reimbursement, the maintenance fee reimbursement and the patent costs reimbursement were estimated based on the most-likely amount and were excluded from the initial transaction price as the most-likely amount was estimated to be zero or the amount was otherwise fully constrained due to the significant uncertainties surrounding such payments. The commercial-based milestone reimbursement and the sales-based royalty payments will be recognized when the related sales occur as they were determined to relate predominantly to the licenses granted and therefore have also been excluded from the transaction price. The total transaction price at the inception of the arrangement was allocated to the performance obligations in the aggregate, as the Beam Development and Commercialization License and the Beam Research License were delivered simultaneously with one another, at inception of the arrangement, when the licenses were made available for Beam’s use and benefit. Accordingly, the satisfaction of each performance obligation occurs at inception of the arrangement and the transaction price at the inception of the arrangement is recognized in its entirety at such time. The Company will re-evaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur. There were no changes to the transaction price during the year ended December 31, 2018. During the year ended December 31, 2018, the Company recognized revenue under the Beam License Agreement of approximately $4.0 million. The revenue is classified as collaboration and other research and development revenues in the accompanying consolidated statement of operations and the Beam preferred stock is classified in restricted cash and other non-current assets. Other Agreements Licensing Agreements The Company is a party to a number of license agreements under which the Company licenses patents, patent applications and other intellectual property from third parties. The following is a summary of such in-license agreements that are significant to the Company’s business. Cas9-I License Agreement In October 2014, the Company entered into an agreement (the “Cas9-I License Agreement”) with Broad and Harvard to license certain patent rights owned or co‑owned by, or among, Broad, the Massachusetts Institute of Technology (“MIT”), and Harvard (collectively, the “Institutions”). Consideration for the granting of the license included the payment of an upfront license issuance fee of $0.2 million and the issuance of 561,531 shares of the Company’s common stock. The Institutions are collectively entitled to receive clinical and regulatory milestone payments totaling up to $14.8 million in the aggregate per licensed product approved in the United States, European Union, and Japan for the treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States. If the Company undergoes a change of control during the term of the license agreement, the clinical and regulatory milestone payments will be increased by a certain percentage in the mid‑double digits. The Company is also obligated to make additional payments to the Institutions, collectively, of up to an aggregate of $54.0 million upon the occurrence of certain sales milestones per licensed product for the treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States. The Institutions are collectively entitled to receive clinical and regulatory milestone payments totaling up to $4.1 million in the aggregate per licensed product approved in the U.S. and at least one jurisdiction outside the U.S. for the treatment of a human disease based on certain criteria. The Company is also obligated to make additional payments to the Institutions, collectively, of up to an aggregate of $36.0 million upon the occurrence of certain sales milestones per licensed product for the treatment of a rare disease meeting certain criteria. The Institutions are entitled to receive from the Company nominal annual license fees and a mid‑single digit percentage royalties on net sales of products for the prevention or treatment of human disease and ranging from low single digit to high single digit percentage royalties on net sales of other products and services, made by the Company, its affiliates, or its sublicensees. The royalty percentage depends on the product and service, and whether such licensed product or licensed service is covered by a valid claim within the certain patent rights that the Company licenses from the Institutions. In December 2016, the Company entered into the Cpf1 License Agreement with Broad, for specified patent rights (the “Cpf1 Patent Rights”) related primarily to Cpf1 compositions of matter and their use for gene editing. Concurrently with entering into the Cpf1 License Agreement, the Company, Broad, and Harvard amended and restated the Cas9-I License Agreement as described below and the Company and Broad entered into the Cas9‑II License Agreement for specified patent rights (the “Cas9-II Patent Rights”) related primarily to certain Cas9 compositions of matter and their use for genome editing. The Company paid an upfront fee in aggregate of $16.5 million, which included the Initial Notes, under these agreements which was recorded in research and development expenses during 2016. Cpf1 License Agreement Pursuant to the Cpf1 License Agreement, Broad, on behalf of itself, Harvard, MIT, Wageningen, and the University of Tokyo (“UTokyo” and, together with Broad, Harvard, MIT, and Wageningen, the “Cpf1 Institutions”) granted the Company an exclusive, worldwide, royalty‑bearing, sublicensable license to the Cpf1 Patent Rights, to make, have made, use, have used, sell, offer for sale, have sold, export and import products in the field of the prevention or treatment of human disease using gene therapy, editing of genetic material, or targeting of genetic material, subject to certain limitations and retained rights (collectively, the “Cpf1 Exclusive Field”), as well as a non‑exclusive, worldwide, royalty‑bearing sublicensable license to the Cpf1 Patent Rights for all other purposes, subject to certain limitations and retained rights. The Company is obligated to use commercially reasonable efforts to research, develop, and commercialize products in the Cpf1 Exclusive Field. The Company is also required to achieve certain development milestones within specified time periods for products covered by the Cpf1 Patent Rights, with Broad having the right to terminate the Cpf1 License Agreement if the Company fails to achieve these milestones within the required time periods. Broad and Wageningen are collectively entitled to receive clinical and regulatory milestone payments totaling up to $20.0 million in the aggregate per licensed product approved in the United States, European Union, and Japan for the prevention or treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States. The Company is also obligated to make additional payments to Broad and Wageningen, collectively, of up to an aggregate of $54.0 million upon the occurrence of certain sales milestones per licensed product for the prevention or treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States. Broad and Wageningen are collectively entitled to receive clinical and regulatory milestone payments totaling up to $6.0 million in the aggregate per licensed product approved in the United States, European Union and Japan for the prevention or treatment of a human disease that afflicts fewer than a specified number of patients in the aggregate in the United States or a specified number of patients per year in the United States (an “Ultra‑Orphan Disease”). The Company is also obligated to make additional payments to Broad and Wageningen, collectively, of up to an aggregate of $36.0 million upon the occurrence of certain sales milestones per licensed product for the prevention or treatment of an Ultra‑Orphan Disease. Broad and Wageningen, collectively, are entitled to receive, on a product‑by‑product and country‑by‑country basis, mid single‑digit percentage royalty on net sales of licensed products for the prevention or treatment of human disease, and royalties on net sales of other licensed products and licensed services, made by the Company, its affiliates, or its sublicensees. The royalty percentage depends on the product and service, and whether such licensed product or licensed service is covered by a valid claim within the Cpf1 Patent Rights. If the Company is legally required to pay royalties to a third party on net sales of the Company’s products because such third party holds patent rights that cover such licensed product, then the Company can credit up to a specified percentage of the amount paid to such third party against the royalties due to Broad and Wageningen in the same period. Such credit may not exceed 50% of the applicable royalties paid by the Company to the applicable third party. The Company’s obligation to pay royalties will expire on a product‑by‑product and country‑by‑country basis upon the later of the expiration of the last to expire valid claim of the Cpf1 Patent Rights that covers each licensed product or service in each country or the tenth anniversary of the date of the first commercial sale of the licensed product or licensed service. If the Company sublicenses any of the Cpf1 Patent Rights to a third party, Broad and Wageningen, collectively, have the right to receive sublicense income, depending on the stage of development of the products or services in question at the time of the sublicense. Under the Cpf1 License Agreement, Broad and Wageningen are also entitled, collectively, to receive success payments in the event the Company’s market capitalization reaches specified thresholds (the “Cpf1 Market Cap Success Payments”) or a Company sale for consideration in excess of those thresholds (the “Cpf1 Company Sale Success Payments” and, collectively with the Cpf1 Market Cap Success Payments, the “Cpf1 Success Payments”). The Cpf1 Success Payments payable to Broad and Wageningen are triggered when the Company’s market capitalization reaches certain amounts ranging from $750.0 million to $10.0 billion for a specified period of time, and collectively the Cpf1 Success Payments will not exceed, in aggregate, $125.0 million, which maximum amount would be payable only if the Company reaches a market capitalization threshold of $10.0 billion and has at least one product candidate covered by a claim of a patent right licensed to the Company under either the Cpf1 License Agreement or the Cas9‑I License Agreement that is or was the subject of a clinical trial pursuant to development efforts by the Company or any Company affiliate or sublicensee. The Cpf1 Market Cap Success Payments are payable by the Company in cash or in the form of promissory notes on substantially the same terms and conditions as the Initial Notes, as described more fully in Note 8, except that the maturity date of such notes will, subject to certain exceptions, be 150 days following issuance. Following a change in control of the Company, Cpf1 Market Cap Success Payments are required to be made in cash. Cpf1 Company Sale Success Payments are payable solely in cash. The Company triggered the first and second Cpf1 Success Payments during 2017 when the Company’s market capitalization reached $750 million and $1.0 billion, respectively, as described more fully in Note 8. Unless terminated earlier, the term of the Cpf1 License Agreement will expire on a country‑by‑country basis, upon the expiration of the last to expire valid claim of the Cpf1 Patent Rights in such country. The Company has the right to terminate the Cpf1 License Agreement at will upon four months’ written notice to Broad. Either party may terminate the Cpf1 License Agreement upon a specified period of notice in the event of the other party’s uncured material breach of a material obligation, such notice period varying depending on the nature of the breach. Broad may terminate the Cpf1 License Agreement immediately if the Company challenges the enforceability, validity, or scope of any Cpf1 Patent Right or assist a third party to do so, or in the event of the Company’s bankruptcy or insolvency. Amendment and Restatement of Cas9-I License Agreement In December 2016, the Company amended and restated the Cas9‑I License Agreement (such agreement, as amended, the “Amended and Restated Cas9-I License Agreement”) to exclude additional fields from the scope of the exclusive license previously granted to the Company, to make the exclusive license to three targets become non‑exclusive, subject to the limitation that each of Broad and Harvard would only be permitted to grant a license to only one third party at a time with respect to each such target within the field of the exclusive license, and to revise certain provisions relating to the rights of Harvard and Broad to grant further licenses under specified circumstances to third parties that wish to develop and commercialize products that target a particular gene and that otherwise would fall within the scope of the exclusive license under this agreement, so that Harvard and Broad together would have rights substantially similar to the equivalent rights possessed by Broad under the Cpf1 License Agreement to designate gene targets for which the designating institution, whether alone or together with an affiliate or third party, has an interest in researching and developing products that would otherwise be covered by rights licensed by Harvard and/or Broad to the Company under this agreement, the Cpf1 License Agreement or the Cas9‑II License Agreement. In March 2017, the Company and Harvard and Broad further amended the Amended and Restated Cas9-I License Agreement to (i) grant an exclusive license from Broad to the Company with respect to certain patent rights that The Rockefeller University (“Rockefeller”) has or may have rights in and to and for which Rockefeller has, under a certain inter-institutional agreement that Broad and Rockefeller entered into in February 2017, appointed Broad as sole and exclusive agent for the purposes of licensing and (ii) provide to Rockefeller certain rights, including with respect to patent enforcement, indemnification, insurance, confidentiality, reservation of certain rights, and publicity, that are generally consistent with those granted to Broad, Harvard, MIT and the Howard Hughes Medical Institute under the Amended and Restated Cas9-I License Agreement. Cas9‑II License Agreement Pursuant to the Cas9‑II License Agreement, Broad, on behalf of itself, MIT, Harvard, and the University of Iowa Research Foundation, granted the Company an exclusive, worldwide, royalty bearing sublicensable license to certain of the Cas9‑II Patent Rights as well as a non‑exclusive, worldwide, royalty‑bearing sublicensable license to all of the Cas9‑II Patent Rights, in each case on terms substantially similar to the licenses granted to the Company under the Cpf1 License Agreement except, among other things, for the following commitment amounts. Under the Cas9‑II License Agreement, the Company will pay an upfront license fee in a low seven digit dollar amount and will have to pay an annual license maintenance fee. The Company is obligated to pay clinical and regulatory milestone payments per licensed product approved in the United States, European Union and Japan for the prevention or treatment of a human disease that afflicts at least a specified number of patients in the aggregate in the United States totaling up to $3.7 million in the aggregate, and sales milestone payments for any such licensed product totaling up to $13.5 million in the aggregate. In addition, the Company is obligated to pay clinical and regulatory milestone payments totaling up to $1.1 million in the aggregate per licensed product approved in the United States and the European Union or Japan for the prevention or treatment of a human disease that afflicts fewer than a specified number of patients in the United States, plus sales milestone payments of up to $9.0 million for any such licensed product. Consistent with the Cpf1 License Agreement, the licensors are entitled to royalties on net sales of products for the prevention or treatment of human disease and other products and services made by the Company, its affiliates, or its sublicensees. Royalties due under other license agreements are creditable against these royalties up to a specified amount in the same period. Lastly, Broad is entitled to receive success payments if the Company’s market capitalization reaches specified thresholds ascending from $1.0 billion to $9.0 billion or upon a sale of the Company for consideration in excess of those thresholds. The potential success payments range from a low seven digit dollar amount to a low eight digit dollar amount and will not exceed, in aggregate, $30.0 million, which maximum amount would be owed only if the Company reaches a market capitalization threshold of $9.0 billion and has at least one product candidate covered by a claim of a patent right licensed to the Company under either the Cas9-I License Agreement or the Cas9-II License Agreement that is or was the subject of a clinical trial pursuant to development efforts by the Company or any Company affiliate or sublicensee. The Company triggered the first Success Payment under the Cas9-II License Agreement during the fourth quarter of 2017 when the Company’s market capitalization reached $1.0 billion, which the Company settled in January 2018, as more fully described in Note 8.

