Adverum Biotechnologies (ADVM) 10-Q 8 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 30, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	ADVM
Entity Registrant Name	Adverum Biotechnologies, Inc.
Entity Central Index Key	0001501756
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Small Business	true
Entity Common Stock, Shares Outstanding		63,434,619

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 144,107	$ 154,949
Short-term investments	45,381	50,130
Prepaid expenses and other current assets	3,649	3,675
Total current assets	193,137	208,754
Operating lease right-of-use asset	22,592
Property and equipment, net	4,145	3,586
Restricted cash	999	999
Deposit and other long-term assets	174	156
Total assets	221,047	213,495
Current liabilities:
Accounts payable	1,752	1,707
Accrued expenses and other current liabilities	5,032	8,784
Lease liability, current portion	3,826
Deferred rent, current portion		228
Total current liabilities	10,610	10,719
Deferred rent, net of current portion		1,366
Lease liability, net of current portion	22,078
Other noncurrent liabilities	216	243
Total liabilities	32,904	12,328
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock
Common stock	6	6
Additional paid-in capital	523,923	522,503
Accumulated other comprehensive loss	(754)	(799)
Accumulated deficit	(335,032)	(320,543)
Total stockholders’ equity	188,143	201,167
Total liabilities and stockholders' equity	$ 221,047	$ 213,495

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Collaboration and license revenue		$ 216
Type of Revenue [Extensible List]	us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Operating expenses:
Research and development	$ 10,131	$ 12,794
General and administrative	5,576	5,368
Total operating expenses	15,707	18,162
Operating loss	(15,707)	(17,946)
Other income, net	1,218	746
Net loss	(14,489)	(17,200)
Other comprehensive loss:
Net unrealized gain on marketable securities	3	17
Foreign currency translation adjustment	42	(75)
Comprehensive loss	$ (14,444)	$ (17,258)
Net loss per share — basic and diluted	$ (0.23)	$ (0.30)
Weighted-average common shares used to compute net loss per share - basic and diluted	63,125	57,420

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive (Loss)/Income [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 184,028	$ 5	$ 439,048	$ (963)	$ (254,062)
Balance, shares at Dec. 31, 2017		49,015,339
Stock-based compensation expense	3,429		3,429
Adoption of Topic 606	6,146				6,146
Issuance of common stock upon follow-on offerings, net of issuance costs	70,191	$ 2	70,189
Issuance of common stock upon follow-on offerings, net of issuance costs, shares		11,642,128
Issuance of common stock upon exercise of stock options	308		308
Issuance of common stock upon exercise of stock options, shares		1,361,546
Issuance of common stock upon release of restricted stock units, shares		328,952
Restricted stock unit withholdings, shares		(115,593)
Taxes paid for RSUs	(801)		(801)
Foreign currency translation adjustment	(75)			(75)
Unrealized gain on marketable securities, net	17			17
Net loss	(17,200)				(17,200)
Balance at Mar. 31, 2018	246,043	$ 7	512,173	(1,021)	(265,116)
Balance, shares at Mar. 31, 2018		62,232,372
Balance at Dec. 31, 2018	201,167	$ 6	522,503	(799)	(320,543)
Balance, shares at Dec. 31, 2018		62,965,468
Stock-based compensation expense	1,762		1,762
Issuance of common stock upon exercise of stock options	$ 162		162
Issuance of common stock upon exercise of stock options, shares	118,000	118,482
Issuance of common stock upon release of restricted stock units, shares		397,302
Restricted stock unit withholdings, shares		(145,603)
Taxes paid for RSUs	$ (504)		(504)
Foreign currency translation adjustment	42			42
Unrealized gain on marketable securities, net	3			3
Net loss	(14,489)				(14,489)
Balance at Mar. 31, 2019	$ 188,143	$ 6	$ 523,923	$ (754)	$ (335,032)
Balance, shares at Mar. 31, 2019		63,335,649

