Adverum Biotechnologies (ADVM) 10-K 18 Mar 24 2023 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Mar. 08, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
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	100 Cardinal Way
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, par value $0.0001 per share
Trading Symbol	ADVM
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Document Financial Statement Error Correction	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 151.8
Entity Common Stock, Shares Outstanding		207,549,152
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Central Index Key	0001501756

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2023
Audit Information [Abstract]
Auditor Name	Ernst & Young LLP
Auditor Firm ID	42
Auditor Location	San Francisco, California

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 75,000	$ 68,431
Short-term investments	21,526	117,158
Prepaid expenses and other current assets	6,247	5,006
Total current assets	102,773	190,595
Operating lease right-of-use assets	52,266	78,934
Property and equipment, net	14,764	34,927
Restricted cash	1,976	2,503
Deposit and other long-term assets	1,231	1,413
Total assets	173,010	308,372
Current liabilities:
Accounts payable	1,921	2,238
Accrued expenses and other current liabilities	12,584	16,767
Lease liability, current portion	10,409	13,241
Total current liabilities	24,914	32,246
Long-term liabilities:
Lease liability, net of current portion	64,627	93,561
Other non-current liabilities	0	1,047
Total liabilities	89,541	126,854
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.0001 par value, 5,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.0001 par value, 300,000 shares authorized at December 31, 2023: 101,433 and 100,117 shares issued and outstanding at December 31, 2023 and 2022, respectively	10	10
Additional paid-in capital	1,003,709	985,651
Accumulated other comprehensive loss	(473)	(1,531)
Accumulated deficit	(919,777)	(802,612)
Total stockholders’ equity	83,469	181,518
Total liabilities and stockholders’ equity	$ 173,010	$ 308,372

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	101,433,000	100,117,000
Common stock, shares outstanding (in shares)	101,433,000	100,117,000

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Statement [Abstract]
License revenue	$ 3,600	$ 0
Operating expenses:
Research and development	77,676	99,277
General and administrative	49,915	57,858
Total operating expenses	127,591	157,135
Operating loss	(123,991)	(157,135)
Other income, net	5,748	2,673
Net loss before income taxes	(118,243)	(154,462)
Income tax benefit (provision)	1,078	(74)
Net loss	(117,165)	(154,536)
Other comprehensive loss:
Net unrealized gain (loss) on marketable securities	1,057	(788)
Foreign currency translation adjustment	1	(29)
Comprehensive loss	$ (116,107)	$ (155,353)
Net loss per share - basic (in USD per share)	$ (1.16)	$ (1.56)
Net loss per share - diluted (in USD per share)	$ (1.16)	$ (1.56)
Weighted-average common shares outstanding - basic (in shares)	100,824	99,251
Weighted-average common shares outstanding - diluted (in shares)	100,824	99,251

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2021		98,381
Beginning balance at Dec. 31, 2021	$ 316,185	$ 10	$ 964,965	$ (714)	$ (648,076)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	20,079		20,079
Common stock issued upon exercise of stock options, shares (in shares)		15
Common stock issued upon exercise of stock options	3		3
Common stock issued under employee stock purchase plan (in shares)		886
Common stock issued under employee stock purchase plan	604		604
Common stock issued upon release of restricted stock units (in shares)		835
Net unrealized loss (gain) on marketable securities	(788)			(788)
Foreign currency translation adjustment	(29)			(29)
Net loss	$ (154,536)				(154,536)
Ending balance (in shares) at Dec. 31, 2022	100,117	100,117
Ending balance at Dec. 31, 2022	$ 181,518	$ 10	985,651	(1,531)	(802,612)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense	$ 17,569		17,569
Common stock issued upon exercise of stock options, shares (in shares)	1	1
Common stock issued upon exercise of stock options	$ 1		1
Common stock issued under employee stock purchase plan (in shares)		824
Common stock issued under employee stock purchase plan	488		488
Common stock issued upon release of restricted stock units (in shares)		491
Net unrealized loss (gain) on marketable securities	1,057			1,057
Foreign currency translation adjustment	1			1
Net loss	$ (117,165)				(117,165)
Ending balance (in shares) at Dec. 31, 2023	101,433	101,433
Ending balance at Dec. 31, 2023	$ 83,469	$ 10	$ 1,003,709	$ (473)	$ (919,777)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net loss	$ (117,165)	$ (154,536)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	5,644	6,528
Stock-based compensation expense	17,569	20,079
Net accretion of discount on marketable securities, net	(1,935)	(880)
Non-cash lease expense	13,027	4,040
Loss on disposal of property and equipment	50	122
Impairment of long-lived assets	224	2,124
Other	1	(1,417)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	298	1,653
Deposit and other long-term assets and deferred rent receivable	182	(394)
Accounts payable	(369)	845
Accrued expenses and other liabilities	(5,206)	138
Lease liability	(3,222)	13,607
Net cash used in operating activities	(90,902)	(108,091)
Cash flows from investing activities:
Purchases of marketable securities	(36,718)	(104,363)
Maturities of marketable securities	134,401	257,899
Purchases of property and equipment	(808)	(11,816)
Net cash provided by investing activities	96,875	141,720
Cash flows from financing activities:
Payment of deferred offering costs	(420)	0
Proceeds from issuance of common stock pursuant to option exercises	1	3
Proceeds from employee stock purchase plan	488	604
Net cash provided by financing activities	69	607
Net increase in cash, cash equivalents and restricted cash	6,042	34,236
Cash, cash equivalents and restricted cash at beginning of period	70,934	36,698
Cash, cash equivalents and restricted cash at end of period	76,976	70,934
Cash and cash equivalents	75,000	68,431
Restricted cash	1,976	2,503
Cash, cash equivalents and restricted cash at end of period	76,976	70,934
Supplemental schedule of noncash investing information
Non-cash settlement of operating lease liability	14,903	0
Remeasurement of operating lease right-of-use assets and liabilities	13,711	2,842
Fixed assets in accounts payable and current liabilities	$ 91	$ 64