Common Stock

12 Months Ended

Dec. 31, 2018

Common Stock

Common Stock

11. Common Stock

The voting, dividend, and liquidation rights of the holders of the common stock are subject to and qualified by the rights, powers, and preferences of holders of the preferred stock that may be issued from time to time. The common stock had the following characteristics as of December 31, 2018:

Voting

The holders of shares of common stock are entitled to one vote for each share of common stock held at any meeting of stockholders and at the time of any written action in lieu of a meeting.

Dividends

The holders of shares of common stock are entitled to receive dividends, if and when declared by the Company’s board of directors. Cash dividends may not be declared or paid to holders of shares of common stock until all unpaid dividends on the redeemable convertible preferred stock have been paid in accordance with their terms. No dividends have been declared or paid by the Company since its inception.

Shares Reserved for Future Issuance


	As of December 31,
	2018	2017
Shares reserved for outstanding stock option awards under the 2013 Stock Incentive Plan, as amended	873,373	1,220,567
Shares reserved for outstanding stock option awards under the 2015 Stock Incentive Plan	3,709,225	2,921,987
Shares reserved for outstanding inducement stock option award	107,188	225,000
Remaining shares reserved, but unissued, for future awards under the 2015 Stock Incentive Plan	3,233,031	2,502,338
Remaining shares reserved, but unissued, for future awards under the 2015 Employee Stock Purchase Plan	1,175,224	751,242
	9,098,041	7,621,134

March 2018 Common Stock Sales Agreement

In March 2018, the Company entered into a sales agreement with Cowen and Company LLC (“Cowen”), under which the Company from time to time can issue and sell shares of its common stock through Cowen in at-the-market offerings (“2018 ATM Program”) for aggregate sales proceeds of $150.0 million. The common stock will be distributed at the market prices prevailing at the time of sale. All sales of shares will be made pursuant to an effective shelf registration statement on Form S-3 filed with the Securities and Exchange Commission (“SEC”). The Company will pay Cowen a commission of 3% of the aggregate gross proceeds the Company receives from all sales of the Company’s common stock under the sales agreement. In November 2018, the Company sold an aggregate of 1,107,000 shares of its common stock under the 2018 ATM Program at an average price of $26.95 per share for net proceeds of $28.4 million.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2018

Stock-Based Compensation

Stock-Based Compensation

12. Stock‑Based Compensation

2013 Stock Incentive Plan

In September 2013, the board of directors adopted the 2013 Stock Incentive Plan, which was subsequently amended (as amended, the “2013 Plan”), which provides for the grant of incentive stock options and nonqualified stock options or other awards including restricted stock awards, unrestricted stock awards, and restricted stock units to the Company’s employees, officers, directors, advisors, and consultants for the purchase of up to 1,057,692 shares of the Company’s common stock. In June 2014, the 2013 Plan was amended to increase the number of shares reserved thereunder by 1,365,384 shares. In April 2015, the 2013 Plan was amended to increase the number of shares reserved thereunder by 153,846 shares. In July 2015, the 2013 Plan was amended to increase the number of shares reserved thereunder by 3,740,847 shares.

The terms of stock awards agreements, including vesting requirements, are determined by the board of directors and are subject to the provisions of the 2013 Plan. The stock options granted to employees generally vest over a four-year period and expire ten years from the date of grant. Certain awards contain performance based vesting criteria. There has only been one such award to date. Certain options provide for accelerated vesting in the event of a change in control, as defined in the applicable options. Awards granted to non-employee consultants generally vest monthly over a period of one to four years. In connection with the IPO, the Company’s board of directors determined to grant no further awards under the 2013 Plan.

2015 Stock Incentive Plan

The Company’s board of directors adopted and the Company’s stockholders approved the 2015 stock incentive plan (the “2015 Plan”), which became effective immediately prior to the effectiveness of the registration statement related to the IPO. The 2015 Plan provides for the grant of incentive stock options, nonstatutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock‑based awards. The Company’s employees, officers, directors and consultants and advisors are eligible to receive awards under the 2015 Plan.

The number of shares reserved for issuance under the 2015 Plan is subject to further increases for (a) any additional shares of the Company’s common stock subject to outstanding awards under the 2013 Plan that expire, terminate, or are otherwise surrendered, cancelled, forfeited, or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right and (b) annual increases, to be added as of the first day of each fiscal year, from January 1, 2017 until, and including, January 1, 2026, equal to the lowest of 2,923,076 shares of common stock, 4% of the number of shares of common stock outstanding on such first day of the fiscal year in question and an amount determined by the Company’s board of directors. In January 2019, the shares under the 2015 Plan were increased by 1,961,156 shares pursuant to the annual increase described in the prior sentence.

2015 Employee Stock Purchase Plan

The Company’s board of directors adopted and the Company’s stockholders approved the 2015 employee stock purchase plan (the “2015 ESPP”), which became effective upon the closing of the IPO. The number of shares reserved for issuance under the 2015 ESPP is subject to annual increases, to be added as of the first day of each fiscal year, from January 1, 2017 until, and including, January 1, 2026, in an amount equal to the least of (a) 769,230 shares of common stock, (b) 1% of the total number of shares of common stock outstanding on the first day of the applicable year, and (c) an amount determined by the board of directors. The first offering under the 2015 ESPP opened on December 1, 2017. In January 2019, the shares under the 2015 ESPP Plan were increased by 490,289 shares pursuant to the annual increase described in the prior sentence.

Founder Awards

In September 2013, the Company issued 2,403,845 shares of restricted stock to its non‑employee founders for services rendered subject to certain repurchase rights. The shares vested 25% upon the first issuance of shares of Series A Preferred Stock and then 1.5625% a month through the fourth anniversary of the vesting commencement date. These shares of restricted stock were subject to repurchase rights. Accordingly, the Company recorded the proceeds from the issuance of restricted stock as a liability in its consolidated balance sheets. The restricted stock liability was reclassified into stockholders’ equity (deficit) as the restricted stock vested. In June 2014, one founder ceased to be in the Company’s service and the Company repurchased 285,457 shares of unvested restricted stock from the founder for $74. The remaining founder awards completed vesting in August 2017.

Stock‑based compensation expense associated with these awards was recognized as the awards vested. Unvested awards were remeasured at each reporting period end to reflect the current fair value of such awards on a straight‑line basis.

Stock‑Based Compensation Expense

Total compensation cost recognized for all stock‑based compensation awards in the consolidated statements of operations was as follows (in thousands):


	Year Ended
	December 31,
	2018		2017		2016
Research and development	$	14,734	$	15,131	$	12,647
General and administrative		11,864		8,233		4,234
Total stock-compensation expense	$	26,598	$	23,364	$	16,881

Restricted Stock

From time to time, upon approval by the Company’s board of directors, certain employees and advisors have been granted restricted shares of common stock. These shares of restricted stock are subject to repurchase rights. Accordingly, the Company has recorded the proceeds from the issuance of restricted stock as a liability in the consolidated balance sheets. The restricted stock liability is reclassified into stockholders’ equity as the restricted stock vests. A summary of the status of and changes in unvested restricted stock as of December 31, 2017 and 2018 is as follows:


		Weighted
		Average
		Grant Date
		Fair Value
	Shares	Per Share
Unvested Restricted Common Stock as of December 31, 2017	513,225	$	18.70
Issued	—		—
Vested	(243,225)	$	8.32
Forfeited	—		—
Unvested Restricted Common Stock as of December 31, 2018	270,000	$	28.05

The expense related to restricted stock awards granted to employees and non-employees was $0 million and $2.4 million, respectively, for the year ended December 31, 2018. The expense related to restricted stock awards granted to employees and non‑employees was $0.5 million and $4.1 million, respectively, for the year ended December 31, 2017. The expense related to restricted stock awards granted to employees and non‑employees was $0 and $8.3 million, respectively, for the year ended December 31, 2016.

As of December 31, 2018, the Company had no unrecognized stock‑based compensation expense related to its employee unvested restricted stock awards and $6.0 million in unrecognized stock-based compensation expense related to its non-employee unvested restricted stock awards which is expected to be recognized over a remaining weighted average vesting period of 3.7 years.

Stock Options

Certain of the Company’s stock option agreements allowed for the exercise of unvested awards. During 2014, options to purchase 75,304 shares of common stock for $0.03 per share were exercised prior to their vesting. The unvested shares were subject to repurchase by the Company if the employees ceased to provide service to the Company, with or without cause. As such, the Company did not treat the exercise of unvested options as a substantive exercise. The Company recorded the proceeds from the exercise of unvested stock options as a liability in the consolidated balance sheets. The liability for unvested common stock subject to repurchase was reclassified into stockholders’ equity as the shares vested. As of June 30, 2018, the early exercise stock options were fully vested.

