Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2016	Nov. 01, 2016
Document and Entity Information
Entity Registrant Name	Editas Medicine, Inc.
Entity Central Index Key	0001650664
Document Type	10-Q
Document Period End Date	Sep. 30, 2016
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		36,655,936
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q3

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 199,874	$ 143,180
Accounts receivable	1,122	1,019
Prepaid expenses and other current assets	2,453	786
Total current assets	203,449	144,985
Property and equipment, net	37,072	2,130
Restricted cash and other non-current assets	1,632	2,248
Total assets	242,153	149,363
Current liabilities:
Accounts payable	3,718	1,381
Accrued expenses	9,492	5,456
Deferred rent, current portion		88
Other current liabilities	547
Total current liabilities	13,757	6,925
Deferred rent, net of current portion	353
Deferred revenue	25,800	25,321
Warrant to purchase redeemable securities		289
Construction financing lease obligation, net of current portion	32,048
Other non-current liabilities	19	27
Total liabilities	71,977	32,562
Commitments and contingencies (see note 6)
Stockholders’ equity (deficit)
Preferred stock, $0.0001 par value, 5,000,000 shares and no shares authorized, at September 30, 2016 and December 31, 2015, respectively; no shares issued or outstanding at September 30, 2016 and December 31, 2015, respectively
Common stock, $0.0001 par value per share: 195,000,000 shares and 92,000,000 shares authorized at September 30, 2016 and December 31, 2015, respectively; 36,651,129 and 4,869,829 shares issued and 35,608,637 and 3,233,638 shares outstanding at September 30, 2016 and December 31, 2015, respectively	4
Additional paid-in capital	316,322	5,234
Accumulated deficit	(146,150)	(88,348)
Total stockholders’ equity (deficit)	170,176	(83,114)
Total liabilities, redeemable convertible preferred stock and stockholders’ equity (deficit)	$ 242,153	149,363
Series A-1 redeemable convertible
Current liabilities:
Redeemable convertible preferred stock		21,137
Series A-2 redeemable convertible
Current liabilities:
Redeemable convertible preferred stock		59,027
Series B redeemable convertible
Current liabilities:
Redeemable convertible preferred stock		$ 119,751

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	0
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	92,000,000
Common stock, shares issued	36,651,129	4,869,829
Common stock, shares outstanding	35,608,637	3,233,638
Series A-1 redeemable convertible
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	21,320,000
Redeemable convertible preferred stock, shares issued	0	21,260,000
Redeemable convertible preferred stock, shares outstanding	0	21,260,000
Series A-2 redeemable convertible
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	16,890,699
Redeemable convertible preferred stock, shares issued	0	16,890,699
Redeemable convertible preferred stock, shares outstanding	0	16,890,699
Series B redeemable convertible
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock, shares authorized	0	26,666,660
Redeemable convertible preferred stock, shares issued	0	26,666,660
Redeemable convertible preferred stock, shares outstanding	0	26,666,660

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Condensed Consolidated Statements of Operations and Comprehensive Loss
Collaboration and other research and development revenues	$ 962	$ 670	$ 5,155	$ 837
Operating expenses:
Research and development	10,832	3,850	30,144	13,020
General and administrative	11,295	4,202	33,215	10,756
Total operating expenses	22,127	8,052	63,359	23,776
Operating loss	(21,165)	(7,382)	(58,204)	(22,939)
Other income (expense), net
Other income (expense), net	3	21	(22)	(37,219)
Interest income (expense), net	142	(44)	419	(109)
Total other income (expense), net	145	(23)	397	(37,328)
Net loss and comprehensive loss	(21,020)	(7,405)	(57,807)	(60,267)
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	(21,020)	(7,405)	(57,807)	(60,267)
Accretion of redeemable convertible preferred stock to redemption value		(104)	(47)	(295)
Net loss attributable to common stockholders	$ (21,020)	$ (7,509)	$ (57,854)	$ (60,562)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.59)	$ (2.57)	$ (1.86)	$ (25.53)
Weighted-average common shares outstanding, basic and diluted	35,505,429	2,925,843	31,040,670	2,371,976

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flow from operating activities
Net loss	$ (57,807)	$ (60,267)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	13,099	1,562
Depreciation	714	323
Non-cash interest expense		45
Changes in fair value of warrant liability	87	92
Change in fair value of preferred stock tranche asset or liability		35,551
Changes in fair value of anti-dilutive protection liability		1,609
Changes in deferred rent	265	(71)
Changes in operating assets and liabilities:
Accounts receivable	(103)	(1,040)
Prepaid expenses and other current assets	(1,667)	(147)
Other non-current assets	2,235
Accounts payable	2,095	(1,080)
Accrued expenses	4,034	823
Deferred revenue	479	25,165
Net cash (used in) provided by operating activities	(36,569)	2,565
Cash flow from investing activities
Purchases of property and equipment	(2,817)	(1,030)
Changes in restricted cash	(1,619)
Net cash used in investing activities	(4,436)	(1,030)
Cash flow from financing activities
Proceeds from equipment loan, net of issuance costs		1,500
Proceeds from the issuance of redeemable convertible preferred stock and tranche rights, net of issuance costs		141,711
Payments of equipment loan principal		(70)
Proceeds from the issuance of common stock and restricted stock		2
Proceeds from initial public offering of common stock, net of issuance costs	97,488
Proceeds from stock option exercises	211
Net cash provided by financing activities	97,699	143,143
Net increase in cash and cash equivalents	56,694	144,678
Cash and cash equivalents, beginning of period	143,180	10,623
Cash and cash equivalents, end of period	199,874	155,301
Supplemental disclosure of cash and non-cash activities:
Conversion of preferred stock to common stock upon closing of the initial public offering	199,915
Capitalization of construction-in-progress related to facility lease obligation	32,595
Fixed asset additions included in accounts payable and accrued expenses	244
Initial public offering costs incurred but unpaid at period end		661
Reclassification of warrants to additional paid in capital	376
Accretion of redeemable convertible preferred stock to redemption value	47	295
Reclassification of liability for common stock subject to repurchase	$ 8	14
Conversion of anti-dilutive protection liability to common stock		1,936
Reclassification of preferred stock tranche liability upon settlement		37,038
Accrual of final payment fee on equipment loan and debt discount		$ 60

