HilleVax (HLVX) 10-K 20 Mar 24 2023 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Mar. 11, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Registrant Name	HILLEVAX, INC.
Entity Central Index Key	0001888012
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Small Business	true
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		49,700,828
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity File Number	001-41365
Entity Tax Identification Number	85-0545060
Entity Address Address Line1	321 Harrison Avenue
Entity Address City Or Town	Boston
Entity Address State Or Province	MA
Entity Address Postal Zip Code	02118
Entity Incorporation State Country Code	DE
City Area Code	617
Local Phone Number	213-5054
Title of each class	Common Stock, $0.0001 par value per share
Trading Symbol	HLVX
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Public Float			$ 258
ICFR Auditor Attestation Flag	false
Name of each exchange on which registered	NASDAQ
Document Annual Report	true
Document Transition Report	false
Auditor Firm ID	42
Auditor Name	Ernst & Young LLP
Auditor Location	San Diego, California
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement (the Proxy Statement) for its 2024 Annual Meeting of Stockholders, which the registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year ended December 31, 2023 , are incorporated by reference into Part III of this Annual Report on Form 10-K.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 216,678	$ 279,401
Marketable securities	86,805
Prepaid expenses and other current assets	7,195	11,212
Total current assets	310,678	290,613
Property and equipment, net	14,018	5,586
Operating lease right-of-use assets	18,082	19,359
Restricted cash	1,631	1,631
Other assets	25	22
Total assets	344,434	317,211
Current liabilities:
Accounts payable (includes related party amounts of $0 and $141, respectively)	7,461	4,744
Accrued expenses (includes related party amounts of $33 and $140, respectively)	18,553	8,210
Accrued interest	134	55
Current portion of operating lease liability	3,118	37
Total current liabilities	29,266	13,046
Operating lease liability, net of current portion	22,831	21,569
Long-term debt, net of debt discount	25,244	14,792
Other long-term liabilities	1,568	575
Total liabilities	78,909	49,982
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock, $0.0001 par value; authorized shares - 50,000,000 at December 31, 2023 and December 31, 2022; no shares issued and outstanding at December 31, 2023 and December 31, 2022
Common stock, $0.0001 par value; authorized shares - 500,000,000 at December 31, 2023 and December 31, 2022; issued shares - 48,497,853 and 39,240,746 at December 31, 2023 and December 31, 2022, respectively; outstanding shares - 47,666,438 and 37,656,037 at December 31, 2023 and December 31, 2022, respectively	5	4
Additional paid-in capital	654,986	532,499
Accumulated other comprehensive loss	(907)	(281)
Accumulated deficit	(388,559)	(264,993)
Total stockholders' equity	265,525	267,229
Total liabilities and stockholders' equity	$ 344,434	$ 317,211

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Accounts payable	$ 7,461	$ 4,744
Accrued expenses	$ 18,553	$ 8,210
Preferred stock par value	$ 0.0001	$ 0.0001
Preferred stock shares authorized	50,000,000	50,000,000
Preferred stock shares issued	0	0
Preferred stock shares outstanding	0	0
Common stock par value	$ 0.0001	$ 0.0001
Common stock shares authorized	500,000,000	500,000,000
Common stock shares issued	48,497,853	39,240,746
Common stock shares outstanding	47,666,438	37,656,037
Related party
Accounts payable	$ 0	$ 141
Accrued expenses	$ 33	$ 140