Description of the Business

Description of the Business	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of the Business	Description of the Business Nature of the Business —Adverum Biotechnologies, Inc. (the “Company” or “Adverum”) was incorporated in Delaware on July 17, 2006 and is headquartered in Redwood City, California. The Company aims to establish gene therapy as a new standard of care for highly prevalent ocular diseases. The Company develops gene therapy product candidates intended to provide durable efficacy by inducing sustained expression of a therapeutic protein. 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 $919.8 million as of December 31, 2023. 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 December 31, 2023, the Company had cash, cash equivalents and short-term investments of $96.5 million, which the Company believes will be sufficient to fund its operations into late 2025.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation —The Company’s consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. Use of Estimates —The preparation of financial statements in conformity with U.S. GAAP requires management to make judgements, estimates and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses, and related disclosures. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. Accounting estimates and judgements are inherently uncertain, and the actual results could differ from these estimates Foreign Currency —Assets and liabilities of non-U.S. subsidiaries that operate in a local currency environment, where the local currency is the functional currency, are translated to U.S. dollars at exchange rates in effect at the balance sheet date, with the resulting translation adjustments directly recorded to a separate component of accumulated other comprehensive loss. Upon sale or upon complete or substantially complete liquidation of an investment in a foreign entity, the amount attributable to that entity and accumulated in the translation adjustment component of equity is removed from the separate component of equity and reported as part of the gain or loss on sale or liquidation of the investment for the period during which the sale or liquidation occurs. Income and expense accounts are translated at average exchange rates for the period. Transactions which are not in the functional currency of the entity are remeasured into the functional currency and gains or losses resulting from the remeasurement recorded in other income, net. Cash and Cash Equivalents —The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents. Cash and cash equivalents include cash held in banks, money market accounts and highly liquid debt securities. Cash equivalents are stated at fair value. Restricted Cash —Restricted cash primarily consists of cash collateral to letter of credit provided to the landlord in relation to a lease agreement. See Note 5, Leases for additional information. Short-Term Investments —All short-term investments in debt securities have been classified as “available for sale” and are carried at fair value. Unrealized gains and losses, net of any related tax effects, are excluded from earnings and are included in other comprehensive loss and reported as a separate component of stockholders’ equity until realized. The cost of securities sold is based on the specific-identification method. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Interest on short-term investments is included in other income, net in the Company’s consolidated statements of operations and comprehensive loss. In accordance with the Company’s investment policy, management invests to diversify credit risk and only invests in securities with high credit quality, including U.S. government securities. The Company assesses available-for-sale debt securities on a quarterly basis to see whether any unrealized loss is due to credit-related factors. Factors considered in determining whether an impairment is credit-related include the extent to which the investment’s fair value is less than its cost basis, declines in published credit ratings, changes in interest rates, and any other adverse factors related to the security. If it is determined that a credit-related impairment exists, the Company will measure the credit loss based on a discounted cash flow model. Credit-related impairments on available-for-sale debt securities are recognized as an allowance for credit losses with a corresponding adjustment to other income, net in the Company’s consolidated statement of operations. The unrealized loss position that is not credit-related is recorded, net of any related tax effects, in other comprehensive income until realized. There were no credit-related losses recognized for the periods presented. Accrued Interest Receivable —Accrued interest receivable related to the Company’s available-for-sale debt securities is presented within prepaid expenses and other current assets on the Company’s consolidated balance sheets. The Company has elected to exclude accrued interest receivable from both the fair value and the amortized cost basis of available-for-sale debt securities for the purposes of identifying and measuring any impairment. The Company writes off accrued interest receivable once it has determined that the asset is not realizable. Any write offs of accrued interest receivable are recorded by reversing interest income, recognizing credit loss expense, or a combination of both. To date, the Company has not written off any accrued interest receivables associated with its available-for-sale debt securities. Segment Reporting —The Company operates and manages its business as one reporting and operating segment, which is the business of developing and commercializing gene therapeutics. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. Concentrations of Credit Risk and Other Uncertainties —Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents and short-term investments. Risks associated with cash, cash equivalents, short-term investments are mitigated by the Company’s investment policy, which limits the Company’s investing to securities having specified credit ratings. Management believes that the Company is not exposed to significant credit risk. The Company is subject to certain risks and uncertainties, including, but not limited to changes in any of the following areas that the Company believes could have a material adverse effect on future financial position or results of operations: the ability to obtain future financing; regulatory approval and market acceptance of, and reimbursement for, the Company’s product candidates; performance of third-party clinical research organizations and manufacturers; development of sales channels; protection of intellectual property; litigation or claims against the Company based on intellectual property, patent, product, regulatory or other factors; and the Company’s ability to attract and retain employees necessary to support growth. Property and Equipment —Property and equipment are recorded at cost, net of accumulated depreciation and amortization. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets, generally three Impairment of Long-Lived Assets —Long-lived assets, including property and equipment and finite-lived intangible assets, are reviewed for impairment whenever facts or circumstances either internally or externally may indicate that the carrying value of an asset may not be recoverable. If there is an indication of impairment, the Company tests for recoverability by comparing the estimated undiscounted future cash flows expected to result from the use of the asset to the carrying amount of the asset or asset group. If the asset or asset group is determined to be impaired, any excess of the carrying value of the asset or asset group over its estimated fair value is recognized as an impairment loss The Company recorded within research and development expense in the consolidated statements of operations and comprehensive loss impairment charges of $0.2 million and $2.1 million for the years ended December 31, 2023 and 2022, respectively. See Note 3, Balance Sheet Components for additional information. Leases — For long-term operating leases, the Company recognizes a right-of-use asset and a lease liability on the Company's consolidated balance sheets. The Company determines if an arrangement contains a lease and the classification of the lease at inception. An arrangement contains a lease if there is an identified asset and if the Company controls the use of the identified asset throughout the period of use. The lease liability is determined as the present value of future lease payments reduced by lease incentives, if any, using an estimated rate of interest that it would pay to borrow equivalent funds on a collateralized basis at the lease commencement date or modification date, as applicable. In order to determine the incremental borrowing rate, the Company determines its credit rating, adjusts the credit rating for the nature of the collateral, and benchmarks the borrowing rate against observable yields on comparable securities with a similar term. The incremental borrowing rate, the ROU asset and the lease liability are reevaluated upon a lease modification. It bases the ROU asset on the lease liability adjusted for any prepaid or deferred rent. The Company elected to combine lease and non-lease components for all underlying assets groups. The Company determines the lease term at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. For short term leases, the Company does not recognize a right-of-use asset and lease liability and recognizes the lease expense over the term of the lease on a straight-line basis. Rent expense for operating leases is recognized on a straight-line basis over the lease term and is included in operating expenses on the statements of operations and comprehensive loss. The variable lease payments primarily consist of common area maintenance and other operating costs. Sublease income for operating leases is classified as a reduction of rent expense in operating expenses. The difference between sublease income recorded and cash received from the subtenant accrues as a deferred rent receivable. During the year ended December 31, 2022, the Company reassessed the probability of collection of the deferred rent receivable from the subtenant over the remaining term of a sublease. The Company assessed the collectability to be less than probable and recognized an adjustment to eliminate the deferred rent receivable as a current period adjustment to sublease income, resulting in an increase in general and administrative expenses during the year ended December 31, 2022. Revenue Recognition —The Company has primarily generated revenue through license, research and collaboration arrangements with its strategic partners. The Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, Revenue from Contracts with Customers, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Research and Development Expenses —Research and development expenses are charged to expense as incurred. Research and development expenses include primarily personnel-related costs, stock-based compensation expense, laboratory supplies, consulting costs, external contract research and development expenses, including expenses incurred under agreements with contract research organizations (“CROs”), the cost of acquiring, developing and manufacturing clinical trial materials, and overhead expenses, such as rent, equipment depreciation, insurance and utilities. Advance payments for goods or services for future research and development activities are deferred and expensed as the goods are delivered or the related services are performed. The Company estimates research and clinical trial expenses based on the services performed pursuant to contracts with research institutions and clinical research organizations that conduct and manage nonclinical studies and clinical trials on the Company’s behalf. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. These estimates are based on communications with the third-party service providers and the Company’s estimates of accrued expenses and on information available at each balance sheet date. If the actual timing of the performance of services or the level of effort varies from the estimate, the Company adjusts the accrual accordingly. Fair Value Measurements —Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The carrying amounts of the Company’s financial instruments, including cash equivalents approximate their fair values due to their short-term maturities. See Note 3, Fair Value Measurements for the methodologies and assumptions used in valuing financial instruments. Stock-based Compensation Expense —Stock-based compensation expense related to stock awards to employees is measured at fair value of the award on the date of the grant. The Company estimates the grant-date fair value, and the resulting stock-based compensation expense, using the Black-Scholes valuation model for stock options and employee stock purchase and using intrinsic value, which is the closing price of its common stock on the date of the grant, for restricted stock units (“RSUs”) and performance stock units (“PSUs”). Expense recognition of PSU and performance-based options commences when the associated performance-based criteria are determined to be probable. The fair value of the award that is ultimately expected to vest is recognized as expense on a straight-line basis over the requisite service period, which is generally the vesting period. The Black-Scholes valuation model requires the use of following assumptions: Expected Term —The expected term assumption represents the period that the Company’s stock-based awards are expected to be outstanding and is determined using the simplified method. Expected Volatility —Expected volatility is based on the Company’s historical stock price volatility. Expected Dividend —The Black-Scholes valuation model calls for a single expected dividend yield as an input. The Company has never paid dividends and has no plans to pay dividends. Risk-Free Interest Rate —The risk-free interest rate is based on the U.S. Treasury zero-coupon issues in effect at the time of grant for periods corresponding with the expected term of option. Income Taxes —The Company accounts for income taxes using the asset and liability method. The Company records deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. In evaluating the ability to recover its deferred income tax assets, the Company considers all available positive and negative evidence, including its operating results, ongoing tax planning and forecasts of future taxable income on a jurisdiction-by-jurisdiction basis. In the event the Company determines that it would be able to realize its deferred income tax assets in the future in excess of their net recorded amount, it would make an adjustment to the valuation allowance that would reduce the provision for income taxes. Conversely, in the event that all or part of the net deferred tax assets are determined not to be realizable in the future, an adjustment to the valuation allowance would be charged to earnings in the period when such determination is made. As of December 31, 2023 and 2022, the Company has recorded a full valuation allowance on its deferred tax assets. Tax benefits related to uncertain tax positions are recognized when it is more likely than not that a tax position will be sustained upon examination. Interest and penalties related to unrecognized tax liabilities are included within the provision for income tax. Comprehensive Loss —Comprehensive loss comprises net loss and other comprehensive loss. Other comprehensive loss consists of foreign currency translation adjustments and unrealized gain or loss on marketable securities. Basic and Diluted 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, and employee stock purchase plan (“ESPP”) 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. Recently Adopted 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. 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. The Company adopted ASU 2016-13 on January 1, 2023, using the modified retrospective approach. The adoption of ASU 2016-13 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	12 Months Ended
	Dec. 31, 2023
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 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 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 bonds 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 (in thousands): December 31, 2023 Amortized Unrealized Unrealized Estimated Level 1 Money market funds $ 10,204 $ — $ — $ 10,204 Level 2 Commercial paper 64,693 — (35) 64,658 U.S. government and agency securities 17,616 4 (17) 17,603 Total cash equivalents and short-term investments 92,513 4 (52) 92,465 Less: Cash equivalents (70,972) — 33 (70,939) Total short-term investments $ 21,541 $ 4 $ (19) $ 21,526 December 31, 2022 Amortized Unrealized Unrealized Estimated Level 1 Money market funds $ 10,235 $ — $ — $ 10,235 Level 2 U.S. government and agency securities 59,487 — (824) 58,663 Commercial paper 102,722 — (246) 102,476 Corporate bonds 2,059 — (35) 2,024 Total cash equivalents and short-term investments 174,503 — (1,105) 173,398 Less: Cash equivalents (56,256) — 16 (56,240) Total short-term investments $ 118,247 $ — $ (1,089) $ 117,158 As the Company may sell these securities at any time for use in current operations even if the securities have not yet reached maturity, all marketable securities are classified as current assets in the Company’s consolidated balance sheets. As of December 31, 2023, all marketable securities had a remaining maturity of less than one year. The Company held 19 debt securities in an unrealized loss position with an aggregate fair value at December 31, 2023 of $71.3 million. These are highly liquid funds with high credit ratings with final maturity of less than one year from the balance sheet date. There were no individual securities that were in a significant unrealized loss position as of December 31, 2023 and 2022. The Company has not recorded an allowance for credit losses as of December 31, 2023 and 2022 related to these securities. The accrued interest receivable on available-for-sale marketable securities was immaterial at December 31, 2023 or 2022. The Company regularly reviews the securities in an unrealized loss position and evaluates the current expected credit loss by considering factors such as historical experience, market data, issuer-specific factors, and current economic conditions. The Company does not intend to sell the investments and it is not more likely than not that the Company will be required to sell the investments before recovery of their amortized cost bases. The Company has not recorded any impairment charges on available-for-sale securities. During the years ended December 31, 2023 and 2022, the Company performed an impairment test to measure certain laboratory equipment at fair value. The assets are measured at fair value using Level 3 inputs on a non-recurring basis as a result of the occurrence of certain triggering events indicating the carrying value of the assets may not be recoverable. The analysis was based on a market price in a secondary market place for similar laboratory equipment. The fair value of the assets was lower than the carrying value and as such impairment charges of $0.2 million and $2.1 million were recognized for the years ended December 31, 2023 and 2022, respectively. The assets indicated as impaired were written down to their estimated fair value. The fair value of the assets was nil and $0.2 million at December 31, 2023 and 2022.