Nature of business	9 Months Ended
Nature of business	Sep. 30, 2016
Nature of business
Nature of business	1. Nature of business Editas Medicine, Inc. (the “Company”) is a research stage company dedicated to treating patients with genetically defined diseases by correcting their disease‑causing genes. 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, and has financed its operations through various equity and debt financings, including the initial public offering of its common stock (the “IPO”), private placements of preferred stock and an equipment loan, and from upfront, milestone and research and development fees paid under a research collaboration with Juno Therapeutics, Inc. (“Juno Therapeutics”). 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. In February 2016, the Company completed its IPO whereby the Company sold 6,785,000 shares of its common stock, inclusive of 885,000 shares of common stock sold by the Company pursuant to the full exercise of an overallotment option granted to the underwriters in connection with the offering, at a price to the public of $16.00 per share. The shares began trading on the NASDAQ Global Select Market on February 3, 2016. The aggregate net proceeds received by the Company from the offering were $97.5 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. In connection with the IPO, the board of directors and the stockholders of the Company approved a one-for-2.6 reverse stock split of the Company’s issued and outstanding common stock. The reverse stock split became effective on January 15, 2016. All share and per share amounts in the condensed consolidated financial statements have been retroactively adjusted for all periods presented to give effect to the reverse stock split, including reclassifying an amount equal to the reduction in par value to additional paid-in capital. Upon the closing of the IPO, all outstanding shares of convertible preferred stock converted into 24,929,709 shares of common stock. As of September 30, 2016, there were 35,608,637 shares of common stock outstanding. The significant increase in shares outstanding in the first quarter of 2016 is expected to impact the year-over-year comparability of the Company’s net loss per share calculations for the next six months. The Company has incurred annual net operating losses in every year since its inception. The Company had an accumulated deficit of $146.2 million at September 30, 2016, and will require substantial additional capital to fund its operations. The Company has not generated any product revenues and has financed its operations primarily through a public offering, private placements of its equity securities, an equipment loan, and funding from its collaboration with Juno Therapeutics. 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	9 Months Ended
Summary of significant accounting policies	Sep. 30, 2016
Summary of significant accounting policies
Summary of significant accounting policies	2. Summary of significant accounting policies Unaudited interim financial information The condensed consolidated financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2015 (the “Annual Report”). The unaudited condensed consolidated financial statements include the accounts of Editas Medicine, Inc. and its wholly owned subsidiary. All intercompany transactions and balances of the subsidiary have been eliminated in consolidation. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The three months ended September 30, 2016 and 2015 are referred to as the third quarter of 2016 and 2015, respectively. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. Use of estimates The preparation of condensed consolidated financial statements in conformity with United States generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the condensed 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, valuation of the redeemable convertible preferred stock tranche liability and the anti‑dilutive protection liability, valuation of the warrant liability, deferred tax valuation allowances, the fair value of common stock prior to the completion of the IPO, and construction lease financing obligations. 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. Summary of significant accounting policies The Company’s significant accounting policies are described in Note 2, “Summary of Significant Accounting Policies,” in the Annual Report. There have been no material changes to the significant accounting policies previously disclosed in the Annual Report. Recent accounting pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014‑09, Revenue From Contracts With Customers (“ASU No. 2014-09”). ASU No. 2014‑09 amends Accounting Standards Codification (“ASC”) Topic 605, Revenue Recognition, by outlining a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. ASU No. 2014‑09 will be effective for the Company for interim and annual periods beginning after December 15, 2017. The Company is evaluating the impact that this ASU may have on its consolidated financial statements. In August 2014, the FASB issued ASU No. 2014‑15, Presentation of Financial Statements—Going Concern, which requires management to assess an entity’s ability to continue as a going concern every reporting period, and provide certain disclosures if management has substantial doubt about the entity’s ability to operate as a going concern, or an express statement if not, by incorporating and expanding upon certain principles that are currently in U.S. auditing standards. This guidance is effective for the annual period ending after December 15, 2016, and for annual periods and interim periods within annual periods beginning thereafter. Early application is permitted. The Company is in process of evaluating this guidance and determining the expected effect on its consolidated financial statements, but does not expect it to have a significant impact on the Company's results of operations, cash flows or financial position. In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which applies to all leases and will require lessees to put most leases on the balance sheet, but recognize expense in a manner similar to the current standard. ASU 2016-02 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 for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. Full retrospective application is prohibited. The Company is evaluating the impact that this ASU may have on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting (“ASU No. 2016-09”), which simplifies share-based payment accounting through a variety of amendments. The standard will be effective for annual reporting periods and interim periods within those annual periods, beginning after December 15, 2016, and early adoption is permitted. The Company is currently evaluating the potential impact ASU 2016-09 may have on its financial position.

Fair Value Measurements

9 Months Ended

Sep. 30, 2016

Fair Value Measurements

Fair Value Measurements

3. Fair Value Measurements

The Company classifies fair value based measurements using a three-level hierarchy that prioritizes the inputs used to measure fair value. This hierarchy requires entities to maximize the use of observable inputs and minimize the use of unobservable inputs. The three levels of inputs used to measure fair value are as follows: Level 1, quoted market prices in active markets for identical assets or liabilities; Level 2, observable inputs other than quoted market prices included in Level 1 such as quoted market prices for markets that are not active or other inputs that are observable or can be corroborated by observable market data; and Level 3, unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities, including estimates and assumptions developed by the Company, reflective of those that a market participant would use, as inputs to certain pricing models, discounted cash flow methodologies and similar techniques that use significant unobservable inputs.

Assets measured at fair value on a recurring basis as of September 30, 2016 were as follows (in thousands):


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	September 30,		Identical Assets		Inputs		Inputs
Financial Assets:	2016		(Level 1)		(Level 2)		(Level 3)
Cash and cash equivalents	$	199,874	$	199,874	$	—	$	—
Money market funds, included in other current assets		320		320		—		—
Money market funds, included in other non-current assets		1,619		1,619		—		—
Total financial assets	$	201,813	$	201,813	$	—	$	—

Assets and liabilities measured at fair value on a recurring basis as of December 31, 2015 were as follows (in thousands):


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	December 31,		Identical Assets		Inputs		Inputs
Financial Assets:	2015		(Level 1)		(Level 2)		(Level 3)
Cash and cash equivalents	$	143,180	$	143,180	$	—	$	—
Money market funds, included in other current assets		320		320		—		—
Total financial assets	$	143,500	$	143,500	$	—	$	—

Financial Liabilities:
Warrant liability	$	289	$	—	$	—	$	289
Total financial liabilities	$	289	$	—	$	—	$	289

The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial liabilities (in thousands):


		Warrant
		Liability
Fair value at December 31, 2015	$	289
Changes in fair value recognized in other expense		87
Reclassification to additional paid-in capital in connection with IPO		(376)
Fair value at September 30, 2016	$	—

There were no transfers between fair value measurement levels during the nine month period ended September 30, 2016 or 2015. The fair value of the preferred stock warrant liability was determined based on “Level 3” inputs utilizing the Black-Scholes option pricing model. Upon the completion of the IPO, the Company’s 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.

Cash and cash equivalents

The Company considers all highly liquid securities with original final maturities of three months or less from the date of purchase to be cash equivalents. As of September 30, 2016 and December 31, 2015, cash and cash equivalents comprised of funds in cash and money market accounts.

- 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

Accrued expenses

9 Months Ended

Sep. 30, 2016

Accrued expenses

Accrued expenses

4. Accrued expenses

Accrued expenses consisted of the following (in thousands):


	As of
	September 30,		December 31,
	2016		2015
Patent and license fees	$	5,762	$	3,395
Deferred initial public offering costs		—		283
Employee compensation costs		1,930		1,016
Professional services		1,163		382
Other		637		380
Total	$	9,492	$	5,456

Property and equipment, net

9 Months Ended

Sep. 30, 2016

Property and equipment, net

Property and equipment, net

5. Property and equipment, net

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


	As of
	September 30,		December 31,
	2016		2015
Construction-in-progress	$	32,595	$	—
Laboratory equipment		4,734		2,215
Computer equipment		726		447
Furniture and office equipment		169		74
Leasehold improvements		191		23
Total property and equipment		38,415		2,759
Less: accumulated depreciation		(1,343)		(629)
Property and equipment, net	$	37,072	$	2,130

Commitments and contingencies	9 Months Ended
Commitments and contingencies	Sep. 30, 2016
Commitments and contingencies.
Commitments and contingencies	6. Commitments and contingencies Facility leases In December 2013, the Company entered into an agreement to sublease its facility under a non‑cancelable operating lease that was set to expire at the end of September 2016. In August 2016, the Company amended the sublease to extend the expiration date from September 30, 2016 until the earlier of (i) 30 days following the date on which the Company gives the landlord written notice that it intends to vacate the premises and (ii) November 30, 2016. In September 2016, the Company delivered notice of its intent to vacate as of October 31, 2016, such that the sublease expired on November 1, 2016. Pursuant to the sublease agreement, the Company maintained restricted cash of $0.3 million in a collateral account that was held until the termination of the Company’s obligations under the agreement. The sublease agreement could not be extended beyond the expiration date of the sublease. The sublease contained escalating rent clauses which required higher rent payments in future years. The Company expensed rent on a straight‑line basis over the term of the sublease, including any rent‑free periods. The deposit is recorded in prepaid expenses and other current assets in the accompanying condensed consolidated balance sheet as of September 30, 2016 and December 31, 2015. In November 2015, the Company entered into a real estate license agreement to sublease from the licensor additional laboratory space in Cambridge, Massachusetts. The term of the lease is from December 1, 2015 to November 30, 2016. The Company’s contractual obligation related to lease payments over the term of the sublease is approximately $1.9 million. The Company delivered notice of its intent to vacate these premises in September 2016, in accordance with its right to cancel the sublease upon no less than 30 days’ written notice, provided that the Company remains liable to continue to pay the monthly rental fee for the remainder of the term unless the licensor can sublease the space. If the licensor can sublease the space to another party, the Company will be credited the lesser of (i) the rental fee paid by such party corresponding to the remainder of the term and (ii) 50% of the rental for the remainder of the term. Hurley Street, Cambridge, MA In February 2016, the Company entered into a lease agreement for approximately 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 condensed consolidated financial statement as of September 30, 2016. 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 facility lease obligation, on its balance sheet for the total amount of the project costs incurred whether funded by the Company or the landlord. As of September 30, 2016, the Company had recorded construction in progress of $32.6 million, which was included in property and equipment, net, and a corresponding facility lease obligation of $32.6 million. The Company did not pay any cash to the landlord related to the building for the nine months ended September 30, 2016. 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 will remain on the Company’s balance sheet at its historical cost, and such asset will 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. During the nine months ended September 30, 2016, the Company recognized $0.4 million of non-cash rental expense attributable to the land. 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 base rent is subject to increases over the term of the lease. The non-cancelable minimum annual lease payments for the annual periods beginning upon commencement of the lease are $3.9 million, $4.0 million, $4.1 million, $4.2 million and $4.3 million in the first five years of the lease, respectively, and $9.2 million in total thereafter, plus the Company’s share of the facility operating expenses and other costs that are reimbursable to the landlord under the lease. The Company began using this space as its headquarters in October 2016 and rental payments for this property began in November 2016. 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. 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 $16.0 million and $3.9 million in expense for such reimbursement during the nine months ended September 30, 2016 and 2015, respectively. During the three months ended September 30, 2016 and 2015, the Company recognized $5.0 million and $1.1 million in expense for such reimbursement, respectively. Massachusetts General Hospital In August 2016, the Company entered into an exclusive patent license agreement (the “2016 MGH Agreement”) with The General Hospital Corporation, d/b/a Massachusetts General Hospital (“MGH”). Pursuant to the terms of such license, the Company is required to make certain success payments to MGH, payable in cash or common stock (the “MGH Success Payments”) at the Company’s election. The MGH Success Payments are payable, if and when, the Company’s market capitalization reaches specified thresholds or upon a sale of the Company for consideration in excess of those thresholds, as discussed more fully in Note 7 (collectively the “Payment Conditions”). The MGH 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 the agreement at will upon 90 days written notice to MGH. Absent any of the Payment Conditions being achieved prior to termination, the Company would not be obligated to pay any MGH Success Payments. As such, the Company will recognize the expense and liability associated with each MGH Success Payment upon achievement of the associated Payment Conditions, if ever. The Company did not incur any expenses related to the MGH Success Payments during the three or nine months ended September 30, 2016. Litigation The Company is not a party to any litigation and did not have contingency reserves established for any litigation liabilities as of September 30, 2016 or December 31, 2015.