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net loss	$ (14,489)	$ (17,200)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	426	459
Stock-based compensation expense	1,762	3,429
Amortization of premium and accrued interest on marketable securities	(129)
Amortization of operating lease right-of-use asset	539
Other	40	183
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(91)	818
Other asset	(18)
Accounts payable	(136)	(1,046)
Accrued expenses and other current liabilities	(2,363)	107
Deferred revenue		292
Deferred rent		(26)
Lease liability	1,242
Net cash used in operating activities	(13,217)	(12,984)
Cash flows from investing activities:
Purchases of marketable securities	(22,454)	(30,374)
Maturities of marketable securities	27,385	55,973
Purchases of property and equipment	(2,186)	(216)
Net cash provided by investing activities	2,745	25,383
Cash flows from financing activities:
Proceeds from offerings of common stock, net of issuance costs		70,191
Proceeds from issuance of common stock pursuant to option exercises	162	308
Taxes paid related to net share settlement of restricted stock units	(504)	(801)
Proceeds from a financing arrangement		100
Repayment of loan	(28)
Net cash provided by (used in) financing activities	(370)	69,798
Net increase (decrease) in cash and cash equivalents and restricted cash	(10,842)	82,197
Cash and cash equivalents and restricted cash at beginning of period	155,948	70,519
Cash and cash equivalents and restricted cash at end of period	145,106	152,716
Supplemental schedule of noncash investing and financing information
Fixed assets in accounts payable, accrued expenses and other current liabilities	$ 413	$ 153

