Adverum Biotechnologies (ADVM) 10-Q 6 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 29, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-36579
Entity Registrant Name	Adverum Biotechnologies, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-5258327
Entity Address, Address Line One	800 Saginaw Drive,
Entity Address, City or Town	Redwood City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94063
City Area Code	650
Local Phone Number	656-9323
Title of 12(b) Security	Common Stock, $0.0001 par value
Trading Symbol	ADVM
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		97,934,777
Entity Central Index Key	0001501756
Current Fiscal Year End Date	--12-31
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 45,422	$ 62,424
Short-term investments	358,596	367,305
Prepaid expenses and other current assets	5,837	4,709
Total current assets	409,855	434,438
Operating lease right-of-use assets	19,044	19,376
Property and equipment, net	28,379	27,725
Restricted cash		999
Deposit and other long-term assets	493	29
Total assets	461,551	482,567
Current liabilities:
Accounts payable	2,056	2,810
Accrued expenses and other current liabilities	13,355	13,588
Lease liability, current portion	4,512	4,473
Total current liabilities	19,923	20,871
Lease liability, net of current portion	25,694	26,235
Other non-current liabilities	1,114	1,114
Total liabilities	46,731	48,220
Stockholders’ equity:
Preferred stock	0	0
Common stock	10	10
Additional paid-in capital	946,098	937,134
Accumulated other comprehensive loss	(316)	(261)
Accumulated deficit	(530,972)	(502,536)
Total stockholders’ equity	414,820	434,347
Total liabilities and stockholders' equity	$ 461,551	$ 482,567

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
License revenue	$ 7,500	$ 0
Revenue from Contract with Customer, Product and Service [Extensible List]	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 19,980	$ 14,751
General and administrative	16,163	9,040
Total operating expenses	36,143	23,791
Operating loss	(28,643)	(23,791)
Other income, net	207	885
Net loss	(28,436)	(22,906)
Other comprehensive loss:
Net unrealized loss on marketable securities	(22)	(54)
Foreign currency translation adjustment	(33)	(54)
Comprehensive loss	$ (28,491)	$ (23,014)
Net loss per share — basic and diluted (in USD per share)	$ (0.29)	$ (0.31)
Weighted-average common shares used to compute net loss per share - basic and diluted (in shares)	97,750	73,797

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive (Loss)/Income	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019		67,329,000
Beginning balance at Dec. 31, 2019	$ 174,957	$ 7	$ 560,704	$ (725)	$ (385,029)
Stock-based compensation expense	3,409		3,409
Issuance of common stock, net of issuance costs (in shares)		10,925,000
Issuance of common stock, net of issuance costs	140,873	$ 1	140,872
Common stock issued upon exercise of stock options (in shares)		1,310,000
Common stock issued upon exercise of stock options	$ 9,650		9,650
Common stock issued upon net exercise of warrants (in shares)	7,000
Common stock issued upon release of restricted stock units (in shares)		462,000
Restricted stock surrendered for taxes (in shares)		(155,000)
Restricted stock surrendered for taxes	$ (1,922)		(1,922)
Foreign currency translation adjustments	(54)			(54)
Unrealized gain (loss) on marketable securities, net	(54)			(54)
Net loss	(22,906)				(22,906)
Ending balance (in shares) at Mar. 31, 2020		79,878,000
Ending balance at Mar. 31, 2020	303,953	$ 8	712,713	(833)	(407,935)
Beginning balance (in shares) at Dec. 31, 2020		97,549,000
Beginning balance at Dec. 31, 2020	434,347	$ 10	937,134	(261)	(502,536)
Stock-based compensation expense	7,224		7,224
Issuance of common stock, net of issuance costs (in shares)		121,000
Issuance of common stock, net of issuance costs	$ 1,689		1,689
Common stock issued upon exercise of stock options (in shares)	9,000	9,000
Common stock issued upon exercise of stock options	$ 51		51
Common stock issued upon release of restricted stock units (in shares)		248,000
Foreign currency translation adjustments	(33)			(33)
Unrealized gain (loss) on marketable securities, net	(22)			(22)
Net loss	(28,436)				(28,436)
Ending balance (in shares) at Mar. 31, 2021		97,927,000
Ending balance at Mar. 31, 2021	$ 414,820	$ 10	$ 946,098	$ (316)	$ (530,972)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders Equity (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Stockholders' Equity [Abstract]
Stock issuance costs	$ 5	$ 332