Revenue

Revenue	12 Months Ended
	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Revenue	Revenue Lexeo 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 additional payments upon the achievement of certain milestones. Additionally, the Company will receive royalty payments on net sales subject to a cap and reductions based on patent expiry, anti-stacking, and a defined royalty floor percentage. In February 2023, Lexeo notified the Company that it had achieved the first development milestone; accordingly, the Company received and recognized $3.5 million of license revenue during the year ended December 31, 2023.

Leases

Leases	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Leases	Leases Redwood City The Company has a lease for a facility in Redwood City, which provided a total of tenant improvement allowances of $6.8 million. Related to this lease, the Company provided the landlord with a letter of credit in the amount of $2.7 million. The Redwood City lease expires in December 2031, with an option to extend for a period of eight years. Prior to September 30, 2023, the Company had two facility leases in Redwood City with the same landlord (the “Redwood City Premises”). In March 2023, the Company entered into an amendment to accelerate the lease expiration of one of its Redwood City Premises from December 31, 2031 to September 30, 2023. Concurrently, the Company entered into an agreement to increase the tenant improvement allowance towards the second of its Redwood City Premises. The Company accounted for this amendment as a lease modification in accordance with ASC 842-10-25-11(d). As a result of the modification the Company revalued the lease liability based on the new and remaining lease terms, which resulted in a reduction to the lease liability with a corresponding reduction of the right-of-use asset of $8.3 million. The estimated value of non-cash consideration, composed primarily of leasehold improvements and furniture and fixtures, was $14.9 million, which was fully amortized as of September 30, 2023. There was no charge recognized in the consolidated statement of operations. In October 2023, the Company entered into an amendment to the letter of credit which reduced the amount to $1.9 million, which is classified as restricted cash under long-term assets on the Company's consolidated balance sheets. North Carolina On January 8, 2021, the Company entered into an operating lease agreement for a building in North Carolina (“NC Premises”). The lease commenced in April 2021, when the Company obtained control of the NC Premises, and the lease term expires in October 2037 with two options to extend the lease term for a period of five years each. On October 26, 2021, the Company entered into a sublease agreement with a subtenant for the NC Premises through October 2037, the remainder of the lease term, and concurrently changed the lease payment terms of the head lease. In addition, the remainder of the tenant improvement allowance under the original lease of approximately $22.7 million was transferred to the subtenant. This change in the Company’s payment terms with the landlord at the time of the sublease was considered to be a lease modification and the Company remeasured the lease liability and right-of-use asset on the modification date, with no amounts recognized in the consolidated statement of operations. The base annual rental rates, payment schedules and amounts under the sublease agreement are substantially the same as the original payment terms by Adverum to the landlord. On April 3, 2023, the Company entered into an amendment of the lease of its NC Premises with the landlord and subtenant. Under this amendment, the parties agreed to substantially reduce the total tenant improvement allowance in exchange for lower monthly rent. The Company accounted for this amendment as a lease modification in accordance with ASC 842-10-25-11(d). The Company remeasured the lease liability, resulting in a reduction to the lease liability with a corresponding reduction of the right-of-use asset of $5.7 million in the quarter ended June 30, 2023. There was no charge recognized in the consolidated statement of operations. During the year ended December 31, 2022, management reassessed the probability of collection of the deferred rent receivable from the subtenant over the remaining term of a sublease. Management assessed the collectability to be less than probable and the Company recognized an adjustment to eliminate the deferred rent receivable as a current period adjustment to sublease income, resulting in an increase in general and administrative expenses during the year ended December 31, 2022. The deferred rent receivable was zero as of December 31, 2023 and 2022. As of December 31, 2023, the weighted-average remaining lease term was 11.6 years for the Company's leases and the weighted-average Incremental Borrowing Rate (“IBR”) was 11.7%. As of December 31, 2022, the weighted-average remaining lease term was 10.2 years for the Company's leases and the weighted-average IBR was 9.9%. The following table summarizes the undiscounted future non-cancellable lease payments under the lease agreements as of December 31, 2023 (in thousands): December 31, Operating Leases Sublease Payment Receivable 2024 $ 11,086 $ 5,248 2025 11,448 5,405 2026 11,821 5,568 2027 12,207 5,735 2028 12,606 5,907 Thereafter 82,047 60,509 Total undiscounted lease payments $ 141,215 $ 88,372 Less: Imputed Interest (66,179) Total $ 75,036 Rent expense for the years ended December 31, 2023, and 2022 was $25.3 million and $17.2 million, respectively. Included in rent expense for the years ended December 31, 2023, and 2022 were variable lease costs for utilities, parking, maintenance, and real estate taxes of $2.4 million and $2.3 million, respectively. Cash paid for amounts included in the measurement of lease liabilities for the twelve months ended December 31, 2023 and 2022 was $12.8 million and $6.0 million, respectively. Sublease income was $5.3 million and $(0.3) million for the years ended December 31, 2023 and 2022, respectively, which was classified in general and administrative expense.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Components	Balance Sheet Components Property and Equipment, Net Property and equipment, net consisted of the following: December 31, 2023 2022 (In thousands) Laboratory equipment $ 14,638 $ 14,382 Leasehold improvements 13,586 34,336 Computer equipment and software 868 1,325 Furniture and fixtures — 868 Construction in progress 184 1,010 Total property and equipment 29,276 51,921 Less accumulated depreciation and amortization (14,512) (16,994) Property and equipment, net $ 14,764 $ 34,927 Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: December 31, 2023 2022 (In thousands) Employee compensation $ 8,040 $ 8,710 Accrued nonclinical, clinical and process development costs 3,367 6,854 Accrued professional fees 351 532 State income tax payable 101 254 Other 725 417 Total accrued expenses and other current liabilities $ 12,584 $ 16,767

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies License Agreements The Company is a party to various agreements, principally relating to licensed technology that requires future payments relating to milestones or royalties on future sales of specified products. During the year ended December 31, 2023, the Company recognized $3.5 million of license revenue during the year ended December 31, 2023 for the first development milestone in the Lexeo License Agreement. See Note 4, Revenue, for additional information. No milestones were achieved during the year ended December 31, 2022 related to any of the Company's agreements. Because achievement of these milestones is not fixed and determinable, such amounts have not been included on the Company’s consolidated statements of operations and comprehensive loss. Legal Proceedings On November 22, 2022, Lyudmila Pazyuk (“Plaintiff”) filed a derivative complaint (Pazyuk v. Machado et al. C.A. No. 2022-1062-MTZ) (the “Action”) in the Delaware Court of Chancery (the “Court”) on behalf of Adverum against Adverum’s nine current directors and four former directors (the “Individual Defendants”). The Action asserts claims against the Individual Defendants for allegedly awarding the Directors excessive compensation. The Individual Defendants have denied, and continue to deny, any and all allegations of wrongdoing or liability asserted in the Action. Nonetheless, solely to eliminate the uncertainty, distraction, disruption, burden, risk and expense of further litigation, the Individual Defendants entered into a Stipulation and Agreement of Settlement, Compromise and Release (the “Stipulation”) on January 24, 2024. Pursuant to the terms of the Stipulation, the Defendants have agreed to implement and maintain certain changes to Adverum’s director compensation policies and practices. If approved by the Court, Adverum will also be responsible for the payment of the plaintiff’s attorneys’ fees of up to $0.6 million. The proposed settlement, as set forth in the Stipulation, is subject to final approval by the Court. If approved, the proposed settlement will (i) fully resolve the Action by dismissing all asserted claims with prejudice and (ii) release all claims related to the allegations in the Action. On January 31, 2024, the Court entered a

