Atara Biotherapeutics (ATRA) 10-K28 Mar 242023 FY Annual reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2023	Mar. 20, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Trading Symbol	ATRA
Entity Registrant Name	ATARA BIOTHERAPEUTICS, INC.
Entity Central Index Key	0001604464
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity File Number	001-36548
Entity Tax Identification Number	46-0920988
Entity Address, Address Line One	2380 Conejo Spectrum Street
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	Thousand Oaks
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	91320
City Area Code	805
Local Phone Number	623-4211
Entity Incorporation, State or Country Code	DE
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes
Document Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Auditor Firm ID	34
Auditor Name	DELOITTE & TOUCHE LLP
Auditor Location	San Francisco, California
Entity Public Float			$ 161,602,451
Entity Common Stock, Shares Outstanding		119,359,230
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement relating to its 2024 Annual Meeting of Stockholders are incorporated by reference into Part III of this Report where indicated. Such proxy statement will be filed with the U.S. Securities and Exchange Commission within 120 days after the end of the fiscal year to which this report relates.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 25,841	$ 92,942
Short-term investments	25,884	149,877
Restricted cash	146	146
Accounts receivable	34,108	40,221
Inventories	9,706	1,586
Other current assets	6,184	10,308
Total current assets	101,869	295,080
Property and equipment, net	3,856	6,300
Operating lease assets	54,935	68,022
Other assets	4,844	7,018
Total assets	165,504	376,420
Current liabilities:
Accounts payable	3,684	6,871
Accrued compensation	11,519	17,659
Accrued research and development expenses	17,364	24,992
Deferred revenue	77,833	8,000
Other current liabilities	31,826	21,394
Total current liabilities	142,226	78,916
Deferred revenue - long-term	37,562	77,000
Operating lease liabilities - long-term	45,693	58,064
Liability related to the sale of future revenues - long-term	34,623	30,236
Other long-term liabilities	4,631	5,564
Total liabilities	264,735	249,780
Commitments and contingencies (Note 10)
Stockholders' equity (deficit):
Common stock-$0.0001 par value, 500,000 shares authorized as of December 31, 2023 and 2022, respectively; 106,447 and 95,927 shares issued and outstanding as of December 31, 2023 and 2022, respectively	11	10
Additional paid-in capital	1,870,112	1,821,721
Accumulated other comprehensive (loss) income	(204)	(2,067)
Accumulated deficit	(1,969,150)	(1,693,024)
Total stockholders' equity (deficit)	(99,231)	126,640
Total liabilities and stockholders' equity (deficit)	$ 165,504	$ 376,420

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	106,447,000	95,927,000
Common stock, shares outstanding	106,447,000	95,927,000

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]
Commercialization revenue	$ 7,886	$ 0
License and collaboration revenue	687	63,573
Revenue from Contract with Customer, Including Assessed Tax, Total	8,573	63,573
Costs and operating expenses:
Cost of commercialization revenue	8,886	0
Research and development expenses	224,785	272,533
General and administrative expenses	50,908	71,553
Total costs and operating expenses	284,579	344,086
Loss from operations	(276,006)	(280,513)
Other income (expense), net:
Interest income	5,426	3,059
Interest expense	(5,285)	(373)
Gain on sale of ATOM Facility (See Note 7)	0	50,237
Other income (expense), net:	(246)	(700)
Total other income (expense), net	(105)	52,223
Loss before provision for income taxes	(276,111)	(228,290)
Provision for income taxes	15	12
Net loss	(276,126)	(228,302)
Other comprehensive gain (loss):
Unrealized gain (loss) on available-for-sale securities	1,863	(1,699)
Comprehensive loss	$ (274,263)	$ (230,001)
Net loss per common share:
Basic net loss per common share	$ (2.61)	$ (2.24)
Diluted net loss per common share	$ (2.61)	$ (2.24)
Basic weighted-average shares outstanding	105,912	101,990
Diluted weighted-average shares outstanding	105,912	101,990

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit
Beginning balance at Dec. 31, 2021	$ 279,614	$ 9	$ 1,744,695	$ (368)	$ (1,464,722)
Beginning balance (in shares) at Dec. 31, 2021		91,671
Issuance of common stock through ATM facilities, net of commissions and offering costs, value	21,891		21,891
Issuance of common stock through ATM facilities, net of commissions and offering costs, shares		1,619
RSU settlements, net of shares withheld	(623)	$ 1	(624)
RSU settlements, net of shares withheld, shares		2,204
Issuance of common stock pursuant to employee stock awards	1,921		1,921
Issuance of common stock pursuant to employee stock awards, shares		433
Stock-based compensation expense	53,838		53,838
Net Income (Loss)	(228,302)				(228,302)
Unrealized gain (loss) on available-for-sale securities	(1,699)			(1,699)
Ending balance at Dec. 31, 2022	126,640	$ 10	1,821,721	(2,067)	(1,693,024)
Ending balance (in shares) at Dec. 31, 2022		95,927
Issuance of common stock through ATM facilities, net of commissions and offering costs, value	2,172	$ 1	2,171
Issuance of common stock through ATM facilities, net of commissions and offering costs, shares		3,038
Exercise of pre-funded warrants, shares		2,916
RSU settlements, net of shares withheld	(94)		(94)
RSU settlements, net of shares withheld, shares		3,670
Issuance of common stock pursuant to employee stock awards	928		928
Issuance of common stock pursuant to employee stock awards, shares		896
Stock-based compensation expense	45,386		45,386
Net Income (Loss)	(276,126)				(276,126)
Unrealized gain (loss) on available-for-sale securities	1,863			1,863
Ending balance at Dec. 31, 2023	$ (99,231)	$ 11	$ 1,870,112	$ (204)	$ (1,969,150)
Ending balance (in shares) at Dec. 31, 2023		106,447

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
At The Market Offering \| Common Stock
Stock issuance, discounts, commissions and offering costs	$ 351	$ 517

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating activities
Net loss	$ (276,126)	$ (228,302)
Adjustments to reconcile net loss to net cash used in operating activities:
Gain on sale of ATOM Facility	0	(50,237)
Stock-based compensation expense	45,386	53,838
Depreciation and amortization expense	4,829	5,653
Accretion of liability related to sale of future revenues	4,792	0
Non-cash operating lease expense	11,795	8,915
Amortization of investment premiums	792	1,024
Other non-cash items, net	214	147
Changes in operating assets and liabilities:
Accounts receivable	6,113	(39,235)
Inventories	(8,120)	(1,586)
Other current assets	273	1,836
Other assets	1,043	(266)
Accounts payable	(3,130)	(9,211)
Accrued compensation	(6,140)	(7,491)
Accrued research and development expenses	(3,663)	11,541
Other current liabilities	11,064	2,067
Deferred revenue	30,395	(11,468)
Operating lease liabilities	(12,636)	(8,009)
Other long-term liabilities	142	354
Net cash used in operating activities	(192,977)	(270,430)
Investing activities
Purchases of short-term investments	(83,648)	(180,589)
Proceeds from maturities and sales of short-term investments	208,712	292,973
Purchases of property and equipment	(1,223)	(4,193)
Proceeds from sale of property and equipment	25	0
Net proceeds from sale of ATOM Facility	0	94,765
Net cash provided by (used in) investing activities	123,866	202,956
Financing activities
Proceeds from issuance of common stock through ATM facilities, net	2,136	21,891
Proceeds from employee stock awards	928	1,921
Proceeds from sale of future revenues, net	0	30,605
Taxes paid related to net share settlement of restricted stock units	(94)	(623)
Principal payments on finance lease obligations	(947)	(518)
Other financing activities, net	(13)	(192)
Net cash provided by financing activities	2,010	53,084
Increase (decrease) in cash, cash equivalents and restricted cash	(67,101)	(14,390)
Cash, cash equivalents and restricted cash at beginning of period	93,088	107,478
Cash, cash equivalents and restricted cash at end of period	25,987	93,088
Non-cash investing and financing activities
Property and equipment purchases included in accounts payable and other accrued liabilities	132	61
Accrued costs related to ATM facilities	78	0
Proceeds from issuance of common stock through ATM facilities not yet received	114	0
Accrued transaction costs related to sale of future revenues	0	332
Supplemental cash flow disclosure
Cash paid for interest	447	335
Cash paid for income taxes	$ 2	$ 19

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Pay vs Performance Disclosure
Net Income (Loss)	$ (276,126)	$ (228,302)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended	12 Months Ended
Insider Trading Arrangements	Dec. 31, 2023	Dec. 31, 2023
Trading Arrangements, by Individual
Material Terms of Trading Arrangement		Ite m 9B. Other Information During the three months ended December 31, 2023, none of the Company's directors or executive officers adopted or terminated any contract, instruction or written plan for the purchase or sale of Company securities that was intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) or any “non-Rule 10b5-1 trading arrangement” as defined in Item 408 of Regulation S-K under the Securities Exchange Act of 1934, as amended.
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Description of Business