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (28,436)	$ (22,906)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,166	599
Stock-based compensation expense	7,224	3,409
Amortization of premium/(discount) and accrued interest on marketable securities	855	(179)
Other	(42)	(48)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,279)	6,345
Other assets	(464)	(8)
Operating lease right-of-use asset	332	557
Accounts payable	(763)	2,514
Accrued expenses and other current liabilities	(396)	(3,429)
Lease liability	(502)	(470)
Net cash used in operating activities	(22,305)	(13,616)
Cash flows from investing activities:
Purchases of marketable securities	(82,667)	(127,733)
Maturities of marketable securities	90,650	61,200
Purchases of property and equipment	(1,404)	(4,210)
Net cash provided by (used in) investing activities	6,579	(70,743)
Cash flows from financing activities:
Proceeds from offerings of common stock, net of issuance costs	1,694	140,923
Proceeds from issuance of common stock pursuant to option exercises	51	9,650
Taxes paid related to net share settlement of restricted stock units	0	(1,922)
Repayment of loan	(240)	(27)
Net cash provided by financing activities	1,505	148,624
Net (decrease) increase in cash and cash equivalents and restricted cash	(14,221)	64,265
Cash and cash equivalents and restricted cash at beginning of period	63,423	66,896
Cash and cash equivalents and restricted cash at end of period	49,202	131,161
Cash and cash equivalents and restricted cash at end of period	49,202	131,161
Supplemental schedule of noncash investing and financing information
Fixed assets in accounts payable, accrued expenses and other current liabilities	$ 805	$ 3,474

Organization and Basis of Prese

Organization and Basis of Presentation	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Organization and Basis of Presentation	Organization and Basis of Presentation Adverum Biotechnologies, Inc. (the “Company” or “Adverum”) was incorporated in Delaware on July 17, 2006 and is headquartered in Redwood City, California. The Company is a clinical-stage gene therapy company targeting unmet medical needs in ocular and rare diseases. The Company develops gene therapy product candidates intended to provide durable efficacy by inducing sustained expression of a therapeutic protein. The Company’s core capabilities include novel vector discovery, preclinical and clinical development, and pre-commercial planning. In addition, the Company has in-house manufacturing expertise, specifically in scalable process development, assay development, and current Good Manufacturing Practices (“GMP”) quality control, and has leased a GMP commercial manufacturing facility to support its commercial plans for the Company’s lead product candidate, ADVM-022. On April 28, 2021, Adverum announced a Suspected Unexpected Serious Adverse Reaction (“SUSAR”) of hypotony (clinically-relevant decrease in ocular pressure), with panuveitis and loss of vision in the treated eye, in its INFINITY clinical trial evaluating ADVM-022 for the treatment of diabetic patients with macular edema. The Company has unmasked the study and is assessing and monitoring this patient and all patients treated with ADVM-022 and is working closely with investigators, the data monitoring committee (“DMC”), scientific advisory board, and healthcare authorities. The patient impacted by the SUSAR event is undergoing in-person assessments with leading retina specialists across the U.S. who are working with Adverum to gain an understanding of the causes of the SUSAR and to develop a treatment plan for the patient. In addition, all patients who have received ADVM-022 have been requested to see their treating physician for an evaluation, including ophthalmic and advanced imaging assessments to collect additional data. Adverum, working with its expert advisors, is conducting a thorough review of data from the ADVM-022 program, taking into account learnings from the SUSAR, and plans to report its findings as the analysis progresses. 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 $531.0 million as of March 31, 2021. The Company expects to incur losses and have negative net cash flows from operating activities as it engages in further research and development activities. As of March 31, 2021, the Company had cash, cash equivalents and short-term investments of $404.0 million, which the Company believes will be sufficient to fund its operations for at least twelve months from the date of issuance of these financial statements. Basis of Presentation —The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These unaudited condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three months ended March 31, 2021 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, 2020 is derived from the audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete consolidated financial statements. The full extent to which the novel coronavirus disease ("COVID-19") pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses and manufacturing, clinical trials and research and development costs, is dependent upon future developments that are highly uncertain at this time. 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, 2020 filed with the SEC.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Use of Estimates The accompanying condensed consolidated financial statements have been prepared in accordance with U.S. GAAP. The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the condensed consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other market-specific and relevant assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Recent Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-13, Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments (“ Topic 326 ”) and also issued subsequent amendments to the initial guidance: ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. The standard requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. Topic 326 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. Topic 326 will become effective for the Company on January 1, 2023. Early adoption is permitted. The Company is currently evaluating the impact of adopting Topic 326, but does not expect the effect of adoption to be material. In December 2019, the FASB issued Accounting Standards Update No. 2019-12, Income Taxes (" Topic 740" ): Simplifying the Accounting for Income Taxes ("ASU 2019-12"). The ASU simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The ASU also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This standard is effective for fiscal years beginning after December 15, 2020. The Company adopted this standard as of January 1, 2021 on a prospective basis in accordance with ASC 250, Accounting Changes and Error Corrections. Adoption of the new guidance had no significant impact on the Company's consolidated financial statements.