Organization and Basis of Prese

Organization and Basis of Presentation	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Adverum Biotechnologies, Inc. (the “Company”) is a clinical-stage gene therapy company targeting unmet medical needs in ocular and rare diseases. The Company develops gene therapy product candidates designed to provide durable efficacy by inducing sustained expression of a therapeutic protein. The Company’s core capabilities include clinical development, novel vector discovery, and in-house manufacturing expertise, specifically in scalable process development, assay development, and current Good Manufacturing Practices (“cGMP”) quality control. Since the Company’s inception, it has devoted its efforts to performing research and development activities, filing patent applications, hiring personnel and raising capital to support these activities. The Company has not generated any revenue from the sale of products since its inception. The Company has experienced net losses since its inception and had an accumulated deficit of $335.0 million as of March 31, 2019. The Company expects to incur losses and have negative net cash flows from operating activities as it engages in further research and development activities. The Company believes that it has sufficient funds to continue operations into 2021. Basis of Presentation —The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These unaudited condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three months ended March 31, 2019, are not necessarily indicative of the results to be expected for the full year or any other future period. The balance sheet as of December 31, 2018 is derived from the audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete consolidated financial statements. The accompanying unaudited condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 filed with the SEC.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Use of Estimates The accompanying consolidated financial statements have been prepared in accordance with U.S. GAAP. The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Recently Adopted Accounting Pronouncements Leases The Company adopted Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) (“Topic 842”) on January 1, 2019. For its long-term operating leases, the Company recognizes a right-of-use asset and a lease liability on its condensed consolidated balance sheets. The Company adopted the new standard using the modified retrospective approach and recorded a lease liability of $24.7 million, and a right‑to‑use asset of $23.1 million, and no adjustment to the accumulated deficit. In connection with the lease adoption, the Company also derecognized deferred rent of $1.5 million. The adoption of the new standard did not have an impact on the condensed consolidated statement of operations. The lease liability is determined as the present value of future lease payments using an estimated rate of interest that the Company would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. In order to estimate the incremental borrowing rate, management estimated its credit rating, adjusted the credit rating for the nature of the collateral, and benchmarked the borrowing rate against observable yields on comparable securities with a similar term. As of the adoption date, the Company estimated the incremental borrowing rate to be 8.5%. The Company based the right-of-use asset on the liability adjusted for any prepaid or deferred rent. The Company determined the lease term at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. Rent expense for the operating lease is recognized on a straight-line basis over the lease term and included it in operating expenses on the statements of operations and comprehensive loss. Variable lease payments include lease operating expenses. The Company elected the practical expedients permitted under Topic 842, which among other things, allowed the Company to carry forward the historical lease classification of those leases in place as of January 1, 2019. The Company elected to exclude from its condensed consolidated balance sheets recognition of leases having a term of 12 months or less (short-term leases) and elected to not separate lease components and non-lease components for its long-term real-estate leases. Share-based payment to nonemployees In June 2018, the FASB issued ASU 2018-07, “Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting” that expands the scope of ASC Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. The Company adopted ASU 2018–07 on January 1, 2019 and the impact of the adoption resulted in lower stock-based compensation of $0.5 million in the three months ended March 31, 2019.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements and Fair Value of Financial Instruments	3. Fair Value Measurements and Fair Value of Financial Instruments The authoritative guidance on the fair value hierarchy for disclosure of fair value measurements is as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. 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. The fair value of Level 1 securities is determined using quoted prices in active markets for identical assets. Level 1 securities consist of highly liquid money market funds. Financial assets and liabilities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. U.S. government and agency securities, commercial paper, corporate bond and certificates of deposit are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. In certain cases where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3 within the valuation hierarchy. The following is a summary of the Company’s cash equivalents and short-term investments: March 31, 2019 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value (In thousands) Level 1: Money market funds $ 43 $ — $ — $ 43 Level 2: U.S. government and agency securities 1,795 — — 1,795 Commercial paper 166,194 3 (34 ) 166,163 Corporate bonds 16,920 19 — 16,939 Total cash equivalents and short-term investments 184,952 22 (34 ) 184,940 Less: cash equivalents (139,585 ) — 26 (139,559 ) Total short-term investments $ 45,367 $ 22 $ (8 ) $ 45,381 December 31, 2018 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value (In thousands) Level 1: Money market funds $ 126 $ — $ — $ 126 Level 2: U.S. government and agency securities 25,792 1 (4 ) 25,789 Commercial paper 147,606 — — 147,606 Corporate bonds 27,778 5 (17 ) 27,766 Certificates of deposit 1,420 — — 1,420 Total cash equivalents and short-term investments 202,722 6 (21 ) 202,707 Less: cash equivalents (152,577 ) — — (152,577 ) Total short-term investments $ 50,145 $ 6 $ (21 ) $ 50,130 There were no transfers within the hierarchy during the three months ended March 31, 2019 or 2018. The Company’s marketable securities as of March 31, 2019 mature within one year. Management regularly reviews all of the Company’s investments for other-than-temporary declines in estimated fair value. Management’s review includes the consideration of the cause of the impairment, including the creditworthiness of the security issuers, the number of securities in an unrealized loss position, the severity and duration of the unrealized losses, whether management has the intent to sell the securities and whether it is more likely than not that the Company will be required to sell the securities before the recovery of their amortized cost basis. Management determined that the gross unrealized losses on the Company’s marketable securities as of March 31, 2019 were temporary in nature. Therefore, none of the Company’s marketable securities were other-than-temporarily impaired as of March 31, 2019.

