0001628280-24-007592 | 10-K | XBRL Viewer

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Workforce Reduction - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2023	Dec. 31, 2023
Restructuring Cost and Reserve [Line Items]
Percentage of workforce reduction	25.00%
Incurred cost		$ 5,520
Accrued Liabilities and Other Liabilities
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, current		$ 1,900

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Oct. 01, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of other investments	$ 12,923	$ 5,000	$ 36,447
Other Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of other investments	10,000	$ 5,000
PACT
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock at fair value				$ 2,900
PACT \| Other Investment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Preferred stock at fair value				$ 2,900
Impairment of other investments	$ 2,900

Basis of Presentation and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	Basis of Presentation and Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary. All significant intercompany transactions and balances have been eliminated in consolidation. Liquidity and Management’s Plan The Company discovers and develops product candidates that involve experimental technologies. The product candidates may require several years and substantial expenditures to complete and ultimately may be unsuccessful. The Company plans to finance operations with available cash resources or from the issuance of equity or debt securities. The Company believes that its available cash, cash equivalents and marketable securities as of December 31, 2023 will be adequate to fund its operations at least through the next 12 months from the date these consolidated financial statements are issued. Summary of Significant Accounting Policies Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect reported amounts and related disclosures. Specific accounts that require management estimates include, but are not limited to, stock-based compensation, valuation of success payments, valuation of other investments, revenue recognition and accrued expenses. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Actual results could differ materially from those estimates. In June 2022, the Company recorded adjustments to revenue related to a change in estimate in connection with the Collaboration and License Agreement, entered into in 2019 and amended in June 2020 and December 2021 (“GSK Agreement”) with GlaxoSmithKline Intellectual Property (No. 5) Limited and Glaxo Group Limited (together, “GSK”). The Company and GSK mutually agreed to conclude research activities on an undisclosed target for hematological cancers in June 2022. As a result, the Company decreased the related estimated project costs, which resulted in an increase in the measure of proportional cumulative performance. These adjustments increased revenue by $83.6 million, decreased net loss by $83.6 million and resulted in a $0.34 reduction in the Company’s basic and diluted net loss per common share for the year ended December 31, 2022. Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ equity that are excluded from net loss. For the years ended December 31, 2023, 2022 and 2021, this was comprised of net unrealized gains and losses on the Company’s marketable securities. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in commercial paper and money market accounts. Restricted cash is cash held in a bank account and is used as collateral associated with the Company’s corporate credit card program. Marketable Securities The Company generally invests its excess cash in investment grade short- to intermediate-term fixed income securities. Such investments are classified as available-for-sale and are carried at fair value, with the unrealized gains and losses reported as a component of comprehensive loss. Realized gains and losses on available-for-sale securities are included in other income (expense), net. The cost of investments sold is based on the specific-identification method. The Company classifies those investments that are not required for use in current operations and that mature in more than 12 months as non-current marketable securities in the accompanying consolidated balance sheets. Each reporting period, the Company evaluates whether declines in fair value below carrying value are due to expected credit losses, as well as the Company’s ability and intent to hold the investment until a forecasted recovery occurs. Expected credit losses, if any, are recorded as an allowance through other income (expense), net. Valuation of Other Investments The Company determines at the inception of each arrangement whether an investment or other interest is considered a variable interest entity (“VIE”). If the investment or other interest is determined to be a VIE, the Company evaluates whether it is considered the primary beneficiary. The primary beneficiary of a VIE is the party that meets both of the following criteria: (i) has the power to direct the activities that most significantly impact the VIE’s economic performance; and (ii) has the obligation to absorb losses or the right to receive benefits from the VIE. For any investments in VIEs in which the Company is considered the primary beneficiary, the assets, liabilities and results of operations of the VIE would be included in its consolidated financial statements. As of December 31, 2023 and 2022, there were no VIEs for which the Company was the primary beneficiary. The Company accounts for its strategic equity interests in common stock and in-substance common stock in non‑publicly traded companies for which it does not have the ability to exercise significant influence in accordance with Accounting Standards Codification (“ASC”) 321, Investments – Equity Securities (“ASC 321”). Upon acquisition, these investments are measured at cost, which represents the then fair value. Under ASC 321, the Company can elect to subsequently measure the investments at initial cost, minus impairment and any changes, plus or minus, resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer (“measurement alternative”). This election must be made for each investment separately. The Company has made this election for all investments in this category and will continue to measure these investments using this method until they no longer qualify to be measured in accordance with this method. Changes in the carrying value of other investments are recognized through net loss. Each reporting period, the Company performs a qualitative assessment to evaluate whether the investment is impaired. The Company’s assessment includes a review of recent operating results and trends, recent sales/acquisitions of the investee securities and other factors that raise concerns about the investee’s ability to continue as a going concern. If the investment is impaired, an impairment charge is recognized in the amount by which the carrying amount of the investment exceeds the estimated fair value of the investment, with the impairment charge recognized through net loss. See Note 5, Other Investments, for details related to investment impairments recognized during the years ended December 31, 2023, 2022 and 2021. Additionally, the Company holds an equity warrant investment giving it the right to acquire stock of a non‑publicly traded company. Equity warrant investments are recorded within other assets at the estimated fair value, with gains and losses recognized in other income (expense), net. For the year ended December 31, 2022, in conjunction with the impairment of one of the Company’s other investments, the associated equity warrant investment’s fair value was determined to be negligible. The Company reduced the equity warrant investment’s fair value to zero for the year ended December 31, 2022. See Note 6, Fair Value Measurements, for additional details regarding the equity warrant investment. Property and Equipment, Net Property and equipment primarily consist of laboratory equipment, computer equipment and software, furniture and fixtures and leasehold improvements. Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is calculated using the straight-line method based on the estimated useful lives of the related assets, which are generally three to five years. For leasehold improvements, amortization is calculated using the straight‑line method based on the shorter of the useful life or the lease term. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is recorded in other operating income, net in the period realized. Maintenance and repairs are expensed as incurred. The Company reviews its property and equipment for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Valuation of Long-lived Assets Long-lived assets are reviewed each reporting period for impairment or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable, which may warrant adjustments to carrying values or estimated useful lives. Recoverability is measured by comparison of the carrying amount of an asset group to the future net undiscounted cash flows that the assets are expected to generate. If the carrying amount of an asset group exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There has been no impairment of long-lived assets for any of the periods presented. Leases The Company leases certain office, laboratory and manufacturing spaces. In addition to minimum rent, the leases require payment of real estate taxes, insurance, common area maintenance charges and other executory costs. At inception of a contract, the Company determines whether an arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. For all leases, the Company determines the classification of the lease as either operating or financing. As of December 31, 2023 and 2022, all of the Company’s leases were classified as operating leases. The Company recognizes right-of-use (“ROU”) assets and lease liabilities at the lease commencement date based on the present value of future lease payments over the lease term. As the Company’s leases do not provide an implicit rate, an incremental borrowing rate at each lease commencement date is used to determine the present value of future lease payments. The incremental borrowing rate is the rate of interest that the Company would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. To estimate the incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating. The ROU asset includes any lease payments made prior to the lease commencement date and is reduced by any lease incentives received or deemed payable to the Company. The lease term may include options to extend or terminate the lease when it is reasonably certain that a lease option will be exercised. Lease expense is recognized on a straight-line basis over the lease term within operating expenses on the Consolidated Statements of Operations and Comprehensive Loss. The Company has elected the practical expedient to not separate lease and non-lease components for real estate leases. Additionally, the Company has elected the short-term lease recognition exemption for all short-term leases and as a result, lease liabilities and ROU assets are not included on the consolidated balance sheets for leases with an initial term of 12 months or less. Fair Value Measurements The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. The fair value hierarchy prioritizes valuation inputs based on the observable nature of those inputs. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs: Level 1 – Quoted prices in active markets for identical assets or liabilities. Level 2 – Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. The Company’s financial instruments, in addition to those presented in Note 6, Fair Value Measurements, include cash, restricted cash, other investments, accounts payable and accrued liabilities and other current liabilities. The carrying amount of cash, restricted cash, accounts payable and accrued liabilities and other current liabilities approximate fair value because of the short-term nature of these instruments. As described in Note 5, Other Investments, other investments are carried at cost, minus impairment and any changes, plus or minus, resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. Revenue Recognition The Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements within the scope of ASC 606, Revenue from Contracts with Customers, (“ASC 606”) the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the performance obligation is satisfied. In applying the ASC 606 framework, the Company must apply judgment to determine the nature of the promises within a revenue contract and whether those promises represent distinct performance obligations. In determining the transaction price, the Company does not include amounts subject to uncertainties unless it is probable that there will be no significant reversal of cumulative revenue when the uncertainty is resolved. Milestone and other forms of variable consideration that the Company may earn are subject to significant uncertainties of research and development related achievements, which generally are deemed not probable until such milestones are actually achieved. For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes 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). Additionally, the Company develops assumptions that require judgment to determine the standalone selling price of each performance obligation identified in the contract. The Company then allocates the total transaction price to each performance obligation based on the estimated standalone selling prices of each performance obligation, for which it recognizes revenue as or when the performance obligations are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the variable consideration 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. Under the Company’s license agreements, the Company grants the license to a customer as it exists at the point of transfer and the nature of the license is a right to use the Company’s intellectual property as transferred. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees 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 bundled with other promises, the Company utilizes 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. Research and Development Expense The Company records expense for research and development costs as incurred. Research and development expenses consist of costs incurred by the Company for the discovery and development of its technology platforms and product candidates and includes costs incurred in connection with strategic collaborations, costs to license technology, personnel-related costs, including stock-based compensation expense, facility and technology related costs, research and laboratory expenses, as well as other expenses, which include consulting fees and other costs. Upfront payments and milestones paid to third parties in connection with technology platforms that have not reached technological feasibility and do not have an alternative future use are expensed as incurred. Clinical expenses are a component of research and development expense. The Company accrues and expenses clinical trial services performed by third parties based upon actual work completed in accordance with agreements established with its service providers. The Company estimates the costs through discussions with internal personnel and external service providers as to the progress or stage of completion of services and the agreed-upon fees to be paid for such services. General and Administrative Expense General and administrative costs are expensed as incurred and include personnel-related expenses, including stock-based compensation expense for personnel in executive, legal, finance and other administrative functions, legal costs, transaction costs related to collaboration and licensing agreements, as well as fees paid for accounting and tax services, consulting fees and facilities costs not otherwise included in research and development expenses. Legal costs include those related to corporate, dispute and patent matters. Success Payments The Company granted rights to success payments to Fred Hutchinson Cancer Center (“Fred Hutch”) and The Board of Trustees of the Leland Stanford Junior University (“Stanford”) pursuant to the terms of its research and collaboration agreements with each of those entities. Pursuant to the terms of these agreements, on each contractually prescribed measurement date, the Company may be required to make success payments based on increases in the estimated per share fair value of the Company’s common stock. See Note 3, License, Collaboration and Success Payment Agreements. The success payments are accounted for under ASC 718, Compensation – Stock Compensation, with the expense being recorded in research and development expenses. Once the service period is complete, the instrument continues to be remeasured each reporting period with all changes in value recognized immediately in other income (expense), net. The success payment liability is estimated at fair value at inception and at each subsequent reporting period, and the expense is accreted over the service period of the research and collaboration agreement. To determine the estimated fair value of the success payments, the Company uses a Monte Carlo simulation methodology which models the future movement of stock prices based on several key variables combined with empirical knowledge of the process governing the behavior of the stock price. The following variables were incorporated in the estimated fair value of the success payment liability: estimated fair value of the Company’s common stock, expected volatility, risk-free interest rate and the estimated number and timing of valuation measurement dates on the basis of which payments may be triggered. The computation of expected volatility was estimated based on available information about the historical volatility of stocks of similar publicly traded companies for a period matching the expected term assumption. Concentrations of Credit Risk and Off-balance Sheet Risk The Company maintains its cash, cash equivalents and restricted cash with high quality, accredited financial institutions. Restricted cash is cash held in a bank account and is used as collateral associated with the Company’s corporate credit card program. Cash, cash equivalents and restricted cash amounts, at times, may exceed federally insured limits. The Company also makes short-term investments in money market funds, U.S. Treasury securities, U.S. government agency securities and corporate debt securities, which can be subject to certain credit risk. However, the Company mitigates the risks by investing in high-grade instruments, limiting exposure to any one issuer or type of investment and monitoring the ongoing creditworthiness of the financial institutions and issuers. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to significant risk on these funds. The Company has no off‑balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements. Claims and Contingencies From time to time, the Company may become involved in litigation and proceedings relating to claims arising from the ordinary course of business. The Company accrues a liability if the likelihood of an adverse outcome is probable and the amount is estimable. If the likelihood of an adverse outcome is only reasonably possible (as opposed to probable), or if an estimate is not determinable, the Company provides disclosure of a material claim or contingency. Stock-based Compensation Under ASC 718, the Company measures and recognizes expense for restricted stock awards (“RSAs”), restricted stock units (“RSUs”), employee stock purchases related to the Employee Stock Purchase Plan and stock options granted to employees, directors and consultants based on the fair value of the awards on the date of grant. The fair value of stock options is estimated using the Black-Scholes option pricing model. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions including: stock price volatility, the expected term of stock options, the risk-free interest rate, expected dividends, and the fair value of the underlying common stock on the date of grant. The expected volatility is based on the historical volatility of the stock of similar entities within the Company’s industry over periods commensurate with the Company’s expected term assumption. The expected term of stock option grants represents the period the options are expected to remain outstanding and is based on the “simplified” method where the expected term is the midpoint between the vesting date and the end of the contractual term for each option. The Company generally uses the simplified method as provided for under the applicable guidance for entities with a limited history of relevant stock option exercise activity. The Company bases the risk-free interest rate on the interest rate payable on U.S. Treasury securities in effect at the time of grant for a period that is commensurate with the assumed expected option term. In reference to the expected dividend yield assumption, the Company has not historically paid, and does not expect for the foreseeable future to pay, a dividend. Stock-based compensation expense for RSAs, RSUs and stock options is recognized on a straight-line basis over the requisite service period, which is generally the vesting period of the respective award. The Company accounts for forfeitures as they occur. The Company also granted stock options that vest in conjunction with certain performance conditions to certain key employees. At each reporting date, the Company is required to evaluate whether achievement of the performance conditions is probable. Compensation expense is recorded over the appropriate service period based upon the Company’s assessment of accomplishing each performance provision. Income Taxes The Company determines its deferred tax assets and liabilities based on the differences between the financial reporting and tax basis of assets and liabilities. The deferred tax assets and liabilities are measured using the enacted tax rates that will be in effect when the differences are expected to reverse. A valuation allowance is recorded when it is more likely than not that the deferred tax asset will not be recovered. The Company applies judgment in the determination of the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. The Company recognizes any material interest and penalties related to unrecognized tax benefits in income tax expense. Segments Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment and one reportable segment. Recently Issued Accounting Pronouncements Segment Reporting In November 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which expands disclosures about a public entity’s reportable segments and requires more enhanced information about a reportable segment’s expenses, interim segment profit or loss, and how a public entity’s chief operating decision maker uses reported segment profit or loss information in assessing segment performance and allocating resources. Entities with a single reportable segment are required to provide all the updated and existing segment disclosures required by Topic 280. The amendments are effective for annual periods beginning after December 15, 2023 and interim periods within fiscal years beginning after December 15, 2024 on a retrospective basis. The Company is assessing the effect of the new disclosure requirements and does not anticipate the adoption will have a material impact. Income Taxes In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which includes amendments that further enhance income tax disclosures, primarily through standardization and disaggregation of rate reconciliation categories and income taxes paid by jurisdiction. The amendments are effective for annual periods beginning after December 15, 2024 and may be applied either prospectively or retrospectively. The Company is assessing the effect of the new disclosure requirements and does not anticipate the adoption will have a material impact.