The following is a summary of stock option activity for the year ended December 31, 2018:


		Weighted Average		Remaining	Aggregate Intrinsic
	Shares	Exercise Price		Contractual Life	Value (in thousands)
Outstanding at December 31, 2017	4,372,136	$	17.28	8.5	$	60,591
Granted	1,884,411	$	35.29	—		—
Exercised	(752,674)	$	13.78	—		—
Cancelled	(814,087)	$	24.88	—		—
Outstanding at December 31, 2018	4,689,786	$	23.80	7.9	$	20,686
Exercisable at December 31, 2018	2,061,769	$	18.34	7.0	$	15,222

The table above reflects restricted stock issued upon exercise of unvested stock options as exercised on the dates that the shares are no longer subject to repurchase. The Company had no unvested restricted common stock outstanding at December 31, 2018 and had 4,572 shares of unvested restricted common stock outstanding at December 31, 2017, resulting from the exercise of unvested stock options.

The total intrinsic value of options exercised for the years ended December 31, 2018, 2017 and 2016 was $15.9 million, $5.0 million and $0.9 million, respectively.

Using the Black‑Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the years ended December 31, 2018, 2017, and 2016 was $24.91, $16.07 and $14.10, respectively. The expense related to options granted to employees and directors was $19.9 million, $12.3 million and $6.0 million for the years ended December 31, 2018, 2017, and 2016, respectively.

The fair value of each option issued to employees and directors was estimated at the date of grant using the Black‑Scholes option pricing model with the following weighted‑average assumptions:


	Year Ended
	December 31,
	2018		2017		2016
Expected volatility	77.5	%	77.8	%	78.4	%
Expected term (in years)	6.25		6.25		6.25
Risk free interest rate	2.9	%	2.1	%	1.5	%
Expected dividend yield	—		—		—

There were no options granted to persons other than employees and directors during the year ended December 31, 2018. For the years ended December 31, 2018, 2017 and 2016, the fair value of each option issued to persons other than employees and directors was estimated at the date of grant using the Black‑Scholes option pricing model with the weighted‑average assumptions set forth in the table below:


	Year Ended
	December 31,
	2018	2017	2016
Expected volatility	—	—	76.5	%
Expected term (in years)	—	—	10.0
Risk free interest rate	—	—	1.6	%
Expected dividend yield	—	—	—

As of December 31, 2018, the Company had unrecognized stock‑based compensation expense related to its employee stock options of $47.4 million which the Company expects to recognize over a remaining weighted average vesting period of 2.45 years.

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2018
401(k) Savings Plan
401(k) Savings Plan	13. 401(k) Savings Plan The Company has a defined‑contribution savings plan under Section 401(k) of the Internal Revenue Code of 1986, as amended (the “401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pretax basis. Effective in 2017, the Company will provide a 200% match of employee contributions up to a limit on the Company’s contributions of the lesser of $6,000 and 3% of the employee’s salary. The Company made $0.7 million and $0.5 million in contributions to the 401(k) Plan for the years ended December 31, 2018 and 2017, respectively.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Taxes

Income Taxes

14. Income Taxes

The Company had no income tax expense due to operating losses incurred for the years ended December 31, 2018, 2017 and 2016.

A reconciliation of the income tax expense computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows:


	Year Ended
	December 31,
	2018		2017		2016
Income tax computed at federal statutory tax rate	21.0	%	34.0	%	34.0	%
State taxes, net of federal benefit	6.4	%	5.9	%	3.5	%
General business credit carryovers	4.4	%	2.5	%	1.5	%
Non-deductible expenses	0.6	%	(2.1)	%	(3.6)	%
Federal tax rate reduction	—	%	(24.7)	%	—	%
Change in valuation allowance	(32.4)	%	(15.6)	%	(35.4)	%
	—	%	—	%	—	%

On December 22, 2017, legislation commonly known as the Tax Cuts and Jobs Act (the “Tax Act”) was signed into law. The Tax Act, among other changes, reduces the U.S. federal corporate tax rate from 34% to 21%, requires taxpayers to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. The Company does not currently have any foreign subsidiaries and the international aspects of the Tax Act are not applicable.

In December 2017, the SEC staff issued Staff Accounting Bulletin No. 118 to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Act. As of December 31, 2018, the Company had completed its accounting for all of the tax effects of the enactment of the Tax Act; including the effects on its existing deferred tax balances. The Company has not recognized any material adjustment to the provisional estimate that was previously recorded related to the Tax Act.

The principal components of the Company’s deferred tax assets and liabilities consist of the following at December 31, 2018 and 2017 (in thousands):


	Year Ended
	December 31,
	2018		2017
Deferred tax assets:
Net operating loss carryforwards	$	20,302	$	27,726
Tax credit carryforwards		10,059		5,259
Accrued expenses		3,099		2,079
Capitalized patent costs		33,101		26,307
Deferred revenue		34,039		7,151
Construction financing lease obligation		9,100		9,352
Other		8,347		4,978
Total deferred tax assets		118,047		82,852
Less valuation allowance		(109,091)		(73,301)
Net deferred tax assets		8,956		9,551
Deferred tax liabilities—depreciation and amortization		(8,956)		(9,551)
Net deferred taxes	$	—	$	—

The Company has incurred net operating losses (“NOL”) since inception. At December 31, 2018 and 2017, the Company had federal and state net operating loss carryforwards of $147.8 million and $202.7 million, respectively, which expire beginning in 2035 and will continue to expire through 2037. As of December 31, 2018 and 2017, the Company had federal and state research and development tax credits carryforwards of $10.8 million and $5.6 million, respectively, which expire beginning in 2028 and will continue to expire through 2038.

Under the provisions of the Internal Revenue Code of 1986, as amended (the “Code”), the NOL and tax credit carryforward are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. NOL and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Code, respectively, as well as other similar state provisions. The Company conducted an analysis under Section 382 to determine if historical changes in ownership through December 31, 2017 would limit or otherwise restrict its ability to utilize its NOL and research and development credit carryforwards. As a result of this analysis, the Company does not believe there are any significant limitations on its ability to utilize these carryforwards. However, future changes in ownership occurring after December 31, 2017 could affect the limitation in future years, and any limitation may result in expiration of a portion of the NOL or research and development credit carryforwards before utilization.

Management has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which principally comprise of NOL carryforwards, research and development credit carryforwards and capitalized license and patent costs. The Company’s management has determined that it is more likely than not that the Company will not recognize the benefits of its federal and state deferred tax assets, and as a result, a valuation allowance of $109.1 million and $73.3 million has been established at December 31, 2018 and 2017, respectively. The increase in the valuation allowance of $35.8 million for the year ended December 31, 2018 was primarily due to current period pre-tax losses incurred and research tax credits generated.

The Company applies ASC 740 related to accounting for uncertainty in income taxes. The Company’s reserves related to income taxes are based on a determination of whether, and how much of, a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. At December 31, 2018 and 2017, the Company had no unrecognized tax benefits. Interest and penalty charges, if any, related to unrecognized tax benefits would be classified as income tax expense in the accompanying statements of operations.

The Company has not as yet conducted a study of its research and development credit carry forwards. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development credits, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated balance sheets or statements of operations if an adjustment were required.

The Company files income tax returns in the U.S. federal tax jurisdiction, the Massachusetts state jurisdiction and the California state jurisdiction. The Company will file an initial Colorado tax return for 2018. Since the Company is in a loss carryforward position, the Company is generally subject to examination by the U.S. federal, state and local income tax authorities for all tax years in which a loss carryforward is available. The Company did not have any international operations as of December 31, 2018. There are no federal or state audits in process.

Net Loss per Share

12 Months Ended

Dec. 31, 2018

Net Loss per Share

Net Loss per Share

15. Net Loss per Share

Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock and potentially dilutive securities outstanding for the period determined using the treasury stock and if converted methods. Contingently issuable shares are included in the calculation of basic loss per share as of the beginning of the period in which all the necessary conditions have been satisfied. Contingently issuable shares are included in diluted loss per share based on the number of shares, if any, that would be issuable under the terms of the arrangement if the end of the reporting period was the end of the contingency period, if the results are dilutive.

For purposes of the diluted net loss per share calculation, stock options are considered to be common stock equivalents, but they were excluded from the Company’s calculation of diluted net loss per share allocable to common stockholders because their inclusion would have been anti-dilutive. Therefore, basic and diluted net loss per share applicable to common stockholders was the same for all periods presented.

Upon the closing of the November 2018 ATM Offering, the January 2018 ATM Offering, the 2017 December Offering and the 2017 March Offering, the Company sold 1,107,000 shares, 1,429,205 shares, 2,265,500 shares and 4,600,000 shares of common stock, respectively. The issuance of these shares resulted in a significant increase in the Company’s weighted-average shares outstanding for the years ended December 31, 2018 and 2017 and is expected to continue to impact the year-over-year comparability of the Company’s net loss per share calculations for the next twelve months.

The following common stock equivalents were excluded from the calculation of diluted net loss per share allocable to common stockholders because their inclusion would have been anti-dilutive:


	As of December 31,
	2018	2017
Unvested restricted common stock	270,000	513,225
Outstanding stock options	4,689,786	4,372,126
Estimated number of shares issuable for convertible notes (1)	—	244,896
Total	4,959,786	5,130,247

(1)

Represents the number of shares of common stock that would have been issued if the Company had elected to pay the December Success Payment Notes, as discussed in Note 8, in shares of the Company’s common stock, based on the closing price of the common stock on December 31, 2017. The number of shares issued, for purposes of this presentation, is calculated by dividing the principal of the notes payable, including accrued interest, by the common stock price per share.

The table above reflects restricted stock issued upon exercise of unvested stock options as exercised on the dates that the shares are no longer subject to repurchase.

Selected Quarterly Financial Data

12 Months Ended

Dec. 31, 2018

Selected Quarterly Financial Data

Selected Quarterly Financial Data

17. Selected Quarterly Financial Data (unaudited) –

The following table contains selected quarterly financial information from 2018 and 2017. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period.


	Three Months Ended
	March 31, 2018		June 30, 2018		September 30, 2018		December 31, 2018
		(in thousands, except per share data)
Total collaboration and other research and development revenues	$	3,927	$	7,372	$	14,519	$	6,119
Total operating expenses		35,486		47,029		30,777		32,372
Total other income (expense), net		620		934		1,020		1,199
Net loss	$	(30,939)	$	(38,723)	$	(15,238)	$	(25,054)
Net loss applicable to common stockholders	$	(30,939)	$	(38,723)	$	(15,238)	$	(25,054)
Net loss per share applicable to common stockholders — basic and diluted	$	(0.67)	$	(0.82)	$	(0.32)	$	(0.52)


	Three Months Ended
	March 31, 2017		June 30, 2017		September 30, 2017		December 31, 2017
		(in thousands, except per share data)
Total collaboration and other research and development revenues	$	682	$	3,097	$	6,282	$	3,667
Total operating expenses		31,309		29,212		33,031		40,109
Total other income (expense), net		(470)		(324)		150		253
Net loss	$	(31,097)	$	(26,439)	$	(26,599)	$	(36,189)
Net loss applicable to common stockholders	$	(31,097)	$	(26,439)	$	(26,599)	$	(36,189)
Net loss per share applicable to common stockholders — basic and diluted	$	(0.85)	$	(0.65)	$	(0.64)	$	(0.84)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Summary of Significant Accounting Policies

Principles of Consolidation

Unaudited Interim Financial Information

Basis of Presentation

Reclassification

Certain prior period amounts have been reclassified for consistency with the current period presentation. These reclassifications had no effect on previously reported results of operations.

