Sutro Biopharma (STRO) 10-Q 13 May 24 2024 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2024	May 08, 2024
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Trading Symbol	STRO
Entity Registrant Name	SUTRO BIOPHARMA, INC.
Entity Central Index Key	0001382101
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-38662
Entity Tax Identification Number	47-0926186
Entity Address, Address Line One	111 Oyster Point Blvd
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	881-6500
Entity Common Stock, Shares Outstanding		81,794,334
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common stock, $0.001 par value
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE
Entity Interactive Data Current	Yes

Condensed Balance Sheets (Unaud

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 65,218	$ 69,268
Marketable securities	202,384	264,413
Investment in equity securities	45,616	41,937
Accounts receivable	31,300	36,078
Prepaid expenses and other current assets	10,064	9,846
Total current assets	354,582	421,542
Property and equipment, net	20,630	21,940
Operating lease right-of-use assets	21,594	22,815
Marketable securities, non-current	0	0
Other non-current assets	5,739	3,567
Restricted cash	857	872
Total assets	403,402	470,736
Current liabilities:
Accounts payable	7,511	9,440
Accrued compensation	7,077	14,686
Deferred revenue—current	20,502	20,666
Operating lease liability - current	6,673	6,420
Debt—current		4,061
Accrued expenses and other current liabilities	37,746	38,473
Total current liabilities	79,509	93,746
Deferred revenue - non-current	46,313	53,379
Operating lease liability - non-current	21,397	23,154
Deferred royalty obligation related to the sale of future royalties	156,465	149,114
Other non-current liabilities	1,694	1,694
Total liabilities	305,378	321,087
Commitments and contingencies (Note 7)
Stockholders’ equity:
Preferred stock, $0.001 par value -10,000,000 shares authorized as of March 31, 2024 and December 31, 2023; no shares issued and outstanding as of March 31, 2024 and December 31, 2023
Common stock, $0.001 par value - 300,000,000 shares authorized as of March 31, 2024 and December 31, 2023; 62,456,546 and61,009,829 shares issued and outstanding as of March 31, 2024 and December 31, 2023, respectively	62	61
Additional paid-in-capital	715,696	708,975
Accumulated other comprehensive income (loss)	(113)	21
Accumulated deficit	(617,621)	(559,408)
Total stockholders’ equity	98,024	149,649
Total Liabilities and Stockholders’ Equity	$ 403,402	$ 470,736

Condensed Balance Sheets (Una_2

Condensed Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	62,456,546	61,009,829
Common stock, shares outstanding	62,456,546	61,009,829

Condensed Statements of Operati

Condensed Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Income Statement [Abstract]
Revenue	$ 13,008	$ 12,674
Operating expenses
Research and development	56,878	39,399
General and administrative	12,721	15,512
Total operating expenses	69,599	54,911
Loss from operations	(56,591)	(42,237)
Interest income	4,096	2,560
Unrealized gain (loss) on equity securities	3,679	(6,992)
Non-cash interest expense related to the sale of future royalties	(7,184)
Interest and other income (expense), net	(2,213)	(2,986)
Loss before provision for income taxes	(58,213)	(49,655)
Provision for income taxes		395
Net loss	$ (58,213)	$ (50,050)
Net loss per share, basic	$ (0.95)	$ (0.85)
Net loss per share, diluted	$ (0.95)	$ (0.85)
Weighted-average shares used in computing basic net loss per share	61,457,793	58,723,432
Weighted-average shares used in computing diluted net loss per share	61,457,793	58,723,432

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net loss	$ (58,213)	$ (50,050)
Other comprehensive (loss) income :
Net unrealized (loss) income on available-for-sale securities	(134)	511
Comprehensive loss	$ (58,347)	$ (49,539)

Condensed Statements of Stockho

Condensed Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balances at Dec. 31, 2022	$ 217,048	$ 58	$ 670,223	$ (618)	$ (452,615)
Common Stock Balance, Shares at Dec. 31, 2022		57,499,541
Exercise of common stock options	314		314
Exercise of common stock options, Shares		53,060
Issuance of common stock under Employee Stock Purchase Plan	1,097		1,097
Issuance of common stock under Employee Stock Purchase Plan, Shares		239,060
Vesting of restricted stock units, Shares		801,769
Stock transaction associated with taxes withheld on restricted stock units	(451)		(451)
Stock transaction associated with taxes withheld on restricted stock units,Shares		(73,003)
Stock-based compensation expense	6,021		6,021
Issuance of common stock in connection with At-The-Market sale, net of issuance costs	10,923	$ 2	10,921
Issuance of common stock in connection with At-The-Market sale, net of issuance costs, Shares		1,641,374
Net unrealized gain (loss) on available-for-sale securities	511			511
Net loss	(50,050)				(50,050)
Balances at Mar. 31, 2023	185,413	$ 60	688,125	(107)	(502,665)
Common Stock Balance, Shares at Mar. 31, 2023		60,161,801
Balances at Dec. 31, 2023	149,649	$ 61	708,975	21	(559,408)
Common Stock Balance, Shares at Dec. 31, 2023		61,009,829
Exercise of common stock options	117		117
Exercise of common stock options, Shares		23,748
Issuance of common stock under Employee Stock Purchase Plan	911		911
Issuance of common stock under Employee Stock Purchase Plan, Shares		284,362
Vesting of restricted stock units		$ 1	(1)
Vesting of restricted stock units, Shares		1,215,729
Stock transaction associated with taxes withheld on restricted stock units	(374)		(374)
Stock transaction associated with taxes withheld on restricted stock units,Shares		(77,122)
Stock-based compensation expense	6,068		6,068
Net unrealized gain (loss) on available-for-sale securities	(134)			(134)
Net loss	(58,213)				(58,213)
Balances at Mar. 31, 2024	$ 98,024	$ 62	$ 715,696	$ (113)	$ (617,621)
Common Stock Balance, Shares at Mar. 31, 2024		62,456,546

Condensed Statements of Stock_2

Condensed Statements of Stockholders' Equity (Parenthetical) (Unaudited) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)
ATM
Common stock, issuance costs	$ 308

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating activities
Net loss	$ (58,213)	$ (50,050)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,761	1,615
Accretion of discount on marketable securities	(2,656)	(1,786)
Stock-based compensation	6,068	6,021
Non-cash lease expenses	1,221	641
Unrealized (gain) / loss on equity securities	(3,679)	6,992
Non-cash interest expense on deferred royalty obligation	7,184	0
Other	189	(13)
Changes in operating assets and liabilities:
Accounts receivable	4,778	(2,751)
Prepaid expenses and other assets	(2,390)	(7,424)
Accounts payable	(1,897)	198
Accrued compensation	(7,609)	(6,786)
Accrued expenses and other liabilities	(765)	(2,399)
Deferred revenue	(7,230)	(4,412)
Change in operating lease liability	(1,503)	(837)
Net cash used in operating activities	(64,741)	(60,991)
Investing activities
Purchases of marketable securities	(135,001)	(52,764)
Maturities of marketable securities	199,262	112,102
Sales of marketable securities	290	9,055
Purchases of equipment and leasehold improvements	(446)	(942)
Net cash provided by investing activities	64,105	67,451
Financing activities
Proceeds from sales of common stock, net of issuance costs		10,923
Payment of debt	(4,083)	(3,125)
Proceeds from exercise of common stock options	117	314
Taxes paid related to net shares settlement of restricted stock units	(374)	(451)
Proceeds from employee stock purchase plan	911	1,097
Net cash (used in) provided by financing activities	(3,429)	8,758
Net (decrease) increase in cash, cash equivalents and restricted cash	(4,065)	15,218
Cash, cash equivalents and restricted cash at beginning of period	70,140	48,126
Cash, cash equivalents and restricted cash at end of period	66,075	63,344
Supplemental disclosure of cash flow information:
Cash paid for interest	63	393
Income tax paid	10
Supplemental disclosure of non-cash investing and financing information:
Purchases of equipment included in accounts payable and accrued expense	219	371
Financing component associated with program fees	2,160	2,543
Deferred offering cost included in accounts payable and accrued expenses	$ 528	$ 101