Description of Business	12 Months Ended
Description of Business	Dec. 31, 2023
Description Of Business [Abstract]
Description of Business	1. Description of Business Atara Biotherapeutics, Inc. (Atara, we, our or the Company) was incorporated in August 2012 in Delaware . Atara is a leader in T-cell immunotherapy, leveraging its novel allogeneic Epstein-Barr Virus (EBV) T-cell platform to develop transformative therapies for patients with cancer and autoimmune disease. We have several T-cell immunotherapies in clinical development and are progressing multiple next-generation allogeneic chimeric antigen receptor T-cell (CAR T) programs. Our most advanced T-cell immunotherapy program, tab-cel ® (tabelecleucel), has received marketing authorization approval under the proprietary name Ebvallo by the European Commission (EC) for commercial sale and use in the European Union (EU) and by the Medicines and Healthcare products Regulatory Agency (MHRA) for commercial sale and use in the United Kingdom (UK). Tab-cel is currently in Phase 3 development in the US. In October 2021, we entered into a commercialization agreement (Pierre Fabre Commercialization Agreement) with Pierre Fabre Medicament (Pierre Fabre), as amended in September 2022, pursuant to which we granted to Pierre Fabre an exclusive, field-limited license to commercialize and distribute Ebvallo in Europe and select emerging markets in the Middle East, Africa, Eastern Europe and Central Asia (the Initial Territory), following regulatory approval. In October 2023, we amended and restated the Pierre Fabre Commercialization Agreement (A&R Commercialization Agreement). Pursuant to the A&R Commercialization Agreement, Pierre Fabre’s exclusive rights to research, develop, manufacture, commercialize and distribute Ebvallo are expanded to include all other countries in the world (Additional Territory) in addition to the Initial Territory (together, the Territory), subject to our performance of certain obligations. See Note 5 for further information. In December 2022, we sold a portion of our right to receive royalties and certain milestones in Ebvallo under the Pierre Fabre Commercialization Agreement to HCR Molag Fund L.P. (HCRx) for a total investment amount of $ 31.0 million, subject to a repayment cap between 185 % and 250 % of the total investment amount by HCRx. See Note 6 for further information. We have licensed rights to T-cell product candidates from Memorial Sloan Kettering Cancer Center (MSK), rights related to our next-generation CAR T programs from MSK, and rights to know-how and technology from the Council of the Queensland Institute of Medical Research (QIMR Berghofer). See Note 8 for further information. In January 2022, we entered into an asset purchase agreement with FUJIFILM Diosynth Biotechnologies California, Inc. (FDB) and, for certain limited purposes, FUJIFILM Holdings America Corporation, to sell all of the Company’s right, title and interest in and to certain assets related to the Atara T-Cell Operations and Manufacturing facility (ATOM Facility) located in Thousand Oaks, California for $ 100 million in cash, subject to potential post-closing adjustments pursuant to the asset purchase agreement (the Fujifilm Transaction). The closing of the Fujifilm Transaction occurred on April 4, 2022, at which time 136 of our ATOM Facility employees transitioned to FDB as part of the transaction. We also entered into a Master Services and Supply Agreement and related Statements of Work with FDB (collectively, the Fujifilm MSA) which became effective upon the closing and could extend for up to ten years. Pursuant to the Fujifilm MSA, FDB will supply us with specified quantities of our cell therapy product candidates and any products approved by regulatory authorities, manufactured in accordance with cGMP standards. See Note 8 for further information. In November 2023, we announced a reduction in force that reduced our workforce by approximately 30 %. We recognized $ 6.7 million in total for severance and related benefits for employees laid off under the reduction in force. These charges are one-time termination benefits and are all cash charges. Refer to Note 9 for further information. Certain prior year amounts, which are not material, have been reclassified to conform to current year presentation in the consolidated statements of operations and comprehensive income (loss) and the notes to consolidated financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Principles of Consolidation The consolidated financial statements include the accounts of Atara and our wholly owned subsidiaries. All intercompany balances and transactions are eliminated in consolidation. Segment and Geographic Information We operate and manage our business as one operating and reportable segment, which is the business of developing therapeutics. Our Chief Executive Officer, who is our chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. Substantially all of our assets are located in the U.S. All commercialization and collaboration revenue recognized in 2023 related to our agreements with Pierre Fabre, a French company. Of the $ 63.6 million license and collaboration revenue recognized in 2022, $ 61.8 million related to our agreements with Bayer, a German company, and $ 1.8 million related to our agreements with Pierre Fabre, a French company. Use of Estimates We prepare our consolidated financial statements in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP), which requires us to make estimates and assumptions that affect the amounts reported in our consolidated financial statements and accompanying notes. The level of uncertainty in estimates and assumptions increases with the length of time until the underlying transactions are completed. Significant estimates and assumptions relied upon in preparing these financial statements include those related to revenue recognition, accrued research and development expenses, stock-based compensation expense, liability related to the sale of future revenues and income taxes. Additionally, we use available market information to assess the fair value of our short-term investments. Actual results could differ materially from those estimates. If actual amounts differ from estimates, we include the updates in our consolidated results of operations in the period the actual amounts become known. Historically, the aggregate differences, if any, between our estimates and actual amounts in any year have not had a material effect on our consolidated financial statements. Liquidity Risk We have incurred significant operating losses since inception and have relied primarily on public and private equity financings and receipts from commercialization and license and collaboration agreements to fund our operations. As we continue to incur losses, our transition to profitability will depend on the successful development, approval and commercialization of product candidates and on the achievement of sufficient revenues to support our cost structure. We may never achieve sustained operating cash inflows or profitability. Going Concern We have incurred operating losses since inception and we expect that existing cash, cash equivalents and short-term investments as of December 31, 2023, will not be sufficient to fund our planned operations for at least 12 months after the issuance of the accompanying consolidated financial statements. Although we anticipate the receipt of certain payments from the amended and restated Pierre Fabre Commercialization Agreement in 2024 and 2025, such payments are contingent upon the successful filing and approval of the tab-cel BLA, as well as the completion of specific development and regulatory activities by us and actions taken by third parties, and are, therefore, uncertain at this time. To alleviate the conditions that raise substantial doubt about our ability to continue as a going concern, we plan to secure additional capital, potentially through a combination of public or private security offerings; use of our ATM facility as described in Note 9; and/or strategic transactions. We may also need to raise additional funding as required based on the status of our development programs and our projected cash flows. Although we have been successful in raising capital in the past, and expect to continue to raise capital as required, there is no assurance that we will be successful in obtaining sufficient funding on terms acceptable to us to fund continuing operations, if at all, or identify and enter into any strategic transactions that will provide the capital that we will require. If we are unable to obtain sufficient funding on acceptable terms, we could be forced to delay, limit, reduce or terminate preclinical studies, clinical studies or other development activities for one or more of our product candidates, which could have a material adverse effect on our business, results of operations, and financial condition. Accordingly, we have concluded that substantial doubt exists with respect to our ability to continue as a going concern for at least 12 months after the issuance of the accompanying consolidated financial statements. The consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty. Concentration of Credit Risk and Other Uncertainties We place cash and cash equivalents in the custody of financial institutions that management believes are of high credit quality, the amount of which at times, may be in excess of the amount insured by the Federal Deposit Insurance Corporation. We also make short-term investments in money market funds; U.S. Treasury, government agency and corporate debt obligations; commercial paper; certificates of deposit; and asset-backed securities, which can be subject to certain credit risk. We strive to mitigate this credit risk by investing in high-grade instruments, limiting our exposure to any one issuer and monitoring the ongoing creditworthiness of the financial institutions and issuers. Currency Translation Transactions and monetary assets and liabilities that are denominated in a foreign currency are translated into U.S. dollars at the current exchange rate on the transaction date and as of each balance sheet date, respectively, with gains or losses on foreign exchange changes recognized in interest and other income (expense), net in the consolidated statements of operations and comprehensive loss. Foreign currency-denominated monetary assets and liabilities as of December 31, 2023 were not material. Cash, Cash Equivalents and Short-Term Investments Cash and cash equivalents are defined as highly liquid investments with original maturities of 90 days or less at the date of purchase. Investments with original maturities of greater than 90 days are classified as short-term investments on the balance sheet. As our entire investment portfolio is considered available for use in current operations, we classify all investments as available-for-sale and as current assets, even though the stated maturity may be more than one year from the current balance sheet date. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive loss, which is a separate component of stockholders’ equity in the consolidated balance sheet. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity, which are recorded to interest income in the consolidated statements of operations and comprehensive loss. Changes in the fair value of available-for-sale securities impact the consolidated statements of operations and comprehensive loss only when such securities are sold, if an allowance for credit losses is recognized or if an impairment is recognized. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. We regularly review our investment portfolio to determine if any security is impaired, which would require us to record an allowance for credit losses or impairment charge in the period any such determination is made. In making this judgment, we evaluate, among other things, the duration and extent to which the fair value of a security is less than its cost, our intent to sell or whether it is more likely than not that we will be required to sell the security before recovery of its amortized cost basis, the financial condition of the issuer and any changes thereto, and, as necessary, the portion of a decline in fair value that is credit-related. This assessment could change in the future due to new developments or changes in assumptions related to any particular security. Realized gains and losses, allowances for credit losses and impairments on available-for-sale securities, if any, are recorded to other income (expense), net in the statements of operations and comprehensive loss. Fair Value Measurement The carrying amounts of certain of our financial instruments including cash equivalents, accounts receivable, other current assets, accounts payable and accrued liabilities approximate fair value due to their short maturities. Short-term investments are comprised of available-for-sale securities, which are carried at fair value. Financial Instruments Our financial assets are measured at fair value on a recurring basis using the following hierarchy to prioritize valuation inputs, in accordance with applicable GAAP: Level 1: Quoted prices in active markets for identical assets or liabilities that we have the ability to access Level 2: Observable market-based inputs or unobservable inputs that are corroborated by market data such as quoted prices, interest rates and yield curves Level 3: Inputs that are unobservable data points that are not corroborated by market data We review the fair value hierarchy classification on a quarterly basis. Changes in the ability to observe valuation inputs may result in a reclassification of levels of certain securities within the fair value hierarchy. We recognize transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs. There have been no transfers between Level 1, Level 2, and Level 3 in any periods presented. 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. Treasury, government agency and corporate debt obligations, commercial paper and asset-backed securities are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. Financial assets and liabilities are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies, or similar techniques, and at least one significant model assumption or input is unobservable. We have no Level 3 financial assets or liabilities. Accounts Receivable, net Accounts receivable are recorded net of estimates of variable consideration for which reserves are established and which result from discounts and chargebacks that are offered within contracts between us and a limited number of specialty pharmacies and a specialty distributor in the United States. These reserves are classified as reductions of accounts receivable. We estimate the allowance for doubtful accounts using the current expected credit loss model, or CECL model. Under the CECL model, the allowance for doubtful accounts reflects the net amount expected to be collected from the accounts receivable. We evaluate the collectability of these cash flow based on the asset’s amortized cost, the risk of loss even when that risk is remote, losses over an asset’s contractual life, and other relevant information available to us. Accounts receivable balances are written off against the allowance when it is probable that the receivable will not be collected. Given the nature and history of our accounts receivable, we determined that an allowance for doubtful accounts was not required for the periods presented. Inventories Inventories are stated at the lower of cost or estimated net realizable value, on a specific identification basis. We use actual costs to determine our cost basis for inventories. Inventories consist of raw materials, work-in-process and finished goods. We begin capitalizing costs as inventory when the product candidate receives regulatory approval and when the manufacturing facility producing such inventory is qualified by the relevant regulatory agency. Prior to regulatory approval and qualification, we record such production costs related to product candidates as research and development expenses. Any manufactured product that is available for commercial sale is recorded to inventory; to the extent it is later used for clinical studies, such inventory costs are then recorded within research and development expenses. We periodically assess the recoverability of our inventory and reduce the carrying value of the inventory when items are determined to be obsolete, defective or in excess of forecasted sales requirements. Inventory write-downs for excess, defective and obsolete inventory are recorded as a cost of sales. Property and Equipment, net Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from three to five years , except for leasehold improvements, which are depreciated on a straight-line basis over the lesser of the estimated useful life of the leasehold improvement or the lease term. Costs incurred to acquire, construct or install property and equipment during the construction stage of a capital project or costs incurred to purchase and develop internal use software during the application development stage are recorded as construction in progress. Maintenance and repairs are charged to operations as incurred. Long-lived Assets We evaluate the carrying amount of our long-lived assets whenever events or changes in circumstances indicate that the assets may not be recoverable. An impairment loss would be recognized when estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount of the asset. To date, there have been no such impairment losses. Asset Retirement Obligation (ARO) An ARO is a legal obligation associated with the retirement of long-lived assets pertaining to leasehold improvements. These liabilities are initially recorded at fair value and the related asset retirement costs are capitalized by increasing the carrying amount of the related assets by the same amount as the liability. Asset retirement costs are subsequently depreciated over the useful lives of the related assets. Subsequent to initial recognition, we record period-to-period changes in the ARO liability resulting from the passage of time and revisions to either the timing or the amount of the original estimate of undiscounted cash flows. We derecognize ARO liabilities when the related obligations are settled. Leases We determine if a contract is or contains a lease at contract inception. Operating leases are included in operating lease assets, other current liabilities, and operating lease liabilities on our consolidated balance sheets. Our policy is to not recognize right-of-use (ROU) assets and lease liabilities for short-term operating leases with terms of 12 months or less; we recognize short-term lease expense for these leases on a straight-line basis over the lease term. Long-term operating lease ROU assets and long-term operating lease liabilities are presented separately and operating lease liabilities payable in the next twelve months are recorded in other current liabilities. Finance lease ROU assets are recorded in other assets and the related finance lease liabilities are presented in other current liabilities and other long-term liabilities. Lease assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. The lease term includes renewal options that we are reasonably certain of exercising as of the commencement date. None of the lease terms used to calculate the future minimum lease payments at commencement date include renewal options. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of future payments. The incremental borrowing rate for our leases is determined based on lease term and currency in which lease payments are made, adjusted for impacts of collateral. Lease assets also includes any lease payments made and excludes lease incentives and initial direct costs incurred. Operating lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. Finance lease assets are amortized over the shorter of the lease term or the asset’s estimated useful life. Our facilities and equipment operating leases have lease and non-lease components and we have made a policy election to account for the lease and non-lease components as a single lease component. We are considered the sub-lessor for certain of our leases where we have entered into a sub-lease agreement with or have assigned our lease to another party. Rental income was not material for any period presented and we record rental income as a reduction to rent expense within operating expenses. We analyze whether or not amendments to existing leases classify as a lease modification or a full or partial termination of the existing lease. To the extent a partial lease termination is identified, our accounting policy is to decrease the existing right-of-use asset on a basis proportionate to the reduction in lease liability resulting from the partial termination. Accruals of Research and Development Costs We record accruals for estimated research and development costs based on an evaluation of our vendors’ progress towards completion of specific tasks, using data such as patient enrollment, clinical site activations or information provided to us by our vendors regarding their actual costs incurred. Payments for these activities are based on the terms of individual contracts and payment timing may differ significantly from the period in which the services are performed. We determine accrual estimates through reports from and discussions with internal personnel and outside service providers as to the progress or state of completion of studies, or the services completed. Our estimates of accrued expenses as of each balance sheet date are based on the facts and circumstances known at the time. Costs that are paid in advance of performance are deferred as a prepaid asset and recognized as expense as the services are provided. Sale of Future Revenues To the extent that we account for the sale of future revenues as debt in accordance with ASC 470, we amortize the liability and recognize interest expense related to the sale of future revenues using the effective interest rate method over the estimated life of the underlying agreement. The liability and related interest expense are based on our current estimate of expected future payments over the life of the arrangement. We re-assess the amount and timing of expected payments each reporting period using a combination of internal projections and forecasts from external resources and record interest expense on the carrying value of the liability using the imputed effective interest rate on a prospective basis. Revenue Recognition For contracts that are determined to be within the scope of Accounting Standards Codification Topic 606 (Accounting Standards Update (ASU) No. 2014-09), Revenue from Contracts with Customers , and all subsequent amendments (collectively, ASC 606), revenue is recognized as we satisfy performance obligations and when a customer obtains control of the promised goods or services. The amount of revenue recognized reflects the consideration to which we expect to be entitled to receive in exchange for these goods and services. To achieve this core principle, we apply the following five steps (i) identify the contract with the 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 we satisfy a performance obligation. We only apply the five-step model to contracts when we determine that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration. Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct and are distinct in the context of the contract. To the extent a contract includes multiple promised goods and services, we apply judgment to determine whether promised goods and services are both capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation. The transaction price is determined based on the consideration to which we will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration, we estimate the amount of variable consideration that should be included in the transaction price utilizing either the expected value method or the most likely amount method, depending on the nature of the variable consideration. Variable consideration is included in the transaction price if, in our judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Any estimates, including the effect of the constraint on variable consideration, are evaluated at each reporting period for any changes. Determining the transaction price requires significant judgment, which is discussed in further detail for our out-license agreements in Note 5. Our out-license agreements do not contain a significant financing component. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. We typically determine standalone selling prices using an expected cost plus margin approach model. We satisfy performance obligations either over time or at a point in time. Revenue is recognized over time if either (i) the customer simultaneously receives and consumes the benefits provided by our performance, (ii) our performance creates or enhances an asset that the customer controls as the asset is created or enhanced or (iii) our performance does not create an asset with an alternative use to the entity and we have an enforceable right to payment for performance completed to date. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. If we do not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring control of a promised good or service to a customer. As discussed in further detail in Note 5, the terms of our customer contracts include potential payments to us for some or all of the following: nonrefundable, upfront fees; development, regulatory, and commercial milestone payments; research and development funding payments; royalties on the net sales of licensed products; and transition plan cost reimbursements for certain development, safety, regulatory, and process science services. These payments relate to promised goods or services for which revenue will be recognized upon our satisfaction of the underlying performance obligations. Licenses of intellectual property : If the license of our intellectual property is determined to be distinct from the other performance obligations identified in an arrangement, we recognize revenues from consideration allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are combined with other promises, we utilize judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. Upfront payments : Upfront payments and fees are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until we have satisfied our obligations under these arrangements. Milestone payments : At the inception of each arrangement that includes development milestone payments, we evaluate the probability of reaching the milestones and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur in the future, the associated milestone value is included in the transaction price. The transaction price is then allocated to each performance obligation on a relative standalone selling price basis, for which we recognize revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, we re-evaluate the probability of achievement of such development milestones and any related constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license and collaboration revenues and the consolidated statements of operations and comprehensive loss in the period of adjustment. Royalties : For arrangements that include sales-based royalties, including milestone payments based on levels of sales, if the license is deemed to be the predominant item to which the royalties relate, we recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied, or partially satisfied. To date, we have not recognized material royalty revenue resulting from our out-licensing agreements. Transition plan cost reimbursements : Reimbursements for certain development, safety, regulatory and manufacturing services are recorded as revenue as we perform the services and related obligations identified within the transition plans for our customers. Certain judgments affect the application of our revenue recognition policy. For example, we record short-term and long-term deferred revenue based on our best estimate of when such revenue will be recognized. Short-term deferred revenue consists of amounts that are expected to be recognized as revenue in the next 12 months, and long-term deferred revenue consists of amounts that we expect will be recognized after the next 12 months. This estimate is based on forecasted patient demand, our current operating plan and expected dates of technology transfer, and if these items should change in the future, we may recognize a different amount of deferred revenue over the next 12-month period. Cost of commercialization revenue Cost of commercialization revenue consists primarily of expenses associated with cell selection services performed for Pierre Fabre, in-license sales-related milestone costs, period manufacturing expenses and adjustments to reduce inventory to the lower of cost or net realizable value. Costs incurred to produce Ebvallo prior to regulatory approval, referred to as zero cost inventories, have been recorded as research and development expense in our consolidated statement of operations and comprehensive income (loss). All tab-cel (Ebvallo) sold to Pierre Fabre in the year ended December 31, 2023 was zero cost inventories. Once we begin selling Ebvallo produced after receiving regulatory approval and in a qualified manufacturing facility, and as revenue is recognized on such Ebvallo sales, cost of commercialization revenue will also include direct and indirect costs related to the production of Ebvallo. Such costs include, but are not limited to, CMO costs, quality testing and validation, materials used in production, and an allocation of compensation, benefits and overhead costs associated with employees involved with production. In 2023 and 2022, cost of commercialization revenue included adjustments of $ 6.6 million and $ 0.0 million, respectively, to write-off of inventories and to reflect them at the lower of cost or net realizable value. Research and Development Expense Research and development expense consists of costs incurred in performing research and development activities, including compensation and benefits for research and development employees; expenses incurred under agreements with contract research organizations and investigative sites that conduct clinical and preclinical studies; expense incurred under agreements with contract manufacturing organizations related to acquiring and manufacturing clinical study materials and other supplies to support the manufacture of our product candidates; payments under licensing and research and development agreements; other outside services and consulting costs, and facilities, information technology and overhead expenses. Research and development costs are expensed as incurred. Stock-Based Compensation Expense We account for stock-based compensation expense, including the expense of restricted common stock awards, grants of restricted stock units (RSUs), and stock options that may be settled in shares of our common stock, based on the fair values of the equity instruments issued. The fair value is determined on the measurement date, which is generally the date of grant. The fair value of our RSUs is measured at the closing market price of our common stock on the measurement date. The fair value for our stock option awards is determined at the grant date using the Black-Scholes valuation model. In determining the fair value of stock option awards granted, we use the Black-Scholes valuation model and assumptions include: Expected term – We derived the expected term using the “simplified” method (the expected term is determined as the average of the time-to-vesting and the contractual life of the options), as we have limited historical information to develop expectations about future exercise patterns and post vesting employment termination behavior. Expected volatility – In 2021 and 2022, volatility was estimated using an average of Atara’s historical volatility and comparable public companies’ volatility for similar terms. Beginning in 2023, volatility is based solely on Atara’s stock price historical volatility. Expected dividend – We have not historically declared or paid dividends to our stockholders and have no plans to pay dividends; therefore, we assumed an expected dividend yield of 0 %. Risk-free interest rate – The risk-free interest rate is based on the yield on U.S. Treasury securities with the expected term of the associated award. For awards with performance-based vesting criteria, we assess the probability of the achievement of the performance conditions at the end of each reporting period and begin to recognize the share-based compensation costs when it becomes probable that the performance conditions will be met. For awards that are subject to both service and performance conditions, no expense is recognized until it is probable that performance conditions will be met. Stock-based compensation expense for awards with time-based vesting criteria is recognized as expense on a straight-line basis over the requisite service period. Stock-based

Net Loss per Common Share

Net Loss per Common Share	12 Months Ended
Net Loss per Common Share	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss per Common Share	3. Net Loss per Common Share Basic net loss per common share is calculated by dividing net loss by the weighted-average number of shares of common stock and pre-funded warrants outstanding during the period, without consideration of common share equivalents. Diluted net loss per common share is computed by dividing net loss by the weighted-average number of shares of common stock, pre-funded warrants and common share equivalents outstanding for the period. The pre-funded warrants are included in the computation of basic and diluted net loss per common share as the exercise price is negligible and the pre-funded warrants are fully vested and exercisable. Common share equivalents are only included in the calculation of diluted net loss per common share when their effect is dilutive. Potential dilutive securities, which include unvested RSUs, unvested performance-based RSUs and performance-based options to purchase common stock for which established performance criteria have been achieved as of the end of the respective periods, vested and unvested options to purchase common stock and shares to be issued under our employee stock purchase plan (ESPP), have been excluded from the computation of diluted net loss per share as the effect is antidilutive. Therefore, the denominator used to calculate both basic and diluted net loss per common share is the same in all periods presented. The following table represents the potential common shares issuable pursuant to outstanding securities as of the dates listed that were excluded from the computation of diluted net loss per common share, as their inclusion would have an antidilutive effect: As of December 31, 2023 2022 Unvested RSUs 6,261,213 6,698,858 Vested and unvested options 10,706,651 10,336,634 ESPP share purchase rights 185,843 86,782 Total 17,153,707 17,122,274

Financial Instruments

Financial Instruments	12 Months Ended
Financial Instruments	Dec. 31, 2023
Financial Instruments Disclosure [Abstract]
Financial Instruments	4. Financial Instruments The following tables summarize the estimated fair value and related valuation input hierarchy of our available-for-sale securities as of each period end: Total Total Total Total Amortized Unrealized Unrealized Estimated As of December 31, 2023: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 14,376 $ — $ — $ 14,376 U.S. Treasury obligations Level 2 9,928 1 — 9,929 Corporate debt obligations Level 2 26,089 — ( 205 ) 25,884 Total available-for-sale securities 50,393 1 ( 205 ) 50,189 Less: amounts classified as cash equivalents ( 24,304 ) ( 1 ) — ( 24,305 ) Amounts classified as short-term investments $ 26,089 $ — $ ( 205 ) $ 25,884 Total Total Total Total Amortized Unrealized Unrealized Estimated As of December 31, 2022: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 78,033 $ — $ — $ 78,033 U.S. Treasury obligations Level 2 63,013 3 ( 394 ) 62,622 Government agency obligations Level 2 8,086 — ( 48 ) 8,038 Corporate debt obligations Level 2 82,598 4 ( 1,513 ) 81,089 Commercial paper Level 2 996 — — 996 Asset-backed securities Level 2 6,343 — ( 119 ) 6,224 Total available-for-sale securities 239,069 7 ( 2,074 ) 237,002 Less: amounts classified as cash equivalents ( 87,122 ) ( 3 ) — ( 87,125 ) Amounts classified as short-term investments $ 151,947 $ 4 $ ( 2,074 ) $ 149,877 The amortized cost and fair value of our available-for-sale securities by contractual maturity were as follows: As of December 31, 2023 As of December 31, 2022 Amortized Estimated Amortized Estimated Cost Fair Value Cost Fair Value (in thousands) (in thousands) Maturing within one year $ 50,393 $ 50,189 $ 202,323 $ 201,359 Maturing in one to five years — — 36,746 35,643 Total available-for-sale securities $ 50,393 $ 50,189 $ 239,069 $ 237,002 We considered the current and expected future global economic and market conditions, including, but not limited to, the wars in Ukraine and the Middle East and increased tensions between the U.S. and China, and determined that our investments have not been significantly impacted. As of December 31, 2023, no significant facts or circumstances were present to indicate a deterioration in the creditworthiness of the issuers of the available-for-sale securities we hold, and we have no requirement or intention to sell these securities before maturity or recovery of their amortized cost basis. For all securities with a fair value less than its amortized cost basis, we determined the decline in fair value below amortized cost basis to be non-credit related and no allowance for losses has been recorded. During the years ended December 31, 2023 and 2022, we did not recognize any impairment losses on our investments. We have elected the practical expedient to exclude the applicable accrued interest from both the fair value and the amortized cost basis of our available-for-sale securities for purposes of identifying and measuring an impairment. We present accrued interest receivable related to our available-for-sale securities in other current assets, separate from short-term investments, on our consolidated balance sheet. As of December 31, 2023 and 2022 , accrued interest receivable was $ 0.3 million and $ 0.8 million, respectively. Our accounting policy is to not measure an allowance for credit losses for accrued interest receivables and to write-off any uncollectible accrued interest receivable as a reversal of interest income in a timely manner, which we consider to be in the period in which we determine the accrued interest will not be collected by us. We have no t written off any accrued interest receivables for the years ended December 31, 2023 and 2022. In addition, restricted cash collateralized by money market funds is a financial asset measured at fair value and is a Level 1 financial instrument under the fair value hierarchy. The following table provides a reconciliation of cash, cash equivalents and restricted cash within the consolidated balance sheets that sum to the total of the same such amounts in the consolidated statement of cash flows: December 31, December 31, 2023 2022 (in thousands) Cash and cash equivalents $ 25,841 $ 92,942 Restricted cash – short-term 146 146 Total cash, cash equivalents and restricted cash $ 25,987 $ 93,088