Other Investments (Details) $ in Thousands	1 Months Ended	12 Months Ended
Other Investments (Details) $ in Thousands	Dec. 31, 2021 USD ($)	Dec. 31, 2023 USD ($) entity	Dec. 31, 2022 USD ($) entity	Dec. 31, 2021 USD ($)	Oct. 01, 2022 USD ($)
Schedule of Investments [Line Items]
Other investments		$ 32,001	$ 44,924
Variable interest entity, number of entities company is not primary beneficiary \| entity		1	2
Variable interest entity maximum loss exposure, amount		$ 13,000	$ 15,900
Impairment of other investments		12,923	5,000	$ 36,447
PACT
Schedule of Investments [Line Items]
Preferred stock at fair value					$ 2,900
Variable Interest Entity, Not Primary Beneficiary
Schedule of Investments [Line Items]
Other investments		13,000	15,900
Other Investment
Schedule of Investments [Line Items]
Cumulative impairments of strategic investments		15,000	5,000
Impairment of other investments		10,000	$ 5,000
Other Investment \| PACT
Schedule of Investments [Line Items]
Preferred stock at fair value					$ 2,900
Impairment of other investments		$ 2,900
PACT
Schedule of Investments [Line Items]
Impairment of other investments	$ 36,400			$ 36,400

Fair Value Measurements - Schedule of Estimated Fair Value of Success Payment Liability Assumptions (Details)	Dec. 31, 2023 $ / shares	Dec. 31, 2022 $ / shares
Fred Hutch
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of common stock (USD per share)	$ 1.94	$ 3.47
Fred Hutch \| Risk-free interest rate \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	0.0351	0.0358
Fred Hutch \| Risk-free interest rate \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	0.0519	0.0465
Fred Hutch \| Expected volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	0.800	0.800
Fred Hutch \| Expected term (in years) \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	0.46	0.46
Fred Hutch \| Expected term (in years) \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	3.97	4.97
Stanford
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of common stock (USD per share)	$ 1.94	$ 3.47
Stanford \| Risk-free interest rate \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	0.0351	0.0358
Stanford \| Risk-free interest rate \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	0.0519	0.0465
Stanford \| Expected volatility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	0.800	0.800
Stanford \| Expected term (in years) \| Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	0.46	0.46
Stanford \| Expected term (in years) \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Success payment liability, measurement input (as a percent)	5.75	6.75

Employee Benefit Plan (Details) - USD ($)	12 Months Ended
Employee Benefit Plan (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Retirement Benefits [Abstract]
Defined benefit plan, plan assets, contributions by employer	$ 1,200,000	$ 1,000,000	$ 0

Employee Benefit Plan	12 Months Ended
Employee Benefit Plan	Dec. 31, 2023
Retirement Benefits [Abstract]
Employee Benefit Plan	Employee Benefit Plan In January 2019, the Company adopted a 401(k) retirement and savings plan (the “401(k) Plan”) covering all of its employees. The 401(k) Plan allows employees to make pre- and post-tax contributions up to the maximum allowable amount set by the IRS. Beginning in 2022, the Company sponsors a defined-contribution savings plan with matching 401(k) contributions based upon the amount of the employees’ contributions subject to certain limitations. The Company made matching contributions to the 401(k) Plan on behalf of participants of $1.2 million and $1.0 million for the year ended December 31, 2023 and 2022, respectively, and none for the year ended December 31, 2021.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

Stock-based Compensation - Schedule of Stock-Based Compensation Expense by Classification (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 47,084	$ 81,924	$ 62,201
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	18,207	16,721	15,328
General and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Total stock-based compensation expense	$ 28,877	$ 65,203	$ 46,873

Income Taxes - Schedule of Changes to Company’s Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 400	$ 796
Additions based on tax position related to the current year	0	0
Adjustments based on prior year tax positions	0	(396)
Ending balance	$ 400	$ 400

Accrued Liabilities and Other Current Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Accrued Liabilities and Other Liabilities [Abstract]
Accrued compensation and related benefits	$ 14,634	$ 15,447
Current lease liabilities	6,273	4,534
Accrued research and development expenses	5,331	4,760
Other	1,493	2,352
Accrued legal	395	930
Accrued property and equipment	0	732
Total accrued liabilities and other current liabilities	$ 28,126	$ 28,755
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Total accrued liabilities and other current liabilities	Total accrued liabilities and other current liabilities

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

Stock-based Compensation - Schedule of RSA and RSU Activity (Details) - Restricted Stock Units (RSUs)	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Number of Shares
Balance at beginning of period (in shares) \| shares	872,077
Granted (in shares) \| shares	2,621,177
Vested (in shares) \| shares	(598,024)
Forfeited (in shares) \| shares	(822,375)
Balance at end of period (in shares) \| shares	2,072,855
Weighted-Average Grant Date Fair Value per Share
Unvested shares of beginning balance (in dollars per share) \| $ / shares	$ 5.98
Granted (in dollars per share) \| $ / shares	2.22
Vested (in dollars per share) \| $ / shares	3.75
Forfeited (in dollars per share) \| $ / shares	3.22
Unvested shares of ending balance (in dollars per share) \| $ / shares	$ 2.96

Related Party Disclosures (Tables)

12 Months Ended

Dec. 31, 2023

Schedule of Total Income Attributable to Sonoma Sublease

Total operating income from Sonoma and income solely attributable to the Sonoma Sublease are shown in the table below (in thousands). Total operating income includes income attributable to the sublease, as well as additional operating fees recognized in “other operating income, net” such as common area maintenance charges. See Note 9, Leases, for more detail on the Sonoma Sublease.


	Year Ended December 31,
	2023		2022		2021
Sonoma other operating income, net	$	2,592	$	2,635	$	1,791
Sonoma sublease income	$	1,861	$	1,861	$	620

Leases - Schedule of Operating Lease Commitments Including Expected Lease Incentives to be Received (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
2024	$ 11,347
2025	11,859
2026	12,209
2027	12,569
2028	12,940
Thereafter	22,585
Total undiscounted lease payments	83,509
Less: imputed interest	(20,342)
Total operating lease liabilities	63,167
Operating Lease Liability
Short-term portion of lease liabilities (included in accrued liabilities and other current liabilities)	6,273	$ 4,534
Operating lease liabilities, non-current	56,894	$ 63,168
Total	$ 63,167

Accrued Liabilities and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Accrued Liabilities and Other Liabilities [Abstract]

Schedule of Accrued Liabilities and Other Current Liabilities

Accrued liabilities and other current liabilities consisted of the following (in thousands):


	December 31,
	2023		2022
Accrued compensation and related benefits	$	14,634	$	15,447
Current lease liabilities	6,273		4,534
Accrued research and development expenses	5,331		4,760
Other	1,493		2,352
Accrued legal	395		930
Accrued property and equipment	—		732
Total accrued liabilities and other current liabilities	$	28,126	$	28,755

Fair Value Measurements - Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Financial assets:
Total financial assets	$ 544,787	$ 694,495
Financial liabilities:
Success payment liabilities	1,576	4,356
Total financial liabilities	1,576	4,356
U.S. Treasury securities
Financial assets:
Marketable securities	374,356	271,799
U.S. government agency securities
Financial assets:
Marketable securities	48,750	134,045
Corporate debt securities
Financial assets:
Marketable securities	59,606	220,681
Money market funds
Financial assets:
Cash and cash equivalents	62,075	67,970
Level 1
Financial assets:
Total financial assets	62,075	67,970
Financial liabilities:
Success payment liabilities	0	0
Total financial liabilities	0	0
Level 1 \| U.S. Treasury securities
Financial assets:
Marketable securities	0	0
Level 1 \| U.S. government agency securities
Financial assets:
Marketable securities	0	0
Level 1 \| Corporate debt securities
Financial assets:
Marketable securities	0	0
Level 1 \| Money market funds
Financial assets:
Cash and cash equivalents	62,075	67,970
Level 2
Financial assets:
Total financial assets	482,712	626,525
Financial liabilities:
Success payment liabilities	0	0
Total financial liabilities	0	0
Level 2 \| U.S. Treasury securities
Financial assets:
Marketable securities	374,356	271,799
Level 2 \| U.S. government agency securities
Financial assets:
Marketable securities	48,750	134,045
Level 2 \| Corporate debt securities
Financial assets:
Marketable securities	59,606	220,681
Level 2 \| Money market funds
Financial assets:
Cash and cash equivalents	0	0
Level 3
Financial assets:
Total financial assets	0	0
Financial liabilities:
Success payment liabilities	1,576	4,356
Total financial liabilities	1,576	4,356
Level 3 \| U.S. Treasury securities
Financial assets:
Marketable securities	0	0
Level 3 \| U.S. government agency securities
Financial assets:
Marketable securities	0	0
Level 3 \| Corporate debt securities
Financial assets:
Marketable securities	0	0
Level 3 \| Money market funds
Financial assets:
Cash and cash equivalents	$ 0	$ 0

Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance, (in shares) at Dec. 31, 2020	194,474,000
Beginning balance at Dec. 31, 2020	$ 1,010,968
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of convertible preferred stock to common stock (in shares)	(194,474,000)
Conversion of convertible preferred stock to common stock	$ (1,010,968)
Ending balance, (in shares) at Dec. 31, 2021	0
Ending balance at Dec. 31, 2021	$ 0
Beginning balance, (in shares) at Dec. 31, 2020		15,570,000
Beginning balance at Dec. 31, 2020	(292,528)	$ 2	$ 41,357	$ 256	$ (334,143)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from initial public offering, net of issuance costs (in shares)		25,000,000
Proceeds from initial public offering, net of issuance costs	391,802	$ 2	391,800
Conversion of convertible preferred stock to common stock (in shares)		194,474,000
Conversion of convertible preferred stock to common stock	1,010,968	$ 20	1,010,948
Issuance of common stock upon exercise of stock options (in shares)		2,750,000
Issuance of common stock upon exercise of stock options	9,442		9,442
Stock-based compensation (in shares)		4,944,000
Stock-based compensation	62,201		62,201
Other comprehensive (loss) Income	(1,879)			(1,879)
Net loss	(250,219)				(250,219)
Ending balance, (in shares) at Dec. 31, 2021		242,738,000
Ending balance at Dec. 31, 2021	929,787	$ 24	1,515,748	(1,623)	(584,362)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		3,601,000
Issuance of common stock upon exercise of stock options	9,577	$ 1	9,576
Issuance of common stock under employee stock purchase plan (in share)		475,000
Issuance of common stock under employee stock purchase plan	1,519		1,519
Issuance of common stock in connection with restricted stock units, net of tax (in share)		153,000
Issuance of common stock in connection with restricted stock units, net of tax	(461)		(461)
Stock-based compensation (in shares)		2,600,000
Stock-based compensation	81,924		81,924
Other comprehensive (loss) Income	(5,976)			(5,976)
Net loss	$ (183,118)				(183,118)
Ending balance, (in shares) at Dec. 31, 2022	249,567,343	249,567,000
Ending balance at Dec. 31, 2022	$ 833,252	$ 25	1,608,306	(7,599)	(767,480)
Ending balance, (in shares) at Dec. 31, 2023	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	2,996,262	2,996,000
Issuance of common stock upon exercise of stock options	$ 306		306
Issuance of common stock under employee stock purchase plan (in share)		987,000
Issuance of common stock under employee stock purchase plan	1,894		1,894
Issuance of common stock in connection with restricted stock units, net of tax (in share)		408,000
Issuance of common stock in connection with restricted stock units, net of tax	(457)		(457)
Stock-based compensation	47,084		47,084
Other comprehensive (loss) Income	7,505			7,505
Net loss	$ (234,632)				(234,632)
Ending balance, (in shares) at Dec. 31, 2023	253,957,709	253,958,000
Ending balance at Dec. 31, 2023	$ 654,952	$ 25	$ 1,657,133	$ (94)	$ (1,002,112)

Cash Equivalents and Marketable Securities - Schedule of Fair Value and Amortized Cost of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Marketable Securities [Line Items]
Amortized Cost	$ 145,647	$ 123,554	$ 293,828
Amortized Cost	544,881	702,094
Gross Unrealized Gains	240	4
Gross Unrealized Losses	(334)	(7,603)
Fair Value	544,787	694,495
Classified as:
Cash equivalents	127,705	107,780
Marketable securities	400,576	516,598
Marketable securities, non-current	16,506	70,117
Total cash equivalents and marketable securities	544,787	694,495
U.S. Treasury securities
Marketable Securities [Line Items]
Amortized Cost	374,214	277,056
Gross Unrealized Gains	237	0
Gross Unrealized Losses	(95)	(5,257)
Fair Value	374,356	271,799
U.S. government agency securities
Marketable Securities [Line Items]
Amortized Cost	48,924	135,460
Gross Unrealized Gains	3	1
Gross Unrealized Losses	(177)	(1,416)
Fair Value	48,750	134,045
Corporate debt securities
Marketable Securities [Line Items]
Amortized Cost	59,668	221,608
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(62)	(930)
Fair Value	59,606	220,681
Money market funds
Marketable Securities [Line Items]
Amortized Cost	62,075	67,970
Fair Value	$ 62,075	$ 67,970

Related-Party Transactions

12 Months Ended

Dec. 31, 2023

Related-Party Transactions

In September 2021, the Company entered into a sublease with Sonoma (“Sonoma Sublease”), with whom the Company has common stockholders with board seats, whereby the Company agreed to sublease approximately 18,000 square feet of space in South San Francisco, California currently leased by the Company. Dr. Klausner, the Chair of the Company’s board of directors, also serves as Board Chair of the board of directors of Sonoma. As a part of the Sonoma Sublease, a $4.6 million tenant improvement contribution payment was made by Sonoma, which is recognized over the term of the Sonoma Sublease. As of both December 31, 2023 and 2022, there were accrued liabilities and other current liabilities of $0.5 million, and as of December 31, 2023 and 2022, other non-current liabilities of $3.0 million and $3.5 million, respectively, in connection with the Sonoma Sublease. Total operating income from Sonoma and income solely attributable to the Sonoma Sublease are shown in the table below (in thousands). Total operating income includes income attributable to the sublease, as well as additional operating fees recognized in “other operating income, net” such as common area maintenance charges. See Note 9, Leases, for more detail on the Sonoma Sublease.


	Year Ended December 31,
	2023		2022		2021
Sonoma other operating income, net	$	2,592	$	2,635	$	1,791
Sonoma sublease income	$	1,861	$	1,861	$	620

The Company was party to the GSK Agreement, who is a holder of more than 10% of the Company’s outstanding common stock. See Note 3, License, Collaboration, and Success Payment Agreements. Revenue recognized in connection with the GSK agreement was zero, $84.7 million and $10.5 million for the years ended December 31, 2023, 2022 and 2021, respectively. GSK terminated the GSK Agreement effective December 24, 2022. See Note 3, License, Collaboration, and Success Payment Agreements, for additional details regarding the termination of the GSK Agreement.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Consolidated Statements of Convertible Preferred Stock and Stockholders’ Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Statement of Stockholders' Equity [Abstract]
Stock issuance costs	$ 33,198

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock authorized (in shares)	10,000,000	10,000,000
Preferred stock issued (in shares)	0	0
Preferred stock outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock authorized (in shares)	500,000,000	500,000,000
Common stock issued (in shares)	253,958,000	249,567,000
Common stock outstanding (in shares)	253,957,709	249,567,343

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On February 28, 2024, the Company entered into a sales agreement (the “Sales Agreement”) with Cowen and Company, LLC as the Company’s sales agent (“Agent”) with respect to an at-the-market offering program. In accordance with the terms of the Sales Agreement, the Company may offer and sell from time to time through the Agent shares of the Company’s common stock having an aggregate offering amount of up to $150.0 million (“the Placement Shares”). Sales of the Placement Shares, if any, will be made at prevailing market prices on Nasdaq at the time of sale, or as otherwise agreed with the Agent, by any method permitted by law deemed to be an “at-the-market offering” as defined in Rule 415 of the Securities Act of 1933, as amended. The Company will pay commissions to the Agent of up to 3% of the gross proceeds of the sale of the Placement Shares sold under the Sales Agreement and reimburse the Agent for certain expenses. Neither the Company nor the Agent are obligated to sell any shares and, to date, the Company has not made any sales under the Sales Agreement.