Significant Agreements	9 Months Ended
Significant Agreements	Sep. 30, 2016
Significant Agreements
Significant Agreements	7. 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. 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. The parties will pursue 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. The collaborative program of research to be undertaken by the parties pursuant to the 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 three 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 three 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”). Under the terms of the Collaboration Agreement, the Company granted to Juno Therapeutics during the Research Program Term a nonexclusive, worldwide, royalty‑free, sublicensable (subject to certain conditions) license under certain of the intellectual property controlled by the Company solely for the purpose of conducting 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) use certain genome editing reagents generated under the research program to research, evaluate and conduct preclinical testing and development of certain engineered T cells and (iv) evaluate the data developed in the conduct of activities under the research plan (the “Research License”). Additionally, as it relates to two of the three research areas, 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, the Company granted to Juno Therapeutics a non‑exclusive, milestone and royalty‑bearing, sub licensable 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 IND 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). Lastly, as it relates to the third research area, the Company granted to Juno Therapeutics a milestone and royalty‑bearing, sublicensable license under certain of the intellectual property controlled by the Company to use the genome editing reagents generated under the research program that are associated with certain CAR or TCR engineered T cell products to research, develop, make and have made, use, offer for sale, sell, import or export those CAR or 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). The Collaboration Agreement will be managed on an overall basis by a project leader from each of the Company and Juno Therapeutics. The project leaders will serve as the contact point between the parties with respect to the research program and will be primarily responsible for facilitating the flow of information, interaction, and collaboration between the parties. In addition, the activities under the Collaboration Agreement during the Research Program Term will be governed by a joint research committee (“JRC”) formed by an equal number of representatives from the Company and Juno Therapeutics. The JRC will oversee, review and recommend direction of the research program. Among other responsibilities, the JRC will monitor and report research progress and ensure open and frequent exchange between the parties regarding research program activities. Under the terms of the Collaboration Agreement, the Company received a $25.0 million up‑front, non‑refundable, non‑creditable cash payment. In addition, Juno Therapeutics will pay to the Company an aggregate of up to $22.0 million in research and development funding over the initial five year term of the research program across the three research areas consisting primarily of funding for up to a specified maximum number of full time equivalents personnel each year over the initial five year term of the research program across three research areas. Under the terms of the 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 three research areas. However, for two of the three research areas, Juno Therapeutics has 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 would be 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, the Company is eligible to receive up to a $77.5 million in development milestone payments and up to $80 million in regulatory milestone payments. In addition, the Company is eligible to receive additional development and regulatory milestone payments for subsequent products developed within each of the three 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 three research areas. Development milestone payments are 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. In addition, to the extent any of the product candidates covered by the licenses conveyed to Juno Therapeutics are commercialized, the Company would be entitled to receive tiered royalty payments of low double digits based on a percentage of net sales. 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. In May 2016, the Company achieved a $2.5 million milestone under the collaboration resulting from technical progress in a research program to create engineered T cells with CARs and TCRs to treat cancer. 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 September 30, 2016, the next potential milestone payment that the Company may be entitled to receive under the agreement is a substantive milestone payment of $2.5 million for the achievement of certain development criteria. The Company would recognize the milestone payment as revenue upon achievement. There are no cancellation, termination or refund provisions in the Collaboration Agreement that contain material financial consequences to the Company. Unless earlier terminated, the Collaboration Agreement will continue in full force and effect, on a product‑by‑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 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 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 Collaboration Agreement for convenience upon not less than six months prior written notice to the Company. The Company may terminate the 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 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 Collaboration Agreement. If Juno Therapeutics terminates the 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 Collaboration Agreement for convenience or if the Company terminates the Collaboration Agreement as a result of Juno Therapeutics’ uncured material breach or default, then the licenses conveyed to Juno will terminate. Accounting Analysis The Company evaluated the Collaboration Agreement in accordance with the provisions of ASC, Topic 605-25, Revenue Recognition—Multiple Element Arrangements. The Company’s arrangement with Juno Therapeutics contains the following deliverables: (i) research and development services during the Initial Research Program Term (the “R&D Services Deliverable”), (ii) the Research License, (iii) the Development and Commercialization Licenses related to each of the three research areas (each, the “Development and Commercialization License Deliverable” for the respective research area), (iv) significant and incremental discount related to the option to purchase up to three additional Development and Commercialization Licenses for two of the research areas (each, the “Discount Deliverable” for the associated option) and (v) JRC services during the Initial Research Program Term (the “JRC Deliverable”). The Company has determined that the options to purchase additional development and commercialization licenses within two of the research program areas related to other gene targets are substantive options. Juno Therapeutics is not contractually obligated to exercise the options. Moreover, as a result of the uncertain outcome of the discovery, research and development activities, there is significant uncertainty as to whether Juno Therapeutics will decide to exercise its option for any additional gene targets within either of the two applicable research areas. Consequently, the Company is at risk with regard to whether Juno Therapeutics will exercise the options. However, the Company has determined that the options to purchase additional development and commercialization licenses with respect to other gene targets within the two applicable research program areas are priced at a significant and incremental discount. As a result, the Company has concluded that the discounts to purchase development and commercialization licenses for up to three additional gene targets within both of the research areas represent separate elements in the arrangement at inception. Accordingly, the deliverables identified at inception of the arrangement include six separate deliverables related to the significant and incremental discount inherent in the pricing of the option to purchase up to three additional development and commercialization licenses for two of the research areas included within the research program. The Company has concluded that the Research License deliverable does not qualify for separation from the R&D Services Deliverable. As it relates to the assessment of standalone value, the Company has determined that Juno Therapeutics cannot fully exploit the value of the Research License deliverable without receipt of the R&D Services Deliverable. This is primarily due to the fact that Juno Therapeutics must rely upon the Company to provide the research and development services included in the research plan because the services incorporate technology that is proprietary to the Company. The services to be provided by the Company involve unique skills and specialized expertise, particularly as it relates to genome editing technology that is not available in the marketplace. Accordingly, Juno Therapeutics must obtain the research and development services from the Company which significantly limits the ability for Juno Therapeutics to utilize the Research License for its intended purpose on a standalone basis. Therefore, the Research License deliverable does not have standalone value from the R&D Services Deliverable. As a result, the Research License deliverable and the R&D Services Deliverable have been combined as a single unit of accounting (the “R&D Services Unit of Accounting”). Conversely, the Company has concluded that each of the other deliverables identified at the inception of the arrangement has standalone value from each of the other elements based on their nature. Factors considered in this determination included, among other things, the capabilities of the collaboration partner, whether any other vendor sells the item separately, whether the value of the deliverable is dependent on the other elements in the arrangement, whether there are other vendors that can provide the items and if the customer could use the item for its intended purpose without the other deliverables in the arrangement. Additionally, the Collaboration Agreement does not include a general right of return. Accordingly, each of the other deliverables included in the Juno Therapeutics arrangement qualifies as a separate unit of accounting. Therefore, the Company has identified eleven units of accounting in connection with its obligations under the collaboration arrangement with Juno Therapeutics as follows: (i) the R&D Services Unit of Accounting, (ii) three units of accounting related to the Development and Commercialization Licenses for each of the three research areas, (iii) six units of accounting related to each of the Discount Deliverables, and (iv) the JRC Deliverable. The Company has determined that neither vendor specific objective evidence of selling price nor third-party evidence of selling price is available for any of the units of accounting identified at inception of the arrangement with Juno Therapeutics. Accordingly, the selling price of each unit of accounting was determined based on the Company’s best estimate of selling price (“BESP”). The Company developed the BESP for all of the units of accounting included in the Collaboration Agreement with the objective of determining the price at which it would sell such an item if it were to be sold regularly on a standalone basis. The Company developed the BESP for the R&D Services Unit of Accounting and the JRC Deliverable primarily based on the nature of the services to be performed and estimates of the associated effort and cost of the services, adjusted for a reasonable profit margin that would be expected to be realized under similar contracts. The Company developed the BESP for each of the Development and Commercialization License units of accounting 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 Company developed the BESP for each of the Discount Deliverables based on the estimated value of the associated in‑the‑money options. In developing such estimate, the Company considered the period to exercise the option, an appropriate discount rate and the likelihood that a market participant who was entitled to the discount would exercise the option. Allocable arrangement consideration at inception is comprised of: (i) the up‑front payment of $25.0 million, (ii) the research support of $20.0 million and (iii) payments related to specialized materials costs of $2.0 million. The research support of $20.0 million and payments related to specialized materials costs of $2.0 million represent contingent revenue features because the Company’s retention of the associated arrangement consideration is dependent upon its future performance of research support services and development of specialized materials. The aggregate allocable arrangement consideration of $47.0 million was allocated among the separate units of accounting using the relative selling price method as follows: (i) R&D Services Unit of Accounting: $16.7 million, (ii) Development and Commercialization License for the first research area: $9.3 million, (iii) Development and Commercialization License for the second research area: $15.4 million, (iv) Development and Commercialization License for the third research area: $0.2 million, (v) the first Discount Deliverable for the first research area: $0.7 million, (vi) the second Discount Deliverable for the first research area: $0.4 million, (vii) the third Discount Deliverable for the first research area: $0.2 million, (viii) the first Discount Deliverable for the second research area: $2.0 million, (ix) the second Discount Deliverable for the second research area: $1.3 million, and (x) the third Discount Deliverable for the second research area: $0.8 million. No amounts were allocated to the JRC Deliverable because the associated BESP was determined to be de minimis. The amounts allocated to each of the development and commercialization licenses are based on the respective BESP calculations, which reflect the level of risk and expected probability of success inherent in the nature of the associated research area. The Company will recognize revenue related to amounts allocated to the R&D Services Unit of Accounting as the underlying services are performed. The Company will recognize revenue related to amounts allocated to each of the Development and Commercialization Licenses upon delivery of the associated license, assuming the research services are substantially complete at the time the license is delivered. 