Use of Estimates

Fair Value of Financial Instruments

Level 1 – Quoted market prices in active markets for identical assets or liabilities.

Level 2 – Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates, and yield curves.

Level 3 – Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use.

Cash, Cash Equivalents, and Restricted Cash


	Year Ended
	As of December 31,
	2018		2017		2016
Cash and cash equivalents	$	134,776	$	146,630	$	185,323
Restricted cash included in "Restricted cash and other non-current assets"		1,619		1,619		1,619
Total	$	136,395	$	148,249	$	186,942

Marketable Securities

Accounts Receivable

Property and Equipment


Asset:		Estimated Useful life
Lab equipment		5 years
Computer equipment and software		3 years
Furniture and equipment		5 years
Leasehold improvements		Shorter of useful life or remaining lease term
Building		30 years

Impairment of Long-lived Assets

Impairment of Long‑lived Assets

Revenue Recognition

To date, the Company has primarily earned revenue under the collaboration and license agreement with Juno Therapeutics and the strategic alliance with Allergan.

Prior to ASC 606 Adoption

Persuasive evidence of an arrangement exists;

Delivery has occurred or services have been rendered;

The seller’s price to the buyer is fixed or determinable; and

Collectability is reasonably assured.

Research and Development Costs

Research and Development Expenses

Patent Costs

Construction Financing Lease Obligation

Operating Lease Obligations

Stock-based Compensation Expense

Stock‑based Compensation Expense

Income taxes

Other Income (Expense), Net

Comprehensive Loss

Corporate Equity Securities

Concentrations of Credit Risk and Off-Balance Sheet Risk

Concentrations of Credit Risk and Off‑Balance Sheet Risk

Segment Information

Net loss per share

Recent Accounting Pronouncements

Recent Accounting Pronouncements - Adopted


	Year Ended
	As of December 31,
	2018		2017		2016
Cash and cash equivalents	$	134,776	$	146,630	$	185,323
Restricted cash included in "Restricted cash and other non-current assets"		1,619		1,619		1,619
Total	$	136,395	$	148,249	$	186,942

The following table presents changes in the Company’s deferred revenue balance as of January 1, 2018 resulting from adoption of ASC 606 (in thousands):


	Balance at December 31, 2017		Adjustments		Balance at January 1, 2018
Contract liabilities:
Deferred revenue	$	(107,963)	$	(474)	$	(108,437)


For the year ended December 31, 2018	Balance at December 31, 2017		Additions		Deductions		Balance at December 31, 2018
Accounts receivable	$	679	$	1,189	$	(1,838)	$	30
Contract liabilities:
Deferred revenue	$	(107,963)	$	(31,497)	$	8,134	$	(131,326)

During the three months and year ended December 31, 2018, the Company recognized revenue as a result of the following (in thousands):


		Three Months Ended		Year Ended
Revenue recognized in the period from:	December 31, 2018
Amounts included in deferred revenue at the beginning of the period	$	1,417	$	5,874
Performance obligations satisfied in previous periods	$	4,645	$	5,956

For additional information regarding revenue recognition from contracts with customers, refer to Note 9.

The Company has included the following financial statement line items for comparability purposes as of and for the three months and year ended December 31, 2018 (in thousands, except per share data):


		Three Months Ended December 31, 2018
	As reported under Topic 606		Balances without adoption of ASC 606		Effect of Change
Collaboration and other research and development revenues	$	6,119	$	5,060	$	1,059
Operating loss	$	(26,253)	$	(27,312)	$	1,059
Net loss attributable to common stockholders	$	(25,054)	$	(26,113)	$	1,059
Net loss per share attributable to common stockholders, basic and diluted	$	(0.52)	$	(0.54)	$	0.02


		Year Ended December 31, 2018
	As reported under Topic 606		Balances without adoption of ASC 606		Effect of Change
Collaboration and other research and development revenues	$	31,937	$	33,993	$	(2,056)
Operating loss	$	(113,727)	$	(111,671)	$	(2,056)
Net loss attributable to common stockholders	$	(109,954)	$	(107,898)	$	(2,056)
Net loss per share attributable to common stockholders, basic and diluted	$	(2.33)	$	(2.29)	$	(0.04)


		As of December 31, 2018
	As reported under Topic 606		Balances without adoption of ASC 606		Effect of Change
Deferred revenue, current	$	(15,712)	$	(17,552)	$	1,840
Deferred revenue, net of current portion	$	(115,614)	$	(111,466)	$	(4,148)
Accumulated deficit	$	(416,278)	$	(414,222)	$	(2,056)

Recent Accounting Pronouncements – Issued But Not Yet Adopted

Summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2018

Schedule of cash, cash equivalents, and restricted cash


	Year Ended
	As of December 31,
	2018		2017		2016
Cash and cash equivalents	$	134,776	$	146,630	$	185,323
Restricted cash included in "Restricted cash and other non-current assets"		1,619		1,619		1,619
Total	$	136,395	$	148,249	$	186,942

Schedule of estimated useful lives of property, plant and equipment


Asset:		Estimated Useful life
Lab equipment		5 years
Computer equipment and software		3 years
Furniture and equipment		5 years
Leasehold improvements		Shorter of useful life or remaining lease term
Building		30 years

Schedule of contract assets and liabilities

The following table presents changes in the Company’s deferred revenue balance as of January 1, 2018 resulting from adoption of ASC 606 (in thousands):


	Balance at December 31, 2017		Adjustments		Balance at January 1, 2018
Contract liabilities:
Deferred revenue	$	(107,963)	$	(474)	$	(108,437)

Schedule of accounts receivable and contract liabilities

The following table presents changes in the Company’s accounts receivable and contract liabilities for the year ended December 31, 2018 (in thousands):


For the year ended December 31, 2018	Balance at December 31, 2017		Additions		Deductions		Balance at December 31, 2018
Accounts receivable	$	679	$	1,189	$	(1,838)	$	30
Contract liabilities:
Deferred revenue	$	(107,963)	$	(31,497)	$	8,134	$	(131,326)

Schedule of change in contract assets and contract liabilities

During the three months and year ended December 31, 2018, the Company recognized revenue as a result of the following (in thousands):


		Three Months Ended		Year Ended
Revenue recognized in the period from:	December 31, 2018
Amounts included in deferred revenue at the beginning of the period	$	1,417	$	5,874
Performance obligations satisfied in previous periods	$	4,645	$	5,956

Schedule of financial statement line items for comparability purposes

The Company has included the following financial statement line items for comparability purposes as of and for the three months and year ended December 31, 2018 (in thousands, except per share data):


		Three Months Ended December 31, 2018
	As reported under Topic 606		Balances without adoption of ASC 606		Effect of Change
Collaboration and other research and development revenues	$	6,119	$	5,060	$	1,059
Operating loss	$	(26,253)	$	(27,312)	$	1,059
Net loss attributable to common stockholders	$	(25,054)	$	(26,113)	$	1,059
Net loss per share attributable to common stockholders, basic and diluted	$	(0.52)	$	(0.54)	$	0.02


		Year Ended December 31, 2018
	As reported under Topic 606		Balances without adoption of ASC 606		Effect of Change
Collaboration and other research and development revenues	$	31,937	$	33,993	$	(2,056)
Operating loss	$	(113,727)	$	(111,671)	$	(2,056)
Net loss attributable to common stockholders	$	(109,954)	$	(107,898)	$	(2,056)
Net loss per share attributable to common stockholders, basic and diluted	$	(2.33)	$	(2.29)	$	(0.04)


		As of December 31, 2018
	As reported under Topic 606		Balances without adoption of ASC 606		Effect of Change
Deferred revenue, current	$	(15,712)	$	(17,552)	$	1,840
Deferred revenue, net of current portion	$	(115,614)	$	(111,466)	$	(4,148)
Accumulated deficit	$	(416,278)	$	(414,222)	$	(2,056)

ASU 2016-18

Schedule of cash, cash equivalents, and restricted cash

The following table presents cash, cash equivalents and restricted cash as reported on the consolidated balance sheets that equal the total amounts on the consolidated statements of cash flows (in thousands):


	Year Ended
	As of December 31,
	2018		2017		2016
Cash and cash equivalents	$	134,776	$	146,630	$	185,323
Restricted cash included in "Restricted cash and other non-current assets"		1,619		1,619		1,619
Total	$	136,395	$	148,249	$	186,942

Cash Equivalents, Marketable Securities and Corporate Equity Securities (Tables)

12 Months Ended

Dec. 31, 2018

Cash Equivalents, Marketable Securities and Corporate Equity Securities

Schedule of cash equivalents, marketable securities and corporate equity securities

Cash equivalents, marketable securities and corporate equity securities consisted of the following at December 31, 2018 (in thousands):


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
December 31, 2018	Cost		Gains		Losses		Value
Cash equivalents and marketable securities:
Money market funds	$	130,049	$	—	$	—	$	130,049
U.S. Treasuries		208,754		—		(24)		208,730
Government agency securities		29,940		—		(5)		29,935
Equity securities included in other non-current assets:
Corporate equity securities		3,667		—		—		3,667
Total	$	372,410	$	—	$	(29)	$	372,381

Cash equivalents and marketable securities consisted of the following at December 31, 2017 (in thousands):


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
December 31, 2017	Cost		Gains		Losses		Value
Cash equivalents and marketable securities:
Money market funds	$	134,635	$	—	$	—	$	134,635
U.S. Treasuries		135,601		—		(47)		135,554
Government agency securities		58,979		—		(29)		58,950
Total cash equivalents and marketable securities	$	329,215	$	—	$	(76)	$	329,139

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Measurements

Schedule of assets measured at fair value on a recurring basis

Assets measured at fair value on a recurring basis as of December 31, 2018 are as follows (in thousands):


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	December 31,		Identical Assets		Inputs		Inputs
Financial Assets	2018		(Level 1)		(Level 2)		(Level 3)
Cash equivalents:
Money market funds	$	130,049	$	130,049	$	—	$	—
U.S. Treasuries		4,487		4,487		—		—
Marketable securities:
U.S. Treasuries		204,243		204,243		—		—
Government agency securities		29,935		29,935		—		—
Restricted cash and other non-current assets:
Corporate equity securities		3,667		—		3,667		—
Money market funds		1,619		1,619		—		—
Total financial assets	$	374,000	$	370,333	$	3,667	$	—

Assets and liabilities measured at fair value on a recurring basis as of December 31, 2017 are as follows (in thousands):