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (234,632)	$ (183,118)	$ (250,219)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	47,084	81,924	62,201
Depreciation and amortization expense	20,250	18,020	13,624
Impairment of other investments	12,923	5,000	36,447
Net amortization and accretion on marketable securities	(9,596)	(930)	1,901
Change in fair value of success payment liabilities	(2,780)	(5,130)	3,713
Non-cash lease (income) expense	(1,873)	(1,553)	911
Loss on property and equipment disposals, net	1,509	103	1,210
Change in fair value of equity warrant	0	1,067	256
Gain on other investments	0	(2,923)	0
Gain on net operating lease liability disposal	0	0	(308)
Changes in operating assets and liabilities:
Prepaid expenses, other current assets and other assets	3,125	(1,968)	(6,987)
Accounts payable	1,464	667	91
Accrued liabilities and other current liabilities	(719)	(463)	4,542
Deferred revenue	0	(84,653)	(10,508)
Operating lease liabilities, non-current	0	4,855	13,202
Other non-current liabilities	(449)	(453)	3,675
Net cash used in operating activities	(163,694)	(169,555)	(126,249)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchases of property and equipment	(2,686)	(24,276)	(65,504)
Purchases of marketable securities	(476,880)	(406,316)	(673,465)
Sales and maturities of marketable securities	663,614	419,052	617,396
Net cash provided by (used in) investing activities	184,048	(11,540)	(121,573)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from exercise of stock options	306	9,577	9,442
Proceeds from employee stock purchase plan	1,894	1,519	0
Taxes paid related to net share settlement of equity awards	(457)	(461)	0
Proceeds from initial public offering, net of issuance costs	0	0	391,802
Net cash provided by financing activities	1,743	10,635	401,244
Net increase (decrease) in cash, cash equivalents and restricted cash	22,097	(170,460)	153,422
Cash, cash equivalents and restricted cash at beginning of period	123,834	294,294	140,872
Cash, cash equivalents and restricted cash at end of period	145,931	123,834	294,294
Represented by:
Cash and cash equivalents	145,647	123,554	293,828
Restricted cash	284	280	466
Total	145,931	123,834	294,294
SUPPLEMENTAL CASH FLOW INFORMATION
Cash paid for amounts included in the measurement of lease liabilities	10,845	10,870	8,546
Cash received for amounts related to tenant improvement allowances	0	4,761	13,295
Non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued liabilities	29	1,325	4,605
Remeasurement of operating lease right-of-use asset for lease modification	0	31	3,873
Acquisition of PACT Series D convertible preferred shares	0	2,923	0
Conversion of convertible preferred stock to common stock upon closing of initial public offering	$ 0	$ 0	$ 1,010,968

Stock-based Compensation - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Number of Stock Options
Beginning Balance (in shares)	53,849,045
Granted (in shares)	12,399,063
Exercised (in shares)	(2,996,262)
Canceled or forfeited (in shares)	(7,655,015)
Ending Balance (in shares)	55,596,831	53,849,045
Options Exercisable (in shares)	33,965,690
Weighted-Average Exercise Price per Share
Beginning Balance (in dollars per share)	$ 5.09
Granted (in dollars per share)	2.29
Exercised (in dollars per share)	0.10
Cancelled or forfeited (in dollars per share)	5.03
Ending Balance (in dollars per share)	4.75	$ 5.09
Options Exercisable (in dollars per share)	$ 5.06
Weighted-Average Remaining Contractual Life (years)
Options Outstanding	6 years 10 months 20 days	7 years 10 months 2 days
Options Exercisable	5 years 9 months 3 days
Aggregate Intrinsic Value
Options Outstanding	$ 7,368	$ 24,887
Options Exercisable	$ 7,303

Fair Value Measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following table sets forth the fair value of the Company’s financial assets and liabilities measured at fair value on a recurring basis based on the three-tier fair value hierarchy (in thousands):


	December 31, 2023
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds	$	62,075	$	—	$	—	$	62,075
U.S. Treasury securities	—		374,356		—		374,356
U.S. government agency securities	—		48,750		—		48,750
Corporate debt securities	—		59,606		—		59,606
Total financial assets	$	62,075	$	482,712	$	—	$	544,787
Financial liabilities:
Success payment liabilities	$	—	$	—	$	1,576	$	1,576
Total financial liabilities	$	—	$	—	$	1,576	$	1,576


	December 31, 2022
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds	$	67,970	$	—	$	—	$	67,970
U.S. Treasury securities	—		271,799		—		271,799
U.S. government agency securities	—		134,045		—		134,045
Corporate debt securities	—		220,681		—		220,681
Total financial assets	$	67,970	$	626,525	$	—	$	694,495
Financial liabilities:
Success payment liabilities	$	—	$	—	$	4,356	$	4,356
Total financial liabilities	$	—	$	—	$	4,356	$	4,356

The Company measures the fair value of money market funds based on quoted prices in active markets for identical assets or liabilities. The Level 2 marketable securities include U.S. Treasury securities, U.S. government agency securities and corporate debt securities, which securities are valued using third-party pricing sources. The pricing services applied industry standard valuation models. Inputs utilized include market pricing based on real-time trade data for the same or similar securities and other significant inputs derived from or corroborated by observable market data.

The Company’s success payment liabilities are Level 3 financial instruments, which are estimated using Monte Carlo simulations. Monte Carlo simulations model the future movement of stock prices based on several key variables combined with empirical knowledge of the process governing the behavior of the stock price. The following variables were incorporated in the estimated fair value of the success payment liabilities: fair value of the Company’s common stock, expected volatility, the risk-free interest rate and the estimated number and timing of valuation measurement dates on the basis of which payments may be triggered. The computation of expected volatility was estimated based on available information about the historical volatility of stocks of similar publicly traded companies for a period matching the expected term assumption.

The following assumptions were incorporated into the calculation of the estimated fair value of the Fred Hutch success payment liability:


	December 31,
	2023			2022
Fair value of common stock	$	1.94		$	3.47
Risk-free interest rate	3.51% - 5.19%			3.58% - 4.65%
Expected volatility	80.0		%	80.0		%
Expected term (in years)	0.46 - 3.97			0.46 - 4.97

The following assumptions were incorporated into the calculation of the estimated fair value of the Stanford success payment liability:


	December 31,
	2023			2022
Fair value of common stock	$	1.94		$	3.47
Risk-free interest rate	3.51% - 5.19%			3.58% - 4.65%
Expected volatility	80.0		%	80.0		%
Expected term (in years)	0.46 - 5.75			0.46 - 6.75

The Company utilizes estimates and assumptions in determining the estimated success payment liabilities and associated changes in fair value. A small change in the valuation of the Company’s common stock may have a relatively large change in the estimated fair value of the success payment liability and associated changes in fair value.

The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial assets and liabilities (in thousands):


	Equity Warrant Investment		Success Payment Liabilities
Balance at December 31, 2021	$	1,067	$	9,486
Change in fair value (1)	(1,067)		(5,130)
Balance at December 31, 2022	—		4,356
Change in fair value (1)	—		(2,780)
Balance at December 31, 2023	$	—	$	1,576

__________

(1)The change in the fair value associated with the Fred Hutch success payment liabilities for the year ended December 31, 2023 is recorded in other income (expense), net. The change in the fair value associated with the Fred Hutch success payment liabilities for the year ended December 31, 2022, and the change in the fair value associated with the Stanford success payment liabilities for the years ended December 31, 2023 and 2022, respectively, are recorded as research and development expenses. (See Note 3, License, Collaboration and Success Payment Agreements). Changes in fair value associated with the equity warrant investment held are recorded in other income (expense), net.

In October 2022, the Company received non-voting PACT Series D convertible preferred stock with an estimated fair value of $2.9 million using the cost approach (See Note 3, License, Collaboration and Success Payment Agreements). Under this approach, the fair value of an asset is measured by the cost to reconstruct or replace such asset with another one of like utility. The fair value of PACT was estimated by using significant unobservable inputs, including an estimate of insignificant fair value associated with PACT intangible assets. Accordingly, the Company classified the fair value measurement of PACT preferred stock on October 1, 2022 as Level 3 under the fair value hierarchy. In June 2023, the Company performed a qualitative assessment of potential indicators of impairment of the PACT Series D convertible preferred stock investment, resulting in a $2.9 million impairment expense for the year ended December 31, 2023. See Note 5, Other Investments, for additional details regarding the PACT investment impairment.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net loss	$ (234,632)	$ (183,118)	$ (250,219)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
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-Name Accounting Standards Codification
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-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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Reference 28: http://www.xbrl.org/2003/role/disclosureRef
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Reference 29: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net, consisted of the following (in thousands):


	December 31,
	2023		2022
Leasehold improvements	$	118,319	$	116,930
Laboratory equipment	33,368		31,982
Computer equipment and software	1,672		1,630
Furniture and fixtures	814		717
Construction in progress	128		4,148
Property and equipment, at cost	154,301		155,407
Less: Accumulated depreciation and amortization	(51,647)		(32,384)
Total property and equipment, net	$	102,654	$	123,023

Leases

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Leases

The Company’s lease portfolio is comprised of operating leases for laboratory, office and manufacturing facilities located in South San Francisco, California, and Seattle and Bothell, Washington with contractual periods expiring between December 2028 and March 2031. In addition to minimum rent, the leases require payment of real estate taxes, insurance, common area maintenance charges and other executory costs. These additional charges are considered variable lease costs and are recognized in the period in which the costs are incurred.

In 2018, the Company entered into an operating lease for approximately 34,000 square feet of office and laboratory space in Seattle, Washington, with an initial lease term expiring in December 2028. The Company has two five‑year options to extend the lease, which are not reasonably assured.

In 2019, the Company entered into two operating lease agreements for a combined approximately 73,000 square feet of space to develop a cell therapy manufacturing facility located in Bothell, Washington, with initial terms expiring in May 2030. The Company has two 90-month options to extend the leases, which are not reasonably assured.

In 2019, the Company entered into an operating lease agreement for approximately 108,000 square feet of office and laboratory space located in South San Francisco, California. The initial lease term expires in January 2031 with the option to extend the term for another 10 years, which is not reasonably assured. In January 2021, the Company amended the lease term to extend the lease expiration to March 2031, which resulted in an increase to the right-of-use asset and lease liability of $4.2 million.

The following table summarizes the Company’s future minimum operating lease commitments, including expected lease incentives to be received, as of December 31, 2023 (in thousands):


Year Ending December 31:
2024	$	11,347
2025	11,859
2026	12,209
2027	12,569
2028	12,940
Thereafter	22,585
Total undiscounted lease payments	83,509
Less: imputed interest	(20,342)
Total operating lease liabilities	$	63,167

Reported as of December 31, 2023:
Short-term portion of lease liabilities (included in accrued liabilities and other current liabilities)	$	6,273
Operating lease liabilities, non-current	56,894
Total	$	63,167

The operating lease costs for all operating leases were $9.0 million, $9.3 million and $9.4 million for the years ended December 31, 2023, 2022 and 2021, respectively. The operating lease costs and total commitments for short-term leases were de minimis for the years ended December 31, 2023, 2022 and 2021. Variable lease costs for operating leases were $5.4 million, $5.1 million and $4.1 million for the years ended December 31, 2023, 2022 and 2021, respectively. The weighted-average remaining lease terms for operating leases were 6.8 years and 7.8 years as of December 31, 2023 and 2022, respectively. The weighted-average discount rates for operating leases were 8.5% as of both December 31, 2023 and 2022.

In May 2021, the Company entered into a sublease, whereby the Company agreed to sublease approximately 11,000 square feet of its space in South San Francisco, California currently leased by the Company. The sublease is classified as an operating lease and will expire in March 2031. The Company recognized sublease income for this sublease of $0.8 million for both the years ended December 31, 2023 and 2022 and $0.4 million for the year ended December 31, 2021.

In September 2021, the Company entered into a sublease with Sonoma Biotherapeutics, Inc. (“Sonoma”), a related party, whereby the Company agreed to sublease approximately 18,000 square feet of space in South San Francisco, California currently leased by the Company. See Note 17, Related-Party Transactions. As a part of the sublease, in September 2021, the Company received a $4.6 million tenant improvement contribution payment, which will be recognized over the term of the sublease. The sublease is classified as an operating lease and will expire in March 2031. The Company recognized Sonoma sublease income of $1.9 million for both the years ended December 31, 2023 and 2022 and $0.6 million for the year ended December 31, 2021.

The Company’s sublease income is recognized within other operating income, net in the Consolidated Statements of Operations and Comprehensive Loss.

Leases

The following table summarizes the Company’s future minimum operating lease commitments, including expected lease incentives to be received, as of December 31, 2023 (in thousands):


Year Ending December 31:
2024	$	11,347
2025	11,859
2026	12,209
2027	12,569
2028	12,940
Thereafter	22,585
Total undiscounted lease payments	83,509
Less: imputed interest	(20,342)
Total operating lease liabilities	$	63,167

Reported as of December 31, 2023:
Short-term portion of lease liabilities (included in accrued liabilities and other current liabilities)	$	6,273
Operating lease liabilities, non-current	56,894
Total	$	63,167

The Company’s sublease income is recognized within other operating income, net in the Consolidated Statements of Operations and Comprehensive Loss.

Workforce Reduction

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities [Abstract]

Workforce Reduction

In November 2023, the Company announced a reduction in its workforce to reduce operating costs and improve operating efficiency, pursuant to which the Company’s workforce was reduced by approximately 25%. The execution of the reduction in workforce was substantially completed by the end of 2023. The Company incurred approximately $5.5 million in expenses related to one-time severance payments and other employee‑related costs as follows for the year ended December 31, 2023 (in thousands):


	Year Ended December 31, 2023
Research and development	$	4,630
General and administrative	$	890
Total expense	$	5,520

The workforce reduction expenses were incurred in 2023 and cash payments were significantly completed by the end of 2023. The Company has accrued liabilities of approximately $1.9 million related to the workforce reduction, which were included in the Company’s Consolidated Balance Sheet within Accrued Liabilities and Other Current Liabilities as of December 31, 2023.

Income Taxes - Schedule of Reconciliation of Federal Statutory Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Federal statutory tax (as a percent)	21.00%	21.00%	21.00%
State tax, net of federal benefit (as a percent)	7.45%	5.10%	6.39%
Valuation allowance (as a percent)	(29.10%)	(28.89%)	(22.43%)
Collaboration revenue (as a percent)	0.00%	6.72%	0.00%
Stock-based compensation (as a percent)	(2.25%)	(6.11%)	(5.92%)
Tax credits (as a percent)	2.96%	2.33%	0.99%
Other (as a percent)	(0.06%)	(0.15%)	(0.03%)
Effective income tax rate (as a percent)	(0.00%)	0.00%	(0.00%)

Net Loss Per Share	12 Months Ended
Net Loss Per Share	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per ShareBasic and diluted net loss per share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. The Company’s potentially dilutive shares, which include unvested RSAs, unvested RSUs and options to purchase common stock, are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. Shares subject to options to purchase common stock, unvested RSAs and unvested RSUs were all excluded from consideration in the calculation of diluted net loss per share in all periods presented due to their anti-dilutive effects.

Subsequent Events (Details) - Cowen and Company, LLC - Subsequent Event - At The Market Offering $ in Millions	Feb. 28, 2024 USD ($)
Subsequent Event [Line Items]
Sale of stock, maximum aggregate offering amount	$ 150.0
Commissions payment, percentage of gross sale proceeds	3.00%

Property and Equipment, Net

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

Property and equipment, net, consisted of the following (in thousands):


	December 31,
	2023		2022
Leasehold improvements	$	118,319	$	116,930
Laboratory equipment	33,368		31,982
Computer equipment and software	1,672		1,630
Furniture and fixtures	814		717
Construction in progress	128		4,148
Property and equipment, at cost	154,301		155,407
Less: Accumulated depreciation and amortization	(51,647)		(32,384)
Total property and equipment, net	$	102,654	$	123,023

Depreciation and amortization expense was $20.2 million, $18.0 million and $13.5 million for the years ended December 31, 2023, 2022 and 2021, respectively.

Workforce Reduction (Tables)

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities [Abstract]

Schedule of Restructuring Expenses

The Company incurred approximately $5.5 million in expenses related to one-time severance payments and other employee‑related costs as follows for the year ended December 31, 2023 (in thousands):


	Year Ended December 31, 2023
Research and development	$	4,630
General and administrative	$	890
Total expense	$	5,520

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($)
$ in Thousands

12 Months Ended

Dec. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

Revenues

^[1]

$ 130

$ 84,683

$ 10,650

Related Party

Revenues

$ 0

$ 84,653

$ 10,509

[1]	Includes related-party revenue of zero, $84,653 and $10,509 for the years ended December 31, 2023, 2022 and 2021, respectively.

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

+ Details

Consolidated Statements of Operations and Comprehensive Loss - USD ($)
shares in Thousands, $ in Thousands

12 Months Ended

Dec. 31, 2023

Dec. 31, 2022

Dec. 31, 2021

Statement of Comprehensive Income [Abstract]

Revenues

^[1]

$ 130

$ 84,683

$ 10,650

Operating expenses:

Research and development

182,945

159,188

138,693

General and administrative

66,983

117,307

89,057

Other operating income, net

(2,790)

(4,754)

(2,324)

Total operating expenses

247,138

271,741

225,426

Loss from operations

(247,008)

(187,058)

(214,776)

Interest income, net

23,453

7,053

1,165

Other income (expense), net

1,846

1,887

(161)

Impairment of other investments

(12,923)

(5,000)

(36,447)

Total other income (loss), net

12,376

3,940

(35,443)

Net loss

(234,632)

(183,118)

(250,219)

Other comprehensive loss:

Net unrealized gain (loss) on marketable securities

7,505

(5,976)

(1,879)

Comprehensive loss

$ (227,127)

$ (189,094)

$ (252,098)

Net loss per common share, basic (in dollars per share)

$ (0.93)

$ (0.74)

$ (1.84)

Net loss per common share, diluted (in dollars per share)

$ (0.93)

$ (0.74)

$ (1.84)

Weighted-average shares used to compute net loss per common share, basic (in shares)

250,983

247,080

135,918

Weighted-average shares used to compute net loss per common share, diluted (in shares)

250,983

247,080

135,918

[1]	Includes related-party revenue of zero, $84,653 and $10,509 for the years ended December 31, 2023, 2022 and 2021, respectively.

