Adverum Biotechnologies (ADVM) 10-Q8 Nov 172017 Q3 Quarterly reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2017	Oct. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Trading Symbol	ADVM
Entity Registrant Name	Adverum Biotechnologies, Inc.
Entity Central Index Key	1,501,756
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		45,041,468

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 31,713	$ 222,170
Short-term investments	154,929
Receivable from collaborative partner		886
Prepaid expenses and other current assets	2,881	2,218
Total current assets	189,523	225,274
Property and equipment, net	3,347	4,169
Deposit and other non-current assets	340	140
Intangible assets	5,000	5,000
Total assets	198,210	234,583
Current liabilities:
Accounts payable	1,580	1,474
Restructuring liabilities		25
Accrued expenses and other current liabilities	6,062	6,451
Deferred rent, current portion	121	96
Deferred revenue, current portion	1,850	1,850
Total current liabilities	9,613	9,896
Long-term liabilities:
Deferred rent, net of current portion	257	352
Deferred revenue, net of current portion	5,711	7,099
Deferred tax liability	1,250	1,250
Other non-current liabilities	387	386
Total liabilities	17,218	18,983
Commitments and contingencies (Note 10)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 5,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value, 300,000,000 shares authorized at September 30, 2017 and December 31, 2016; 43,517,412 and 41,805,009 shares issued and outstanding at September 30, 2017 and December 31, 2016, respectively	5	4
Additional paid-in capital	420,811	413,518
Accumulated other comprehensive loss	(551)	(7)
Accumulated deficit	(239,273)	(197,915)
Total stockholders’ equity	180,992	215,600
Total liabilities and stockholders’ equity	$ 198,210	$ 234,583

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	43,517,412	41,805,009
Common stock, shares outstanding	43,517,412	41,805,009

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Collaboration revenue	$ 463	$ 395	$ 1,388	$ 967
Operating expenses:
Research and development	10,272	8,362	27,825	23,772
General and administrative	4,762	6,146	16,815	19,578
Goodwill impairment charge		394		49,514
Total operating expenses	15,034	14,902	44,640	92,864
Operating loss	(14,571)	(14,507)	(43,252)	(91,897)
Other income, net
Other income, net	742	206	1,894	544
Total other income, net	742	206	1,894	544
Net loss	(13,829)	(14,301)	(41,358)	(91,353)
Other comprehensive loss:
Net unrealized (loss) gain on marketable securities	35	(6)	(102)
Foreign currency translation adjustment	(183)	(23)	(442)	(13)
Comprehensive loss	$ (13,977)	$ (14,330)	$ (41,902)	$ (91,366)
Net loss per share attributable to common stockholders-basic and diluted	$ (0.32)	$ (0.35)	$ (0.97)	$ (2.66)
Weighted-average common shares outstanding-basic and diluted	43,381	41,416	42,849	34,382

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (41,358)	$ (91,353)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,592	1,116
Stock-based compensation expense	6,839	9,852
Goodwill impairment charge		49,514
Amortization of premium and accrued interest on marketable securities	419
Non-cash research and development expense	60	24
Changes in operating assets and liabilities:
Receivable from collaborative partner	886	(532)
Prepaid expenses and other current assets	(136)	(1,317)
Accounts payable	166	817
Accrued expenses and other current liabilities	(208)	(46)
Restructuring liabilities	(25)	(988)
Deferred revenue	(1,388)	2,936
Deferred rent	(70)	(47)
Net cash used in operating activities	(33,223)	(30,024)
Cash flows from investing activities:
Purchases of investments	(201,038)
Maturities of investments	45,061	37,738
Purchases of property and equipment	(918)	(1,488)
Cash acquired in business acquisition		3,449
Net cash provided by (used in) investing activities	(156,895)	39,699
Cash flows from financing activities:
Proceeds from issuance of common stock pursuant to option exercises	312	633
Taxes paid related to net share settlement of restricted stock units	(292)	(493)
Proceeds from employee stock purchase plan	83	113
Proceeds from financing arrangement		100
Net cash provided by financing activities	103	353
Effect of foreign currency exchange rate on cash and cash equivalents	(442)	(105)
Net increase (decrease) in cash and cash equivalents	(190,457)	9,923
Cash and cash equivalents at beginning of period	222,170	221,348
Cash and cash equivalents at end of period	31,713	231,271
Supplemental schedule of noncash investing and financing information
Unpaid deferred offering costs in accounts payable and accrued expenses	200
Issuance of common stock and exchange of stock options for business combination		64,845
Fixed assets in accounts payable, accrued expenses and other current liabilities	$ 148	$ 771

Organization and Basis of Prese

Organization and Basis of Presentation	9 Months Ended
Organization and Basis of Presentation	Sep. 30, 2017
Accounting Policies [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Adverum Biotechnologies, Inc. (the “Company”, “we” or “us”) was incorporated in Delaware on July 17, 2006 as Avalanche Biotechnologies, Inc. and changed its name to Adverum Biotechnologies, Inc. on May 11, 2016. The Company is headquartered in Menlo Park, California. The Company is a gene therapy company targeting unmet medical needs in serious rare and ocular diseases. Since the Company’s inception, it has devoted its efforts principally to performing research and development activities, including conducting preclinical studies and, early clinical trials, filing patent applications, obtaining regulatory agreements, 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 $239.3 million as of September 30, 2017. 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 its operations through the end of 2019. On May 11, 2016, the Company completed the acquisition of all the outstanding shares of Annapurna Therapeutics SAS, a French simplified joint stock company (“Annapurna”). As a result, Annapurna is now a wholly owned subsidiary of the Company. Upon completion of the acquisition of Annapurna, the Company changed its name to “Adverum Biotechnologies, Inc.”. The Company’s shares of common stock listed on The NASDAQ Global Market, previously trading through the close of business on Wednesday, May 11, 2016 under the ticker symbol “AAVL,” commenced trading on The NASDAQ Global Market under the ticker symbol “ADVM” on May 12, 2016. The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“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 have been 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 and nine months ended September 30, 2017, 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, 2016 has been derived from the Company’s 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, 2016 filed with the SEC.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies The accounting policies followed in the preparation of the interim condensed consolidated financial statements are consistent in all material respects with those presented in Note 2 to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016. Recently-Issued and Not Yet Adopted Accounting Pronouncements — In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in ASC 605 , Revenue Recognition . This ASU is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than required under existing U.S. GAAP including identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 is required to be adopted, using either of two methods: (i) retrospective to each prior reporting period presented with the option to elect certain practical expedients as defined within ASU 2014-09; or (ii) retrospective with the cumulative effect of initially applying ASU 2014-09 recognized at the date of initial application and providing certain additional disclosures. In July 2015, the FASB voted to approve a one-year deferral of the effective date to December 15, 2017 for interim and annual reporting periods beginning after that date and permitted early adoption of the standard, but not before the original effective date of December 15, 2016 . The FASB issued supplemental adoption guidance and clarification to ASU 2014-09 in March 2016, April 2016, May 2016 and December 2016 within ASU 2016-08 Revenue From Contracts With Customers: Principal vs. Agent Considerations , ASU 2016-10 Revenue From Contracts with Customers: Identifying Performance Obligations and Licensing , ASU 2016-12 Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients and ASU 2016-20 Technical Corrections and Improvement to Topic 606 – Revenue from Contracts with Customers , respectively. The ASU will be effective for the Company in the first quarter of 2018. The Company has commenced its implementation activities related to the adoption of ASU 2014-09 and is in the process of applying the five-step model of the new standard to its various revenue related arrangements. The Company has completed step 1 (Identify the contract(s) with a customer) and concluded that its collaboration agreements with Regeneron Pharmaceuticals, Inc. and Editas Medicine, Inc. will be impacted by the adoption of the new revenue standards. The Company is in the process of completing step 2 (Identify the performance obligations in the contract) and has not yet reached a conclusion on whether the distinct criteria evaluated under ASC 605-25 for each performance obligation would result in a similar conclusion under the new revenue standards. Preliminarily, the Company intends to adopt the new standard in the first quarter of 2018 using the retrospective approach noted in (ii) above. The Company is currently evaluating the impact of the adoption of this standard on its condensed consolidated financial statements and related disclosures. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities In February 2016, the FASB issued ASU No. 2016-2, Leases In June 2016, the FASB issued ASU No. 2016-13 Measurement of Credit Losses on Financial Instruments In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash In May 2017, the FASB issued ASU No. 2017-09, Scope of Modification Accounting The Company has reviewed other recent accounting pronouncements and concluded they are either not applicable to the business or no material effect is expected on the consolidated financial statements as a result of future adoption.