Organization and Principal Acti

Organization and Principal Activities	3 Months Ended
	Mar. 31, 2024
Disclosure Text Block [Abstract]
Organization and Principal Activities	1. Organization and Principal Activities Description of Business Sutro Biopharma, Inc. (the “Company”), is a clinical-stage oncology company developing site-specific and novel-format antibody drug conjugates, or ADCs. The Company was incorporated on April 21, 2003 , and is headquartered in South San Francisco , California . The Company operates in one business segment, the development of biopharmaceutical products. Operating segments are components of an enterprise for which separate financial information is available and is evaluated regularly by the Chief Executive Officer, the Company’s chief operating decision maker, in deciding how to allocate resources and assessing performance. The Company operates and manages its business as one operating segment. The Company’s Chief Executive Officer reviews financial information on an aggregate basis for the purposes of allocating and evaluating financial performance. All of the Company’s long-lived assets are maintained in the United States. Liquidity The Company has incurred significant losses and has negative cash flows from operations. As of March 31, 2024, there was an accumulated deficit of $ 617.6 million. Management expects to continue to incur additional substantial losses in the foreseeable future as a result of the Company’s research and development and other operational activities. As of March 31, 2024, the Company had unrestricted cash, cash equivalents, and marketable securities of $ 267.6 million and equity securities of $ 45.6 million, consisting solely of common stock of Vaxcyte, which are available to fund future operations. The Company will need to raise additional capital to support the completion of its research and development activities and to support its operations. The Company believes that its unrestricted cash, cash equivalents, marketable securities and investments in equity securities as of March 31, 2024, will enable the Company to maintain its operations for a period of at least 12 months following the filing date of its condensed financial statements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Use of Estimates The accompanying interim condensed financial statements of the Company are unaudited. These interim condensed financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and the applicable rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial information. Accordingly, they do not include all the information and footnotes required by U.S. GAAP for complete financial statements. The December 31, 2023 condensed balance sheet was derived from the audited financial statements as of that date but does not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The Company bases its estimates on historical experience and market-specific or other relevant assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company’s condensed Balance Sheets and the amounts of expenses and income reported for each of the periods presented are affected by estimates and assumptions, which are used for, but are not limited to, determining research and development periods under collaboration arrangements, stock-based compensation expense, valuation of marketable securities, impairment of long-lived assets, income taxes, deferred royalty obligation related to the sale of future royalties and related non-cash interest expense, and certain accrued liabilities. Actual results could differ from such estimates or assumptions. The accompanying unaudited interim condensed financial statements have been prepared on the same basis as the audited financial statements and, in the opinion of management, reflect all adjustments of a normal recurring nature considered necessary to state fairly the Company’s financial position, results of operations, comprehensive loss, and cash flows for the interim periods. The interim results for the three months ended March 31, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024, or for any other future annual or interim period. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company’s audited financial statements included in the Annual Report on Form 10-K pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934, as amended, for the year ended December 31, 2023. Recent Accounting Pronouncements Not Yet Adopted There were no new accounting pronouncements issued since the Company's filing of the Annual Report on Form 10-K for the year ended December 31, 2023, which could have a significant effect on the Company's condensed financial statements. Cash, Cash Equivalents and Restricted Cash The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company's condensed Balance Sheets that sum to the total of the same amounts shown in the Company's condensed Statements of Cash Flows. March 31, 2024 2023 (in thousands) Cash and cash equivalents $ 65,218 $ 62,472 Restricted cash 857 872 Total cash, cash equivalents, and restricted cash shown in the $ 66,075 $ 63,344 Investments in Equity Securities Vaxcyte common stock held by the Company is measured at fair value at each reporting period based on the closing price of Vaxcyte’s common stock on the last trading day of each reporting period, with any realized or unrealized gains and losses recorded in the Company’s condensed Statements of Operations. Fair Value Measurements Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability, or an exit price, in the principal or most advantageous market for that asset or liability in an orderly transaction between market participants on the measurement date and establishes a fair value hierarchy that requires an entity to maximize the use of observable inputs, where available, and minimize the use of unobservable inputs when measuring fair value. The Company determined the fair value of financial assets and liabilities using the fair value hierarchy that describes three levels of inputs that may be used to measure fair value, as follows: Level 1—Quoted prices in active markets for identical assets and liabilities; Level 2—Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The carrying amounts of accounts receivable, prepaid expenses, accounts payable, accrued liabilities and accrued compensation and benefits approximate fair value due to the short-term nature of these items. The carrying value of the deferred royalty obligation related to the sale of future royalties under the 2015 License Agreement with Vaxcyte approximates its fair value as of March 31, 2024, and is based on our current estimates of future royalties expected to be earned over the estimated life of the royalty term arrangement. See Note 8. Deferred Royalty Obligation Related to the Sale of Future Royalties for a description of the Level 3 inputs used to estimate the fair value of the liability. Revenue Recognition When the Company enters into collaboration agreements, it assesses whether the arrangements fall within the scope of ASC 808, Collaborative Arrangements ("ASC 808") based on whether the arrangements involve joint operating activities and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards. To the extent that the arrangement falls within the scope of ASC 808, the Company assesses whether the payments between the Company and its collaboration partner fall within the scope of other accounting literature. If it concludes that payments from the collaboration partner to the Company represent consideration from a customer, such as license fees and contract research and development activities, the Company accounts for those payments within the scope of Accounting Standards Update (ASU) No. 2014-09 (Topic 606), Revenue from Contracts with Customers (“ASC 606”). Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. However, if the Company concludes that its collaboration partner is not a customer for certain activities and associated payments, such as for certain collaborative research, development, manufacturing and commercial activities, the Company presents such payments as a reduction of research and development expense or general and administrative expense, based on where the Company presents the underlying expense. The Company has no products approved for commercial sale and has not generated any revenue from commercial product sales. The total revenue to date has been generated principally from collaboration and license agreements and to a lesser extent, from manufacturing, supply and services, and materials the Company provides to its collaboration partners. Collaboration Revenue: The Company derives revenue from collaboration arrangements, under which the Company may grant licenses to its collaboration partners to further develop and commercialize its proprietary product candidates. The Company may also perform research and development activities under the collaboration agreements. Consideration under these contracts generally includes a nonrefundable upfront payment, development, regulatory and commercial milestones and other contingent payments, and royalties based on net sales of approved products. Additionally, the collaborations may provide options for the customer to acquire from the Company materials and reagents, clinical product supply or additional research and development services under separate agreements. The Company assesses which activities in the collaboration agreements are considered distinct performance obligations that should be accounted for separately. The Company develops assumptions that require judgement to determine whether the license to the Company’s intellectual property is distinct from the research and development services or participation in activities under the collaboration agreements. At the inception of each agreement, the Company determines the arrangement transaction price, which includes variable consideration, based on the assessment of the probability of achievement of future milestones and contingent payments and other potential consideration. The Company recognizes revenue over time by measuring its progress towards the complete satisfaction of the relevant performance obligation using an appropriate input or output method based on the nature of the service promised to the customer. For arrangements that include multiple performance obligations, the Company allocates the transaction price to the identified performance obligations based on the standalone selling price, or SSP, of each distinct performance obligation. In instances where SSP is not directly observable, the Company develops assumptions that require judgment to determine the SSP for each performance obligation identified in the contract. These key assumptions may include full-time equivalent, or FTE, personnel effort, estimated costs, discount rates and probabilities of clinical development and regulatory success. Upfront Payments : For collaboration arrangements that include a nonrefundable upfront payment, if the license fee and research and development services cannot be accounted for as separate performance obligations, the transaction price is deferred and recognized as revenue over the expected period of performance using a cost-based input methodology. The Company uses judgement to assess the pattern of delivery of the performance obligation. In addition, amounts paid in advance of services being rendered may result in an associated financing component to the upfront payment. Accordingly, the interest on such borrowing cost component will be recorded as interest expense and revenue, based on an appropriate borrowing rate applied to the value of services to be performed by the Company over the estimated service performance period. License Grants: For collaboration arrangements that include a grant of a license to the Company’s intellectual property, the Company considers whether the license grant is distinct from the other performance obligations included in the arrangement. For licenses that are distinct, the Company recognizes revenues from nonrefundable, upfront payments and other consideration allocated to the license when the license term has begun and the Company has provided all necessary information regarding the underlying intellectual property to the customer, which generally occurs at or near the inception of the arrangement. Milestone and Contingent Payments : At the inception of the arrangement and at each reporting date thereafter, the Company assesses whether it should include any milestone and contingent payments or other forms of variable consideration in the transaction price using the most likely amount method. If it is probable that a significant reversal of cumulative revenue would not occur upon resolution of the uncertainty, the associated milestone value is included in the transaction price. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of each milestone and any related constraint and, if necessary, adjusts its estimate of the overall transaction price. Since milestone and contingent payments may become payable to the Company upon the initiation of a clinical study or filing for or receipt of regulatory approval, the Company reviews the relevant facts and circumstances to determine when the Company should update the transaction price, which may occur before the triggering event. When the Company updates the transaction price for milestone and contingent payments, the Company allocates the changes in the total transaction price to each performance obligation in the agreement on the same basis as the initial allocation. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment, which may result in recognizing revenue for previously satisfied performance obligations in such period. The Company’s collaborators generally pay milestones and contingent payments subsequent to achievement of the triggering event. Research and Development Services : For amounts allocated to the Company’s research and development obligations in a collaboration arrangement, the Company recognizes revenue over time using a cost-based input methodology, representing the transfer of goods or services as activities are performed over the term of the agreement. Materials Supply: The Company provides materials and reagents, clinical materials, and services to certain of its collaborators under separate agreements. The consideration for such services is generally based on FTE personnel effort used to manufacture those materials, reimbursed at an agreed upon rate in addition to agreed-upon pricing for the provided materials. The amounts billed are recognized as revenue as the performance obligations are met by the Company. Revenue subject to governmental withholding taxes is recognized on a gross basis with the withholding taxes recorded as a component of income tax expense.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy: March 31, 2024 Total Level 1 Level 2 Level 3 (in thousands) Assets: Money market funds $ 42,498 $ 42,498 $ - $ - Commercial paper 21,379 - 21,379 - Corporate debt securities 44,036 - 44,036 - Equity securities 45,616 45,616 - - Asset-backed securities 44,598 - 44,598 - U.S. government securities 113,130 113,130 - - Total $ 311,257 $ 201,244 $ 110,013 $ - December 31, 2023 Total Level 1 Level 2 Level 3 (in thousands) Assets: Money market funds $ 56,397 $ 56,397 $ - $ - Commercial paper 82,152 - 82,152 - Corporate debt securities 61,894 - 61,894 - Equity securities 41,937 41,937 - - Asset-backed securities 10,505 - 10,505 - U.S. government securities 113,652 113,652 - - U.S. agency securities 4,961 - 4,961 - Total $ 371,498 $ 211,986 $ 159,512 $ - Where applicable, the Company uses quoted market prices in active markets for identical assets to determine fair value. This pricing methodology applies to Level 1 investments, which are comprised of money market funds, U.S. government securities and the shares of Vaxcyte common stock held by the Company. If quoted prices in active markets for identical assets are not available, then the Company uses quoted prices for similar assets or inputs other than quoted prices that are observable, either directly or indirectly. These investments are included in Level 2 and consist of commercial paper, corporate debt securities, asset-backed securities, and U.S. agency securities. These assets are valued using market prices when available, adjusting for accretion of the purchase price to face value at maturity. A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. In certain cases where there is limited activity or less transparency around inputs to valuation, securities are classified as Level 3 within the valuation hierarchy. As of March 31, 2024 and December 31, 2023, the deferred royalty obligation related to the sale of future Vaxcyte royalties was classified as Level 3 within the valuation hierarchy. Refer to Note 8 below for information relating to the Purchase Agreement between the Company and Blackstone, pursuant to which the Company sold to Blackstone its 4 % roy alty, or revenue interest, in potential future net sales of Vaxcyte’s pneumococcal conjugate vaccine, or PCV, products, including VAX-24 and VAX-31. Investments in Equity Securities As of March 31, 2024 and December 31, 2023, the Company held 667,780 shares of Vaxcyte common stock with an estimated fair value of $ 45.6 million and $ 41.9 million, respectively. The Company recognized an unrealized gain of $ 3.7 million and an unrealized loss of $ 7.0 million for the three months ended March 31, 2024 and 2023, respectively.

Cash Equivalents and Marketable

Cash Equivalents and Marketable Securities	3 Months Ended
	Mar. 31, 2024
Cash and Cash Equivalents [Abstract]
Cash Equivalents and Marketable Securities	4. Cash Equivalents and Marketable Securities Cash equivalents and marketable securities consisted of the following: March 31, 2024 Amortized Unrealized Unrealized Fair (in thousands) Money market funds $ 42,498 $ - $ - $ 42,498 Commercial paper 21,391 - ( 12 ) 21,379 Corporate debt securities 44,044 3 ( 11 ) 44,036 Asset-based securities 44,641 - ( 43 ) 44,598 U.S. government securities 113,180 - ( 50 ) 113,130 Total 265,754 3 ( 116 ) 265,641 Less amounts classified as cash equivalents ( 63,257 ) - - ( 63,257 ) Total marketable securities $ 202,497 $ 3 $ ( 116 ) $ 202,384 December 31, 2023 Amortized Unrealized Unrealized Fair (in thousands) Money market funds $ 56,397 $ - $ - $ 56,397 Commercial paper 82,179 1 ( 28 ) 82,152 Corporate debt securities 61,887 12 ( 5 ) 61,894 Asset-based securities 10,505 - – 10,505 U.S. government securities 113,612 40 – 113,652 U.S. agency securities 4,960 1 – 4,961 Total 329,540 54 ( 33 ) 329,561 Less amounts classified as cash equivalents ( 65,144 ) ( 4 ) - ( 65,148 ) Total marketable securities $ 264,396 $ 50 $ ( 33 ) $ 264,413 No marketable securities had maturities of more than one year as of March 31, 2024 and December 31, 2023. There were $ 190.5 million and $ 110.9 million of investments in an unrealized loss position of $ 0.1 million and $ 33,000 as of March 31, 2024 and December 31, 2023, respectively. During the three months ended March 31, 2024 and 2023, the Company did no t record any other-than-temporary impairment charges on its available-for-sale securities. Based on the Company’s procedures under the expected credit loss model, including an assessment of unrealized losses on the portfolio after March 31, 2024 and 2023, the Company concluded that the unrealized losses for its marketable securities were not attributable to credit and therefore an allowance for credit losses for these securities has not been recorded as of March 31, 2024. Also, based on the scheduled maturities of the investments, the Company was more likely than not to hold these investments for a period of time sufficient for a recovery of the Company’s cost basis. The Company recognized no material gains or losses on its cash equivalents and current and non-current marketable securities as of March 31, 2024 and December 31, 2023 and as a result, the Company did not reclassify any amounts out of accumulated other comprehensive income (loss) for the period then ended.