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 154,301	$ 155,407
Less: Accumulated depreciation and amortization	(51,647)	(32,384)
Total property and equipment, net	102,654	123,023
Depreciation and amortization expense	20,200	18,000	$ 13,500
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	118,319	116,930
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	33,368	31,982
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	1,672	1,630
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	814	717
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, at cost	$ 128	$ 4,148

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 145,647	$ 123,554
Marketable securities	400,576	516,598
Prepaid expenses and other current assets	8,463	11,143
Total current assets	554,686	651,295
Restricted cash	284	280
Marketable securities, non-current	16,506	70,117
Other investments	32,001	44,924
Property and equipment, net	102,654	123,023
Operating lease right-of-use assets	39,663	43,242
Other non-current assets	4,235	4,680
Total assets	750,029	937,561
Current liabilities:
Accounts payable	4,817	3,917
Accrued liabilities and other current liabilities	28,126	28,755
Success payment liabilities	1,576	4,356
Total current liabilities	34,519	37,028
Operating lease liabilities, non-current	56,894	63,168
Other non-current liabilities	3,664	4,113
Total liabilities	95,077	104,309
Commitments and contingencies (Note 16)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized at December 31, 2023 and 2022, respectively; no shares issued and outstanding at December 31, 2023 and 2022	0	0
Common stock, $0.0001 par value; 500,000 shares authorized at December 31, 2023 and 2022, respectively; 253,958 and 249,567 shares issued and outstanding at December 31, 2023 and 2022, respectively	25	25
Additional paid-in capital	1,657,133	1,608,306
Accumulated other comprehensive loss	(94)	(7,599)
Accumulated deficit	(1,002,112)	(767,480)
Total stockholders’ equity	654,952	833,252
Total liabilities and stockholders’ equity	$ 750,029	$ 937,561
Common stock authorized (in shares)	500,000,000	500,000,000
Preferred stock authorized (in shares)	10,000,000	10,000,000

Cash Equivalents and Marketable Securities

12 Months Ended

Dec. 31, 2023

Cash and Cash Equivalents [Abstract]

Cash Equivalents and Marketable Securities

The fair value and amortized cost of cash equivalents and marketable securities by major security type are as follows (in thousands):


	December 31, 2023
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Money market funds	$	62,075	$	—	$	—	$	62,075
U.S. Treasury securities	374,214		237		(95)		374,356
U.S. government agency securities	48,924		3		(177)		48,750
Corporate debt securities	59,668		—		(62)		59,606
Total cash equivalents and marketable securities	$	544,881	$	240	$	(334)	$	544,787


Classified as:	Fair Value
Cash equivalents	$	127,705
Marketable securities	400,576
Marketable securities, non-current	16,506
Total cash equivalents and marketable securities	$	544,787


	December 31, 2022
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Money market funds	$	67,970	$	—	$	—	$	67,970
U.S. Treasury securities	277,056		—		(5,257)		271,799
U.S. government agency securities	135,460		1		(1,416)		134,045
Corporate debt securities	221,608		3		(930)		220,681
Total cash equivalents and marketable securities	$	702,094	$	4	$	(7,603)	$	694,495


Classified as:	Fair Value
Cash equivalents	$	107,780
Marketable securities	516,598
Marketable securities, non-current	70,117
Total cash equivalents and marketable securities	$	694,495

The fair values of securities held by the Company in an unrealized loss position for less than 12 months were $117.8 million and $287.8 million, as of December 31, 2023 and 2022, respectively. The fair values of securities held by the Company in an unrealized loss position for greater than 12 months were $43.6 million and $278.7 million as of December 31, 2023 and 2022, respectively. As of December 31, 2023 and 2022, all of the Company’s marketable securities had a maturity date of two years or less, were available for use and were classified as available-for-sale. The Company does not intend to sell these securities nor does the Company believe that it will be required to sell these securities before recovery of their amortized cost basis. The Company determined that there was no material change in the credit risk of the above investments as of both December 31, 2023 and 2022. As such, an allowance for credit losses has not been recognized. Gross realized gains and losses were de minimis for the years ended December 31, 2023 and 2022 and as a

result, amounts reclassified out of accumulated other comprehensive loss for the years ended December 31, 2023 and 2022 were also de minimis. See Note 6, Fair Value Measurements, for additional information regarding cash equivalents and marketable securities.

Stock-based Compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based Compensation

2021 Equity Incentive Plan

In June 2021, the Company adopted the 2021 Equity Incentive Plan (“2021 Plan”), which on the date of the underwriting agreement related to the Company’s IPO became effective with an initial reserve of 26,662,087 shares, plus any shares subject to outstanding awards granted under the 2018 Equity Incentive Plan (“2018 Plan”) that, on or after the effectiveness of the 2021 Plan, terminate or expire before exercise or settlement, are not issued because the award is settled in cash, are forfeited because of the failure to vest or are reacquired or withheld (or not issued) to satisfy a tax withholding obligation or the purchase or exercise price. In addition, the number of shares reserved for issuance under the 2021 Plan automatically increases on January 1 of each year for a period of ten years, beginning on January 1, 2022 and continuing through January 1, 2031, in an amount equal to (1) 5% of the total number of shares of the Company’s common stock outstanding on December 31 of the immediately preceding year, or (2) a lesser number of shares determined by the Company’s board of directors no later than December 31 of the immediately preceding year. On January 1, 2023, the Company reserved an additional 12,478,367 shares of common stock for issuance under the 2021 Plan representing 5% of

the total common shares outstanding as of December 31, 2022. Under the 2021 Plan, the Company may grant incentive stock options, non-statutory stock options, RSAs, RSUs, stock appreciation rights, performance awards and other stock‑based awards. Terms of stock awards, including vesting requirements, are determined by the Company’s board of directors or by a committee authorized by the Company’s board of directors, subject to provisions of the 2021 Plan. The term of any stock option granted under the 2021 Plan cannot exceed ten years. Generally, awards granted by the Company vest over four years, but may be granted with different vesting terms. In conjunction with adopting the 2021 Plan, the Company discontinued the 2018 Plan with respect to new equity awards.

As of December 31, 2023, 26,390,351 shares were available for future issuance pursuant to the 2021 Plan.

2021 Employee Stock Purchase Plan

In June 2021, the Company adopted the 2021 Employee Stock Purchase Plan (“2021 ESPP”), which became effective immediately prior to the execution of the underwriting agreement related to the Company’s IPO with an initial reserve of 2,470,000 shares. The 2021 ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their earnings, subject to plan limitations. Unless otherwise determined by the Company’s board of directors, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first date of an offering or on the purchase date. The number of shares of the Company’s common stock reserved for issuance under the 2021 ESPP automatically increases on January 1 of each year for a period of ten years, beginning on January 1, 2022 and continuing through January 1, 2031, by the lesser of (1) 1% of the total number of shares of the Company’s common stock outstanding on December 31 of the immediately preceding year, and (2) 4,940,000 shares; provided, however, that the Company’s board of directors may act to provide a lesser increase in number of shares. The Company’s board of directors elected to reserve no additional shares under the 2021 ESPP for the year beginning January 1, 2023. The Company may specify offerings with durations not more than 27 months and may specify shorter purchase periods within each offering. Under the 2021 ESPP, 986,391, 475,363 and zero shares have been issued for the years ended December 31, 2023, 2022 and 2021, respectively.

As of December 31, 2023, 3,461,629 shares were available for future issuance pursuant to the 2021 ESPP.

2018 Equity Incentive Plan

In 2018, the Company established the 2018 Plan that provided for the grant of incentive stock options, non‑statutory stock options, RSAs, RSUs, stock appreciation rights and other stock-based awards. Terms of stock awards, including vesting requirements, were determined by the board of directors or by a committee authorized by the Company’s board of directors, subject to provisions of the 2018 Plan. The term of any stock option granted under the 2018 Plan cannot exceed ten years. Generally, awards granted by the Company vest over four years, but could have been granted with different vesting terms. Pursuant to the terms of the 2021 Plan, any shares subject to outstanding options originally granted under the 2018 Plan that terminate, expire or lapse for any reason without the delivery of shares to the holder thereof become available for issuance pursuant to awards granted under the 2021 Plan. While no shares are available for future issuance under the 2018 Plan, it continues to govern outstanding equity awards granted thereunder.

Stock-based Compensation Expense

Stock-based compensation expense by classification included within the Consolidated Statements of Operations and Comprehensive Loss was as follows (in thousands):


	Year Ended December 31,
	2023		2022		2021
Research and development	$	18,207	$	16,721	$	15,328
General and administrative	28,877		65,203		46,873
Total stock-based compensation expense	$	47,084	$	81,924	$	62,201

Stock-based compensation expense for the year ended December 31, 2021 included the impact of an award accelerated in connection with the Company’s IPO of $2.6 million.

Stock Options and RSA Modifications

In November 2023, the Board of Directors of the Company approved, effective November 16, 2023, a one-time repricing of certain stock option awards that had been granted to date under the 2021 Plan and 2018 Plan. The repricing

impacted stock options with exercise prices greater than $2.37 held by employees who remained employed as-of November 16, 2023 and were not impacted by the reduction in workforce. The original exercise prices of the repriced stock options ranged from $2.61 to $17.95 per share for 200 total grantees with 23,416,860 shares repriced. Each stock option was repriced to have a per share exercise price of $1.87, which was the closing price of the Company’s common stock on November 16, 2023. To receive the new exercise price, option holders must remain employed with the Company through November 15, 2024. Additionally, the vesting schedule for the unvested shares underlying repriced stock options held by executives at the level of senior vice president and above was extended for an additional year. There were no changes to the vesting schedules for employees below the level of senior vice president. No changes were made to the expiration dates of or number of shares underlying the repriced stock options. Incremental stock-based compensation expense resulting from the repricing was $8.9 million in the aggregate. Expense for vested awards will be recognized through November 15, 2024 and expense for unvested awards will be recognized over the remaining service life of the option.

In December 2022, the Company’s former chief executive officer (“CEO”) resigned. Under the terms of the separation agreement, the former CEO will be available to provide consulting services to the Company through June 15, 2024, with vested options continuing to be exercisable and unvested options continuing to vest through that date. The Company concluded that the obligation to provide consulting services was nonsubstantive, and therefore resulted in a modification of their options due to the reduction of their service level. As the remaining service period was determined to be nonsubstantive, the entire incremental expense of $3.7 million associated with the modification was recognized in the fourth quarter of 2022.

In 2021, the Company had modifications due to the reduction in the service level for a previous CEO, who resigned as Executive Chairman in the fourth quarter of 2021, as well as an increase to certain awards’ post-termination exercise periods. The modifications in 2021 impacted both vested and unvested awards. Expense associated with vested awards is recognized in the period of the modification and expense associated with unvested awards is recognized over the remaining service life of the options or RSAs. The Company also had option modifications in 2021 for one individual resulting in incremental stock-based compensation expense of $1.0 million.

The following table shows the total incremental stock-based compensation expense associated with modifications for previous CEOs by the year in which the modification occurred in the years December 31, 2023, 2022 and 2021 (in thousands):


	December 31,
	2023		2022		2021
Previous CEO - Options(1)	$	—	$	3,741	$	—
Previous CEO - Options(2)	—		—		21,948
Previous CEO - RSA(2)	—		—		10,908
Total	$	—	$	3,741	$	32,856

__________

(1)The modification for Previous CEO - Options for 2022 is for Ms. Elizabeth Homans, who resigned in December 2022.

(2)The modifications for Previous CEO - Options and Previous CEO - RSA for 2021 are for Dr. Richard Klausner, who resigned as Executive Chairman in October 2021 and is now the Chair of Lyell’s Board.

At December 31, 2023, total stock-based compensation cost related to unvested awards not yet recognized was $65.3 million, which is expected to be recognized over a remaining weighted-average period of 2.7 years.

Restricted Stock Awards

The Company had no unvested RSAs as of both December 31, 2023 and 2022. The fair value of RSAs vested during the years ended December 31, 2023, 2022 and 2021 was zero, $15.2 million and $57.1 million, respectively.

Restricted Stock Units

A summary of the Company’s RSU activity was as follows:


	Number of Shares	Weighted-Average Value at Grant Date Per Share
Unvested RSUs as of December 31, 2022	872,077	$	5.98
RSUs granted	2,621,177	$	2.22
RSUs vested	(598,024)	$	3.75
RSUs forfeited or canceled	(822,375)	$	3.22
Unvested RSUs as of December 31, 2023	2,072,855	$	2.96

The fair value of RSUs vested during the years ended December 31, 2023 and 2022 was $1.4 million and $1.5 million, respectively. No RSUs vested during the year ended December 31, 2021.

Stock Options

A summary of the Company’s stock option activity was as follows:


	Number of Stock Options	Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value (in thousands)
Options outstanding as of December 31, 2022	53,849,045	$	5.09	7.84	$	24,887
Granted	12,399,063	$	2.29
Exercised	(2,996,262)	$	0.10
Canceled or forfeited	(7,655,015)	$	5.03
Options outstanding as of December 31, 2023	55,596,831	$	4.75	6.89	$	7,368
Options exercisable as of December 31, 2023	33,965,690	$	5.06	5.76	$	7,303

The fair value of stock options granted to employees, directors and consultants was estimated on the date of grant using the Black-Scholes option pricing model using the following weighted-average assumptions:


	Year Ended December 31,
	2023		2022		2021
Risk-free interest rate	4.13	%	2.93	%	0.80	%
Expected volatility	88.0	%	87.3	%	78.7	%
Expected term (in years)	6.06		6.03		6.10
Expected dividend yield	0	%	0	%	0	%

The weighted-average grant date fair value of options granted for the years ended December 31, 2023, 2022 and 2021 was $1.69 per share, $3.60 per share and $6.59 per share, respectively. The intrinsic value of options exercised during the years ended December 31, 2023, 2022 and 2021 was $6.5 million, $13.9 million and $16.1 million, respectively.

Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Income Tax Examination [Line Items]
Capitalized research and development	$ 51,159,000	$ 26,199,000
Increase (decrease) in valuation allowance on deferred tax assets	68,300,000	52,900,000
Penalties or interest accrued on income taxes	0	0
Tax Year 2028 \| Capital Loss Carryforward
Income Tax Examination [Line Items]
Tax credit carryforwards	52,500,000
Federal and State
Income Tax Examination [Line Items]
Tax credit carryforwards	24,200,000	15,800,000
Federal
Income Tax Examination [Line Items]
Operating loss carryforwards not subject to expiration	455,200,000	$ 383,300,000
State
Income Tax Examination [Line Items]
Operating loss carryforwards subject to expiration	$ 537,200,000

Cover - USD ($) $ in Millions	12 Months Ended
Cover - USD ($) $ in Millions	Dec. 31, 2023	Feb. 22, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-40502
Entity Registrant Name	Lyell Immunopharma, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	83-1300510
Entity Address, Address Line One	201 Haskins Way
Entity Address, City or Town	South San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94080
City Area Code	650
Local Phone Number	695-0677
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	LYEL
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction Flag	false
Entity Shell Company	false
Entity Public Float			$ 654
Entity Common Stock, Shares Outstanding		254,096,311
Documents Incorporated by Reference	Portions of the registrant’s Proxy Statement for the 2024 Annual Meeting of Stockholders are incorporated herein by reference in Part III of this Annual Report on Form 10-K to the extent stated herein. Such proxy statement will be filed with the Securities and Exchange Commission within 120 days of the registrant’s fiscal year ended December 31, 2023.
Entity Central Index Key	0001806952
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false

Stock-based Compensation - Schedule of Incremental Stock-Based Compensation Expense from Modifications (Details) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
	Nov. 16, 2023 USD ($) grantee $ / shares shares	Dec. 31, 2022 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Options and RSAs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incremental stock-based compensation expense of modifications			$ 0	$ 3,741	$ 32,856
Options \| 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Minimum exercise price of plan modifications (in dollars per share) \| $ / shares	$ 2.37
Original exercise price lower range (in dollars per share) \| $ / shares	2.61
Original exercise price upper range (in dollars per share) \| $ / shares	$ 17.95
Share-based payment arrangement, plan modification, number of grantees affected \| grantee	200
shares repriced (in shares) \| shares	23,416,860
Plan modification, exercise price (in dollars per share) \| $ / shares	$ 1.87
Incremental stock-based compensation expense of modifications	$ 8,900
Options \| Previous CEO \| 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incremental stock-based compensation expense of modifications		$ 3,700	0	3,741	0
Options \| Previous CEO \| 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incremental stock-based compensation expense of modifications			0	0	21,948
Options \| Previous CEO \| 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incremental stock-based compensation expense of modifications					1,000
RSAs \| Previous CEO \| 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Incremental stock-based compensation expense of modifications			$ 0	$ 0	$ 10,908

Income Taxes - Schedule of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Net operating loss carryforwards	$ 133,141	$ 106,530
Tax credit carryforwards	22,409	14,317
Capital loss carryforward	14,368	0
Accrued liabilities and allowances	3,143	3,692
Deferred revenue	793	904
Amortization	5,243	4,585
Capitalized research and development	51,159	26,199
Investment basis difference	4,104	14,235
Lease liability	17,284	17,656
Stock-based compensation	11,244	7,471
Other	470	1,171
Gross deferred tax assets	263,358	196,760
Valuation allowance	(248,420)	(180,132)
Deferred tax assets, net of valuation allowance	14,938	16,628
Deferred tax liabilities:
Operating lease right-of-use assets	(10,853)	(11,277)
Property and equipment	(4,085)	(5,351)
Deferred tax liabilities	(14,938)	(16,628)
Net deferred tax assets	$ 0	$ 0

Basis of Presentation and Significant Accounting Policies - Narrative (Details)

12 Months Ended

Dec. 31, 2023

USD ($)

segment

$ / shares

Dec. 31, 2022

USD ($)

$ / shares

Dec. 31, 2021

USD ($)

$ / shares

Class of Stock [Line Items]

Increase in revenue

^[1]

$ 130,000

$ 84,683,000

$ 10,650,000

Reduction in net loss

$ (234,632,000)

$ (183,118,000)

$ (250,219,000)

Reduction in net loss per common share, basic (in dollars per share) | $ / shares

$ (0.93)

$ (0.74)

$ (1.84)

Reduction in net loss per common share, diluted (in dollars per share) | $ / shares

$ (0.93)

$ (0.74)

$ (1.84)

Equity warrant investment fair value

$ 0

Impairment of long-lived assets

$ 0

Number of operating segments | segment

Number of reportable segments | segment

Minimum

Class of Stock [Line Items]

Estimated life

3 years

Maximum

Class of Stock [Line Items]

Estimated life

5 years

Adjustment To Revenue Related To Change In Estimate | Collaborative Arrangement, Transaction with Party to Collaborative Arrangement | GSK

Class of Stock [Line Items]

Increase in revenue

83,600,000

Reduction in net loss

$ 83,600,000

Reduction in net loss per common share, basic (in dollars per share) | $ / shares

$ 0.34

Reduction in net loss per common share, diluted (in dollars per share) | $ / shares

$ 0.34

[1]	Includes related-party revenue of zero, $84,653 and $10,509 for the years ended December 31, 2023, 2022 and 2021, respectively.

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023
Trading Arrangements, by Individual
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

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of Federal Statutory Income Tax Rate

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations follows:


	Year Ended December 31,
	2023		2022		2021
Federal statutory tax	21.00	%	21.00	%	21.00	%
State tax, net of federal benefit	7.45		5.10		6.39
Valuation allowance	(29.10)		(28.89)		(22.43)
Collaboration revenue	—		6.72		—
Stock-based compensation	(2.25)		(6.11)		(5.92)
Tax credits	2.96		2.33		0.99
Other	(0.06)		(0.15)		(0.03)
Effective income tax rate	0.00	%	0.00	%	0.00	%

Schedule of Deferred Tax Assets

The principal components of the Company’s net deferred tax assets were as follows (in thousands):


	Year Ended December 31,
	2023		2022
Deferred tax assets:
Net operating loss carryforwards	$	133,141	$	106,530
Tax credit carryforwards	22,409		14,317
Capital loss carryforward	14,368		—
Accrued liabilities and allowances	3,143		3,692
Deferred revenue	793		904
Amortization	5,243		4,585
Capitalized research and development	51,159		26,199
Investment basis difference	4,104		14,235
Lease liability	17,284		17,656
Stock-based compensation	11,244		7,471
Other	470		1,171
Gross deferred tax assets	263,358		196,760
Valuation allowance	(248,420)		(180,132)
Deferred tax assets, net of valuation allowance	14,938		16,628
Deferred tax liabilities:
Operating lease right-of-use assets	(10,853)		(11,277)
Property and equipment	(4,085)		(5,351)
Deferred tax liabilities	(14,938)		(16,628)
Net deferred tax assets	$	—	$	—

Schedule of Changes to Company’s Unrecognized Tax Benefits

The following table summarized changes to the Company’s unrecognized tax benefits (in thousands):


	Year Ended December 31,
	2023		2022
Beginning balance	$	400	$	796
Additions based on tax position related to the current year	—		—
Adjustments based on prior year tax positions	—		(396)
Ending balance	$	400	$	400

License, Collaboration and Success Payment Agreements - Schedule of Aggregate Potential Success Payments (Details) - Collaborative Arrangement, Transaction with Party to Collaborative Arrangement	Dec. 31, 2023 USD ($)	Oct. 31, 2020 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares
Fred Hutch
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate success payment(s) (in millions)	$ 0
Fred Hutch \| Ten Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance			10
Per share common stock price required for payment (in dollars per share) \| $ / shares			$ 18.29
Aggregate success payment(s) (in millions)			$ 10,000,000
Fred Hutch \| Twenty Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance			20
Per share common stock price required for payment (in dollars per share) \| $ / shares			$ 36.58
Aggregate success payment(s) (in millions)			$ 40,000,000
Fred Hutch \| Thirty Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance			30
Per share common stock price required for payment (in dollars per share) \| $ / shares			$ 54.86
Aggregate success payment(s) (in millions)			$ 90,000,000
Fred Hutch \| Forty Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance			40
Per share common stock price required for payment (in dollars per share) \| $ / shares			$ 73.15
Aggregate success payment(s) (in millions)			$ 140,000,000
Fred Hutch \| Fifty Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance			50
Per share common stock price required for payment (in dollars per share) \| $ / shares			$ 91.44
Aggregate success payment(s) (in millions)			$ 200,000,000
Stanford
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate success payment(s) (in millions)	$ 0
Stanford \| Ten Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance		10
Per share common stock price required for payment (in dollars per share) \| $ / shares		$ 18.29
Aggregate success payment(s) (in millions)		$ 10,000,000
Stanford \| Twenty Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance		20
Per share common stock price required for payment (in dollars per share) \| $ / shares		$ 36.58
Aggregate success payment(s) (in millions)		$ 40,000,000
Stanford \| Thirty Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance		30
Per share common stock price required for payment (in dollars per share) \| $ / shares		$ 54.86
Aggregate success payment(s) (in millions)		$ 90,000,000
Stanford \| Forty Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance		40
Per share common stock price required for payment (in dollars per share) \| $ / shares		$ 73.15
Aggregate success payment(s) (in millions)		$ 140,000,000
Stanford \| Fifty Times
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance		50
Per share common stock price required for payment (in dollars per share) \| $ / shares		$ 91.44
Aggregate success payment(s) (in millions)		$ 200,000,000

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Schedule of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis


	December 31, 2023
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds	$	62,075	$	—	$	—	$	62,075
U.S. Treasury securities	—		374,356		—		374,356
U.S. government agency securities	—		48,750		—		48,750
Corporate debt securities	—		59,606		—		59,606
Total financial assets	$	62,075	$	482,712	$	—	$	544,787
Financial liabilities:
Success payment liabilities	$	—	$	—	$	1,576	$	1,576
Total financial liabilities	$	—	$	—	$	1,576	$	1,576


	December 31, 2022
	Level 1		Level 2		Level 3		Total
Financial assets:
Money market funds	$	67,970	$	—	$	—	$	67,970
U.S. Treasury securities	—		271,799		—		271,799
U.S. government agency securities	—		134,045		—		134,045
Corporate debt securities	—		220,681		—		220,681
Total financial assets	$	67,970	$	626,525	$	—	$	694,495
Financial liabilities:
Success payment liabilities	$	—	$	—	$	4,356	$	4,356
Total financial liabilities	$	—	$	—	$	4,356	$	4,356

Schedule of Estimated Fair Value of Success Payment Liability Assumptions

The following assumptions were incorporated into the calculation of the estimated fair value of the Fred Hutch success payment liability:


	December 31,
	2023			2022
Fair value of common stock	$	1.94		$	3.47
Risk-free interest rate	3.51% - 5.19%			3.58% - 4.65%
Expected volatility	80.0		%	80.0		%
Expected term (in years)	0.46 - 3.97			0.46 - 4.97

The following assumptions were incorporated into the calculation of the estimated fair value of the Stanford success payment liability:


	December 31,
	2023			2022
Fair value of common stock	$	1.94		$	3.47
Risk-free interest rate	3.51% - 5.19%			3.58% - 4.65%
Expected volatility	80.0		%	80.0		%
Expected term (in years)	0.46 - 5.75			0.46 - 6.75

Schedule of Changes in the Estimated Fair Value of Level 3 Financial Assets

The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial assets and liabilities (in thousands):


	Equity Warrant Investment		Success Payment Liabilities
Balance at December 31, 2021	$	1,067	$	9,486
Change in fair value (1)	(1,067)		(5,130)
Balance at December 31, 2022	—		4,356
Change in fair value (1)	—		(2,780)
Balance at December 31, 2023	$	—	$	1,576

__________

Schedule of Changes in the Estimated Fair Value of Level 3 Financial Liabilities

The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial assets and liabilities (in thousands):


	Equity Warrant Investment		Success Payment Liabilities
Balance at December 31, 2021	$	1,067	$	9,486
Change in fair value (1)	(1,067)		(5,130)
Balance at December 31, 2022	—		4,356
Change in fair value (1)	—		(2,780)
Balance at December 31, 2023	$	—	$	1,576

__________

Cash Equivalents and Marketable Securities - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Marketable Securities [Line Items]
Fair value of securities held in a continuous unrealized loss position for less than twelve months	$ 117.8	$ 287.8
Fair value of securities held in a continuous unrealized loss position for greater than twelve months	$ 43.6	$ 278.7
Maximum
Marketable Securities [Line Items]
Maturity of marketable securities	2 years	2 years

Stockholders’ Equity (Details) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Equity [Abstract]
Preferred stock authorized (in shares)	10,000,000	10,000,000
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock outstanding (in shares)	0	0
Common stock authorized (in shares)	500,000,000	500,000,000
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock outstanding (in shares)	253,957,709	249,567,343

Accrued Liabilities and Other Current Liabilities

12 Months Ended

Dec. 31, 2023

Accrued Liabilities and Other Liabilities [Abstract]

Accrued Liabilities and Other Current Liabilities

Accrued liabilities and other current liabilities consisted of the following (in thousands):


	December 31,
	2023		2022
Accrued compensation and related benefits	$	14,634	$	15,447
Current lease liabilities	6,273		4,534
Accrued research and development expenses	5,331		4,760
Other	1,493		2,352
Accrued legal	395		930
Accrued property and equipment	—		732
Total accrued liabilities and other current liabilities	$	28,126	$	28,755