Significant Agreements

Significant Agreements	3 Months Ended
	Mar. 31, 2019
Research And Development [Abstract]
Significant Agreements	4. Significant Agreements Editas— In January 2018, the Company entered into an agreement to amend its collaboration, option and license agreement with Editas. The Company originally entered into an agreement with Editas in August 2016 pursuant to which the Company and Editas collaborate on certain studies using AAV vectors in connection with Editas’ genome editing technology and the Company grants to Editas an exclusive option to obtain certain exclusive rights to use the Company’s proprietary vectors in up to five ophthalmic indications. In January 2018, the Company and Editas extended the research collaboration, option and license agreement. In consideration for extending the agreement, Editas made a one-time, non-refundable cash payment of $0.5 million to the Company in February 2018. In June 2018, the Company and Editas entered into a subsequent amendment to the agreement to extend the Research Period and First Option Exercise Date (each as defined in the collaboration, option, and license agreement with Editas, as amended). Under the terms of the agreement, as amended, Editas had until November 2018 to exercise the option with respect to a designated initial indication, which Editas declined to do. With respect to the four other indications, Editas may exercise the option until August 2020, provided that the option will expire on August 2019 if Editas has not exercised one option with respect to any other indication by such date. Upon Editas’ timely exercise of the option with respect to the first additional indication for which Editas timely exercise its options, Editas will pay the Company a $1.5 million fee. Upon each subsequent exercise of the option, Editas will pay the Company a $1.0 million fee per indication. If Editas elects to develop a product using certain of the Company’s proprietary vectors, the Company will be eligible to receive up to $15.5 million in development and commercialization milestone payments for such product, and tiered royalties between the mid-single digits and low teens on net sales of such product, subject to certain adjustments. Unless earlier terminated, the agreement will be in effect until the later of the expiration of the option exercise period or the expiration of the royalty term of the last product. At any time after the option is first exercised, Editas may terminate the agreement for convenience in its entirety or on an indication-by-indication or country-by-country basis, upon prior written notice to the Company. The Company may also terminate the agreement if Editas challenges the Company’s patents relating to its proprietary vectors and does not withdraw such challenge within a defined period of time. In addition, either party may terminate the agreement with written notice upon a bankruptcy of the other party or upon an uncured material breach by the other party. Under Topic 606, the transaction price is $1.5 million related to the $1.0 million non-refundable upfront payment for license and research services at contract inception and the one-time, non-refundable cash payment of $0.5 million made by Editas in February 2018 in consideration for extending the agreement. The arrangement provides for additional payments to the Company when certain development and regulatory milestones are achieved. Because these milestone payments are not within the control of the Company and are not considered probable of being achieved until the events occur, the Company did not include them in the transaction price. The transaction price of $1.5 million was allocated to a single performance obligation, research and development. During the three months ended March 31, 2018, the Company recognized revenue of $0.2 million associated with Editas. The remaining performance obligations for Editas were completed during 2018. During the three months ended March 31, 2019, the Company had no recognized revenue from the Editas collaboration agreement.

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	5. Leases In June 2018, the Company entered into an operating lease agreement for new office and laboratory space which consists of approximately 81,000 square feet located in Redwood City, California. The lease term is 10 years beginning September 2018 through February 2029 with two options to extend the lease term for a period of seven years each. The Company has the right to make tenant improvements, including the addition of laboratory space, with a lease incentive allowance of $8.1 million. The rent payments began on March 1, 2019 with an escalation of rent payments each year after an abatement period. In connection with the lease, the Company has provided the landlord with a letter of credit in the amount of $1.0 million. The security for the letter of credit of $1.0 million is classified as restricted cash under long term assets on the condensed consolidated balance sheet. The Company also has an operating lease agreement for its Menlo Park office building which expires on May 8, 2020. The Company may extend this lease for up to four years. The lease agreement provides for an escalation of rent payments each year. The Company adopted Accounting Standards Update (ASU) No. 2016-02, Leases (See Note 2) and recorded right to use assets of $23.1 million and a lease liability of $24.7 million as of January 1, 2019. The estimated incremental borrowing rate used to measure the lease liability is 8.5%. Rent expense recognized under the operating leases, including additional rent charges for utilities, parking, maintenance, and real estate taxes was for the three months ended March 31, 2019 and 2018 was $1.2 million and $0.3 million, respectively. We recognize rent expense on a straight‑line basis over the lease period. The undiscounted future non-cancellable lease payments under the Company’s operating leases as of March 31, 2019 is as follows: Year ending December 31, (In thousands) 2019 (remaining 9 months) $ 2,864 2020 4,221 2021 4,683 2022 4,846 2023 5,016 Thereafter 28,837 Total undiscounted lease payments 50,467 Less: Present value adjustment (17,444 ) Less: Tenant improvement allowance (7,119 ) Total $ 25,904

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	3 Months Ended
	Mar. 31, 2019
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	6. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: March 31, 2019 December (In thousands) Accrued professional services $ 2,434 $ 2,291 Employee compensation 1,341 2,944 Accrued preclinical, clinical and process development costs 887 1,850 Other 370 1,699 Total accrued expenses and other current liabilities $ 5,032 $ 8,784