Collaboration and License Agree

Collaboration and License Agreements and Supply Agreements	3 Months Ended
	Mar. 31, 2024
Collaboration And License Agreements And Supply Agreements [Abstract]
Collaboration and License Agreements and Supply Agreements	5. Collaboration and License Agreements and Supply Agreements The Company has entered into collaboration and license agreements and supply agreements with various pharmaceutical and biotechnology companies. See “Note 5. Collaboration and License Agreements and Supply Agreements” to the Company’s financial statements included in the Annual Report on Form 10-K for the year ended December 31, 2023, or as further described below, for additional information on each of its collaboration agreements. The Company’s accounts receivable balances may contain billed and unbilled amounts from upfront payments, milestones and other contingent payments, as well as reimbursable costs from collaboration and license agreements and supply agreements. The Company performs a regular review of its customers’ credit risk and payment histories, including payments made after the period end. Historically, the Company has not experienced credit loss from its accounts receivable and, therefore, has no t recorded a reserve for estimated credit losses as of March 31, 2024 and December 31, 2023. In accordance with the collaboration, license and supply agreements, the Company recognized revenue as follows: Three Months Ended March 31, 2024 2023 (in thousands) Merck Sharp & Dohme Corporation (“Merck”) $ 6 $ 2,553 Astellas Pharma Inc. (“Astellas”) 11,385 6,272 Tasly Biopharmaceuticals Co., Ltd. (“Tasly”) 970 - Vaxcyte, Inc. ("Vaxcyte") 647 675 Bristol Myers Squibb Company (“BMS”) - 3,166 Merck KGaA, Darmstadt, Germany (operating in the United - 8 Total revenue $ 13,008 $ 12,674 The following table presents the changes in the Company’s deferred revenue balance from the agreements during the three months ended March 31, 2024: Three Months Ended March 31, 2024 (in thousands) Deferred revenue—December 31, 2023 $ 74,045 Additions to deferred revenue - Recognition of revenue in current period ( 7,230 ) Deferred revenue—March 31, 2024 $ 66,815 The Company’s balance of deferred revenue contains upfront and contingent payments for obligations from our agreements which remain partially unsatisfied. The Company expects to recognize approximately $ 20.5 million of the deferred revenue over the next twelve months . Collaboration with Merck 2018 Merck Agreement In July 2018, the Company e ntered into an agreement (the “2018 Merck Agreement”) with Merck for access to the Company’s technology and the identification and preclinical research and development of two target programs, with an option for Merck to engage the Company to continue these activities for a third program, upon the payment of an additional amount, focusing on cytokine derivatives for cancer and autoimmune disorders. In April 2021, Merck initiated the first IND-enabling toxicology study under the first cytokine-derivative program in the collaboration. In December 2021, Merck did not extend the research term for the second research program of the collaboration, which research program reverted to the Company. The first research program of the collaboration is focuse d on MK-1484, a distinct cytokine derivative molecule for the treatment of cancer. The Company is eligible to receive aggregate contingent payments of up to approximately $ 500 million for the target program selected by Merck, assuming the develo pment and sale of the therapeutic candidate and all possible indications identified under the collaboration. If one or more products from the target program is developed for non-oncology or a single indication, the Company will be eligible for reduced aggregate contingent payments. In addition, the Company is eligible to receive tiered royalties ranging from mid-single digit to low-teen digit percentages on the worldwide sales of any commercial products that may result from the collaboration. In July 2022, the first patient was dosed with MK-1484 in a Phase 1 study. As of both March 31, 2024 and December 31, 2023, there was no deferred revenue under the 2018 Merck Agreement and 2021 Amendment. 2020 Merck Master Services Agreement In August 2020, the Company entered into a Pre-Clinical and Clinical Supply Agreement (the “2020 Merck Master Services Agreement”) with Merck, wherein Merck requested the Company to provide development, manufacturing and supply chain management services, including clinical product supply, upon completion of the research programs under the 2018 Merck Agreement. As of both March 31, 2024 and December 31, 2023, there was no deferred revenue under the 2020 Merck Master Services Agreement. Revenues under the 2018 Merck Agreement and the 2020 Merck Master Services Agreement were as follows: Three Months Ended March 31, 2024 2023 (in thousands) Research and development services $ 6 $ 125 Materials supply - 2,428 Total revenue $ 6 $ 2,553 Astellas License and Collaboration Agreement In June 2022, the Company entered into a License and Collaboration Agreement (the “Astellas Agreement”) with Astellas for the development of immunost imulatory antibody-drug conjugates for up to three biological targets, to be identified by Astellas. The Company will conduct research and pre-clinical development of any compound (as designated by Astellas) in each of the three programs in accor dance with the terms of a research plan between the Company and Astellas. Astellas will have an exclusive worldwide license to develop and commercialize any such designated compound, subject to the Company’s rights to participate in cost and profit sharing in the United States, as described below. Pursuant to the Astellas Agreement, the Company received from Astellas a one-time, nonrefundable, non-creditable, upfront payment of $ 90.0 million during the year ended December 31, 2022. Under ASC 808 and ASC 606, the Company determined that both parties are active participants in the activities and are exposed to significant risks and rewards dependent on the success of the development program, and identified four performance obligations under the Astellas Agreement as: (1) performance of services related to the first target program; (2) performance of services related to the second target program; (3) performance of services related to the third target program; and (4) the Company’s estimated future services on the collaboration JSC. The transaction price of $ 90.0 million was allocated among the performance obligations using the Company’s best estimate of the standalone selling price, or SSP, for each of the associated performance obligations. Revenue allocated to the three target programs, which totaled $ 89.1 million, is being recognized on a proportion of performance basis, using FTE cost as the basis of measurement, with such performance expected to occur over an estimated service period of four years for each target program. As it pertains to the JSC performance obligation, the revenue allocated to such performance obligation was $ 0.9 million, and is being recognized on a proportion of performance basis using FTE cost as the basis of measurement, and such effort is expected to be incurred on a relatively consistent basis throughout the term of the Astellas Agreement. Additionally, under ASC 606, the Company determined a financing component associated with the $ 90.0 million upfront payment and has calculated $ 32.6 million as of March 31, 2024, on the unearned revenue portion beyond one year from the effective date of the agreement, which amount is being recognized as interest expense and revenue over the estimated service period for the three target programs. The Company is also eligible to receive up to $ 422.5 million in develo pment, regulatory and commercial milestones for each product candidate, and tiered royalties ranging from low double-digit to mid-teen percentages on worldwide sales of any commercial products that may result from the collaboration, subject to customary deductions under certain circumstances. The Company can also elect to convert any product candidate into a cost and profit-sharing arrangement, for the United States only. In the event the Company makes such election, it will share commercialization costs and profits relating to such product candidate equally with Astellas in the United States, and no royalties will be due from Astellas for net sales of such product candidates in the United States. Revenues under the Astellas Agreement were as follows: Three Months Ended March 31, 2024 2023 (in thousands) Ongoing performance related to $ 7,230 $ 2,572 Research and development services 1,623 1,157 Financing component on unearned revenue 2,160 2,543 Materials supply 372 - Total revenue $ 11,385 $ 6,272 As of March 31, 2024 and December 31, 2023, there was $ 61.8 million and $ 69.0 million of deferred revenue, respectively, related to the upfront payment received by the Company under the Astellas Agreement. Collaboration with Tasly Tasly License Agreement In December 2021, the Company entered into a license agreement with Tasly to grant Tasly an exclusive license to develop and commercialize STRO-002, or luveltamab tazevibulin, or luvelta, in Greater China (the “Tasly License Agreement”). Tasly will pursue the clinical development, regulatory approval, and commercialization of luvelta in multiple indications, including ovarian cancer, non-small cell lung cancer, triple-negative breast cancer, and other indications in Greater China. The Company will retain development and commercial rights of luvelta globally outside of Greater China, including the United States. The Company determined that the Tasly License Agreement falls within the scope of ASC 808, as both parties are active participants in the activities and are exposed to significant risks and rewards dependent on the success of the commercialization of indications for luvelta in Greater China. The Company concluded that the Tasly License Agreement contained the following units of account: i) licensed know-how and Sutro patents, license to trademark rights, and initial regulatory data and information necessary to prepare an IND; and ii) collaboration governance and information sharing activities, such as JSC participation and ongoing regulatory and pharmacovigilance support. The promises related to the licensed know-how and Sutro patents, license to trademark rights, and initial regulatory data and information necessary to prepare an IND are considered to be interdependent and not distinct from each other, representing a combined output. The Company determined that these promises are capable of being distinct from the collaboration governance and information sharing activities discussed below and further determined that this unit of account is a vendor-customer relationship and accounted for it in accordance with ASC 606. All potential future milestones and other payments were considered constrained at the inception of the Tasly License Agreement since the Company could not conclude it was probable that a significant reversal in the amount of revenue recognized would not occur. Since there is only one performance obligation accounted for under ASC 606, no allocation of the transaction price was necessary. The Company determined that the unit of account consisting of collaboration governance and information sharing activities, such as JSC participation and ongoing regulatory and pharmacovigilance support, do not represent a customer-vendor relationship between the Company and Tasly. These promises are considered to be interdependent and not distinct from each other, representing a combined output. However, the Company determined that these promises are capable of being distinct from the intellectual property and data license promises discussed above. As such, based on the nature of the agreement and collaborative activities, the Company determined that the costs associated with these governance and information sharing activities performed under the agreement will be included in research and development expenses in the Statements of Operations, with any reimbursement of costs by Tasly reflected as a reduction of such expenses. During the three months ended March 31, 2024 and 2023, the Company did no t recognize any material reduction of research and development expenses under the Tasly License Agreement. In April 2022, the Company entered into amendment No. 1 (the “Tasly Amendment”) to the Tasly License Agreement with Tasly. Pursuant to the Tasly Amendment, the initial nonrefundable upfront payment due by Tasly was amended to $ 25.0 million, and a $ 15.0 million payment will become payable to the Company upon the achievement of certain regulatory milestones. The Tasly Amendment also added an additional regulatory milestone payment to the Tasly License Agreement, providing additional potential payments totaling up to $ 350.0 million related to development, regulatory and commercialization milestones, beyond the payments described above, and made certain other ministerial edits. During 2023, the Company recognized a $ 5.0 million contingent payment as revenue, net of withholding tax, after Tasly received its first IND clearance by National Medical Products Administration, or NMPA, in Greater China. The withholding tax of $ 0.5 million was recorded as an income tax charge related to the contingent payment. During 2023, the Company also recorded a $ 5.0 million contingent payment, receiv ed by the Company from Tasly related to the first patient dosed in the Company’s REFRaME-O1 trial for luvelta, as deferred revenue, net of withholding tax of $ 0.5 million. The REFRaME-O1 study consists of two parts, Part I being the dose-finding portion and Part II being the portion of the study that will focus on the selected dose from Part I, and is intended to generate data to enable the potential registration of luvelta. Although it currently intends to conduct the REFRaME-O1 study to completion, the Company has the sole discretion to terminate the REFRaME-O1 study at any time. As such, the Company has agreed with Tasly that, in the event the Company terminates the REFRaME-O1 study prior to dosing the first patient in Part II, the Company will refund Tasly the contingent payment received by the Company within 30 days of such study termination. Given the above, the c ontingent payment received by the Company was considered constrained for accounting purposes during the three months ended March 31, 2024, since the Company could not conclude it was probable that a significant reversal in the amount of revenue recognized would not occur. The withholding tax was recorded by the Company as a tax charge related to the received contingent payment. 2023 Tasly Supply Agreement In June 2023, the Company entered into a Master Development and Clinical Supply Agreement (the “2023 Tasly Supply Agreement”) with Tasly, wherein Tasly requested the Company to provide development, manufacturing and supply chain management services, including clinical product supply. Revenues under the Tasly agreements were as follows: Three Months Ended March 31, 2024 2023 (in thousands) Research and development services $ 33 $ – Materials supply 937 – Total revenue $ 970 $ – Agreements with Vaxcyte Vaxcyte Supply Agreement In May 2018, the Company entered into a Supply Agreement (the “Supply Agreement”) with Vaxcyte, wherein Vaxcyte engaged the Company to provide research and development services and to supply extracts and custom reagents, as requested by Vaxcyte. The pricing is based on an agreed upon cost-plus arrangement. During 2020, upon Vaxcyte’s request and their agreement to reimburse the related costs, the Company entered into agreements with third-party contract manufacturing organizations, or CMOs, to conduct process transfers to allow for such CMOs to manufacture and supply extract and custom reagents for Vaxcyte. As part of the agreement with Vaxcyte, should the Company decide to purchase extract from the extract CMO, the Company would be required to reimburse Vaxcyte for a portion of all incurred process transfer costs. As of March 31, 2024 and December 31, 2023, there was $ 7.4 million and $ 6.9 million, respectively, in such accruals related to the Vaxcyte Supply Agreement. For the three months ended March 31, 2024 and 2023, the agreed-upon reimbursements by Vaxcyte of the costs associated with such arrangements, principally for pass-through costs from the CMOs, were $ 1.6 million and $ 1.9 million, respectively, and were accounted for by the Company as a reduction to research and development expense based on the Company’s conclusion that Vaxcyte was not a customer for such activities and associated payments. Vaxcyte Agreement In December 2022, the Company entered into a letter agreement (the “Vaxcyte Agreement”) with Vaxcyte under which the Company granted to Vaxcyte (i) authorization to enter into an agreement with an independent alternate CMO to source cell-free extract solely for the products it licensed from the Company, allowing Vaxcyte to have direct oversight over financial and operational aspects of the relationship with the CMO (“CMO Relationship Rights”), and (ii) a right, but not an obligation, to obtain certain exclusive rights to internally manufacture and/or source extract from certain CMOs and the right to independently develop and make improvements to extract for use in connection with the exploitation of certain vaccine compositions (the “Option”). In November 2023 (the "Exercise Date"), Vaxcyte exercised the Option by submitting written notice thereof to the Company and concurrently paid the Company $ 50.0 million in cash as the first of two installment payments for the Option exercise price. Under the Vaxcyte Agreement, Vaxcyte is obligated to pay the Company an additional $ 25.0 million in cash within six months of the Exercise Date as the second of two installment payments for the Option exercise price. Upon the occurrence of certain regulatory milestones, Vaxcyte would be obligated to pay the Company certain additional payments totaling up to $ 60.0 million in cash. In the event that Vaxcyte undergoes a change of control, certain rights and payments may be accelerated. These contingent payments were considered constrained variable consideration or otherwise not eligible for revenue recognition at inception and as of March 31, 2024. Revenues under the Vaxcyte agreements were as follows: Three Months Ended March 31, 2024 2023 (in thousands) Research and development services $ 647 $ 504 Materials supply - 171 Total revenue $ 647 $ 675 Refer to Note 8 below for information relating to the Purchase Agreement between the Company and Blackstone, pursuant to which the Company sold to Blackstone its 4 % royalty, or revenue interest, in potential future net sales of Vaxcyte products, including VAX-24 and VAX-31. Ipsen Agreement In March 2024, the Company and Ipsen Pharma SAS (“Ipsen”) entered into an Exclusive License Agreement (the “Ipsen License Agreement”) pursuant to which the Company licensed to Ipsen, on an exclusive basis, the right to research, develop, manufacture and commercialize STRO-003. In consideration for the rights and licenses granted by the Company to Ipsen in the Ipsen License Agreement, (i) Ipsen paid the Company an upfront license fee in the amount of $ 50.0 million in April 2024 and (ii) Ipsen Biopharmaceuticals, Inc. (USA) (the “Ipsen USA”), a fully-owned Affiliate of Ipsen, purchased 4,827,373 shares of the Company’s common stock for $ 25.0 million, at a price per share representing a 17 % premium to the volume weighted average price (“VWAP”) of the Company’s common stock for the twenty trading day period prior to the parties’ execution of the Ipsen License Agreement, in accordance with the terms set forth in a certain investment agreement by and between the Company and Ipsen USA dated March 29, 2024 (the “Ipsen Investment Agreement”). Further, pursuant to the Ipsen License Agreement, upon the occurrence of a specified developmental milestone according to a specified timetable, the Company will receive a payment of up to $ 7.0 million and Ipsen is obligated to purchase up to an additional $ 10.0 million in shares of the Company’s common stock at a price per share representing a 17 % premium to the VWAP of the Company’s common stock for the twenty trading day period prior to such milestone achievement, in accordance with the terms set forth in the Ipsen Investment Agreement. The Company is also eligible to receive up to an additional $ 447.0 million in developmental and regulatory milestones, assuming multiple indications, and up to $ 360.0 million in sales milestones, as well as tiered royalty payments ranging from low double-digit to mid-teen digit percentages of annual net sales of STRO-003, subject to certain adjustments specified in the Ipsen License Agreement. The royalty payment obligations under the Ipsen License Agreement expire on a country-by-country basis no earlier than ten years following the first commercial sale of STRO-003 in the applicable country. Ipsen may terminate the Ipsen License Agreement for convenience with sixty calendar days prior written notice or for certain other specified reasons. The Company may terminate the Ipsen License Agreement if Ipsen or any of its Affiliates challenge the validity of any patents controlled by the Company that are licensed under the agreement. Both Ipsen and the Company may terminate the Ipsen License Agreement (i) for material breach by the other party and a failure to cure such breach within the time period specified in the Ipsen License Agreement or (ii) the other party’s bankruptcy event. The Company did not recognize the upfront license fee of $ 50.0 million as the performance obligations related to the Ipsen License Agreement were not satisfied during the three months ended March 31, 2024.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. Commitments and Contingencies Leases The Company leases certain office, labo ratory and manufacturing facilities in South San Francisco, California and San Carlos, California. These leases require monthly lease payments that may be subject to annual increases throughout the lease term. Certain of these leases also include renewal options at the election of the Company to renew or extend the lease for an additional 5 years . These renewal options have not been considered in the determination of the right-of-use assets and lease liabilities associated with these leases as the Company has determined it is not reasonably certain it will exercise such options. The Company recognizes rent expense for these operating leases on a straight-line basis over the lease period. The components of lease costs, which the Company includes in operating expenses in the Company's condensed Statements of Operations, were as follows (in thousands): Three Months Ended March 31, 2024 2023 Operating lease cost $ 1,984 $ 1,538 Short-term lease cost 53 24 Variable lease cost 594 410 Total lease costs $ 2,631 $ 1,972 During the three months ended March 31, 2024 and 2023, the Company recorded operating lease expense of $ 2.0 million and $ 1.5 million, respectively, and paid $ 2.3 million and $ 1.7 million, respectively, of operating lease payments related to the lease liabilities, which the Company includes in net cash used in operating activities in the Company's condensed Statements of Cash Flows. As of March 31, 2024 and December 31, 2023, the weighted-average remaining lease term was 3.6 years and 3.8 years, respectively, and the weighted-average discount rate used to determine the operating lease liability was 10.8 % for both periods. As of March 31, 2024, the maturities of the Company’s operating lease liabilities were as follows (in thousands): Year Ending December 31, Amount (in thousands) Remaining in 2024 $ 6,951 2025 9,533 2026 8,994 2027 8,289 Total lease payments 33,767 Less: imputed interest ( 5,697 ) Operating lease liabilities 28,070 Less: current portion ( 6,673 ) Total lease liabilities, non-current $ 21,397 Indemnification & Other In the ordinary course of business, the Company may provide indemnifications of varying scope and terms to vendors, lessors, business partners, board members, officers, and other parties with respect to certain matters, including, but not limited to, losses arising out of breach of such agreements, services to be provided by the Company, negligence or willful misconduct of the Company, violations of law by the Company, or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with directors and certain officers and employees that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors, officers, or employees. No demands have been made upon the Company to provide indemnification under such agreements, and thus, there are no claims that the Company is aware of that could have a material effect on the Company’s condensed Balance Sheets, condensed Statements of Operations, or condensed Statements of Cash Flows. The Company currently has directors’ and officers’ liability insurance. In addition, the Company enters into agreements in the normal course of business, including with contract research organizations for clinical trials, contract manufacturing organizations for certain manufacturing services, and vendors for preclinical studies and other services and products for operating purposes, which are generally cancelable upon written notice.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	3 Months Ended
	Mar. 31, 2024
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consist of the following: March 31, December 31, 2024 2023 (in thousands) Vaxcyte-related accrual under Vaxcyte Supply Agreement $ 7,375 $ 6,933 CMO-related accrual 6,934 8,195 Clinical trials-related accrual 4,865 4,283 Tax and related expenses 15,165 15,165 Other 3,407 3,897 Total accrued expenses and other current liabilities $ 37,746 $ 38,473