Stock Plans

Stock Plans	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Stock Plans	Stock Plans On December 26, 2006, the Company adopted the 2006 Equity Incentive Plan, which was amended by the board of directors on November 15, 2012 (the “2006 Plan”). The 2006 Plan allowed for the granting of incentive stock options (“ISOs”) and non-qualified stock options (“NSOs”) to the employees, members of the board of directors and consultants of the Company. ISOs were granted only to the Company’s employees, including officers and directors who are also employees. NSOs were granted to employees and consultants. In July 2014, the Company’s board of directors and its stockholders approved the establishment of the 2014 Equity Incentive Award Plan (the “2014 Plan”). Options may no longer be issued under the 2006 Plan after July 30, 2014. In addition, the 2014 Plan provides for annual increases in the number of shares available for issuance thereunder on the first business day of each fiscal year, beginning with the year ended December 31, 2015, equal to four percent (4%) of the number of shares of the Company’s common stock outstanding as of such date or a lesser number of shares as determined by the Company’s board of directors. In October 2017, the Company adopted the 2017 Inducement Plan (the “Inducement Plan”). The Company reserved 600,000 shares for issuance pursuant to stock options and RSUs under the Inducement Plan. The only persons eligible to receive grants of stock options and RSUs under the Inducement Plan are individuals who satisfy the standards for inducement grants under Nasdaq guidance, 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. The 2006 Plan, 2014 Plan and Inducement Plan are referred to collectively as the Plans. As of December 31, 2023, a total of 41,905,487 shares of common stock were reserved for issuance and 3,158,755 shares were available for future grants under the Plans. Stock Options Stock options under the 2014 Plan and the Inducement Plan may be granted for periods of up to 10 years and at prices no less than 100% of the estimated fair value of the shares on the date of grant as determined by the board of directors, provided, however, that the exercise price of an ISO and NSO granted to a 10% stockholder may not be less than 110% of the estimated fair value of the shares on the date of grant. Stock options granted to employees and non-employees generally vest ratably over four years. The following table summarizes stock option activity under the Company’s stock plans and related information: (In thousands, except exercise prices and years) Options Weighted- Weighted- Aggregate Intrinsic Value (a) Balance at December 31, 2022 19,320 $ 3.38 8.0 $ 29 Granted 6,179 1.05 Exercised (1) 1.29 Canceled/forfeited (2,470) 2.46 Balance at December 31, 2023 23,028 $ 4.87 7.2 $ 99 Vested and expected to vest as of December 31, 2023 23,028 $ 4.87 7.2 $ 99 Exercisable at December 31, 2023 10,352 $ 8.42 5.9 $ 48 (a) The aggregate intrinsic value is calculated as the difference between the stock option exercise price and the closing price of the Company’s common stock as quoted on a national exchange. The total intrinsic value of stock options exercised during the years ended December 31, 2023 and 2022 was not material. Options granted during the year ended December 31, 2022 included 2.5 million shares of performance-based stock options with both performance and service vesting conditions. No performance-based stock options were granted in the year ended December 31, 2023. The fair value of each stock option issued was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions: Options Employee Stock Purchase Plan Years ended December 31, Years ended December 31, 2023 2022 2023 2022 Expected volatility 90% 89% 78% 77% Expected term (in years) 6.0 6.0 1.3 1.2 Expected dividend yield — — — — Risk-free interest rate 4.2% 2.6% 5.0% 3.0% The weighted-average fair values of options granted during the years ended December 31, 2023 and 2022 were $0.80 and $0.93, respectively. As of December 31, 2023, there was $16.1 million of unrecognized stock-based compensation expense related to stock options that was expected to be recognized over a weighted-average period of 2.3 years. RSUs 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 2–4 year period. The following table summarizes the RSU activity under the Company’s stock plans and related information: (In thousands, except grant date fair value and years) Number of Weighted- Weighted- Balance at December 31, 2022 1,693 2.90 1.2 Granted 560 0.77 Vested and released (491) 3.14 Forfeited (219) 2.07 Balance at December 31, 2023 1,543 $ 2.17 1.4 RSUs granted during the year ended December 31, 2022 include 0.4 million shares of PSUs with both performance and service vesting conditions. No PSUs were granted in the year ended December 31, 2023. During the years ended December 31, 2023 and 2022, total fair value of RSUs vested was $1.5 million and $2.8 million, respectively. The number of RSUs vested includes shares of common stock that the Company withheld on behalf of employees or sold to cover to satisfy the minimum statutory tax withholding requirements. As of December 31, 2023, there was $1.0 million of unrecognized compensation cost related to unvested RSUs that is expected to be recognized over a weighted-average period of 1.4 years. ESPP In July 2014, the Company approved the establishment of the 2014 Employee Stock Purchase Plan (the “ESPP”). The Company reserved 208,833 shares of its common stock for issuance and provided for annual increases in the number of shares available for issuance on the first business day of each fiscal year, beginning in 2015, equal to the lesser of one percent (1%) of the number of the Company’s common stock shares outstanding as of such date or a number of shares as determined by the Company’s board of directors. During the year ended December 31, 2023, 824,223 shares were issued under the ESPP. As of December 31, 2023, a total of 6,219,258 shares of common stock were available for future issuance under the ESPP. As of December 31, 2023, there was $0.1 million of unrecognized compensation cost related to the ESPP. Stock-Based Compensation Recognized in the Consolidated Statements of Operations and Comprehensive Loss The following table presents the Company’s stock-based compensation expense: Years ended December 31, 2023 2022 (In thousands) Research and development $ 4,969 $ 7,108 General and administrative 12,600 12,971 Total share-based compensation expense $ 17,569 $ 20,079

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2023
Retirement Benefits [Abstract]
401(k) Savings Plan	401(k) Savings Plan The Company established a defined-contribution savings plan under Section 401(k) of the Code. 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. The amount of contributions that the Company made to the 401(k) Plan during the years ended December 31, 2023 and 2022 was $0.9 million and $1.1 million, respectively.

Restructuring

Restructuring	12 Months Ended
	Dec. 31, 2023
Restructuring and Related Activities [Abstract]
Restructuring	10. Restructuring In July 2022, the Company implemented a restructuring of operations, including reductions in both headcount and expenses, to prioritize its clinical development of ixoberogene soroparvovec (“Ixo-vec”), formerly referred to as ADVM-022, and focus its pipeline strategy on certain highly prevalent ocular diseases. Under the restructuring plan, the Company reduced its workforce by 75 employees (approximately 37%) as of July 6, 2022. Below is a summary of restructuring costs during the year ended December 31, 2022: Severance and Benefits Costs Stock-Based Compensation Total (In thousands) Charges $ 4,632 $ 53 $ 4,685 Cash payments made (4,632) — (4,632) Non-cash — (53) (53) Balance at December 31, 2022 $ — $ — $ — In the year ended December 31, 2022, the Company recorded $4.7 million of restructuring costs, of which $3.7 million was classified as research and development expenses and $1.0 million was classified as general and administrative expenses. The Company completed the restructuring in the fourth quarter of 2022.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following table presents domestic and foreign components of loss before provision for income taxes: Years ended December 31, 2023 2022 (In thousands) U.S. $ (118,089) $ (154,002) Foreign (154) (460) Loss before income taxes $ (118,243) $ (154,462) The components of the Company’s income tax (benefit) provision were as follows: Years ended December 31, 2023 2022 (In thousands) Current: Foreign $ (1,078) $ 74 Total current tax (benefit) provision (1,078) 74 Deferred Foreign — — Total deferred tax provision — — Total income tax (benefit) provision $ (1,078) $ 74 The income tax provision for the years ended December 31, 2023 and 2022 differed from the amounts computed by applying the statutory federal income tax rate of 21% to pretax loss as a result of the following: Years ended December 31, 2023 2022 (In thousands) Federal income tax benefit at statutory rate $ (24,831) $ (32,437) Stock compensation 6,001 3,414 Non-deductible expenses 21 52 Research and development tax credits (1,810) (2,529) Change in valuation allowance 18,479 31,542 Foreign rate differential (14) (46) Impact of internal reorganization 1,323 103 Uncertain tax positions (1,078) — Other 831 (25) Total tax (benefit) provision $ (1,078) $ 74 Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. The following table presents significant components of the Company’s deferred tax assets and liabilities: As of December 31, 2023 2022 (In thousands) Deferred tax assets: Net operating loss carryforwards $ 127,961 $ 111,709 Accruals, reserve and other 1,760 2,053 Tax credit carryforwards 24,702 21,439 Stock-based compensation 7,305 10,705 Property and equipment — 279 Intangibles 11 1,562 Lease obligation 17,708 26,241 Capital losses 9,850 9,850 Section 174 R&D capitalization 29,455 23,697 Total deferred tax assets before valuation allowance 218,752 207,535 Valuation allowance (205,103) (188,141) Total deferred tax assets 13,649 19,394 Deferred tax liabilities: Right-of-use assets (12,335) (19,394) Property and equipment (1,314) — Total deferred tax liabilities $ (13,649) $ (19,394) Net deferred tax assets $ — $ — The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of operating losses, the Company has concluded that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2023 and 2022. The valuation allowance increased approximately $17.0 million and $39.7 million during the years ended December 31, 2023 and 2022, respectively mainly driven by net operating losses (“NOLs”). As of December 31, 2023, the Company had U.S. federal NOLs carryforwards of approximately $493.0 million to offset any future federal income. Approximately $57.3 million of NOLs expire at various years beginning with 2036. As of December 31, 2023, the Company also had U.S. state NOL carryforwards of approximately $300.8 million to offset any future state income. U.S. state NOLs expire at various years beginning with 2037. At December 31, 2023, the Company also had approximately $49.3 million of foreign net operating loss carryforwards which may be available to offset future foreign income; these carryforwards do not expire. As of December 31, 2023, the Company had federal research and development tax credit carryforwards of approximately $20.3 million available to reduce future tax liabilities which expire at various years beginning with 2036. As of December 31, 2023, the Company had state credit carryforwards of approximately $17.6 million available to reduce future tax liabilities which do not expire. Effective January 1, 2022, the Tax Cuts and Jobs Act (“TCJA”) eliminated the option to deduct research and development expenditures in the current year and requires taxpayers to capitalize such expenses pursuant to Internal Revenue Code Section 174. The capitalized expenses are amortized over a 5-year period for domestic expenses and a 15-year period for foreign expenses. As a result of this provision of the TCJA, deferred tax assets related to capitalized research expenses increased to $29.5 million, net of amortization on research expenses capitalized as of December 31, 2023. Under Section 382 and 383 of the Code, our ability to utilize NOL carryforwards or other tax attributes such as research tax credits, in any taxable year may be limited if we have experienced an “ownership change.” Generally, a Section 382 ownership change occurs if there is a cumulative increase of more than 50 percentage points in the stock ownership of one or more stockholders or groups of stockholders who own at least 5% of a corporation’s stock within a specified testing period. Similar rules may apply under state tax laws. Due to a June 30, 2020 ownership change, we determined that certain NOLs and research and development tax credits for both federal and state purposes are subject to the 382 limitation; however, it was determined that there should be no material impact to the ability of the utilization before expiration. The Company files income tax returns in the U.S. federal, state, and foreign jurisdictions. The federal, state and foreign income tax returns are open under the statute of limitations subject to tax examinations for the tax years ended December 31, 2017 through December 31, 2022. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service, state or foreign tax authorities to the extent utilized in a future period. The Company has total unrecognized tax benefits as of December 31, 2023 and 2022 of approximately $24.6 million and $24.7 million, respectively. If the unrecognized tax benefits for uncertain tax positions as of December 31, 2023, is recognized, there will be no impact to the effective tax rate as the tax benefit would increase the net deferred tax assets, which is currently offset with a full valuation allowance. A reconciliation of the unrecognized tax benefits is as follows: Years ended December 31, 2023 2022 (In thousands) Unrecognized tax benefits as of the beginning of the year $ 24,745 $ 21,944 Increase related to tax positions taken during the prior year 43 274 Increase related to tax position take during the current year 3,301 2,527 Decrease related to tax position taken during the current year (3,475) — Unrecognized tax benefits as of the end of the year $ 24,614 $ 24,745 As of December 31, 2023 and 2022, the Company accrued interest and penalties related to uncertain tax positions of nil and $0.3 million, respectively. There are no ongoing examinations by taxing authorities at this time.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss 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: As of December 31, 2023 2022 (In thousands) Stock options 23,028 19,320 Restricted stock units 1,543 1,693 ESPP 169 307 24,740 21,320