Fair Value Measurements and Fai

Fair Value Measurements and Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements and Fair Value of Financial Instruments	Fair Value Measurements and Fair Value of Financial Instruments The authoritative guidance on the fair value hierarchy for disclosure of fair value measurements is as follows: Level 1 : Quoted prices in active markets for identical assets or liabilities. Level 2 : Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 : Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The fair value of Level 1 securities is determined using quoted prices in active markets for identical assets. Level 1 securities consist of highly liquid money market funds. Financial assets and liabilities are considered Level 2 when their fair values are determined using inputs that are observable in the market or can be derived principally from or corroborated by observable market data such as pricing for similar securities, recently executed transactions, cash flow models with yield curves, and benchmark securities. In addition, Level 2 financial instruments are valued using comparisons to like-kind financial instruments and models that use readily observable market data as their basis. U.S. government and agency securities, commercial paper, and corporate bond are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. The following is a summary of the Company’s cash equivalents and short-term investments: March 31, 2021 Amortized Cost Basis Unrealized Gains Unrealized Estimated Fair Value (In thousands) Level 1: Money market funds $ 14,745 $ — $ — $ 14,745 Level 2: U.S. government and agency securities 258,245 116 — 258,361 Commercial paper 117,176 — (19) 117,157 Corporate bonds 10,183 — (8) 10,175 Total cash equivalents and short-term investments 400,349 116 (27) 400,438 Less: cash equivalents (41,843) — 1 (41,842) Total short-term investments $ 358,506 $ 116 $ (26) $ 358,596 December 31, 2020 Amortized Cost Basis Unrealized Gains Unrealized Estimated Fair Value (In thousands) Level 1: Money market funds $ 178 $ — $ — $ 178 Level 2: U.S. government and agency securities 328,583 121 (5) 328,699 Commercial paper 97,324 — (5) 97,319 Total cash equivalents and short-term investments 426,085 121 (10) 426,196 Less: cash equivalents (58,894) — 3 (58,891) Total short-term investments $ 367,191 $ 121 $ (7) $ 367,305 As of March 31, 2021, $7.0 million of marketable securities had remaining maturities between one

Revenue

Revenue	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue	Revenue On January 25, 2021, the Company and Lexeo Therapeutics, Inc (“Lexeo”) entered into a License Agreement pursuant to which the Company granted Lexeo an exclusive, worldwide, royalty-bearing license to certain of the Company's intellectual property to develop, manufacture, and commercialize a gene therapy product to treat cardiomyopathy due to Friedreich's ataxia. Upon execution of the agreement, Lexeo paid the Company a one-time, non-creditable and non-refundable upfront payment of $7.5 million. Under the terms of the agreement, the Company is eligible to receive development and commercial milestone payments and royalties on sales of Lexeo's licensed products once commercialized. Under Topic 606, the initial transaction price is the $7.5 million the Company received for the license granted. The arrangement provides for additional payments to the Company when certain development and commercial milestones are achieved. Because these milestone payments are not within the control of the Company and are not considered probable of being achieved until the events occur, the Company did not include them in the transaction price. The transaction price of $7.5 million was allocated to a combined performance obligation that was fulfilled on or before March 31, 2021. Therefore, the Company recognized the $7.5 million upfront payment as license revenue for the quarter ended March 31, 2021.