Acquisition of Annapurna

Acquisition of Annapurna	9 Months Ended
Acquisition of Annapurna	Sep. 30, 2017
Business Combinations [Abstract]
Acquisition of Annapurna	3. Acquisition of Annapurna (a) Purchase Price Allocation On May 11, 2016, the Company completed the acquisition of all outstanding equity interests of Annapurna. Annapurna was a privately held French limited liability company with two wholly-owned subsidiaries, Annapurna, Inc. in the U.S. and Annapurna Therapeutics Limited in Ireland. Annapurna is a biopharmaceutical company focused on discovering and developing novel gene therapy products for people living with severe rare diseases. The primary reasons for the acquisition were to expand the technology platforms within the Company’s research and development portfolio and to apply the Company’s resources and expertise in gene vectors development to advance Annapurna’s programs through development and clinical trials. Annapurna’s results of operations and fair value of assets acquired and liabilities assumed are included in the Company’s condensed consolidated financial statements from the date of acquisition. The purchase price consideration was $64.8 million, which was based on the Company’s common stock closing price on NASDAQ on the acquisition closing date of $4.14 per share. A total of 14,087,246 shares of the Company’s common stock were issued to shareholders of Annapurna in exchange for all common and preferred stock outstanding at the closing date. Annapurna stockholders did not receive any fractional shares of the Company’s common stock in connection with the acquisition. Instead of receiving any fractional shares, each Annapurna stockholder was paid an amount in cash (without interest) equal to such fraction amount multiplied by the average 10 business days sale price of the Company’s common stock on NASDAQ from the acquisition date. Annapurna Series O preferred shares issued to founders were canceled prior to the acquisition date and were not included in the purchase price consideration. Vesting of certain of Annapurna’s options and unvested common stock shares was accelerated at the closing date. The fair value of awards related to the accelerated vesting of options and shares of $0.9 million was excluded from the purchase price consideration and included in the Company’s operating expenses post acquisition. A portion of the purchase price was attributed to the exchange of Annapurna’s options and other rights to purchase capital stock outstanding at the acquisition closing date for corresponding common stock options of the Company at an exchange ratio of 9.54655. The Company reserved 3,673,940 shares for the future exercise of the Company’s stock options. The total fair value of assumed Annapurna stock options and stock-based awards was estimated at $14.7 million on the acquisition date, using the Black-Scholes pricing model, assuming no dividends, expected volatilities of 80% and 89%, risk-free interest rates of 1.4% and 1.1%, and expected lives of six and ten years for employees and non-employees awards, respectively. Of the total fair value, $7.4 million was attributed as pre-combination service and included as part of the total purchase price consideration. The post-combination attribution of $7.2 million was recognized as compensation expense over the remaining requisite service period. The Company included $0.9 million in stock-based compensation expense related to the vesting of exchanged stock options and day-one post combination compensation expenses related to the accelerated vesting of options and shares in its condensed consolidated statement of operations during the second quarter of 2016. Total purchase price consideration was estimated as follows (in thousands): Fair value of common shares issued $ 58,321 Fair value of the Company's common share options exchanged for Annapurna stock options and other awards attributable to pre-combination services 7,422 Less: value of common stock and options accelerated vesting at the closing date (898 ) Total purchase price consideration $ 64,845 The transaction was accounted for using the acquisition method based on ASC 805, Business Combinations, The allocation of total purchase price consideration is as follows (in thousands): Cash $ 3,449 Prepaid expenses and other assets 865 Property and equipment 185 Acquired intangible assets 16,200 Goodwill 49,514 Accounts payable (1,118 ) Accrued liabilities (1,848 ) Other noncurrent liabilities (377 ) Deferred tax liabilities (2,025 ) Total purchase price allocation $ 64,845 The identifiable intangible assets acquired consist of IPR&D assets related to products in development, as summarized in the table below (in thousands): IPR&D - Alpha-1 antitrypsin deficiency $ 11,700 IPR&D - Hereditary angioedema 4,500 Total acquired intangible assets $ 16,200 The fair value of each IPR&D asset is estimated using the income approach and calculated using cash flow projections adjusted for inherent risks regarding regulatory approval, promotion, and distribution, discounted at a rate of approximately 11.0%. Goodwill, which represents the excess of the purchase price over the fair values assigned to the net assets acquired, was estimated in the amount of $49.5 million The following pro forma financial information combines the results of operations of Adverum and Annapurna as though the businesses had been combined as of the beginning of fiscal year 2016. The pro forma financial information is presented for informational purposes only, and is not indicative of the results of operations that would have been achieved in the current or any future periods. The following table presents the unaudited pro forma results for the nine months ended September 30, 2016 (in thousands, except per share data). Nine Months Ended September 30, 2016 Pro forma information Collaboration revenue $ 967 Net loss $ (95,167 ) Basic and diluted loss per share $ (2.31 ) Weighted-average common shares outstanding - basic and diluted 41,118 Pro-forma adjustments included the following: • Actual acquisition-related transaction costs of $2.5 million were excluded from pro forma results above as these expenses were incurred prior to the closing of the acquisition. • Stock-based compensation expense of $0.9 million related to accelerated vesting associated with the acquisition was excluded from the pro forma results above. • Stock-based compensation expense related to options granted to executives upon the acquisition closing of $0.2 million was included in pro forma results above. • Interest expense of $1.0 million related to convertible notes and changes in fair value of preferred stock warrants was excluded from the pro-forma results above, as the convertible notes and warrants were settled prior to the acquisition closing. • $0.4 million of bonuses paid in connection with the closing of the acquisition in May 2016 were excluded from the pro forma results above. The unaudited condensed pro forma information does not include any anticipated synergies that may be achievable subsequent to the date of acquisition.

Cash Equivalents and Short-Term

Cash Equivalents and Short-Term Investments	9 Months Ended
Cash Equivalents and Short-Term Investments	Sep. 30, 2017
Cash And Cash Equivalents [Abstract]
Cash Equivalents and Short-Term Investments	4. Cash Equivalents and Short-Term Investments The following is a summary of the Company’s available-for-sale securities as of September 30, 2017 (in thousands): September 30, 2017 Amortized Cost Basis Unrealized Losses Unrealized Gains Estimated Fair Value Money market funds $ 1,763 $ — $ — $ 1,763 Certificates of deposit 9,978 — — 9,978 Commercial paper 32,295 — — 32,295 U.S. government agency 72,756 (70 ) 1 72,687 Corporate bonds 63,105 (33 ) — 63,072 Total cash equivalents and short-term investments 179,897 (103 ) 1 179,795 Less: cash equivalents (24,866 ) — — (24,866 ) Total short-term investments $ 155,031 $ (103 ) $ 1 $ 154,929 The following table is a summary of the cost and estimated fair value of the Company’s available-for-sale securities based on stated effective maturities as of September 30, 2017 (in thousands): September 30, 2017 Amortized Cost Basis Estimated Fair Value Mature within one year $ 151,769 $ 151,725 Mature after one year to three years 28,128 28,070 Total cash equivalents and short-term investments $ 179,897 $ 179,795 As of December 31, 2016, all of the Company’s investments were held in money market funds and were treated as cash equivalents. Management determined that the gross unrealized losses of $0.1 million on the Company’s available-for-sale securities as of September 30, 2017 were temporary in nature. Therefore, none of the Company’s available-for-sale securities were other-than-temporarily impaired as of September 30, 2017.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements and Fair Value of Financial Instruments	5. Fair Value Measurements and Fair Value of Financial Instruments The authoritative guidance on fair value measurements establishes a three-tier fair value hierarchy for disclosure of fair value measurements 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. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. The fair value of Level 1 securities are 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 bonds and certificate 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. Level 3 liabilities that were measured at estimated fair value on a recurring basis consist of a financing arrangement entered into during the year ended December 31, 2016. During the periods presented, the Company has not changed the manner in which it values liabilities that are measured at estimated fair value using Level 3 inputs. There were no transfers within the hierarchy during the three and nine months ended September 30, 2017. The following table summarizes, for assets recorded at fair value on a recurring basis, the respective fair value and the classification by level of input within the fair value hierarchy as described above (in thousands): Quoted Prices Significant Other Significant Total In Active Markets Observable Inputs Unobservable Inputs Carrying Value (Level 1) (Level 2) (Level 3) September 30, 2017 Assets: Money market funds $ 1,763 $ 1,763 $ — $ — Certificates of deposit 9,978 — 9,978 — Commercial paper 32,295 — 32,295 — U.S. government agency 72,687 — 72,687 — Corporate bonds 63,072 — 63,072 — Total cash equivalents and short term investments $ 179,795 $ 1,763 $ 178,032 $ — Other noncurrent liability: Financing arrangement $ 74 $ — $ — $ 74 December 31, 2016 Assets: Money market funds $ 215,916 $ 215,916 $ — $ — Total cash equivalents $ 215,916 $ 215,916 $ — $ — Other noncurrent liability: Financing arrangement $ 74 $ — $ — $ 74 Non-financial assets such as intangible assets, property, plant, and equipment are evaluated for impairment and adjusted to their fair value using Level 3 inputs, only when impairment is recognized. Fair values are considered Level 3 when management makes significant assumptions in developing a discounted cash flow model based upon a number of considerations including projections of revenues, earnings and a discount rate.