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Private Placement On February 5, 2024, the Company entered into a securities purchase agreement, pursuant to which the Company sold 105,500,057 shares of its common stock and, in lieu of common stock, pre-funded warrants to purchase an aggregate of 750,000 shares of common stock (the “Pre-Funded Warrants”) to certain institutional and accredited investors in a private placement (the “Private Placement”). The purchase price per share is $1.20, or $1.1999 per Pre-Funded Warrant, which represents the purchase price per share minus the $0.0001 per share exercise price of each Pre-Funded Warrant. Concurrently with the Private Placement, the Company also entered into a securities purchase agreement with two directors of the Company. The Company issued and sold 230,000 shares at $1.35, on otherwise substantially the same terms as those set forth in the Securities Purchase Agreement. At the close of the Private Placement on February 7, 2024, the Company received total gross proceeds of $127.8 million, before deducting placement agent fees and offering expenses. Reverse Stock Split On June 9, 2023 and March 8, 2024, the Company’s stockholders and Board of Directors, respectively, approved an amendment to the Company’s Amended and Restated Certificate of Incorporation to effect a 1-for-10 reverse split of all outstanding shares of the Company's common stock (the “Reverse Stock Split”). Such amendment will not change the par value per share or the number of authorized shares of common stock. No fractional shares shall be issued as a result of the Reverse Stock Split, and holders of such fractional shares shall be paid a sum in cash equal to such fraction multiplied by the closing sales price of the Company’s common stock as reported on the Nasdaq Capital Market on the last business day before the date the certificate of amendment is filed with the Secretary of State of the State of Delaware, such amount rounded to the nearest whole cent. The Reverse Stock Split will decrease the number of issued and outstanding shares at the time, in thousands, from approximately 207,549 to approximately 20,755; it will decrease the number of outstanding warrants from 750,000 to 75,000, and will change the exercise price on these warrants from $0.0001 to $0.001. Trading is expected to begin on a split-adjusted basis on March 21, 2024. All shares and per share information presented in these consolidated financial statements does not reflect the upcoming stock split. Adjusting for the Reverse Stock Split, the number of issued and outstanding shares as of December 31, 2023, in thousands, will decrease from approximately 101,433 to approximately 10,143. The following unaudited pro forma financial information presents the Company's basic and diluted net loss per share upon effectiveness of the Reverse Stock Split for the periods indicated (in thousands except per share data): Year ended December 31, Net loss $ (117,165) Net loss per share - basic and diluted $ (11.62) Weighted-average common shares outstanding - basic and diluted 10,082

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation —The Company’s consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates
Foreign Currency	Foreign Currency —Assets and liabilities of non-U.S. subsidiaries that operate in a local currency environment, where the local currency is the functional currency, are translated to U.S. dollars at exchange rates in effect at the balance sheet date, with the resulting translation adjustments directly recorded to a separate component of accumulated other comprehensive loss. Upon sale or upon complete or substantially complete liquidation of an investment in a foreign entity, the amount attributable to that entity and accumulated in the translation adjustment component of equity is removed from the separate component of equity and reported as part of the gain or loss on sale or liquidation of the investment for the period during which the sale or liquidation occurs. Income and expense accounts are translated at average exchange rates for the period. Transactions which are not in the functional currency of the entity are remeasured into the functional currency and gains or losses resulting from the remeasurement recorded in other income, net.
Cash and Cash Equivalents	Cash and Cash Equivalents —The Company considers all highly liquid investments purchased with original maturities of three months or less at the date of purchase to be cash equivalents. Cash and cash equivalents include cash held in banks, money market accounts and highly liquid debt securities. Cash equivalents are stated at fair value.
Restricted Cash	Restricted Cash —Restricted cash primarily consists of cash collateral to letter of credit provided to the landlord in relation to a lease agreement. See Note 5, Leases for additional information.
Short-Term Investments	Short-Term Investments —All short-term investments in debt securities have been classified as “available for sale” and are carried at fair value. Unrealized gains and losses, net of any related tax effects, are excluded from earnings and are included in other comprehensive loss and reported as a separate component of stockholders’ equity until realized. The cost of securities sold is based on the specific-identification method. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity. Interest on short-term investments is included in other income, net in the Company’s consolidated statements of operations and comprehensive loss. In accordance with the Company’s investment policy, management invests to diversify credit risk and only invests in securities with high credit quality, including U.S. government securities. The Company assesses available-for-sale debt securities on a quarterly basis to see whether any unrealized loss is due to credit-related factors. Factors considered in determining whether an impairment is credit-related include the extent to which the investment’s fair value is less than its cost basis, declines in published credit ratings, changes in interest rates, and any other adverse factors related to the security. If it is determined that a credit-related impairment exists, the Company will measure the credit loss based on a discounted cash flow model. Credit-related impairments on available-for-sale debt securities are recognized as an allowance for credit losses with a corresponding adjustment to other income, net in the Company’s consolidated statement of operations. The unrealized loss position that is not credit-related is recorded, net of any related tax effects, in other comprehensive income until realized. There were no credit-related losses recognized for the periods presented.
Accrued Interest Receivable	Accrued Interest Receivable —Accrued interest receivable related to the Company’s available-for-sale debt securities is presented within prepaid expenses and other current assets on the Company’s consolidated balance sheets. The Company has elected to exclude accrued interest receivable from both the fair value and the amortized cost basis of available-for-sale debt securities for the purposes of identifying and measuring any impairment. The Company writes off accrued interest receivable once it has determined that the asset is not realizable. Any write offs of accrued interest receivable are recorded by reversing interest income, recognizing credit loss expense, or a combination of both. To date, the Company has not written off any accrued interest receivables associated with its available-for-sale debt securities.
Segment Reporting	Segment Reporting —The Company operates and manages its business as one reporting and operating segment, which is the business of developing and commercializing gene therapeutics. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance.
Concentrations of Credit Risk and Other Uncertainties	Concentrations of Credit Risk and Other Uncertainties —Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents and short-term investments. Risks associated with cash, cash equivalents, short-term investments are mitigated by the Company’s investment policy, which limits the Company’s investing to securities having specified credit ratings. Management believes that the Company is not exposed to significant credit risk. The Company is subject to certain risks and uncertainties, including, but not limited to changes in any of the following areas that the Company believes could have a material adverse effect on future financial position or results of operations: the ability to obtain future financing; regulatory approval and market acceptance of, and reimbursement for, the Company’s product candidates; performance of third-party clinical research organizations and manufacturers; development of sales channels; protection of intellectual property; litigation or claims against the Company based on intellectual property, patent, product, regulatory or other factors; and the Company’s ability to attract and retain employees necessary to support growth.
Property and Equipment	Property and Equipment —Property and equipment are recorded at cost, net of accumulated depreciation and amortization. Depreciation is recorded using the straight-line method over the estimated useful lives of the assets, generally three
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets —Long-lived assets, including property and equipment and finite-lived intangible assets, are reviewed for impairment whenever facts or circumstances either internally or externally may indicate that the carrying value of an asset may not be recoverable. If there is an indication of impairment, the Company tests for recoverability by comparing the estimated undiscounted future cash flows expected to result from the use of the asset to the carrying amount of the asset or asset group. If the asset or asset group is determined to be impaired, any excess of the carrying value of the asset or asset group over its estimated fair value is recognized as an impairment loss The Company recorded within research and development expense in the consolidated statements of operations and comprehensive loss impairment charges of $0.2 million and $2.1 million for the years ended December 31, 2023 and 2022, respectively. See Note 3, Balance Sheet Components for additional information.
Leases	Leases — For long-term operating leases, the Company recognizes a right-of-use asset and a lease liability on the Company's consolidated balance sheets. The Company determines if an arrangement contains a lease and the classification of the lease at inception. An arrangement contains a lease if there is an identified asset and if the Company controls the use of the identified asset throughout the period of use. The lease liability is determined as the present value of future lease payments reduced by lease incentives, if any, using an estimated rate of interest that it would pay to borrow equivalent funds on a collateralized basis at the lease commencement date or modification date, as applicable. In order to determine the incremental borrowing rate, the Company determines its credit rating, adjusts the credit rating for the nature of the collateral, and benchmarks the borrowing rate against observable yields on comparable securities with a similar term. The incremental borrowing rate, the ROU asset and the lease liability are reevaluated upon a lease modification. It bases the ROU asset on the lease liability adjusted for any prepaid or deferred rent. The Company elected to combine lease and non-lease components for all underlying assets groups. The Company determines the lease term at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. For short term leases, the Company does not recognize a right-of-use asset and lease liability and recognizes the lease expense over the term of the lease on a straight-line basis. Rent expense for operating leases is recognized on a straight-line basis over the lease term and is included in operating expenses on the statements of operations and comprehensive loss. The variable lease payments primarily consist of common area maintenance and other operating costs.
Revenue Recognition	Revenue Recognition —The Company has primarily generated revenue through license, research and collaboration arrangements with its strategic partners. The Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, Revenue from Contracts with Customers, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.
Research and Development Expenses	Research and Development Expenses —Research and development expenses are charged to expense as incurred. Research and development expenses include primarily personnel-related costs, stock-based compensation expense, laboratory supplies, consulting costs, external contract research and development expenses, including expenses incurred under agreements with contract research organizations (“CROs”), the cost of acquiring, developing and manufacturing clinical trial materials, and overhead expenses, such as rent, equipment depreciation, insurance and utilities. Advance payments for goods or services for future research and development activities are deferred and expensed as the goods are delivered or the related services are performed.
Fair Value Measurements	Fair Value Measurements —Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The carrying amounts of the Company’s financial instruments, including cash equivalents approximate their fair values due to their short-term maturities. See Note 3, Fair Value Measurements for the methodologies and assumptions used in valuing financial instruments.
Stock-based Compensation Expense	Stock-based Compensation Expense —Stock-based compensation expense related to stock awards to employees is measured at fair value of the award on the date of the grant. The Company estimates the grant-date fair value, and the resulting stock-based compensation expense, using the Black-Scholes valuation model for stock options and employee stock purchase and using intrinsic value, which is the closing price of its common stock on the date of the grant, for restricted stock units (“RSUs”) and performance stock units (“PSUs”). Expense recognition of PSU and performance-based options commences when the associated performance-based criteria are determined to be probable. The fair value of the award that is ultimately expected to vest is recognized as expense on a straight-line basis over the requisite service period, which is generally the vesting period. The Black-Scholes valuation model requires the use of following assumptions: Expected Term —The expected term assumption represents the period that the Company’s stock-based awards are expected to be outstanding and is determined using the simplified method. Expected Volatility —Expected volatility is based on the Company’s historical stock price volatility. Expected Dividend —The Black-Scholes valuation model calls for a single expected dividend yield as an input. The Company has never paid dividends and has no plans to pay dividends. Risk-Free Interest Rate —The risk-free interest rate is based on the U.S. Treasury zero-coupon issues in effect at the time of grant for periods corresponding with the expected term of option.
Income Taxes	Income Taxes —The Company accounts for income taxes using the asset and liability method. The Company records deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. In evaluating the ability to recover its deferred income tax assets, the Company considers all available positive and negative evidence, including its operating results, ongoing tax planning and forecasts of future taxable income on a jurisdiction-by-jurisdiction basis. In the event the Company determines that it would be able to realize its deferred income tax assets in the future in excess of their net recorded amount, it would make an adjustment to the valuation allowance that would reduce the provision for income taxes. Conversely, in the event that all or part of the net deferred tax assets are determined not to be realizable in the future, an adjustment to the valuation allowance would be charged to earnings in the period when such determination is made. As of December 31, 2023 and 2022, the Company has recorded a full valuation allowance on its deferred tax assets. Tax benefits related to uncertain tax positions are recognized when it is more likely than not that a tax position will be sustained upon examination. Interest and penalties related to unrecognized tax liabilities are included within the provision for income tax.
Comprehensive Loss	Comprehensive Loss
Basic and Diluted Net Loss Per Share	Basic and Diluted 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, and employee stock purchase plan (“ESPP”) 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.
Recent Adopted Accounting Pronouncements	Recently Adopted 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. 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. The Company adopted ASU 2016-13 on January 1, 2023, using the modified retrospective approach. The adoption of ASU 2016-13 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)	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Schedule of Cash Equivalents and Short-term Investments	The following is a summary of the Company’s cash equivalents and short-term investments (in thousands): December 31, 2023 Amortized Unrealized Unrealized Estimated Level 1 Money market funds $ 10,204 $ — $ — $ 10,204 Level 2 Commercial paper 64,693 — (35) 64,658 U.S. government and agency securities 17,616 4 (17) 17,603 Total cash equivalents and short-term investments 92,513 4 (52) 92,465 Less: Cash equivalents (70,972) — 33 (70,939) Total short-term investments $ 21,541 $ 4 $ (19) $ 21,526 December 31, 2022 Amortized Unrealized Unrealized Estimated Level 1 Money market funds $ 10,235 $ — $ — $ 10,235 Level 2 U.S. government and agency securities 59,487 — (824) 58,663 Commercial paper 102,722 — (246) 102,476 Corporate bonds 2,059 — (35) 2,024 Total cash equivalents and short-term investments 174,503 — (1,105) 173,398 Less: Cash equivalents (56,256) — 16 (56,240) Total short-term investments $ 118,247 $ — $ (1,089) $ 117,158