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating expenses:
Research and development (includes related party amounts of $362 and $2,426, respectively)	$ 106,683	$ 45,908
In-process research and development - related party		2,500
General and administrative (includes related party amounts of $0 and $40, respectively)	26,662	16,705
Total operating expenses	133,345	65,113
Loss from operations	(133,345)	(65,113)
Other income (expense):
Interest income	9,706	3,875
Interest expense (includes related party amounts of $0 and $717, respectively)	(2,392)	(3,414)
Change in fair value of convertible promissory notes (includes related party amounts of $0 and $13,196, respectively)		(51,469)
Change in fair value of warrant liabilities - related party		(43,575)
Other income (expense)	2,465	(113)
Total other income (expense)	9,779	(94,696)
Net loss	(123,566)	(159,809)
Other comprehensive loss:
Pension and other postemployment benefits	(620)	(281)
Unrealized loss on marketable securities	(6)
Total comprehensive loss	$ (124,192)	$ (160,090)
Net loss per share, basic	$ (3.04)	$ (5.89)
Net loss per share, diluted	$ (3.04)	$ (5.89)
Weighted-average shares of common stock outstanding, basic	40,598,482	27,147,314
Weighted-average shares of common stock outstanding, diluted	40,598,482	27,147,314

Consolidated Statements of Op_2

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Interest expense, related party	$ 2,392	$ 3,414
Change in fair value of convertible promissory notes, related party	0	13,196
Related party
Research and development expenses	362	2,426
General and administrative, related party	0	40
Interest expense, related party	$ 0	$ 717

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Initial Public Offering	Underwritten Public Offering	Common Stock	Common Stock Initial Public Offering	Common Stock Underwritten Public Offering	Additional Paid-in Capital	Additional Paid-in Capital Initial Public Offering	Additional Paid-in Capital Underwritten Public Offering	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance at Dec. 31, 2021	$ (100,757)			$ 1			$ 4,426				$ (105,184)
Beginning Balance, Shares at Dec. 31, 2021				6,599,886
Issuance of common stock		$ 209,515			$ 1			$ 209,514
Issuance of common stock, Shares					13,529,750
Conversion of August 2021 Notes and accrued interest into common shares	215,364			$ 1			215,363
Conversion of August 2021 Notes and accrued interest into common shares, Shares				10,672,138
Conversion of Takeda Warrant liability into equity	100,020						100,020
Exercise of Takeda Warrant	1			$ 1
Exercise of Takeda Warrant, Shares				5,883,500
Vesting of restricted shares, Shares				958,777
Stock - based compensation	3,003						3,003
Issuance of common stock under share-based compensation arrangements	173						173
Issuance of common stock under share-based compensation arrangements Shares				11,986
Pension and other postemployment benefits	(281)									$ (281)
Net loss	(159,809)										(159,809)
Ending Balance at Dec. 31, 2022	267,229			$ 4			532,499			(281)	(264,993)
Ending Balance, Shares at Dec. 31, 2022				37,656,037
Issuance of common stock			$ 107,790			$ 1			$ 107,789
Issuance of common stock, Shares						9,200,000
Vesting of restricted shares, Shares				683,410
Stock - based compensation	13,590						13,590
Issuance of common stock under share-based compensation arrangements	1,108						1,108
Issuance of common stock under share-based compensation arrangements Shares				126,991
Unrealized loss on marketable securities	(6)									(6)
Pension and other postemployment benefits	(620)									(620)
Net loss	(123,566)										(123,566)
Ending Balance at Dec. 31, 2023	$ 265,525			$ 5			$ 654,986			$ (907)	$ (388,559)
Ending Balance, Shares at Dec. 31, 2023				47,666,438

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Common Stock
Net of issuance costs	$ 20,491