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	Leases Redwood City, CA Existing Lease The Company leases its office and laboratory space pursuant to an operating lease ("Existing Lease"), which commenced on September 1, 2018 and expires in February 2029. Upon the execution of the Existing Lease, the Company provided the landlord with a letter of credit in the amount of $1.0 million, which is classified as restricted cash under long term assets on the Company's condensed consolidated balance sheet. Rent expense for the three months ended March 31, 2021 and 2020 was $1.3 million, and $1.7 million, respectively, which includes variable lease costs for utilities, parking, maintenance, and real estate taxes. Variable lease expenses for the three months ended March 31, 2021 and 2020 were $0.4 million and $0.5 million, respectively. The undiscounted future non-cancellable lease payments under the Existing Lease as of March 31, 2021 is as follows: Year ending December 31, (In thousands) 2021 (remaining 9 months) $ 3,532 2022 4,846 2023 5,016 2024 5,191 2025 5,373 Thereafter 18,273 Total undiscounted lease payments 42,231 Less: Present value adjustment (12,025) Total $ 30,206 Redwood City, CA Expansion Lease On April 22, 2021, the Company entered into the first amendment to the Existing Lease pursuant to which the Company will lease an additional approximately 79,675 rentable square feet (the “Expansion Premises”) with a term of 10 years ("Expansion Lease"). The Expansion Premises will provide additional needed space at the Company's corporate headquarters. The Expansion Lease also extends the term of the Existing Lease to expire coterminously with the Expansion Lease, with an option to extend the Existing Lease and the Expansion Lease for a period of eight years. The Company plans to occupy the Expansion Premises in the second half of 2021. The monthly base rent for the Expansion Premises will start at $454,148 and will increase annually throughout the term of the Expansion Lease. In addition, the Company will pay the landlord certain operating expenses, property management fees and taxes related to the Expansion Premises on an annual basis. The Expansion Lease provides a total of tenant improvement allowances for up to $10.2 million. Upon the execution of the Expansion Lease, the Company provided the landlord with a letter of credit in the amount of $2.5 million, which will replace the letter of credit delivered in connection with the Existing Lease. North Carolina Lease On January 8, 2021, the Company entered into an operating lease agreement pursuant to which the Company will lease approximately 174,000 rentable square feet located at 14 TW Alexander Drive, Durham, North Carolina ("NC Premises"). The NC Premises will support the Company’s commercial manufacturing of its novel gene therapy candidates and is expected to be production-ready by the end of 2023. The lease term is 16.5 years beginning upon delivery of the Premises in April 2021 with two options to extend the lease term for a period of five years each. The Company has the right to make tenant improvements with a lease incentive allowance of up to $42.4 million. The rent payments begin in eighteen months after the lease commencement date. The lease agreement provides for an escalation of rent payment each year. In connection with the lease, the Company provided the landlord with a letter of credit in the amount of $2.8 million, which is classified as restricted cash under long term assets on the condensed consolidated balance sheet. Under Topic 842, the Company will measure and record right-of-use asset and operating lease liability for this long-term operating lease starting in the quarter when the lease commences. The table below summarizes the undiscounted future non-cancellable lease payments for the Expansion Premises and the NC Premises under the respective lease agreements. Year ending December 31, (In thousands) 2021 (remaining 9 months) $ — 2022 4,588 2023 11,484 2024 11,857 2025 12,242 Thereafter 150,841 Total undiscounted lease payments $ 191,012