Significant Agreements

Significant Agreements	9 Months Ended
Significant Agreements	Sep. 30, 2017
Research And Development [Abstract]
Significant Agreements	6. Significant Agreements University of California — In May 2010, the Company entered into a license agreement with the Regents of University of California (“Regents”), as amended in September 2013. Under the license agreement, the Regents have granted to the Company an exclusive (even as to the Regents) license, with the right to grant sublicenses, under the Regents’ undivided interest in patent rights covering a method of using recombinant gene delivery vectors for treating or preventing diseases of the eye, to develop, make, have made, use offer for sale, import, export and sell products covered by such patent rights in all fields of use in the United States. The licensed patent rights are jointly owned by the Regents and Chiron Corporation, but the Company’s license extends only to the Regents’ interest in such patent rights. Under the license agreement, the Company is required to diligently proceed with the development, manufacture and sale of licensed products, which includes obligations to meet certain development-stage milestones within specified periods of time, and to market the resulting licensed products in sufficient quantity to meet market demand. The Company has the right and option to extend the date by which it must meet any milestone by six-months up to two times by paying an extension fee for each such extension. The Company has paid the Regents a license fee of $100,000. The Company is also obligated to make milestone payments totaling up to $900,000 upon reaching certain stages of development of the licensed products for one indication, and totaling up to $500,000 for each subsequent indication for which licensed products are developed, for up to a maximum of two additional indications. Through September 30, 2017, none of these goals had been achieved, and no milestones were payable. The Company must pay the Regents a low single-digit royalty on net sales of the licensed products by the Company or its sublicensees, subject to a minimum annual royalty payment of $50,000 beginning in the calendar year after the first commercial sale of a licensed product, until the patent rights upon which such royalties are based expire or are held invalid, which is currently expected to occur in 2020, subject to any potential patent term extensions. The Company is obligated to reimburse the Regents for expenses associated with the prosecution and maintenance of the licensed patents. Finally, the Company is obligated to pay the Regents a mid-teen percentage of non-royalty licensing revenue that the Company receives from sublicensees. The Company’s license agreement with the Regents continues in effect for the life of the last-to-expire patent. The Company may terminate this agreement without cause at any time upon 30 days’ prior written notice to the Regents. The Regents may terminate this agreement for a breach by the Company that remains uncured for 60 days, if the Company becomes insolvent, if the Company directly or through a third party files a claim that a licensed patent right is invalid or unenforceable or if the Company fails to meet or extend the date for meeting certain diligence milestones. Regeneron— In May 2014, the Company entered into a research collaboration and license agreement with Regeneron Pharmaceuticals, Inc. (“Regeneron”) to discover, develop and commercialize novel gene therapy products for the treatment of ophthalmologic diseases. The collaboration covers up to eight distinct therapeutic targets (“collaboration targets”). The Company and Regeneron collaborate during the initial research period of three years that can be extended by Regeneron for up to an additional five years. During the research period, Regeneron has the option to obtain an exclusive worldwide license for a collaboration target’s further development by giving written notice to the Company and paying $2.0 million per target. If Regeneron exercises its option, it will be responsible for all further development and commercialization of the target. The Company is then eligible to receive contingent payments of up to $80.0 million upon achievement of certain development and regulatory milestones for product candidates directed toward each collaboration target, for a combined total of up to $640.0 million in potential milestone payments for product candidates directed toward all eight collaboration targets, plus a royalty in the low- to mid-single-digits on worldwide net sales of collaboration products. For any two collaboration targets, the Company has an option to share up to 35% of the worldwide product candidate development costs and profits. If the Company exercises this option, the Company will not be eligible for milestone and royalty payments as discussed above but rather the Company will share development costs and profits with Regeneron. The agreement will expire with respect to each collaboration target upon the earlier of the (a) expiration of the research term if the option right has not been triggered by the end of the research term or (b) expiration of the option right if the option right has not been exercised by Regeneron. If the option right has been exercised, the agreement in connection with each collaboration target will expire upon expiration of all payment obligations by Regeneron. In addition, the agreement, or Regeneron’s rights to any target development under the agreement, may terminate early under the following situations: • Regeneron may terminate the agreement for convenience at any time on a target by target basis or in totality upon a 30-day notice. • Each party can terminate the agreement if another party commits a material breach or material default in performance of its obligations and such breach or default is not cured within 60 days. • The agreement is automatically terminated upon initiation of any bankruptcy proceedings, reorganization or dissolution of either party. • The Company can terminate the agreement upon 30-day notice if Regeneron challenges the validity, scope or enforceability of any Company patent. On February 23, 2017, Regeneron notified Adverum that, pursuant to the terms of the research collaboration and license agreement, it extended the research term of the collaboration for an additional three years, through May 1, 2020. Under the Company’s research, collaboration and license agreement with Regeneron, the Company is required to have a mutually agreed-on research plan with Regeneron in order to invoice Regeneron for services performed. The Company does not currently have a research plan in place, and, consequently, we are not currently receiving any reimbursements from Regeneron. Editas— In August 2016, the Company entered into a collaboration, option and license agreement with Editas Medicine, Inc. (“Editas”) pursuant to which the Company and Editas will collaborate on certain studies using adeno-associated viral (“AAV”) vectors in connection with Editas’ genome editing technology and the Company will grant to Editas an exclusive option to obtain certain exclusive rights to use the Company’s proprietary vectors in up to five ophthalmic indications (“Indications”). The Company received a $1.0 million non-refundable upfront payment during the year ended December 31, 2016, with $0.5 million of such payment to be credited against Editas’ obligation to fund research and development costs. Under the terms of the agreement, both the Company and Editas will be subject to exclusivity obligations. Under the terms of the agreement, Editas may exercise the option, with respect to a designated initial Indication, until the first anniversary of the effective date of the agreement. With respect to the four other Indications, Editas may exercise the option until the third anniversary of the effective date, provided that the option will expire on the second anniversary of the effective date if Editas has not exercised the option with respect to the initial Indication or any other Indication by such date. Upon each 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. Cornell University— The Company had been a party to a master service agreement (“MSA”) with Cornell University (“Cornell”) originally established in August 2014 and amended in December 2015. 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 its termination of the MSA, the Company recorded $2.0 million of estimated costs associated with the termination of the MSA as of September 30, 2017. This MSA included services relating to the Company’s gene therapy programs ADVM-043, ADVM-053 and severe allergy. The Company’s three licensing agreements with Cornell for these programs remain unchanged. The decision to terminate the MSA was due to Cornell’s failure to deliver therapeutic material of ADVM-043 suitable for use in human patients. As a result of this decision, the Company has contracted with large-scale contract manufacturing organizations that comply with current good manufacturing practice industry standards and can produce product quantities for both the Company’s planned clinical trials and potential commercial supply. This is part of the Company’s upgrade of the manufacturing process for ADVM-043, implementing its proprietary, highly-scalable baculovirus-based production system, in advance of the Company’s plans to begin patient enrollment in a Phase 1/2 clinical trial in the fourth quarter of 2017. Under the MSA, Cornell provided assistance in regulatory affairs, overall project management, and parameter development. The MSA, as amended, provided for Annapurna to pay Cornell $13.3 million ratably over 4 years for these services as services were performed. In December 2015, Annapurna entered into three licensing agreements with Cornell, pursuant to which Annapurna will advance its gene therapy programs ADVM-043, ADVM-053, and severe allergy, which originally were initiated at the Department of Genetic Medicine at Weill Cornell. A1AT Deficiency License Agreement : Under this agreement, Annapurna holds an exclusive license to certain technology related to alpha-1 antitrypsin (A1AT) deficiency and rights to an Investigational New Drug (IND) application to initiate clinical studies of gene therapy for A1AT. HAE License Agreement : Under this agreement, Annapurna holds an exclusive license to certain technology related to hereditary angioedema (HAE) and a non-exclusive license to certain other intellectual property related to the HAE program. Allergy License Agreement : Under this agreement, Annapurna holds an exclusive license to certain patents related to allergens and a non-exclusive license to certain other technology related to allergens. Across these three license agreements, Cornell is entitled to receive aggregate annual maintenance fees ranging from $30,000 to $300,000 per year, up to $16.0 million in aggregate milestone payments and royalties on sales in the low single-digits, subject to adjustments and minimum thresholds. For the nine months ended September 30, 2017, annual maintenance fees were immaterial. No milestone payments were probable to achieve and none were recorded as of September 30, 2017. Annapurna may terminate any of these license agreements for convenience upon ninety days written notice. Cornell may terminate any of the license agreements for material breach if such breach is not cured within a specified number of days. Cornell may also terminate the HAE License Agreement and/or the Allergy License Agreement if Annapurna commences any action and files a written claim asserting that any portion of the licensed patent rights is invalid or unenforceable. Ronald Crystal, M.D., Chairman, Department of Genetic Medicine, the Bruce Webster Professor of Internal Medicine and a Professor of Genetic Medicine and of Medicine at Weill Cornell Medicine, served as a consultant to Annapurna since inception and continues to provide services to the Company for the annual compensation of up to $0.3 million. REGENXBIO— A1AT Deficiency/Allergy License Agreement : In October 2015, Annapurna entered into an exclusive worldwide license to certain intellectual property in order to make, have made, use, import, sell and offer for sale certain licensed products for the treatment of A1AT deficiency. Also, under this agreement, Annapurna has an option to be granted an exclusive worldwide license to certain intellectual property related to the treatment of severe allergies, which option expired in October 2016. Under this license agreement, REGENXBIO, Inc. (“REGENXBIO”) is eligible to receive annual maintenance fees, up to approximately $20.0 million in combined milestone payments and royalties in the mid-to-high single digits. Unless earlier terminated, this license agreement will be in effect on a country-by-country, licensed product-by-licensed product basis until the expiration, lapse, abandonment, or invalidation of the last claim of the licensed intellectual property to expire, lapse, or become abandoned or unenforceable for the applicable licensed product. Annapurna may terminate this license agreement for any reason upon six months’ prior written notice. REGENXBIO may terminate this license agreement if Annapurna is a specified number of days late in paying money due under the license agreement, or if Annapurna, its affiliates, or any sublicensees become insolvent or, effective immediately, if they commence any action against REGENEXBIO or its licensors to declare or render any claim of the licensed patent rights invalid or unenforceable. Either party may terminate this license agreement for material breach if such breach is not cured within a specified number of days. In April 2017, the Company notified REGENXBIO that Annapurna exercised its right to terminate the license agreement for any reason upon six months’ prior written notice. The termination is effective in October 2017. Friedreich’s Ataxia License Agreement : In April 2014, Annapurna entered into an exclusive worldwide license to certain intellectual property related to the FA program to make, have made, use, import, sell and offer for sale licensed products using AAVrh10 for FA where the vector is administered by any route except directly to the central nervous system (“FA Systemic”). Under the terms of this license agreement, Annapurna also had an option to obtain a non-exclusive worldwide license to make, have made, use, import, sell and offer for sale licensed products using a single vector for each of FA where the vector is administered directly to the central nervous system (“FA CNS”) and FA Systemic. Under this license agreement, REGENXBIO is eligible to receive annual maintenance fees, up to $13.85 million in combined milestone fees and royalties in the mid-to-high single digits. The option to obtain a non-exclusive license to FA Systemic expired in April 2015 and the option to obtain a non-exclusive license for FA CNS expired in April 2016. Annapurna is obligated to achieve certain development milestones with respect to each licensed disease indication, including the filing of an IND application for each licensed disease indication within a specified time period, which Annapurna may extend for additional time for a specified number of extensions upon the payment of a fee. Unless earlier terminated, this license agreement expires upon the expiration, lapse, abandonment, or invalidation of the last claim of the licensed intellectual property to expire, lapse, or become abandoned or unenforceable in all the countries of the world. Annapurna Therapeutics Limited may terminate this license agreement upon six months’ prior written notice. REGENXBIO may terminate this license agreement if Annapurna Therapeutics Limited is a specified number of days late in paying money due under the license agreement, or if Annapurna Therapeutics Limited, its affiliates, or any sublicensees become insolvent or, effective immediately, if they commence any action against REGENXBIO or its licensors to declare or render any claim of the licensed patent rights invalid or unenforceable. Either party may terminate this license agreement for material breach if such breach is not cured within a specified number of days. During the nine months ended September 30, 2017, expenses associated with the REGENXBIO agreements were $0.2 million. Inserm Transfert— In July 2014, Annapurna entered into an agreement with Inserm Transfert (Inserm) whereby Annapurna holds an exclusive license to certain patents to develop, make, have made, use, import, offer for sale and sell or otherwise distribute products for the treatment of FA and a non-exclusive license to certain other intellectual property related to the FA program. The agreement was amended in October 2015 to increase the scope of the intellectual property under the licenses. Under this agreement, Inserm is entitled to receive certain de minimis license payments, certain development milestone payments of up to approximately €2.0 million in the aggregate and royalties on sales in the low single-digits, subject to adjustments. No milestone payments were probable to achieve and none were recorded as of September 30, 2017. Unless earlier terminated, this agreement will be in effect on a country-by-country, licensed product-by-licensed product basis the last claim of the licensed intellectual property Inserm may terminate this license agreement if Annapurna becomes the subject of a voluntary or involuntary petition in bankruptcy or fails to meet development milestones and such failure is not cured within a specified number of days. Inserm may also terminate the license granted to Annapurna in a given country if Annapurna (i) before regulatory approval of a product in any country, has ceased conducting any development of products in all countries for 12 consecutive months or (ii) after regulatory approval of a product in a given country, has ceased marketing such product in such country for 12 consecutive months. Pursuant to the terms of the agreement with Inserm, the Company’s acquisition of Annapurna triggered a one-time payment to Inserm of €250,000, which was recorded to research and development expense in the Company’s consolidated statement of operations during the year ended December 31, 2016. During the nine months ended September 30, 2017, expenses associated with the Inserm Transfert agreements were $0.3 million.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
Property and Equipment, Net	Sep. 30, 2017
Property Plant And Equipment [Abstract]
Property and Equipment, Net	7. Property and Equipment, Net Property and equipment, net consists of the following (in thousands): September 30, 2017 December Computer equipment and software $ 480 $ 300 Laboratory equipment 4,933 4,285 Furniture and fixtures 552 552 Leasehold improvements 1,541 1,522 Construction in progress 16 104 Total property and equipment 7,522 6,763 Less accumulated depreciation and amortization (4,175 ) (2,594 ) Property and equipment, net $ 3,347 $ 4,169 Depreciation and amortization expense related to property and equipment for the three months ended September 30, 2017 and 2016 was $0.5 million and $0.4 million, respectively. Depreciation and amortization expense related to property and equipment for the nine months ended September 30, 2017 and 2016 was $1.6 million and $1.1 million, respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
Accrued Expenses and Other Current Liabilities	Sep. 30, 2017
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	8. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following (in thousands): September 30, 2017 December Employees’ compensation expenses $ 1,628 $ 2,570 Accrued preclinical costs 805 1,683 Accrued clinical and process development costs 669 1,142 Accrued professional services 725 894 Accrued contract settlement 2,000 — Other 235 162 Total accrued expenses and other current liabilities $ 6,062 $ 6,451