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	December 31,		Identical Assets		Inputs		Inputs
Financial Assets	2017		(Level 1)		(Level 2)		(Level 3)
Cash and cash equivalents:
Money market funds	$	134,635	$	134,635	$	—	$	—
U.S. Treasuries		11,995		11,995		—		—
Marketable securities:
U.S. Treasuries		123,559		123,559		—		—
Government agency securities		58,950		58,950		—		—
Money market funds, included in restricted cash		1,619		1,619		—		—
Total financial assets	$	330,758	$	330,758	$	—	$	—

Prepaid Expenses and Other Current Assets (Tables)

12 Months Ended

Dec. 31, 2018

Prepaid Expenses and Other Current Assets

Schedule of prepaid expenses and other current assets

Prepaid expense and other current assets consisted of the following (in thousands):


	As of
	December 31,
	2018		2017
Prepaid expenses	$	2,918	$	1,864
Other		2,873		517
Total	$	5,791	$	2,381

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2018

Property and Equipment, Net

Schedule of property and equipment, net

Property and equipment, net consisted of the following (in thousands):


	As of
	December 31,
	2018		2017
Building	$	35,167	$	35,167
Laboratory equipment		10,892		7,415
Computer equipment		733		550
Leasehold improvements		289		177
Furniture and office equipment		166		96
Software		118		95
Total property and equipment		47,365		43,500
Less: accumulated depreciation		(7,133)		(4,058)
Property and equipment, net	$	40,232	$	39,442

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2018

Accrued Expenses

Schedule of accrued expenses

Accrued expenses consisted of the following (in thousands):


	As of
	December 31,
	2018		2017
Employee related expenses	$	5,201	$	3,708
Sublicensing and success payment expenses		3,750		2,000
Intellectual property and patent related fees		1,939		2,370
Process and platform development expenses		1,044		2,301
Professional service expenses		475		487
Other expenses		404		183
Total	$	12,813	$	11,049

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies

Schedule of future annual minimum lease payments

The non-cancelable minimum annual lease payments, excluding the Company’s share of the facility operating expenses and other costs that are reimbursable to the landlord under the lease, consist of the following (in thousands):


Year ended December 31,	11 Hurley Street Lease
2019		4,155
2020		4,257
2021		4,362
2022		4,470
2023 (partial year)		3,802
2024 and thereafter		-
Total minimum lease payments	$	21,046

Common Stock (Tables)

12 Months Ended

Dec. 31, 2018

Common Stock

Schedule of shares reserved for future issuance


	As of December 31,
	2018	2017
Shares reserved for outstanding stock option awards under the 2013 Stock Incentive Plan, as amended	873,373	1,220,567
Shares reserved for outstanding stock option awards under the 2015 Stock Incentive Plan	3,709,225	2,921,987
Shares reserved for outstanding inducement stock option award	107,188	225,000
Remaining shares reserved, but unissued, for future awards under the 2015 Stock Incentive Plan	3,233,031	2,502,338
Remaining shares reserved, but unissued, for future awards under the 2015 Employee Stock Purchase Plan	1,175,224	751,242
	9,098,041	7,621,134

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Stock-Based Compensation

Schedule of stock-based compensation expense

Total compensation cost recognized for all stock‑based compensation awards in the consolidated statements of operations was as follows (in thousands):


	Year Ended
	December 31,
	2018		2017		2016
Research and development	$	14,734	$	15,131	$	12,647
General and administrative		11,864		8,233		4,234
Total stock-compensation expense	$	26,598	$	23,364	$	16,881

Schedule of changes in unvested restricted stock


		Weighted
		Average
		Grant Date
		Fair Value
	Shares	Per Share
Unvested Restricted Common Stock as of December 31, 2017	513,225	$	18.70
Issued	—		—
Vested	(243,225)	$	8.32
Forfeited	—		—
Unvested Restricted Common Stock as of December 31, 2018	270,000	$	28.05

Schedule of stock option activity


		Weighted Average		Remaining	Aggregate Intrinsic
	Shares	Exercise Price		Contractual Life	Value (in thousands)
Outstanding at December 31, 2017	4,372,136	$	17.28	8.5	$	60,591
Granted	1,884,411	$	35.29	—		—
Exercised	(752,674)	$	13.78	—		—
Cancelled	(814,087)	$	24.88	—		—
Outstanding at December 31, 2018	4,689,786	$	23.80	7.9	$	20,686
Exercisable at December 31, 2018	2,061,769	$	18.34	7.0	$	15,222

Schedule of assumptions used to value stock options

The fair value of each option issued to employees and directors was estimated at the date of grant using the Black‑Scholes option pricing model with the following weighted‑average assumptions:


	Year Ended
	December 31,
	2018		2017		2016
Expected volatility	77.5	%	77.8	%	78.4	%
Expected term (in years)	6.25		6.25		6.25
Risk free interest rate	2.9	%	2.1	%	1.5	%
Expected dividend yield	—		—		—


	Year Ended
	December 31,
	2018	2017	2016
Expected volatility	—	—	76.5	%
Expected term (in years)	—	—	10.0
Risk free interest rate	—	—	1.6	%
Expected dividend yield	—	—	—

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Taxes

Schedule of reconciliation of effective income tax rate


	Year Ended
	December 31,
	2018		2017		2016
Income tax computed at federal statutory tax rate	21.0	%	34.0	%	34.0	%
State taxes, net of federal benefit	6.4	%	5.9	%	3.5	%
General business credit carryovers	4.4	%	2.5	%	1.5	%
Non-deductible expenses	0.6	%	(2.1)	%	(3.6)	%
Federal tax rate reduction	—	%	(24.7)	%	—	%
Change in valuation allowance	(32.4)	%	(15.6)	%	(35.4)	%
	—	%	—	%	—	%

Schedule of components of deferred tax assets and liabilities

The principal components of the Company’s deferred tax assets and liabilities consist of the following at December 31, 2018 and 2017 (in thousands):


	Year Ended
	December 31,
	2018		2017
Deferred tax assets:
Net operating loss carryforwards	$	20,302	$	27,726
Tax credit carryforwards		10,059		5,259
Accrued expenses		3,099		2,079
Capitalized patent costs		33,101		26,307
Deferred revenue		34,039		7,151
Construction financing lease obligation		9,100		9,352
Other		8,347		4,978
Total deferred tax assets		118,047		82,852
Less valuation allowance		(109,091)		(73,301)
Net deferred tax assets		8,956		9,551
Deferred tax liabilities—depreciation and amortization		(8,956)		(9,551)
Net deferred taxes	$	—	$	—

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2018

Net Loss per Share

Schedule of anti-dilutive common stock equivalents


	As of December 31,
	2018	2017
Unvested restricted common stock	270,000	513,225
Outstanding stock options	4,689,786	4,372,126
Estimated number of shares issuable for convertible notes (1)	—	244,896
Total	4,959,786	5,130,247

(1)

Selected Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2018

Selected Quarterly Financial Data

Schedule of selected quarterly financial information


	Three Months Ended
	March 31, 2018		June 30, 2018		September 30, 2018		December 31, 2018
		(in thousands, except per share data)
Total collaboration and other research and development revenues	$	3,927	$	7,372	$	14,519	$	6,119
Total operating expenses		35,486		47,029		30,777		32,372
Total other income (expense), net		620		934		1,020		1,199
Net loss	$	(30,939)	$	(38,723)	$	(15,238)	$	(25,054)
Net loss applicable to common stockholders	$	(30,939)	$	(38,723)	$	(15,238)	$	(25,054)
Net loss per share applicable to common stockholders — basic and diluted	$	(0.67)	$	(0.82)	$	(0.32)	$	(0.52)


	Three Months Ended
	March 31, 2017		June 30, 2017		September 30, 2017		December 31, 2017
		(in thousands, except per share data)
Total collaboration and other research and development revenues	$	682	$	3,097	$	6,282	$	3,667
Total operating expenses		31,309		29,212		33,031		40,109
Total other income (expense), net		(470)		(324)		150		253
Net loss	$	(31,097)	$	(26,439)	$	(26,599)	$	(36,189)
Net loss applicable to common stockholders	$	(31,097)	$	(26,439)	$	(26,599)	$	(36,189)
Net loss per share applicable to common stockholders — basic and diluted	$	(0.85)	$	(0.65)	$	(0.64)	$	(0.84)

Nature of Business (Details) - USD ($) $ in Thousands		1 Months Ended			3 Months Ended
Nature of Business (Details) - USD ($) $ in Thousands	Feb. 29, 2016	Nov. 30, 2018	Dec. 31, 2017	Mar. 31, 2017	Mar. 31, 2018	Dec. 31, 2018
Liquidity
Accumulated deficit			$ (305,850)			$ (416,278)
Initial Public Offering
Liquidity
Aggregate net proceeds	$ 97,500
2017 March Offering
Liquidity
Aggregate net proceeds				$ 96,700
2017 December Offering
Liquidity
Aggregate net proceeds			$ 57,200
January 2018 ATM Offering
Liquidity
Aggregate net proceeds					$ 48,500
November 2018 ATM Offering
Liquidity
Aggregate net proceeds		$ 28,400

Summary Of Significant Accounting Policies - Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash, Cash Equivalents, and Restricted Cash
Restricted cash	$ 1,600	$ 1,600	$ 1,600
Cash and cash equivalents	134,776	146,630	185,323
Restricted cash included in "Restricted cash and other non-current assets"	1,619	1,619	1,619
Total	$ 136,395	$ 148,249	$ 186,942	$ 143,500

Summary Of Significant Accounting Policies - Accounts Receivable (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable
Bad debt write-offs	$ 0	$ 0
Allowance for doubtful accounts	$ 0	$ 0

Summary Of Significant Accounting Policies - Property And Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and equipment policy
Impairment losses	$ 0	$ 0	$ 0
Laboratory equipment
Property and equipment policy
Estimated useful life	5 years
Computer equipment and software
Property and equipment policy
Estimated useful life	3 years
Furniture and office equipment
Property and equipment policy
Estimated useful life	5 years
Building
Property and equipment policy
Estimated useful life	30 years

Summary Of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 01, 2018	Dec. 31, 2018
Accounts receivable
Accounts receivable, Balance at Beginning of Period	$ 679	$ 679
Accounts Receivable, Additions		1,189
Accounts Receivable, Deductions		(1,838)
Accounts receivable, Balance at End of Period		30
Contract liabilities, deferred Revenue:
Deferred revenue, Balance at Beginning of Period	(107,963)	(107,963)
Deferred revenue, Additions		(31,497)
Deferred revenue, Deductions		8,134
Deferred revenue, Balance at End of Period		(131,326)
Effect of Change \| ASU 2014-09
Contract liabilities, deferred Revenue:
Deferred revenue, Balance at Beginning of Period	(107,963)	$ (107,963)
Deferred revenue, Adjustments	(474)
Deferred revenue, Balance at End of Period	(108,437)
Increase in deferred revenue and Accumulated deficit	$ 500