Balance Sheet Components

Balance Sheet Components	3 Months Ended
	Mar. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	Balance Sheet Components Property and Equipment, Net Property and equipment, net consists of the following: March 31, 2021 December 31, 2020 (In thousands) Computer equipment and software $ 765 $ 599 Laboratory equipment 9,639 9,354 Furniture and fixtures 1,259 1,259 Leasehold improvements 24,702 24,631 Construction in progress 3,244 1,954 Total property and equipment 39,609 37,797 Less accumulated depreciation and amortization (11,230) (10,072) Property and equipment, net $ 28,379 $ 27,725 Depreciation and amortization expense related to property and equipment for the three months ended March 31, 2021 and 2020 was $1.2 million and $0.6 million, respectively. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: March 31, 2021 December 31, 2020 (In thousands) Employee compensation $ 5,644 $ 8,344 Accrued preclinical, clinical and process development costs 4,033 2,844 Accrued professional services 2,759 1,075 Other 919 1,325 Total accrued expenses and other current liabilities $ 13,355 $ 13,588

Equity Incentive Awards

Equity Incentive Awards	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Equity Incentive Awards	Equity Incentive Awards Stock Options The following table summarizes the Company’s option activity and related information: Number of Weighted- Balance at December 31, 2020 10,432 $ 11.65 Options granted 3,301 12.92 Options exercised (9) 5.86 Options forfeited (375) 9.00 Balance at March 31, 2021 13,349 $ 12.04 Exercisable as of March 31, 2021 4,559 $ 8.41 Restricted Stock Units (“RSUs”) The following table summarizes the Company’s RSUs activity and related information: Number of Units Weighted- Outstanding at December 31, 2020 540 $ 6.41 Granted 382 12.25 Vested and released (249) 5.20 Forfeited (1) 14.10 Outstanding at March 31, 2021 672 $ 10.16 Stock-Based Compensation Expense The following table presents, by operating expense, the Company’s stock-based compensation expense: Three Months Ended 2021 2020 (In thousands) Research and development $ 2,339 $ 1,248 General and administrative 4,885 2,161 Total stock-based compensation expense $ 7,224 $ 3,409 During the three months ended March 31, 2021, the Company recorded approximately $0.2 million of stock-based compensation expense as a result of the modification of the vesting and exercisability of stock awards associated with the departure of two of its executives.

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period. Diluted net loss per share is computed by giving effect to all potential dilutive common stock equivalents outstanding for the period using the treasury stock method. Outstanding stock options, RSUs, rights under the employee stock purchase plan (“ESPP”) and warrants are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. The following common stock equivalents outstanding at the end of the periods presented were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: March 31, 2021 March 31, 2020 (In thousands) Stock options 13,349 9,072 Restricted stock units 672 735 ESPP 86 45 Warrants to purchase common stock — 80 14,107 9,932

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation —The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and follow the requirements of the Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP can be condensed or omitted. These unaudited condensed consolidated financial statements have been prepared on the same basis as the Company’s annual consolidated financial statements and, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, which are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three months ended March 31, 2021 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, 2020 is derived from the audited consolidated financial statements at that date but does not include all of the information required by U.S. GAAP for complete consolidated financial statements. The full extent to which the novel coronavirus disease ("COVID-19") pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses and manufacturing, clinical trials and research and development costs, is dependent upon future developments that are highly uncertain at this time.
Use of Estimates	Use of Estimates The accompanying condensed consolidated financial statements have been prepared in accordance with U.S. GAAP. The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities and the reported amounts of expenses in the condensed consolidated financial statements and the accompanying notes. On an ongoing basis, management evaluates its estimates, including those related to clinical trial accruals, fair value of assets and liabilities, income taxes, and stock-based compensation. Management bases its estimates on historical experience and on various other
Recent Accounting Pronouncements	Recent Accounting Pronouncements In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") 2016-13, Financial Instruments – Credit Losses: Measurement of Credit Losses on Financial Instruments (“ Topic 326 ”) and also issued subsequent amendments to the initial guidance: ASU 2018-19, ASU 2019-04, ASU 2019-05, and ASU 2019-11. The standard requires that financial assets measured at amortized cost be presented at the net amount expected to be collected. The measurement of expected credit losses is based on historical experience, current conditions, and reasonable and supportable forecasts that affect collectability. Topic 326 also eliminates the concept of “other-than-temporary” impairment when evaluating available-for-sale debt securities and instead focuses on determining whether any impairment is a result of a credit loss or other factors. An entity will recognize an allowance for credit losses on available-for-sale debt securities rather than an other-than-temporary impairment that reduces the cost basis of the investment. Topic 326 will become effective for the Company on January 1, 2023. Early adoption is permitted. The Company is currently evaluating the impact of adopting Topic 326, but does not expect the effect of adoption to be material. In December 2019, the FASB issued Accounting Standards Update No. 2019-12, Income Taxes (" Topic 740" ): Simplifying the Accounting for Income Taxes ("ASU 2019-12"). The ASU simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The ASU also improve consistent application of and simplify GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This standard is effective for fiscal years beginning after December 15, 2020. The Company adopted this standard as of January 1, 2021 on a prospective basis in accordance with ASC 250, Accounting Changes and Error Corrections. Adoption of the new guidance had no significant impact on the Company's consolidated financial statements.