Other Non-Current Liabilities

Other Non-Current Liabilities	9 Months Ended
Other Non-Current Liabilities	Sep. 30, 2017
Other Liabilities Disclosure [Abstract]
Other Non-Current Liabilities	9. Other Non-current Liabilities In August 2015, Banque Publique d’Investissement (“BPI France”) granted Annapurna a €0.5 million interest free conditional advance. Payments are scheduled in equal quarterly amounts of €25,000 from September 30, 2017 to June 30, 2022. This payment schedule will be modified if the Company receives revenue from license or product sales before advances are paid in full. The Company calculated 7% imputed interest expense on these advances that was recorded as a discount at the issuance date. The discount is amortized as an interest expense over the life of the advances. As of September 30, 2017, the carrying value of this interest-free conditional advance, which approximates its fair value, was $0.4 million, of which $0.3 million is recorded within other non-current liabilities and $0.1 million within accrued expenses and other current liabilities in the Company’s condensed consolidated balance sheets. Interest expense for this interest-free conditional advance was immaterial for the three and nine months ended September 30, 2017. In July 2016, the Company entered into a sponsored research agreement with The Alpha-1 Project, Inc. (“TAP”) to fund the Company’s A1AT research activities of up to $0.3 million, of which $0.1 million was received during the year ended December 31, 2016 (“TAP financing arrangement”). The Company may repay up to 4.5 times the received amount if and when certain product approval and sales milestones are achieved. As of September 30, 2017, the estimated fair value of the TAP financing arrangement was $0.1 million, which was recorded within other noncurrent liabilities in the Company’s condensed consolidated balance sheets.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Facility Lease Agreement The Company leases its office building under a non-cancelable lease agreement, 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 records rent expense on a straight-line basis over the term of the lease. Rent expense recognized under the operating lease, including additional rent charges for utilities, parking, maintenance, and real estate taxes was $1.4 million and $1.3 million for the nine months ended September 30, 2017 and 2016, respectively. Collaborations and License Agreements The Company is a party to various agreements, principally relating to licensed technology that requires payment of annual maintenance fees and future payments relating to milestones or royalties on future sales of specified products. The Company expenses the annual maintenance fees on a straight-line basis and accrues the aggregate balances until invoiced or paid. Through September 30, 2017, none of the goals had been achieved under the license agreements and no cash milestones were accrued or payable. Since the achievement of these milestones is not fixed and determinable, such commitments have not been included in the Company’s condensed consolidated balance sheets. Guarantees and Indemnifications In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for indemnification for certain liabilities. The exposure under these agreements is unknown because it involves claims that may be made against the Company in the future but have not yet been made. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. The Company also has indemnification obligations to its directors and executive officers for specified events or occurrences, subject to some limits, while they are serving at the Company’s request in such capacities. There have been no claims to date and the Company believes the fair value of these indemnification agreements is minimal. Accordingly, the Company has not recorded any liabilities for these agreements as of September 30, 2017. 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. In July 2015, three securities class action lawsuits were filed against the Company and certain of its officers in the United States District Court for the Northern District of California, each on behalf of a purported class of persons and entities who purchased or otherwise acquired the Company’s publicly traded securities between July 31, 2014 and June 15, 2015. The lawsuits assert claims under the Securities Exchange Act of 1934, as amended (the “Exchange Act”) and Securities Act of 1933, as amended (the “Securities Act”) and allege that the defendants made materially false and misleading statements and omitted allegedly material information related to, among other things, the Phase 2a clinical trial for AVA-101, a product candidate which is no longer being developed, and the prospects of AVA-101. The complaints seek unspecified damages, attorneys’ fees and other costs. In December 2015, a putative securities class action lawsuit was filed against the Company, the Company’s board of directors, underwriters of the Company’s January 13, 2015, follow-on public stock offering, and two of the Company’s institutional stockholders, in the Superior Court of the State of California for the County of San Mateo. The complaint alleges that, in connection with the Company’s follow-on stock offering, the defendants violated the Securities Act by allegedly making materially false and misleading statements and by allegedly omitting material information related to the Phase 2a clinical trial for AVA-101 and the prospects of AVA-101. The complaint seeks unspecified compensatory and rescissory damages, attorneys’ fees and other costs. The plaintiff has dismissed the two institutional stockholder defendants. On March 16, 2017, the Company reached an agreement to settle the asserted actions. The proposed aggregate amount of the settlement is $13.0 million, of which $1.0 million would be contributed by the Company to cover its indemnification obligations to the underwriters, and the remainder would be contributed by the Company’s insurers. The settlement is subject to definitive documentation, shareholder notice and court approval. The Company and the defendants have denied and continue to deny each and all of the claims alleged in the actions, and the settlement does not assign or reflect any admission of fault, wrongdoing or liability as to any defendant. If final court approval is not obtained with respect to the settlement or the settlement otherwise does not become effective and litigation resumes, adverse outcomes in the actions could result in substantial damages. The Company recorded $1.0 million as general and administrative expense during the three months ended March 31, 2017, when the amount and time of settlement became estimable and probable.