Deferred Royalty Obligation rel

Deferred Royalty Obligation related to the Sale of Future Royalties	3 Months Ended
	Mar. 31, 2024
Deferred Royalty Obligation [Abstract]
Deferred Royalty Obligation related to the Sale of Future Royalties	8. Deferred Royalty Obligation related to the Sale of Future Royalties In June 2023, the Company entered into the Purchase Agreement with Blackstone, pursuant to which the Company sold to Blackstone its 4 % royalty, or revenue interest, in the potential future net sales of Vaxcyte products, including the Purchased Interest under the 2015 License Agreement. As described in Note 5. Collaboration and License Agreements and Supply Agreements, Vaxcyte Agreement, following agreement with Vaxcyte on the Form Definitive Agreement and upon effectiveness of the amendment No. 3 to the 2015 License Agreement, the revenue interest in the 4 % royalty on potential future net sales of Vaxcyte products other than Vaxcyte’s PCV products reverted to the Company. The Company retains the right to discover and develop vaccines for the treatment or prophylaxis of any disease that is not caused by an infectious pathogen, including cancer. In June 2023, Blackstone made an upfront payment of $ 140.0 million to the Company and will also pay up to an additional $ 250.0 million upon the achievement of various return thresholds as set forth in the Purchase Agreement. Under the Purchase Agreement, and in connection with its sale of the Purchased Interest, the Company has agreed to certain covenants with respect to the exercise of its rights under the 2015 License Agreement, including with respect to the Company’s right to amend, assign and terminate the 2015 License Agreement. The Purchase Agreement contains other customary terms and conditions, including representations and warranties, covenants, and indemnification obligations in favor of each party. The Company recorded the $ 140.0 million upfront payment from Blackstone as a deferred royalty obligation related to the sale of future royalties on the Company's condensed Balance Sheets. Due to the Company's then ongoing manufacturing obligations under the 2015 License Agreement, the Company accounted for the proceeds as imputed debt and, therefore, will recognize future non-cash royalty revenues. Non-cash interest expense will be recognized over the estimated life of the royalty term arrangement using the effective interest method based on the imputed interest rate derived from estimated amounts and timing of potential future royalty payments to be received from Vaxcyte. As part of the sale, the Company incurred approximately $ 3.8 million in transaction costs, which are being amortized over the estimated life of the royalty term arrangement using the effective interest method. As future royalties are earned from Vaxcyte by Blackstone, the balance of the deferred royalty obligation will be amortized over the estimated life of the royalty term arrangement. There are a number of factors that could materially affect the fair value of the deferred royalty obligation. Such factors include, but are not limited to, the amount and timing of potential future royalty payments to be earned and received by Blackstone from Vaxcyte under the 2015 License Agreement, changing standards of care, the introduction of competing products, manufacturing or other delays, intellectual property matters, adverse events that result in governmental health authority imposed restrictions on the use of the vaccine products, and other events or circumstances that could result in reduced royalty payments from Vaxcyte to Blackstone, which are not within the Company's control, and all of which would result in a reduction or increase of non-cash royalty revenues and the non-cash interest expense over the estimated life of the royalty term arrangement. The Company periodically assesses the estimated royalty payments to be earned by Blackstone from Vaxcyte and, to the extent that the amount or timing of such payments is materially different than our original estimates, the Company prospectively adjusts the imputed interest rate and the related amortization of the deferred royalty obligation. As of March 31, 2024, the effective interest rate used by the Company to amortize the liability is 19.0 %. During the three months ended March 31, 2024 and 2023, the Company recognized approximately $ 7.2 million and zero , respectively, of non-cash interest expense on the deferred royalty obligation, which amount will increase such balance. As of March 31, 2024, Blackstone has not received any royalty payment from Vaxcyte and, therefore, the deferred royalty obligation has not begun to be amortized. The following table shows the activity of the deferred royalty obligation for the three months ended March 31, 2024: March 31, 2024 (in thousands) Liability related to sale of future Vaxcyte royalties - beginning balance $ 149,114 Non-cash interest expense associated with the sale of future Vaxcyte royalties 7,184 Amortization of issuance costs 167 Liability related to the sale of future Vaxcyte royalties - ending balance $ 156,465

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2024
Stockholders' Equity Note [Abstract]
Stockholders' Equity	9. Stockholders’ Equity Common Stock Holders of common stock are entitled to one vote per share on all matters to be voted upon by the stockholders of the Company. The Company has reserved common stock, on an if-converted basis, for issuance as follows: March 31, December 31, 2024 2023 Common stock options issued and outstanding 8,749,825 7,905,032 Common stock awards issued and outstanding 6,222,549 5,244,873 Remaining shares reserved for issuance under 2018 Equity 1,801,715 1,777,919 Shares reserved for issuance under 2018 Employee 745,303 914,911 Warrants to purchase common stock 127,616 127,616 Total 17,647,008 15,970,351 Preferred Stock As of March 31, 2024 and December 31, 2023, the Company had 10,000,000 shares of preferred stock authorized with a par value of $ 0.001 per share. No shares of preferred stock were outstanding as of March 31, 2024 and December 31, 2023.