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, delivery is deemed to occur upon the designation by Juno Therapeutics of the specific target or product, as applicable, whereupon the license becomes effective. The Company will recognize revenue related to amounts allocated to each of the Discount Deliverables upon the earlier of exercise of the associated option or upon lapsing of the underlying right, if the respective option expires unexercised. The Company has evaluated all of the milestones that may be received in connection with the Juno Therapeutics arrangement. In evaluating if a milestone is substantive, the Company assesses whether: (i) 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 the Company’s performance to achieve the milestone, (ii) the consideration relates solely to past performance, and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. All development and regulatory milestones are considered substantive on the basis of the contingent nature of the milestone, specifically reviewing factors such as the scientific, clinical, regulatory, commercial and other risks that must be overcome to achieve the milestone as well as the level of effort and investment required. Accordingly, such amounts will be recognized as revenue in full in the period in which the associated milestone is achieved, assuming all other revenue recognition criteria are met. All commercial milestones will be accounted for in the same manner as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met. The Company will recognize royalty revenue in the period of sale of the related product(s), based on the underlying contract terms, provided that the reported sales are reliably measurable and the Company has no remaining performance obligations, assuming all other revenue recognition criteria are met. During the three months ended September 30, 2016 and 2015, the Company recognized revenue totaling approximately $0.8 million and $0.7 million, respectively, with respect to the collaboration with Juno Therapeutics. During the nine months ended September 30, 2016 and 2015, the Company recognized revenue totaling approximately $4.9 million ($2.5 million of which related to the first milestone payment) and $0.8 million, respectively, with respect to the collaboration with Juno Therapeutics. The revenue is classified as collaboration and other research and development revenue in the accompanying condensed consolidated statement of operations. As of September 30, 2016, there was approximately $25.8 million of deferred revenue related to the Company’s collaboration with Juno Therapeutics, all of which is classified as long‑term in the accompanying condensed consolidated balance sheet. In addition, as of September 30, 2016, the Company has recorded accounts receivable of $1.0 million related to reimbursable research and development costs under the Collaboration Agreement for activities performed during the third quarter of 2016. Cystic Fibrosis Foundation Therapeutics, Inc. Award Agreement In May 2016, the Company entered into an award agreement (the “CF Award Agreement”) with the Cystic Fibrosis Foundation Therapeutics, Inc. (“CFFT”), a non-profit drug discovery and development affiliate of the Cystic Fibrosis Foundation, pursuant to which it received a development award for up to $5.0 million in funding over the agreement’s three year term (the “Award”). The funding from the Award is supporting the Company’s cystic fibrosis development program and related technology research and development. The Company is required to contribute additional funds to the program in an amount equal to the funds contributed by CFFT under the agreement. Pursuant to the terms of the CF Award Agreement, the Company is obligated to make royalty payments to CFFT contingent upon commercialization of an editing package, a delivery package, or a combination thereof, for modification of the cystic fibrosis transmembrane conductance regulator gene, the research or development of which was derived in whole or in part from the development program (a “CF Product”), including payments each equal to two times the amount the Company receives under the agreement, following the first commercial sale of a CF Product in the United States and the European Union, respectively. The Company is also obligated to make a payment to CFFT equal to two times the amount the Company receives under the CF Award Agreement, due in the first calendar year in which the aggregate cumulative net sales of a CF Product exceed $100 million. The payments due will not, in the aggregate, exceed ten percent of net sales of a CF Product in a year; the remaining obligation will be carried forward to subsequent year(s) until the payment of any such remaining payment does not, in the aggregate, exceed ten percent of net sales of a CF Product. The Company is also obligated to make payments to CFFT of up to two times the Award amount if the Company transfers, sells or licenses the development program technology, or if the Company enters into a change of control transaction, with such payments to be credited against the payments due upon commercialization. Following the first year anniversary of the effective date of the agreement, either party can terminate the agreement without cause by providing 90 days’ notice. The Company’s payment obligations survive the termination of the CF Award Agreement. During the nine months ended September 30, 2016, the Company recognized revenue of $0.2 million with respect to the Award. The revenue is classified as collaboration and other research and development revenue in the accompanying condensed consolidated statement of operations. Adverum Biotechnologies, Inc. Collaboration, Option, and License Agreement In August 2016, the Company entered into an agreement with Adverum Biotechnologies, Inc. (“Adverum”) to explore the delivery of genome editing medicines to treat up to five inherited retinal diseases. Under the terms of the agreement, the Company paid an upfront non-refundable fee of $1.0 million to evaluate Adverum’s next generation adeno-associated viral vectors (“AAVs”) for use in clinical development. The Company will support all preclinical activities related to this agreement, including research and development activities to be performed by Adverum, with $0.5 million of the upfront fee being creditable against this funding obligation. Accordingly, the Company has deferred and capitalized $0.5 million of the $1.0 million upfront fee as an advance payment for future research and development activities which the Company believes will be incurred in the future. The capitalized amount will be expensed as research and development expenses in the Company’s consolidated statements of operations as the related services are performed. The Company expensed the remaining $0.5 million as research and development expense in the accompanying statement of operations during the three and nine months ended September 30, 2016. Additionally, the Company may pay, at its discretion, an additional fee of $1.0 million, per exercise, to exercise an option to receive an exclusive license to Adverum’s next generation AAVs for use in an indication chosen under the agreement. Adverum is also entitled to receive development and regulatory milestone payments up to a maximum of a mid-single digit millions of dollars per license based on the achievement of specific events for a product candidate that includes an Adverum vector (“Adverum Product”) and a low to mid-single digit millions of dollars based on the achievement of specific events for a product candidate that doesn’t include an Adverum vector (“Non-Adverum Product”). Adverum is also entitled to receive certain commercial milestone payments for Adverum Products up to a maximum amount of a low double digit million dollar amount per product. The Company is also obligated to pay Adverum single digit to low double digit percentage royalties on net sales of Adverum Products and low single digit percentage royalties on sales of Non-Adverum Products sold in applicable territories during the royalty term. 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 Company anticipates entering into these types of license agreements in the future. The Company believes the following agreements are significant to the business: The General Hospital Corporation License Agreements—In August 2014, the Company entered into an agreement to license certain patent rights owned or co‑owned by MGH. Consideration for the granting of the license included the payment of an upfront license fee of $0.1 million, the issuance of 66,848 shares of the Company’s common stock, which was based on 0.5% of the Company’s outstanding stock on a fully diluted basis, and the right to receive future issuances of shares of common stock to maintain MGH’s ownership following the third tranche of the Company’s Series A redeemable convertible preferred stock financing (e.g. anti‑dilution protection liability), which was settled in June 2015. MGH is entitled to nominal annual license fees and to receive future clinical, regulatory and commercial milestone payments aggregating to a maximum of $3.7 million and aggregate of $1.8 million upon the occurrence of certain sales milestones. The Company is also obligated to pay MGH low single digit percentage royalties on net sales of products for the prevention or treatment of human disease, and ranging from low single digit to low double digit percentage royalties on net sales of other products and services made by the Company, its affiliates or its sublicenses. 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 MGH. In August 2016, the Company entered into the 2016 MGH Agreement to license certain patent rights owned or co-owned by MGH (the “Additional MGH Patent Rights”). Consideration for granting the license included the payment of an upfront nonrefundable license fee of $0.8 million, which the Company recorded as research and development expense in the accompanying consolidated statement of operations. Under the 2016 MGH Agreement, MGH is entitled to nominal annual license fees, clinical and regulatory milestone payments totaling less than $1.0 million in the aggregate per licensed product up to four licensed products or processes to achieve the specified clinical and regulatory milestones, and commercial sales milestone payments totaling up to $4.9 million in the aggregate, consisting of milestone payments due upon the first commercial sales for up to four licensed products or processes and milestone payments due upon annual net sales of products or processes meeting specified thresholds. The Company is also obligated to pay MGH royalties of less than 1% on net sales of products and processes for the prevention or treatment of human disease, and royalties of a low single-digit percentage on net sales of products and processes for the prevention or treatment of a non-human animal disease, made by the Company, its affiliates, or its sublicensees. The royalty percentages that the Company is obligated to pay are subject to reduction if at the time of sale the applicable product or process is not covered by a valid claim within the Additional MGH Patent Rights. Under the 2016 MGH Agreement, the Company is obligated to reimburse MGH for all patent costs and future reasonable costs associated with the prosecution, filing, and maintenance of the licensed patents. MGH is also entitled under the 2016 MGH Agreement to receive MGH Success Payments of up to $6.0 million in the event the Company’s market capitalization reaches specified thresholds exceeding a low ten digit dollar amount, on or prior to the expiration or termination of the 2016 MGH Agreement (or if earlier, a Company sale) (“Market Cap Success Payments”) or a Company sale for consideration in excess of those thresholds (“Company Sale Success Payments”). Additional Market Cap Success Payments become payable, and the amount of potential Company Sale Success Payments would increase further, if the Company’s market capitalization reaches additional higher thresholds and the Company has at least one product candidate that is covered by a claim of an Additional MGH Patent Right and that (i) is the subject of a Phase 1 clinical trial of which the Company or an affiliate or sublicensee of the Company is the sponsor, (ii) was the subject of a Phase 1 clinical trial of which the Company or an affiliate or sublicensee of the Company was the sponsor with the Company having determined to conduct a subsequent clinical trial with respect to such product candidate, or (iii) has been approved for sale in either the United States or European Union. Market Cap Success Payments are payable in cash or shares of Company common stock at the Company’s discretion, and Company Sale Success Payments are payable solely in cash. For additional information regarding the 2016 MGH Agreement, see Note 6 to these condensed consolidated financial statements. The Broad Institute, Inc., The President and Fellows of Harvard College, and Massachusetts Institute of Technology License Agreement—In October 2014, the Company entered into an agreement with Harvard and Broad to license certain patent rights owned or co‑owned by, or among, Harvard, Massachusetts Institute of Technology (“MIT”), and the Broad (collectively, the “Institutions”). Consideration for the granting of the license included the payment of an upfront license issuance fee of $0.2 million, the issuance of 561,531 shares of the Company’s common stock, which was equal to 4.2% of the Company’s outstanding stock on a fully diluted basis and, the right to receive future issuances of shares of common stock to maintain the Institutions’ ownership following the third tranche of the Series A Preferred Stock financing (e.g. anti‑dilution protection liability), which was settled in June 2015. 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. Duke University License Agreement—In October 2014, the Company entered into an exclusive license agreement with Duke University (“Duke”) to access intellectual property and technology related to the CRISPR/Cas9 and TALEN genome editing systems. In consideration for the granting of the license, the Company paid Duke an upfront fee of $0.1 million. Duke is entitled to receive clinical, regulatory, and commercial milestone payments totaling up to $0.6 million in the aggregate per licensed product. The Company is also obligated to pay to Duke nominal annual license fees and low single digit royalties based on annual net sales of licensed products and licensed services by the Company and its affiliates and sublicensees. Each of the above license agreements obligates the Company to use commercially reasonable efforts to research, develop, and commercialize products for the prevention or treatment of human disease. The Company is also required to achieve certain development milestones within specific time periods. Each licensor has the right to terminate the license if the Company fails to achieve the development milestones. Each license agreement requires the Company to pay an annual license maintenance fee and reimburse the licensor for expenses associated with the prosecution and maintenance of the licensed patent rights. The Company recorded the upfront issuance fees and the fair value of the common stock issued to the licensors as research and development expense (as the licenses do not have alternative future use) in accordance with ASC Topic 730, Research and Development. The anti‑dilutive protection obligation was classified as a liability and was recorded at its grant date fair value on the effective date of the respective agreements with the initial fair value being recorded to research and development expense as it represented additional consideration paid to the licensor in connection with the license agreement. The anti-dilution liability was settled in June 2015.