Summary Of Significant Accounting Policies - Contract asset and liability (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018
Change in contract asset and contract liability balances
Amounts included in the contract liability at the beginning of the period	$ 1,417	$ 5,874
Performance obligations satisfied in previous periods	$ 4,645	$ 5,956

Summary Of Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash, Cash Equivalents, and Restricted Cash
Cash and cash equivalents	$ 134,776				$ 146,630				$ 134,776	$ 146,630	$ 185,323
Restricted cash included in "Restricted cash and other non-current assets"	1,619				1,619				1,619	1,619	1,619
Total	136,395				148,249				136,395	$ 148,249	$ 186,942	$ 143,500
Collaboration and other research and development revenues	6,119	$ 14,519	$ 7,372	$ 3,927	3,667	$ 6,282	$ 3,097	$ 682	$ 31,937
Revenue type									us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Operating loss	(26,253)								$ (113,727)	$ (119,933)	$ (97,188)
Net Loss	$ (25,054)	$ (15,238)	$ (38,723)	$ (30,939)	(36,189)	$ (26,599)	$ (26,439)	$ (31,097)	$ (109,954)	$ (120,324)	$ (97,183)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.52)								$ (2.33)	$ (2.98)	$ (3.02)
Deferred revenue, current	$ (15,712)				(13,238)				$ (15,712)	$ (13,238)
Deferred revenue, net of current portion	(115,614)				(94,725)				(115,614)	(94,725)
Accumulated deficit	(416,278)				(305,850)				(416,278)	(305,850)
Adjustment to valuation allowance									35,800
Juno Therapeutics
Cash, Cash Equivalents, and Restricted Cash
Collaboration and other research and development revenues									$ 6,400	4,900
Revenue type									us-gaap:ServiceMember
Deferred revenue, net of current portion	(29,200)				(26,400)				$ (29,200)	(26,400)
Allergan \| Strategic Alliance
Cash, Cash Equivalents, and Restricted Cash
Collaboration and other research and development revenues									$ 21,500	$ 8,800
Revenue type									us-gaap:ServiceMember	us-gaap:ServiceMember
Deferred revenue, net of current portion	(86,400)				(68,300)				$ (86,400)	$ (68,300)
ASU 2014-09 \| As originally reported under Topic 606
Cash, Cash Equivalents, and Restricted Cash
Collaboration and other research and development revenues	5,060								33,993
Operating loss	(27,312)								(111,671)
Net Loss	$ (26,113)								$ (107,898)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.54)								$ (2.29)
Deferred revenue, current	$ (17,552)								$ (17,552)
Deferred revenue, net of current portion	(111,466)								(111,466)
Accumulated deficit	(414,222)								(414,222)
ASU 2014-09 \| Effect of Change
Cash, Cash Equivalents, and Restricted Cash
Collaboration and other research and development revenues	1,059								(2,056)
Operating loss	1,059								(2,056)
Net Loss	$ 1,059								$ (2,056)
Net loss per share attributable to common stockholders, basic and diluted	$ 0.02								$ (0.04)
Deferred revenue, current	$ 1,840								$ 1,840
Deferred revenue, net of current portion	(4,148)								(4,148)
Accumulated deficit	(2,056)								(2,056)
ASU 2016-18
Cash, Cash Equivalents, and Restricted Cash
Cash and cash equivalents	134,776				146,630				134,776	146,630	$ 185,323
Restricted cash included in "Restricted cash and other non-current assets"	1,619				1,619				1,619	1,619	1,619
Total	$ 136,395				$ 148,249				$ 136,395	$ 148,249	$ 186,942

Cash Equivalents, Marketable Securities and Corporate Equity Securities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	$ 372,410	$ 329,215
Gross Unrealized Losses	(29)	(76)
Fair Value	$ 372,381	329,139
Number of securities in an unrealized loss position \| item	38
Securities held by the Company in an unrealized loss position for less than 12 months	$ 210,700
Number of securities in an unrealized loss position for more than 12 months \| item	0
Realized gains (losses) on available-for-sale securities	$ 0	0
Government agency securities
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	3,667
Fair Value	3,667
Money market funds
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	130,049	134,635
Fair Value	130,049	134,635
U.S. Treasuries
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	208,754	135,601
Gross Unrealized Losses	(24)	(47)
Fair Value	208,730	135,554
Government agency securities
Cash Equivalents, Marketable Securities and Corporate Equity Securities
Amortized Cost	29,940	58,979
Gross Unrealized Losses	(5)	(29)
Fair Value	$ 29,935	$ 58,950

Fair Value Measurements - Recurring Basis (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($) item
Financial Assets
Marketable securities	$ 372,381	$ 329,139
Transfers between levels \| item	0	0
Government agency securities
Financial Assets
Marketable securities	$ 3,667
Money market funds
Financial Assets
Marketable securities	130,049	$ 134,635
U.S. Treasuries
Financial Assets
Marketable securities	208,730	135,554
Government agency securities
Financial Assets
Marketable securities	29,935	58,950
Recurring
Financial Assets
Total financial assets	374,000	330,758
Recurring \| U.S. Treasuries
Financial Assets
Cash and cash equivalents		11,995
Marketable securities	204,243	123,559
Recurring \| Government agency securities
Financial Assets
Marketable securities	29,935	58,950
Recurring \| Corporate equity securities
Financial Assets
Restricted cash	3,667
Recurring \| Money market funds
Financial Assets
Cash and cash equivalents	130,049	134,635
Marketable securities		1,619
Restricted cash	1,619
Recurring \| U.S. Treasuries
Financial Assets
Cash and cash equivalents	4,487
Recurring \| Level 1
Financial Assets
Total financial assets	370,333	330,758
Recurring \| Level 1 \| U.S. Treasuries
Financial Assets
Cash and cash equivalents		11,995
Marketable securities	204,243	123,559
Recurring \| Level 1 \| Government agency securities
Financial Assets
Marketable securities	29,935	58,950
Recurring \| Level 1 \| Money market funds
Financial Assets
Cash and cash equivalents	130,049	134,635
Marketable securities		$ 1,619
Restricted cash	1,619
Recurring \| Level 1 \| U.S. Treasuries
Financial Assets
Cash and cash equivalents	4,487
Recurring \| Level 2
Financial Assets
Total financial assets	3,667
Recurring \| Level 2 \| Corporate equity securities
Financial Assets
Restricted cash	$ 3,667

Prepaid Expenses And Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Prepaid Expenses and Other Current Assets
Prepaid expenses	$ 2,918	$ 1,864
Other	2,873	517
Total	$ 5,791	$ 2,381

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and equipment disclosures
Total property and equipment	$ 47,365	$ 43,500
Less: accumulated depreciation	(7,133)	(4,058)
Property and equipment, net	40,232	39,442
Depreciation	3,254	2,683	$ 1,202
Building
Property and equipment disclosures
Total property and equipment	35,167	35,167
Laboratory equipment
Property and equipment disclosures
Total property and equipment	10,892	7,415
Computer equipment
Property and equipment disclosures
Total property and equipment	733	550
Leasehold improvements
Property and equipment disclosures
Total property and equipment	289	177
Furniture and office equipment
Property and equipment disclosures
Total property and equipment	166	96
Software
Property and equipment disclosures
Total property and equipment	$ 118	$ 95

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accrued Expenses
Employee related expenses	$ 5,201	$ 3,708
Sublicensing and success payment expenses	3,750	2,000
Intellectual property and patent related fees	1,939	2,370
Process and platform development expenses	1,044	2,301
Professional service expenses	475	487
Other expenses	404	183
Total	$ 12,813	$ 11,049

Commitments and Contingencies - Operating Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Feb. 28, 2017 ft²	Oct. 31, 2016	Feb. 29, 2016 USD ($) ft²
Future annual minimum lease payments
Rent expense	$ 1,800	$ 1,200	$ 2,500
Hurley Street Lease
Commitments and contingencies
Leased space ( in square feet) \| ft²						59,783
Security deposit						$ 1,600
Estimated useful life			30 years
Extended lease option (in years)					5 years
Future annual minimum lease payments
2019	4,155
2020	4,257
2021	4,362
2022	4,470
2023	3,802
Total minimum lease payments	$ 21,046
Facility Sublease Arrangement
Commitments and contingencies
Leased space ( in square feet) \| ft²				10,000

Commitments and Contingencies - Research Funding Payments (Details) - Sponsored Research Agreement - Broad - USD ($) $ in Millions	1 Months Ended
	Jun. 30, 2018	Dec. 31, 2018
Commitments and contingencies
First research funding amount due and payable		$ 5.0
Second research funding amount due and payable		$ 7.5
Promissory notes issued	$ 12.5
Research Funding Payments
Commitments and contingencies
First research funding amount due and payable	5.0
Second research funding amount due and payable	$ 7.5

Commitments and Contingencies - Notes Payable (Details) - USD ($) $ in Thousands			1 Months Ended							12 Months Ended
	Dec. 06, 2017	Mar. 28, 2017	Jun. 30, 2018	Jan. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Aug. 31, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017
Notes Payable
Notes paid in cash											$ 600
2016 License Agreements
Commitments and contingencies
Market Capitalization					$ 1,000,000			$ 750,000			$ 1,000,000
Broad and Wageningen University \| Cpf1 License Agreement
Notes Payable
Promissory notes issued									$ 10,000
Interest rate (as a percentage)									4.80%
Success Payments								5,000
Broad and Wageningen University \| Cpf1 License Agreement \| Success Payment Notes
Notes Payable
Promissory notes issued								$ 5,000
Broad \| 2016 License Agreements
Notes Payable
Promissory notes issued	$ 7,500	$ 5,000
Broad \| Cpf1 License Agreement
Notes Payable
Common stock issued						371,166	108,104
Success Payments					$ 7,500
Broad \| Cpf1 License Agreement \| Success Payment Notes
Notes Payable
Promissory notes issued										$ 7,500
Common stock issued				225,909			271,347
Broad \| Sponsored Research Agreement
Notes Payable
Promissory notes issued			$ 12,500
Common stock issued			330,617
Broad \| Sponsored Research Agreement \| Initial Notes
Notes Payable
Promissory notes issued			$ 12,500
Interest rate (as a percentage)			4.80%
Wageningen University \| 2016 License Agreements
Notes Payable
Promissory notes issued		$ 5,000
Wageningen University \| Cpf1 License Agreement
Notes Payable
Notes paid in cash							$ 200
Wageningen University \| Cpf1 License Agreement \| Success Payment Notes
Notes Payable
Notes paid in cash							$ 400
The General Hospital (MGH) \| 2016 License Agreements
Notes Payable
Common stock issued				80,000
Success Payments										$ 2,000