Fair Value Measurements and F_2

Fair Value Measurements and Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Summary of Cash Equivalents and Short-term Investments	The following is a summary of the Company’s cash equivalents and short-term investments: March 31, 2021 Amortized Cost Basis Unrealized Gains Unrealized Estimated Fair Value (In thousands) Level 1: Money market funds $ 14,745 $ — $ — $ 14,745 Level 2: U.S. government and agency securities 258,245 116 — 258,361 Commercial paper 117,176 — (19) 117,157 Corporate bonds 10,183 — (8) 10,175 Total cash equivalents and short-term investments 400,349 116 (27) 400,438 Less: cash equivalents (41,843) — 1 (41,842) Total short-term investments $ 358,506 $ 116 $ (26) $ 358,596 December 31, 2020 Amortized Cost Basis Unrealized Gains Unrealized Estimated Fair Value (In thousands) Level 1: Money market funds $ 178 $ — $ — $ 178 Level 2: U.S. government and agency securities 328,583 121 (5) 328,699 Commercial paper 97,324 — (5) 97,319 Total cash equivalents and short-term investments 426,085 121 (10) 426,196 Less: cash equivalents (58,894) — 3 (58,891) Total short-term investments $ 367,191 $ 121 $ (7) $ 367,305

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Schedule of Undiscounted Future Lease Payments under Operating Lease	The undiscounted future non-cancellable lease payments under the Existing Lease as of March 31, 2021 is as follows: Year ending December 31, (In thousands) 2021 (remaining 9 months) $ 3,532 2022 4,846 2023 5,016 2024 5,191 2025 5,373 Thereafter 18,273 Total undiscounted lease payments 42,231 Less: Present value adjustment (12,025) Total $ 30,206 The table below summarizes the undiscounted future non-cancellable lease payments for the Expansion Premises and the NC Premises under the respective lease agreements. Year ending December 31, (In thousands) 2021 (remaining 9 months) $ — 2022 4,588 2023 11,484 2024 11,857 2025 12,242 Thereafter 150,841 Total undiscounted lease payments $ 191,012

Balance Sheet Components (Table

Balance Sheet Components (Tables)	3 Months Ended
	Mar. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consists of the following: March 31, 2021 December 31, 2020 (In thousands) Computer equipment and software $ 765 $ 599 Laboratory equipment 9,639 9,354 Furniture and fixtures 1,259 1,259 Leasehold improvements 24,702 24,631 Construction in progress 3,244 1,954 Total property and equipment 39,609 37,797 Less accumulated depreciation and amortization (11,230) (10,072) Property and equipment, net $ 28,379 $ 27,725
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: March 31, 2021 December 31, 2020 (In thousands) Employee compensation $ 5,644 $ 8,344 Accrued preclinical, clinical and process development costs 4,033 2,844 Accrued professional services 2,759 1,075 Other 919 1,325 Total accrued expenses and other current liabilities $ 13,355 $ 13,588