Stock-based compensation

9 Months Ended

Sep. 30, 2016

Stock-based compensation

Stock-based compensation

8. Stock‑based compensation

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


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2016		2015		2016		2015
Research and development	$	2,619	$	921	$	10,021	$	1,391
General and administrative		1,072		136		3,078		171
Total stock-compensation expense	$	3,691	$	1,057	$	13,099	$	1,562

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 condensed consolidated balance sheets included as a component of accrued expenses or other long term liabilities based on the scheduled vesting dates. The restricted stock liability is reclassified into stockholders’ equity (deficit) as the restricted stock vests. A summary of the status of and changes in unvested restricted stock as of September 30, 2016 is as follows:


		Weighted
		Average
		Grant Date
		Fair Value
	Shares	Per Share
Unvested Restricted Common Stock as of December 31, 2015	1,596,853	$	0.0188
Issued	—		—
Vested	(580,662)	$	0.0162
Unvested Restricted Common Stock as of September 30, 2016	1,016,191	$	0.0203

For the nine months ended September 30, 2016, the expense related to restricted stock awards granted to employees and non‑employees was $0 and $7.0 million, respectively. For the nine months ended September 30, 2015, the expense related to restricted stock awards granted to employees and non‑employees was $0 and $1.2 million, respectively.

As of September 30, 2016, the Company had no unrecognized stock‑based compensation expense related to its employee unvested restricted stock awards. As of September 30, 2016, the Company had unrecognized stock‑based compensation expense related to its non‑employee unvested restricted stock awards of $4.1 million which is expected to be recognized over the remaining weighted average vesting period of 0.8 years.