Stock Plans

Stock Plans	9 Months Ended
Stock Plans	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock Plans	11. Stock Plans The Company’s 2014 Equity Incentive Award Plan (“2014 Plan”) permits the issuance of stock options (“options”), restricted stock units (RSUs) and other types of awards to employees, directors, and consultants. As of September 30, 2017, a total of 14,834,856 shares of common stock were authorized for issuance and 1,631,908 shares were available for future grants under the 2014 Plan. In July 2014, the Company’s board of directors and its stockholders approved the establishment of the 2014 Employee Stock Purchase Plan (“2014 ESPP”). During the nine months ended September 30, 2017 and 2016, 35,954 shares and 52,002 shares, respectively, were issued under the 2014 ESPP. A total of 1,000,783 shares of common stock were reserved for issuance under the 2014 ESPP and were available for issuance under the 2014 ESPP as of September 30, 2017. The following table summarizes option activity under the Company’s stock plans and related information: Weighted- Number Weighted- Average Remaining Aggregate of Options Average Exercise Contractual Life Intrinsic Value (a) (in thousands) Price (In years) (in thousands) Balance at December 31, 2016 7,449 $ 4.46 Options granted 1,897 2.80 Options exercised (1,491 ) 0.21 Options cancelled (485 ) 10.08 Balance at September 30, 2017 7,370 $ 4.52 7.8 $ 11,518 Vested and expected to vest as of September 30, 2017 7,370 $ 4.52 7.8 $ 11,518 Exercisable as of September 30, 2017 3,459 $ 4.91 6.8 $ 7,227 (a) The aggregate intrinsic value is calculated as the difference between the option exercise price and the closing price of common stock of $3.65 per share as of September 30, 2017. The options granted during 2016, included stock options for 3,673,940 shares of the Company’s common stock granted in exchange for Annapurna stock options at $0.21 exercise price per share. A total of 1,428,000 shares of stock options granted outside of the 2014 Plan in June 2016 and December 2015 were not included in the table above. The weighted-average fair values of options granted during the nine months ended September 30, 2017 and 2016 were $1.95 and $1.27, respectively. The total intrinsic value of options exercised during the nine months ended September 30, 2017 and 2016 were $3.7 million and $7.1 million, respectively. The Company has recorded aggregate stock-based compensation expense related to the issuance of stock awards to employees and nonemployees in the condensed consolidated statement of operations and comprehensive loss as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Research and development $ 1,698 $ 1,608 $ 4,335 $ 5,748 General and administrative 1,002 1,334 2,504 4,104 Total share-based compensation $ 2,700 $ 2,942 $ 6,839 $ 9,852 During the three and nine months ended September 30, 2016, respectively, stock-based compensation expense included additional charges related to stock modifications in connection with the separation agreements for certain of the Company’s executive officers. For the three months ended September 30, 2016, an additional charge of $0.5 million was recorded within general and administrative expense. For the nine months ended September 30, 2016, an additional charge of $1.4 million was recorded within research and development expense and $1.5 million was recorded within general and administrative expense. As of September 30, 2017, unrecognized compensation cost related to unvested employee options was $10.5 million, which is expected to be recognized over a weighted-average remaining period of 2.4 years. Restricted Stock Units RSUs are share awards that entitle the holder to receive freely tradable shares of the Company’s common stock upon vesting. The fair value of RSUs is based upon the closing sales price of the Company’s common stock on the grant date. RSUs granted to employees generally vest over a two to four year period. The following table summarizes the RSU activity under the Company’s stock plans and related information: Weighted-Average Weighted-Average Number of Grant-Date Remaining Units (in thousands) Fair Value (in dollars) Contractual Term (in years) Outstanding at December 31, 2016 1,049 $ 5.47 1.7 Granted 2,246 2.72 Vested and released (290 ) 6.64 Forfeited (537 ) 3.90 Outstanding at September 30, 2017 2,468 $ 3.17 1.8 The total fair value of RSUs that vested during the nine months ended September 30, 2017 and 2016 was $1.9 million and $4.0 million, respectively. As of September 30, 2017, unrecognized compensation cost related to unvested RSUs was $6.5 million, which is expected to be recognized over a weighted-average remaining period of 3.1 years. Stock Options Granted to Employees The fair value of each option issued to employees was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions: Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Option grants: Expected volatility 84 % 81 % 81 % 81 % Expected term (in years) 5.8 6.0 6.0 5.9 Expected dividend yield — — — — Risk-free interest rate 1.8 % 1.4 % 1.9 % 1.3 % Stock Options Granted to Non-Employees Stock-based compensation related to options granted to non-employees is measured and recognized as the options are earned. The Company believes that the estimated fair value of the options is more readily measurable than the fair value of the services rendered. The following weighted-average assumptions were used in estimating non-employees’ stock-based compensation expenses: Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Option grants: Expected volatility 87 % 84 % 84 % 83 % Expected term (in years) 8.8 8.0 8.9 7.5 Expected dividend yield — — — — Risk-free interest rate 2.2 % 1.6 % 2.2 % 1.6 % As of September 30, 2017, unrecognized stock-based compensation expense related to non-employees’ options was $0.7 million, which was expected to be recognized over a weighted-average remaining period of 1.8 years.

401(k) Savings Plan

401(k) Savings Plan	9 Months Ended
401(k) Savings Plan	Sep. 30, 2017
Postemployment Benefits [Abstract]
401(k) Savings Plan	12. 401(k) Savings Plan The Company established a defined-contribution savings plan under Section 401(k) of the Code (the 401(k) Plan). The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pretax basis. For the nine months ended September 30, 2017 and 2016, the Company contributed $0.3 million and $0.2 million, respectively, to the 401(k) Plan.

Net Loss per Share

Net Loss per Share	9 Months Ended
Net Loss per Share	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Loss per Share	13. 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. Diluted net loss per share is the same as basic net loss per share for all periods presented, since the effects of potentially dilutive securities are antidilutive. We have excluded warrants and equity awards to purchase approximately 10.0 million and 8.7 million shares of the Company’s common stock that were outstanding as of September 30, 2017 and 2016, respectively, in the computation of diluted net loss per share attributable to common stockholders because their effect was antidilutive.

Subsequent Event

Subsequent Event	9 Months Ended
Subsequent Event	Sep. 30, 2017
Subsequent Events [Abstract]
Subsequent Event	14. Subsequent Event On October 6, 2017, our Board of Directors adopted the Adverum Biotechnologies, Inc. 2017 Inducement Plan (the “Inducement Plan”) pursuant to which we reserved 600,000 shares for issuance pursuant to stock options and restricted stock units under the Inducement Plan. The only persons eligible to receive grants of stock options and restricted stock units under Inducement Plan are individuals who satisfy the standards for inducement grants under Nasdaq Marketplace Rule 5635(c)(4) and the related guidance under Nasdaq IM 5635-1 – that is, generally, a person not previously an employee or director of Adverum, or following a bona fide period of non-employment, as an inducement material to the individual's entering into employment with Adverum.

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2017
Accounting Policies [Abstract]
Recently-Issued and Not Yet Adopted Accounting Pronouncements	Recently-Issued and Not Yet Adopted Accounting Pronouncements — In May 2014, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes the revenue recognition requirements in ASC 605 , Revenue Recognition . This ASU is based on the principle that revenue is recognized to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. ASU 2014-09 defines a five-step process to achieve this core principle and, in doing so, it is possible more judgment and estimates may be required within the revenue recognition process than required under existing U.S. GAAP including identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. ASU 2014-09 is required to be adopted, using either of two methods: (i) retrospective to each prior reporting period presented with the option to elect certain practical expedients as defined within ASU 2014-09; or (ii) retrospective with the cumulative effect of initially applying ASU 2014-09 recognized at the date of initial application and providing certain additional disclosures. In July 2015, the FASB voted to approve a one-year deferral of the effective date to December 15, 2017 for interim and annual reporting periods beginning after that date and permitted early adoption of the standard, but not before the original effective date of December 15, 2016 . The FASB issued supplemental adoption guidance and clarification to ASU 2014-09 in March 2016, April 2016, May 2016 and December 2016 within ASU 2016-08 Revenue From Contracts With Customers: Principal vs. Agent Considerations , ASU 2016-10 Revenue From Contracts with Customers: Identifying Performance Obligations and Licensing , ASU 2016-12 Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients and ASU 2016-20 Technical Corrections and Improvement to Topic 606 – Revenue from Contracts with Customers , respectively. The ASU will be effective for the Company in the first quarter of 2018. The Company has commenced its implementation activities related to the adoption of ASU 2014-09 and is in the process of applying the five-step model of the new standard to its various revenue related arrangements. The Company has completed step 1 (Identify the contract(s) with a customer) and concluded that its collaboration agreements with Regeneron Pharmaceuticals, Inc. and Editas Medicine, Inc. will be impacted by the adoption of the new revenue standards. The Company is in the process of completing step 2 (Identify the performance obligations in the contract) and has not yet reached a conclusion on whether the distinct criteria evaluated under ASC 605-25 for each performance obligation would result in a similar conclusion under the new revenue standards. Preliminarily, the Company intends to adopt the new standard in the first quarter of 2018 using the retrospective approach noted in (ii) above. The Company is currently evaluating the impact of the adoption of this standard on its condensed consolidated financial statements and related disclosures. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities In February 2016, the FASB issued ASU No. 2016-2, Leases In June 2016, the FASB issued ASU No. 2016-13 Measurement of Credit Losses on Financial Instruments In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash In May 2017, the FASB issued ASU No. 2017-09, Scope of Modification Accounting The Company has reviewed other recent accounting pronouncements and concluded they are either not applicable to the business or no material effect is expected on the consolidated financial statements as a result of future adoption.

Acquisition of Annapurna (Table

Acquisition of Annapurna (Tables)	9 Months Ended
Acquisition of Annapurna (Tables)	Sep. 30, 2017
Business Combinations [Abstract]
Summary of Total Purchase Price Consideration Estimated	Total purchase price consideration was estimated as follows (in thousands): Fair value of common shares issued $ 58,321 Fair value of the Company's common share options exchanged for Annapurna stock options and other awards attributable to pre-combination services 7,422 Less: value of common stock and options accelerated vesting at the closing date (898 ) Total purchase price consideration $ 64,845
Components of Allocation of Total Purchase Price Consideration	The allocation of total purchase price consideration is as follows (in thousands): Cash $ 3,449 Prepaid expenses and other assets 865 Property and equipment 185 Acquired intangible assets 16,200 Goodwill 49,514 Accounts payable (1,118 ) Accrued liabilities (1,848 ) Other noncurrent liabilities (377 ) Deferred tax liabilities (2,025 ) Total purchase price allocation $ 64,845
Summary of Identifiable Intangible Assets Acquired	The identifiable intangible assets acquired consist of IPR&D assets related to products in development, as summarized in the table below (in thousands): IPR&D - Alpha-1 antitrypsin deficiency $ 11,700 IPR&D - Hereditary angioedema 4,500 Total acquired intangible assets $ 16,200
Schedule of Pro Forma Financial Information	The following table presents the unaudited pro forma results for the nine months ended September 30, 2016 (in thousands, except per share data). Nine Months Ended September 30, 2016 Pro forma information Collaboration revenue $ 967 Net loss $ (95,167 ) Basic and diluted loss per share $ (2.31 ) Weighted-average common shares outstanding - basic and diluted 41,118

Cash Equivalents and Short-Te22

Cash Equivalents and Short-Term Investments (Tables)	9 Months Ended
Cash Equivalents and Short-Term Investments (Tables)	Sep. 30, 2017
Cash And Cash Equivalents [Abstract]
Summary of Available-for-Sale Securities	The following is a summary of the Company’s available-for-sale securities as of September 30, 2017 (in thousands): September 30, 2017 Amortized Cost Basis Unrealized Losses Unrealized Gains Estimated Fair Value Money market funds $ 1,763 $ — $ — $ 1,763 Certificates of deposit 9,978 — — 9,978 Commercial paper 32,295 — — 32,295 U.S. government agency 72,756 (70 ) 1 72,687 Corporate bonds 63,105 (33 ) — 63,072 Total cash equivalents and short-term investments 179,897 (103 ) 1 179,795 Less: cash equivalents (24,866 ) — — (24,866 ) Total short-term investments $ 155,031 $ (103 ) $ 1 $ 154,929
Summary of Cost and Estimated Fair Value of Available-for-Sale Securities Based on Stated Effective Maturities	The following table is a summary of the cost and estimated fair value of the Company’s available-for-sale securities based on stated effective maturities as of September 30, 2017 (in thousands): September 30, 2017 Amortized Cost Basis Estimated Fair Value Mature within one year $ 151,769 $ 151,725 Mature after one year to three years 28,128 28,070 Total cash equivalents and short-term investments $ 179,897 $ 179,795