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities
Net loss	$ (123,566)	$ (159,809)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	879	1
Stock-based compensation	13,590	3,003
Change in fair value of convertible promissory notes (includes related party amounts of $0 and $13,196, respectively)		51,469
Change in fair value of warrant liabilities - related party		43,575
Amortization of operating lease right-of-use assets	1,277	1,147
Amortization of debt discount	567	292
Issuance of PIK interest debt	548	87
Acquired in-process research and development - related party		2,500
Net accretion/amortization of premiums and discounts on marketable securities	(2,921)
Loss on disposal of property and equipment		42
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	4,017	(11,071)
Accounts payable, accrued expenses and other long-term liabilities (includes related party amounts of $(248) and $(4,652), respectively)	14,404	2,819
Accrued interest (includes related party amounts of $0 and ($717), respectively)	79	2,852
Operating lease right-of-use assets and liabilities	4,343	1,104
Net cash used in operating activities	(86,783)	(61,989)
Cash flows from investing activities
Cash paid for purchased in-process research and development		(2,500)
Purchases of property and equipment	(10,748)	(4,014)
Purchases of marketable securities	(143,790)
Proceeds from sales or maturities of marketable securities	59,900
Net cash used in investing activities	(94,638)	(6,514)
Cash flows from financing activities
Proceeds from issuance of common stock under share-based compensation arrangements	1,108
Proceeds from issuance of common stock in initial public offering		230,006
Payment of initial public offering costs		(19,702)
Proceeds from issuance of common stock in underwritten public offering, net of issuance costs	107,790
Proceeds from issuance of long-term debt, net of issuance costs	9,800	14,665
Net cash provided by financing activities	118,698	224,969
Net increase (decrease) in cash, cash equivalents and restricted cash	(62,723)	156,466
Cash and, cash equivalents and restricted cash-beginning of period	281,032	124,566
Cash, cash equivalents and restricted cash-end of period	218,309	281,032
Supplemental disclosure of cash flow information
Cash paid for interest	1,392	193
Supplemental disclosure of noncash investing and financing activities
Operating lease		20,317
Unpaid property and equipment purchases	136	1,573
Conversion of convertible promissory notes and interest into common stock		215,364
Conversion of warrant liability into equity		100,020
Accreted final interest payment fees	$ 463	252
Settlement of ESPP liability in common stock		$ 173

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Statement of Cash Flows [Abstract]
Change in fair value of convertible promissory notes, related party	$ 0	$ 13,196
Related parties accounts payable, accrued expenses and other long-term liabilities	(248)	(4,652)
Related parties accrued interest	$ 0	$ (717)

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pay vs Performance Disclosure
Net Income (Loss)	$ (123,566)	$ (159,809)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2023
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	Rule 10b5-1 Trading Arrangements On October 12, 2023 , Aditya Kohli , Director and former Chief Operating Officer , adopted a rule 10b5-1 trading arrangement that is intended to satisfy the affirmative defense of Rule 10b5-1(c) for the sale of up to 108,000 shares of our common stock until May 22, 2024 .
Name	Aditya Kohli
Title	Director and former Chief Operating Officer
Rule 10b5-1 Arrangement Adopted	true
Adoption Date	October 12, 2023
Expiration Date	May 22, 2024

Insider Trading Policies and Pr

Insider Trading Policies and Procedures	3 Months Ended
	Dec. 31, 2023
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