Significant Agreements - Summary of Agreement (Details) $ in Thousands	1 Months Ended						3 Months Ended								8 Months Ended	12 Months Ended
	Jul. 31, 2018 USD ($)	May 31, 2018 USD ($) item	Jul. 31, 2017 USD ($)	Mar. 31, 2017 USD ($) item	May 31, 2016 USD ($)	May 31, 2015 USD ($) item	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Collaboration and other research and development revenues							$ 6,119	$ 14,519	$ 7,372	$ 3,927	$ 3,667	$ 6,282	$ 3,097	$ 682		$ 31,937
Revenue type																us-gaap:ServiceMember	us-gaap:ServiceMember	us-gaap:ServiceMember
Revenue recognized related to milestone payment															$ 0
Additional revenue related to cumulative catch-up adjustments															0
Advance payment on future research and development activities							2,918				1,864				2,918	$ 2,918	$ 1,864
Research and development																90,654	83,159	$ 56,979
Deferred revenue							131,326				107,963				131,326	131,326	107,963
Deferred revenue, long-term							115,614				94,725				115,614	115,614	94,725
Accounts receivable							30				679				30	30	679
Juno Therapeutics
Allocable arrangement consideration - R&D Services Unit of Accounting							10,700								10,700	10,700
Allocable arrangement consideration - Development and Commercialization License for the first research area							3,600								3,600	3,600
Allocable arrangement consideration - Development and Commercialization License for the second research area							6,000								6,000	6,000
Allocable arrangement consideration - Development and Commercialization License for the third research area							100								100	100
Allocable arrangement consideration - Development and Commercialization License for the fourth research area							18,300								18,300	18,300
Allocable arrangement consideration - First additional Development and Commercialization License for the first research area							300								300	300
Allocable arrangement consideration - Second additional Development and commercialization license for the first research area							200								200	200
Allocable arrangement consideration - Third additional Development and commercialization license for the first research area							100								100	100
Allocable arrangement consideration - First additional Development and commercialization license for the second research area							800								800	800
Allocable arrangement consideration - Second additional Development and commercialization license for the second research area							500								500	500
Allocable arrangement consideration - Third additional Development and commercialization license for the second research area							300								300	300
Collaboration and other research and development revenues																$ 6,400	4,900
Revenue type																us-gaap:ServiceMember
Revenue recognized related to milestone payment																	2,500
Research and development																	500
Deferred revenue							32,000				26,400				32,000	$ 32,000	26,400
Deferred revenue, long-term							29,200				26,400				29,200	29,200	26,400
Accounts receivable							0				500				0	$ 0	500
Allergan
Number of additional licenses \| item																2
One time payment to acquire the license							25,000								25,000	$ 25,000
Allergan \| Maximum
Potential development milestone payments							42,000								42,000	42,000
Potential regulatory and commercial milestone payments							75,000								75,000	75,000
Potential commercial milestone payments							90,000								90,000	90,000
Collaboration and License Agreement \| Juno Therapeutics
Number of research areas \| item						3
Agreement term						5 years
Extensions \| item						2
Extension period						1 year
Upfront fee received						$ 25,000
Additional upfront fee received		$ 5,000
Potential research and development funding						$ 22,000
Number of additional licenses \| item						3
Potential fee receivable for each gene target licensed						$ 2,500
Potential development milestone payments						77,500
Potential regulatory milestone payments						80,000
Potential commercial milestone payments						$ 75,000
Milestone payment received under license agreement			$ 2,500		$ 2,500
Next possible milestone payment							2,500								2,500	2,500
Amended Collaboration and License Agreement \| Juno Therapeutics
Number of research areas \| item		4
Number of milestones related to technical progress \| item		2
Milestone payment receivable related to technical progress		$ 2,500
Potential development milestone payments		80,000
Potential regulatory milestone payments		$ 80,000
Number of milestone payment received \| item		2
Milestone payment received under license agreement		$ 2,500
Additional revenue related to cumulative catch-up adjustments																3,000
Research and development																1,700
Strategic Alliance \| Allergan
Agreement term				7 years
Extension period				1 year
Upfront fee received				$ 90,000
Number of Collaboration Development Programs \| item				5
Number of Committee Members \| item				3
Option exercise price per CDP				$ 15,000										15,000
Extension fee for Initial Option Period				5,000										5,000
Option exercise price for development and commercialization license				$ 22,500										$ 22,500
Collaboration and other research and development revenues																$ 21,500	$ 8,800
Revenue type																us-gaap:ServiceMember	us-gaap:ServiceMember
Program expense after option exercise																$ 5,900
Research and development																1,700	$ 14,100
Deferred revenue							99,200				81,200				99,200	99,200	81,200
Deferred revenue, long-term							86,400				$ 68,300				86,400	86,400	$ 68,300
Research and development expense							6,000								6,000	6,000
Accrued research and development expenses							3,800								3,800	3,800
Contract termination notice																	90 days
Option exercise payment received	$ 15,000															15,000
Strategic Alliance \| Allergan \| Prepaid expenses and other current assets
Research and development expense							2,300								2,300	2,300
Strategic Alliance \| Allergan \| Other current liabilities
Accrued research and development expenses							600								600	600
Strategic Alliance \| Allergan \| Maximum
Extension period				10 years
Sponsored Research Agreement \| Broad
First research funding amount due and payable							5,000								5,000	5,000
Second research funding amount due and payable							7,500								7,500	7,500
Research and development																12,500
Sponsored Research Agreement \| Broad \| Maximum
Research funding amount due and payable							$ 125,000								$ 125,000	125,000
License Agreement \| Beam Therapeutics, Inc
Collaboration and other research and development revenues																$ 4,000
Revenue type																us-gaap:ServiceMember
Non-cash consideration aggregate fair value received		$ 3,600
Contract termination notice		90 days

Significant Agreements - Accounting Analysis (Details) $ in Millions		1 Months Ended	8 Months Ended	12 Months Ended
	Jan. 02, 2018 USD ($)	Nov. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) item
Juno Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total transaction price			$ 12.3	$ 40.7
Allergan
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of development and commercialization licenses \| item				5
Total transaction price	$ 90.0	$ 25.0		$ 115.0
Collaboration and License Agreement \| Juno Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction price upfront fee received				25.0
Transaction price research and development expenses funding				2.9
Milestone payments received				2.7
Amended Collaboration and License Agreement \| Juno Therapeutics
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Transaction price upfront fee received				5.0
Milestone payments received				5.0
License Agreement \| Beam Therapeutics, Inc
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total transaction price				$ 3.8

Significant Agreements - Other Agreements (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Dec. 31, 2016	Oct. 31, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017	Dec. 16, 2016
Notes payable				$ 7,500
Research and development			$ 90,654	83,159	$ 56,979
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| License Patent Rights
Upfront fee		$ 200
Stock issued to licensors		561,531
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Cpf1 License Agreement
Research and development	$ 16,500
License Agreement Contract Termination Term			4 months
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Cpf1 Market Cap Success Payments
Market capitalization				$ 1,000,000		$ 750,000
Notes payable payment terms			150 days
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Cas9-II License Agreement
Market capitalization			$ 1,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Maximum \| Cpf1 License Agreement
Royalties credit paid to third party (as a percent)			50.00%
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Maximum \| Cpf1 Success Payments
Success Payments			$ 10,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Maximum \| Cpf1 Market Cap Success Payments
Success Payments			125,000
Market capitalization threshold			10,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Maximum \| Cas9-II License Agreement
Success Payments			30,000
Market capitalization threshold			9,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Minimum \| Cpf1 Success Payments
Success Payments			750,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Minimum \| Cas9-II License Agreement
Market capitalization threshold			1,000,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Rare disease \| Maximum
Potential liability for future sales milestone payments		$ 36,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| Rare disease \| Maximum \| Cpf1 License Agreement
Potential liability for future sales milestone payments			36,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| United States Europe And Japan \| Maximum \| License Patent Rights
Potential liability for future clinical and regulatory milestone payments related to product approval		14,800
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| United States Europe And Japan \| Human disease \| Maximum \| Cpf1 License Agreement
Potential liability for future clinical and regulatory milestone payments related to product approval			20,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| United States Europe And Japan \| Human disease \| Maximum \| Cas9-II License Agreement
Potential liability for future sales milestone payments			13,500
Potential liability for future clinical and regulatory milestone payments related to product approval							$ 3,700
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| United States Europe And Japan \| Rare disease \| Maximum \| Cpf1 License Agreement
Potential liability for future clinical and regulatory milestone payments related to product approval			6,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| United States Europe And Japan \| Rare disease \| Maximum \| Cas9-II License Agreement
Potential liability for future sales milestone payments			9,000
Potential liability for future clinical and regulatory milestone payments related to product approval			1,100
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| United States and one other \| Human disease \| Maximum \| License Patent Rights
Potential liability for future clinical and regulatory milestone payments related to product approval		4,100
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| UNITED STATES \| Human disease \| Maximum \| License Patent Rights
Potential liability for future sales milestone payments		$ 54,000
Broad, Massachusetts Institute of Technology, or MIT, and Harvard (Institutions) \| UNITED STATES \| Human disease \| Maximum \| Cpf1 License Agreement
Potential liability for future sales milestone payments			$ 54,000

Preferred Stock (Details) - shares	Dec. 31, 2018	Dec. 31, 2017	Feb. 08, 2016
Preferred Stock
Authorized common stock	195,000,000	195,000,000	195,000,000
Authorized preferred stock	5,000,000	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Common Stock (Details) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
Common Stock (Details) $ / shares in Units, $ in Thousands	Mar. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) Vote shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)
Common Stock, Capital Shares Reserved for Future Issuance		9,098,041	7,621,134
Proceeds from offering of common stock, net of issuance costs \| $		$ 76,789	$ 154,143	$ 97,488
Cowen and Company LLC (“Cowen)
Aggregate sales proceeds of stock \| $	$ 150,000
Commission payable (as a percent)	3.00%
March2018 Common Stock Sales Agreement [Member] \| Cowen and Company LLC (“Cowen)
Number of common stock issued	1,107,000
Price per share \| $ / shares	$ 26.95
Proceeds from offering of common stock, net of issuance costs \| $	$ 28,400
Common Stock.
Voting rights per share \| Vote		1
Dividends, Common Stock \| $		$ 0	$ 0	$ 0
Common Stock. \| Outstanding stock options
Common Stock, Capital Shares Reserved for Future Issuance		107,188	225,000
2013 Plan \| Common Stock. \| Outstanding stock options
Common Stock, Capital Shares Reserved for Future Issuance		873,373	1,220,567
2015 Plan \| Common Stock.
Common Stock, Capital Shares Reserved for Future Issuance		3,233,031	2,502,338
2015 Plan \| Common Stock. \| Outstanding stock options
Common Stock, Capital Shares Reserved for Future Issuance		3,709,225	2,921,987
2015 Employee Stock Purchase Plan
Common Stock, Capital Shares Reserved for Future Issuance		1,175,224	751,242