Basis of Presentation and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary.
Consolidations	All significant intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions that affect reported amounts and related disclosures. Specific accounts that require management estimates include, but are not limited to, stock-based compensation, valuation of success payments, valuation of other investments, revenue recognition and accrued expenses. Management bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Actual results could differ materially from those estimates. In June 2022, the Company recorded adjustments to revenue related to a change in estimate in connection with the Collaboration and License Agreement, entered into in 2019 and amended in June 2020 and December 2021 (“GSK Agreement”) with GlaxoSmithKline Intellectual Property (No. 5) Limited and Glaxo Group Limited (together, “GSK”). The Company and GSK mutually agreed to conclude research activities on an undisclosed target for hematological cancers in June 2022. As a result, the Company decreased the related estimated project costs, which resulted in an increase in the measure of proportional cumulative performance.
Comprehensive Loss	Comprehensive Loss Comprehensive loss includes net loss and certain changes in stockholders’ equity that are excluded from net loss. For the years ended December 31, 2023, 2022 and 2021, this was comprised of net unrealized gains and losses on the Company’s marketable securities.
Cash and Cash Equivalents	The Company considers all highly liquid investments purchased with original maturities of three months or less from the purchase date to be cash equivalents. Cash equivalents consist primarily of amounts invested in commercial paper and money market accounts.
Restricted Cash	Restricted cash is cash held in a bank account and is used as collateral associated with the Company’s corporate credit card program.
Marketable Securities	Marketable Securities The Company generally invests its excess cash in investment grade short- to intermediate-term fixed income securities. Such investments are classified as available-for-sale and are carried at fair value, with the unrealized gains and losses reported as a component of comprehensive loss. Realized gains and losses on available-for-sale securities are included in other income (expense), net. The cost of investments sold is based on the specific-identification method. The Company classifies those investments that are not required for use in current operations and that mature in more than 12 months as non-current marketable securities in the accompanying consolidated balance sheets. Each reporting period, the Company evaluates whether declines in fair value below carrying value are due to expected credit losses, as well as the Company’s ability and intent to hold the investment until a forecasted recovery occurs. Expected credit losses, if any, are recorded as an allowance through other income (expense), net.
Valuation of Other Investments	Valuation of Other Investments The Company determines at the inception of each arrangement whether an investment or other interest is considered a variable interest entity (“VIE”). If the investment or other interest is determined to be a VIE, the Company evaluates whether it is considered the primary beneficiary. The primary beneficiary of a VIE is the party that meets both of the following criteria: (i) has the power to direct the activities that most significantly impact the VIE’s economic performance; and (ii) has the obligation to absorb losses or the right to receive benefits from the VIE. For any investments in VIEs in which the Company is considered the primary beneficiary, the assets, liabilities and results of operations of the VIE would be included in its consolidated financial statements. As of December 31, 2023 and 2022, there were no VIEs for which the Company was the primary beneficiary. The Company accounts for its strategic equity interests in common stock and in-substance common stock in non‑publicly traded companies for which it does not have the ability to exercise significant influence in accordance with Accounting Standards Codification (“ASC”) 321, Investments – Equity Securities (“ASC 321”). Upon acquisition, these investments are measured at cost, which represents the then fair value. Under ASC 321, the Company can elect to subsequently measure the investments at initial cost, minus impairment and any changes, plus or minus, resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer (“measurement alternative”). This election must be made for each investment separately. The Company has made this election for all investments in this category and will continue to measure these investments using this method until they no longer qualify to be measured in accordance with this method. Changes in the carrying value of other investments are recognized through net loss. Each reporting period, the Company performs a qualitative assessment to evaluate whether the investment is impaired. The Company’s assessment includes a review of recent operating results and trends, recent sales/acquisitions of the investee securities and other factors that raise concerns about the investee’s ability to continue as a going concern. If the investment is impaired, an impairment charge is recognized in the amount by which the carrying amount of the investment exceeds the estimated fair value of the investment, with the impairment charge recognized through net loss. See Note 5, Other Investments, for details related to investment impairments recognized during the years ended December 31, 2023, 2022 and 2021. Additionally, the Company holds an equity warrant investment giving it the right to acquire stock of a non‑publicly traded company. Equity warrant investments are recorded within other assets at the estimated fair value, with gains and losses recognized in other income (expense), net. For the year ended December 31, 2022, in conjunction with the impairment of one of the Company’s other investments, the associated equity warrant investment’s fair value was determined to be negligible. The Company reduced the equity warrant investment’s fair value to zero for the year ended December 31, 2022.
Property and Equipment, Net	Property and Equipment, Net Property and equipment primarily consist of laboratory equipment, computer equipment and software, furniture and fixtures and leasehold improvements. Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is calculated using the straight-line method based on the estimated useful lives of the related assets, which are generally three to five years. For leasehold improvements, amortization is calculated using the straight‑line method based on the shorter of the useful life or the lease term. When assets are retired or otherwise disposed of, the cost and related accumulated depreciation and amortization are removed from the balance sheet and the resulting gain or loss is recorded in other operating income, net in the period realized. Maintenance and repairs are expensed as incurred. The Company reviews its property and equipment for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable.
Valuation of Long-lived Assets	Valuation of Long-lived Assets Long-lived assets are reviewed each reporting period for impairment or whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable, which may warrant adjustments to carrying values or estimated useful lives. Recoverability is measured by comparison of the carrying amount of an asset group to the future net undiscounted cash flows that the assets are expected to generate. If the carrying amount of an asset group exceeds its estimated future cash flows, an impairment charge is recognized in the amount by which the carrying amount of the asset group exceeds the fair value of the asset group. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset.
Leases	Leases The Company leases certain office, laboratory and manufacturing spaces. In addition to minimum rent, the leases require payment of real estate taxes, insurance, common area maintenance charges and other executory costs. At inception of a contract, the Company determines whether an arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. For all leases, the Company determines the classification of the lease as either operating or financing. As of December 31, 2023 and 2022, all of the Company’s leases were classified as operating leases. The Company recognizes right-of-use (“ROU”) assets and lease liabilities at the lease commencement date based on the present value of future lease payments over the lease term. As the Company’s leases do not provide an implicit rate, an incremental borrowing rate at each lease commencement date is used to determine the present value of future lease payments. The incremental borrowing rate is the rate of interest that the Company would pay to borrow equivalent funds on a collateralized basis at the lease commencement date. To estimate the incremental borrowing rate, a credit rating applicable to the Company is estimated using a synthetic credit rating analysis since the Company does not currently have a rating agency-based credit rating. The ROU asset includes any lease payments made prior to the lease commencement date and is reduced by any lease incentives received or deemed payable to the Company. The lease term may include options to extend or terminate the lease when it is reasonably certain that a lease option will be exercised. Lease expense is recognized on a straight-line basis over the lease term within operating expenses on the Consolidated Statements of Operations and Comprehensive Loss. The Company has elected the practical expedient to not separate lease and non-lease components for real estate leases. Additionally, the Company has elected the short-term lease recognition exemption for all short-term leases and as a result, lease liabilities and ROU assets are not included on the consolidated balance sheets for leases with an initial term of 12 months or less.
Fair Value Measurements	Fair Value Measurements The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. The fair value hierarchy prioritizes valuation inputs based on the observable nature of those inputs. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs: Level 1 – Quoted prices in active markets for identical assets or liabilities. Level 2 – Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 – Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. The Company’s financial instruments, in addition to those presented in Note 6, Fair Value Measurements, include cash, restricted cash, other investments, accounts payable and accrued liabilities and other current liabilities. The carrying amount of cash, restricted cash, accounts payable and accrued liabilities and other current liabilities approximate fair value because of the short-term nature of these instruments. As described in Note 5, Other Investments, other investments are carried at cost, minus impairment and any changes, plus or minus, resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the Company expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements within the scope of ASC 606, Revenue from Contracts with Customers, (“ASC 606”) the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the performance obligation is satisfied. In applying the ASC 606 framework, the Company must apply judgment to determine the nature of the promises within a revenue contract and whether those promises represent distinct performance obligations. In determining the transaction price, the Company does not include amounts subject to uncertainties unless it is probable that there will be no significant reversal of cumulative revenue when the uncertainty is resolved. Milestone and other forms of variable consideration that the Company may earn are subject to significant uncertainties of research and development related achievements, which generally are deemed not probable until such milestones are actually achieved. For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes 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). Additionally, the Company develops assumptions that require judgment to determine the standalone selling price of each performance obligation identified in the contract. The Company then allocates the total transaction price to each performance obligation based on the estimated standalone selling prices of each performance obligation, for which it recognizes revenue as or when the performance obligations are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the variable consideration 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. Under the Company’s license agreements, the Company grants the license to a customer as it exists at the point of transfer and the nature of the license is a right to use the Company’s intellectual property as transferred. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue from non-refundable, upfront fees 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 bundled with other promises, the Company utilizes 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.
Research and Development Expense	Research and Development Expense The Company records expense for research and development costs as incurred. Research and development expenses consist of costs incurred by the Company for the discovery and development of its technology platforms and product candidates and includes costs incurred in connection with strategic collaborations, costs to license technology, personnel-related costs, including stock-based compensation expense, facility and technology related costs, research and laboratory expenses, as well as other expenses, which include consulting fees and other costs. Upfront payments and milestones paid to third parties in connection with technology platforms that have not reached technological feasibility and do not have an alternative future use are expensed as incurred. Clinical expenses are a component of research and development expense. The Company accrues and expenses clinical trial services performed by third parties based upon actual work completed in accordance with agreements established with its service providers. The Company estimates the costs through discussions with internal personnel and external service providers as to the progress or stage of completion of services and the agreed-upon fees to be paid for such services.
General and Administrative Expense	General and Administrative Expense General and administrative costs are expensed as incurred and include personnel-related expenses, including stock-based compensation expense for personnel in executive, legal, finance and other administrative functions, legal costs, transaction costs related to collaboration and licensing agreements, as well as fees paid for accounting and tax services, consulting fees and facilities costs not otherwise included in research and development expenses. Legal costs include those related to corporate, dispute and patent matters.
Success Payments	Success Payments The Company granted rights to success payments to Fred Hutchinson Cancer Center (“Fred Hutch”) and The Board of Trustees of the Leland Stanford Junior University (“Stanford”) pursuant to the terms of its research and collaboration agreements with each of those entities. Pursuant to the terms of these agreements, on each contractually prescribed measurement date, the Company may be required to make success payments based on increases in the estimated per share fair value of the Company’s common stock. See Note 3, License, Collaboration and Success Payment Agreements. The success payments are accounted for under ASC 718, Compensation – Stock Compensation, with the expense being recorded in research and development expenses. Once the service period is complete, the instrument continues to be remeasured each reporting period with all changes in value recognized immediately in other income (expense), net. The success payment liability is estimated at fair value at inception and at each subsequent reporting period, and the expense is accreted over the service period of the research and collaboration agreement. To determine the estimated fair value of the success payments, the Company uses a Monte Carlo simulation methodology which models the future movement of stock prices based on several key variables combined with empirical knowledge of the process governing the behavior of the stock price. The following variables were incorporated in the estimated fair value of the success payment liability: estimated fair value of the Company’s common stock, expected volatility, risk-free interest rate and the estimated number and timing of valuation measurement dates on the basis of which payments may be triggered. The computation of expected volatility was estimated based on available information about the historical volatility of stocks of similar publicly traded companies for a period matching the expected term assumption.
Concentrations of Credit Risk	Concentrations of Credit Risk and Off-balance Sheet Risk The Company maintains its cash, cash equivalents and restricted cash with high quality, accredited financial institutions. Restricted cash is cash held in a bank account and is used as collateral associated with the Company’s corporate credit card program. Cash, cash equivalents and restricted cash amounts, at times, may exceed federally insured limits. The Company also makes short-term investments in money market funds, U.S. Treasury securities, U.S. government agency securities and corporate debt securities, which can be subject to certain credit risk. However, the Company mitigates the risks by investing in high-grade instruments, limiting exposure to any one issuer or type of investment and monitoring the ongoing creditworthiness of the financial institutions and issuers. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to significant risk on these funds.
Off-balance Sheet Risk	The Company has no off‑balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements.
Claims and Contingencies	Claims and Contingencies From time to time, the Company may become involved in litigation and proceedings relating to claims arising from the ordinary course of business. The Company accrues a liability if the likelihood of an adverse outcome is probable and the amount is estimable. If the likelihood of an adverse outcome is only reasonably possible (as opposed to probable), or if an estimate is not determinable, the Company provides disclosure of a material claim or contingency.
Stock-based Compensation	Stock-based Compensation Under ASC 718, the Company measures and recognizes expense for restricted stock awards (“RSAs”), restricted stock units (“RSUs”), employee stock purchases related to the Employee Stock Purchase Plan and stock options granted to employees, directors and consultants based on the fair value of the awards on the date of grant. The fair value of stock options is estimated using the Black-Scholes option pricing model. The Black-Scholes option pricing model requires inputs based on certain subjective assumptions including: stock price volatility, the expected term of stock options, the risk-free interest rate, expected dividends, and the fair value of the underlying common stock on the date of grant. The expected volatility is based on the historical volatility of the stock of similar entities within the Company’s industry over periods commensurate with the Company’s expected term assumption. The expected term of stock option grants represents the period the options are expected to remain outstanding and is based on the “simplified” method where the expected term is the midpoint between the vesting date and the end of the contractual term for each option. The Company generally uses the simplified method as provided for under the applicable guidance for entities with a limited history of relevant stock option exercise activity. The Company bases the risk-free interest rate on the interest rate payable on U.S. Treasury securities in effect at the time of grant for a period that is commensurate with the assumed expected option term. In reference to the expected dividend yield assumption, the Company has not historically paid, and does not expect for the foreseeable future to pay, a dividend. Stock-based compensation expense for RSAs, RSUs and stock options is recognized on a straight-line basis over the requisite service period, which is generally the vesting period of the respective award. The Company accounts for forfeitures as they occur. The Company also granted stock options that vest in conjunction with certain performance conditions to certain key employees. At each reporting date, the Company is required to evaluate whether achievement of the performance conditions is probable. Compensation expense is recorded over the appropriate service period based upon the Company’s assessment of accomplishing each performance provision.
Income Taxes	Income Taxes The Company determines its deferred tax assets and liabilities based on the differences between the financial reporting and tax basis of assets and liabilities. The deferred tax assets and liabilities are measured using the enacted tax rates that will be in effect when the differences are expected to reverse. A valuation allowance is recorded when it is more likely than not that the deferred tax asset will not be recovered. The Company applies judgment in the determination of the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. The Company recognizes any material interest and penalties related to unrecognized tax benefits in income tax expense.
Segments	Segments Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment and one reportable segment.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements Segment Reporting In November 2023, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which expands disclosures about a public entity’s reportable segments and requires more enhanced information about a reportable segment’s expenses, interim segment profit or loss, and how a public entity’s chief operating decision maker uses reported segment profit or loss information in assessing segment performance and allocating resources. Entities with a single reportable segment are required to provide all the updated and existing segment disclosures required by Topic 280. The amendments are effective for annual periods beginning after December 15, 2023 and interim periods within fiscal years beginning after December 15, 2024 on a retrospective basis. The Company is assessing the effect of the new disclosure requirements and does not anticipate the adoption will have a material impact. Income Taxes In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures, which includes amendments that further enhance income tax disclosures, primarily through standardization and disaggregation of rate reconciliation categories and income taxes paid by jurisdiction. The amendments are effective for annual periods beginning after December 15, 2024 and may be applied either prospectively or retrospectively. The Company is assessing the effect of the new disclosure requirements and does not anticipate the adoption will have a material impact.

Leases - Narrative (Details) ft² in Thousands, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2021 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2019 ft² renewal_option contract	Sep. 30, 2021 USD ($) ft²	May 31, 2021 ft²	Dec. 31, 2018 ft² renewal_option
Lessee, Lease, Description [Line Items]
Increase to lease liability		$ 0	$ 4,855	$ 13,202
Operating lease cost		9,000	9,300	9,400
Variable lease cost		$ 5,400	$ 5,100	4,100
Weighted average remaining lease term of operating leases		6 years 9 months 18 days	7 years 9 months 18 days
Operating lease, weighted average discount rate (as a percent)		8.50%	8.50%
South San Francisco, California
Lessee, Lease, Description [Line Items]
Sonoma sublease income		$ 800	$ 800	400
Rentable area (in square feet) \| ft²							11
Related Party
Lessee, Lease, Description [Line Items]
Rentable area (in square feet) \| ft²						18
Related Party \| Sonoma
Lessee, Lease, Description [Line Items]
Sonoma sublease income		$ 1,861	$ 1,861	$ 620
Rentable area (in square feet) \| ft²						18
Tenant improvements						$ 4,600
Building \| Expires in December 2028
Lessee, Lease, Description [Line Items]
Area of space (in square feet) \| ft²								34
Number of renewal options \| renewal_option								2
Renewal term								5 years
Building \| Expires in May 2030
Lessee, Lease, Description [Line Items]
Area of space (in square feet) \| ft²					73
Number of renewal options \| renewal_option					2
Renewal term					90 months
Number of operating lease agreements \| contract					2
Building \| Expires in January 2031
Lessee, Lease, Description [Line Items]
Area of space (in square feet) \| ft²					108
Renewal term					10 years
Increase to right of use asset	$ 4,200
Increase to lease liability	$ 4,200

Other Investments	12 Months Ended
Other Investments	Dec. 31, 2023
Investments, All Other Investments [Abstract]
Other Investments	Other Investments From time to time, the Company makes minority ownership strategic investments. As of December 31, 2023 and 2022, the aggregate carrying amounts of the Company’s strategic investments in non-publicly traded companies were $32.0 million and $44.9 million, respectively. These investments are measured at initial cost, minus impairment, if any, and plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. Cumulative impairments of strategic investments in equity investments without readily determinable fair values still held as of December 31, 2023 and 2022 were $15.0 million and $5.0 million, respectively. As a part of the acquisition of each of the Company’s other investments, the Company determines whether an investment or other interest is considered a variable interest. The Company held an interest in one entity as of December 31, 2023 and two entities as of December 31, 2022, that were concluded to be variable interests for which the Company was not the primary beneficiary as the Company did not have the not have the power to direct the activities that most significantly impact the economic performance of the VIEs. As of December 31, 2023 and 2022, the carrying value and maximum exposure to loss of the Company’s variable interests were $13.0 million and $15.9 million, respectively, which are recorded in other investments in the Company’s Consolidated Balance Sheets. In October 2022, the Company received shares of PACT’s Series D non-voting convertible preferred stock (See Note 3, License, Collaboration and Success Payment Agreements). The Company recognized its investment in PACT preferred stock at its estimated fair value of $2.9 million on October 1, 2022, which was included in the Company’s Consolidated Balance Sheet within other investments as of December 31, 2022. During the years ended December 31, 2023, 2022 and 2021, the Company performed qualitative assessments of potential indicators of impairment and determined that indicators existed for certain of its other investments. While there was no single event or factor in each instance, the Company considered the underlying companies’ operating cash flow requirements over the next year, liquid asset balances to fund those requirements and the underlying companies’ inability to raise funds as indicators of impairment. Due to these indicators, the Company assessed the valuation of these investments and determined the fair values to be negligible and the impairments to be other-than-temporary in nature. As a result, the Company recorded impairment expenses of $2.9 million for the PACT Series D convertible preferred stock investment and $10.0 million for another investment for the year ended December 31, 2023, $5.0 million for an investment for the year ended December 31, 2022 and $36.4 million for the PACT Series C-1 convertible preferred stock investment for the year ended December 31, 2021. The impairment expenses were recorded within impairment of other investments on the Consolidated Statements of Operations and Comprehensive Loss and as reductions to the investment balances within other investments on the Consolidated Balance Sheets.

Related-Party Transactions - Schedule of Total Income Attributable to Sonoma Sublease (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Sonoma other operating income, net	$ 2,790	$ 4,754	$ 2,324
Related Party \| Sonoma
Related Party Transaction [Line Items]
Sonoma other operating income, net	2,592	2,635	1,791
Sonoma sublease income	$ 1,861	$ 1,861	$ 620

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Collaboration and License Agreements The Company has entered into certain collaboration and license agreements, including those identified in Note 3, License, Collaboration and Success Payment Agreements above, with third parties that include the funding of certain development, manufacturing and commercialization efforts with the potential for future milestone and royalty payments upon the achievement of pre-established developmental, regulatory and/or commercial milestones. The Company’s obligation to fund these efforts is contingent upon continued involvement in the programs and/or the lack of any adverse events that could cause the discontinuance of the programs, including termination of such agreements. Due to the nature of these agreements, the future potential payments are inherently uncertain, and accordingly no amounts had been recorded for the potential future achievement of these targets as of December 31, 2023 and 2022.