Fair Value Measurements and F23

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Financial Assets Measured and Recognized at Fair Value on Recurring Basis	The following table summarizes, for assets recorded at fair value on a recurring basis, the respective fair value and the classification by level of input within the fair value hierarchy as described above (in thousands): Quoted Prices Significant Other Significant Total In Active Markets Observable Inputs Unobservable Inputs Carrying Value (Level 1) (Level 2) (Level 3) September 30, 2017 Assets: Money market funds $ 1,763 $ 1,763 $ — $ — Certificates of deposit 9,978 — 9,978 — Commercial paper 32,295 — 32,295 — U.S. government agency 72,687 — 72,687 — Corporate bonds 63,072 — 63,072 — Total cash equivalents and short term investments $ 179,795 $ 1,763 $ 178,032 $ — Other noncurrent liability: Financing arrangement $ 74 $ — $ — $ 74 December 31, 2016 Assets: Money market funds $ 215,916 $ 215,916 $ — $ — Total cash equivalents $ 215,916 $ 215,916 $ — $ — Other noncurrent liability: Financing arrangement $ 74 $ — $ — $ 74

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
Property and Equipment, Net (Tables)	Sep. 30, 2017
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consists of the following (in thousands): September 30, 2017 December Computer equipment and software $ 480 $ 300 Laboratory equipment 4,933 4,285 Furniture and fixtures 552 552 Leasehold improvements 1,541 1,522 Construction in progress 16 104 Total property and equipment 7,522 6,763 Less accumulated depreciation and amortization (4,175 ) (2,594 ) Property and equipment, net $ 3,347 $ 4,169

Accrued Expenses and Other Cu25

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
Accrued Expenses and Other Current Liabilities (Tables)	Sep. 30, 2017
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following (in thousands): September 30, 2017 December Employees’ compensation expenses $ 1,628 $ 2,570 Accrued preclinical costs 805 1,683 Accrued clinical and process development costs 669 1,142 Accrued professional services 725 894 Accrued contract settlement 2,000 — Other 235 162 Total accrued expenses and other current liabilities $ 6,062 $ 6,451

Stock Plans (Tables)

Stock Plans (Tables)	9 Months Ended
Stock Plans (Tables)	Sep. 30, 2017
Stock-Based Compensation Expense Related to Issuance of Stock Awards to Employees and Nonemployees	The Company has recorded aggregate stock-based compensation expense related to the issuance of stock awards to employees and nonemployees in the condensed consolidated statement of operations and comprehensive loss as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Research and development $ 1,698 $ 1,608 $ 4,335 $ 5,748 General and administrative 1,002 1,334 2,504 4,104 Total share-based compensation $ 2,700 $ 2,942 $ 6,839 $ 9,852
Summary of Restricted Stock Units Activity	The following table summarizes the RSU activity under the Company’s stock plans and related information: Weighted-Average Weighted-Average Number of Grant-Date Remaining Units (in thousands) Fair Value (in dollars) Contractual Term (in years) Outstanding at December 31, 2016 1,049 $ 5.47 1.7 Granted 2,246 2.72 Vested and released (290 ) 6.64 Forfeited (537 ) 3.90 Outstanding at September 30, 2017 2,468 $ 3.17 1.8
Schedule of Fair Value of Option Issued to Employees Valuation Assumptions	The fair value of each option issued to employees was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions: Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Option grants: Expected volatility 84 % 81 % 81 % 81 % Expected term (in years) 5.8 6.0 6.0 5.9 Expected dividend yield — — — — Risk-free interest rate 1.8 % 1.4 % 1.9 % 1.3 %
Non Employee Stock Option [Member]
Schedule of Non-Employee Stock Option Plan Valuation Assumptions	The following weighted-average assumptions were used in estimating non-employees’ stock-based compensation expenses: Three Months Ended Nine Months Ended September 30, September 30, 2017 2016 2017 2016 Option grants: Expected volatility 87 % 84 % 84 % 83 % Expected term (in years) 8.8 8.0 8.9 7.5 Expected dividend yield — — — — Risk-free interest rate 2.2 % 1.6 % 2.2 % 1.6 %
2006 and 2014 Equity Incentive Plan [Member]
Summary of Stock Options Activity	The following table summarizes option activity under the Company’s stock plans and related information: Weighted- Number Weighted- Average Remaining Aggregate of Options Average Exercise Contractual Life Intrinsic Value (a) (in thousands) Price (In years) (in thousands) Balance at December 31, 2016 7,449 $ 4.46 Options granted 1,897 2.80 Options exercised (1,491 ) 0.21 Options cancelled (485 ) 10.08 Balance at September 30, 2017 7,370 $ 4.52 7.8 $ 11,518 Vested and expected to vest as of September 30, 2017 7,370 $ 4.52 7.8 $ 11,518 Exercisable as of September 30, 2017 3,459 $ 4.91 6.8 $ 7,227 (a) The aggregate intrinsic value is calculated as the difference between the option exercise price and the closing price of common stock of $3.65 per share as of September 30, 2017.

Organization and Basis of Pre27

Organization and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Date of incorporation	Jul. 17, 2006
Change of entity name date	May 11, 2016
Accumulated deficit	$ (239,273)	$ (197,915)

Acquisition of Annapurna - Addi

Acquisition of Annapurna - Additional Information (Detail)	May 11, 2016USD ($)Segment$ / sharesshares	May 31, 2016USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)
Business Acquisition [Line Items]
Total purchase price consideration							$ 64,845,000
Stock Options [Member]
Business Acquisition [Line Items]
Expected volatility			84.00%	81.00%		81.00%	81.00%
Risk-free interest rate			1.80%	1.40%		1.90%	1.30%
Expected term (in years)			5 years 9 months 18 days	6 years		6 years	5 years 10 months 25 days
Non Employee Stock Option [Member]
Business Acquisition [Line Items]
Expected volatility			87.00%	84.00%		84.00%	83.00%
Risk-free interest rate			2.20%	1.60%		2.20%	1.60%
Expected term (in years)			8 years 9 months 18 days	8 years		8 years 10 months 25 days	7 years 6 months
Annapurna Therapeutics SAS [Member]
Business Acquisition [Line Items]
Date of acquisition						May 11, 2016
Total purchase price consideration	$ 64,845,000
Fair value of awards related to accelerated vesting of options and shares	$ 900,000
Common stock exchange ratio			9.54655			9.54655
Goodwill, description						Goodwill represented expected synergies of two combined companies.
Acquisition costs			$ 0	$ 0		$ 0	$ 2,500,000
Fair value, discounted rate	11.00%
Goodwill	$ 49,514,000
Number of reporting unit \| Segment	1
Interest expense related to convertible notes and changes in fair value of preferred stock warrants							1,000,000
Bonuses paid		$ 400,000
Annapurna Therapeutics SAS [Member] \| IPR&D [Member]
Business Acquisition [Line Items]
Impairment of intangible assets								$ 11,200,000
Annapurna Therapeutics SAS [Member] \| Stock Options [Member]
Business Acquisition [Line Items]
Shares reserved for future exercise of stock options \| shares	3,673,940
Fair value of estimated stock options and stock-based awards at acquisition	$ 14,700,000
Dividends	0.00%
Expected volatility	80.00%
Risk-free interest rate	1.40%
Expected term (in years)	6 years
Fair value of stock options attributed as pre-combination service and included as part of acquisition consideration	$ 7,400,000
Fair value of stock options post-combination attribution recognized as compensation expense	$ 7,200,000
Stock-based compensation expense related to vesting of stock options					$ 900,000		900,000
Annapurna Therapeutics SAS [Member] \| Stock Options [Member] \| Executives [Member]
Business Acquisition [Line Items]
Stock-based compensation expense related to vesting of stock options							$ 200,000
Annapurna Therapeutics SAS [Member] \| Non Employee Stock Option [Member]
Business Acquisition [Line Items]
Dividends	0.00%
Expected volatility	89.00%
Risk-free interest rate	1.10%
Expected term (in years)	10 years
Annapurna Therapeutics SAS [Member] \| Common Shares [Member]
Business Acquisition [Line Items]
Number of shares issued to acquired an entity \| shares	14,087,246
Share price of common stock on date of acquisition \| $ / shares	$ 4.14

Acquisition of Annapurna - Summ

Acquisition of Annapurna - Summary of Total Purchase Price Consideration Estimated (Detail) - USD ($) $ in Thousands	May 11, 2016	Sep. 30, 2016
Business Acquisition [Line Items]
Total purchase price consideration		$ 64,845
Annapurna Therapeutics SAS [Member]
Business Acquisition [Line Items]
Less: value of common stock and options accelerated vesting at the closing date	$ (898)
Total purchase price consideration	64,845
Annapurna Therapeutics SAS [Member] \| Common Shares [Member]
Business Acquisition [Line Items]
Fair value of common shares issued/common share options exchanged	58,321
Annapurna Therapeutics SAS [Member] \| Common Shares [Member] \| Stock Options [Member]
Business Acquisition [Line Items]
Fair value of common shares issued/common share options exchanged	$ 7,422

Acquisition of Annapurna - Comp

Acquisition of Annapurna - Components of Allocation of Total Purchase Price Consideration (Detail) - Annapurna Therapeutics SAS [Member] $ in Thousands	May 11, 2016USD ($)
Business Acquisition [Line Items]
Cash	$ 3,449
Prepaid expenses and other assets	865
Property and equipment	185
Acquired intangible assets	16,200
Goodwill	49,514
Accounts payable	(1,118)
Accrued liabilities	(1,848)
Other noncurrent liabilities	(377)
Deferred tax liabilities	(2,025)
Total purchase price allocation	$ 64,845