Equity Incentive Plans, Equity

Equity Incentive Plans, Equity Inducement Plans, Employee Stock Purchase Plan and Stock-Based Compensation	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Equity Incentive Plans, Equity Inducement Plans, Employee Stock Purchase Plan and Stock-Based Compensation	10. Equity Incentive Plans , Equity Inducement Plans, Employee Stock Purchase Plan and Stock-Based Compensation 2004 Equity Incentive Plan, 2018 Equity Incentive Plan, 2021 Equity Inducement Plan, and Amended and Restated 2021 Equity Inducement Plan In September 2018, the Company adopted the 2018 Equit y Incentive Plan (“2018 Plan”), which became effective on September 25, 2018. As a result, the Company will not grant any additional awards under the 2004 Equity Incentive Plan (“2004 Plan”). The terms of the 2004 Plan and applicable award agreements will continue to govern any outstanding awards thereunder. In addition to the shares of common stock reserved for future issuance under the 2004 Plan that were added to the 2018 Plan upon its effective date, the Company initially reserved 2,300,000 shares of common stock for issuance under the 2018 Plan. In addition, the number of shares of common stock reserved for issuance under the 2018 Plan will automatically increase on the first day of January for a period of up to ten years , commencing on January 1, 2019, in an amount equal to 5 % of the total number of shares of the Company’s capital stock outstanding on the last day of the preceding year (rounded to the nearest whole share), or a lesser number of shares determined by the Company’s board of directors. As a result, common stock reserved for issuance under the 2018 Plan was increased by 3,050,491 shares on January 1, 2024. In August 2021, the Company adopted the 2021 Equity Inducement Plan (“2021 Plan”), which became effective on August 4, 2021. Upon its effective date, the Company initially reserved 750,000 shares of common stock for issuance pursuant to non-qualified stock options and restricted stock units (“RSUs”) under the 2021 Plan. In accordance with Rule 5635(c)(4) of the Nasdaq listing rules, equity awards under the 2021 Plan may only be made to an employee if he or she is granted such equity awards in connection with his or her commencement of employment with the Company and such grant is an inducement material to his or her entering into employment with the Company or such subsidiary. In addition, awards under the 2021 Plan may only be made to employees who have not previously been an employee or member of the Board (or any parent or subsidiary of the Company) or following a bona fide period of non-employment of the employee by the Company (or a parent or subsidiary of the Company). At all times, the Company will reserve and keep available a sufficient number of shares as will be required to satisfy the requirements of all outstanding awards granted under the 2021 Plan. In August 2022, the Company amended and restated the 2021 Plan (the “Amended and Restated 2021 Plan”) and reserved an additional 750,000 shares of common stock available for issuance under the Amended and Restated 2021 Plan to be granted by the Company to certain employees as a material inducement to their acceptance of employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). Additionally, in February 2023, the Company amended and restated the Amended and Restated 2021 Plan and reserved an additional 500,000 shares of common stock available for issuance under the Amended and Restated 2021 Plan to be granted by the Company to certain employees as a material inducement to their acceptance of employment with the Company in accordance with Nasdaq Listing Rule 5635(c)(4). The total number of shares reserved for issuance pursuant to the Amended and Restated 2021 Plan is 2,000,000 shares. As of March 31, 2024, the Company had a total of 1,801,715 shares available for grant under the 2018 Plan and the 2021 Plan. The following table summarizes option activity under the Company’s 2004 Plan, 2018 Plan and 2021 Plan: Shares Weighted- Stock options outstanding at December 31, 2023 7,905,032 $ 11.24 Granted 976,750 4.55 Exercised ( 23,748 ) 4.91 Canceled and forfeited ( 108,209 ) 7.83 Stock options outstanding at March 31, 2024 8,749,825 10.55 Stock options exercisable at March 31, 2024 5,985,449 $ 12.29 Restricted Stock Units During the three months ended March 31 , 2024, the Company granted 2,309,030 shares of restricted common stock units (“RSUs”) to certain employees. These RSUs vest annually, and generally, will become fully vested over four years . A summary of the status and activity of non-vested RSUs during the three months ended March 31, 2024 is as follows: Number of Weighted Non-vested December 31, 2023 5,244,873 $ 8.31 Granted 2,309,030 4.54 Vested and released ( 1,215,729 ) 9.90 Canceled and forfeited ( 115,625 ) 8.22 Non-vested March 31, 2024 6,222,549 $ 6.60 2018 Employee Stock Purchase Plan In September 2018, the Company adopted the 201 8 Employee Stock Purchase Plan (“ESPP”), which became effective on September 26, 2018, in order to enable eligible employees to purchase shares of the Company’s common stock. The Company initially reserved 230,000 shares of common stock for sale under the ESPP. The aggregate number of shares reserved for sale under the ESPP will automatically increase on the first day of January for a period of up to ten years , commencing on January 1, 2019, in an amount equal to 1 % of the total number of shares of the Company’s capital stock outstanding on the last day of the preceding year (rounded to the nearest whole share), or a lesser number of shares determined by the Company’s board of directors. As a result, common stock reserved for issuance under the ESPP was increased by 114,754 shares on January 1, 2023. The aggregate number of shares issued over the term of the Company’s ESPP, subject to stock-splits, recapitalizations or similar events, may not exceed 2,300,000 shares of the Company’s common stock. As of March 31, 20 24, 1,554,697 shares had been purchased and 745,303 shares were available for future issuance under the ESPP. Stock-Based Compensation Expense The Company believes that the fair value of the stock options, RSUs and ESPP shares is more reliably measurable than the fair value of services received. Total stock-based compensation expense recognized was as follows: Three Months Ended March 31, 2024 2023 (in thousands) Research and development expense: $ 3,174 $ 2,821 General and administrative expense: 2,894 3,200 Total $ 6,068 $ 6,021 As of March 31, 2024, unrecogni zed stock-based compensation expense related to the unvested stock options and RSUs granted was $ 12.1 million and $ 36.5 million, respectively. The remaining unrecognized compensation cost related to the unvested stock options and RSUs is expected to be recognized over a weighted-average period of 2.3 years and 2.6 years, respectively. As of March 31, 2024, there was $ 0.6 million of unrecognized stock-based compensation expense related to the ESPP. As of March 31, 2023, unrecognized stock-based compensation expense related to the unvested stock options and RSUs granted was $ 18.0 million and $ 45.0 million, respectively. The remaining unrecognized compensation cost related to the unvested stock options and RSUs is expected to be recognized over a weighted-average period of 2.4 years and 2.9 years, respectively. As of March 31, 2023, there was $ 0.5 million of unrecognized stock-based compensation expense related to the ESPP.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Net Loss Per Share	11. Net Loss Per Share The following table sets forth the computation of the Company’s basic and diluted net loss per share. Three Months Ended March 31, 2024 2023 (in thousands, except share and per share amounts) Numerator: Net loss $ ( 58,213 ) $ ( 50,050 ) Denominator: Shares used in computing net loss per share 61,457,793 58,723,432 Net loss per share, basic and diluted $ ( 0.95 ) $ ( 0.85 ) The following common stock equivalents were excluded from the computation of diluted net loss per share for the period ended March 31, 2024 and 2023, because including them would have been antidilutive: As of March 31, 2024 2023 Common stock options issued and outstanding 8,749,825 8,336,599 Restricted stock units issued and outstanding 6,222,549 5,354,600 Warrants to purchase common stock 127,616 127,616 Shares to be issued under employee stock purchase plan 33,575 31,381 Total 15,133,565 13,850,196