Convertible Preferred Stock (Details) - shares	Dec. 31, 2023	Dec. 31, 2021	Jun. 17, 2021	Dec. 31, 2020
Equity [Abstract]
Outstanding shares of convertible preferred stock converted into shares of common stock (in shares)			194,474,431
Convertible preferred stock outstanding (in shares)	0	0		194,474,000

Leases (Tables)

12 Months Ended

Dec. 31, 2023

Leases [Abstract]

Schedule of Future Minimum Operating Lease Commitments, Including Expected Lease Incentives to be Received

The following table summarizes the Company’s future minimum operating lease commitments, including expected lease incentives to be received, as of December 31, 2023 (in thousands):


Year Ending December 31:
2024	$	11,347
2025	11,859
2026	12,209
2027	12,569
2028	12,940
Thereafter	22,585
Total undiscounted lease payments	83,509
Less: imputed interest	(20,342)
Total operating lease liabilities	$	63,167

Reported as of December 31, 2023:
Short-term portion of lease liabilities (included in accrued liabilities and other current liabilities)	$	6,273
Operating lease liabilities, non-current	56,894
Total	$	63,167

Schedule of Current and Non-current Lease Liabilities

The following table summarizes the Company’s future minimum operating lease commitments, including expected lease incentives to be received, as of December 31, 2023 (in thousands):


Year Ending December 31:
2024	$	11,347
2025	11,859
2026	12,209
2027	12,569
2028	12,940
Thereafter	22,585
Total undiscounted lease payments	83,509
Less: imputed interest	(20,342)
Total operating lease liabilities	$	63,167

Reported as of December 31, 2023:
Short-term portion of lease liabilities (included in accrued liabilities and other current liabilities)	$	6,273
Operating lease liabilities, non-current	56,894
Total	$	63,167

License, Collaboration and Success Payment Agreements - Narrative (Details)		1 Months Ended		12 Months Ended
	Oct. 01, 2022 USD ($)	Dec. 31, 2021 USD ($)	May 31, 2019 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) $ / shares	Dec. 31, 2022 USD ($) $ / shares	Dec. 31, 2021 USD ($) $ / shares	Oct. 31, 2020 USD ($) $ / shares	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) $ / shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Research and development expense				$ 182,945,000	$ 159,188,000	$ 138,693,000
Reduction in net loss				$ (234,632,000)	$ (183,118,000)	$ (250,219,000)
Reduction in net loss per common share, basic (in dollars per share) \| $ / shares				$ (0.93)	$ (0.74)	$ (1.84)
Reduction in net loss per common share, diluted (in dollars per share) \| $ / shares				$ (0.93)	$ (0.74)	$ (1.84)
Impairment of other investments				$ 12,923,000	$ 5,000,000	$ 36,447,000
Gain on other investments				0	2,923,000	0
PACT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Impairment of other investments		$ 36,400,000				36,400,000
Other Investment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Impairment of other investments				10,000,000	5,000,000
Series A Convertible Preferred Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Convertible preferred stock, par value (in dollars per share) \| $ / shares							$ 1.83			$ 1.83
PACT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Gain on other investments	$ 2,900,000
PACT \| Other Investment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Impairment of other investments				2,900,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Fred Hutch
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Annual license maintenance payments										$ 50,000
Aggregate research payments due										$ 12,000,000
Term of collaborative arrangement for research										6 years
Research and development expense				900,000	1,700,000	4,200,000
Potential aggregate success payments				0
Term of success payment agreement										9 years
Trigger period from IPO date										1 year
Trigger period thereafter										2 years
Success payment expense/(gain)				(1,900,000)	(3,900,000)	1,200,000
Fair value of potential success payments due				700,000	2,500,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Fred Hutch \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance										10
Potential aggregate success payments										$ 10,000,000
Per share common stock price required for payment (in dollars per share) \| $ / shares										$ 18.29
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Fred Hutch \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance										50
Potential aggregate success payments										$ 200,000,000
Per share common stock price required for payment (in dollars per share) \| $ / shares										$ 91.44
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Stanford
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Annual license maintenance payments									$ 50,000
Aggregate research payments due							$ 12,000,000
Term of collaborative arrangement for research							4 years
Research and development expense				3,000,000	3,000,000	3,000,000
Potential aggregate success payments				0
Term of success payment agreement							9 years
Trigger period from IPO date							1 year
Trigger period thereafter							2 years
Success payment liability				900,000	1,900,000
Success payment expense/(gain)				(900,000)	(1,200,000)	2,500,000
Fair value of potential success payments due				1,100,000	3,300,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Stanford \| License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Commercial milestone payments due									2,500,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Stanford \| Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance							10
Potential aggregate success payments							$ 10,000,000
Per share common stock price required for payment (in dollars per share) \| $ / shares							$ 18.29
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Stanford \| Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Multiple of initial equity value at issuance							50
Potential aggregate success payments							$ 200,000,000
Per share common stock price required for payment (in dollars per share) \| $ / shares							$ 91.44
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| Stanford \| Maximum \| License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Potential milestone payments due									$ 3,700,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| GSK
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Recognized revenue				0	84,700,000	$ 10,500,000
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| GSK \| Adjustment To Revenue Related To Change In Estimate
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Recognized revenue					83,600,000
Reduction in net loss					$ 83,600,000
Reduction in net loss per common share, basic (in dollars per share) \| $ / shares					$ 0.34
Reduction in net loss per common share, diluted (in dollars per share) \| $ / shares					$ 0.34
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| GSK \| License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Contract liabilities			$ 45,000,000	0
Stock Purchase Agreement portion of transaction price			58,600,000
Transaction price			$ 103,600,000
Contract assets				$ 0
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| GSK \| Series AA Convertible Preferred Stock \| License
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Stock sold under Stock Purchase Program (in shares) \| shares			30,253,189
Price per share of stock sold under Stock Purchase Program (in dollars per share) \| $ / shares			$ 6.78
Fair value per share of stock sold under Stock Purchase Program (in dollars per share) \| $ / shares			$ 4.84
Collaborative Arrangement, Transaction with Party to Collaborative Arrangement \| PACT
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Strategic equity investment								$ 36,400,000

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of Stock-based Compensation Expense by Classification

Stock-based compensation expense by classification included within the Consolidated Statements of Operations and Comprehensive Loss was as follows (in thousands):


	Year Ended December 31,
	2023		2022		2021
Research and development	$	18,207	$	16,721	$	15,328
General and administrative	28,877		65,203		46,873
Total stock-based compensation expense	$	47,084	$	81,924	$	62,201

Schedule of Incremental Stock-Based Compensation Expense from Modifications


	December 31,
	2023		2022		2021
Previous CEO - Options(1)	$	—	$	3,741	$	—
Previous CEO - Options(2)	—		—		21,948
Previous CEO - RSA(2)	—		—		10,908
Total	$	—	$	3,741	$	32,856

__________

(1)The modification for Previous CEO - Options for 2022 is for Ms. Elizabeth Homans, who resigned in December 2022.

Schedule of RSU Activity

A summary of the Company’s RSU activity was as follows:


	Number of Shares	Weighted-Average Value at Grant Date Per Share
Unvested RSUs as of December 31, 2022	872,077	$	5.98
RSUs granted	2,621,177	$	2.22
RSUs vested	(598,024)	$	3.75
RSUs forfeited or canceled	(822,375)	$	3.22
Unvested RSUs as of December 31, 2023	2,072,855	$	2.96

Schedule of Stock Option Activity

A summary of the Company’s stock option activity was as follows:


	Number of Stock Options	Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Life (in years)	Aggregate Intrinsic Value (in thousands)
Options outstanding as of December 31, 2022	53,849,045	$	5.09	7.84	$	24,887
Granted	12,399,063	$	2.29
Exercised	(2,996,262)	$	0.10
Canceled or forfeited	(7,655,015)	$	5.03
Options outstanding as of December 31, 2023	55,596,831	$	4.75	6.89	$	7,368
Options exercisable as of December 31, 2023	33,965,690	$	5.06	5.76	$	7,303

Schedule of Assumptions Used in Black-Scholes Option-Pricing Model for Estimating Fair Value of Stock Options Granted


	Year Ended December 31,
	2023		2022		2021
Risk-free interest rate	4.13	%	2.93	%	0.80	%
Expected volatility	88.0	%	87.3	%	78.7	%
Expected term (in years)	6.06		6.03		6.10
Expected dividend yield	0	%	0	%	0	%

Workforce Reduction - Schedule of Restructuring Expenses (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Restructuring Cost and Reserve [Line Items]
Incurred cost	$ 5,520
Research and development
Restructuring Cost and Reserve [Line Items]
Incurred cost	4,630
General and administrative
Restructuring Cost and Reserve [Line Items]
Incurred cost	$ 890

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Stock-based Compensation - Schedule of Assumptions Used in Black-Scholes Option-Pricing Model for Estimating Fair Value of Stock Options Granted (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-Based Payment Arrangement [Abstract]
Risk-free interest rate (as a percent)	4.13%	2.93%	0.80%
Expected volatility (as a percent)	88.00%	87.30%	78.70%
Expected term (in years)	6 years 21 days	6 years 10 days	6 years 1 month 6 days
Expected dividend yield (as a percent)	0.00%	0.00%	0.00%

License, Collaboration and Success Payment Agreements

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

License, Collaboration and Success Payment Agreements

Fred Hutch

License Agreement - In 2018, the Company entered into a license agreement with Fred Hutch that grants the Company a worldwide, sublicensable license under certain patent rights (exclusive) and certain technology (non-exclusive) to research, develop and commercialize products and processes for all fields of use employing chimeric antigen receptors (“CARs”) and/or T-cell receptors (“TCRs”), subject to certain exceptions.

The Company is required to pay Fred Hutch annual license maintenance payments of $50,000 on the second anniversary of the effective date, and each anniversary of the effective date thereafter until the first commercial sale of a licensed product.

Collaboration - In 2018, the Company entered into a research and collaboration agreement with Fred Hutch (“Fred Hutch Collaboration Agreement”) focused on research and development of cancer immunotherapy products. The Company funded aggregate research performed by Fred Hutch of $12.0 million under the Fred Hutch Collaboration Agreement with the research conducted in accordance with a research plan and budget approved by the parties. The Fred Hutch Collaboration Agreement has a six-year term. The Company incurred $0.9 million, $1.7 million and $4.2 million in expense in connection with the Fred Hutch Collaboration Agreement for the years ended December 31, 2023, 2022 and 2021, respectively.

Success Payments - In 2018, the Company granted Fred Hutch rights to certain success payments, pursuant to the terms of the Fred Hutch Collaboration Agreement. The potential payments for the Fred Hutch success payments are based on multiples of increased value ranging from 10x to 50x based on a comparison of the per share fair market value of the Company’s common stock relative to the original $1.83 per share issuance price of the Company’s Series A convertible preferred stock, which converted into an equal number of shares of the Company’s common stock in connection with the Company’s IPO. The aggregate success payments to Fred Hutch are not to exceed $200.0 million, which would only occur upon a 50x increase in value. Each threshold is associated with a success payment, ascending from $10.0 million at $18.29 per share to $200.0 million at $91.44 per share, payable if such threshold is reached during the measurement period. Any previous success payments made are credited against the success payment owed as of any valuation date, such that Fred Hutch does not receive multiple success payments in connection with the same threshold. The term of the success payment agreement ends on the earlier to occur of (i) the nine-year anniversary of the date of the agreement and (ii) a change in control transaction.

The following table summarizes the aggregate potential success payments, which are payable to Fred Hutch in cash or cash equivalents, or at the Company’s discretion, publicly-tradeable shares of the Company’s common stock:


Multiple of initial equity value at issuance	10x		20x		30x		40x		50x
Per share common stock price required for payment	$	18.29	$	36.58	$	54.86	$	73.15	$	91.44
Aggregate success payment(s) (in millions)	$	10	$	40	$	90	$	140	$	200

The success payments will be owed if the per share fair value of the Company’s common stock on the contractually specified valuation measurement dates during the term of the success payment agreement equals or exceeds the above outlined multiples. The valuation measurement dates are triggered by the following events: the one-year anniversary of the Company’s IPO and each two-year anniversary of the Company’s IPO thereafter, the closing of a change in control transaction and the last day of the term of the success payment agreement, unless the term has ended due to the

closing of a change of control transaction. As of December 31, 2023, no success payments have been incurred as the per share fair value of the Company’s common stock was below the price required for payment.

The success payment liability was estimated at fair value at inception and at each subsequent reporting period and the associated expense was accreted over the service period of the success payment obligations as research and development expense through 2022. As of December 31, 2022, the Company’s associated success payment liability was fully accreted to fair value as Fred Hutch had provided the requisite service obligation to earn the potential success payment consideration under the continued collaboration. For the year ended December 31, 2023 and future periods, the change in the Fred Hutch success payment liability fair value is recognized in other income (expense), net. The success payment liability was $0.7 million and $2.5 million as of December 31, 2023 and 2022, respectively. With respect to the Fred Hutch Collaboration Agreement success payment obligations, the Company recognized gains of $1.9 million and $3.9 million for the years ended December 31, 2023 and 2022, respectively and success payment expense of $1.2 million for the year ended December 31, 2021.

Stanford

License Agreement - In 2019, the Company entered into a license agreement with Stanford to license specified patent rights. The Company is required to pay Stanford annual license maintenance payments of $50,000 on the second anniversary of the effective date, and each anniversary of the effective date thereafter until the date of the first commercial sale of a licensed product.

Milestone payments to Stanford of up to a maximum of $3.7 million per target are payable upon achievement of certain specified clinical and regulatory milestones. The Company is also obligated to pay Stanford $2.5 million collectively for all licensed products upon the achievement of a certain commercial milestone. Additionally, low single‑digit tiered royalties based on annual net sales of the licensed products are payable to Stanford.

Collaboration Agreement - In October 2020, the Company entered into a research and collaboration agreement with Stanford (“Stanford Collaboration Agreement”), focused on research and development of cellular immunotherapy products. The Stanford Collaboration Agreement has a four-year term. The Company is committed to fund aggregate research performed by Stanford of $12.0 million under the Stanford Collaboration Agreement, and the research will be conducted in accordance with a research plan and budget approved by the parties. The Company incurred $3.0 million in expense in connection with the Stanford Collaboration Agreement for each of the years ended December 31, 2023, 2022, and 2021, respectively.

Success Payments - In October 2020, the Company granted Stanford rights to certain success payments, pursuant to the terms of the Stanford Collaboration Agreement. The potential payments for the Stanford Collaboration Agreement success payments are based on multiples of increased value ranging from 10x to 50x based on a comparison of the per share fair market value of the Company’s common stock relative to the original $1.83 per share issuance price of the Company’s Series A convertible preferred stock, which converted into an equal number of shares of the Company’s common stock in connection with the closing of the Company’s IPO. The aggregate success payments to Stanford are not to exceed $200.0 million, which would only occur upon a 50 times increase in value. Each threshold is associated with a success payment, ascending from $10.0 million at $18.29 per share to $200.0 million at $91.44 per share, payable if such threshold is reached during the measurement period. Any previous success payments made are credited against the success payment owed as of any valuation date, so that Stanford does not receive multiple success payments in connection with the same threshold. The term of each success payment agreement ends on the earlier to occur of (i) the nine year anniversary of the date of the agreement and (ii) a change in control transaction.

The following table summarizes the aggregate potential success payments, which are payable to Stanford in cash or cash equivalents, or at the Company’s discretion, publicly-tradeable shares of the Company’s common stock:


Multiple of initial equity value at issuance	10x		20x		30x		40x		50x
Per share common stock price required for payment	$	18.29	$	36.58	$	54.86	$	73.15	$	91.44
Aggregate success payment(s) (in millions)	$	10	$	40	$	90	$	140	$	200

The estimated fair values of the success payments to Stanford as of December 31, 2023 and 2022 were $1.1 million and $3.3 million, respectively. The success payment liability is estimated at the fair value at inception and at each subsequent reporting period and the expense is accreted over the service period of the Stanford Collaboration Agreement as research and development expense. The success payment liability was $0.9 million and $1.9 million as of December 31, 2023 and 2022, respectively. With respect to the Stanford Collaboration Agreement success payment obligations, the Company recognized gains of $0.9 million and $1.2 million for the year ended December 31, 2023 and 2022, respectively and success payment expense of $2.5 million for the year ended December 31, 2021.

GSK

In 2019, the Company entered into the GSK Agreement with GSK for potential T‑cell therapies that apply the Company’s platform technologies and cell therapy innovations with TCRs or CARs under distinct collaboration programs. The GSK Agreement defined two initial collaboration targets, LYL331 and LYL132, and allowed GSK to nominate seven additional targets through July 2024, though no additional targets were nominated over the life of the GSK Agreement. The Company was expected to perform research and development services for each selected target up until a defined point (the “GSK Option Point”), at which time GSK would decide whether or not to exercise an option to obtain a license from the Company (“License Option”) and take over the future development and commercialization. In April 2021, GSK exercised the License Option on LYL331 (NY-ESO-1 TCR with c-Jun) and assumed sole responsibility for future development and commercialization of the program at its own cost and expense. The investigational new drug (“IND”) application for LYL132 was cleared in January 2022, though no patients were treated, and the IND for LYL331 was not submitted to the U.S. Food and Drug Administration. GSK terminated the GSK Agreement effective December 24, 2022 and Lyell has also discontinued any further work on these programs. There are no future performance obligations associated with the GSK Agreement.

The Company received a non-refundable upfront payment of $45.0 million under the GSK Agreement. In connection with the GSK Agreement, in May 2019, the Company also entered into a stock purchase agreement with GSK, pursuant to which the Company agreed to sell 30,253,189 shares of Series AA convertible preferred stock at a price of $6.78 per share, which was above the issuance date estimated fair value of $4.84 per share. The difference between the per share values resulted in $58.6 million additional deemed consideration, bringing the total upfront consideration of the GSK Agreement to $103.6 million.