Stock Options

Certain of the Company’s stock option agreements allow 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 are subject to repurchase by the Company if the employees cease to provide service to the Company, with or without cause. As such, the Company does not treat the exercise of unvested options as a substantive exercise. The Company has recorded the proceeds from the exercise of unvested stock options as a liability in the condensed consolidated balance sheets as a component of accrued expenses or other long term liabilities based on the scheduled vesting dates. The liability for unvested common stock subject to repurchase is reclassified into stockholders’ equity (deficit) as the shares vest.

The following is a summary of stock option activity for the nine months ended September 30, 2016:


		Weighted Average		Remaining	Aggregate Intrinsic
	Shares	Exercise Price		Contractual Life (years)	Value (in thousands)
Outstanding at December 31, 2015	1,713,385	$	6.31	9.6	$	15,580
Granted	1,450,441	$	21.36
Exercised	(60,357)	$	3.47
Cancelled	(12,659)	$	9.71
Outstanding at September 30, 2016	3,090,810	$	13.41	9.1	$	11,639
Vested and expected to vest at September 30, 2016	3,040,552	$	13.41	9.1	$	11,449
Exercisable at September 30, 2016	362,474	$	5.20	8.8	$	3,055

The table above reflects unvested stock options as exercised on the dates that the shares are no longer subject to repurchase. The Company had 26,301 and 39,338 shares of unvested restricted common stock outstanding at September 30, 2016 and December 31, 2015, respectively, resulting from the exercise of unvested stock options.

Using the Black‑Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the three and nine months ended September 30, 2016 and 2015 was $15.01 and $4.71, respectively. The expense related to options granted to employees and directors was $4.0 million and $0.3 million for the nine months ended September 30, 2016 and 2015, 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:


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2016		2015		2016		2015
Risk free interest rate	1.3	%	1.8	%	1.4	%	1.7	%
Expected dividend yield	—		—		—		—
Expected term (in years)	6.25		6.25		6.25		6.25
Expected volatility	76.5	%	79.2	%	78.9	%	80.0	%

There were 100,000 options granted to persons other than employees and directors during the nine months ended September 30, 2016. For the three and nine months ended September 30, 2016 and 2015, 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:


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2016		2015		2016		2015
Risk free interest rate	1.6	%	2.2	%	1.6	%	2.2	%
Expected dividend yield	—		—		—		—
Expected term (in years)	10.0		10.0		10.0		9.8
Expected volatility	76.5	%	80.0	%	76.5	%	79.6	%

As of September 30, 2016, the Company had unrecognized stock‑based compensation expense related to its employee stock options of $22.8 million which the Company expects to recognize over the remaining weighted average vesting period of 3.0 years.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References + Details

Net loss per share

9 Months Ended

Sep. 30, 2016

Net loss per share

Net loss per share

9. 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 common shares 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 common shares 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 and warrants 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. Contingently issuable shares of common stock pursuant to the 2016 MGH Agreement (Note 6) are excluded from the calculation of basic and diluted net loss per share calculation as the Payment Conditions have not been satisfied.

Upon the closing of the IPO in February 2016, the Company sold 6,785,000 shares of common stock and issued an additional 24,929,709 shares of common stock in connection with the automatic conversion of its redeemable convertible preferred stock. The issuance of these shares resulted in a significant increase in the Company’s weighted-average shares outstanding for the nine months ended September 30, 2016 when compared to the comparable prior year period and is expected to continue to impact the year-over-year comparability of the Company’s net loss per share calculations for the next six 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 September 30,
	2016	2015
Redeemable convertible preferred stock	—	24,929,709
Warrant to purchase redeemable convertible preferred stock	—	23,076
Unvested restricted common stock	1,016,191	1,809,639
Outstanding stock options	3,090,810	1,199,371
Total	4,107,001	27,961,795

Related-party transactions	9 Months Ended
Related-party transactions	Sep. 30, 2016
Related-party transactions
Related-party transactions	10. Related‑party transactions During the nine months ended September 30, 2016 and 2015, the Company paid a related party $1.3 million and $1.2 million in rent and facility-related fees, respectively. In addition, during the nine months ended September 30, 2015 the Company paid one of its investors $0.1 million in professional fees.

Summary of significant accounting policies (Policies)	9 Months Ended
Summary of significant accounting policies (Policies)	Sep. 30, 2016
Summary of significant accounting policies
Unaudited interim financial information	Unaudited interim financial information The condensed consolidated financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2015 (the “Annual Report”). The unaudited condensed consolidated financial statements include the accounts of Editas Medicine, Inc. and its wholly owned subsidiary. All intercompany transactions and balances of the subsidiary have been eliminated in consolidation. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The three months ended September 30, 2016 and 2015 are referred to as the third quarter of 2016 and 2015, respectively. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period.
Use of estimates	Use of estimates The preparation of condensed consolidated financial statements in conformity with United States generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the condensed 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, valuation of the redeemable convertible preferred stock tranche liability and the anti‑dilutive protection liability, valuation of the warrant liability, deferred tax valuation allowances, the fair value of common stock prior to the completion of the IPO, and construction lease financing obligations. 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.
Recent accounting pronouncements	Recent accounting pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014‑09, Revenue From Contracts With Customers (“ASU No. 2014-09”). ASU No. 2014‑09 amends Accounting Standards Codification (“ASC”) Topic 605, Revenue Recognition, by outlining a single comprehensive model for entities to use in accounting for revenue arising from contracts with customers. ASU No. 2014‑09 will be effective for the Company for interim and annual periods beginning after December 15, 2017. The Company is evaluating the impact that this ASU may have on its consolidated financial statements. In August 2014, the FASB issued ASU No. 2014‑15, Presentation of Financial Statements—Going Concern, which requires management to assess an entity’s ability to continue as a going concern every reporting period, and provide certain disclosures if management has substantial doubt about the entity’s ability to operate as a going concern, or an express statement if not, by incorporating and expanding upon certain principles that are currently in U.S. auditing standards. This guidance is effective for the annual period ending after December 15, 2016, and for annual periods and interim periods within annual periods beginning thereafter. Early application is permitted. The Company is in process of evaluating this guidance and determining the expected effect on its consolidated financial statements, but does not expect it to have a significant impact on the Company's results of operations, cash flows or financial position. In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which applies to all leases and will require lessees to put most leases on the balance sheet, but recognize expense in a manner similar to the current standard. ASU 2016-02 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 for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. Full retrospective application is prohibited. The Company is evaluating the impact that this ASU may have on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting (“ASU No. 2016-09”), which simplifies share-based payment accounting through a variety of amendments. The standard will be effective for annual reporting periods and interim periods within those annual periods, beginning after December 15, 2016, and early adoption is permitted. The Company is currently evaluating the potential impact ASU 2016-09 may have on its financial position.

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2016

Fair Value Measurements

Schedule of assets and liabilities measured at fair value on a recurring basis

Assets measured at fair value on a recurring basis as of September 30, 2016 were as follows (in thousands):


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	September 30,		Identical Assets		Inputs		Inputs
Financial Assets:	2016		(Level 1)		(Level 2)		(Level 3)
Cash and cash equivalents	$	199,874	$	199,874	$	—	$	—
Money market funds, included in other current assets		320		320		—		—
Money market funds, included in other non-current assets		1,619		1,619		—		—
Total financial assets	$	201,813	$	201,813	$	—	$	—

Assets and liabilities measured at fair value on a recurring basis as of December 31, 2015 were as follows (in thousands):


			Quoted Prices		Significant
			in Active		Other		Significant
			Markets for		Observable		Unobservable
	December 31,		Identical Assets		Inputs		Inputs
Financial Assets:	2015		(Level 1)		(Level 2)		(Level 3)
Cash and cash equivalents	$	143,180	$	143,180	$	—	$	—
Money market funds, included in other current assets		320		320		—		—
Total financial assets	$	143,500	$	143,500	$	—	$	—

Financial Liabilities:
Warrant liability	$	289	$	—	$	—	$	289
Total financial liabilities	$	289	$	—	$	—	$	289

Summary of the changes in the fair value of the Company’s Level 3 financial liabilities

The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial liabilities (in thousands):


		Warrant
		Liability
Fair value at December 31, 2015	$	289
Changes in fair value recognized in other expense		87
Reclassification to additional paid-in capital in connection with IPO		(376)
Fair value at September 30, 2016	$	—

Accrued expenses (Tables)

9 Months Ended

Sep. 30, 2016

Accrued expenses

Schedule of accrued expenses

Accrued expenses consisted of the following (in thousands):


	As of
	September 30,		December 31,
	2016		2015
Patent and license fees	$	5,762	$	3,395
Deferred initial public offering costs		—		283
Employee compensation costs		1,930		1,016
Professional services		1,163		382
Other		637		380
Total	$	9,492	$	5,456