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2024
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events In April 2024, the Company closed an underwritten offering with BofA Securities, Inc., pursuant to which the Company issued and sold 14,478,764 shares of its common stock at an offering price of $ 5.18 per share. The gross proceeds from these sales were approximately $ 75.0 million, before deducting fees and offering expenses. In April 2024, the Company issued 4,827,373 shares to Ipsen USA at a price of $ 5.18 per share under the Ipsen Investment Agreement, and received gross proceeds of $ 25.0 million.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation and Use of Estimates	Basis of Presentation and Use of Estimates The accompanying interim condensed financial statements of the Company are unaudited. These interim condensed financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and the applicable rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial information. Accordingly, they do not include all the information and footnotes required by U.S. GAAP for complete financial statements. The December 31, 2023 condensed balance sheet was derived from the audited financial statements as of that date but does not include all of the information and footnotes required by U.S. GAAP for complete financial statements. The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The Company bases its estimates on historical experience and market-specific or other relevant assumptions that it believes are reasonable under the circumstances. The amounts of assets and liabilities reported in the Company’s condensed Balance Sheets and the amounts of expenses and income reported for each of the periods presented are affected by estimates and assumptions, which are used for, but are not limited to, determining research and development periods under collaboration arrangements, stock-based compensation expense, valuation of marketable securities, impairment of long-lived assets, income taxes, deferred royalty obligation related to the sale of future royalties and related non-cash interest expense, and certain accrued liabilities. Actual results could differ from such estimates or assumptions. The accompanying unaudited interim condensed financial statements have been prepared on the same basis as the audited financial statements and, in the opinion of management, reflect all adjustments of a normal recurring nature considered necessary to state fairly the Company’s financial position, results of operations, comprehensive loss, and cash flows for the interim periods. The interim results for the three months ended March 31, 2024 are not necessarily indicative of the results that may be expected for the year ending December 31, 2024, or for any other future annual or interim period. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company’s audited financial statements included in the Annual Report on Form 10-K pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934, as amended, for the year ended December 31, 2023.
Recent Accounting Pronouncements Not Yet Adopted	Recent Accounting Pronouncements Not Yet Adopted There were no new accounting pronouncements issued since the Company's filing of the Annual Report on Form 10-K for the year ended December 31, 2023, which could have a significant effect on the Company's condensed financial statements.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company's condensed Balance Sheets that sum to the total of the same amounts shown in the Company's condensed Statements of Cash Flows. March 31, 2024 2023 (in thousands) Cash and cash equivalents $ 65,218 $ 62,472 Restricted cash 857 872 Total cash, cash equivalents, and restricted cash shown in the $ 66,075 $ 63,344
Investments in Equity Securities	Investments in Equity Securities Vaxcyte common stock held by the Company is measured at fair value at each reporting period based on the closing price of Vaxcyte’s common stock on the last trading day of each reporting period, with any realized or unrealized gains and losses recorded in the Company’s condensed Statements of Operations.
Fair Value Measurements	Fair Value Measurements Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability, or an exit price, in the principal or most advantageous market for that asset or liability in an orderly transaction between market participants on the measurement date and establishes a fair value hierarchy that requires an entity to maximize the use of observable inputs, where available, and minimize the use of unobservable inputs when measuring fair value. The Company determined the fair value of financial assets and liabilities using the fair value hierarchy that describes three levels of inputs that may be used to measure fair value, as follows: Level 1—Quoted prices in active markets for identical assets and liabilities; Level 2—Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The carrying amounts of accounts receivable, prepaid expenses, accounts payable, accrued liabilities and accrued compensation and benefits approximate fair value due to the short-term nature of these items. The carrying value of the deferred royalty obligation related to the sale of future royalties under the 2015 License Agreement with Vaxcyte approximates its fair value as of March 31, 2024, and is based on our current estimates of future royalties expected to be earned over the estimated life of the royalty term arrangement. See Note 8. Deferred Royalty Obligation Related to the Sale of Future Royalties for a description of the Level 3 inputs used to estimate the fair value of the liability.
Revenue Recognition	Revenue Recognition When the Company enters into collaboration agreements, it assesses whether the arrangements fall within the scope of ASC 808, Collaborative Arrangements ("ASC 808") based on whether the arrangements involve joint operating activities and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards. To the extent that the arrangement falls within the scope of ASC 808, the Company assesses whether the payments between the Company and its collaboration partner fall within the scope of other accounting literature. If it concludes that payments from the collaboration partner to the Company represent consideration from a customer, such as license fees and contract research and development activities, the Company accounts for those payments within the scope of Accounting Standards Update (ASU) No. 2014-09 (Topic 606), Revenue from Contracts with Customers (“ASC 606”). Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. However, if the Company concludes that its collaboration partner is not a customer for certain activities and associated payments, such as for certain collaborative research, development, manufacturing and commercial activities, the Company presents such payments as a reduction of research and development expense or general and administrative expense, based on where the Company presents the underlying expense. The Company has no products approved for commercial sale and has not generated any revenue from commercial product sales. The total revenue to date has been generated principally from collaboration and license agreements and to a lesser extent, from manufacturing, supply and services, and materials the Company provides to its collaboration partners. Collaboration Revenue: The Company derives revenue from collaboration arrangements, under which the Company may grant licenses to its collaboration partners to further develop and commercialize its proprietary product candidates. The Company may also perform research and development activities under the collaboration agreements. Consideration under these contracts generally includes a nonrefundable upfront payment, development, regulatory and commercial milestones and other contingent payments, and royalties based on net sales of approved products. Additionally, the collaborations may provide options for the customer to acquire from the Company materials and reagents, clinical product supply or additional research and development services under separate agreements. The Company assesses which activities in the collaboration agreements are considered distinct performance obligations that should be accounted for separately. The Company develops assumptions that require judgement to determine whether the license to the Company’s intellectual property is distinct from the research and development services or participation in activities under the collaboration agreements. At the inception of each agreement, the Company determines the arrangement transaction price, which includes variable consideration, based on the assessment of the probability of achievement of future milestones and contingent payments and other potential consideration. The Company recognizes revenue over time by measuring its progress towards the complete satisfaction of the relevant performance obligation using an appropriate input or output method based on the nature of the service promised to the customer. For arrangements that include multiple performance obligations, the Company allocates the transaction price to the identified performance obligations based on the standalone selling price, or SSP, of each distinct performance obligation. In instances where SSP is not directly observable, the Company develops assumptions that require judgment to determine the SSP for each performance obligation identified in the contract. These key assumptions may include full-time equivalent, or FTE, personnel effort, estimated costs, discount rates and probabilities of clinical development and regulatory success. Upfront Payments : For collaboration arrangements that include a nonrefundable upfront payment, if the license fee and research and development services cannot be accounted for as separate performance obligations, the transaction price is deferred and recognized as revenue over the expected period of performance using a cost-based input methodology. The Company uses judgement to assess the pattern of delivery of the performance obligation. In addition, amounts paid in advance of services being rendered may result in an associated financing component to the upfront payment. Accordingly, the interest on such borrowing cost component will be recorded as interest expense and revenue, based on an appropriate borrowing rate applied to the value of services to be performed by the Company over the estimated service performance period. License Grants: For collaboration arrangements that include a grant of a license to the Company’s intellectual property, the Company considers whether the license grant is distinct from the other performance obligations included in the arrangement. For licenses that are distinct, the Company recognizes revenues from nonrefundable, upfront payments and other consideration allocated to the license when the license term has begun and the Company has provided all necessary information regarding the underlying intellectual property to the customer, which generally occurs at or near the inception of the arrangement. Milestone and Contingent Payments : At the inception of the arrangement and at each reporting date thereafter, the Company assesses whether it should include any milestone and contingent payments or other forms of variable consideration in the transaction price using the most likely amount method. If it is probable that a significant reversal of cumulative revenue would not occur upon resolution of the uncertainty, the associated milestone value is included in the transaction price. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of each milestone and any related constraint and, if necessary, adjusts its estimate of the overall transaction price. Since milestone and contingent payments may become payable to the Company upon the initiation of a clinical study or filing for or receipt of regulatory approval, the Company reviews the relevant facts and circumstances to determine when the Company should update the transaction price, which may occur before the triggering event. When the Company updates the transaction price for milestone and contingent payments, the Company allocates the changes in the total transaction price to each performance obligation in the agreement on the same basis as the initial allocation. Any such adjustments are recorded on a cumulative catch-up basis in the period of adjustment, which may result in recognizing revenue for previously satisfied performance obligations in such period. The Company’s collaborators generally pay milestones and contingent payments subsequent to achievement of the triggering event. Research and Development Services : For amounts allocated to the Company’s research and development obligations in a collaboration arrangement, the Company recognizes revenue over time using a cost-based input methodology, representing the transfer of goods or services as activities are performed over the term of the agreement. Materials Supply: The Company provides materials and reagents, clinical materials, and services to certain of its collaborators under separate agreements. The consideration for such services is generally based on FTE personnel effort used to manufacture those materials, reimbursed at an agreed upon rate in addition to agreed-upon pricing for the provided materials. The amounts billed are recognized as revenue as the performance obligations are met by the Company. Revenue subject to governmental withholding taxes is recognized on a gross basis with the withholding taxes recorded as a component of income tax expense.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2024
Accounting Policies [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the Company's condensed Balance Sheets that sum to the total of the same amounts shown in the Company's condensed Statements of Cash Flows. March 31, 2024 2023 (in thousands) Cash and cash equivalents $ 65,218 $ 62,472 Restricted cash 857 872 Total cash, cash equivalents, and restricted cash shown in the $ 66,075 $ 63,344

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities Measured on Recurring Basis	The following table sets forth the fair value of the Company’s financial assets and liabilities measured on a recurring basis by level within the fair value hierarchy: March 31, 2024 Total Level 1 Level 2 Level 3 (in thousands) Assets: Money market funds $ 42,498 $ 42,498 $ - $ - Commercial paper 21,379 - 21,379 - Corporate debt securities 44,036 - 44,036 - Equity securities 45,616 45,616 - - Asset-backed securities 44,598 - 44,598 - U.S. government securities 113,130 113,130 - - Total $ 311,257 $ 201,244 $ 110,013 $ - December 31, 2023 Total Level 1 Level 2 Level 3 (in thousands) Assets: Money market funds $ 56,397 $ 56,397 $ - $ - Commercial paper 82,152 - 82,152 - Corporate debt securities 61,894 - 61,894 - Equity securities 41,937 41,937 - - Asset-backed securities 10,505 - 10,505 - U.S. government securities 113,652 113,652 - - U.S. agency securities 4,961 - 4,961 - Total $ 371,498 $ 211,986 $ 159,512 $ -

Cash Equivalents and Marketab_2

Cash Equivalents and Marketable Securities (Tables)	3 Months Ended
	Mar. 31, 2024
Cash and Cash Equivalents [Abstract]
Schedule of Cash Equivalents and Marketable Securities	Cash equivalents and marketable securities consisted of the following: March 31, 2024 Amortized Unrealized Unrealized Fair (in thousands) Money market funds $ 42,498 $ - $ - $ 42,498 Commercial paper 21,391 - ( 12 ) 21,379 Corporate debt securities 44,044 3 ( 11 ) 44,036 Asset-based securities 44,641 - ( 43 ) 44,598 U.S. government securities 113,180 - ( 50 ) 113,130 Total 265,754 3 ( 116 ) 265,641 Less amounts classified as cash equivalents ( 63,257 ) - - ( 63,257 ) Total marketable securities $ 202,497 $ 3 $ ( 116 ) $ 202,384 December 31, 2023 Amortized Unrealized Unrealized Fair (in thousands) Money market funds $ 56,397 $ - $ - $ 56,397 Commercial paper 82,179 1 ( 28 ) 82,152 Corporate debt securities 61,887 12 ( 5 ) 61,894 Asset-based securities 10,505 - – 10,505 U.S. government securities 113,612 40 – 113,652 U.S. agency securities 4,960 1 – 4,961 Total 329,540 54 ( 33 ) 329,561 Less amounts classified as cash equivalents ( 65,144 ) ( 4 ) - ( 65,148 ) Total marketable securities $ 264,396 $ 50 $ ( 33 ) $ 264,413

Collaboration and License Agr_2

Collaboration and License Agreements and Supply Agreements (Tables)	3 Months Ended
	Mar. 31, 2024
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Summary of Recognized Revenue	In accordance with the collaboration, license and supply agreements, the Company recognized revenue as follows: Three Months Ended March 31, 2024 2023 (in thousands) Merck Sharp & Dohme Corporation (“Merck”) $ 6 $ 2,553 Astellas Pharma Inc. (“Astellas”) 11,385 6,272 Tasly Biopharmaceuticals Co., Ltd. (“Tasly”) 970 - Vaxcyte, Inc. ("Vaxcyte") 647 675 Bristol Myers Squibb Company (“BMS”) - 3,166 Merck KGaA, Darmstadt, Germany (operating in the United - 8 Total revenue $ 13,008 $ 12,674
Summary of Deferred Revenue Balance	The following table presents the changes in the Company’s deferred revenue balance from the agreements during the three months ended March 31, 2024: Three Months Ended March 31, 2024 (in thousands) Deferred revenue—December 31, 2023 $ 74,045 Additions to deferred revenue - Recognition of revenue in current period ( 7,230 ) Deferred revenue—March 31, 2024 $ 66,815
Vaxcyte, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Summary of Recognized Revenue	Revenues under the Vaxcyte agreements were as follows: Three Months Ended March 31, 2024 2023 (in thousands) Research and development services $ 647 $ 504 Materials supply - 171 Total revenue $ 647 $ 675
2020 Merck Master Services Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Summary of Recognized Revenue	Revenues under the 2018 Merck Agreement and the 2020 Merck Master Services Agreement were as follows: Three Months Ended March 31, 2024 2023 (in thousands) Research and development services $ 6 $ 125 Materials supply - 2,428 Total revenue $ 6 $ 2,553
Astellas License and Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Summary of Recognized Revenue	Revenues under the Astellas Agreement were as follows: Three Months Ended March 31, 2024 2023 (in thousands) Ongoing performance related to $ 7,230 $ 2,572 Research and development services 1,623 1,157 Financing component on unearned revenue 2,160 2,543 Materials supply 372 - Total revenue $ 11,385 $ 6,272
Tasly License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Summary of Recognized Revenue	Revenues under the Tasly agreements were as follows: Three Months Ended March 31, 2024 2023 (in thousands) Research and development services $ 33 $ – Materials supply 937 – Total revenue $ 970 $ –

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Schedule of Components of Lease Costs	The components of lease costs, which the Company includes in operating expenses in the Company's condensed Statements of Operations, were as follows (in thousands): Three Months Ended March 31, 2024 2023 Operating lease cost $ 1,984 $ 1,538 Short-term lease cost 53 24 Variable lease cost 594 410 Total lease costs $ 2,631 $ 1,972
Schedule of Maturities of Operating Lease Liabilities	As of March 31, 2024, the maturities of the Company’s operating lease liabilities were as follows (in thousands): Year Ending December 31, Amount (in thousands) Remaining in 2024 $ 6,951 2025 9,533 2026 8,994 2027 8,289 Total lease payments 33,767 Less: imputed interest ( 5,697 ) Operating lease liabilities 28,070 Less: current portion ( 6,673 ) Total lease liabilities, non-current $ 21,397

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2024
Payables and Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consist of the following: March 31, December 31, 2024 2023 (in thousands) Vaxcyte-related accrual under Vaxcyte Supply Agreement $ 7,375 $ 6,933 CMO-related accrual 6,934 8,195 Clinical trials-related accrual 4,865 4,283 Tax and related expenses 15,165 15,165 Other 3,407 3,897 Total accrued expenses and other current liabilities $ 37,746 $ 38,473