Out-license Agreements

Out-license Agreements	12 Months Ended
Out-license Agreements	Dec. 31, 2023
License Collaboration And Manufacturing Agreements [Abstract]
Out-license Agreements	5. Out- license Agreements Pierre Fabre Commercialization Agreement In October 2021, we entered into the Pierre Fabre Commercialization Agreement, pursuant to which, we granted to Pierre Fabre an exclusive, field-limited license to commercialize and distribute Ebvallo in Europe and select emerging markets in the Initial Territory following regulatory approval. In September 2022, we entered into Amendment No. 1 to the Pierre Fabre Commercialization Agreement (the PF Amendment). Under the terms of the PF Amendment, following European Commission approval of Ebvallo for EBV+ PTLD and subsequent filing of the Marketing Authorization Application (MAA) transfer to Pierre Fabre, we are entitled to receive an additional $ 30 million milestone payment in exchange for, among other things, a reduction in: (i) royalties we are eligible to receive as a percentage of net sales of Ebvallo in the Territory, and (ii) the supply price mark up on Ebvallo purchased by Pierre Fabre. Additionally, we agreed to extend the time period for provision of certain services to Pierre Fabre in the Initial Territory at our cost pursuant to the Pierre Fabre Commercialization Agreement. In December 2022, we sold a portion of our right to receive royalties and certain milestone payments related to Ebvallo in the Initial Territory under the Pierre Fabre Commercialization Agreement to HCRx for a total investment amount of $ 31.0 million, subject to a repayment cap between 185 % and 250 % of the total investment amount by HCRx. See Note 6 for further information related to the agreement with HCRx. In October 2023, we entered into the A&R Commercialization Agreement with Pierre Fabre. Pursuant to the A&R Commercialization Agreement, Pierre Fabre’s exclusive rights to research, develop, manufacture, commercialize and distribute tab-cel are expanded to include all other countries in the world (Additional Territory) in addition to the Initial Territory (together, the Territory), subject to our performance of certain obligations as described below. Pierre Fabre paid us an upfront cash payment of $ 45.0 million for the exclusive license grant for the Initial Territory in the fourth quarter of 2021. In December 2022, we met the contractual right to receive $ 40.0 million in milestone payments upon certain regulatory milestones, for which the cash was received in January 2023. Subject to the terms of the royalty purchase agreement with HCRx, as described in Note 6, we are entitled to receive an aggregate of up to $ 308.0 million in remaining milestone payments upon achieving certain regulatory and commercial milestones in addition to double-digit tiered royalties as a percentage of net sales of Ebvallo in the Initial Territory, until the later of 12 years after the first commercial sale in each such country, the expiration of specified patent rights, or the expiration of all regulatory exclusivity for Ebvallo on a country-by-country basis. In December 2023, upon the effective date of the A&R Commercialization Agreement, we met the contractual right to receive an additional upfront cash payment of $ 20.0 million for the expanded exclusive license grant in the Additional Territory, for which the cash was received in January 2024. We will also be entitled to receive an aggregate of up to $ 620.0 million in additional payments upon achieving certain regulatory and commercial milestones relating to tab-cel in the Additional Territory. We will be eligible to receive significant double-digit tiered royalties as a percentage of net sales of tab-cel in the Additional Territory until the later of 12 years after the first commercial sale in each such country, the expiration of specified patent rights in each such country, or the expiration of all regulatory exclusivity for tab-cel on a country-by-country basis. We have entered into a separate manufacturing and supply agreement with Pierre Fabre for us to manufacture Ebvallo for Pierre Fabre to use in the Initial Territory based on a fixed price through December 31, 2023 and at a price equal to cost plus a margin for orders placed after December 31, 2023, subject to a maximum annual increase. Pierre Fabre will assume the responsibility and cost for the manufacture and supply of tab-cel (Ebvallo) in the Territory upon the Manufacturing Transition Date, which is defined as the earlier of: i) all activities relating to the transfer of tab-cel manufacturing, pursuant to the A&R Commercialization Agreement, from Atara to Pierre Fabre have been completed to the reasonable satisfaction of both parties, or ii) December 31, 2025, through the remainder of the term of the A&R Commercialization Agreement. Pierre and we are to use commercially reasonable efforts to achieve this prior to the earlier transfer date from Atara to Pierre Fabre of the first marketing authorization in the Additional Territory or the first BLA (PF Transfer Date). Prior to the Manufacturing Transition Date, we are responsible for manufacturing and supplying tab-cel (Ebvallo) to Pierre Fabre in the Territory. Without transfer of the manufacturing technology, no other party can manufacture Ebvallo. Cell selection is the process of identifying the appropriate cell line from available tab-cel inventory to be used for a patient. We are responsible for the performance of cell selection services in the Initial Territory at our cost through the earlier of the PF Transfer Date, June 30, 2025 or a date otherwise agreed to by Pierre Fabre and us. To the extent that the transfer of cell selection technology occurs subsequent to June 30, 2025, we will be responsible for the performance of cell selection services in the Initial Territory at Pierre Fabre’s cost until cell selection technology is transferred to Pierre Fabre. Without transfer of the cell selection technology, no other party can provide such services. We are responsible for the performance of cell selection services in the Additional Territory through the earlier of the PF Transfer Date or a date otherwise agreed to by Pierre Fabre and us, at the sole expense of Pierre Fabre. As part of the Pierre Fabre Commercialization Agreement, we formed a joint steering committee (JSC) with Pierre Fabre that provides oversight, decision making and implementation guidance regarding the commercialization activities, the responsibilities of which has been expanded to cover the incremental scope of the A&R Commercialization Agreement. During the applicable period specified in the A&R Commercialization Agreement, we will be responsible for various development, safety, process science, and regulatory activities, including obtaining regulatory approval in the United States for tab-cel for EBV-associated post-transplant lymphoproliferative disease. Pierre Fabre will pay us for these services in accordance with the A&R Commercialization Agreement. Pierre Fabre will be responsible, at its cost, for obtaining and maintaining all other required regulatory approvals and for commercialization and distribution of tab-cel in the Additional Territory, including conducting any other clinical study required. We will own any intellectual property rights developed solely by us under the Agreement. Accounting Analysis Identification of the Contract We assessed this arrangement in accordance with ASC 606 and concluded that the promises in the A&R Commercialization Agreement represent transactions with a customer. Identification of the Promises and Performance Obligations We identified four performance obligations under the A&R Commercialization Agreement, consisting of the following material promises: (1) the transfer of intellectual property rights in the form of a license in the Initial Territory, the obligation to participate in the JSC, a material right for purchases associated with the manufacture and supply of Ebvallo and the performance of cell-selection services. We concluded that the individual promises are not distinct because Pierre Fabre cannot benefit from the license without the other services and vice versa, since Pierre Fabre is not capable of carrying out the manufacturing and supply and cell selection services on their own, until the transfer of the related technologies occur. Consequently, these promises represent a single performance obligation, collectively referred to as the Initial Territory Obligation. (2) the transfer of intellectual property rights in the form of a license in the Additional Territory, the manufacture and supply of tab-cel and the performance of cell-selection services, as well as the promises to transfer the related technologies, and perform certain development, safety and regulatory services. We concluded that the promises are not distinct because Pierre Fabre cannot benefit from the license without the other services and vice versa. Consequently, these promises represent a single performance obligation, collectively referred to as the Additional Territory Obligation. (3) performance of certain process science services, referred to as the Process Sciences Obligation (4) the sale of certain intermediate inventory used in the production of tab-cel in existence on the Manufacturing Transition Date, referred to as the Intermediate Inventory Obligation. Determination of the Transaction Price Under the Pierre Fabre Commercialization Agreement, we determined that the $ 45.0 million upfront payment constituted the entire consideration to be included in the transaction price at the outset of the arrangement, and the $ 40.0 million in development milestones achieved in December 2022 were added to the transaction price upon meeting the related milestone criteria. The remaining potential development and commercial milestone payments that we are eligible to receive were excluded from the transaction price, as the milestone amounts were fully constrained based on the probability of achievement or have not been earned. None of the future royalty and sales-based milestone payments were included in the transaction price, as the potential payments represent sales-based consideration. We will reevaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, as necessary, we will adjust our estimate of the transaction price. Upon the effective date of the A&R Commercialization Agreement, the $ 20.0 million additional upfront payment received and estimated revenue for the development, safety, regulatory and process science services were added to the transaction price. The remaining potential development and commercial milestone payments that we are eligible to receive were excluded from the transaction price, as the milestone amounts were fully constrained based on the probability of achievement or have not been earned. None of the future royalty and sales-based milestone payments were included in the transaction price, as the potential payments represent sales-based consideration. Any consideration associated with the Intermediate Inventory Obligation was excluded from the transaction price as the amount was fully constrained based on uncertainty surrounding available inventory on the Manufacturing Transition Date. We will reevaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, as necessary, we will adjust our estimate of the transaction price. Allocation of the Transaction Price to Performance Obligations The transaction price was allocated to each performance obligation based on their relative standalone selling price. We developed the estimated standalone selling price for each of the A&R Commercialization Agreement performance obligations with the objective of determining the price at which we would sell such an item if it were to be sold regularly on a standalone basis. Recognition of Revenue Commercialization revenue associated with the Initial Territory Obligation will be recognized over the period during which the material right exists, which would end upon the Manufacturing Transition Date. Based on these considerations and our forecast of the timing and associated costs of the purchases related to the manufacture and supply of Ebvallo and estimated timing of technology transfer, we estimate the material right in the Initial Territory will exist for approximately one to two years. We reassess this evaluation each reporting period. Commercialization revenue associated with sales of Ebvallo to Pierre Fabre under the Initial Territory Obligation is deferred until we have performed the associated cell selection services, or once cell selection technology transfer to Pierre Fabre has been complete. At that point, Pierre Fabre would be able to utilize the Ebvallo it had purchased from us on its own. Commercialization revenue associated with the Additional Territory Obligation and the Process Sciences Obligation will be recognized using a cost-based input method based on the amount of actual costs incurred relative to the total budgeted costs expected to be incurred for the respective performance obligations. A cost-based input method of revenue recognition requires us to make estimates of costs to complete our performance obligation. In making such estimates, significant judgment is required to evaluate assumptions related to cost estimates. The cumulative effect of revisions to estimated costs to complete our performance obligation will be recorded in the period in which changes are identified and amounts can be reasonably estimated. We expect to recognize revenue associated with the Additional Territory Obligation and the Process Sciences Obligation over a period of approximately two years. We reassess this evaluation each reporting period. The transfer of control occurs over the respective time period and, in our judgment, is the best measure of progress towards satisfying the performance obligation. A significant change in these assumptions and estimates could have a material impact on the timing and amount of revenue recognized in future periods. We expect to recognize revenue associated with the Intermediate Inventory Obligation at a point in time on the Manufacturing Transition Date, which is when title and risk of loss, and thus, control, of the intermediate inventory transfers to Pierre Fabre. Deferred revenue activity related to commercialization revenue for the year ended December 31, 2023 was as follows: Total (in thousands) Deferred revenue, December 31, 2022 $ 85,000 Additions 38,170 Recognized into commercialization revenue ( 7,775 ) Deferred revenue December 31, 2023 115,395 Less: deferred revenue – current portion ( 77,833 ) Deferred revenue – long-term, December 31, 2023 $ 37,562 During the year ended December 31, 2023, we recognized $ 5.0 million of revenue that was included in the deferred revenue balance as of December 31, 2022. Costs incurred relating to performing the services within the Additional Territory Obligation and Process Sciences Obligation consist of third party expenses and for time incurred by our employees to satisfy requirements set forth by the A&R Commercialization Agreement. These costs are included in research and development expenses in the consolidated statements of operations and comprehensive income (loss) during the year ended December 31, 2023. Such costs were not material for the year ended December 31, 2023. Under the A&R Commercialization Agreement, we conduct an early access program observational study at the sole cost and expense of Pierre Fabre. We recognize the costs incurred associated with this study within research and development expenses, which is directly offset by revenue recorded within license and collaboration revenue. The license and collaboration revenue associated with the early access program for the year ended December 31, 2023 was $ 0.7 million, as compared to $ 1.8 million for the year December 31, 2022. Bayer Agreements In December 2020, we entered into a research, development and license agreement (Bayer License Agreement) with Bayer AG (Bayer) pursuant to which we granted to Bayer an exclusive, field-limited license under the applicable patents and know-how owned or controlled by us and our affiliates covering or related to ATA2271 and ATA3271 (the Licensed Products). Under the terms of the Bayer License Agreement, we were responsible at our cost for all mutually agreed preclinical and clinical activities for ATA2271 through the first in human Phase 1 clinical study in collaboration with MSK, following which Bayer was responsible for the further development of ATA2271 at its cost. Bayer was responsible for the development of ATA3271, except for certain mutually agreed preclinical, translational, manufacturing and supply chain activities to be performed by us relating to ATA3271, in each case at Bayer’s cost. Bayer was also solely responsible for commercializing the Licensed Products at its cost. In March 2021, we entered into a Technology Transfer Agreement with Bayer (the Bayer Tech Transfer Agreement), which was contemplated as part of the Bayer License Agreement, to transfer to Bayer the ATA3271 manufacturing process being developed as part of the CMC services in the Bayer License Agreement. In March 2021, we also entered into a Manufacturing and Supply Agreement with Bayer (the Bayer Manufacturing Agreement), which was contemplated as part of the Bayer License Agreement, to manufacture Phase 1 and 2 allogeneic mesothelin-directed CAR T-cell therapies for Bayer to use in clinical trials at a price based on our costs plus a reasonable margin, which is consistent with our standalone selling price. Collectively, the Bayer License Agreement, the Manufacturing and Supply Agreement and the Technology Transfer Agreement are referred to as “the Bayer Agreements”. In May 2022, Bayer notified us of its decision to terminate the Bayer Agreements, and on August 2, 2022, we entered into the Termination, Amendment and Program Transfer Agreement with which terminated the Bayer Agreements (the Bayer Termination Agreement) with an effective date of July 31, 2022. Upon the termination effective date, full product development and commercialization rights related to ATA2271 and ATA3271 reverted to Atara. In return for certain activities performed by Atara prior to the termination effective date, Bayer paid Atara $ 4.2 million in September 2022. Utilizing the cost-based input method, we recognized license and collaboration revenue of $ 61.8 million for 2022. As a result of the termination, no license and collaboration revenue related to the Bayer Agreements was recognized for the year ended December 31, 2023, and there was no deferred revenue related to the Bayer Agreements as of December 31, 2023 or December 31, 2022.

Liability Related to the Sale o

Liability Related to the Sale of Future Royalties	12 Months Ended
Liability Related to the Sale of Future Royalties	Dec. 31, 2023
Liability for Future Policy Benefit, after Reinsurance [Abstract]
Liability Related to the Sale of Future Revenues	6. Liability Related to the Sale of Future Revenues In December 2022, we entered into a Purchase and Sale Agreement (the HCRx Agreement) with HCR Molag Fund, L.P., a Delaware limited partnership, (HCRx). In exchange for a payment of $ 31.0 million (the Investment Amount) to Atara, net of certain transaction expenses, HCRx obtained the right to receive certain Ebvallo royalties and milestone payments payable by Pierre Fabre under the Pierre Fabre Commercialization Agreement up to an agreed upon multiple of the Investment Amount. Under the HCRx Agreement, HCRx is entitled to receive tiered royalties on net sales of Ebvallo in the Initial Territory in amounts ranging from the mid-single digits to double digits based on annual net sales. HCRx is also entitled to certain milestone payments due to Atara from Pierre Fabre. The total royalties and milestones payable to HCRx are capped between 185 % and 250 % of the Investment Amount, depending upon the timing of such royalties and milestones. Upon meeting the cap amount, HCRx’s right to receive royalties and milestone payments will terminate and all rights will revert to Atara. To the extent a certain milestone within the Pierre Fabre Commercialization Agreement is not achieved on or prior to June 30, 2026, we will be required to make a one-time cash payment in the amount of $ 9.0 million to HCRx, and HCRx shall transfer all of its right, title and interest in this certain $ 9.0 million milestone payment to Atara. This payment, if required, would be included in the calculation of aggregate payments made to HCRx. The gross proceeds of the Investment Amount of $ 31.0 million were recorded as a liability related to the sale of future revenues, net of transaction costs of $ 0.4 million, and is be amortized using the effective interest method over the life of the arrangement. To determine the amortization of the recorded liability, we are required to estimate the total amount of future payments to be received by HCRx. The sum of these amounts less the $ 31.0 million proceeds we received will be recorded as interest expense over the life of the HCRx Agreement. We will estimate the effective interest rate used to record non-cash interest expense under the HCRx Agreement based on the estimate of future royalty payments to be received by HCRx. As of December 31, 2023, the annual effective interest rate was approximately 12 %. Over the life of the arrangement, the actual effective interest rate will be affected by the amount and timing of the actual and forecasted royalty and milestone payments to HCRx. At each reporting date, we reassess our estimate of the timing and amounts of future payments made to HCRx, and prospectively adjust the effective interest rate and amortization of the liability as necessary. The following table presents the changes in the liability related to the sale of future revenues under the HCRx Agreement for the year ended December 31, 2023: (in thousands) Liability related to sale of future revenues as of December 31, 2022 $ 30,236 Accretion of interest expense on liability related to sale of future revenues 4,792 Amortization of debt discount and debt issuance costs 79 Repayment of the liability ( 31 ) Liability related to sale of future revenues as of December 31, 2023 35,076 Less: current portion classified within other accrued liabilities ( 453 ) Long-term liability related to sale of future revenues $ 34,623

Sale of ATOM Facility

Sale of ATOM Facility	12 Months Ended
Sale of ATOM Facility	Dec. 31, 2023
Discontinued Operations and Disposal Groups [Abstract]
Sale of ATOM Facility	7. Sale of ATOM Facility On April 4, 2022, we completed the sale of the ATOM Facility to FDB for net proceeds of $ 94.8 million, after deducting transaction costs of $ 4.6 million and other adjustments to the purchase price. The sale resulted in a gain of $ 50.2 million included within other income (expense), net for the year end December 31, 2022. As disclosed in Note 8, although we have assigned the lease for the ATOM Facility to FDB, we have not received novation from the landlord. Therefore, the lease-related assets and liabilities for the ATOM Facility remain on our balance sheet. Refer to the summary of assets sold and gain on sale of the ATOM Facility: (in thousands) Net proceeds from sale of ATOM Facility $ 94,765 Assets sold: Other current assets $ 190 Property and equipment, net 44,299 Other assets 39 Less: Assets sold 44,528 Gain on sale of ATOM Facility $ 50,237 In connection with the sale, we entered into a Transition Services Agreement (TSA) with FDB, pursuant to which we assisted FDB in the transition of certain functions, including, but not limited to, information technology, finance and technical operations. FDB reimbursed us at cost for all third party expenses incurred in conjunction with the TSA and for time incurred by our employees to satisfy requirements set forth by the TSA. The reimbursements are recorded as reductions to the related Operating expenses and the amounts associated with reimbursements for employee time incurred were not material for the years ended December 31, 2023 and 2022. The TSA was terminated in March 2023.

Leases

Leases	12 Months Ended
Leases	Dec. 31, 2023
Leases [Abstract]
Leases	8. Leases We lease office space for our corporate headquarters in Thousand Oaks, California. In November 2018, we entered into a lease agreement for this office space that expires in February 2026 and for which we have the option to extend the lease for an additional period of five years after the initial term. In March 2021, we entered into a new lease agreement for approximately 33,659 square feet of office, lab and warehouse space in Thousand Oaks, California. During the third quarter of 2021, the initial 10.5 -year lease term commenced, upon substantial completion of the landlord’s work as defined under the agreement. Base rent is subject to annual increases of 3 % with each annual anniversary of the rent commencement date. We have the option to extend this lease for two additional five-year periods after the initial term. Additionally, in 2021, we entered into an amended lease agreement for our office and lab space in Aurora, Colorado, to add additional lab space. In November 2023, we entered into an amended lease agreement for our office and lab space in Aurora, Colorado, to extend the term of the lease agreement to April 2025. In February 2017, we entered into a lease agreement (the ATOM Lease) for approximately 90,580 square feet of office, lab and cellular therapy manufacturing space in Thousand Oaks, California. The initial 15-year term of the headlease commenced on February 15, 2018 , upon the substantial completion of landlord’s work as defined under the agreement. In April 2022, we assigned the ATOM Lease to FDB in connection with the closing of the sale of the ATOM Facility to FDB. Under ASC 842, we are considered to be the sub-lessor of the ATOM Lease. We have not received novation from the landlord and therefore have not been relieved of our primary obligations under the headlease. Therefore, the ROU asset and lease liability for the ATOM Facility remain on our balance sheet. We evaluated our vendor contracts to identify embedded leases and determined that the Fujifilm MSA contained items that constituted a lease under ASC 842, Leases, as Atara has the right to substantially all of the economic benefits from the use of the asset and can direct the use of the asset. We concluded that the Fujifilm MSA contains an embedded operating lease for certain dedicated processing rooms for the manufacturing of Atara product and an embedded finance lease for certain freezers dedicated for our use. The Fujifilm MSA includes contractual obligations in the form of payments for the processing rooms and the freezers, each over a term of five years. As a result, we added ROU assets and lease liabilities for the processing rooms and freezers for the initial term of the lease in the amounts of $ 50.8 million and $ 4.8 million, respectively. In November 2023, we agreed to forego the use of one processing room for approximately one year in return for a reduction in contractual obligations under the Fujifilm MSA. We have the option to subsequently reclaim the processing room or release it to FDB for the remainder of the initial term. We lease office space in South San Francisco, California under a non-cancellable lease agreement. In December 2021, we entered into a second amendment with the landlord to extend the lease term through May 2025. The amended lease agreement does not include an option to extend the lease term. In connection with the amended lease, we are required to maintain a letter of credit in the amount of $ 0.1 million to the landlord. In October 2022, we entered into a sub-lease agreement with a third party for this office space. The sub-lease term commenced in November 2022 and expires in May 2025, with no option to extend the sub-lease term. We have not received novation from the landlord and therefore have not been relieved of our primary obligations under the headlease. Therefore, the ROU asset and lease liability for the South San Francisco office remain on our balance sheet. The maturities of lease liabilities under our operating and finance leases as of December 31, 2023 were as follows: Operating Leases Finance Leases Years Ending December 31, (in thousands) 2024 $ 17,209 $ 1,219 2025 18,486 1,263 2026 17,271 1,285 2027 5,760 436 2028 3,319 — Thereafter 12,459 — Total lease payments $ 74,504 $ 4,203 Less: amount representing interest ( 17,547 ) ( 673 ) Present value of lease liabilities $ 56,957 $ 3,530 Balance as of December 31, 2023 Other current liabilities $ 11,264 $ 915 Operating lease liabilities – long-term 45,693 — Other long-term liabilities — 2,615 Total $ 56,957 $ 3,530 The components of lease cost were as follows: Year Ended Year Ended December 31, 2023 December 31, 2022 (in thousands) Operating lease cost: Operating lease cost $ 17,192 $ 14,245 Short-term lease cost 201 386 Total operating lease cost $ 17,393 $ 14,631 Finance lease cost: Amortization expense $ 976 $ 872 Interest on lease liabilities 416 373 Total finance lease cost $ 1,392 $ 1,245 Other information related to leases was as follows: Year Ended Year Ended December 31, 2023 December 31, 2022 (in thousands, except lease term and discount rate) Supplemental Cash Flows Information Cash paid for amounts included in the measurement of Operating cash flows for operating leases $ 16,660 $ 13,417 Operating cash flows for finance leases 416 335 Financing cash flows for finance leases 947 518 Operating lease assets obtained in exchange for lease obligations: $ 312 $ 50,779 Finance lease assets obtained in exchange for lease obligations: — 4,795 Non-cash (decrease) increase to operating lease assets due to remeasurement of lease liabilities: ( 1,589 ) — Weighted Average Remaining Lease Term Operating leases 5.2 years 5.9 years Finance leases 3.3 years 4.2 years Weighted Average Discount Rate Operating leases 11.4 % 9.9 % Finance leases 10.4 % 10.4 % Asset Retirement Obligation Our asset retirement obligation (ARO) consists of a contractual requirement to remove the tenant improvements at the ATOM Facility in Thousand Oaks, California and restore the facility to a condition specified in the lease agreement. Although we assigned the ATOM Lease to FDB in connection with the closing of the sale of the ATOM Facility to FDB in April 2022, we have not received novation from the landlord. Therefore, the ARO associated with the ATOM Facility remains on our balance sheet. We recorded an estimate of the fair value of our ARO liability in other long-term liabilities and the ARO asset as a long-term asset in the period incurred. The fair value of the ARO asset is amortized over the lease term. The fair value of our ARO was estimated by discounting projected cash flows over the estimated life of the related assets using our credit adjusted risk-free rate. As of December 31, 2023 and December 31, 2022, the ARO asset and liability were not material.