Acquisition of Annapurna - Su31

Acquisition of Annapurna - Summary of Identifiable Intangible Assets Acquired (Detail) - Annapurna Therapeutics SAS [Member] $ in Thousands	May 11, 2016USD ($)
Acquired Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets	$ 16,200
IPR&D [Member]
Acquired Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets	16,200
IPR&D [Member] \| Alpha-1 Antitrypsin Deficiency [Member]
Acquired Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets	11,700
IPR&D [Member] \| Hereditary Angioedema [Member]
Acquired Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets	$ 4,500

Acquisition of Annapurna - Sche

Acquisition of Annapurna - Schedule of Pro Forma Financial Information (Detail) - Annapurna Therapeutics SAS [Member] $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2016USD ($)$ / sharesshares
Pro forma information
Collaboration revenue	$ 967
Net loss	$ (95,167)
Basic and diluted loss per share \| $ / shares	$ (2.31)
Weighted-average common shares outstanding - basic and diluted \| shares	41,118

Cash Equivalents and Short-Te33

Cash Equivalents and Short-Term Investments - Summary of Available-for-Sale Securities (Detail) $ in Thousands	Sep. 30, 2017USD ($)
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	$ 155,031
Unrealized Losses	(103)
Unrealized Gains	1
Estimated Fair Value	154,929
Less: Cash Equivalents, Amortized Cost Basis	(24,866)
Less: Cash Equivalents, Unrealized Losses	0
Less: Cash Equivalents, Unrealized Gains	0
Less: Cash Equivalents, Estimated Fair Value	(24,866)
Money Market Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	1,763
Estimated Fair Value	1,763
Certificates of Deposit [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	9,978
Estimated Fair Value	9,978
Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	32,295
Estimated Fair Value	32,295
U.S. Government Agency [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	72,756
Unrealized Losses	(70)
Unrealized Gains	1
Estimated Fair Value	72,687
Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	63,105
Unrealized Losses	(33)
Estimated Fair Value	63,072
Total Cash Equivalents and Short-term Investments [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost Basis	179,897
Unrealized Losses	(103)
Unrealized Gains	1
Estimated Fair Value	$ 179,795

Cash Equivalents and Short-Te34

Cash Equivalents and Short-Term Investments - Summary of Cost and Estimated Fair Value of Available-for-Sale Securities Based on Stated Effective Maturities (Detail) $ in Thousands	Sep. 30, 2017USD ($)
Investments Debt And Equity Securities [Abstract]
Amortized Cost Basis, Mature within one year	$ 151,769
Amortized Cost Basis, Mature after one year to three years	28,128
Amortized Cost Basis, Total cash equivalents and short-term investments	179,897
Estimated Fair Value, Mature within one year	151,725
Estimated Fair Value, Mature after one year to three years	28,070
Estimated Fair Value, Total cash equivalents and short-term investments	$ 179,795

Cash Equivalents and Short-Te35

Cash Equivalents and Short-Term Investments - Additional Information (Detail)	Sep. 30, 2017USD ($)
Available For Sale Securities [Abstract]
Gross unrealized losses on available-for-sale-securities temporary	$ 100,000
Available-for-sale securities other-than-temporarily impaired	$ 0

Fair Value Measurements and F36

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Liabilities transferred within Level 3	$ 0	$ 0

Fair Value Measurements and F37

Fair Value Measurements and Fair Value of Financial Instruments - Financial Assets Measured and Recognized at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets:
Assets	$ 179,795	$ 215,916
Corporate Bonds [Member]
Assets:
Assets	63,072
Financing Arrangement [Member]
Other noncurrent liability:
Other noncurrent liability	74	74
Money Market Funds [Member]
Assets:
Assets	1,763	215,916
Commercial Paper [Member]
Assets:
Assets	32,295
Certificates of Deposit [Member]
Assets:
Assets	9,978
US Government Agency [Member]
Assets:
Assets	72,687
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Assets	1,763	215,916
Quoted Prices in Active Markets (Level 1) [Member] \| Money Market Funds [Member]
Assets:
Assets	1,763	215,916
Significant Other Observable Inputs (Level 2) [Member]
Assets:
Assets	178,032
Significant Other Observable Inputs (Level 2) [Member] \| Corporate Bonds [Member]
Assets:
Assets	63,072
Significant Other Observable Inputs (Level 2) [Member] \| Commercial Paper [Member]
Assets:
Assets	32,295
Significant Other Observable Inputs (Level 2) [Member] \| Certificates of Deposit [Member]
Assets:
Assets	9,978
Significant Other Observable Inputs (Level 2) [Member] \| US Government Agency [Member]
Assets:
Assets	72,687
Significant Unobservable Inputs (Level 3) [Member] \| Financing Arrangement [Member]
Other noncurrent liability:
Other noncurrent liability	$ 74	$ 74

Significant Agreements - Additi

Significant Agreements - Additional Information (Detail)

Feb. 23, 2017

Apr. 30, 2017

Dec. 31, 2016Agreement

Aug. 31, 2016USD ($)

Dec. 31, 2015USD ($)Agreement

Oct. 31, 2015USD ($)

Oct. 31, 2015EUR (€)

May 31, 2014USD ($)Target

Apr. 30, 2014USD ($)

May 31, 2010USD ($)

Sep. 30, 2017USD ($)

Dec. 31, 2016USD ($)

Dec. 31, 2016EUR (€)

Regeneron Corporation [Member]

License Agreement [Line Items]

Agreement termination scenario description

Regeneron may terminate the agreement for convenience at any time on a target by target basis or in totality upon a 30-day notice.Each party can terminate the agreement if another party commits a material breach or material default in performance of its obligations and such breach or default is not cured within 60 days.The agreement is automatically terminated upon initiation of any bankruptcy proceedings, reorganization or dissolution of either party.The Company can terminate the agreement upon 30-day notice if Regeneron challenges the validity, scope or enforceability of any Company patent.

Potential target of collaborations | Target

Initial collaboration term

3 years

Additional collaboration term

5 years

Collaboration fee for exclusive worldwide license per target

$ 2,000,000

Potential milestone earnings

640,000,000

Reimbursement of research and development expense

35.00%

Collaboration agreement extension period

3 years

Collaboration agreement expiration date

May 1,
2020

Regeneron Corporation [Member] | Development and Regulatory Milestone [Member]

License Agreement [Line Items]

Potential milestone earnings

$ 80,000,000

University of California [Member]

License Agreement [Line Items]

Right and option to extend date to meet milestone, period

6 months

Right and option to extend date to meet milestone, description

The Company has the right and option to extend the date by which it must meet any milestone by six-months up to two times by paying an extension fee for each such extension.

License fee paid

$ 100,000

Aggregate amount of milestone payments for one indication

900,000

Additional milestone payments recognized

$ 0

Non-royalty licensing revenue, description

mid-teen percentage

Agreement termination scenario description

The Company may terminate this agreement without cause at any time upon 30 days’ prior written notice to the Regents. The Regents may terminate this agreement for a breach by the Company that remains uncured for 60 days, if the Company becomes insolvent, if the Company directly or through a third party files a claim that a licensed patent right is invalid or unenforceable or if the Company fails to meet or extend the date for meeting certain diligence milestones.

License agreement termination notice period

30 days

University of California [Member] | Maximum [Member]

License Agreement [Line Items]

Additional milestone payments for up to two additional indications

500,000

University of California [Member] | Minimum [Member]

License Agreement [Line Items]

Annual royalty payment

$ 50,000

Editas Medicine Inc [Member]

License Agreement [Line Items]

Non-refundable upfront payment received

$ 1,000,000

Non-refundable upfront payment, obligation to fund research and development costs

$ 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

Editas Medicine Inc [Member] | Maximum [Member]

License Agreement [Line Items]

Potential milestone earnings

$ 15,500,000

Cornell University [Member]

License Agreement [Line Items]

Additional milestone payments recognized

$ 0

Agreement termination scenario description

Annapurna may terminate any of these license agreements for convenience upon ninety days written notice. Cornell may terminate any of the license agreements for material breach if such breach is not cured within a specified number of days. Cornell may also terminate the HAE License Agreement and/or the Allergy License Agreement if Annapurna commences any action and files a written claim asserting that any portion of the licensed patent rights is invalid or unenforceable.

License agreement termination notice period

90 days

Number of license agreements | Agreement

Service fees payable

$ 13,300,000

Service fees, payable period

4 years

Aggregate milestone payments and royalties on sales

$ 16,000,000

Cornell University [Member] | Master Service Agreement [Member]

License Agreement [Line Items]

Estimated costs associated with the termination

2,000,000

Agreement termination effective date

Jan. 6,
2017

Cornell University [Member] | Maximum [Member]

License Agreement [Line Items]

Annual maintenance fee payable

300,000

Cornell University [Member] | Maximum [Member] | Consultant [Member]

License Agreement [Line Items]

Annual compensation

300,000

Cornell University [Member] | Minimum [Member]

License Agreement [Line Items]

Annual maintenance fee payable

$ 30,000

REGENXBIO [Member]

License Agreement [Line Items]

Agreement termination scenario description

Annapurna Therapeutics Limited may terminate this license agreement upon six months’ prior written notice. REGENXBIO may terminate this license agreement if Annapurna Therapeutics Limited is a specified number of days late in paying money due under the license agreement, or if Annapurna Therapeutics Limited, its affiliates, or any sublicensees become insolvent or, effective immediately, if they commence any action against REGENXBIO or its licensors to declare or render any claim of the licensed patent rights invalid or unenforceable. Either party may terminate this license agreement for material breach if such breach is not cured within a specified number of days.

License agreement termination notice period

6 months

Expenses associated with license agreement

$ 200,000

REGENXBIO [Member] | A1AT Deficiency/Allergy License Agreement [Member]

License Agreement [Line Items]

Agreement termination scenario description

Annapurna may terminate this license agreement for any reason upon six months’ prior written notice. REGENXBIO may terminate this license agreement if Annapurna is a specified number of days late in paying money due under the license agreement, or if Annapurna, its affiliates, or any sublicensees become insolvent or, effective immediately, if they commence any action against REGENEXBIO or its licensors to declare or render any claim of the licensed patent rights invalid or unenforceable. Either party may terminate this license agreement for material breach if such breach is not cured within a specified number of days.