Property and equipment, net (Tables)

9 Months Ended

Sep. 30, 2016

Property and equipment, net

Schedule of property and equipment, net

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


	As of
	September 30,		December 31,
	2016		2015
Construction-in-progress	$	32,595	$	—
Laboratory equipment		4,734		2,215
Computer equipment		726		447
Furniture and office equipment		169		74
Leasehold improvements		191		23
Total property and equipment		38,415		2,759
Less: accumulated depreciation		(1,343)		(629)
Property and equipment, net	$	37,072	$	2,130

Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 2016

Schedule of stock-based compensation expense

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


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2016		2015		2016		2015
Research and development	$	2,619	$	921	$	10,021	$	1,391
General and administrative		1,072		136		3,078		171
Total stock-compensation expense	$	3,691	$	1,057	$	13,099	$	1,562

Schedule of changes in unvested restricted stock


		Weighted
		Average
		Grant Date
		Fair Value
	Shares	Per Share
Unvested Restricted Common Stock as of December 31, 2015	1,596,853	$	0.0188
Issued	—		—
Vested	(580,662)	$	0.0162
Unvested Restricted Common Stock as of September 30, 2016	1,016,191	$	0.0203

For the nine months ended September 30, 2016, the

Schedule of stock option activity


		Weighted Average		Remaining	Aggregate Intrinsic
	Shares	Exercise Price		Contractual Life (years)	Value (in thousands)
Outstanding at December 31, 2015	1,713,385	$	6.31	9.6	$	15,580
Granted	1,450,441	$	21.36
Exercised	(60,357)	$	3.47
Cancelled	(12,659)	$	9.71
Outstanding at September 30, 2016	3,090,810	$	13.41	9.1	$	11,639
Vested and expected to vest at September 30, 2016	3,040,552	$	13.41	9.1	$	11,449
Exercisable at September 30, 2016	362,474	$	5.20	8.8	$	3,055

Employees and directors

Schedule of assumptions used to value stock options


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2016		2015		2016		2015
Risk free interest rate	1.3	%	1.8	%	1.4	%	1.7	%
Expected dividend yield	—		—		—		—
Expected term (in years)	6.25		6.25		6.25		6.25
Expected volatility	76.5	%	79.2	%	78.9	%	80.0	%

Non-employees

Schedule of assumptions used to value stock options


	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2016		2015		2016		2015
Risk free interest rate	1.6	%	2.2	%	1.6	%	2.2	%
Expected dividend yield	—		—		—		—
Expected term (in years)	10.0		10.0		10.0		9.8
Expected volatility	76.5	%	80.0	%	76.5	%	79.6	%

Net loss per share (Tables)

9 Months Ended

Sep. 30, 2016

Net loss per share

Schedule of anti-dilutive common stock equivalents


	As of September 30,
	2016	2015
Redeemable convertible preferred stock	—	24,929,709
Warrant to purchase redeemable convertible preferred stock	—	23,076
Unvested restricted common stock	1,016,191	1,809,639
Outstanding stock options	3,090,810	1,199,371
Total	4,107,001	27,961,795

Nature of business (Details) $ / shares in Units, $ in Thousands				1 Months Ended
	Feb. 08, 2016 $ / shares shares	Feb. 03, 2016 USD ($)	Jan. 15, 2016	Feb. 29, 2016 shares	Sep. 30, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Liquidity
Common stock, shares outstanding					35,608,637	3,233,638
Accumulated deficit \| $					$ (146,150)	$ (88,348)
Initial Public Offering
Liquidity
Shares sold	6,785,000			6,785,000
Price to the public \| $ / shares	$ 16.00
Aggregate net proceeds \| $		$ 97,500
Reverse stock split			0.3846
Shares issues upon conversion of preferred stock	24,929,709			24,929,709
Common stock, shares outstanding					35,608,637
Overallotment Option
Liquidity
Shares sold	885,000

Fair Value Measurements (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financial Assets
Cash and cash equivalents	$ 199,874	$ 143,180
Total financial assets	201,813	143,500
Financial Liabilities
Warrant Liability		289
Total financial liabilities		289
Money market funds \| Other current assets
Financial Assets
Restricted cash	320	320
Money market funds \| Other non-current assets
Financial Assets
Restricted cash	1,619
Level 1
Financial Assets
Cash and cash equivalents	199,874	143,180
Total financial assets	201,813	143,500
Level 1 \| Money market funds \| Other current assets
Financial Assets
Restricted cash	320	320
Level 1 \| Money market funds \| Other non-current assets
Financial Assets
Restricted cash	$ 1,619
Level 3
Financial Liabilities
Warrant Liability		289
Total financial liabilities		$ 289

Fair Value Measurements Assumptions And Level 3 Rollforward (Details) - Warrant Liability $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($)
Roll-forward of the fair value of liabilities measured at fair value on a recurring basis
Balance, beginning of period	$ 289
Changes in fair value recognized in other expense	87
Reclassification to additional paid-in capital in connection with IPO	$ (376)

Accrued Expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Accrued expenses
Patent and license fees	$ 5,762	$ 3,395
Deferred initial public offering costs		283
Employee compensation costs	1,930	1,016
Professional services	1,163	382
Other	637	380
Total	$ 9,492	$ 5,456

Property And Equipment Net (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Property and equipment disclosures
Property and equipment, gross	$ 38,415	$ 2,759
Less: accumulated depreciation	(1,343)	(629)
Property and equipment, net	37,072	2,130
Construction-in-progress
Property and equipment disclosures
Property and equipment, gross	32,595
Laboratory equipment
Property and equipment disclosures
Property and equipment, gross	4,734	2,215
Computer equipment
Property and equipment disclosures
Property and equipment, gross	726	447
Furniture and office equipment
Property and equipment disclosures
Property and equipment, gross	169	74
Leasehold improvements
Property and equipment disclosures
Property and equipment, gross	$ 191	$ 23

Commitments And Contingencies Operating Leases (Details)	9 Months Ended
	Sep. 30, 2016 USD ($)	Feb. 29, 2016 USD ($) ft²
Operating Leased Assets [Line Items]
Construction financing lease obligation, net of current portion	$ 32,048,000
Facility Sublease Arrangement
Operating Leased Assets [Line Items]
Collateral held	300,000
Laboratory Sublease Cambridge
Operating Leased Assets [Line Items]
Contractual obligation related to lease payments	$ 1,900,000
Cancellation period	30 days
Cancellation recovery percentage of sublease income	$ 50
Hurley Street, Cambridge, MA
Operating Leased Assets [Line Items]
Leased space ( in square feet) \| ft²		59,783
Security deposit		$ 1,600,000
Rent expense	400,000
Construction in progress	32,600,000
Construction financing lease obligation, net of current portion	$ 32,600,000
Estimated useful life	30 years
Extended lease option (in years)	5 years
Minimum lease payments year 1	$ 3,900,000
Minimum lease payments year 2	4,000,000
Minimum lease payments year 3	4,100,000
Minimum lease payments year 4	4,200,000
Minimum lease payments year 5	4,300,000
Minimum lease payments thereafter	$ 9,200,000