Restructuring

Restructuring	12 Months Ended
Restructuring	Dec. 31, 2023
Restructuring and Related Activities [Abstract]
Restructuring	9. Restructuring On August 8, 2022 we announced a strategic reduction in workforce of approximately 20 % to focus our activities as an organization centered on research and development. The workforce reduction included total restructuring charges of $ 6.0 million, comprised primarily of severance payments, wages for the 60-day notice period in accordance with the California Worker Adjustment and Retraining Notification (WARN) Act and continuing health care coverage for a period of time after separation. In most cases, the severance payments were paid as a lump sum in October 2022. Certain of the notified employees had employment agreements which provided for separation benefits in the form of salary continuation; these benefits were paid between October 2022 and November 2023, and there are no further payments required for this reduction in workforce as of December 31, 2023. All of the costs were cash expenditures and represented one-time termination benefits. On November 1, 2023 we announced a strategic reduction in workforce of approximately 30 %. The workforce reduction resulted in total restructuring charges of $ 6.7 million, comprised primarily of severance payments and wages for the 60-day notice period in accordance with the California WARN Act. In most cases, the severance payments were paid as a lump sum in January 2024. All of the costs are cash expenditures and represent one-time termination benefits. The following is a summary of restructuring charges associated with the reductions in force for the periods presented: Year Ended December 31, Year Ended December 31, 2023 2022 (in thousands) Research and development expense $ 5,619 $ 2,544 General and administrative expense 1,111 3,420 Total restructuring charges $ 6,730 $ 5,964 The following restructuring liability activity was recorded in connection with the reduction in force for the year ended December 31, 2023, with all of the $ 4.9 million liability balance as of December 31, 2023 included within other current liabilities on the accompanying consolidated balance sheet: Year ended December 31, Year ended December 31, 2023 2022 (in thousands) Liability balance, January 1 $ 1,545 $ — Restructuring charges 6,730 5,964 Cash payments ( 3,352 ) ( 4,419 ) Liability balance, December 31 $ 4,923 $ 1,545

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies MSK Agreements In June 2015, we entered into an exclusive license agreement with MSK for three clinical stage T-cell therapies. We are required to make payments to MSK based on achievement of specified regulatory and sales-related milestones, as well as mid-single-digit percentage tiered royalty payments based on future sales of products resulting from the development of the licensed product candidates, if any. In addition, under certain circumstances, we are required to make certain minimum annual royalty payments to MSK, which are creditable against earned royalties owed for the same annual period. We are also required to pay a low double-digit percentage of any consideration we receive for sublicensing the licensed rights. The license agreement expires on a product-by-product and country-by-country basis on the latest of: (i) expiration of the last licensed patent rights related to each licensed product, (ii) expiration of any market exclusivity period granted by law with respect to each licensed product, and (iii) a specified number of years after the first commercial sale of the licensed product in each country. Upon expiration of the license agreement, we will retain non-exclusive rights to the licensed products. In May and December 2018, we licensed additional technology from MSK. We are obligated to make additional milestone payments based on achievement of specified development, regulatory and sales-related milestones as well as mid-single-digit percentage tiered royalty payments based on future sales of products resulting from the development of the licensed product candidates, if any. In March 2021, we amended and restated our license agreement with MSK to terminate our license to certain rights and license additional know-how rights not otherwise covered by our existing agreements. QIMR Berghofer Agreements In October 2015, we entered into an exclusive license agreement and a research and development collaboration agreement with QIMR Berghofer. Under the terms of the license agreement, we obtained an exclusive, worldwide license to develop and commercialize allogeneic T-cell therapy programs utilizing technology and know-how developed by QIMR Berghofer. In September 2016, the exclusive license agreement and research and development collaboration agreement were amended and restated. Under the amended and restated agreements, we obtained an exclusive, worldwide license to develop and commercialize additional T-cell programs, as well as the option to license additional technology that we exercised in June 2018. We further amended and restated our license agreement and research and development collaboration agreements with QIMR Berghofer in August 2019, August 2020 and December 2021, in each case, to terminate our license to certain rights. Our current license agreement also provides for various milestone and royalty payments to QIMR Berghofer based on future product sales, if any. Under the terms of our current research and development collaboration agreement, we are also required to reimburse the cost of agreed-upon development activities related to programs developed under the collaboration. These payments are expensed on a straight-line basis over the related development periods. The agreement also provides for various milestone payments to QIMR Berghofer based on achievement of certain developmental and regulatory milestones. Other In-license and Collaboration Agreements From time to time, we have entered into other license and collaboration agreements with other parties. For example, we licensed rights related to our MSK-partnered next-generation CAR T programs from the National Institutes of Health in December 2018. Milestones and royalties under each of the above agreements are contingent upon future events and will be recorded as expense when the underlying milestones are achieved or royalties are earned. Sales related milestone and royalty costs related to Ebvallo are recorded in cost of commercialization revenue, whereas regulatory milestone costs are recorded in research and development expense. As of December 31, 2023 and 2022, there were no material outstanding obligations for milestones and royalties under our in-license and collaboration agreements. CRL Manufacturing Agreement In December 2019, we entered into a Commercial Manufacturing Services Agreement (the CRL MSA) with Cognate BioServices, Inc., which was acquired by Charles River Laboratories Inc. (CRL) in March 2021. Pursuant to the CRL MSA, CRL provides manufacturing services for our product and certain of our product candidates. We further amended the CRL MSA to extend the term until the earlier of March 31, 2024 or upon receipt of certain batches of our product and product candidates. We are currently in negotiations with CRL for a new commercial drug product supply agreement to be effective upon the expiration of the CRL MSA. However, there can be no assurance that we will be able to enter into a new commercial drug product supply agreement with CRL on terms favorable or acceptable to us, or at all. If we are unable to enter into a new commercial drug product supply agreement or extend the CRL MSA, we may need to identify alternative sources of drug product supply. Fujifilm Master Services and Supply Agreement In January 2022, we entered into the Fujifilm MSA, which became effective upon the closing of the sale of the ATOM Facility on April 4, 2022 and could extend for up to ten years . Pursuant to the Fujifilm MSA, FDB will supply us with specified quantities of our cell therapy products and product candidates, manufactured in accordance with cGMP standards. We have certain non-cancellable minimum commitments to purchase products and services over the first five years of the Fujifilm MSA. The Fujifilm MSA does not obligate us to purchase products and product candidates exclusively from FDB. Other Research, Development and Manufacturing Agreements We may enter into other contracts in the normal course of business with clinical research organizations for clinical trials, with CMOs for product, product candidates and clinical supplies, and with other vendors for preclinical studies, supplies and other services for our operating purposes. These contracts generally provide for termination on notice. As of December 31, 2023 and December 31, 2022, there were no material amounts accrued related to contract termination charges. Minimum Commitments The non-cancellable minimum commitments for products and services, subject to agreements with a term of greater than one year with clinical research organizations and CMOs, excluding those recognized on our balance sheet, as of December 31, 2023 are set forth below: Calendar Year Remaining Minimum Commitment as of December 31, 2023 (in thousands) 2024 14,085 2025 13,308 2026 9,605 2027 3,388 Total $ 40,386 We have incurred $ 19.4 million and $ 14.2 million against such minimum commitments for the years ended December 31 , 2023 and 2022, respectively. As of December 31, 2023 and December 31, 2022 , we have accrued $ 11.2 million and $ 9.2 million in research and development expenses related to minimum purchase commitments. Indemnification Agreements In the normal course of business, we enter into contracts and agreements that contain a variety of representations and warranties and provide for indemnification for certain liabilities. The exposure under these agreements is unknown because it involves claims that may be made against us in the future but have not yet been made. To date, we have not paid any claims or been required to defend any action related to our indemnification obligations. However, we may record charges in the future as a result of these indemnification obligations. We also have indemnification obligations to our directors and executive officers for specified events or occurrences, subject to some limits, while they are serving at our request in such capacities. There have been no claims to date and we consider the fair value of these indemnification agreements to be minimal. Accordingly, we did no t record liabilities for these agreements as of December 31, 2023 and 2022. Contingencies From time to time, we may be involved in legal proceedings, as well as demands, claims and threatened litigation, which arise in the normal course of our business or otherwise. The ultimate outcome of any litigation is uncertain and unfavorable outcomes could have a negative impact on our results of operations and financial condition. Regardless of outcome, litigation can have an adverse impact on us because of the defense costs, diversion of management resources and other factors. We are not currently involved in any material legal proceedings.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Stockholders' Equity	11. Stockholders’ Equity Our authorized capital stock consists of 520,000,000 shares, all with a par value of $ 0.0001 per share, of which 500,000,000 shares are designated as common stock and 20,000,000 shares are designated as preferred stock. There were no shares of preferred stock outstanding as of December 31, 2023 and 2022. Equity Offerings As part of our July 2019 underwritten public offering, we issued and sold pre-funded warrants to purchase 2,945,026 shares of common stock in an underwritten public offering pursuant to a shelf registration on Form S-3. Each pre-funded warrant entitles the holder to purchase one share of common stock at an exercise price of $ 0.0001 per share and expires seven years from the date of issuance. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital. Per the terms of the warrant agreement, a holder of the outstanding warrants is not entitled to exercise any portion of any pre-funded warrant if, upon exercise of the warrant, the holder’s ownership (together with its affiliates) of our common stock or combined voting power of our securities beneficially owned by such holder (together with its affiliates) would exceed 9.99 % after giving effect to the exercise (the Maximum Ownership Percentage). Upon at least 61 days’ prior notice to us by the holder, any holder may increase or decrease the Maximum Ownership Percentage to any other percentage not to exceed 19.99 %. During the year ended December 31, 2023, 361,260 of the July 2019 pre-funded warrants were exercised, and, as of December 31, 2023, pre-funded warrants to purchase 2,527,266 shares of our common stock from the July 2019 offering were outstanding. In May 2020, we issued and sold pre-funded warrants to purchase 2,866,961 shares of common stock at a public offering price of $ 11.3199 per warrant in an underwritten public offering pursuant to a shelf registration on Form S-3. In December 2020, we issued and sold pre-funded warrants to purchase 2,040,816 shares of common stock at a public offering price of $ 24.4999 per warrant in an underwritten public offering pursuant to a shelf registration on Form S-3. The terms of the pre-funded warrants issued and sold as part of the 2020 public offerings were similar to those issued and sold in 2019. During the year ended December 31, 2023, 1,898,578 and 656,107 of the May 2020 and December 2020 pre-funded warrants, respectively, were exercised. As of December 31, 2023, 968,383 and 1,384,709 of the pre-funded warrants to purchase shares of our common stock issued and sold as part of the May 2020 and December 2020 underwritten public offerings, respectively, were outstanding. In January 2024, we issued and sold pre-funded warrants to purchase 27,272,727 shares of common stock at a price of $ 0.5499 per warrant in a registered direct offering pursuant to a shelf registration on Form S-3. The gross proceeds from this sale were $ 15.0 million, resulting in net proceeds of $ 14.8 million, after deducting underwriting discounts and commissions and estimated offering expenses payable by us. Each of the January 2024 pre-funded warrants issued entitles the holder to purchase one share of common stock at an exercise price of $ 0.0001 per share, with no expiration date. These warrants were recorded as a component of stockholders’ equity within additional paid-in capital. Per the terms of the warrant agreement, a holder of the outstanding warrants is not entitled to exercise any portion of any pre-funded warrant if, upon exercise of the warrant, the holder’s ownership (together with its affiliates) of our common stock or combined voting power of our securities beneficially owned by such holder (together with its affiliates) would exceed 9.99 % after giving effect to the exercise (Maximum Ownership Percentage). Upon at least 61 days’ prior notice to us by the holder, any holder may increase or decrease the Maximum Ownership Percentage to any other percentage not to exceed 19.99 %. ATM Facilities In the past three years, we have entered into two separate sales agreements with Cowen and Company, LLC (Cowen): in November 2021 (the 2021 ATM Facility) and in November 2023 (the 2023 ATM Facility). Each ATM facility provides or provided for the sale, in our sole discretion, of shares of our common stock having an aggregate offering price of up to $ 100.0 million, through Cowen, as our sales agent. We filed a registration statement on Form S-3 registering the offer and sale of these shares under the Securities Act (the 2023 Registration Statement). Upon the effectiveness of the 2023 Registration Statement, the 2021 ATM Facility was terminated, and no further sales can be made under the 2021 ATM Facility. The issuance and sale of these shares by us pursuant to the ATM facilities are deemed “at the market” offerings defined in Rule 415 under the Securities Act of 1933, as amended (the Securities Act), and were registered under the Securities Act. Commissions of up to 3.0 % are due on the gross sales proceeds of the common stock sold under each ATM facility. During the year ended December 31, 2022, we sold an aggregate of 1,618,672 shares of common stock under the ATM facilities, at an average price of $ 13.84 per share, for gross proceeds of $ 22.4 million and net proceeds of $ 22.0 million, after deducting commissions and other offering expenses payable by us. During the year ended December 31, 2023 , we sold an aggregate of 3,038,432 shares of common stock under the ATM facilities, at an average price of $ 0.83 per share, for gross proceeds of $ 2.5 million and net proceeds of $ 2.2 million, after deducting commissions and other offering expenses payable by us. Approximately $ 0.1 million of the $ 2.2 million net proceeds were received on January 2, 2024. As of December 31, 2023, we had $ 98.2 million of common stock remaining and available to be sold under the 2023 ATM Facility. From January 1, 2024 through March 15, 2024, we sold an additional 12,321,365 shares of common stock under the 2023 ATM Facility, at an average price of $ 0.77 per share, for gross proceeds of $ 9.5 million and net proceeds of $ 9.3 million, after deducting commissions and other offering expenses payable by us. As of March 15, 2024, we had $ 88.7 million of common stock remaining and available to be sold under the 2023 ATM Facility, subject to certain conditions as specified in the agreement. Equity Incentive Plans In March 2014, we adopted the 2014 Equity Incentive Plan (2014 EIP), which was amended and restated on October 15, 2014 upon the pricing of our initial public offering (IPO). The 2014 EIP provides for annual increases in the number of shares available for issuance thereunder on the first business day of each fiscal year, beginning with 2015 and ending in 2024, equal to five percent 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 our board of directors. Under the terms of the 2014 EIP, we may grant stock options, RSAs and RSUs to employees, directors, consultants and other service providers. RSUs generally vest over two to four years. The fair value of RSUs, including those with performance conditions, is determined as the closing stock price on the date of grant. The 2014 EIP expires March 31, 2024, after which no new awards can be granted. All awards granted prior to the 2014 EIP expiration continue to remain outstanding and governed in accordance with the rules set forth in the 2014 EIP and the terms of the associated grant notice. In February 2018, we adopted the 2018 Inducement Plan (Inducement Plan), under which we may grant options, stock appreciation rights, RSAs and RSUs to new employees. In November 2020, September 2021 and June 2022, we amended the Inducement Plan to reserve an additional 1,500,000 shares of the Company’s common stock for issuance under the Inducement Plan in each case. Stock options are granted with exercise prices at no less than 100 % of the 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 option granted to a 10% shareholder cannot be less than 110% of the fair value of the shares on the date of grant. The estimated fair value of the shares is generally equal to the closing market price of the Company’s common stock on the measurement date. Options granted generally vest over two to four years and expire in seven to ten years . In 2022, we granted performance-based stock options to certain of our employees that provide for the issuance of stock options to purchase common stock if specified Company performance criteria related to business development initiatives are achieved. The number of performance-based awards that ultimately vests depends upon if performance criteria are achieved within a specified timeline, as well as the employee’s continuous service, as defined in the 2014 EIP, through the date of vesting. None of the performance criteria were achieved and the awards were subsequently forfeited. As of December 31, 2023 , a total of 20,326,356 shares of common stock were reserved for issuance under the 2014 EIP, of which 5,714,772 shares were available for future grant and 14,611,584 shares were subject to outstanding options and RSUs, including performance-based awards. As of December 31, 2023 , 4,773,147 shares of common stock were reserved for issuance under the Inducement Plan, of which 2,397,366 shares were available for future grant and 2,375,781 shares were subject to outstanding options and RSUs. Restricted Stock Units The following is a summary of RSU activity under our 2014 EIP and Inducement Plan: RSUs Shares Weighted Balance as of December 31, 2022 6,708,608 $ 10.61 Granted 5,635,916 $ 3.57 Forfeited ( 2,388,808 ) $ 7.91 Vested ( 3,688,003 ) $ 8.89 Balance as of December 31, 2023 6,267,713 $ 6.32 The weighted average grant date fair value of RSUs granted during the years ended December 31, 2023 and 2022 was $ 3.57 and $ 8.26 , respectively. The estimated fair value of RSUs that vested in the years ended December 31, 2023 and 2022 was $ 32.8 million and $ 34.4 million, respectively. As of December 31, 2023 , there was $ 35.9 million of unrecognized stock-based compensation expense related to RSUs that is expected to be recognized over a weighted average period of 2.0 years. The aggregate intrinsic value of the RSUs outstanding as of December 31, 2023 was $ 3.2 million. Under our RSU settlement procedures, for some of the RSUs granted to our employees, we withhold shares at settlement to cover the estimated payroll withholding tax obligations. During 2023 , we settled 3,688,003 shares underlying RSUs, of which 51,244 shares underlying RSUs were net settled by withholding 18,203 shares. The value of the shares underlying RSUs withheld was $ 0.1 million, based on the closing price of our common stock on the settlement date. During 2022 , we settled 2,247,296 shares underlying RSUs, of which 114,444 shares underlying RSUs were net settled by withholding 43,524 shares. The value of the shares underlying RSUs withheld was $ 0.6 million, based on the closing price of our common stock on the settlement date. The value of RSUs withheld in each period was remitted to the appropriate taxing authorities and has been reflected as a financing activity in our consolidated statements of cash flows. Stock Options The following is a summary of stock option activity under our 2014 EIP and Inducement Plan: Shares Weighted Average Exercise Price Weighted Average Aggregate Balance as of December 31, 2022 10,645,555 $ 16.88 6.4 $ 42 Granted 4,693,897 3.64 Exercised — — Forfeited or expired ( 4,619,801 ) 15.60 Balance as of December 31, 2023 10,719,651 $ 11.63 6.5 $ — Vested and expected to vest as of 10,719,651 $ 11.63 6.5 $ — Exercisable as of December 31, 2023 6,389,752 $ 15.40 5.1 $ — Aggregate intrinsic value represents the difference between the closing stock price of our common stock on December 31, 2023 and the exercise price of outstanding, in-the-money options. As of December 31, 2023 , there was $ 16.6 million of unrecognized stock-based compensation expense related to stock options that is expected to be recognized over a weighted average period of 1.9 years. This excludes unrecognized stock-based compensation expense for performance-based stock options that were deemed not probable of vesting in accordance with U.S. GAAP. No options for shares of our common stock were exercised during the year ended December 31, 2023 . Options for 15,989 shares of our common stock were exercised during the year ended December 31, 2022, with an intrinsic value of $ 0.1 million. As we believe it is more likely than not that no stock option related tax benefits will be realized, we do no t record any net tax benefits related to exercised options. The fair value of each option issued was estimated at the date of grant using the Black-Scholes valuation model. The following table summarizes the weighted-average assumptions used as inputs to the Black-Scholes model and resulting weighted-average grant date fair values of stock options granted during the periods indicated: Year ended December 31, 2023 2022 Assumptions: Expected term (years) 5.80 6.0 Expected volatility 83.9 % 73.2 % Risk-free interest rate 4.2 % 2.1 % Expected dividend yield 0.0 % 0.0 % Fair Value: Weighted-average estimated grant date fair value per share $ 2.62 $ 5.88 Options granted 4,693,897 3,615,971 Total estimated grant date fair value $ 12,298,010 $ 21,261,909 The estimated fair value of stock options that vested in the years ended December 31, 2023 and 2022 was $ 17.0 million and $ 23.2 million, respectively. Employee Stock Purchase Plan In May 2014, we adopted the 2014 Employee Stock Purchase Plan (“2014 ESPP”), which became effective on October 15, 2014 upon the pricing of our IPO. The 2014 ESPP permits eligible employees to purchase common stock at a discount through payroll deductions during defined offering periods. Eligible employees can purchase shares of the Company’s common stock at 85 % of the lower of the fair market value of the common stock at (i) the beginning of the offering period or (ii) at the end of the purchase period. We recorded $ 0.7 million and $ 1.1 million of expense related to the 2014 ESPP in the years ended December 31, 2023 and 2022 , respectively. A total of 896,246 and 417,081 shares were purchased under the ESPP during the years ended December 31, 2023 and 2022, respectively. As of December 31, 2023 , there was $ 0.1 million of unrecognized stock-based compensation expense related to the ESPP that is expected to be recognized by the end of second quarter of 2024. The 2014 ESPP provides for annual increases in the number of shares available for issuance thereunder on the first business day of each fiscal year, beginning with 2015 and ending in 2024, equal to the lower of (i) one percent of the number of shares of our common stock outstanding as of such date, (ii) 230,769 shares of our common stock, or (iii) a lesser number of shares as determined by our board of directors. As of December 31, 2023 , there were 2,279,049 shares authorized under the 2014 ESPP. Reserved Shares The following shares of common stock were reserved for future issuance under our equity incentive plans as of December 31, 2023: Total Shares Reserved 2014 Equity Incentive Plan 20,326,356 2018 Inducement Plan 4,773,147 2014 Employee Stock Purchase Plan 10,593 Total reserved shares of common stock 25,110,096 Stock-based Compensation Expense The following is a summary of stock-based compensation expense for the periods presented: Year Ended December 31, 2023 2022 (in thousands) Research and development $ 26,529 $ 31,363 General and administrative 18,857 22,475 Total stock-based compensation expense $ 45,386 $ 53,838