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Schedule of Undiscounted Future Lease Payments under Operating Lease	The following table summarizes the undiscounted future non-cancellable lease payments under the lease agreements as of December 31, 2023 (in thousands): December 31, Operating Leases Sublease Payment Receivable 2024 $ 11,086 $ 5,248 2025 11,448 5,405 2026 11,821 5,568 2027 12,207 5,735 2028 12,606 5,907 Thereafter 82,047 60,509 Total undiscounted lease payments $ 141,215 $ 88,372 Less: Imputed Interest (66,179) Total $ 75,036

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following: December 31, 2023 2022 (In thousands) Laboratory equipment $ 14,638 $ 14,382 Leasehold improvements 13,586 34,336 Computer equipment and software 868 1,325 Furniture and fixtures — 868 Construction in progress 184 1,010 Total property and equipment 29,276 51,921 Less accumulated depreciation and amortization (14,512) (16,994) Property and equipment, net $ 14,764 $ 34,927
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: December 31, 2023 2022 (In thousands) Employee compensation $ 8,040 $ 8,710 Accrued nonclinical, clinical and process development costs 3,367 6,854 Accrued professional fees 351 532 State income tax payable 101 254 Other 725 417 Total accrued expenses and other current liabilities $ 12,584 $ 16,767

Stock Plans (Tables)

Stock Plans (Tables)	12 Months Ended
	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Schedule of Stock Options Activity	The following table summarizes stock option activity under the Company’s stock plans and related information: (In thousands, except exercise prices and years) Options Weighted- Weighted- Aggregate Intrinsic Value (a) Balance at December 31, 2022 19,320 $ 3.38 8.0 $ 29 Granted 6,179 1.05 Exercised (1) 1.29 Canceled/forfeited (2,470) 2.46 Balance at December 31, 2023 23,028 $ 4.87 7.2 $ 99 Vested and expected to vest as of December 31, 2023 23,028 $ 4.87 7.2 $ 99 Exercisable at December 31, 2023 10,352 $ 8.42 5.9 $ 48 (a) The aggregate intrinsic value is calculated as the difference between the stock option exercise price and the closing price of the Company’s common stock as quoted on a national exchange.
Schedule of Fair Value of Option Issued Valuation Assumptions	The fair value of each stock option issued was estimated at the date of grant using the Black-Scholes valuation model with the following weighted-average assumptions: Options Employee Stock Purchase Plan Years ended December 31, Years ended December 31, 2023 2022 2023 2022 Expected volatility 90% 89% 78% 77% Expected term (in years) 6.0 6.0 1.3 1.2 Expected dividend yield — — — — Risk-free interest rate 4.2% 2.6% 5.0% 3.0%
Schedule of Restricted Stock Units Activity	The following table summarizes the RSU activity under the Company’s stock plans and related information: (In thousands, except grant date fair value and years) Number of Weighted- Weighted- Balance at December 31, 2022 1,693 2.90 1.2 Granted 560 0.77 Vested and released (491) 3.14 Forfeited (219) 2.07 Balance at December 31, 2023 1,543 $ 2.17 1.4
Schedule of Stock-based Compensation Expense	The following table presents the Company’s stock-based compensation expense: Years ended December 31, 2023 2022 (In thousands) Research and development $ 4,969 $ 7,108 General and administrative 12,600 12,971 Total share-based compensation expense $ 17,569 $ 20,079

Restructuring (Tables)