Deferred Royalty Obligation r_2

Deferred Royalty Obligation related to the Sale of Future Royalties (Tables)	3 Months Ended
	Mar. 31, 2024
Deferred Royalty Obligation [Abstract]
Schedule of Royalty Obligation transaction	The following table shows the activity of the deferred royalty obligation for the three months ended March 31, 2024: March 31, 2024 (in thousands) Liability related to sale of future Vaxcyte royalties - beginning balance $ 149,114 Non-cash interest expense associated with the sale of future Vaxcyte royalties 7,184 Amortization of issuance costs 167 Liability related to the sale of future Vaxcyte royalties - ending balance $ 156,465

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2024
Stockholders' Equity Note [Abstract]
Schedule of Common Stock Reserved for Future Issuance	The Company has reserved common stock, on an if-converted basis, for issuance as follows: March 31, December 31, 2024 2023 Common stock options issued and outstanding 8,749,825 7,905,032 Common stock awards issued and outstanding 6,222,549 5,244,873 Remaining shares reserved for issuance under 2018 Equity 1,801,715 1,777,919 Shares reserved for issuance under 2018 Employee 745,303 914,911 Warrants to purchase common stock 127,616 127,616 Total 17,647,008 15,970,351

Equity Incentive Plans, Equit_2

Equity Incentive Plans, Equity Inducement Plans, Employee Stock Purchase Plan and Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Summary of Option Activity	The following table summarizes option activity under the Company’s 2004 Plan, 2018 Plan and 2021 Plan: Shares Weighted- Stock options outstanding at December 31, 2023 7,905,032 $ 11.24 Granted 976,750 4.55 Exercised ( 23,748 ) 4.91 Canceled and forfeited ( 108,209 ) 7.83 Stock options outstanding at March 31, 2024 8,749,825 10.55 Stock options exercisable at March 31, 2024 5,985,449 $ 12.29
Summary of Status and Activity of Non-vested RSUs	A summary of the status and activity of non-vested RSUs during the three months ended March 31, 2024 is as follows: Number of Weighted Non-vested December 31, 2023 5,244,873 $ 8.31 Granted 2,309,030 4.54 Vested and released ( 1,215,729 ) 9.90 Canceled and forfeited ( 115,625 ) 8.22 Non-vested March 31, 2024 6,222,549 $ 6.60
Schedule of Stock-Based Compensation Expense Recognized	Total stock-based compensation expense recognized was as follows: Three Months Ended March 31, 2024 2023 (in thousands) Research and development expense: $ 3,174 $ 2,821 General and administrative expense: 2,894 3,200 Total $ 6,068 $ 6,021

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Summary of Computation of Company's Basic and Diluted Net Loss Per Share	The following table sets forth the computation of the Company’s basic and diluted net loss per share. Three Months Ended March 31, 2024 2023 (in thousands, except share and per share amounts) Numerator: Net loss $ ( 58,213 ) $ ( 50,050 ) Denominator: Shares used in computing net loss per share 61,457,793 58,723,432 Net loss per share, basic and diluted $ ( 0.95 ) $ ( 0.85 )
Summary of Common Stock Equivalents of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share	The following common stock equivalents were excluded from the computation of diluted net loss per share for the period ended March 31, 2024 and 2023, because including them would have been antidilutive: As of March 31, 2024 2023 Common stock options issued and outstanding 8,749,825 8,336,599 Restricted stock units issued and outstanding 6,222,549 5,354,600 Warrants to purchase common stock 127,616 127,616 Shares to be issued under employee stock purchase plan 33,575 31,381 Total 15,133,565 13,850,196

Organization and Principal Ac_2

Organization and Principal Activities - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($) Segment	Dec. 31, 2023 USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Date of incorporation	Apr. 21, 2003
Headquartered in	South San Francisco
Headquartered in state	CA
Number of operating segments | Segment	1
Accumulated deficit	$ 617,621	$ 559,408
Unrestricted cash, cash equivalents and marketable securities	$ 267,600
Substantial doubt about going concern, within one year	false
Vaxcyte
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Unrestricted cash, cash equivalents and equity securities at carrying value	$ 45,600
Minimum
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Period from issuance date of unaudited interim condensed financial statements	12 months

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023
Accounting Policies [Abstract]
Cash and cash equivalents	$ 65,218	$ 69,268	$ 62,472
Restricted cash	857	$ 872	872
Total cash, cash equivalents, and restricted cash shown in the condensed Statements of Cash Flows	$ 66,075		$ 63,344

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Details) - Fair Value Measurements Recurring - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Assets:
Total	$ 311,257	$ 371,498
Level 1
Assets:
Total	201,244	211,986
Level 2
Assets:
Total	110,013	159,512
Money Market Funds
Assets:
Total	42,498	56,397
Money Market Funds | Level 1
Assets:
Total	42,498	56,397
Commercial Paper
Assets:
Total	21,379	82,152
Commercial Paper | Level 2
Assets:
Total	21,379	82,152
Corporate Debt Securities
Assets:
Total	44,036	61,894
Corporate Debt Securities | Level 2
Assets:
Total	44,036	61,894
Equity Securities
Assets:
Total	45,616	41,937
Equity Securities | Level 1
Assets:
Total	45,616	41,937
Asset-backed Securities
Assets:
Total	44,598	10,505
Asset-backed Securities | Level 2
Assets:
Total	44,598	10,505
U.S. Government Securities
Assets:
Total	113,130	113,652
U.S. Government Securities | Level 1
Assets:
Total	$ 113,130	113,652
U.S. Agency Securities
Assets:
Total		4,961
U.S. Agency Securities | Level 2
Assets:
Total		$ 4,961

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jun. 30, 2023	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Estimated fair value of equity securities		$ 45,616		$ 41,937
Unrealized gain (loss) on equity securities		$ 3,679	$ (6,992)
Vaxcyte, Inc. | Vaxcyte Common Stock
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of shares held		667,780		667,780
Estimated fair value of equity securities		$ 45,600		$ 41,900
Unrealized gain (loss) on equity securities		$ 3,700	$ (7,000)
Blackstone Life Sciences | Royalty | 2015 License Agreement
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Revenue interest percentage	4%	4%

Cash Equivalents and Marketab_3

Cash Equivalents and Marketable Securities - Schedule of Cash Equivalents and Marketable Securities (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	$ 265,754,000	$ 329,540,000
Unrealized Gains	3,000	54,000
Unrealized Losses	(116,000)	(33,000)
Fair Value	265,641,000	329,561,000
Less amounts classified as cash equivalents, Amortized Cost Basis	(65,218,000)	(69,268,000)	$ (62,472,000)
Marketable Securities
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	202,497,000	264,396,000
Unrealized Gains	3,000	50,000
Unrealized Losses	(116,000)	(33,000)
Fair Value	202,384,000	264,413,000
Cash Equivalents
Cash And Cash Equivalents [Line Items]
Less amounts classified as cash equivalents, Amortized Cost Basis	(63,257,000)	(65,144,000)
Less amounts classified as cash equivalents, Unrealized Gains		(4,000)
Less amounts classified as cash equivalents, Fair Value	(63,257,000)	(65,148,000)
Money Market Funds
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	42,498,000	56,397,000
Fair Value	42,498,000	56,397,000
Commercial Paper
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	21,391,000	82,179,000
Unrealized Gains		1,000
Unrealized Losses	(12,000)	(28,000)
Fair Value	21,379,000	82,152,000
Corporate Debt Securities
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	44,044,000	61,887,000
Unrealized Gains	3,000	12,000
Unrealized Losses	(11,000)	(5,000)
Fair Value	44,036,000	61,894,000
Asset-backed Securities
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	44,641,000	10,505,000
Unrealized Losses	(43,000)
Fair Value	44,598,000	10,505,000
U.S. Government Securities
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis	113,180,000	113,612,000
Unrealized Gains		40,000
Unrealized Losses	(50,000)
Fair Value	$ 113,130,000	113,652,000
U.S. Agency Securities
Cash And Cash Equivalents [Line Items]
Amortized Cost Basis		4,960,000
Unrealized Gains		1,000
Fair Value		$ 4,961,000

Cash Equivalents and Marketab_4

Cash Equivalents and Marketable Securities - Additional Information (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Cash And Cash Equivalents [Line Items]
Long-term marketable securities	$ 0		$ 0
Investments in an unrealized loss position	190,500,000		110,900,000
Unrealized losses	116,000		$ 33,000
Recognition of other-than-temporary impairment	$ 0	$ 0
Maximum
Cash And Cash Equivalents [Line Items]
Marketable securities maturity period	1 year		1 year

Collaboration and License Agr_3

Collaboration and License Agreements and Supply Agreements - Additional Information (Details)	1 Months Ended							3 Months Ended		12 Months Ended
	Apr. 30, 2024 USD ($)	Mar. 31, 2024 USD ($) shares	Nov. 30, 2023 USD ($) Installment	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($) Program PerformanceObligation	Apr. 30, 2022 USD ($)	Jul. 31, 2018 Program	Mar. 31, 2024 USD ($) shares	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) shares	Dec. 31, 2021 USD ($)	Dec. 31, 2022 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts receivable, reserve for credit losses		$ 0						$ 0		$ 0
Common stock, shares issued | shares		62,456,546						62,456,546		61,009,829
Common stock value issued		$ 62,000						$ 62,000		$ 61,000
Vaxcyte, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
First installment milestone payment received			$ 50,000,000
Number of installments | Installment			2
Additional milestone payment receivable			$ 25,000
Additional milestone payment										60,000,000
Blackstone Life Sciences
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received				$ 140,000,000
2015 License Agreement | Blackstone Life Sciences | Royalty
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payment received				$ 140,000,000
Revenue interest percentage				4%				4%
2018 Merck Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue		0						$ 0		0
2018 Merck Agreement | Merck Sharp & Dohme Corp
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Number of target programs | Program							2
Revenue recognition aggregate contingent payments eligible to receive											$ 500,000,000
Milestone method revenue recognition description								If one or more products from the target program is developed for non-oncology or a single indication, the Company will be eligible for reduced aggregate contingent payments. In addition, the Company is eligible to receive tiered royalties ranging from mid-single digit to low-teen digit percentages on the worldwide sales of any commercial products that may result from the collaboration.
2020 Merck Master Services Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue		0						$ 0		0
Supply Agreement | Vaxcyte, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursements expenses accruals		7,400,000						7,400,000		6,900,000
Reimbursements expenses								1,600,000	$ 1,900,000
Astellas License and Collaboration Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue		61,800,000						61,800,000		69,000,000
Number of target programs | Program					3
Upfront payment received								90,000,000
Transaction price					$ 90,000,000
Estimated service period					4 years
Recognition of up front payment					$ 89,100,000
Upfront payment revenue not recognized								32,600,000
Nonrefundable, non-creditable upfront payment receivable												$ 90,000,000
Number of performance obligations | PerformanceObligation					4
Maximum amount eligible to receive for development, regulatory and commercial milestones for each product candidate		422,500,000						422,500,000
Astellas License and Collaboration Agreement | Future Services on Collaboration Joint Steering Committee ("JSC")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Recognition of up front payment					$ 900,000
Tasly License Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum potential payments related to development regulatory commercialization contingent payments and milestones						$ 350,000,000
Reduction of research and development expenses recognized								0	$ 0
Initial licensing payment due						25,000,000
Initial licensing payment in escrow						$ 15,000,000
Revenue recognized from contingent payment										5,000,000
Income tax charge related to contingent payment										$ 500,000
Maximum refund period on termination of study										30 days
Contingent payment recognized as deferred revenue										$ 5,000,000
Withholding tax on deferred revenue										$ 500,000
Ipsen Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payment received		$ 7,000,000
Upfront license fee								$ 50,000,000
Common stock, shares issued | shares		4,827,373						4,827,373
Common stock value issued		$ 25,000,000						$ 25,000,000
Additional purchase of Common Stock		$ 10,000,000						$ 10,000,000
Percentage of VWAP premium		0.17
Payment related to development and regulatory milestone		$ 447,000,000
Payments related to sales milestone		$ 360,000,000
Ipsen Agreement | Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront license fee	$ 50,000,000