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies The Company was a party to a master services agreement (“MSA”) with Cornell University (“Cornell”) originally established in August 2014 and amended in December 2015. Under the MSA, Cornell provided assistance in regulatory affairs, overall project management, and parameter development. The MSA, as amended, provided for the Company to pay Cornell $13.3 million ratably over four years for these services as services were performed. In December 2016, the Company informed Cornell that the Company decided to terminate the MSA for material breach, effective January 6, 2017. Subsequently, Cornell informed the Company that it disputes the validity of the Company’s termination of the MSA. Although the Company intends to defend the validity of the termination of the MSA, the Company recorded $2.0 million of estimated costs associated with the termination of the MSA during the year ended December 31, 2017. This MSA included services relating to gene therapy programs directed to A1AT deficiency, HAE and severe allergy. The Company’s license agreements with Cornell remained in effect despite the termination of the MSA. Legal Proceedings From time to time, the Company may become involved in litigation and other legal actions. The Company estimates the range of liability related to any pending litigation where the amount and range of loss can be estimated. The Company records its best estimate of a loss when the loss is considered probable. Where a liability is probable and there is a range of estimated loss with no best estimate in the range, the Company records a charge equal to at least the minimum estimated liability for a loss contingency when both of the following conditions are met: (i) information available prior to issuance of the financial statements indicates that it is probable that a liability had been incurred at the date of the financial statements and (ii) the range of loss can be reasonably estimated. There have been no material changes from the legal proceedings described in our annual report on Form 10-K for the period ended December 31, 2018.

Equity Incentive Awards

Equity Incentive Awards	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Awards	8. Equity Incentive Awards The following table summarizes the Company’s option activity and related information: Number of Options (in thousands) Weighted- Average Exercise Price Balance at December 31, 2018 6,447 $ 5.83 Options granted 1,875 3.61 Options exercised (118 ) 1.37 Options cancelled (235 ) 4.21 Balance at March 31, 2019 7,969 $ 5.42 Exercisable as of March 31, 2019 3,760 $ 6.60 Restricted Stock Units (“RSUs”) The following table summarizes the Company’s RSUs activity and related information: Number of Units (in thousands) Weighted- Average Grant- Date Fair Value Outstanding at December 31, 2018 2,397 $ 9.23 Granted 240 3.50 Vested and released (397 ) 4.72 Forfeited (511 ) 4.81 Outstanding at March 31, 2019 1,729 $ 4.70 Stock-Based Compensation Expense The following table presents, by operating expense, the Company’s stock-based compensation expense: Three Months Ended March 31, 2019 2018 (In thousands) Research and development $ 631 $ 2,378 General and administrative 1,131 1,051 Total stock-based compensation expense $ 1,762 $ 3,429

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Net Loss per Share	9. Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period. Diluted net loss per share is computed by giving effect to all potential dilutive common stock equivalents outstanding for the period using the treasury stock method. Outstanding stock options, RSUs, employee stock purchase plan (“ESPP”) and warrants are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. The Company excluded approximately 9.9 million and 9.5 million shares of potentially dilutive securities as of March 31, 2019 and 2018, respectively, from the computations of diluted weighted-shares outstanding because their effect would be anti-dilutive.