Restructuring (Tables)	12 Months Ended
	Dec. 31, 2023
Restructuring and Related Activities [Abstract]
Schedule of Restructuring Cost	Below is a summary of restructuring costs during the year ended December 31, 2022: Severance and Benefits Costs Stock-Based Compensation Total (In thousands) Charges $ 4,632 $ 53 $ 4,685 Cash payments made (4,632) — (4,632) Non-cash — (53) (53) Balance at December 31, 2022 $ — $ — $ —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Schedule of Components of Loss Before Income Taxes	The following table presents domestic and foreign components of loss before provision for income taxes: Years ended December 31, 2023 2022 (In thousands) U.S. $ (118,089) $ (154,002) Foreign (154) (460) Loss before income taxes $ (118,243) $ (154,462)
Schedule of Components of Income Tax (Benefit) Provision	The components of the Company’s income tax (benefit) provision were as follows: Years ended December 31, 2023 2022 (In thousands) Current: Foreign $ (1,078) $ 74 Total current tax (benefit) provision (1,078) 74 Deferred Foreign — — Total deferred tax provision — — Total income tax (benefit) provision $ (1,078) $ 74
Schedule of Reconciliation of Income Tax Expense Computed Statutory Federal Income Tax and Financial Statements	The income tax provision for the years ended December 31, 2023 and 2022 differed from the amounts computed by applying the statutory federal income tax rate of 21% to pretax loss as a result of the following: Years ended December 31, 2023 2022 (In thousands) Federal income tax benefit at statutory rate $ (24,831) $ (32,437) Stock compensation 6,001 3,414 Non-deductible expenses 21 52 Research and development tax credits (1,810) (2,529) Change in valuation allowance 18,479 31,542 Foreign rate differential (14) (46) Impact of internal reorganization 1,323 103 Uncertain tax positions (1,078) — Other 831 (25) Total tax (benefit) provision $ (1,078) $ 74
Schedule of Deferred Tax Assets	The following table presents significant components of the Company’s deferred tax assets and liabilities: As of December 31, 2023 2022 (In thousands) Deferred tax assets: Net operating loss carryforwards $ 127,961 $ 111,709 Accruals, reserve and other 1,760 2,053 Tax credit carryforwards 24,702 21,439 Stock-based compensation 7,305 10,705 Property and equipment — 279 Intangibles 11 1,562 Lease obligation 17,708 26,241 Capital losses 9,850 9,850 Section 174 R&D capitalization 29,455 23,697 Total deferred tax assets before valuation allowance 218,752 207,535 Valuation allowance (205,103) (188,141) Total deferred tax assets 13,649 19,394 Deferred tax liabilities: Right-of-use assets (12,335) (19,394) Property and equipment (1,314) — Total deferred tax liabilities $ (13,649) $ (19,394) Net deferred tax assets $ — $ —
Schedule of Unrecognized Tax Benefits	A reconciliation of the unrecognized tax benefits is as follows: Years ended December 31, 2023 2022 (In thousands) Unrecognized tax benefits as of the beginning of the year $ 24,745 $ 21,944 Increase related to tax positions taken during the prior year 43 274 Increase related to tax position take during the current year 3,301 2,527 Decrease related to tax position taken during the current year (3,475) — Unrecognized tax benefits as of the end of the year $ 24,614 $ 24,745

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2023
Earnings Per Share [Abstract]
Schedule of Antidilutive Common Stock Equivalents Excluded from Calculation of Diluted Net Loss 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: As of December 31, 2023 2022 (In thousands) Stock options 23,028 19,320 Restricted stock units 1,543 1,693 ESPP 169 307 24,740 21,320

Subsequent Events (Tables)

Subsequent Events (Tables)	12 Months Ended
	Dec. 31, 2023
Subsequent Events [Abstract]
Schedule of Unaudited Pro Forma Financial Information	The following unaudited pro forma financial information presents the Company's basic and diluted net loss per share upon effectiveness of the Reverse Stock Split for the periods indicated (in thousands except per share data): Year ended December 31, Net loss $ (117,165) Net loss per share - basic and diluted $ (11.62) Weighted-average common shares outstanding - basic and diluted 10,082

Description of the business - A

Description of the business - Additional Information (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accumulated deficit	$ 919,777	$ 802,612
Cash, cash equivalents, and short-term investments	$ 96,500

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of reportable segments | segment	1
Number of operating segments | segment	1
Impairment of long-lived assets	$ 224	$ 2,124
Sublease income	5,300	(300)
Deferred rent receivable	$ 0	$ 0
Minimum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of assets (in years)	3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of assets (in years)	5 years

Fair Value Measurements and F_3

Fair Value Measurements and Fair Value of Financial Instruments - Schedule of Cash Equivalents and Short-term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 21,541	$ 118,247
Unrealized Gains	4	0
Unrealized Losses	(19)	(1,089)
Estimated Fair Value	21,526	117,158
Less: Cash equivalents, amortized cost basis	(70,972)	(56,256)
Less: Cash equivalents	0	0
Less: Cash equivalents, unrealized losses	33	16
Less: Cash equivalents, estimated fair value	(70,939)	(56,240)
Total cash equivalents and short-term investments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	92,513	174,503
Unrealized Gains	4	0
Unrealized Losses	(52)	(1,105)
Estimated Fair Value	92,465	173,398
Level 1 | Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	10,204	10,235
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	10,204	10,235
Level 2 | Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	64,693	102,722
Unrealized Gains	0	0
Unrealized Losses	(35)	(246)
Estimated Fair Value	64,658	102,476
Level 2 | U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	17,616	59,487
Unrealized Gains	4	0
Unrealized Losses	(17)	(824)
Estimated Fair Value	$ 17,603	58,663
Level 2 | Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis		2,059
Unrealized Gains		0
Unrealized Losses		(35)
Estimated Fair Value		$ 2,024

Fair Value Measurements and F_4

Fair Value Measurements and Fair Value of Financial Instruments - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($)
Property, Plant and Equipment [Line Items]
Number of securities, unrealized loss position | security	19
Marketable securities in an unrealized loss	$ 71,300
Impairment of long-lived assets	224	$ 2,124
Laboratory equipment
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets	200	2,100
Fair value of laboratory equipment	$ 0	$ 200

Revenue (Details)

Revenue (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 25, 2021	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
License revenue		$ 3,600	$ 0
Lexeo Therapeutics, Inc
Disaggregation of Revenue [Line Items]
License fees received	$ 7,500
License revenue		$ 3,500

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands		1 Months Ended	3 Months Ended	12 Months Ended
	Jan. 08, 2021 segment	Mar. 31, 2023 USD ($) lease	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Oct. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Aug. 31, 2023 lease	Oct. 26, 2021 USD ($)
Lessee, Lease, Description [Line Items]
Restricted cash				$ 1,976	$ 2,503
Number of leased facilities | lease								2
Leases with accelerated expiration | lease		1
Lease liability		$ 8,300		(3,222)	13,607
Non-cash settlement of operating lease liability		$ 14,900		14,903	0
Remeasurement of operating lease right-of-use assets and liabilities			$ 5,700	13,711	2,842
Deferred rent receivable				0	0
Rent expense				25,300	17,200
Variable lease costs				2,400	2,300
Operating lease, payments				12,800	6,000
Sublease income				5,300	$ (300)
Building
Lessee, Lease, Description [Line Items]
Leasehold improvement allowance				$ 6,800
Restricted cash						$ 1,900	$ 2,700
Lease renewal term (in years)				8 years
Manufacturing Facility
Lessee, Lease, Description [Line Items]
Leasehold improvement allowance									$ 22,700
Lease renewal term (in years)	5 years
Number of renewal contracts | segment	2
Weighted-average remaining lease term (in years)				11 years 7 months 6 days	10 years 2 months 12 days
Weighted-average IBR (as percent)				11.70%	9.90%

Leases - Schedule of Future Non

Leases - Schedule of Future Non-cancellable Lease Payments under Operating Lease (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Operating Leases
2024	$ 11,086
2025	11,448
2026	11,821
2027	12,207
2028	12,606
Thereafter	82,047
Total undiscounted lease payments	141,215
Less: Imputed Interest	(66,179)
Total	75,036
Sublease Payment Receivable
2024	5,248
2025	5,405
2026	5,568
2027	5,735
2028	5,907
Thereafter	60,509
Total undiscounted lease payments	$ 88,372

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 29,276	$ 51,921
Less accumulated depreciation and amortization	(14,512)	(16,994)
Property and equipment, net	14,764	34,927
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	14,638	14,382
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	13,586	34,336
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	868	1,325
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	0	868
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 184	$ 1,010

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Employee compensation	$ 8,040	$ 8,710
Accrued nonclinical, clinical and process development costs	3,367	6,854
Accrued professional fees	351	532
State income tax payable	101	254
Other	725	417
Total accrued expenses and other current liabilities	$ 12,584	$ 16,767

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Thousands		12 Months Ended
	Nov. 22, 2022 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) milestone
Other Commitments [Line Items]
License revenue		$ 3,600	$ 0
Pazyuk v. Machado et al. C.A. | Pending Litigation
Other Commitments [Line Items]
Payment of fee	$ 600
Lexeo Therapeutics, Inc
Other Commitments [Line Items]
License revenue		$ 3,500
License agreements, milestones achieved | milestone			0

Stock Plans - Additional Inform

Stock Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Oct. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of stock options exercised	$ 0	$ 0
Granted (in shares)	6,179,000
Weighted-average fair values of options granted (in USD per share)	$ 0.80	$ 0.93
Unrecognized stock-based compensation expense related to awards	$ 16.1
Unrecognized stock-based compensation, weighted-average period (in years)	2 years 3 months 18 days
Stock-Based Compensation
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized for issuance (in shares)	41,905,487
Shares available for future grants (in shares)	3,158,755
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award price as a percentage of grant date fair value, minimum	100%
Incentive Stock Options (ISOs) and Non-Qualified Stock Options (NSOs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award price as a percentage of grant date fair value, minimum	110%
Significant stockholder threshold ownership percentage	10%
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of performance units both performance and service vesting conditions (in shares)		400,000
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation, weighted-average period (in years)	1 year 4 months 24 days
Shares of performance units both performance and service vesting conditions (in shares)	560,000
Total fair values of RSUs vested	$ 1.5	$ 2.8
Unrecognized compensation cost	$ 1
Restricted stock units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted to employees and non-employees vesting period (in years)	2 years
Restricted stock units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted to employees and non-employees vesting period (in years)	4 years
2014 Equity Incentive Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future issuance (as percent)	4%
2017 Inducement Plan | Stock Options and Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares available for future grant (in shares)			600,000
2014 Plan And Inducement Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted to employees and non-employees vesting period (in years)	4 years
2014 Plan And Inducement Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted period	10 years
2014 Plan And Inducement Plan | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	0	2,500,000
2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares available for future grant (in shares)	208,833
Shares available for future grants (in shares)	6,219,258
Unrecognized compensation cost	$ 0.1
Percentage increase in shares issued	1%
Common stock issued (in shares)	824,223