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes Losses before provision for income taxes were as follows in each period presented: Year Ended December 31, 2023 2022 (in thousands) United States $ ( 276,360 ) $ ( 228,395 ) Foreign 249 105 Total loss before provision for income taxes $ ( 276,111 ) $ ( 228,290 ) The components of provision for income taxes were as follows in each period presented: Year Ended December 31, 2023 2022 (in thousands) Current provision for income taxes: State $ 1 $ — Foreign 14 12 Total current provision for income taxes $ 15 $ 12 A reconciliation of statutory tax rates to effective tax rates were as follows in each of the periods presented: Year Ended December 31, 2023 2022 Federal income taxes at statutory rate 21.0 % 21.0 % Research tax credits 4.3 % 7.8 % Stock-based compensation ( 4.5 %) ( 3.8 %) Other ( 0.4 %) ( 0.2 %) Change in valuation allowance ( 20.4 %) ( 24.8 %) Effective tax rate 0.0 % 0.0 % Deferred tax assets and liabilities reflect the net tax effects of (a) temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes and (b) operating loss and tax credit carryforwards. Significant components of our deferred tax assets and liabilities were as follows for each of the dates presented: As of December 31, 2023 2022 (in thousands) Deferred tax assets: Net operating loss carryforwards $ 323,581 $ 302,591 Capitalized research expenses 72,229 50,522 Tax credit carryforwards 30,580 19,427 Stock-based compensation 14,033 19,201 Deferred revenue 17,018 10,069 Operating lease liabilities 12,035 15,857 License fees 5,926 6,877 Other 11,187 13,169 Total deferred tax assets 486,589 437,713 Valuation allowance ( 474,982 ) ( 422,493 ) Total deferred tax assets 11,607 15,220 Deferred tax liabilities: Operating lease assets ( 11,607 ) ( 15,220 ) Total deferred tax liabilities ( 11,607 ) ( 15,220 ) Net deferred tax assets (liabilities) $ — $ — Beginning January 1, 2022, the Tax Cuts and Jobs Act (the Tax Act) 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 (IRC) 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 Tax Act, deferred tax assets related to capitalized research expenses pursuant to IRC Section 174 increased by $ 21.7 million and $ 43.7 million for the years ended December 31, 2023 and 2022, respectively. These increases were partially offset by amortization on research expenses capitalized in prior years. Our tax credit carryforwards increased by $ 11.2 million, as compared to 2022, due to research and development and orphan drug credits generated during the current year. We regularly evaluate the positive and negative evidence in determining the realizability of our deferred tax assets. Based upon the weight of available evidence, which includes our historical operating performance and reported cumulative net losses since inception, we maintained a full valuation allowance on the net deferred tax assets as of December 31, 2023 and 2022. We intend to maintain a full valuation allowance on our deferred tax assets until sufficient positive evidence exists to support reversal of the valuation allowance. The valuation allowance increased by $ 52.5 million for the year ended December 31, 2023 due to the increase in our net deferred tax assets. In August 2022, the CHIPS and Science Act (CHIPS Act) and the IRA were enacted, neither of which are expected to have a material impact to our financial statements. The American Rescue Plan Act (ARA) was signed into law on March 11, 2021. We do not expect the ARA to have a material impact on our financial statements, however, given the potential changes to IRC Section 162(m) effective in 2027 as a result of the ARA, we will continue to monitor and assess. Under the Tax Act, federal NOLs generated in tax years beginning on or after January 1, 2018 may be carried forward indefinitely, but the utilization of such federal NOLs is limited to 80% of taxable income in future years. Since enactment, the IRS and Treasury have issued final and proposed regulations including clarifying guidance on several topics addressed by the Tax Act. Not all states conform to the Tax Act or and other states have varying conformity to the Tax Act. As of December 31, 2023, for federal income tax purposes, we had NOL carryforwards of approximately $ 1.1 billion of which $ 23.3 million begin to expire in 2035 and the remaining may be carried forward indefinitely, research & development tax credits of $ 34.6 million which begin to expire in 2032 , and orphan drug tax credits of $ 111.8 million which begin to expire in 2035 . For state income tax purposes, we had NOL carryforwards of approximately $ 1.3 billion which begin to expire in 2030 , research & development tax credits of $ 43.5 million which may be carried forward indefinitely, and California Completes tax credit of $ 2.0 million, which begins to expire in 2025 . Under IRC Section 382, as amended, substantial restrictions exist on the utilization of NOL and tax credit carryforwards in the event a corporation experienced an “ownership change.” Generally, a Section 382 “ownership change” occurs if one or more stockholders or groups of stockholders who owns at least 5% of a corporation’s stock increases its ownership by more than 50 percentage points over its lowest ownership percentage within a specified testing period. Similar rules may apply under state tax laws. Accordingly, our ability to utilize NOL and tax credit carryforwards may be limited as a result of such ownership changes, and such a limitation could result in the expiration of carryforwards before they are utilized. We have completed a Section 382 study of transactions in our stock through December 31, 2023. The study concluded that we have experienced ownership changes since inception. However, this is not expected to result in the expiration of tax attribute carryforwards prior to utilization. The changes in the balance of gross unrecognized tax benefits, which excludes interest and penalties, for the years ended December 31, 2022 and 2023 are as follows: (In thousands) Balance as of January 1, 2022 144,067 Gross increases for tax positions related to current year 7,683 Gross increases for tax positions related to prior year — Gross decreases for tax positions related to prior year ( 785 ) Balance as of December 31, 2022 150,965 Gross increases for tax positions related to current year 5,538 Gross increases for tax positions related to prior year 3,843 Gross decreases for tax positions related to prior year — Balance as of December 31, 2023 $ 160,346 We currently have a full valuation allowance against our U.S. net deferred tax assets, which would impact the timing of the effective tax rate benefit should any uncertain tax position be favorably settled in the future. The reversal of unrecognized tax benefits would not affect our effective tax rate to the extent we continue to maintain a full valuation allowance against our deferred tax assets. Our policy is to account for interest and penalties related to uncertain tax positions as a component of the income tax provision. We have no accrued interest and penalties as of December 31, 2023 and 2022 due to available tax losses. Our significant jurisdictions are the U.S. federal jurisdiction and the California state jurisdiction. All of our tax years remain open to examination by the U.S. federal and California tax authorities. We also file in other state, local and foreign jurisdictions in which we operate, and such tax years remain open to examination. As of December 31, 2023, we are not permanently reinvested with respect to its foreign earnings and have not recorded deferred income taxes and withholding taxes as these taxes are immaterial to the financial statements.

Supplemental Balance Sheet Info

Supplemental Balance Sheet Information	12 Months Ended
Supplemental Balance Sheet Information	Dec. 31, 2023
Supplemental Balance Sheet Information [Abstract]
Supplemental Balance Sheet Information	13. Supplemental Balance Sheet Information Inventories Inventories consist of the following as of each period: December 31, December 31, 2023 2022 (in thousands) Raw Materials $ 2,335 $ 1,214 Work-in-process 7,371 372 Total inventories $ 9,706 $ 1,586 Property and equipment, net Property and equipment consisted of the following as of each period end: December 31, December 31, 2023 2022 (in thousands) Leasehold improvements $ 904 $ 875 Lab equipment 15,540 14,797 Machinery and equipment 572 572 Computer equipment and software 1,279 1,149 Furniture and fixtures 1,272 1,297 Construction in progress 158 32 Property and equipment, gross 19,725 18,722 Less: accumulated depreciation ( 15,869 ) ( 12,422 ) Property and equipment, net $ 3,856 $ 6,300 Depreciation expense was $ 3.7 million and $ 4.7 million for the years ended December 31, 2023 and 2022, respectively. Other current liabilities Other current liabilities consisted of the following as of each period end: December 31, December 31, 2023 2022 (in thousands) Accrued operating expenses $ 19,007 $ 7,435 Current portion of operating lease liabilities 11,264 12,806 Current portion of finance lease liabilities 915 834 Other accrued liabilities 640 319 Total other current liabilities $ 31,826 $ 21,394