Summary of significant accoun_2

Summary of significant accounting policies (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The accompanying consolidated financial statements have been prepared in accordance with U.S. GAAP. The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Leases	Recently Adopted Accounting Pronouncements Leases The Company adopted Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842) (“Topic 842”) on January 1, 2019. For its long-term operating leases, the Company recognizes a right-of-use asset and a lease liability on its condensed consolidated balance sheets. The Company adopted the new standard using the modified retrospective approach and recorded a lease liability of $24.7 million, and a right‑to‑use asset of $23.1 million, and no adjustment to the accumulated deficit. In connection with the lease adoption, the Company also derecognized deferred rent of $1.5 million. The adoption of the new standard did not have an impact on the condensed consolidated statement of operations. The lease liability is determined as the present value of future lease payments using an estimated rate of interest that the Company would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. In order to estimate the incremental borrowing rate, management estimated its credit rating, adjusted the credit rating for the nature of the collateral, and benchmarked the borrowing rate against observable yields on comparable securities with a similar term. As of the adoption date, the Company estimated the incremental borrowing rate to be 8.5%. The Company based the right-of-use asset on the liability adjusted for any prepaid or deferred rent. The Company determined the lease term at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. Rent expense for the operating lease is recognized on a straight-line basis over the lease term and included it in operating expenses on the statements of operations and comprehensive loss. Variable lease payments include lease operating expenses. The Company elected the practical expedients permitted under Topic 842, which among other things, allowed the Company to carry forward the historical lease classification of those leases in place as of January 1, 2019. The Company elected to exclude from its condensed consolidated balance sheets recognition of leases having a term of 12 months or less (short-term leases) and elected to not separate lease components and non-lease components for its long-term real-estate leases.
Accounting Standard Update Recently Adopted	Share-based payment to nonemployees In June 2018, the FASB issued ASU 2018-07, “Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting” that expands the scope of ASC Topic 718 to include share-based payment transactions for acquiring goods and services from nonemployees. The Company adopted ASU 2018–07 on January 1, 2019 and the impact of the adoption resulted in lower stock-based compensation of $0.5 million in the three months ended March 31, 2019.

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Summary of Cash Equivalents and Short-term Investments	The following is a summary of the Company’s cash equivalents and short-term investments: March 31, 2019 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value (In thousands) Level 1: Money market funds $ 43 $ — $ — $ 43 Level 2: U.S. government and agency securities 1,795 — — 1,795 Commercial paper 166,194 3 (34 ) 166,163 Corporate bonds 16,920 19 — 16,939 Total cash equivalents and short-term investments 184,952 22 (34 ) 184,940 Less: cash equivalents (139,585 ) — 26 (139,559 ) Total short-term investments $ 45,367 $ 22 $ (8 ) $ 45,381 December 31, 2018 Amortized Cost Basis Unrealized Gains Unrealized Loses Estimated Fair Value (In thousands) Level 1: Money market funds $ 126 $ — $ — $ 126 Level 2: U.S. government and agency securities 25,792 1 (4 ) 25,789 Commercial paper 147,606 — — 147,606 Corporate bonds 27,778 5 (17 ) 27,766 Certificates of deposit 1,420 — — 1,420 Total cash equivalents and short-term investments 202,722 6 (21 ) 202,707 Less: cash equivalents (152,577 ) — — (152,577 ) Total short-term investments $ 50,145 $ 6 $ (21 ) $ 50,130

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Schedule of Undiscounted Future Lease Payments under Operating Lease	The undiscounted future non-cancellable lease payments under the Company’s operating leases as of March 31, 2019 is as follows: Year ending December 31, (In thousands) 2019 (remaining 9 months) $ 2,864 2020 4,221 2021 4,683 2022 4,846 2023 5,016 Thereafter 28,837 Total undiscounted lease payments 50,467 Less: Present value adjustment (17,444 ) Less: Tenant improvement allowance (7,119 ) Total $ 25,904

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2019
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: March 31, 2019 December (In thousands) Accrued professional services $ 2,434 $ 2,291 Employee compensation 1,341 2,944 Accrued preclinical, clinical and process development costs 887 1,850 Other 370 1,699 Total accrued expenses and other current liabilities $ 5,032 $ 8,784

Equity Incentive Awards (Tables

Equity Incentive Awards (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Options Activity	The following table summarizes the Company’s option activity and related information: Number of Options (in thousands) Weighted- Average Exercise Price Balance at December 31, 2018 6,447 $ 5.83 Options granted 1,875 3.61 Options exercised (118 ) 1.37 Options cancelled (235 ) 4.21 Balance at March 31, 2019 7,969 $ 5.42 Exercisable as of March 31, 2019 3,760 $ 6.60
Summary of Restricted Stock Units Activity	The following table summarizes the Company’s RSUs activity and related information: Number of Units (in thousands) Weighted- Average Grant- Date Fair Value Outstanding at December 31, 2018 2,397 $ 9.23 Granted 240 3.50 Vested and released (397 ) 4.72 Forfeited (511 ) 4.81 Outstanding at March 31, 2019 1,729 $ 4.70
Stock-Based Compensation Expense	The following table presents, by operating expense, the Company’s stock-based compensation expense: Three Months Ended March 31, 2019 2018 (In thousands) Research and development $ 631 $ 2,378 General and administrative 1,131 1,051 Total stock-based compensation expense $ 1,762 $ 3,429