License agreement termination notice period

6 months

Aggregate milestone payments and royalties on sales

$ 20,000,000

License agreement termination effective date

2017-10

REGENXBIO [Member] | Friedreich's Ataxia License Agreement [Member]

License Agreement [Line Items]

Aggregate milestone payments and royalties on sales

$ 13,850,000

Inserm Transfert [Member]

License Agreement [Line Items]

Additional milestone payments recognized

$ 0

Agreement termination scenario description

Annapurna may terminate this agreement upon 60 days’ prior written notice. Inserm may terminate this license agreement if Annapurna becomes the subject of a voluntary or involuntary petition in bankruptcy or fails to meet development milestones and such failure is not cured within a specified number of days. Inserm may also terminate the license granted to Annapurna in a given country if Annapurna (i) before regulatory approval of a product in any country, has ceased conducting any development of products in all countries for 12 consecutive months or (ii) after regulatory approval of a product in a given country, has ceased marketing such product in such country for 12 consecutive months.

License agreement termination notice period

60 days

Aggregate milestone payments and royalties on sales | €

€ 2,000,000

Expenses associated with license agreement

$ 300,000

Inserm Transfert [Member] | Research and Development Expense [Member]

License Agreement [Line Items]

One-time payment due to termination of license agreement | €

€ 250,000

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 7,522	$ 6,763
Less accumulated depreciation and amortization	(4,175)	(2,594)
Property and equipment, net	3,347	4,169
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	480	300
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	4,933	4,285
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	552	552
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	1,541	1,522
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 16	$ 104

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 500	$ 400	$ 1,592	$ 1,116

Accrued Expenses and Other Cu41

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accrued Expenses And Other Current Liabilities [Abstract]
Employees’ compensation expenses	$ 1,628	$ 2,570
Accrued preclinical costs	805	1,683
Accrued clinical and process development costs	669	1,142
Accrued professional services	725	894
Accrued contract settlement	2,000
Other	235	162
Total accrued expenses and other current liabilities	$ 6,062	$ 6,451

Other Non-Current Liabilities -

Other Non-Current Liabilities - Additional Information (Detail)	1 Months Ended	9 Months Ended		12 Months Ended
	Jul. 31, 2016USD ($)	Sep. 30, 2017EUR (€)	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2017USD ($)	Aug. 31, 2015EUR (€)
Line Of Credit Facility [Line Items]
Proceeds from financing arrangement			$ 100,000
Financing arrangement included in other noncurrent liabilities				$ 386,000	$ 387,000
The Alpha-1 Project, Inc. [Member]
Line Of Credit Facility [Line Items]
Proceeds from financing arrangement				$ 100,000
Financing arrangement included in other noncurrent liabilities					$ 100,000
The Alpha-1 Project, Inc. [Member] \| Maximum [Member]
Line Of Credit Facility [Line Items]
Potential milestone earnings	$ 300,000
Expected percentage of milestone repayments	450.00%
BPI France [Member]
Line Of Credit Facility [Line Items]
Interest free conditional advance, maximum borrowing capacity \| €						€ 500,000
Interest free conditional advance, frequency of payments		Quarterly
Interest free conditional advance, periodic payment \| €		€ 25,000
Interest free conditional advance, beginning date of periodic payment		Sep. 30, 2017
Interest free conditional advance, ending date of periodic payment		Jun. 30, 2022
Interest free conditional advance, imputed interest rate					7.00%
Interest free conditional advance					$ 400,000
BPI France [Member] \| Other Noncurrent Liabilities [Member]
Line Of Credit Facility [Line Items]
Interest free conditional advance					300,000
BPI France [Member] \| Accrued Expenses and Other Current Liabilities [Member]
Line Of Credit Facility [Line Items]
Interest free conditional advance					$ 100,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Mar. 16, 2017USD ($)	Dec. 31, 2015Claim	Jul. 31, 2015Claim	Sep. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Sep. 30, 2016USD ($)	Sep. 30, 2017USD ($)Claim	Sep. 30, 2016USD ($)
Other Commitments [Line Items]
Lease renewal term							4 years
Lease expiration date							May 8, 2020
Rent expense							$ 1,400,000	$ 1,300,000
Accrued royalties				$ 0			0
Claims paid to date related to indemnification issues							$ 0
Number of claims to date \| Claim		1	3				0
Accruals or expenses related to indemnification issues							$ 0
Proposed aggregate amount of settlement	$ 13,000,000
General and administrative expense				$ 4,762,000		$ 6,146,000	$ 16,815,000	$ 19,578,000
Indemnification Obligations [Member]
Other Commitments [Line Items]
Proposed aggregate amount of settlement	$ 1,000,000
General and administrative expense					$ 1,000,000

Stock Plans - Additional Inform

Stock Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of stock options granted	1,428,000
Weighted-average fair values of options granted			$ 1.95	$ 1.27
Total intrinsic value of options exercised			$ 3.7	$ 7.1
Unrecognized compensation cost related to unvested employee options			$ 10.5
Unrecognized stock-based compensation, weighted-average remaining period			2 years 4 months 25 days
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation, weighted-average remaining period			3 years 1 month 7 days
Total fair values of RSUs vested			$ 1.9	4
Unrecognized compensation cost			6.5
Non Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to unvested employee options			$ 0.7
Unrecognized stock-based compensation, weighted-average remaining period			1 year 9 months 19 days
Minimum [Member] \| Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted to employees vesting period			2 years
Maximum [Member] \| Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted to employees vesting period			4 years
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense for modifications				1.4
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense for modifications		$ 0.5		$ 1.5
Annapurna Therapeutics SAS [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total number of stock options granted					3,673,940
Stock options exercise price granted					$ 0.21
2014 Equity Incentive Award Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized for issuance			14,834,856
Shares available for future grants			1,631,908
Total number of stock options granted			1,897,000
Stock options exercise price granted			$ 2.80
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grants			1,000,783
Common stock, shares issued			35,954	52,002
Common stock shares available for future grant			1,000,783

Stock Plans - Summary of Stock

Stock Plans - Summary of Stock Options Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 30, 2016	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Number of Options [Roll Forward]
Number of Options, Options granted	1,428,000
2014 Equity Incentive Award Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Options [Roll Forward]
Number of Options, Beginning Balance		7,449,000
Number of Options, Options granted		1,897,000
Number of Options, Options exercised		(1,491,000)
Number of Options, Options cancelled		(485,000)
Number of Options, Ending Balance		7,370,000
Number of Options, Vested and expected to vest		7,370,000
Number of Options, Exercisable		3,459,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Beginning Balance		$ 4.46
Weighted-Average Exercise Price, Options granted		2.80
Weighted-Average Exercise Price, Options exercised		0.21
Weighted-Average Exercise Price, Options cancelled		10.08
Weighted-Average Exercise Price, Ending Balance		4.52
Weighted-Average Exercise Price, Vested and expected to vest		4.52
Weighted-Average Exercise Price, Exercisable		$ 4.91
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-Average Remaining Contractual Life (In years)		7 years 9 months 18 days
Weighted-Average Remaining Contractual Life (In years), Vested and expected to vest		7 years 9 months 18 days
Weighted-Average Remaining Contractual Life (In years), Exercisable		6 years 9 months 18 days
Aggregate Intrinsic Value, Options outstanding		$ 11,518
Aggregate Intrinsic Value, Vested and expected to vest		11,518
Aggregate Intrinsic Value, Exercisable		$ 7,227

Stock Plans - Summary of Stoc46

Stock Plans - Summary of Stock Options Activity (Parenthetical) (Detail)	9 Months Ended
	Sep. 30, 2017$ / shares
Equity [Abstract]
Aggregate intrinsic value of option per share	$ 3.65

Stock Plans - Stock-Based Compe

Stock Plans - Stock-Based Compensation Expense Related to Issuance of Stock Awards to Employees and Nonemployees (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation	$ 2,700	$ 2,942	$ 6,839	$ 9,852
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation	1,698	1,608	4,335	5,748
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total share-based compensation	$ 1,002	$ 1,334	$ 2,504	$ 4,104

Stock Plans - Summary of Restri

Stock Plans - Summary of Restricted Stock Units Activity (Detail) - Restricted Stock Units [Member] - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Units, Beginning Balance	1,049,000
Number of Units, Granted	2,246,000
Number of Units, Vested and released	(290,000)
Number of Units, Forfeited	(537,000)
Number of Units, Ending Balance	2,468,000	1,049,000
Weighted-Average Grant-Date Fair Value, Beginning Balance	$ 5.47
Weighted-Average Grant-Date Fair Value, Granted	2.72
Weighted-Average Grant-Date Fair Value, Vested and released	6.64
Weighted-Average Grant-Date Fair Value, Forfeited	3.90
Weighted-Average Grant-Date Fair Value, Ending Balance	$ 3.17	$ 5.47
Weighted-Average Remaining Contractual Term (In years)	1 year 9 months 18 days	1 year 8 months 12 days

Stock Plans - Schedule of Emplo

Stock Plans - Schedule of Employees Stock Purchase Plan Valuation Assumptions (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	84.00%	81.00%	81.00%	81.00%
Expected term (in years)	5 years 9 months 18 days	6 years	6 years	5 years 10 months 25 days
Risk-free interest rate	1.80%	1.40%	1.90%	1.30%
Non Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	87.00%	84.00%	84.00%	83.00%
Expected term (in years)	8 years 9 months 18 days	8 years	8 years 10 months 25 days	7 years 6 months
Risk-free interest rate	2.20%	1.60%	2.20%	1.60%

401(k) Savings Plan - Additiona

401(k) Savings Plan - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Compensation And Retirement Disclosure [Abstract]
Contribution by company	$ 0.3	$ 0.2

Net Loss per Share - Additional

Net Loss per Share - Additional Information (Detail) - shares shares in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share	10	8.7

Subsequent Event - Additional I

Subsequent Event - Additional Information (Detail)	Oct. 06, 2017shares
Subsequent Event [Member] \| 2017 Inducement Plan [Member] \| Stock Options and Restricted Stock Units [Member]
Subsequent Event [Line Items]
Shares reserved for issuance	600,000