Equity Incentive Awards (Tables

Equity Incentive Awards (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Summary of Stock Options Activity	The following table summarizes the Company’s option activity and related information: Number of Weighted- Balance at December 31, 2020 10,432 $ 11.65 Options granted 3,301 12.92 Options exercised (9) 5.86 Options forfeited (375) 9.00 Balance at March 31, 2021 13,349 $ 12.04 Exercisable as of March 31, 2021 4,559 $ 8.41
Summary of Restricted Stock Units Activity	The following table summarizes the Company’s RSUs activity and related information: Number of Units Weighted- Outstanding at December 31, 2020 540 $ 6.41 Granted 382 12.25 Vested and released (249) 5.20 Forfeited (1) 14.10 Outstanding at March 31, 2021 672 $ 10.16
Stock-Based Compensation Expense	The following table presents, by operating expense, the Company’s stock-based compensation expense: Three Months Ended 2021 2020 (In thousands) Research and development $ 2,339 $ 1,248 General and administrative 4,885 2,161 Total stock-based compensation expense $ 7,224 $ 3,409

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following common stock equivalents outstanding at the end of the periods presented were excluded from the calculation of diluted net loss per share for the periods indicated because including them would have had an anti-dilutive effect: March 31, 2021 March 31, 2020 (In thousands) Stock options 13,349 9,072 Restricted stock units 672 735 ESPP 86 45 Warrants to purchase common stock — 80 14,107 9,932

Organization and Basis of Pre_2

Organization and Basis of Presentation (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ 530,972	$ 502,536
Cash, cash equivalents, and short-term investments	$ 404,000

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Summary of Cash Equivalents and Short-term Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 358,506	$ 367,191
Unrealized Gains	116	121
Unrealized Losses	(26)	(7)
Estimated Fair Value	358,596	367,305
Less: Cash Equivalents, Amortized Cost Basis	(41,843)	(58,894)
Less: Cash equivalents, unrealized gains	0	0
Less: Cash equivalents, unrealized losses	1	3
Less: Cash equivalents, estimated fair value	(41,842)	(58,891)
Corporate Bonds | Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	10,183
Unrealized Gains	0
Unrealized Losses	(8)
Estimated Fair Value	10,175
Total Cash Equivalents and Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	400,349	426,085
Unrealized Gains	116	121
Unrealized Losses	(27)	(10)
Estimated Fair Value	400,438	426,196
Money market funds | Level 1
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	14,745	178
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	14,745	178
U.S. government and agency securities | Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	258,245	328,583
Unrealized Gains	116	121
Unrealized Losses	0	(5)
Estimated Fair Value	258,361	328,699
Commercial paper | Level 2
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	117,176	97,324
Unrealized Gains	0	0
Unrealized Losses	(19)	(5)
Estimated Fair Value	$ 117,157	$ 97,319

Fair Value Measurements and F_4

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Detail)	Mar. 31, 2021USD ($)
Debt Securities, Available-for-sale [Line Items]
Marketable securities	$ 7,000,000
Other than temporary impaired investments	$ 0
Minimum
Debt Securities, Available-for-sale [Line Items]
Marketable securities term	1 year
Maximum
Debt Securities, Available-for-sale [Line Items]
Marketable securities term	2 years

Revenue (Detail)

Revenue (Detail) - USD ($) $ in Thousands	Jan. 25, 2021	Mar. 31, 2021	Mar. 31, 2020
Revenue from Contract with Customer [Abstract]
License revenue	$ 7,500	$ 7,500	$ 0

Leases - Additional Information

Leases - Additional Information (Detail)	Apr. 22, 2021USD ($)ft²	Jan. 08, 2021USD ($)ft²leaseExtensionOption	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)
Lessee, Lease, Description [Line Items]
Restricted cash					$ 999,000
Office Building And Laboratory
Lessee, Lease, Description [Line Items]
Restricted cash			$ 1,000,000
Rent expense			1,300,000	$ 1,700,000
Variable lease costs			400,000	$ 500,000
Building | Subsequent Event
Lessee, Lease, Description [Line Items]
Restricted cash	$ 2,500,000
Rent expense	$ 454,148
Area of real estate property | ft²	79,675
Lease term	10 years
Lease renewal term	8 years
Leasehold improvement allowance	$ 10,200,000
Manufacturing Facility
Lessee, Lease, Description [Line Items]
Restricted cash			$ 2,800,000
Area of real estate property | ft²		174,000
Term of contract		16 years 6 months
Number of renewal contracts | leaseExtensionOption		2
Renewal term		5 years
Tenant improvement allowance		$ 42,400,000