Collaboration and License Agr_4

Collaboration and License Agreements and Supply Agreements - Summary of Recognized Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	$ 13,008	$ 12,674
Vaxcyte Agreements
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	647	675
Vaxcyte Agreements | Research and Development Services
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	647	504
Vaxcyte Agreements | Materials Supply
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue		171
Collaboration and License Agreements and Supply Agreements
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	13,008	12,674
Collaboration and License Agreements and Supply Agreements | Bristol-Myers Squibb Company ("BMS")
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue		3,166
Collaboration and License Agreements and Supply Agreements | Merck Sharp & Dohme Corporation ("Merck")
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	6	2,553
Collaboration and License Agreements and Supply Agreements | Astellas Pharma Inc. ("Astellas")
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	11,385	6,272
Collaboration and License Agreements and Supply Agreements | Tasly Biopharmaceuticals Co., Ltd. ("Tasly")
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	970
Collaboration and License Agreements and Supply Agreements | Vaxcyte
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	647	675
Collaboration and License Agreements and Supply Agreements | Merck KGaA, Darmstadt, Germany (operating in the United States and Canada under the name ''EMD Serono'')
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue		8
2020 Merck Master Services Agreement
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	6	2,553
2020 Merck Master Services Agreement | Research and Development Services
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	6	125
2020 Merck Master Services Agreement | Materials Supply
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue		2,428
Astellas License and Collaboration Agreement
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	11,385	6,272
Astellas License and Collaboration Agreement | Ongoing Performance Related to Unsatisfied Performance Obligations
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	7,230	2,572
Astellas License and Collaboration Agreement | Research and Development Services
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	1,623	1,157
Astellas License and Collaboration Agreement | Financing Component on Unearned Revenue
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	2,160	$ 2,543
Astellas License and Collaboration Agreement | Materials Supply
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	372
Tasly License Agreement
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	970
Tasly License Agreement | Research and Development Services
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	33
Tasly License Agreement | Materials Supply
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Total revenue	$ 937

Collaboration and License Agr_5

Collaboration and License Agreements and Supply Agreements - Performance Obligations - Additional Information (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-04-01 $ in Millions	Mar. 31, 2024 USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue, remaining performance obligation, amount	$ 20.5
Revenue, remaining performance obligation, expected timing of satisfaction, period	12 months

Collaboration and License Agr_6

Collaboration and License Agreements and Supply Agreements - Summary of Deferred Revenue Balance (Details) - Collaboration and License Agreements and Supply Agreements $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Revenue Recognition Multiple Deliverable Arrangements [Line Items]
Deferred revenue	$ 74,045
Recognition of revenue in current period	(7,230)
Deferred revenue	$ 66,815

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Loss Contingencies [Line Items]
Operating lease expense	$ 2	$ 1.5
Operating lease payments	$ 2.3	$ 1.7
Operating lease, weighted average remaining lease term	3 years 7 months 6 days		3 years 9 months 18 days
Operating lease, weighted average discount rate, percent	10.80%		10.80%
San Carlos Lease | California
Loss Contingencies [Line Items]
Lease extension period	5 years
Lease renewal term	5 years

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Components of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Operating lease cost	$ 1,984	$ 1,538
Short-term lease cost	53	24
Variable lease cost	594	410
Total lease costs	$ 2,631	$ 1,972

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Remaining in 2024	$ 6,951
2025	9,533
2026	8,994
2027	8,289
Total lease payments	33,767
Less: imputed interest	(5,697)
Operating lease liabilities	28,070
Less: current portion	(6,673)	$ (6,420)
Total lease liabilities, non-current	$ 21,397	$ 23,154

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Tax and related expenses	$ 15,165	$ 15,165
Other	3,407	3,897
Total accrued expenses and other current liabilities	37,746	38,473
Supply Agreement | Vaxcyte
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration and license agreements and supply agreement accruals	7,375	6,933
CMO
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration and license agreements and supply agreement accruals	6,934	8,195
Clinical Trials
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Collaboration and license agreements and supply agreement accruals	$ 4,865	$ 4,283

Deferred Royalty Obligation r_3

Deferred Royalty Obligation related to the Sale of Future Royalties Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Jun. 30, 2023	Mar. 31, 2024	Mar. 31, 2023
Deferred Royalty Obligation [Line Items]
Non-cash interest expense on deferred royalty obligation		$ 7,184	$ 0
Percentage of interest rate amortize liability		19%
Blackstone Life Sciences
Deferred Royalty Obligation [Line Items]
Upfront payment received	$ 140,000
Blackstone Life Sciences | Maximum
Deferred Royalty Obligation [Line Items]
Milestone payment receivable	250,000
2015 License Agreement | Blackstone Life Sciences
Deferred Royalty Obligation [Line Items]
Transaction costs incurred	3,800
2015 License Agreement | Blackstone Life Sciences | Royalty
Deferred Royalty Obligation [Line Items]
Upfront payment received	$ 140,000
Revenue interest percentage	4%	4%
Amendment 3 2015 License Agreement | Vaxcyte | Royalty
Deferred Royalty Obligation [Line Items]
Revenue interest percentage		4%

Deferred Royalty Obligation r_4

Deferred Royalty Obligation related to the Sale of Future Royalties - Schedule of Royalty Obligation transaction (Details) - Vaxcyte, Inc. $ in Thousands	3 Months Ended
	Mar. 31, 2024 USD ($)
Deferred Royalty Obligation [Line Items]
Liability related to sale of future Vaxcyte royalties - beginning balance	$ 149,114
Non-cash interest expense associated with the sale of future Vaxcyte royalties	7,184
Amortization of issuance costs	167
Liability related to the sale of future Vaxcyte royalties - ending balance	$ 156,465

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - $ / shares	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Stockholders Equity [Line Items]
Voting rights per share	one vote per share
Preferred stock shares authorized	10,000,000	10,000,000
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, outstanding	0	0

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details) - shares	Mar. 31, 2024	Dec. 31, 2023
Stockholders Equity [Line Items]
Reserved common stock	17,647,008	15,970,351
Common Stock Options Issued and Outstanding
Stockholders Equity [Line Items]
Reserved common stock	8,749,825	7,905,032
Common Stock Awards Issued and Outstanding
Stockholders Equity [Line Items]
Reserved common stock	6,222,549	5,244,873
Remaining Shares Reserved for Issuance under 2018 Equity Incentive Plan and 2021 Equity Inducement Plan
Stockholders Equity [Line Items]
Reserved common stock	1,801,715	1,777,919
Shares Reserved for Issuance Under 2018 Employee Stock Purchase Plan
Stockholders Equity [Line Items]
Reserved common stock	745,303	914,911
Warrants to Purchase Common Stock
Stockholders Equity [Line Items]
Reserved common stock	127,616	127,616

Equity Incentive Plans, Equit_3

Equity Incentive Plans, Equity Inducement Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Additional Information (Details) - USD ($) $ in Millions			3 Months Ended
	Sep. 26, 2018	Sep. 25, 2018	Mar. 31, 2024	Mar. 31, 2023	Jan. 01, 2024	Dec. 31, 2023	Feb. 28, 2023	Jan. 01, 2023	Aug. 31, 2022	Aug. 04, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved common stock			17,647,008			15,970,351
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted common stock granted			2,309,030
Shares vesting period			4 years
2018 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved common stock		2,300,000
Annual increase period of common stock reserved for issuance		10 years
Maximum number of shares issuable					3,050,491
2018 Equity Incentive Plan | Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost related to unvested granted			$ 36.5	$ 45
Remaining unrecognized compensation cost expected to be recognized over weighted-average period			2 years 7 months 6 days	2 years 10 months 24 days
2018 Equity Incentive Plan | Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost related to unvested granted			$ 12.1	$ 18
Remaining unrecognized compensation cost expected to be recognized over weighted-average period			2 years 3 months 18 days	2 years 4 months 24 days
2018 Equity Incentive Plan | Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense			$ 0.6	$ 0.5
2018 Equity Incentive Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in stock reserved for issuance as percentage of capital stock outstanding on last day of preceding year		5%
2021 Equity Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved common stock										750,000
Amended and Restated 2021 Equity Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved common stock			2,000,000				500,000		750,000
2018 Equity Incentive Plan and 2021 Equity Inducement Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for grant			1,801,715
2018 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Reserved common stock	230,000
Annual increase period of common stock reserved for issuance	10 years
Maximum number of shares issuable	2,300,000		1,554,697
Shares available for grant			745,303
Shares available for grant, increase								114,754
2018 Employee Stock Purchase Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in stock reserved for issuance as percentage of capital stock outstanding on last day of preceding year	1%

Equity Incentive Plans, Equit_4

Equity Incentive Plans, Equity Inducement Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Summary of Option Activity (Details) - 2004 Plan, 2018 Plan and 2021 Plan	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options outstanding, Beginning Balance, Shares | shares	7,905,032
Granted, Shares | shares	976,750
Exercised, Shares | shares	(23,748)
Canceled and forfeited, Shares | shares	(108,209)
Stock options outstanding, Ending Balance, Shares | shares	8,749,825
Stock options exercisable, Shares | shares	5,985,449
Stock options outstanding, Weighted - Average Exercise Price, Beginning Balance | $ / shares	$ 11.24
Weighted - Average Exercise Price, Granted | $ / shares	4.55
Weighted - Average Exercise Price, Exercised | $ / shares	4.91
Weighted - Average Exercise Price, Canceled and forfeited | $ / shares	7.83
Stock options outstanding, Weighted - Average Exercise Price, Ending Balance | $ / shares	10.55
Stock options exercisable, Weighted - Average Exercise Price, Exercisable | $ / shares	$ 12.29

Equity Incentive Plans, Equit_5

Equity Incentive Plans, Equity Inducement Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Summary of Status and Activity of Non-vested RSUs (Details) - Restricted Stock Units	3 Months Ended
	Mar. 31, 2024 $ / shares shares
Number of shares
Non-vested, Beginning Balance | shares	5,244,873
Granted | shares	2,309,030
Vested and released | shares	(1,215,729)
Canceled and forfeited | shares	(115,625)
Non-vested, Ending balance | shares	6,222,549
Weighted Average Grant-Date Fair Value
Non-vested, Beginning Balance | $ / shares	$ 8.31
Granted | $ / shares	4.54
Vested and released | $ / shares	9.90
Canceled and forfeited | $ / shares	8.22
Non-vested, Ending balance | $ / shares	$ 6.60

Equity Incentive Plans, Employe

Equity Incentive Plans, Employee Stock Purchase Plan and Stock-Based Compensation - Schedule of Stock-Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6,068	$ 6,021
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	3,174	2,821
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,894	$ 3,200

Provision For Income Taxes - Ad

Provision For Income Taxes - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2023 USD ($)
Income Tax Disclosure [Abstract]
Income tax expense	$ 395

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Computation of Company's Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Numerator:
Net loss	$ (58,213)	$ (50,050)
Denominator:
Weighted-average shares used in computing basic net loss per share	61,457,793	58,723,432
Weighted-average shares used in computing diluted net loss per share	61,457,793	58,723,432
Net loss per share, basic	$ (0.95)	$ (0.85)
Net loss per share, diluted	$ (0.95)	$ (0.85)

Net Loss Per Share - Summary _2

Net Loss Per Share - Summary of Common Stock Equivalents of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share (Details) - shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share	15,133,565	13,850,196
Common Stock Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share	8,749,825	8,336,599
Restricted Stock Units Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share	6,222,549	5,354,600
Warrants to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share	127,616	127,616
Shares to be Issued Under Employee Stock Purchase Plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share	33,575	31,381

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Event $ / shares in Units, $ in Millions	1 Months Ended
	Apr. 30, 2024 USD ($) $ / shares shares
Ipsen Investment Agreement | Ipsen USA
Subsequent Event [Line Items]
Shares of common stock | shares	4,827,373
Offering price | $ / shares	$ 5.18
Proceeds from Issuance of Common Stock | $	$ 25
Common Stock | BofA Securities, Inc
Subsequent Event [Line Items]
Shares of common stock | shares	14,478,764
Offering price | $ / shares	$ 5.18
Proceeds from Issuance of Common Stock | $	$ 75