Stock Plans - Schedule of Stock

Stock Plans - Schedule of Stock Options Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Options Outstanding
Beginning Balance (in shares)	19,320
Granted (in shares)	6,179
Exercised (in shares)	(1)
Cancelled/forfeited (in shares)	(2,470)
Ending Balance (in shares)	23,028	19,320
Vested and expected to vest (in shares)	23,028
Exercisable (in shares)	10,352
Weighted- Average Exercise Price
Beginning Balance (in USD per share)	$ 3.38
Granted (in USD per share)	1.05
Exercised (in USD per share)	1.29
Cancelled/forfeited (in USD per share)	2.46
Ending Balance (in USD per share)	4.87	$ 3.38
Vested and expected to vest (in USD per share)	4.87
Exercisable (in USD per share)	$ 8.42
Weighted- Average Remaining Contract Life (in years)
Weighted- Average Remaining Contract Life (in years)	7 years 2 months 12 days	8 years
Vested and expected to vest	7 years 2 months 12 days
Exercisable	5 years 10 months 24 days
Outstanding, Aggregate Intrinsic Value	$ 99	$ 29
Vested and expected to vest, Aggregate Intrinsic Value	99
Exercisable, Aggregate Intrinsic Value	$ 48

Stock Plans - Schedule of Fair

Stock Plans - Schedule of Fair Value of Option Issued Valuation Assumptions (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	90%	89%
Expected term (in years)	6 years	6 years
Expected dividend yield	0%	0%
Risk-free interest rate	4.20%	2.60%
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	78%	77%
Expected term (in years)	1 year 3 months 18 days	1 year 2 months 12 days
Expected dividend yield	0%	0%
Risk-free interest rate	5%	3%

Stock Plans - Schedule of Restr

Stock Plans - Schedule of Restricted Stock Units Activity (Details) - Restricted stock units - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Units
Beginning Balance (in shares)	1,693
Granted (in shares)	560
Vested and released (in shares)	(491)
Forfeited (in shares)	(219)
Ending Balance (in shares)	1,543	1,693
Weighted- Average Grant Date Fair Value
Beginning Balance (in USD per share)	$ 2.90
Granted (in USD per share)	0.77
Vested and released (in USD per share)	3.14
Forfeited (in USD per share)	2.07
Ending Balance (in USD per share)	$ 2.17	$ 2.90
Weighted- Average Remaining Contractual Term (in years)
Weighted- Average Remaining Contractual Term (in years)	1 year 4 months 24 days	1 year 2 months 12 days

Stock Plans - Schedule of Sto_2

Stock Plans - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total share-based compensation expense	$ 17,569	$ 20,079
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total share-based compensation expense	4,969	7,108
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total share-based compensation expense	$ 12,600	$ 12,971

401(k) Savings Plan (Details)

401(k) Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Retirement Benefits [Abstract]
Contribution by company	$ 0.9	$ 1.1

Restructuring - Additional info

Restructuring - Additional information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)	Jul. 06, 2022 employee
Restructuring Cost and Reserve [Line Items]
Number of employees | employee		75
Number of employees (as percent)		37%
Restructuring charges	$ 4,685
Research and development
Restructuring Cost and Reserve [Line Items]
Restructuring charges	3,700
General and administrative
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 1,000

Restructuring - Schedule of Res

Restructuring - Schedule of Restructuring Costs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Restructuring Cost and Reserve [Line Items]
Charges	$ 4,685
Cash payments made	(4,632)
Non-cash	(53)
Balance at December 31, 2022	0
Severance and Benefits Costs
Restructuring Cost and Reserve [Line Items]
Charges	4,632
Cash payments made	(4,632)
Non-cash	0
Balance at December 31, 2022	0
Stock-Based Compensation
Restructuring Cost and Reserve [Line Items]
Charges	53
Cash payments made	0
Non-cash	(53)
Balance at December 31, 2022	$ 0

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Loss Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
U.S.	$ (118,089)	$ (154,002)
Foreign	(154)	(460)
Net loss before income taxes	$ (118,243)	$ (154,462)

Income Taxes- Schedule of Compo

Income Taxes- Schedule of Components of Income Tax (Benefit) Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Current:
Foreign	$ (1,078)	$ 74
Total current tax (benefit) provision	(1,078)	74
Deferred
Foreign	0	0
Total deferred tax provision	0	0
Total income tax (benefit) provision	$ (1,078)	$ 74

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Tax Expense Computed Statutory Federal Income Tax and Financial Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Federal income tax benefit at statutory rate	$ (24,831)	$ (32,437)
Stock compensation	6,001	3,414
Non-deductible expenses	21	52
Research and development tax credits	(1,810)	(2,529)
Change in valuation allowance	18,479	31,542
Foreign rate differential	(14)	(46)
Impact of internal reorganization	1,323	103
Uncertain tax positions	(1,078)	0
Other	831	(25)
Total income tax (benefit) provision	$ (1,078)	$ 74

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 127,961	$ 111,709
Accruals, reserve and other	1,760	2,053
Tax credit carryforwards	24,702	21,439
Stock-based compensation	7,305	10,705
Property and equipment	0	279
Intangibles	11	1,562
Lease obligation	17,708	26,241
Capital losses	9,850	9,850
Section 174 R&D capitalization	29,455	23,697
Total deferred tax assets before valuation allowance	218,752	207,535
Valuation allowance	(205,103)	(188,141)
Total deferred tax assets	13,649	19,394
Deferred tax liabilities:
Right-of-use assets	(12,335)	(19,394)
Property and equipment	(1,314)	0
Total deferred tax liabilities	(13,649)	(19,394)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Taxes [Line Items]
Increase in valuation allowance due to net operating loss	$ 17,000	$ 39,700
Section 174 R&D capitalization	29,455	23,697
Unrecognized tax benefits	24,614	24,745	$ 21,944
Accrued interest or penalties related to uncertain tax positions	0	$ 300
Domestic tax authority
Income Taxes [Line Items]
NOL carryforwards	493,000
NOL carryforwards subject to expiration	57,300
Domestic tax authority | Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax credit carryforwards	20,300
State credit carryforwards
Income Taxes [Line Items]
NOL carryforwards	300,800
State credit carryforwards | Research Tax Credit Carryforward
Income Taxes [Line Items]
Tax credit carryforwards	17,600
Foreign Tax Authority
Income Taxes [Line Items]
NOL carryforwards	$ 49,300

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits as of the beginning of the year	$ 24,745	$ 21,944
Increase related to tax positions taken during the prior year	43	274
Increase related to tax position take during the current year	3,301	2,527
Decrease related to tax position taken during the current year	(3,475)	0
Unrecognized tax benefits as of the end of the year	$ 24,614	$ 24,745

Net Loss per Share (Details)

Net Loss per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share (in shares)	24,740	21,320
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share (in shares)	23,028	19,320
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share (in shares)	1,543	1,693
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive common stock equivalents excluded from calculation of diluted net loss per share (in shares)	169	307

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) $ / shares in Units, $ in Millions			9 Months Ended
	Feb. 07, 2024 USD ($)	Feb. 05, 2024 director $ / shares shares	Mar. 08, 2024 shares	Mar. 21, 2024 $ / shares shares	Dec. 31, 2023 $ / shares shares	Dec. 31, 2022 shares
Subsequent Event [Line Items]
Exercise price (in USD per share) | $ / shares					$ 0.0001
Shares of common stock (in shares)					101,433,000	100,117,000
Common stock, shares outstanding (in shares)					101,433,000	100,117,000
Number of warrant shares outstanding and exercisable (in shares)					750,000,000
Pro Forma
Subsequent Event [Line Items]
Shares of common stock (in shares)					10,143,000
Common stock, shares outstanding (in shares)					10,143,000
Subsequent Event
Subsequent Event [Line Items]
Shares of common stock (in shares)			207,549,000
Common stock, shares outstanding (in shares)			207,549,000
Reverse stock split ratio			0.10
Subsequent Event | Private Placement
Subsequent Event [Line Items]
Number of shares issued in transaction (in shares)		105,500,057
Share price (in USD per share) | $ / shares		$ 1.20
Total gross proceeds | $	$ 127.8
Subsequent Event | Private Placement | Pre-Funded Warrants
Subsequent Event [Line Items]
Common stock issued upon exercise of warrants (in shares)		750,000
Share price (in USD per share) | $ / shares		$ 1.1999
Exercise price (in USD per share) | $ / shares		$ 0.0001
Subsequent Event | Private Placement | Two Directors
Subsequent Event [Line Items]
Number of shares issued in transaction (in shares)		230,000
Share price (in USD per share) | $ / shares		$ 1.35
Number of directors | director		2
Subsequent Event | Pro Forma
Subsequent Event [Line Items]
Exercise price (in USD per share) | $ / shares				$ 0.001
Shares of common stock (in shares)				20,755,000
Common stock, shares outstanding (in shares)				20,755,000
Number of warrant shares outstanding and exercisable (in shares)				75,000,000

Subsequent Events - Schedule of

Subsequent Events - Schedule of Unaudited Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Subsequent Event [Line Items]
Net loss	$ (117,165)	$ (154,536)
Net loss per share - basic (in USD per share)	$ (1.16)	$ (1.56)
Net loss per share - diluted (in USD per share)	$ (1.16)	$ (1.56)
Weighted-average common shares used to compute net loss per share - basic (in shares)	100,824	99,251
Weighted-average common shares outstanding - diluted (in shares)	100,824	99,251
Pro Forma
Subsequent Event [Line Items]
Net loss	$ (117,165)
Net loss per share - basic (in USD per share)	$ (11.62)
Net loss per share - diluted (in USD per share)	$ (11.62)
Weighted-average common shares used to compute net loss per share - basic (in shares)	10,082
Weighted-average common shares outstanding - diluted (in shares)	10,082