Organization and Basis of Pre_2

Organization and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Accumulated deficit	$ (335,032)	$ (320,543)

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Lease liability	$ 25,904
Right-to-use asset	22,592
Stock-based compensation	$ (1,762)	$ (3,429)
ASU No. 2016-2, Leases [Member]
Summary Of Significant Accounting Policies [Line Items]
Lease liability			$ 24,700
Right-to-use asset			23,100
Adjustment to accumulated deficit			$ 0
Estimated incremental borrowing rate	8.50%		8.50%
Restatement Adjustment [Member] | ASU No. 2016-2, Leases [Member]
Summary Of Significant Accounting Policies [Line Items]
Derecognized deferred rent			$ 1,500
Restatement Adjustment [Member] | ASU 2018-07 [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock-based compensation	$ 500

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Summary of Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 45,367	$ 50,145
Unrealized Gains	22	6
Unrealized Loses	(8)	(21)
Estimated Fair Value	45,381	50,130
Less: Cash Equivalents, Amortized Cost Basis	(139,585)	(152,577)
Less: Cash Equivalents, Unrealized Gains	0	0
Less: Cash Equivalents, Unrealized Loses	26	0
Less: Cash Equivalents, Estimated Fair Value	(139,559)	(152,577)
Money Market Funds [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	43	126
Estimated Fair Value	43	126
U.S. Government Agency Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	1,795	25,792
Unrealized Gains		1
Unrealized Loses		(4)
Estimated Fair Value	1,795	25,789
Commercial Paper [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	166,194	147,606
Unrealized Gains	3
Unrealized Loses	(34)
Estimated Fair Value	166,163	147,606
Certificates of Deposit [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis		1,420
Estimated Fair Value		1,420
Corporate Bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	16,920	27,778
Unrealized Gains	19	5
Unrealized Loses		(17)
Estimated Fair Value	16,939	27,766
Total Cash Equivalents and Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	184,952	202,722
Unrealized Gains	22	6
Unrealized Loses	(34)	(21)
Estimated Fair Value	$ 184,940	$ 202,707

Fair Value Measurements and F_4

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Available For Sale Securities [Abstract]
Liabilities transferred within Level 3	$ 0	$ 0
Marketable securities other-than-temporarily impaired	$ 0

Significant Agreements - Additi

Significant Agreements - Additional Information (Detail) - USD ($)	1 Months Ended		3 Months Ended
	Feb. 28, 2018	Aug. 31, 2016	Mar. 31, 2019	Mar. 31, 2018
License Agreement [Line Items]
Revenue recognized				$ 216,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Editas Medicine Inc [Member]
License Agreement [Line Items]
Initial payments received	$ 500,000
Collaboration, option and license agreement fee receivable per indication		$ 1,000,000
Range of tiered royalties receivable on net sales			between the mid-single digits and low teens
Revenue recognized			$ 0	$ 200,000
Type of Revenue [Extensible List]			us-gaap:LicenseAndServiceMember	us-gaap:LicenseAndServiceMember
Editas Medicine Inc [Member] | Topic 606 [Member]
License Agreement [Line Items]
Initial payments received	$ 500,000
Collaboration, option and license agreement fee receivable per indication		1,500,000
Non-refundable upfront payment received		1,000,000
Editas Medicine Inc [Member] | Additional Indication [Member]
License Agreement [Line Items]
Collaboration, option and license agreement fee receivable per indication		1,500,000
Editas Medicine Inc [Member] | Maximum [Member]
License Agreement [Line Items]
Potential milestone earnings		$ 15,500,000