Significant Agreements Juno Therapeutics Collaboration Agreement (Details) $ in Thousands		1 Months Ended			3 Months Ended		9 Months Ended
	May 26, 2015 item	Aug. 31, 2016 USD ($) item	May 31, 2016 USD ($)	May 31, 2015 USD ($) item	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Collaboration and other research and development revenues					$ 962	$ 670	$ 5,155	$ 837
Deferred revenue					25,800		25,800		$ 25,321
Accounts receivable					1,122		1,122		$ 1,019
Juno Therapeutics
Collaboration and other research and development revenues					800	$ 700	4,900	$ 800
Deferred revenue					25,800		25,800
Accounts receivable					1,000		1,000
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
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
Next possible milestone payment					2,500		2,500
Number of options to purchase Development and Commercialization License \| item				3
Number of deliverables \| item				6
Number of accounting units \| item				11
Number of accounting units for Development and Commercialization License \| item				3
Number of accounting units for discount deliverables \| item				6
Allocable arrangement consideration - upfront payment				$ 25,000
Allocable arrangement consideration - research support				20,000
Allocable arrangement consideration - specialized material costs				2,000
Allocable arrangement consideration - aggregate arrangement consideration				47,000
Allocable arrangement consideration - R&D Services Unit of Accounting				16,700
Allocable arrangement consideration - Development and Commercialization License for the first research area				9,300
Allocable arrangement consideration - Development and Commercialization License for the second research area				15,400
Allocable arrangement consideration - Development and Commercialization License for the third research area				200
Allocable arrangement consideration - first Discount Deliverable for the first research area				700
Allocable arrangement consideration - second Discount Deliverable for the first research area				400
Allocable arrangement consideration - third Discount Deliverable for the first research area				200
Allocable arrangement consideration - first Discount Deliverable for the second research area				2,000
Allocable arrangement consideration - second Discount Deliverable for the second research area				1,300
Allocable arrangement consideration - third Discount Deliverable for the second research area				800
Allocable arrangement consideration -JRC Deliverable				$ 0
Collaboration and License Agreement \| Adverum Biotechnologies, Inc
Additional fees		$ 1,000
Maximum number of inherited retinal diseases, to be treated \| item		5
Up-front payment		$ 1,000
Adverum agreement consideration- pre-clinical activities		500
Advance payment on future research and development activities		$ 500
Adverum agreement consideration- research and development activities					$ 500		500
Development award agreement \| Cystic Fibrosis Foundation Therapeutics, Inc.
Agreement term			3 years
Potential research and development funding			$ 5,000
Collaboration and other research and development revenues							$ 200
Net sales threshold for potential milestone payments to be made			$ 100,000
Percentage of net sales threshold for potential milestone payments to be made			10.00%
Contract termination notice			90 days

Significant Agreements Juno Therapeutics Collaboration Agreement (Details2) $ in Thousands	1 Months Ended			3 Months Ended		9 Months Ended
	Aug. 31, 2016 USD ($) item	Oct. 31, 2014 USD ($) shares	Aug. 31, 2014 USD ($) shares	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Research and development				$ 10,832	$ 3,850	$ 30,144	$ 13,020
The General Hospital (MGH) \| License Patent Rights
Upfront fee received			$ 100
Stock issued to licensors \| shares			66,848
Percentage of outstanding shares issued			0.50%
Research and development	$ 800
Potential liability for future clinical and regulatory milestone payments related to product approval	$ 4,900
Number of licensed products \| item	4
Potential liability for future sales milestone payments			$ 1,800
The General Hospital (MGH) \| Maximum \| License Patent Rights
Potential liability for future clinical, regulatory and commercial milestone payments related to product approval	$ 1,000		$ 3,700
Percentage of net sales threshold for potential milestone payments to be made	1.00%
Success Payments	$ 6,000
The General Hospital (MGH) \| UNITED STATES \| Human disease \| License Patent Rights
Potential liability for future sales milestone payments		$ 54,000
Harvard, Broad and MIT (Institutions) \| License Patent Rights
Upfront fee received		$ 200
Stock issued to licensors \| shares		561,531
Percentage of outstanding shares issued		4.20%
Harvard, Broad and MIT (Institutions) \| Rare disease
Potential liability for future sales milestone payments		$ 36,000
Harvard, Broad and MIT (Institutions) \| United States Europe And Japan \| License Patent Rights
Potential liability for future clinical and regulatory milestone payments related to product approval		14,800
Harvard, Broad and MIT (Institutions) \| United States and one other \| License Patent Rights
Potential liability for future clinical and regulatory milestone payments related to product approval		4,100
Duke University \| License Intellectual Property and Technology
Upfront fee received		100
Potential liability for future clinical, regulatory and commercial milestone payments related to product approval		$ 600

Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stock-based compensation disclosures
Compensation expense	$ 3,691	$ 1,057	$ 13,099	$ 1,562
Research and development.
Stock-based compensation disclosures
Compensation expense	2,619	921	10,021	1,391
General and administrative
Stock-based compensation disclosures
Compensation expense	$ 1,072	$ 136	$ 3,078	$ 171

Stock Based Compensation - Restricted Stock and Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Changes in unvested restricted stock
Unvested restricted common stock, beginning of period (in shares)			1,596,853
Vested (in shares)			(580,662)
Unvested restricted common stock, end of period(in shares)	1,016,191		1,016,191		1,596,853
Weighted Average Grant Date Fair Value
Balance, beginning of period			$ 0.0188
Vested (in dollars per share)			0.0162
Balance, beginning of period	$ 0.0203		$ 0.0203		$ 0.0188
Compensation expense	$ 3,691	$ 1,057	$ 13,099	$ 1,562
Changes in unvested stock options
Options exercised prior to vesting (in shares)						75,304
Options exercised prior to vesting , exercise price per share						$ 0.03
Unvested stock options (in shares)	26,301		26,301		39,338
Outstanding, beginning of period (in shares)			1,713,385
Granted (in shares)			1,450,441
Exercised (in shares)			(60,357)
Cancelled (in shares)			(12,659)
Outstanding, end of period (in shares)	3,090,810		3,090,810		1,713,385
Vested and expected to vest (in shares)	3,040,552		3,040,552
Exercisable (in shares)	362,474		362,474
Outstanding, beginning of period (in dollars per share)			$ 6.31
Granted (in dollars per share)			21.36
Exercised (in dollars per share)			3.47
Cancelled (in dollars per share)			9.71
Outstanding, end of period (in dollars per share)	$ 13.41		13.41		$ 6.31
Vested and expected to vest outstanding, weighted average exercise price (in dollars per share)	13.41		13.41
Exercisable (in dollar per share)	$ 5.20		$ 5.20
Remaining contractual life			9 years 1 month 6 days		9 years 7 months 6 days
Vested and expected to vest, remaining contractual life			9 years 1 month 6 days
Exercisable, remaining contractual life			8 years 9 months 18 days
Aggregate intrinsic value	$ 11,639		$ 11,639		$ 15,580
Vesting and expected to vest, aggregate intrinsic value	11,449		11,449
Exercisable, aggregated intrinsic value	$ 3,055		3,055
Employees and directors
Weighted Average Grant Date Fair Value
Compensation expense			$ 4,000	$ 300
Changes in unvested stock options
Weighted average fair value of options granted (per share)	$ 15.01	$ 4.71	$ 15.01	$ 4.71
Employees
Weighted Average Grant Date Fair Value
Unrecognized stock-based compensation expense	$ 22,800		$ 22,800
Period for recognition			3 years
Restricted Stock \| Employees
Weighted Average Grant Date Fair Value
Compensation expense			$ 0	$ 0
Unrecognized stock-based compensation expense	0		0
Restricted Stock \| Non-employees
Weighted Average Grant Date Fair Value
Compensation expense			7,000	$ 1,200
Unrecognized stock-based compensation expense	$ 4,100		$ 4,100
Period for recognition			9 months 18 days

Stock Based Compensation Assumptions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Employees and directors
Assumptions
Risk free interest rate	1.30%	1.80%	1.40%	1.70%
Expected term	6 years 3 months	6 years 3 months	6 years 3 months	6 years 3 months
Expected volatility	76.50%	79.20%	78.90%	80.00%
Employees
Assumptions
Unrecognized stock-based compensation expense	$ 22.8		$ 22.8
Period for recognition			3 years
Non-employees
Assumptions
Risk free interest rate	1.60%	2.20%	1.60%	2.20%
Expected term				9 years 9 months 18 days
Expected volatility	76.50%	80.00%	76.50%	79.60%

Net Loss Per Share (Details) - shares		1 Months Ended	9 Months Ended
Net Loss Per Share (Details) - shares	Feb. 08, 2016	Feb. 29, 2016	Sep. 30, 2016	Sep. 30, 2015
Potentially dilutive securities
Anti-dilutive common stock equivalent shares			4,107,001	27,961,795
Redeemable Convertible Preferred Stock.
Potentially dilutive securities
Anti-dilutive common stock equivalent shares				24,929,709
Warrant to purchase convertible redeemable preferred stock
Potentially dilutive securities
Anti-dilutive common stock equivalent shares				23,076
Restricted Stock
Potentially dilutive securities
Anti-dilutive common stock equivalent shares			1,016,191	1,809,639
Outstanding stock options
Potentially dilutive securities
Anti-dilutive common stock equivalent shares			3,090,810	1,199,371
Initial Public Offering
Potentially dilutive securities
Shares sold	6,785,000	6,785,000
Shares issues upon conversion of preferred stock	24,929,709	24,929,709
Conversion of Stock, Shares Issued	24,929,709	24,929,709

Related-Party Transactions (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Rent and facility related fees
Related Party Transaction [Line Items]
Payments to related party	$ 1.3	$ 1.2
Investor(s) \| Professional fees
Related Party Transaction [Line Items]
Payments to related party	$ 0.1