Subsequent Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Event s In January 2024, we announced a reduction in force of approximately 25 % of total workforce. We expect to recognize approximately $ 4.5 million in total severance and related benefits as a result of this reduction in force, consisting primarily of severance payments and wages for the 60-day notice period in accordance with the California WARN Act. In most cases, the severance will be paid in the first half of 2024. Certain of the notified employees had employment agreements which provided for separation benefits in the form of salary continuation; these benefits will be paid from February 2024 through January 2025. The majority of the associated costs represent cash expenditures.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2023
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of Atara and our wholly owned subsidiaries. All intercompany balances and transactions are eliminated in consolidation.
Segment and Geographic Information	Segment and Geographic Information We operate and manage our business as one operating and reportable segment, which is the business of developing therapeutics. Our Chief Executive Officer, who is our chief operating decision maker, reviews financial information on an aggregate basis for purposes of allocating resources and evaluating financial performance. Substantially all of our assets are located in the U.S. All commercialization and collaboration revenue recognized in 2023 related to our agreements with Pierre Fabre, a French company. Of the $ 63.6 million license and collaboration revenue recognized in 2022, $ 61.8 million related to our agreements with Bayer, a German company, and $ 1.8 million related to our agreements with Pierre Fabre, a French company.
Use of Estimates	Use of Estimates We prepare our consolidated financial statements in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP), which requires us to make estimates and assumptions that affect the amounts reported in our consolidated financial statements and accompanying notes. The level of uncertainty in estimates and assumptions increases with the length of time until the underlying transactions are completed. Significant estimates and assumptions relied upon in preparing these financial statements include those related to revenue recognition, accrued research and development expenses, stock-based compensation expense, liability related to the sale of future revenues and income taxes. Additionally, we use available market information to assess the fair value of our short-term investments. Actual results could differ materially from those estimates. If actual amounts differ from estimates, we include the updates in our consolidated results of operations in the period the actual amounts become known. Historically, the aggregate differences, if any, between our estimates and actual amounts in any year have not had a material effect on our consolidated financial statements.
Liquidity Risk	Liquidity Risk We have incurred significant operating losses since inception and have relied primarily on public and private equity financings and receipts from commercialization and license and collaboration agreements to fund our operations. As we continue to incur losses, our transition to profitability will depend on the successful development, approval and commercialization of product candidates and on the achievement of sufficient revenues to support our cost structure. We may never achieve sustained operating cash inflows or profitability.
Going Concern	Going Concern We have incurred operating losses since inception and we expect that existing cash, cash equivalents and short-term investments as of December 31, 2023, will not be sufficient to fund our planned operations for at least 12 months after the issuance of the accompanying consolidated financial statements. Although we anticipate the receipt of certain payments from the amended and restated Pierre Fabre Commercialization Agreement in 2024 and 2025, such payments are contingent upon the successful filing and approval of the tab-cel BLA, as well as the completion of specific development and regulatory activities by us and actions taken by third parties, and are, therefore, uncertain at this time. To alleviate the conditions that raise substantial doubt about our ability to continue as a going concern, we plan to secure additional capital, potentially through a combination of public or private security offerings; use of our ATM facility as described in Note 9; and/or strategic transactions. We may also need to raise additional funding as required based on the status of our development programs and our projected cash flows. Although we have been successful in raising capital in the past, and expect to continue to raise capital as required, there is no assurance that we will be successful in obtaining sufficient funding on terms acceptable to us to fund continuing operations, if at all, or identify and enter into any strategic transactions that will provide the capital that we will require. If we are unable to obtain sufficient funding on acceptable terms, we could be forced to delay, limit, reduce or terminate preclinical studies, clinical studies or other development activities for one or more of our product candidates, which could have a material adverse effect on our business, results of operations, and financial condition. Accordingly, we have concluded that substantial doubt exists with respect to our ability to continue as a going concern for at least 12 months after the issuance of the accompanying consolidated financial statements. The consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty.
Concentration of Credit Risk and Other Uncertainties	Concentration of Credit Risk and Other Uncertainties We place cash and cash equivalents in the custody of financial institutions that management believes are of high credit quality, the amount of which at times, may be in excess of the amount insured by the Federal Deposit Insurance Corporation. We also make short-term investments in money market funds; U.S. Treasury, government agency and corporate debt obligations; commercial paper; certificates of deposit; and asset-backed securities, which can be subject to certain credit risk. We strive to mitigate this credit risk by investing in high-grade instruments, limiting our exposure to any one issuer and monitoring the ongoing creditworthiness of the financial institutions and issuers.
Currency Translation	Currency Translation Transactions and monetary assets and liabilities that are denominated in a foreign currency are translated into U.S. dollars at the current exchange rate on the transaction date and as of each balance sheet date, respectively, with gains or losses on foreign exchange changes recognized in interest and other income (expense), net in the consolidated statements of operations and comprehensive loss. Foreign currency-denominated monetary assets and liabilities as of December 31, 2023 were not material.
Cash, Cash Equivalents and Short-Term Investments	Cash, Cash Equivalents and Short-Term Investments Cash and cash equivalents are defined as highly liquid investments with original maturities of 90 days or less at the date of purchase. Investments with original maturities of greater than 90 days are classified as short-term investments on the balance sheet. As our entire investment portfolio is considered available for use in current operations, we classify all investments as available-for-sale and as current assets, even though the stated maturity may be more than one year from the current balance sheet date. Available-for-sale securities are carried at fair value, with unrealized gains and losses reported in accumulated other comprehensive loss, which is a separate component of stockholders’ equity in the consolidated balance sheet. The amortized cost of securities is adjusted for amortization of premiums and accretion of discounts to maturity, which are recorded to interest income in the consolidated statements of operations and comprehensive loss. Changes in the fair value of available-for-sale securities impact the consolidated statements of operations and comprehensive loss only when such securities are sold, if an allowance for credit losses is recognized or if an impairment is recognized. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. We regularly review our investment portfolio to determine if any security is impaired, which would require us to record an allowance for credit losses or impairment charge in the period any such determination is made. In making this judgment, we evaluate, among other things, the duration and extent to which the fair value of a security is less than its cost, our intent to sell or whether it is more likely than not that we will be required to sell the security before recovery of its amortized cost basis, the financial condition of the issuer and any changes thereto, and, as necessary, the portion of a decline in fair value that is credit-related. This assessment could change in the future due to new developments or changes in assumptions related to any particular security. Realized gains and losses, allowances for credit losses and impairments on available-for-sale securities, if any, are recorded to other income (expense), net in the statements of operations and comprehensive loss.
Fair Value Measurement	Fair Value Measurement The carrying amounts of certain of our financial instruments including cash equivalents, accounts receivable, other current assets, accounts payable and accrued liabilities approximate fair value due to their short maturities. Short-term investments are comprised of available-for-sale securities, which are carried at fair value.
Financial Instruments	Financial Instruments Our financial assets are measured at fair value on a recurring basis using the following hierarchy to prioritize valuation inputs, in accordance with applicable GAAP: Level 1: Quoted prices in active markets for identical assets or liabilities that we have the ability to access Level 2: Observable market-based inputs or unobservable inputs that are corroborated by market data such as quoted prices, interest rates and yield curves Level 3: Inputs that are unobservable data points that are not corroborated by market data We review the fair value hierarchy classification on a quarterly basis. Changes in the ability to observe valuation inputs may result in a reclassification of levels of certain securities within the fair value hierarchy. We recognize transfers into and out of levels within the fair value hierarchy in the period in which the actual event or change in circumstances that caused the transfer occurs. There have been no transfers between Level 1, Level 2, and Level 3 in any periods presented. 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. Treasury, government agency and corporate debt obligations, commercial paper and asset-backed securities are valued primarily using market prices of comparable securities, bid/ask quotes, interest rate yields and prepayment spreads and are included in Level 2. Financial assets and liabilities are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies, or similar techniques, and at least one significant model assumption or input is unobservable. We have no Level 3 financial assets or liabilities.
Accounts Receivable, net	Accounts Receivable, net Accounts receivable are recorded net of estimates of variable consideration for which reserves are established and which result from discounts and chargebacks that are offered within contracts between us and a limited number of specialty pharmacies and a specialty distributor in the United States. These reserves are classified as reductions of accounts receivable. We estimate the allowance for doubtful accounts using the current expected credit loss model, or CECL model. Under the CECL model, the allowance for doubtful accounts reflects the net amount expected to be collected from the accounts receivable. We evaluate the collectability of these cash flow based on the asset’s amortized cost, the risk of loss even when that risk is remote, losses over an asset’s contractual life, and other relevant information available to us. Accounts receivable balances are written off against the allowance when it is probable that the receivable will not be collected. Given the nature and history of our accounts receivable, we determined that an allowance for doubtful accounts was not required for the periods presented.
Inventories	Inventories Inventories are stated at the lower of cost or estimated net realizable value, on a specific identification basis. We use actual costs to determine our cost basis for inventories. Inventories consist of raw materials, work-in-process and finished goods. We begin capitalizing costs as inventory when the product candidate receives regulatory approval and when the manufacturing facility producing such inventory is qualified by the relevant regulatory agency. Prior to regulatory approval and qualification, we record such production costs related to product candidates as research and development expenses. Any manufactured product that is available for commercial sale is recorded to inventory; to the extent it is later used for clinical studies, such inventory costs are then recorded within research and development expenses. We periodically assess the recoverability of our inventory and reduce the carrying value of the inventory when items are determined to be obsolete, defective or in excess of forecasted sales requirements. Inventory write-downs for excess, defective and obsolete inventory are recorded as a cost of sales.
Property and Equipment, Net	Property and Equipment, net Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets, ranging from three to five years , except for leasehold improvements, which are depreciated on a straight-line basis over the lesser of the estimated useful life of the leasehold improvement or the lease term. Costs incurred to acquire, construct or install property and equipment during the construction stage of a capital project or costs incurred to purchase and develop internal use software during the application development stage are recorded as construction in progress. Maintenance and repairs are charged to operations as incurred.
Long-lived Assets	Long-lived Assets We evaluate the carrying amount of our long-lived assets whenever events or changes in circumstances indicate that the assets may not be recoverable. An impairment loss would be recognized when estimated future cash flows expected to result from the use of the asset and its eventual disposition are less than the carrying amount of the asset. To date, there have been no such impairment losses.
Asset Retirement Obligations ("ARO")	Asset Retirement Obligation (ARO) An ARO is a legal obligation associated with the retirement of long-lived assets pertaining to leasehold improvements. These liabilities are initially recorded at fair value and the related asset retirement costs are capitalized by increasing the carrying amount of the related assets by the same amount as the liability. Asset retirement costs are subsequently depreciated over the useful lives of the related assets. Subsequent to initial recognition, we record period-to-period changes in the ARO liability resulting from the passage of time and revisions to either the timing or the amount of the original estimate of undiscounted cash flows. We derecognize ARO liabilities when the related obligations are settled.
Leases	Leases We determine if a contract is or contains a lease at contract inception. Operating leases are included in operating lease assets, other current liabilities, and operating lease liabilities on our consolidated balance sheets. Our policy is to not recognize right-of-use (ROU) assets and lease liabilities for short-term operating leases with terms of 12 months or less; we recognize short-term lease expense for these leases on a straight-line basis over the lease term. Long-term operating lease ROU assets and long-term operating lease liabilities are presented separately and operating lease liabilities payable in the next twelve months are recorded in other current liabilities. Finance lease ROU assets are recorded in other assets and the related finance lease liabilities are presented in other current liabilities and other long-term liabilities. Lease assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. The lease term includes renewal options that we are reasonably certain of exercising as of the commencement date. None of the lease terms used to calculate the future minimum lease payments at commencement date include renewal options. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of future payments. The incremental borrowing rate for our leases is determined based on lease term and currency in which lease payments are made, adjusted for impacts of collateral. Lease assets also includes any lease payments made and excludes lease incentives and initial direct costs incurred. Operating lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. Finance lease assets are amortized over the shorter of the lease term or the asset’s estimated useful life. Our facilities and equipment operating leases have lease and non-lease components and we have made a policy election to account for the lease and non-lease components as a single lease component. We are considered the sub-lessor for certain of our leases where we have entered into a sub-lease agreement with or have assigned our lease to another party. Rental income was not material for any period presented and we record rental income as a reduction to rent expense within operating expenses. We analyze whether or not amendments to existing leases classify as a lease modification or a full or partial termination of the existing lease. To the extent a partial lease termination is identified, our accounting policy is to decrease the existing right-of-use asset on a basis proportionate to the reduction in lease liability resulting from the partial termination.
Accruals of Research and Development Costs	Accruals of Research and Development Costs We record accruals for estimated research and development costs based on an evaluation of our vendors’ progress towards completion of specific tasks, using data such as patient enrollment, clinical site activations or information provided to us by our vendors regarding their actual costs incurred. Payments for these activities are based on the terms of individual contracts and payment timing may differ significantly from the period in which the services are performed. We determine accrual estimates through reports from and discussions with internal personnel and outside service providers as to the progress or state of completion of studies, or the services completed. Our estimates of accrued expenses as of each balance sheet date are based on the facts and circumstances known at the time. Costs that are paid in advance of performance are deferred as a prepaid asset and recognized as expense as the services are provided.
Sale of Future Revenues Policy Text Block	Sale of Future Revenues To the extent that we account for the sale of future revenues as debt in accordance with ASC 470, we amortize the liability and recognize interest expense related to the sale of future revenues using the effective interest rate method over the estimated life of the underlying agreement. The liability and related interest expense are based on our current estimate of expected future payments over the life of the arrangement. We re-assess the amount and timing of expected payments each reporting period using a combination of internal projections and forecasts from external resources and record interest expense on the carrying value of the liability using the imputed effective interest rate on a prospective basis.
Revenue Recognition	Revenue Recognition For contracts that are determined to be within the scope of Accounting Standards Codification Topic 606 (Accounting Standards Update (ASU) No. 2014-09), Revenue from Contracts with Customers , and all subsequent amendments (collectively, ASC 606), revenue is recognized as we satisfy performance obligations and when a customer obtains control of the promised goods or services. The amount of revenue recognized reflects the consideration to which we expect to be entitled to receive in exchange for these goods and services. To achieve this core principle, we apply the following five steps (i) identify the contract with the 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 we satisfy a performance obligation. We only apply the five-step model to contracts when we determine that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration. Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct and are distinct in the context of the contract. To the extent a contract includes multiple promised goods and services, we apply judgment to determine whether promised goods and services are both capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation. The transaction price is determined based on the consideration to which we will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration, we estimate the amount of variable consideration that should be included in the transaction price utilizing either the expected value method or the most likely amount method, depending on the nature of the variable consideration. Variable consideration is included in the transaction price if, in our judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Any estimates, including the effect of the constraint on variable consideration, are evaluated at each reporting period for any changes. Determining the transaction price requires significant judgment, which is discussed in further detail for our out-license agreements in Note 5. Our out-license agreements do not contain a significant financing component. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The consideration to be received is allocated among the separate performance obligations based on relative standalone selling prices. We typically determine standalone selling prices using an expected cost plus margin approach model. We satisfy performance obligations either over time or at a point in time. Revenue is recognized over time if either (i) the customer simultaneously receives and consumes the benefits provided by our performance, (ii) our performance creates or enhances an asset that the customer controls as the asset is created or enhanced or (iii) our performance does not create an asset with an alternative use to the entity and we have an enforceable right to payment for performance completed to date. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. If we do not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring control of a promised good or service to a customer. As discussed in further detail in Note 5, the terms of our customer contracts include potential payments to us for some or all of the following: nonrefundable, upfront fees; development, regulatory, and commercial milestone payments; research and development funding payments; royalties on the net sales of licensed products; and transition plan cost reimbursements for certain development, safety, regulatory, and process science services. These payments relate to promised goods or services for which revenue will be recognized upon our satisfaction of the underlying performance obligations. Licenses of intellectual property : If the license of our intellectual property is determined to be distinct from the other performance obligations identified in an arrangement, we recognize revenues from consideration allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are combined with other promises, we utilize judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. Upfront payments : Upfront payments and fees are recorded as deferred revenue upon receipt or when due and may require deferral of revenue recognition to a future period until we have satisfied our obligations under these arrangements. Milestone payments : At the inception of each arrangement that includes development milestone payments, we evaluate the probability of reaching the milestones and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur in the future, the associated milestone value is included in the transaction price. The transaction price is then allocated to each performance obligation on a relative standalone selling price basis, for which we recognize revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, we re-evaluate the probability of achievement of such development milestones and any related constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license and collaboration revenues and the consolidated statements of operations and comprehensive loss in the period of adjustment. Royalties : For arrangements that include sales-based royalties, including milestone payments based on levels of sales, if the license is deemed to be the predominant item to which the royalties relate, we recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied, or partially satisfied. To date, we have not recognized material royalty revenue resulting from our out-licensing agreements. Transition plan cost reimbursements : Reimbursements for certain development, safety, regulatory and manufacturing services are recorded as revenue as we perform the services and related obligations identified within the transition plans for our customers. Certain judgments affect the application of our revenue recognition policy. For example, we record short-term and long-term deferred revenue based on our best estimate of when such revenue will be recognized. Short-term deferred revenue consists of amounts that are expected to be recognized as revenue in the next 12 months, and long-term deferred revenue consists of amounts that we expect will be recognized after the next 12 months. This estimate is based on forecasted patient demand, our current operating plan and expected dates of technology transfer, and if these items should change in the future, we may recognize a different amount of deferred revenue over the next 12-month period.
Cost of commercialization revenue	Cost of commercialization revenue Cost of commercialization revenue consists primarily of expenses associated with cell selection services performed for Pierre Fabre, in-license sales-related milestone costs, period manufacturing expenses and adjustments to reduce inventory to the lower of cost or net realizable value. Costs incurred to produce Ebvallo prior to regulatory approval, referred to as zero cost inventories, have been recorded as research and development expense in our consolidated statement of operations and comprehensive income (loss). All tab-cel (Ebvallo) sold to Pierre Fabre in the year ended December 31, 2023 was zero cost inventories. Once we begin selling Ebvallo produced after receiving regulatory approval and in a qualified manufacturing facility, and as revenue is recognized on such Ebvallo sales, cost of commercialization revenue will also include direct and indirect costs related to the production of Ebvallo. Such costs include, but are not limited to, CMO costs, quality testing and validation, materials used in production, and an allocation of compensation, benefits and overhead costs associated with employees involved with production. In 2023 and 2022, cost of commercialization revenue included adjustments of $ 6.6 million and $ 0.0 million, respectively, to write-off of inventories and to reflect them at the lower of cost or net realizable value.
Research and Development Expense	Research and Development Expense Research and development expense consists of costs incurred in performing research and development activities, including compensation and benefits for research and development employees; expenses incurred under agreements with contract research organizations and investigative sites that conduct clinical and preclinical studies; expense incurred under agreements with contract manufacturing organizations related to acquiring and manufacturing clinical study materials and other supplies to support the manufacture of our product candidates; payments under licensing and research and development agreements; other outside services and consulting costs, and facilities, information technology and overhead expenses. Research and development costs are expensed as incurred.
Stock-Based Compensation Expense	Stock-Based Compensation Expense We account for stock-based compensation expense, including the expense of restricted common stock awards, grants of restricted stock units (RSUs), and stock options that may be settled in shares of our common stock, based on the fair values of the equity instruments issued. The fair value is determined on the measurement date, which is generally the date of grant. The fair value of our RSUs is measured at the closing market price of our common stock on the measurement date. The fair value for our stock option awards is determined at the grant date using the Black-Scholes valuation model. In determining the fair value of stock option awards granted, we use the Black-Scholes valuation model and assumptions include: Expected term – We derived the expected term using the “simplified” method (the expected term is determined as the average of the time-to-vesting and the contractual life of the options), as we have limited historical information to develop expectations about future exercise patterns and post vesting employment termination behavior. Expected volatility – In 2021 and 2022, volatility was estimated using an average of Atara’s historical volatility and comparable public companies’ volatility for similar terms. Beginning in 2023, volatility is based solely on Atara’s stock price historical volatility. Expected dividend – We have not historically declared or paid dividends to our stockholders and have no plans to pay dividends; therefore, we assumed an expected dividend yield of 0 %. Risk-free interest rate – The risk-free interest rate is based on the yield on U.S. Treasury securities with the expected term of the associated award. For awards with performance-based vesting criteria, we assess the probability of the achievement of the performance conditions at the end of each reporting period and begin to recognize the share-based compensation costs when it becomes probable that the performance conditions will be met. For awards that are subject to both service and performance conditions, no expense is recognized until it is probable that performance conditions will be met. Stock-based compensation expense for awards with time-based vesting criteria is recognized as expense on a straight-line basis over the requisite service period. Stock-based compensation expense for awards with performance and other vesting criteria is recognized as expense under an accelerated graded vesting model. We account for forfeitures of stock-based awards as they occur.
Defined Contribution Plan	Defined Contribution Plan We have one qualified 401(k) plan covering all eligible employees. Under the plan, employees may contribute up to the statutory allowable amount for any calendar year. We make matching contributions, equal to 50 % of each dollar contributed up to the first 6 % of an individual’s eligible earnings, up to the annual IRS maximum. For the years ended December 31, 2023 and 2022 we recorded matching contributions of approximately $ 1.9 million and $ 2.3 million, respectively.
Income Taxes	Income Taxes We use the asset and liability method to account for income taxes. We record deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect when the differences are expected to reverse. Valuation allowances are provided when necessary to reduce net deferred tax assets to the amount that is more likely than not to be realized. Based on the available evidence, we are unable, at this time, to support the determination that it is more likely than not that our deferred tax assets will be utilized in the future. Accordingly, we recorded a full valuation allowance as of December 31, 2023 and 2022. We intend to maintain valuation allowances until sufficient evidence exists to support their reversal. Tax benefits related to uncertain tax positions are recognized when it is more likely than not that a tax position will be sustained during an audit. Interest and penalties related to unrecognized tax benefits are included within the provision for income tax.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is defined as a change in equity of a business enterprise during a period resulting from transactions from non-owner sources. Our other comprehensive income (loss) is comprised solely of unrealized gains (losses) on available-for-sale securities and is presented net of taxes. There have not been any material reclassifications from other comprehensive income (loss) to net loss recorded during any period presented.
Recent Accounting Pronouncements	Recent Accounting Pronouncements We consider the applicability and impact of any Accounting Standards Updates (ASUs) issued by the Financial Accounting Standards Board (FASB). Other than the ASUs listed below, all other ASUs were assessed and determined to be either not applicable to Atara or are expected to have minimal impact on our consolidated financial statements. In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. The amendment requires disclosure of significant segment expenses that are regularly provided to the chief operating decision maker and included within each reported measure of segment profit or loss, an amount and description of its composition for other segment items, and interim disclosures of a reportable segment’s profit or loss and assets. Additionally, all disclosure requirements under the guidance are also required for public entities with a single reportable segment. The amendments are effective for fiscal years beginning after December 15, 2023, and for interim periods within fiscal years beginning after December 15, 2024. We are currently evaluating this ASU to determine its impact on our disclosures. In December 2023, the FASB issued ASU No. 2023-09 Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which requires enhancements to certain income tax disclosures, most notably the income tax rate reconciliation and income taxes paid. The amendments are effective for fiscal years beginning after December 15, 2024. Early adoption is permitted. We do not expect the adoption of this standard will have a material impact on our disclosures. Additionally, on March 6, 2024, the Securities and Exchange Commission (SEC) issued Final Rule No. 33-11275, The Enhancement and Standardization of Climate-Related Disclosures for Investors . The rule requires registrants to provide climate related disclosures in their annual reports, including, but not limited to, material Scope 1 and Scope 2 GHG emissions (for large accelerated filers and accelerated filers); governance and oversight of material climate-related risks; the material impact of climate risks on the registrant’s strategy, business model, and outlook; risk management processes for material climate-related risks; and material climate targets and goals. Based on our current small reporting company and non-accelerated filer status, certain elements of the rule are effective for fiscal years beginning after December 15, 2026, with the remaining requirements effective for fiscal years beginning after December 15, 2027. We will evaluate the SEC rule to determine its impact on our future financial reporting requirements and related disclosures.

Net Loss per Common Share (Tabl

Net Loss per Common Share (Tables)	12 Months Ended
Net Loss per Common Share (Tables)	Dec. 31, 2023
Earnings Per Share [Abstract]
Antidilutive Securities Excluded From Computation of Diluted Net Loss per Common Share	The following table represents the potential common shares issuable pursuant to outstanding securities as of the dates listed that were excluded from the computation of diluted net loss per common share, as their inclusion would have an antidilutive effect: As of December 31, 2023 2022 Unvested RSUs 6,261,213 6,698,858 Vested and unvested options 10,706,651 10,336,634 ESPP share purchase rights 185,843 86,782 Total 17,153,707 17,122,274

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
Financial Instruments (Tables)	Dec. 31, 2023
Financial Instruments Disclosure [Abstract]
Summary of Estimated Fair Value and Related Valuation Input Hierarchy of Available-for-Sale Securities	The following tables summarize the estimated fair value and related valuation input hierarchy of our available-for-sale securities as of each period end: Total Total Total Total Amortized Unrealized Unrealized Estimated As of December 31, 2023: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 14,376 $ — $ — $ 14,376 U.S. Treasury obligations Level 2 9,928 1 — 9,929 Corporate debt obligations Level 2 26,089 — ( 205 ) 25,884 Total available-for-sale securities 50,393 1 ( 205 ) 50,189 Less: amounts classified as cash equivalents ( 24,304 ) ( 1 ) — ( 24,305 ) Amounts classified as short-term investments $ 26,089 $ — $ ( 205 ) $ 25,884 Total Total Total Total Amortized Unrealized Unrealized Estimated As of December 31, 2022: Input Level Cost Gain Loss Fair Value (in thousands) Money market funds Level 1 $ 78,033 $ — $ — $ 78,033 U.S. Treasury obligations Level 2 63,013 3 ( 394 ) 62,622 Government agency obligations Level 2 8,086 — ( 48 ) 8,038 Corporate debt obligations Level 2 82,598 4 ( 1,513 ) 81,089 Commercial paper Level 2 996 — — 996 Asset-backed securities Level 2 6,343 — ( 119 ) 6,224 Total available-for-sale securities 239,069 7 ( 2,074 ) 237,002 Less: amounts classified as cash equivalents ( 87,122 ) ( 3 ) — ( 87,125 ) Amounts classified as short-term investments $ 151,947 $ 4 $ ( 2,074 ) $ 149,877
Amortized Cost and Fair Value of Available for Sale Securities by Contractual Maturity	The amortized cost and fair value of our available-for-sale securities by contractual maturity were as follows: As of December 31, 2023 As of December 31, 2022 Amortized Estimated Amortized Estimated Cost Fair Value Cost Fair Value (in thousands) (in thousands) Maturing within one year $ 50,393 $ 50,189 $ 202,323 $ 201,359 Maturing in one to five years — — 36,746 35,643 Total available-for-sale securities $ 50,393 $ 50,189 $ 239,069 $ 237,002
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash within the consolidated balance sheets that sum to the total of the same such amounts in the consolidated statement of cash flows: December 31, December 31, 2023 2022 (in thousands) Cash and cash equivalents $ 25,841 $ 92,942 Restricted cash – short-term 146 146 Total cash, cash equivalents and restricted cash $ 25,987 $ 93,088

Out-license Agreements (Tables)

Out-license Agreements (Tables)	12 Months Ended
Out-license Agreements (Tables)	Dec. 31, 2023
License Collaboration And Manufacturing Agreements [Abstract]
Schedule of Deferred Revenue Activity	Deferred revenue activity related to commercialization revenue for the year ended December 31, 2023 was as follows: Total (in thousands) Deferred revenue, December 31, 2022 $ 85,000 Additions 38,170 Recognized into commercialization revenue ( 7,775 ) Deferred revenue December 31, 2023 115,395 Less: deferred revenue – current portion ( 77,833 ) Deferred revenue – long-term, December 31, 2023 $ 37,562