The GSK Agreement was deemed to be within the scope of ASC 606, Revenue from Contracts with Customers, because GSK engaged the Company to initially provide research and development services, which were outputs of its ongoing activities, in exchange for consideration. In June 2022, the Company recorded adjustments to revenue related to a change in estimate in connection with the GSK Agreement due to GSK and the Company mutually agreeing to conclude research activities on an undisclosed target for hematological cancers. The change in estimate decreased the related estimated project costs, which resulted in an increase in the measure of proportional cumulative performance. These adjustments increased revenue by $83.6 million, decreased net loss by $83.6 million and resulted in a $0.34 reduction in the Company’s basic and diluted net loss per common share for the year ended December 31, 2022.

The Company recognized revenue related to the research and development services related to the two initial targets of zero, $84.7 million and $10.5 million for the years ended December 31, 2023, 2022 and 2021 respectively. As of December 31, 2023, there were no contract assets or contract liabilities related to the license contract.

PACT

In June 2020, the Company entered into a commitment agreement (“PACT Commitment Agreement”) with PACT Pharma, Inc. (“PACT”) to jointly develop and test an anti-cancer T-cell therapy against solid tumors, in connection with which it also purchased PACT Series C-1 convertible preferred stock, which was recorded in other investments at $36.4 million in the Company’s Consolidated Balance Sheet. In December 2021, the Company recorded a $36.4 million impairment expense for its investment in PACT.

In February 2021, the Company filed a demand for arbitration seeking, among other things, rescission of the PACT Commitment Agreement. On October 1, 2022, the Company entered into a settlement agreement to resolve its outstanding legal dispute with PACT, pursuant to which PACT issued shares of PACT’s Series D convertible preferred stock to the Company in exchange for the Company’s tender of its PACT Series C-1 convertible preferred stock. The settlement agreement also included the termination of the PACT Commitment Agreement. The Company recorded a gain

of $2.9 million in October 2022 for the estimated fair value of the PACT Series D convertible preferred stock, which was included in other investments in the Company’s Consolidated Balance Sheet as of December 31, 2022. In September 2023, the Company performed a qualitative assessment of potential indicators of impairment of the PACT Series D convertible preferred stock investment, resulting in $2.9 million impairment expense for the year ended December 31, 2023. See Note 5, Other Investments, for additional details regarding the PACT investment impairment.

Stockholders’ Equity	12 Months Ended
Stockholders’ Equity	Dec. 31, 2023
Equity [Abstract]
Stockholders’ Equity	Stockholders’ Equity Preferred Stock The Company is authorized to issue 10.0 million shares of preferred stock with a par value $0.0001 per share. As of December 31, 2023 and 2022, no shares of preferred stock were outstanding. Common Stock The Company is authorized to issue 500.0 million shares of common stock with a par value of $0.0001 per share. As of December 31, 2023 and 2022, there were 253,957,709 shares and 249,567,343 shares of the Company’s common stock outstanding, respectively.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
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Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

The Company has reported pre-tax operating losses for all periods presented. The Company’s net losses are derived solely from within the U.S. The Company has not reflected any benefit for corresponding tax net operating loss carryforwards in the accompanying consolidated financial statements. The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets.

As of December 31, 2023 and 2022, the Company had U.S. federal net operating loss (“NOL”) carryforwards of approximately $455.2 million and $383.3 million, respectively, which were available to reduce future taxable income and do not expire. The Company also had U.S. state NOL carryforwards of $537.2 million that begin to expire in 2038. The Company had gross U.S. federal and state tax credits of $24.2 million and $15.8 million as of December 31, 2023 and

2022, respectively, which may be used to offset future tax liabilities. The federal NOL carryforward period is indefinite, while the tax credits will begin to expire in 2039. The attributed carryforwards may become subject to annual limitations in the event of certain cumulative changes in the ownership interest of significant stockholders. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. As of December 31, 2023, the Company had a capital loss carryforward of $52.5 million, which will expire in 2028.

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations follows:


	Year Ended December 31,
	2023		2022		2021
Federal statutory tax	21.00	%	21.00	%	21.00	%
State tax, net of federal benefit	7.45		5.10		6.39
Valuation allowance	(29.10)		(28.89)		(22.43)
Collaboration revenue	—		6.72		—
Stock-based compensation	(2.25)		(6.11)		(5.92)
Tax credits	2.96		2.33		0.99
Other	(0.06)		(0.15)		(0.03)
Effective income tax rate	0.00	%	0.00	%	0.00	%

The principal components of the Company’s net deferred tax assets were as follows (in thousands):


	Year Ended December 31,
	2023		2022
Deferred tax assets:
Net operating loss carryforwards	$	133,141	$	106,530
Tax credit carryforwards	22,409		14,317
Capital loss carryforward	14,368		—
Accrued liabilities and allowances	3,143		3,692
Deferred revenue	793		904
Amortization	5,243		4,585
Capitalized research and development	51,159		26,199
Investment basis difference	4,104		14,235
Lease liability	17,284		17,656
Stock-based compensation	11,244		7,471
Other	470		1,171
Gross deferred tax assets	263,358		196,760
Valuation allowance	(248,420)		(180,132)
Deferred tax assets, net of valuation allowance	14,938		16,628
Deferred tax liabilities:
Operating lease right-of-use assets	(10,853)		(11,277)
Property and equipment	(4,085)		(5,351)
Deferred tax liabilities	(14,938)		(16,628)
Net deferred tax assets	$	—	$	—

The Tax Cuts and Jobs Act contained a provision that requires the capitalization of Section 174 costs incurred in years beginning on or after January 1, 2022. Section 174 costs are expenditures that represent research and development costs that are incident to the development or improvement of a product, process, formula, invention, computer software or technique. This provision changes the treatment of Section 174 costs such that the expenditures are no longer allowed as an immediate deduction but rather must be capitalized and amortized over five years for domestic research and development and fifteen years for foreign research and development. The Company has included the impact of this provision, which results in a deferred tax asset of approximately $51.2 million as of December 31, 2023.

The Company maintains a full valuation allowance on its net U.S. deferred tax assets. The assessment regarding whether a valuation allowance is required considers the evaluation of both positive and negative evidence when concluding whether it is more likely than not that deferred tax assets are realizable. In making this assessment, significant weight is given to evidence that can be objectively verified. In its evaluation, the Company considered its cumulative loss in recent years and its forecasted losses in the near-term as significant negative evidence. Based upon a review of the four sources of income identified within ASC 740, Accounting for Income Taxes (“ASC 740”), the Company determined that the negative evidence outweighed the positive evidence and a full valuation allowance on its U.S. net deferred tax assets will be maintained. The valuation allowance relates primarily to net U.S. deferred tax assets from net operating loss carryforwards, research and development tax credit carryforwards, research and development expenses capitalized and amortized for tax but deducted for GAAP and stock-based compensation.

The Company will continue to assess the realizability of its deferred tax assets and adjust the valuation allowance as required by ASC 740. The increase in the valuation allowance was $68.3 million and $52.9 million for the years ended December 31, 2023 and 2022, respectively.

The Company evaluates its uncertain tax positions based on a determination of whether it is more likely than not such position will be sustained based upon its technical merits and upon examination by the relevant income tax authorities with all facts known. The Company applies judgment in its measurement of an uncertain tax position recorded in its consolidated financial statements and tax return. As of December 31, 2023 and 2022, there are no penalties or accrued interest recorded in the consolidated financial statements.

The Company is generally subject to examination by the U.S. federal and local income tax authorities for all tax years in which a loss carryforward is available. The Company is currently not under examination by the Internal Revenue Service or other jurisdictions for any tax years.

The following table summarized changes to the Company’s unrecognized tax benefits (in thousands):


	Year Ended December 31,
	2023		2022
Beginning balance	$	400	$	796
Additions based on tax position related to the current year	—		—
Adjustments based on prior year tax positions	—		(396)
Ending balance	$	400	$	400

The Company does not anticipate that the amount of existing unrecognized tax benefits will significantly increase or decrease within the next 12 months.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Related-party Transactions - Narrative (Details) ft² in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Sep. 30, 2021 USD ($) ft²
Related Party Transaction [Line Items]
Accrued liabilities and other current liabilities	$ 28,126	$ 28,755
Other non-current liabilities	$ 3,664	4,113
Related Party
Related Party Transaction [Line Items]
Rentable area (in square feet) \| ft²				18
Related Party \| Minimum \| Lyell Immunopharma \| GSK
Related Party Transaction [Line Items]
Ownership interest (as a percent)	10.00%
Related Party \| Sonoma
Related Party Transaction [Line Items]
Rentable area (in square feet) \| ft²				18
Tenant improvements				$ 4,600
Accrued liabilities and other current liabilities	$ 500	500
Other non-current liabilities	3,000	3,500
Related Party \| GSK
Related Party Transaction [Line Items]
Recognized revenue	$ 0	$ 84,700	$ 10,500

Organization (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2021
Description of Organization [Line Items]
Offering expenses		$ 33,198
Convertible preferred stock
Description of Organization [Line Items]
Conversion of convertible preferred stock to common stock (in shares)	194,474,431
Common Stock
Description of Organization [Line Items]
Issuance of common stock (in shares)		25,000,000
Conversion of convertible preferred stock to common stock (in shares)		194,474,000
IPO \| Common Stock
Description of Organization [Line Items]
Issuance of common stock (in shares)	25,000,000
Sale of stock, price per share (in dollars per share)	$ 17.00
Net proceeds from sale of stock, after underwriting discounts and commissions	$ 391,800
Payments of underwriting discounts and commissions	29,800
Offering expenses	3,400
IPO \| Common Stock Including Additional Paid in Capital
Description of Organization [Line Items]
Converted preferred stock	$ 1,000,000

Organization	12 Months Ended
Organization	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Lyell Immunopharma, Inc. (the “Company”) was incorporated in Delaware in June 2018. The Company is a clinical-stage cell therapy company advancing a pipeline of product candidates for patients with solid tumors utilizing its proprietary ex vivo genetic and epigenetic T‑cell reprogramming technologies. The Company’s primary activities since incorporation have been to develop T‑cell therapies, conduct research and development, acquire technology, enter into strategic collaboration and license arrangements, enable and execute manufacturing activities in support of its product candidate development efforts, organize and staff the Company, conduct business planning, establish its intellectual property portfolio, submit regulatory submissions, execute clinical trials, raise capital and provide general and administrative support for these activities. Initial Public Offering In June 2021, the Company successfully completed its initial public offering (“IPO”) of its common stock. In connection with its IPO, the Company issued and sold 25,000,000 shares of common stock at an IPO price of $17.00 per share. The Company received $391.8 million in net proceeds, after deducting underwriting discounts and commissions of $29.8 million and offering expenses of $3.4 million. Upon the closing of the IPO, 194,474,431 shares of convertible preferred stock then outstanding converted into an equal number of shares of common stock. The related carrying value of the converted preferred stock of $1.0 billion was reclassified to common stock and additional paid in-capital.

Fair Value Measurements - Schedule of Changes in Estimated Fair Value of Financial Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Equity Warrant Investment
Beginning Balance	$ 0
Ending Balance		$ 0
Success Payment Liabilities
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]		Other income (expense), net
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Research and development	Research and development
Equity Warrant Investment \| Level 3
Equity Warrant Investment
Beginning Balance	$ 0	$ 1,067
Changes in fair value	0	(1,067)
Ending Balance	0	0
Success Payment Liabilities \| Level 3
Success Payment Liabilities
Beginning Balance	4,356	9,486
Change in fair value	(2,780)	(5,130)
Ending Balance	$ 1,576	$ 4,356

Cash Equivalents and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2023

Cash and Cash Equivalents [Abstract]

Schedule of Fair Value and Amortized Cost of Cash Equivalents

The fair value and amortized cost of cash equivalents and marketable securities by major security type are as follows (in thousands):


	December 31, 2023
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Money market funds	$	62,075	$	—	$	—	$	62,075
U.S. Treasury securities	374,214		237		(95)		374,356
U.S. government agency securities	48,924		3		(177)		48,750
Corporate debt securities	59,668		—		(62)		59,606
Total cash equivalents and marketable securities	$	544,881	$	240	$	(334)	$	544,787


Classified as:	Fair Value
Cash equivalents	$	127,705
Marketable securities	400,576
Marketable securities, non-current	16,506
Total cash equivalents and marketable securities	$	544,787


	December 31, 2022
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Money market funds	$	67,970	$	—	$	—	$	67,970
U.S. Treasury securities	277,056		—		(5,257)		271,799
U.S. government agency securities	135,460		1		(1,416)		134,045
Corporate debt securities	221,608		3		(930)		220,681
Total cash equivalents and marketable securities	$	702,094	$	4	$	(7,603)	$	694,495


Classified as:	Fair Value
Cash equivalents	$	107,780
Marketable securities	516,598
Marketable securities, non-current	70,117
Total cash equivalents and marketable securities	$	694,495

Schedule of Fair Value and Amortized Cost of Marketable Securities

The fair value and amortized cost of cash equivalents and marketable securities by major security type are as follows (in thousands):


	December 31, 2023
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Money market funds	$	62,075	$	—	$	—	$	62,075
U.S. Treasury securities	374,214		237		(95)		374,356
U.S. government agency securities	48,924		3		(177)		48,750
Corporate debt securities	59,668		—		(62)		59,606
Total cash equivalents and marketable securities	$	544,881	$	240	$	(334)	$	544,787


Classified as:	Fair Value
Cash equivalents	$	127,705
Marketable securities	400,576
Marketable securities, non-current	16,506
Total cash equivalents and marketable securities	$	544,787


	December 31, 2022
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Money market funds	$	67,970	$	—	$	—	$	67,970
U.S. Treasury securities	277,056		—		(5,257)		271,799
U.S. government agency securities	135,460		1		(1,416)		134,045
Corporate debt securities	221,608		3		(930)		220,681
Total cash equivalents and marketable securities	$	702,094	$	4	$	(7,603)	$	694,495


Classified as:	Fair Value
Cash equivalents	$	107,780
Marketable securities	516,598
Marketable securities, non-current	70,117
Total cash equivalents and marketable securities	$	694,495

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
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Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Publisher FASB
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Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Stock-based Compensation - Narrative (Details) - USD ($)		1 Months Ended	12 Months Ended
	Jan. 01, 2023	Jun. 30, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense			$ 47,084,000	$ 81,924,000	$ 62,201,000
Total stock-based compensation cost related to unvested awards not yet recognized			$ 65,300,000
Expected weighted-average period compensation cost to be recognized			2 years 8 months 12 days
Weighted average grant date fair value (in dollars per share)			$ 1.69	$ 3.60	$ 6.59
Intrinsic value of options exercised			$ 6,500,000	$ 13,900,000	$ 16,100,000
IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense					2,600,000
RSAs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested during period			0	15,200,000	57,100,000
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of awards vested during period			$ 1,400,000	$ 1,500,000	$ 0
2021 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for future issuance (in shares)		26,662,087
Award expiration period		10 years
Proportion of stock outstanding (as a percent)		5.00%
Number of additional shares authorized for issuance (in shares)	12,478,367
Increase in proportion of common shares reserved for future issuance (as a percent)	5.00%
Vesting period		4 years
Future issuance of common shares (in shares)			26,390,351
2021 Plan \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period		10 years
2021 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares reserved for future issuance (in shares)		2,470,000
Award expiration period		10 years
Proportion of stock outstanding (as a percent)		1.00%
Number of additional shares authorized for issuance (in shares)	0
Future issuance of common shares (in shares)			3,461,629
Purchase of common stock at discount (as a percent)		15.00%
Purchase price in relation to common stock price (as a percent)		85.00%
Maximum number of shares to be purchased under ESPP (in shares)		4,940,000
Maximum offering period		27 months
Awards issued during period (in shares)			986,391	475,363	0
2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period						10 years
Vesting period						4 years
Future issuance of common shares (in shares)						0

Convertible Preferred Stock	12 Months Ended
Convertible Preferred Stock	Dec. 31, 2023
Equity [Abstract]
Convertible Preferred Stock	Convertible Preferred Stock Upon the closing of the IPO, 194,474,431 shares of convertible preferred stock then outstanding converted into an equal number of shares of common stock. As of December 31, 2023, no shares of convertible preferred stock were outstanding.

License, Collaboration and Success Payment Agreements (Tables)

12 Months Ended

Dec. 31, 2023

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Aggregate Potential Success Payments


Multiple of initial equity value at issuance	10x		20x		30x		40x		50x
Per share common stock price required for payment	$	18.29	$	36.58	$	54.86	$	73.15	$	91.44
Aggregate success payment(s) (in millions)	$	10	$	40	$	90	$	140	$	200


Multiple of initial equity value at issuance	10x		20x		30x		40x		50x
Per share common stock price required for payment	$	18.29	$	36.58	$	54.86	$	73.15	$	91.44
Aggregate success payment(s) (in millions)	$	10	$	40	$	90	$	140	$	200