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)ft²	Mar. 31, 2018USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2018USD ($)
Lessee Lease Description [Line Items]
Restricted cash	$ 999			$ 999
Right-of-use assets	22,592
Lease liability	25,904
Operating lease rent expense	$ 1,200	$ 300
ASU No. 2016-2, Leases [Member]
Lessee Lease Description [Line Items]
Right-of-use assets			$ 23,100
Lease liability			$ 24,700
Estimated incremental borrowing rate	8.50%		8.50%
Redwood City [Member]
Lessee Lease Description [Line Items]
Lease entered date	Jun. 30, 2018
Lease, area of land | ft²	81,000
Lease term	10 years
Lease renewal term	7 years
Lease description	The lease term is 10 years beginning September 2018 through February 2029 with two options to extend the lease term for a period of seven years each.
Lease, option to extend	true
Lease incentive allowance	$ 8,100
Restricted cash	$ 1,000
Menlo Park [Member]
Lessee Lease Description [Line Items]
Lease renewal term	4 years
Lease, option to extend	true
Lease expiration date	May 8, 2020
Letter of Credit [Member] | Redwood City [Member]
Lessee Lease Description [Line Items]
Security deposit	$ 1,000

Leases - Schedule of Undiscount

Leases - Schedule of Undiscounted Future Lease Payments under Operating Lease (Detail) $ in Thousands	Mar. 31, 2019USD ($)
Leases [Abstract]
2019 (remaining 9 months)	$ 2,864
2020	4,221
2021	4,683
2022	4,846
2023	5,016
Thereafter	28,837
Total undiscounted lease payments	50,467
Less: Present value adjustment	(17,444)
Less: Tenant improvement allowance	(7,119)
Total	$ 25,904

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accrued Expenses And Other Current Liabilities [Abstract]
Accrued professional services	$ 2,434	$ 2,291
Employee compensation	1,341	2,944
Accrued preclinical, clinical and process development costs	887	1,850
Other	370	1,699
Total accrued expenses and other current liabilities	$ 5,032	$ 8,784

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - Cornell University [Member] - Master Service Agreement [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Other Commitments [Line Items]
Total minimum lease payments		$ 13.3
Lease term		4 years
Estimated costs associated with the termination	$ 2

Equity Incentive Awards - Summa

Equity Incentive Awards - Summary of Stock Options Activity (Detail)	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Options Outstanding [Roll Forward]
Number of Options, Beginning Balance | shares	6,447,000
Number of Options, Options granted | shares	1,875,000
Number of Options, Options exercised | shares	(118,000)
Number of Options, Options cancelled | shares	(235,000)
Number of Options, Ending Balance | shares	7,969,000
Number of Options, Exercisable | shares	3,760,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Beginning Balance | $ / shares	$ 5.83
Weighted-Average Exercise Price, Options granted | $ / shares	3.61
Weighted-Average Exercise Price, Options exercised | $ / shares	1.37
Weighted-Average Exercise Price, Options cancelled | $ / shares	4.21
Weighted-Average Exercise Price, Ending Balance | $ / shares	5.42
Weighted-Average Exercise Price, Exercisable | $ / shares	$ 6.60

Equity Incentive Awards - Sum_2

Equity Incentive Awards - Summary of Restricted Stock Units Activity (Detail) - Restricted Stock Units [Member]	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Units, Beginning Balance | shares	2,397,000
Number of Units, Granted | shares	240,000
Number of Units, Vested and released | shares	(397,000)
Number of Units, Forfeited | shares	(511,000)
Number of Units, Ending Balance | shares	1,729,000
Weighted-Average Grant-Date Fair Value, Beginning Balance | $ / shares	$ 9.23
Weighted-Average Grant-Date Fair Value, Granted | $ / shares	3.50
Weighted-Average Grant-Date Fair Value, Vested and released | $ / shares	4.72
Weighted-Average Grant-Date Fair Value, Forfeited | $ / shares	4.81
Weighted-Average Grant-Date Fair Value, Ending Balance | $ / shares	$ 4.70

Equity Incentive Awards - Stock

Equity Incentive Awards - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,762	$ 3,429
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	631	2,378
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 1,131	$ 1,051

Net Loss per Share - Additional

Net Loss per Share - Additional Information (Detail) - shares shares in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	9.9	9.5