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
Property and Equipment (Tables)	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following as of each period end: December 31, December 31, 2023 2022 (in thousands) Leasehold improvements $ 904 $ 875 Lab equipment 15,540 14,797 Machinery and equipment 572 572 Computer equipment and software 1,279 1,149 Furniture and fixtures 1,272 1,297 Construction in progress 158 32 Property and equipment, gross 19,725 18,722 Less: accumulated depreciation ( 15,869 ) ( 12,422 ) Property and equipment, net $ 3,856 $ 6,300

Liability Related to the Sale_2

Liability Related to the Sale of Future Royalties (Tables)	12 Months Ended
Liability Related to the Sale of Future Royalties (Tables)	Dec. 31, 2023
Liability for Future Policy Benefit, after Reinsurance [Abstract]
Schedule Of Liability related to the sale of future revenues	The following table presents the changes in the liability related to the sale of future revenues under the HCRx Agreement for the year ended December 31, 2023: (in thousands) Liability related to sale of future revenues as of December 31, 2022 $ 30,236 Accretion of interest expense on liability related to sale of future revenues 4,792 Amortization of debt discount and debt issuance costs 79 Repayment of the liability ( 31 ) Liability related to sale of future revenues as of December 31, 2023 35,076 Less: current portion classified within other accrued liabilities ( 453 ) Long-term liability related to sale of future revenues $ 34,623

Sale of ATOM Facility (Tables)

Sale of ATOM Facility (Tables)	12 Months Ended
Sale of ATOM Facility (Tables)	Dec. 31, 2023
Discontinued Operations and Disposal Groups [Abstract]
Summary of the carrying amount assets sold and the gain on sale	Refer to the summary of assets sold and gain on sale of the ATOM Facility: (in thousands) Net proceeds from sale of ATOM Facility $ 94,765 Assets sold: Other current assets $ 190 Property and equipment, net 44,299 Other assets 39 Less: Assets sold 44,528 Gain on sale of ATOM Facility $ 50,237

Leases (Tables)

Leases (Tables)	12 Months Ended
Leases (Tables)	Dec. 31, 2023
Leases [Abstract]
Schedule of Maturities of Lease Liabilities Under Operating and Finance Leases	The maturities of lease liabilities under our operating and finance leases as of December 31, 2023 were as follows: Operating Leases Finance Leases Years Ending December 31, (in thousands) 2024 $ 17,209 $ 1,219 2025 18,486 1,263 2026 17,271 1,285 2027 5,760 436 2028 3,319 — Thereafter 12,459 — Total lease payments $ 74,504 $ 4,203 Less: amount representing interest ( 17,547 ) ( 673 ) Present value of lease liabilities $ 56,957 $ 3,530 Balance as of December 31, 2023 Other current liabilities $ 11,264 $ 915 Operating lease liabilities – long-term 45,693 — Other long-term liabilities — 2,615 Total $ 56,957 $ 3,530
Components of Lease Cost	The components of lease cost were as follows: Year Ended Year Ended December 31, 2023 December 31, 2022 (in thousands) Operating lease cost: Operating lease cost $ 17,192 $ 14,245 Short-term lease cost 201 386 Total operating lease cost $ 17,393 $ 14,631 Finance lease cost: Amortization expense $ 976 $ 872 Interest on lease liabilities 416 373 Total finance lease cost $ 1,392 $ 1,245
Summary of Other Information Related to Leases	Other information related to leases was as follows: Year Ended Year Ended December 31, 2023 December 31, 2022 (in thousands, except lease term and discount rate) Supplemental Cash Flows Information Cash paid for amounts included in the measurement of Operating cash flows for operating leases $ 16,660 $ 13,417 Operating cash flows for finance leases 416 335 Financing cash flows for finance leases 947 518 Operating lease assets obtained in exchange for lease obligations: $ 312 $ 50,779 Finance lease assets obtained in exchange for lease obligations: — 4,795 Non-cash (decrease) increase to operating lease assets due to remeasurement of lease liabilities: ( 1,589 ) — Weighted Average Remaining Lease Term Operating leases 5.2 years 5.9 years Finance leases 3.3 years 4.2 years Weighted Average Discount Rate Operating leases 11.4 % 9.9 % Finance leases 10.4 % 10.4 %

Restructuring (Tables)

Restructuring (Tables)	12 Months Ended
Restructuring (Tables)	Dec. 31, 2023
Restructuring and Related Activities [Abstract]
Summarizes of future termination benefit payments	The following is a summary of restructuring charges associated with the reductions in force for the periods presented: Year Ended December 31, Year Ended December 31, 2023 2022 (in thousands) Research and development expense $ 5,619 $ 2,544 General and administrative expense 1,111 3,420 Total restructuring charges $ 6,730 $ 5,964
Restructuring Liability Activity	The following restructuring liability activity was recorded in connection with the reduction in force for the year ended December 31, 2023, with all of the $ 4.9 million liability balance as of December 31, 2023 included within other current liabilities on the accompanying consolidated balance sheet: Year ended December 31, Year ended December 31, 2023 2022 (in thousands) Liability balance, January 1 $ 1,545 $ — Restructuring charges 6,730 5,964 Cash payments ( 3,352 ) ( 4,419 ) Liability balance, December 31 $ 4,923 $ 1,545

Commitments And Contingencies (

Commitments And Contingencies (Tables)	12 Months Ended
Commitments And Contingencies (Tables)	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Schedule of Minimum Commitment	The non-cancellable minimum commitments for products and services, subject to agreements with a term of greater than one year with clinical research organizations and CMOs, excluding those recognized on our balance sheet, as of December 31, 2023 are set forth below: Calendar Year Remaining Minimum Commitment as of December 31, 2023 (in thousands) 2024 14,085 2025 13,308 2026 9,605 2027 3,388 Total $ 40,386 We have incurred $ 19.4 million and $ 14.2 million against such minimum commitments for the years ended December 31

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
Stockholders' Equity (Tables)	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Summary of RSU Activity	The following is a summary of RSU activity under our 2014 EIP and Inducement Plan: RSUs Shares Weighted Balance as of December 31, 2022 6,708,608 $ 10.61 Granted 5,635,916 $ 3.57 Forfeited ( 2,388,808 ) $ 7.91 Vested ( 3,688,003 ) $ 8.89 Balance as of December 31, 2023 6,267,713 $ 6.32
Summary of Stock Option Activity	The following is a summary of stock option activity under our 2014 EIP and Inducement Plan: Shares Weighted Average Exercise Price Weighted Average Aggregate Balance as of December 31, 2022 10,645,555 $ 16.88 6.4 $ 42 Granted 4,693,897 3.64 Exercised — — Forfeited or expired ( 4,619,801 ) 15.60 Balance as of December 31, 2023 10,719,651 $ 11.63 6.5 $ — Vested and expected to vest as of 10,719,651 $ 11.63 6.5 $ — Exercisable as of December 31, 2023 6,389,752 $ 15.40 5.1 $ —
Summary of Options Estimated with Weighted Average	The fair value of each option issued was estimated at the date of grant using the Black-Scholes valuation model. The following table summarizes the weighted-average assumptions used as inputs to the Black-Scholes model and resulting weighted-average grant date fair values of stock options granted during the periods indicated: Year ended December 31, 2023 2022 Assumptions: Expected term (years) 5.80 6.0 Expected volatility 83.9 % 73.2 % Risk-free interest rate 4.2 % 2.1 % Expected dividend yield 0.0 % 0.0 % Fair Value: Weighted-average estimated grant date fair value per share $ 2.62 $ 5.88 Options granted 4,693,897 3,615,971 Total estimated grant date fair value $ 12,298,010 $ 21,261,909
Schedule of Common Stock Reserved for Future Issuance Under Equity Incentive Plans	The following shares of common stock were reserved for future issuance under our equity incentive plans as of December 31, 2023: Total Shares Reserved 2014 Equity Incentive Plan 20,326,356 2018 Inducement Plan 4,773,147 2014 Employee Stock Purchase Plan 10,593 Total reserved shares of common stock 25,110,096
Schedule of Stock-based Compensation Related to Stock Awards	The following is a summary of stock-based compensation expense for the periods presented: Year Ended December 31, 2023 2022 (in thousands) Research and development $ 26,529 $ 31,363 General and administrative 18,857 22,475 Total stock-based compensation expense $ 45,386 $ 53,838

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Losses Before Provision for Income Taxes	Losses before provision for income taxes were as follows in each period presented: Year Ended December 31, 2023 2022 (in thousands) United States $ ( 276,360 ) $ ( 228,395 ) Foreign 249 105 Total loss before provision for income taxes $ ( 276,111 ) $ ( 228,290 )
Components of Provision for Income Taxes	The components of provision for income taxes were as follows in each period presented: Year Ended December 31, 2023 2022 (in thousands) Current provision for income taxes: State $ 1 $ — Foreign 14 12 Total current provision for income taxes $ 15 $ 12
Reconciliation of Statutory Tax Rates to Effective Tax Rates	A reconciliation of statutory tax rates to effective tax rates were as follows in each of the periods presented: Year Ended December 31, 2023 2022 Federal income taxes at statutory rate 21.0 % 21.0 % Research tax credits 4.3 % 7.8 % Stock-based compensation ( 4.5 %) ( 3.8 %) Other ( 0.4 %) ( 0.2 %) Change in valuation allowance ( 20.4 %) ( 24.8 %) Effective tax rate 0.0 % 0.0 %
Components of Deferred Tax Assets and Liabilities	Significant components of our deferred tax assets and liabilities were as follows for each of the dates presented: As of December 31, 2023 2022 (in thousands) Deferred tax assets: Net operating loss carryforwards $ 323,581 $ 302,591 Capitalized research expenses 72,229 50,522 Tax credit carryforwards 30,580 19,427 Stock-based compensation 14,033 19,201 Deferred revenue 17,018 10,069 Operating lease liabilities 12,035 15,857 License fees 5,926 6,877 Other 11,187 13,169 Total deferred tax assets 486,589 437,713 Valuation allowance ( 474,982 ) ( 422,493 ) Total deferred tax assets 11,607 15,220 Deferred tax liabilities: Operating lease assets ( 11,607 ) ( 15,220 ) Total deferred tax liabilities ( 11,607 ) ( 15,220 ) Net deferred tax assets (liabilities) $ — $ —
Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits	The changes in the balance of gross unrecognized tax benefits, which excludes interest and penalties, for the years ended December 31, 2022 and 2023 are as follows: (In thousands) Balance as of January 1, 2022 144,067 Gross increases for tax positions related to current year 7,683 Gross increases for tax positions related to prior year — Gross decreases for tax positions related to prior year ( 785 ) Balance as of December 31, 2022 150,965 Gross increases for tax positions related to current year 5,538 Gross increases for tax positions related to prior year 3,843 Gross decreases for tax positions related to prior year — Balance as of December 31, 2023 $ 160,346

Supplemental Balance Sheet In_2

Supplemental Balance Sheet Information (Tables)	12 Months Ended
Supplemental Balance Sheet Information (Tables)	Dec. 31, 2023
Supplemental Balance Sheet Information [Abstract]
Schedule of Inventories	Inventories consist of the following as of each period: December 31, December 31, 2023 2022 (in thousands) Raw Materials $ 2,335 $ 1,214 Work-in-process 7,371 372 Total inventories $ 9,706 $ 1,586
Schedule of Property and Equipment	Property and equipment consisted of the following as of each period end: December 31, December 31, 2023 2022 (in thousands) Leasehold improvements $ 904 $ 875 Lab equipment 15,540 14,797 Machinery and equipment 572 572 Computer equipment and software 1,279 1,149 Furniture and fixtures 1,272 1,297 Construction in progress 158 32 Property and equipment, gross 19,725 18,722 Less: accumulated depreciation ( 15,869 ) ( 12,422 ) Property and equipment, net $ 3,856 $ 6,300
Schedule of Other Current Liabilities	Other current liabilities consisted of the following as of each period end: December 31, December 31, 2023 2022 (in thousands) Accrued operating expenses $ 19,007 $ 7,435 Current portion of operating lease liabilities 11,264 12,806 Current portion of finance lease liabilities 915 834 Other accrued liabilities 640 319 Total other current liabilities $ 31,826 $ 21,394

Description of Business - Addit

Description of Business - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Nov. 01, 2023	Aug. 08, 2022	Apr. 04, 2022	Jan. 31, 2022
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Entity incorporation state	DE
Entity incorporation date	Aug. 01, 2012
Cash consideration pursuant to asset purchase agreement					$ 94.8	$ 100
Reduction in current workforce percentage			30%	20%
Hcrx Agreement [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Proceeds from sale of future revenues, net	$ 31	$ 31
Minimum Cash Repayment	185%
Maximum Cash Repayment	250%

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)
Significant Accounting Policies [Line Items]
Number of reportable segments \| Segment	1
Number of operating segments \| Segment	1
License and collaboration revenue	$ 687	$ 63,573
Cash and cash equivalents maturity period	90 days
Investment maturity period	90 days
Impairment of long-lived assets	$ 0
Expected dividend yield	0%	0%
Defined contribution plan, plan name	401(k)
Defined contribution plan, matching contribution percentage	50%
Defined contribution plan, maximum percentage of an individual's eligible earnings	6%
Defined contribution plan contributions by employer	$ 1,900	$ 2,300
Inventories [Member]
Significant Accounting Policies [Line Items]
Net Realizable Value, Adjustments	$ 6,600	0
Minimum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	3 years
Maximum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life	5 years
Bayer Agreements
Significant Accounting Policies [Line Items]
License and collaboration revenue		61,800
Pierre Fabre Commercialization Agreement
Significant Accounting Policies [Line Items]
License and collaboration revenue		$ 1,800

Net Loss per Common Share - Ant

Net Loss per Common Share - Antidilutive Securities Excluded From Computation of Diluted Net Loss per Common Share (Detail) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	17,153,707	17,122,274
Unvested RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	6,261,213	6,698,858
Employee Stock Option
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	10,706,651	10,336,634
ESPP Share Purchase Rights
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	185,843	86,782

Financial Instruments - Summary

Financial Instruments - Summary of Estimated Fair Value and Related Valuation Input Hierarchy of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value	$ 50,189	$ 237,002
Fair Value, Measurements, Recurring
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	50,393	239,069
Total Unrealized Gain	1	7
Total Unrealized Loss	(205)	(2,074)
Total Fair Value	50,189	237,002
Fair Value, Measurements, Recurring \| Money Market Funds \| Level 1
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	14,376	78,033
Total Unrealized Gain	0	0
Total Unrealized Loss	0	0
Total Fair Value	14,376	78,033
Fair Value, Measurements, Recurring \| U.S. Treasury Obligations \| Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	9,928	63,013
Total Unrealized Gain	1	3
Total Unrealized Loss	0	(394)
Total Fair Value	9,929	62,622
Fair Value, Measurements, Recurring \| Government Agency Obligations \| Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost		8,086
Total Unrealized Gain		0
Total Unrealized Loss		(48)
Total Fair Value		8,038
Fair Value, Measurements, Recurring \| Corporate Debt Obligations \| Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	26,089	82,598
Total Unrealized Gain	0	4
Total Unrealized Loss	(205)	(1,513)
Total Fair Value	25,884	81,089
Fair Value, Measurements, Recurring \| Commercial Paper \| Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost		996
Total Unrealized Gain		0
Total Unrealized Loss		0
Total Fair Value		996
Fair Value, Measurements, Recurring \| Asset-Backed Securities \| Level 2
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost		6,343
Total Unrealized Gain		0
Total Unrealized Loss		(119)
Total Fair Value		6,224
Fair Value, Measurements, Recurring \| Amounts Classified As Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Total Fair Value		87,125
Total Amortized Cost	(24,304)	(87,122)
Total Unrealized Gain	(1)	(3)
Total Unrealized Loss	0	0
Total Fair Value	(24,305)
Fair Value, Measurements, Recurring \| Amounts Classified As Short-Term Investments
Schedule of Available-for-sale Securities [Line Items]
Total Amortized Cost	26,089	151,947
Total Unrealized Gain	0	4
Total Unrealized Loss	(205)	(2,074)
Total Fair Value	$ 25,884	$ 149,877

Financial Instruments - Amortiz

Financial Instruments - Amortized Cost and Fair Value of Available-for-Sale Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Amortized cost
Maturing within one year, Amortized cost	$ 50,393	$ 202,323
Maturing in one to five years, Amortized cost	0	36,746
Total available-for-sale securities, Amortized cost	50,393	239,069
Estimated Fair value
Maturing within one year, Estimated fair value	50,189	201,359
Maturing in one to five years, Estimated fair value	0	35,643
Total available-for-sale securities, Estimated fair value	$ 50,189	$ 237,002

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Financial Instruments Disclosure [Abstract]
Accrued interest receivable	$ 300,000	$ 800,000
Write off, of accrued interest receivable	$ 0	$ 0

Financial Instruments - Reconci

Financial Instruments - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Financial Instruments Disclosure [Abstract]
Cash and cash equivalents	$ 25,841	$ 92,942
Restricted cash - long-term	146	146
Total cash, cash equivalents and restricted cash	$ 25,987	$ 93,088	$ 107,478

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 19,725	$ 18,722
Less: accumulated depreciation and amortization	(15,869)	(12,422)
Property and equipment, net	3,856	6,300
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	904	875
Machinery and Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	572	572
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,272	1,297
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 158	$ 32

Out-license Agreements - Additi

Out-license Agreements - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended			9 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Oct. 31, 2021	Sep. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
License, Collaboration and Manufacturing Agreements [Line Items]
License and collaboration revenue					$ 687	$ 63,573
Deferred revenue, December 31, 2022	$ 115,395	$ 85,000			115,395	85,000
Less: deferred revenue - current portion	77,833				77,833
Deferred revenue - long-term, December 31, 2023	37,562	77,000			37,562	77,000
Deferred revenue, revenue recognized					5,000
Bayer Manufacturing Agreement
License, Collaboration and Manufacturing Agreements [Line Items]
License and collaboration revenue				$ 61,800	0
Deferred revenue, December 31, 2022	0	0			0	0
Receivable for early contract				4,200
Hcrx Agreement [Member]
License, Collaboration and Manufacturing Agreements [Line Items]
Proceeds from sale of future royalties, gross					$ 31,000	31,000
Minimum Cash Repayment					185%
Maximum Cash Repayment					250%
Bayer Agreements
License, Collaboration and Manufacturing Agreements [Line Items]
License and collaboration revenue						61,800
Pierre Fabre Commercialization Agreement
License, Collaboration and Manufacturing Agreements [Line Items]
Upfront cash payment received	$ 20,000		$ 45,000
Royalty eligible to receive term after first commercial sale	12 years		12 years
License and collaboration revenue						1,800
Development or sales-based milestone payments earned or received		40,000		$ 30,000
Determined upfront payment constituted entire consideration included in transaction price			$ 45,000
Milestone payments		$ 40,000				40,000
Pierre Fabre Commercialization Agreement \| Maximum
License, Collaboration and Manufacturing Agreements [Line Items]
Aggregate milestone payments entitle to receive upon achieving certain regulatory and commercial milestones	$ 620,000		$ 308,000		$ 620,000
A&R Commercialization Agreement [Member]
License, Collaboration and Manufacturing Agreements [Line Items]
License and collaboration revenue					700	$ 1,800
Additional Upfront Payment Included inTransaction Price	$ 20,000				$ 20,000

Out-license Agreements - Schedu

Out-license Agreements - Schedule of Deferred Revenue Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
License Collaboration And Manufacturing Agreements [Line Items]
Deferred revenue, December 31, 2022	$ 85,000
Additions	38,170
Recognized into commercialization revenue	(7,775)
Deferred revenue December 31, 2023	115,395
Less: deferred revenue - current portion	(77,833)
Deferred revenue - long-term, December 31, 2023	$ 37,562	$ 77,000