Stock Based Compensation - 2013 Stock Incentive Plan (Details)		1 Months Ended			12 Months Ended
	Jan. 01, 2019 shares	Jul. 31, 2015 shares	Apr. 30, 2015 shares	Jun. 30, 2014 shares	Dec. 31, 2018 item shares	Dec. 31, 2017 shares	Sep. 30, 2013 shares
Stock-based compensation disclosures
Shares reserved for future awards					9,098,041	7,621,134
Employee and Consultant Options
Stock-based compensation disclosures
Options granted (in shares)					1,884,411
2013 Plan
Stock-based compensation disclosures
Shares authorized							1,057,692
Increase to number of shares authorized		3,740,847	153,846	1,365,384
2013 Plan \| Consultant Stock Options
Stock-based compensation disclosures
Expiration period					10 years
2013 Plan \| Performance based awards
Stock-based compensation disclosures
Number of awards with performance vesting criteria \| item					1
2015 Plan \| Subsequent Event
Stock-based compensation disclosures
Increase to number of shares authorized	1,961,156
2015 Employee Stock Purchase Plan
Stock-based compensation disclosures
Shares reserved for future awards					1,175,224	751,242
2015 Employee Stock Purchase Plan \| Subsequent Event
Stock-based compensation disclosures
Increase to number of shares authorized	490,289
Maximum \| 2013 Plan \| Consultant Stock Options
Stock-based compensation disclosures
Vesting period					4 years
Maximum \| 2015 Plan
Stock-based compensation disclosures
Shares reserved for future awards					2,923,076
Percent of shares outstanding reserved for future awards (as a percent)					4.00%
Maximum \| 2015 Employee Stock Purchase Plan
Stock-based compensation disclosures
Shares reserved for future awards					769,230
Percent of shares outstanding reserved for future awards (as a percent)					1.00%
Minimum \| 2013 Plan \| Consultant Stock Options
Stock-based compensation disclosures
Vesting period					1 year

Stock Based Compensation - Founder Awards (Details) - Founder Awards	1 Months Ended
	Jun. 30, 2014 USD ($) item shares	Sep. 30, 2013 shares
Stock-based compensation disclosures
Shares granted		2,403,845
Vesting percentage at issuance of Series A Preferred Stock		25.00%
Monthly vesting percentage after issuance of Series A Preferred Stock		1.5625%
Number of founders not providing service \| item	1
Shares repurchased	285,457
Payments for repurchase of shares \| $	$ 74

Stock-based Compensation - Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock-based compensation disclosures
Compensation expense	$ 26,598	$ 23,364	$ 16,881
Research and development.
Stock-based compensation disclosures
Compensation expense	14,734	15,131	12,647
General and administrative
Stock-based compensation disclosures
Compensation expense	$ 11,864	$ 8,233	$ 4,234

Stock-based Compensation - Restricted Stock and Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Changes in unvested stock options
Compensation expense	$ 26,598	$ 23,364	$ 16,881
Employees
Changes in unvested stock options
Compensation expense	0
Non-employees
Changes in unvested stock options
Compensation expense	$ 2,400
Restricted Stock
Changes in unvested restricted stock
Unvested restricted common stock, beginning of period (in shares)	513,225
Vested (in shares)	(243,225)
Unvested restricted common stock, end of period(in shares)	270,000	513,225
Weighted Average Grant Date Fair Value
Balance, beginning of period	$ 18.70
Vested (in dollars per share)	8.32
Balance, ending of period	$ 28.05	$ 18.70
Restricted Stock \| Employees
Changes in unvested stock options
Compensation expense		$ 500	0
Unrecognized stock-based compensation expense	$ 0
Restricted Stock \| Non-employees
Changes in unvested stock options
Compensation expense		$ 4,100	8,300
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	3 years 8 months 12 days
Unrecognized stock-based compensation expense	$ 6,000
Employee and Consultant Options
Changes in unvested stock options
Outstanding, beginning of period (in shares)	4,372,136
Granted (in shares)	1,884,411
Exercised (in shares)	(752,674)			(75,304)
Cancelled (in shares)	(814,087)
Outstanding, end of period (in shares)	4,689,786	4,372,136
Exercisable (in shares)	2,061,769
Outstanding, beginning of period (in dollars per share)	$ 17.28
Granted (in dollars per share)	35.29
Exercised (in dollars per share)	13.78			$ 0.03
Cancelled (in dollars per share)	24.88
Outstanding, end of period (in dollars per share)	23.80	$ 17.28
Exercisable (in dollar per share)	$ 18.34
Remaining contractual life	7 years 10 months 24 days	8 years 6 months
Exercisable, remaining contractual life	7 years
Aggregate intrinsic value	$ 20,686	$ 60,591
Exercisable, aggregated intrinsic value	$ 15,222
Unvested stock options (in shares)	0	4,572
Intrinsic value of options exercised	$ 15,900	$ 5,000	$ 900
Weighted average fair value of options granted (per share)	$ 24.91	$ 16.07	$ 14.10
Employee and Consultant Options \| Employees and directors
Changes in unvested stock options
Compensation expense	$ 19,900	$ 12,300	$ 6,000
Employee and Consultant Options \| Employees
Changes in unvested stock options
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	2 years 5 months 12 days
Unrecognized stock-based compensation expense	$ 47,400

Stock-based Compensation - Assumptions (Details) - Employee and Consultant Options - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employees and directors
Assumptions
Risk free interest rate	2.90%	2.10%	1.50%
Expected term (in years)	6 years 3 months	6 years 3 months	6 years 3 months
Expected volatility	77.50%	77.80%	78.40%
Employees
Assumptions
Unrecognized stock-based compensation expense	$ 47.4
Period for recognition	2 years 5 months 12 days
Non-employees
Assumptions
Risk free interest rate			1.60%
Expected term (in years)			10 years
Expected volatility			76.50%

401(K) Savings Plan (Details) - USD ($)	12 Months Ended
401(K) Savings Plan (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
401(k) Savings Plan
Employer match (as a percent)	200.00%
Maximum employee contributions eligible for matching contributions	$ 6,000
Maximum employee contributions eligible for matching contributions (as a percent)	3.00%
Contributions to the 401(k) Plan	$ 700,000	$ 500,000

Income Taxes - Effective Income Tax Rate (Details)	12 Months Ended
Income Taxes - Effective Income Tax Rate (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of income tax rate
Income tax computed at federal statutory tax rate	21.00%	34.00%	34.00%
State taxes, net of federal benefit	6.40%	5.90%	3.50%
General business credit carryovers	4.40%	2.50%	1.50%
Non-deductible expenses	0.60%	(2.10%)	(3.60%)
Federal tax rate reduction		(24.70%)
Change in valuation allowance	(32.40%)	(15.60%)	(35.40%)

Income Taxes - Components of Deferred Tax Assets And Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 20,302	$ 27,726
Tax credit carryforwards	10,059	5,259
Accrued expenses	3,099	2,079
Capitalized patent costs	33,101	26,307
Deferred revenue	34,039	7,151
Construction financing lease obligation	9,100	9,352
Other	8,347	4,978
Total deferred tax assets	118,047	82,852
Less valuation allowance	(109,091)	(73,301)
Net deferred tax assets	8,956	9,551
Deferred tax liabilities - depreciation and amortization	$ (8,956)	$ (9,551)

Income Taxes - Net Operating Losses (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Net operating losses	$ 147.8	$ 202.7
Research and development
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$ 10.8	$ 5.6

Income Taxes - Other Narrative Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Section 382 period	3 years
Section 382 percentage	50.00%
Valuation allowance	$ 109,091	$ 73,301
Change in the valuation allowance	35,800
Unrecognized tax benefits	$ 0	$ 0

Net Loss per Share (Details) - shares	1 Months Ended				12 Months Ended
Net Loss per Share (Details) - shares	Nov. 30, 2018	Jan. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Potentially dilutive securities
Anti-dilutive common stock equivalent shares					4,959,786	5,130,247
Restricted Stock
Potentially dilutive securities
Anti-dilutive common stock equivalent shares					270,000	513,225
Outstanding stock options
Potentially dilutive securities
Anti-dilutive common stock equivalent shares					4,689,786	4,372,126
Convertible notes
Potentially dilutive securities
Anti-dilutive common stock equivalent shares						244,896
November 2018 ATM Offering
Potentially dilutive securities
Number of common stock issued	1,107,000
January 2018 ATM Offering
Potentially dilutive securities
Number of common stock issued		1,429,205
2017 December Offering
Potentially dilutive securities
Number of common stock issued			2,265,500
2017 March Offering
Potentially dilutive securities
Number of common stock issued				4,600,000

Related-party Transactions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Rent and facility related fees
Related Party Transaction [Line Items]
Fees paid to related party	$ 0	$ 0	$ 1,400
Fees received from related party	400	800	0
Research And Development Expenses [Member]
Related Party Transaction [Line Items]
Fees paid to related party	$ 800	$ 300	$ 0

Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Data
Total revenue	$ 6,119	$ 14,519	$ 7,372	$ 3,927	$ 3,667	$ 6,282	$ 3,097	$ 682	$ 31,937
Total operating expenses	32,372	30,777	47,029	35,486	40,109	33,031	29,212	31,309	145,664	$ 133,661	$ 103,241
Total other income (expense), net	1,199	1,020	934	620	253	150	(324)	(470)	3,773	(391)	5
Net loss	(25,054)	(15,238)	(38,723)	(30,939)	(36,189)	(26,599)	(26,439)	(31,097)	(109,954)	(120,324)	(97,183)
Net loss applicable to common stockholders	$ (25,054)	$ (15,238)	$ (38,723)	$ (30,939)	$ (36,189)	$ (26,599)	$ (26,439)	$ (31,097)	$ (109,954)	$ (120,324)	$ (97,230)
Net loss per share applicable to common stockholders - basic and diluted	$ (0.52)	$ (0.32)	$ (0.82)	$ (0.67)	$ (0.84)	$ (0.64)	$ (0.65)	$ (0.85)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Initial Public Offering
Stock issuance costs			$ 11.1
2017 March Offering
Stock issuance costs		$ 0.6
2017 December Offering
Stock issuance costs		$ 1.7
January 2018 ATM Offering
Stock issuance costs	$ 0.1
November 2018 ATM Offering
Stock issuance costs	$ 0.6

Related-Party Transactions	12 Months Ended
Related-Party Transactions	Dec. 31, 2018
Related-Party Transactions
Related-Party Transactions	16. Related‑Party Transactions During the year ended December 31, 2016, the Company paid a related party $1.4 million in rent and facility-related fees. The Company did not make any payments to this related party during the years ended December 31, 2018 or 2017. The Company received $0.4 million and $0.8 million in rent and facility-related fees from a related party during the years ended December 31, 2018 and 2017, respectively, in connection with subleasing a portion of its headquarters; no rent or facility-related payments were received from this related party during the year ended December 31, 2016. During the years ended December 31, 2018 and 2017, the Company paid a related party $0.8 million and $0.3 million, respectively, in connection with certain research and development expenses. The Company did not make any payments to this related party during the year ended December 31, 2016.

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2018
Subsequent Events
Subsequent Events	18. Subsequent Events In February 2019, the Company entered into a co-development and commercialization agreement with an affiliate of Allergan to memorialize the Profit-Sharing Arrangement with respect to the LCA10 Program.

Income Taxes - Tax Reform (Details)	12 Months Ended
Income Taxes - Tax Reform (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Tax Cuts and Jobs Act
U.S. Federal corporate tax rate (as a percent)	21.00%	34.00%	34.00%