Leases - Schedule of Undiscount

Leases - Schedule of Undiscounted Future Lease Payments under Operating Lease (Detail) $ in Thousands	Mar. 31, 2021USD ($)
Office Building And Laboratory
Lessee, Lease, Description [Line Items]
2021 (remaining 9 months)	$ 3,532
2022	4,846
2023	5,016
2024	5,191
2025	5,373
Thereafter	18,273
Total undiscounted lease payments	42,231
Less: Present value adjustment	12,025
Total	30,206
Manufacturing Facility And Building
Lessee, Lease, Description [Line Items]
2021 (remaining 9 months)	0
2022	4,588
2023	11,484
2024	11,857
2025	12,242
Thereafter	150,841
Total undiscounted lease payments	$ 191,012

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 39,609	$ 37,797
Less accumulated depreciation and amortization	(11,230)	(10,072)
Property and equipment, net	28,379	27,725
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	765	599
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	9,639	9,354
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	1,259	1,259
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	24,702	24,631
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,244	$ 1,954

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Depreciation and amortization expense	$ 1,166	$ 599

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Employee compensation	$ 5,644	$ 8,344
Accrued preclinical, clinical and process development costs	4,033	2,844
Accrued professional services	2,759	1,075
Other	919	1,325
Total accrued expenses and other current liabilities	$ 13,355	$ 13,588

Equity Incentive Awards - Summa

Equity Incentive Awards - Summary of Stock Options Activity (Detail) shares in Thousands	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Options Outstanding [Roll Forward]
Beginning balance (in shares) | shares	10,432
Options granted (in shares) | shares	3,301
Options exercised (in shares) | shares	(9)
Options forfeited (in shares) | shares	(375)
Ending balance (in shares) | shares	13,349
Exercisable (in shares) | shares	4,559
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance (in USD per share) | $ / shares	$ 11.65
Options granted (in USD per share) | $ / shares	12.92
Options exercised (in USD per share) | $ / shares	5.86
Options forfeited (in USD per share) | $ / shares	9
Ending balance (in USD per share) | $ / shares	12.04
Exercisable (in USD per share) | $ / shares	$ 8.41

Equity Incentive Awards - Sum_2

Equity Incentive Awards - Summary of Restricted Stock Units Activity (Detail) - Restricted stock units shares in Thousands	3 Months Ended
	Mar. 31, 2021$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance (in shares) | shares	540
Granted (in shares) | shares	382
Vested and released (in shares) | shares	(249)
Forfeited (in shares) | shares	(1)
Ending balance (in shares) | shares	672
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance (in USD per share) | $ / shares	$ 6.41
Granted (in USD per share) | $ / shares	12.25
Vested and released (in USD per share) | $ / shares	5.20
Forfeited (in USD per share) | $ / shares	14.10
Ending balance (in USD per share) | $ / shares	$ 10.16

Equity Incentive Awards - Stock

Equity Incentive Awards - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 7,224	$ 3,409
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	2,339	1,248
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 4,885	$ 2,161

Equity Incentive Awards - Addit

Equity Incentive Awards - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)grantee
Equity [Abstract]
Stock-based compensation expense as a result of modification | $	$ 0.2
Stock-based compensation expense, number of grantees affected | grantee	2

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Common Stock Equivalents Outstanding (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	14,107	9,932
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	13,349	9,072
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	672	735
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	86	45
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from net loss per share (in shares)	0	80

Uncategorized Items - advm-2021

Label	Element	Value
Restricted Cash	us-gaap_RestrictedCash	$ 3,780,000
Restricted Cash	us-gaap_RestrictedCash	$ 999,000