Liability Related to the Sale_3

Liability Related to the Sale of Future Revenues - Schedule of liability related to the sale of future royalties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Liability for Future Policy Benefit, after Reinsurance [Abstract]
Accretion of interest expense on liability related to sale of future revenues	$ 4,792	$ 0
Amortization of debt discount and debt issuance costs	79
Proceeds From Sale of Future Royalties,Net	0	30,605
Repayment of the liability	(31)
Liability related to sale of future revenues	35,076
Less: current portion classified within other accrued liabilities	(453)
Liability related to sale of future revenues	$ 34,623	$ 30,236

Liability Related to the Sale_4

Liability Related to the Sale of Future Revenues (Additional Information) (Details) - Hcrx Agreement [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Deferred Revenue Arrangement [Line Items]
Proceeds from sale of future royalties, gross		$ 31
Interest rate of royalties, percentage	12%
Minimum cash repayment	185%
Maximum cash repayment	250%
Net of transaction costs		$ 0.4
Cash Payment	$ 9

Sale of ATOM Facility - Schedul

Sale of ATOM Facility - Schedule of assets and gain sales (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Discontinued Operations and Disposal Groups [Abstract]
Net proceeds from sale of ATOM Facility	$ 0	$ 94,765
Other current assets		190
Property and equipment, net		44,299
Other assets		39
Less: Assets sold		44,528
Gain on sale of ATOM Facility		$ 50,237

Sale of ATOM Facility - Additio

Sale of ATOM Facility - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Apr. 04, 2022	Jan. 31, 2022
Discontinued Operations and Disposal Groups [Abstract]
Cash consideration pursuant to asset purchase agreement		$ 94,800	$ 100,000
Transaction costs		$ 4,600
Impairment loss	$ 50,237

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands		1 Months Ended
Leases - Additional Information (Details) $ in Thousands	Feb. 15, 2018 ft²	Mar. 31, 2021 ft²	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Apr. 04, 2022 USD ($)
Lessee, Lease, Description [Line Items]
Right Of Use Asset And Liabilities			$ 54,935	$ 68,022
Operating Lease, Liability			56,957
Lease option to extend additional term		5 years
Freezers
Lessee, Lease, Description [Line Items]
Right Of Use Asset And Liabilities					$ 50,800
Operating Lease, Liability					$ 4,800
South San Francisco California \| Letter of Credit
Lessee, Lease, Description [Line Items]
Restricted Cash And Cash Equivalents Noncurrent			$ 100
Thousand Oaks California
Lessee, Lease, Description [Line Items]
Lease agreement area of square feet of office, lab and warehouse space \| ft²		33,659
Finance Lease, Term of Contract	15 years	10 years 6 months
Percentage of annual increase in base rent		3%
Lease agreement area of office, lab and cellular therapy manufacturing space \| ft²	90,580
Lease commencement date	Feb. 15, 2018

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities Under Operating and Finance Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Operating leases, 2024	$ 17,209
Operating leases, 2025	18,486
Operating leases, 2026	17,271
Operating leases, 2027	5,760
Operating leases, 2028	3,319
Operating leases, Thereafter	12,459
Operating leases, Total minimum payments	74,504
Less: amount representing interest	(17,547)
Present value of lease liabilities	56,957
Other current liabilities	11,264	$ 12,806
Operating lease liabilities - long-term	45,693	58,064
Finance leases, 2024	1,219
Finance leases, 2025	1,263
Finance leases, 2026	1,285
Finance leases, 2027	436
Finance leases, 2028	0
Finance leases, Thereafter	0
Finance leases, Total minimum payments	4,203
Less: amount representing interest	(673)
Finance Lease, Liability	3,530
Other current liabilities	915	$ 834
Finance Lease Other Long Term Liabilities	$ 2,615

Leases - Components of Lease Co

Leases - Components of Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating lease cost:
Operating lease cost	$ 17,192	$ 14,245
Short-term lease cost	201	386
Total operating lease cost	17,393	14,631
Finance lease cost:
Amortization expense	976	872
Interest on lease liabilities	416	373
Total finance lease cost	$ 1,392	$ 1,245

Leases - Summary of Other Infor

Leases - Summary of Other Information Related to Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows for operating leases	$ 16,660	$ 13,417
Operating cash flows for finance leases	416	335
Financing cash flows for finance leases	947	518
Operating lease assets obtained in exchange for lease obligations:	312	50,779
Finance lease assets obtained in exchange for lease obligations:	0	4,795
Non-cash increase to operating lease assets due to remeasurement of lease liabilities:	$ (1,589)	$ 0
Weighted Average Remaining Lease Term
Operating leases	5 years 2 months 12 days	5 years 10 months 24 days
Finance leases	3 years 3 months 18 days	4 years 2 months 12 days
Weighted Average Discount Rate
Operating leases	11.40%	9.90%
Finance leases	10.40%	10.40%

Restructuring - Summarizes of f

Restructuring - Summarizes of future termination benefit payments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 6,730	$ 5,964
Research and Development Expense [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	5,619	2,544
General and Administrative Expense [Member]
Restructuring Cost and Reserve [Line Items]
Total restructuring charges	$ 1,111	$ 3,420

Restructuring - Restructuring o

Restructuring - Restructuring of Labiality Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Restructuring and Related Activities [Abstract]
Liability balance, beginning balance	$ 1,545	$ 0
Restructuring charges	6,730	5,964
Cash payments	(3,352)	(4,419)
Liability balance, ending balance	$ 4,923	$ 1,545

Restructuring - Additional Info

Restructuring - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2023	Nov. 01, 2023	Aug. 08, 2022
Restructuring and Related Activities [Abstract]
Reduction in current workforce percentage		30%	20%
Supplemental unemployment benefits, severance benefits	$ 6.7	$ 6.7	$ 6
Accrued expense restructuring	$ 4.9

Commitments And Contingencies -

Commitments And Contingencies - Additional Information (Details) - USD ($) $ in Millions		12 Months Ended
	Apr. 04, 2022	Dec. 31, 2023	Dec. 31, 2022
Loss Contingencies [Line Items]
Contractual obligations due to Bayer, MSK and QIMR		$ 0	$ 0
Minimum Commitments Expense		19.4	14.2
Minimum purchase commitments accrued		11.2	9.2
Accrued termination charges		0	0
Liabilities related to indemnification agreements		$ 0	$ 0
Fujifilm Master Services and Supply Agreement
Loss Contingencies [Line Items]
Supply agreement maximum extension term	10 years

Commitment and Contingencies -

Commitment and Contingencies - Schedule of Contract Services with FDB under Fujifilm MSA Minimum Amount Set Forth (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2024	$ 14,085
2025	13,308
2026	9,605
2027	3,388
Total	$ 40,386

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)			1 Months Ended	2 Months Ended	12 Months Ended
	Jan. 02, 2024	Apr. 25, 2022	Jan. 31, 2024	Mar. 15, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	May 31, 2020	Jul. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Authorized capital stock					520,000,000
Common stock, par value					$ 0.0001	$ 0.0001
Common stock, shares authorized					500,000,000	500,000,000
Preferred stock, shares authorized					20,000,000
Preferred stock, shares outstanding					0	0
Shares of common stock, reserved for issuance					25,110,096
Common stock, shares exercised						15,989
Option intrinsic value, exercised						$ 100,000
Net tax benefits related to exercised options					$ 0
Estimated fair value of stock option, vested					17,000,000	23,200,000
Stock-based compensation expense					45,386,000	$ 53,838,000
Common Stock Value Remained Available To Be Sold					$ 98,200,000
May 2020 Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Class of warrant or right exercised					1,898,578
December 2020 Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Class of warrant or right exercised								656,107
Restricted Stock Units (RSUs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant date fair value per share					$ 3.57	$ 8.26
Estimated fair value, vested in period					$ 32,800,000	$ 34,400,000
Unrecognized stock-based compensation expense					$ 35,900,000
Unrecognized stock-based compensation weighted average recognition period					2 years
Aggregate intrinsic value					$ 3,200,000
Restricted stock units, settled					3,688,003	2,247,296
RSU settlements, net of shares withheld, shares					51,244	114,444
Restricted stock units withheld for tax obligations					18,203	43,524
Restricted stock units withheld for tax obligations, value					$ 600,000	$ 100,000
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation weighted average recognition period					1 year 10 months 24 days		2 years 6 months
Unrecognized stock-based compensation					$ 16,600,000
2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual increase in EIP/ESPP, subject to other limitations						5%
Shares of common stock, reserved for issuance					20,326,356
Common stock, shares available for future grant					5,714,772
Outstanding options and RSUs					14,611,584
Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock, reserved for issuance					4,773,147
Common stock, shares available for future grant					2,397,366
Outstanding options and RSUs					2,375,781
Additional shares of common stock, reserved for issuance					1,500,000
2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of employees purchase price of common stock					85%
Shares of common stock, reserved for issuance					10,593
Unrecognized stock-based compensation expense					$ 100,000
Stock-based compensation expense					$ 700,000	$ 1,100,000
Shares purchased					896,246	417,081
Aggregate number of shares authorized					2,279,049
Cowen
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from sale of common stock, net	$ 100,000
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of employees purchase price of common stock					100%
Minimum \| Employees And Non Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation, vesting period					2 years
Stock option granted description terms					the exercise price of an option granted to a 10% shareholder cannot be less than 110% of the fair value of the shares on the date of grant. The estimated fair value of the shares is generally equal to the closing market price of the Company’s common stock on the measurement date. Options granted generally vest over two to four years and expire in seven to ten years.
Share based compensation award expiration period					7 years
Maximum \| Employees And Non Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation, vesting period					4 years
Share based compensation award expiration period					10 years
Maximum \| 2014 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual increase in EIP/ESPP, subject to other limitations					1%
Maximum increase in number of shares available for issuance					230,769
Warrant \| May 2020 Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of warrants issued			27,272,727					2,040,816,000	2,866,961,000
July 2019 Pre-Funded Warrants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Class of warrant or right exercised					361,260
Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common Stock Value Remained Available To Be Sold				$ 88,700,000
Subsequent Event [Member] \| Cowen
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Proceeds from sale of common stock, gross				$ 9,500,000
Underwritten Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued, price per share			$ 0.5499					$ 24.4999	$ 11.3199
Proceeds from sale of common stock, gross	15,000,000
Proceeds from sale of common stock, net	14,800,000
Underwritten Public Offering \| 2019 Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants outstanding					2,527,266
Underwritten Public Offering \| May 2020 Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants outstanding					968,383
Underwritten Public Offering \| December 2020 Warrants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Warrants outstanding					1,384,709
Underwritten Public Offering \| Warrant
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of warrants issued										2,945,026
Number of securities called by each warrant			1,000							1,000
Warrants, exercise price			$ 0.0001							$ 0.0001
Warrants, term		7 years
Maximum ownership Percentage			9.99%		9.99%
Underwritten Public Offering \| Warrant \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Prior notice period		61 days	61 days
Underwritten Public Offering \| Warrant \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum ownership Percentage			19.99%		19.99%
At The Market Offering \| Cowen
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued					3,038,432	1,618,672
Proceeds from sale of common stock, gross					$ 2,500,000	$ 22,400,000
Proceeds from sale of common stock, net	$ 2,200,000				2,200,000	$ 22,000,000
Common stock aggregate offering price					$ 100,000,000
Percentage of commission to be paid on gross sales proceeds of common stock sold					3%
Common stock average price					$ 0.83	$ 13.84
At The Market Offering \| Subsequent Event [Member] \| Cowen
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued				12,321,365
Proceeds from sale of common stock, net				$ 9,300,000
Common stock average price				$ 0.77

Stockholders' Equity - Summary

Stockholders' Equity - Summary of RSU Activity (Details) - Unvested RSUs - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Outstanding as of December 31, 2022	6,708,608
Shares, Granted	5,635,916
Shares, Forfeited	(2,388,808)
Shares, Vested	(3,688,003)
Shares, Outstanding as of December 31, 2023	6,267,713	6,708,608
Weighted Average Grant Date Fair Value, Outstanding as of December 31, 2022	$ 10.61
Weighted Average Grant Date Fair Value, Granted	3.57	$ 8.26
Weighted Average Grant Date Fair Value, Forfeited	7.91
Weighted Average Grant Date Fair Value, Vested	8.89
Weighted Average Grant Date Fair Value, Outstanding as of December 31, 2023	$ 6.32	$ 10.61

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Granted, Shares	4,693,897	3,615,971
Exercised, Shares		(15,989)
Outstanding, Weighted Average Remaining Contractual Term	6 years 6 months
Weighted average remaining contractual term ending balance	6 years 6 months
Stock options vested and expected to vest, Weighted Average Remaining Contractual Term	6 years 6 months
Exercisable, Weighted Average Remaining Contractual Term	5 years 1 month 6 days
2014 EIP and Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, Shares, beginning balance	10,645,555
Granted, Shares	4,693,897
Exercised, Shares	0
Forfeited or expired, Shares	(4,619,801)
Outstanding, Shares, ending balance	10,719,651	10,645,555
Vested and expected to vest, Shares	10,719,651
Exercisable, Shares	6,389,752
Outstanding, Weighted Average Exercise Price, beginning balance	$ 16.88
Granted, Weighted Average Exercise Price	3.64
Exercised, Weighted Average Exercise Price	0
Forfeited or expired, Weighted Average Exercise price	15.6
Outstanding, Weighted Average Exercise Price, ending balance	11.63	$ 16.88
Stock options vested and expected to vest, Weighted Average Exercise Price	11.63
Exercisable, Weighted Average Exercise Price	$ 15.4
Outstanding, Weighted Average Remaining Contractual Term		6 years 4 months 24 days
Weighted average remaining contractual term ending balance		6 years 4 months 24 days
Aggregate intrinsic value	$ 0	$ 42
Vested and expected to vest, Aggregate Intrinsic Value	0
Exercisable, Aggregate Intrinsic Value	$ 0

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Estimated Weighted-Average Assumptions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Expected term (years)	5 years 9 months 18 days	6 years
Expected volatility	83.90%	73.20%
Risk-free interest rate	4.20%	2.10%
Expected dividend yield	0%	0%
Weighted-average estimated grant date fair value per share	$ 2.62	$ 5.88
Options granted	4,693,897	3,615,971
Total estimated grant date fair value	$ 12,298,010	$ 21,261,909

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance Under Equity Incentive Plans (Details)	Dec. 31, 2023 shares
Class Of Stock [Line Items]
Total reserved shares of common stock	25,110,096
Inducement Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	4,773,147
2014 Equity Incentive Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	20,326,356
2018 Inducement Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	4,773,147
2014 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Total reserved shares of common stock	10,593

Stockholders' Equity - Schedu_2

Stockholders' Equity - Schedule of Stock-based Compensation Related to Stock Awards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 45,386	$ 53,838
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	26,529	31,363
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 18,857	$ 22,475

Income Taxes - Losses Before Pr

Income Taxes - Losses Before Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
United States	$ (276,360)	$ (228,395)
Foreign	249	105
Loss before provision for income taxes	$ (276,111)	$ (228,290)

Income Taxes - Components of Pr

Income Taxes - Components of Provision for (Benefit from) Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Current provision for income taxes:
State	$ 1	$ 0
Foreign	14	12
Total current provision for income taxes	$ 15	$ 12

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Statutory Tax Rates to Effective Tax Rates (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal income taxes at statutory rate	21%	21%
Research tax credits	4.30%	7.80%
Stock-based compensation	(4.50%)	(3.80%)
Other	(0.40%)	(0.20%)
Change in valuation allowance	(20.40%)	(24.80%)
Effective tax rate	0%	0%

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 323,581	$ 302,591
Capitalized research expenses	72,229	50,522
Tax credit carryforwards	30,580	19,427
Stock-based compensation	14,033	19,201
Deferred Revenue	17,018	10,069
Operating lease liabilities	12,035	15,857
License fees	5,926	6,877
Other	11,187	13,169
Total deferred tax assets	486,589	437,713
Valuation allowance	(474,982)	(422,493)
Total deferred tax assets	11,607	15,220
Deferred tax liabilities:
Operating lease assets	(11,607)	(15,220)
Total deferred tax liabilities	(11,607)	(15,220)
Net deferred tax assets (liabilities)	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Taxes [Line Items]
Change in capitalized expenses	$ 21,700	$ 43,700
Tax credit carryforward, change in amount	11,200
Increase in valuation allowance tax	52,500
Net operating loss carryforwards, federal	1,100,000
Deferred Tax Assets Tax Credit Carry forwards Orphan Drug	$ 111,800
Deferred Tax Assets Tax Credit Carry forwards Orphan Drug Expiration Years	2035
Tax credit carryforwards	$ 30,580	19,427
Accrued interest and penalties	$ 0	$ 0
Domestic
Income Taxes [Line Items]
Capitalized expenses, amortization period	5 years
Net operating loss carryforwards subject to expiration	$ 23,300
Net tax operating losses, expiration	begin to expire in 2035
Research and development tax credit carryforwards	$ 34,600
Research and development tax credit carryforwards, expiration year	2032
State
Income Taxes [Line Items]
Net tax operating losses, expiration	begin to expire in 2030
Net operating loss carryforwards not subject to expiration	$ 43,500
Net operating loss carryforwards, state	1,300,000
Tax credit carryforwards	$ 2,000
Tax credit carryforwards, expiration year	2025
Foreign
Income Taxes [Line Items]
Capitalized expenses, amortization period	15 years

Income Taxes - Reconciliation_2

Income Taxes - Reconciliation of Beginning and Ending Amount of Gross Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Beginning Balance	$ 150,965	$ 144,067
Gross increases for tax positions related to current year	5,538	7,683
Gross increases for tax positions related to prior year	3,843	0
Gross decreases for tax positions related to prior year	0	(785)
Ending Balance	$ 160,346	$ 150,965

Supplemental Balance Sheet In_3

Supplemental Balance Sheet Information - Schedule of Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Supplemental Balance Sheet Information [Abstract]
Raw Materials	$ 2,335	$ 1,214
Work-in-process	7,371	372
Total inventories	$ 9,706	$ 1,586

Supplemental Balance Sheet In_4

Supplemental Balance Sheet Information - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Supplemental Balance Sheet Information [Line Items]
Property and equipment, gross	$ 19,725	$ 18,722
Less: accumulated depreciation and amortization	(15,869)	(12,422)
Property and equipment, net	3,856	6,300
Leasehold Improvements [Member]
Supplemental Balance Sheet Information [Line Items]
Property and equipment, gross	904	875
Lab Equipment [Member]
Supplemental Balance Sheet Information [Line Items]
Property and equipment, gross	15,540	14,797
Machinery and Equipment [Member]
Supplemental Balance Sheet Information [Line Items]
Property and equipment, gross	572	572
Computer Equipment and Software [Member]
Supplemental Balance Sheet Information [Line Items]
Property and equipment, gross	1,279	1,149
Furniture and Fixtures [Member]
Supplemental Balance Sheet Information [Line Items]
Property and equipment, gross	1,272	1,297
Construction in Progress [Member]
Supplemental Balance Sheet Information [Line Items]
Property and equipment, gross	$ 158	$ 32

Supplemental Balance Sheet In_5

Supplemental Balance Sheet Information - Schedule of Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Supplemental Balance Sheet Information [Abstract]
Accrued operating expenses	$ 19,007	$ 7,435
Current portion of operating lease liabilities	$ 11,264	$ 12,806
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Liabilities, Current	Liabilities, Current
Current portion of finance lease liabilities	$ 915	$ 834
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Liabilities, Current	Liabilities, Current
Other accrued liabilities	$ 640	$ 319
Total other current liabilities	$ 31,826	$ 21,394

Supplemental Balance Sheet In_6

Supplemental Balance Sheet Information - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Supplemental Balance Sheet Information [Abstract]
Depreciation expense	$ 3.7	$ 4.7

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($) $ in Millions	Jan. 08, 2024	Nov. 01, 2023	Aug. 08, 2022
Subsequent Event [Line Items]
Reduction in current workforce percentage		30%	20%
Subsequent Event [Member]
Subsequent Event [Line Items]
Reduction in current workforce percentage	25%
Severance Costs	$ 4.5