Organization

Organization	12 Months Ended
	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	1. Organization Organization HilleVax, Inc. (the “Company” or “HilleVax”) was incorporated in the state of Delaware in March 2020 under the name MokshaCo, Inc. (“MokshaCo”). On February 8, 2021, MokshaCo changed its name to HilleVax and merged with North Bridge V, Inc. (“North Bridge V”) and YamadaCo III, Inc. (“YamadaCo III”), each a Delaware corporation formed in 2019, with HilleVax being the surviving entity (the “Merger”). The Company is a biopharmaceutical company focused on developing and commercializing novel vaccines. Forward Stock Split On April 22, 2022, the Company effected a 1.681 -for-1 forward split of shares of the Company’s common stock (the “Forward Stock Split”). The par value of the common stock was not adjusted as a result of the Forward Stock Split and the authorized shares were increased to 50,000,000 shares of common stock in connection with the Forward Stock Split. The accompanying financial statements and notes to the financial statements give retroactive effect to the Forward Stock Split for all periods presented, unless otherwise indicated. Liquidity and Capital Resources From inception to December 31, 2023, the Company has devoted substantially all of its efforts to organizing and staffing the Company, business planning, raising capital, in-licensing its initial vaccine candidate, HIL-214, preparing for and managing its clinical trials of HIL-214, and providing other general and administrative support for these operations. The Company has a limited operating history, has never generated any revenue, and the sales and income potential of its business is unproven. The Company has incurred net losses and negative cash flows from operating activities since its inception and expects to continue to incur net losses into the foreseeable future as it continues the development and potential commercialization of HIL-214. From inception to December 31, 2023 , the Company has funded its operations through the issuance of convertible promissory notes, commercial bank debt, the sale of 13,529,750 shares of common stock for net proceeds of approximately $ 209.5 million in its initial public offering ("IPO") which closed in May 2022, and the sale of 9,200,000 shares of common stock for net proceeds of approximately $ 107.8 million in its underwritten public offering which closed in September 2023 (see Note 10). The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern. Management is required to perform a two-step analysis over the Company’s ability to continue as a going concern. Management must first evaluate whether there are conditions and events that raise substantial doubt about the Company’s ability to continue as a going concern (Step 1). If management concludes that substantial doubt is raised, management is also required to consider whether its plans alleviate that doubt (Step 2). Management believes that it has sufficient working capital on hand to fund operations through at least the next twelve months from the date these financial statements were issued. There can be no assurance that the Company will be successful in acquiring additional funding, if needed, that the Company’s projections of its future working capital needs will prove accurate, or that any additional funding would be sufficient to continue operations in future years.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The Company's financial statements include the accounts of HilleVax Security Corporation, a wholly-owned subsidiary formed in Massachusetts, and HilleVax GmbH, a wholly-owned subsidiary formed in Zurich, Switzerland. The functional currency of the Company, HilleVax Security Corporation and HilleVax GmbH is the U.S. dollar. The Company’s assets and liabilities that are not denominated in the functional currency are remeasured into U.S. dollars at foreign currency exchange rates in effect at the balance sheet date except for nonmonetary assets, which are remeasured at historical foreign currency exchange rates in effect at the date of transaction. Net realized and unrealized gains and losses from foreign currency transactions and remeasurement are reported in other income (expense), in the consolidated statements of operations and were not material for the periods presented. All intercompany transactions have been eliminated in consolidation. Use of Estimates The Company’s consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to accruals for research and development expenses, and prior to the Company's IPO, the valuation of convertible promissory notes, warrant liabilities and various other equity instruments. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results could differ materially from those estimates and assumptions. Fair Value Option As permitted under Accounting Standards Codification (“ASC”) 825, Financial Instruments , (“ASC 825”), the Company has elected the fair value option to account for its convertible promissory notes issued through May 2022, when the convertible promissory notes converted into equity in connection with the Company's IPO. In accordance with ASC 825, the Company recorded these convertible promissory notes at fair value with changes in fair value recorded in the consolidated statements of operations. As a result of applying the fair value option, direct costs and fees related to the convertible promissory notes were recognized in the statement of operations as incurred and not deferred. Fair Value Measurements The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or non-recurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets. Level 2: Inputs, other than the quoted prices in active markets that are observable either directly or indirectly. Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents include cash in readily available checking accounts and money market funds. Restricted Cash Restricted cash consists of a money market account securing a standby letter of credit issued in connection with the Company’s Boston Lease (as defined and described in Note 6). Marketable Securities Marketable securities represent holdings of available-for-sale marketable debt securities in accordance with the Company’s investment policy. The Company has classified its investments with maturities beyond one year as current, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses reported within accumulated other comprehensive income (loss) as a separate component of stockholders’ equity (deficit) until realized, a determination is made that an other-than-temporary decline in market value has occurred or until the security has experienced a credit loss. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, together with interest on securities sold, is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other income (expense). Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities, and restricted cash. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. Property and Equipment, Net Property and equipment are stated at cost and depreciated on a straight-line basis over the estimated useful life of the related assets as follows: Estimated Useful Life Computer equipment 3 years Lab equipment 5 years Furniture and fixtures 5 years Leasehold improvements 3 – 10 years or term of lease Repairs and maintenance costs are charged to expense as incurred. Leases At the inception of a contractual arrangement, the Company determines whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. Lease terms are determined at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. For its long-term operating leases, the Company recognizes a lease liability and a right-of-use (“ROU”) asset on its balance sheet and recognizes lease expense on a straight-line basis over the lease term. The lease liability is determined as the present value of future lease payments, reduced by any reimbursements for tenant improvements, using the discount rate implicit in the lease or, if the implicit rate is not readily determinable, an estimate of the Company’s incremental borrowing rate. The ROU asset is based on the lease liability, adjusted for any prepaid or deferred rent, and reduced by any reimbursements for tenant improvements. The Company aggregates all lease and non-lease components for each class of underlying assets into a single lease component and variable charges for common area maintenance and other variable costs are recognized as expense as incurred. The Company has elected to not recognize a lease liability or ROU asset in connection with short-term operating leases and recognizes lease expense for short-term operating leases on a straight-line basis over the lease term. The Company does not have any financing leases. Impairment of Long-Lived Assets The Company reviews long-lived assets, such as property and equipment, for impairment whenever events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the fair value of the assets. Fair value would be assessed using discounted cash flows or other appropriate measures of fair value. The Company has not recognized any impairment losses through December 31, 2023 . Research and Development Expenses and Accruals All research and development costs are expensed in the period incurred and consist primarily of salaries, payroll taxes, employee benefits, stock-based compensation charges for those individuals involved in research and development efforts, external research and development costs incurred under agreements with contract research organizations and consultants to conduct and support the Company’s clinical trials of HIL-214. The Company has entered into various research and development contracts with clinical research organizations, clinical manufacturing organizations and other companies. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and payments made in advance of performance are reflected in the accompanying balance sheets as prepaid expenses. The Company records accruals for estimated costs incurred for ongoing research and development activities. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the services, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the prepaid or accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. In-Process Research and Development The Company evaluates whether acquired intangible assets are a business under applicable accounting standards. Additionally, the Company evaluates whether the acquired assets have a future alternative use. Intangible assets that do not have future alternative use are considered acquired in-process research and development. When the acquired in-process research and development assets are not part of a business combination, the value of the consideration paid is expensed on the acquisition date. Patent Costs Costs related to filing and pursuing patent applications are recorded as general and administrative expenses and expensed as incurred since recoverability of such expenditures is uncertain. Stock-Based Compensation Stock-based compensation expense represents the cost of the grant date fair value of equity awards, primarily consisting of stock options, restricted common stock, and employee stock purchase rights, recognized on a straight-line basis over the requisite service period for stock options and restricted common stock, and over the respective offering period for employee stock purchase plan rights. The Company recognizes forfeitures as they occur. Benefit plans The Company has established a defined contribution savings plan for its employees in the United States under Section 401(k) of the Internal Revenue Code, and a defined benefits plan for its employees outside of the United States. The defined benefits plan is valued by an independent actuary using the projected unit credit method. The liabilities correspond to the projected benefit obligations of which the discounted net present value is calculated based on years of employment, expected salary increase, and pension adjustments. The Company reviews its actuarial assumptions on an annual basis and makes modifications to the assumptions based on current rates and trends. This plan is recognized under ASC 715, Compensation - Retirement Benefits . Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the consolidated statements of operations in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (i) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (ii) for those tax positions that meet the more-likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense in the consolidated statements of operations. Any accrued interest and penalties are included within the related tax liability in the consolidated balance sheets. The Company did not recognize any interest or penalties during the periods presented. Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. For the years ended December 31, 2023 and December 31, 2022 , comprehensive loss included losses on the Company's pension benefit obligation and unrealized losses on marketable securities. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions on how to allocate resources and assess performance. The Company views its operations and manages its business as one operating segment. Net Loss Per Share Basic net loss per share is computed by dividing the consolidated net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. The Company has excluded weighted-average unvested shares of 1,232,828 shares and 2,080,038 shares from the basic weighted-average number of common shares outstanding for the years ended December 31, 2023 and 2022, respectively. Diluted net loss per share is computed by dividing the consolidated net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Potentially dilutive common stock equivalents are comprised of unvested common stock, common stock options, and contingently issuable shares under the Company's employee stock purchase plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as inclusion of the potentially dilutive common stock equivalents would be antidilutive. Potentially dilutive securities not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows (in common stock equivalent shares): December 31, 2023 2022 Common stock options 3,896,061 2,111,989 Unvested common stock 1,571,716 1,584,709 ESPP shares 8,473 4,420 Total potentially dilutive shares 5,476,250 3,701,118 Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (“JOBS Act”). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has irrevocably elected to avail itself of this exemption from new or revised accounting standards and, therefore, will not be subject to the same new or revised accounting standards as other public companies that are not emerging growth companies. Recently Adopted Accounting Standards In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2016-13, Financial Instruments – Credit Losses (Topic 326), to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. To achieve this objective, the amendments in Topic 326 replace the incurred loss impairment methodology in current U.S. GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. We adopted Topic 326 on January 1, 2023 . The adoption did no t have a material impact on our consolidated financial statements’. Recently Issued Accounting Pronouncements In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280) . The amendments in this update expand segment disclosure requirements, including new segment disclosure requirements for entities with a single reportable segment among other disclosure requirements. This update is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740) . The amendments in this update expand income tax disclosure requirements, including additional information pertaining to the rate reconciliation, income taxes paid, and other disclosures. This update is effective for annual periods beginning after December 15, 2024. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The Company’s cash, cash equivalents, marketable securities, and restricted cash are carried at fair value, determined according to the fair value hierarchy discussed in Note 2. The carrying values of the Company's prepaid expenses and other current assets, accounts payable, and accrued liabilities, approximate fair value due to their short maturities. The estimated fair value of the Company’s long-term debt approximated the carrying amount given its floating interest rate basis. Warrant liabilities and convertible promissory notes were recorded at fair value on a recurring basis until they converted to equity in connection with the Company's IPO, which closed in May 2022. The following tables present the Company's fair value hierarchy for its assets that are measured at fair value on a recurring basis and indicate the level within the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value (in thousands): Fair Value Measurements at Total Quoted Prices in Significant Significant Cash equivalents Money market funds $ 209,659 $ 209,659 $ — $ — Marketable securities: U.S. treasury notes 43,050 43,050 — — U.S government agency bonds 43,755 — 43,755 — Total $ 296,464 $ 252,709 $ 43,755 $ — Fair Value Measurements at Total Quoted Prices in Significant Significant Cash equivalents Money market funds $ 277,043 $ 277,043 $ — $ — Total $ 277,043 $ 277,043 $ — $ — U.S. government money market funds were valued by the Company based on quoted market prices, which represent a Level 1 measurement within the fair value hierarchy. As of December 31, 2023, the Company’s marketable securities consisted of U.S. Treasury notes which were valued based on Level 1 inputs and agency bonds which were valued based on Level 2 inputs. In determining the fair value of its agency bonds, the Company relied on quoted prices for similar securities in active markets or other inputs that are observable or can be corroborated by observable market data. No ne of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities As of December 31, 2023, the fair value of available-for-sale marketable debt securities by type of security was as follows (in thousands): December 31, 2023 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable securities: U.S. treasury notes $ 43,036 $ 16 $ ( 2 ) $ 43,050 U.S. government agency bonds 43,775 4 ( 24 ) 43,755 Total $ 86,811 $ 20 $ ( 26 ) $ 86,805 At December 31, 2023 , all available-for-sale marketable securities had contractual maturities of less than one year. The Company did no t hold any marketable debt securities as of December 31, 2022. As of December 31, 2023 , the Company reviewed its investment portfolio to assess the unrealized losses on its available-for-sale investments. In making this assessment, the Company considered the extent to which fair value is less than amortized cost, any changes to the rating of the security by a rating agency, and adverse conditions specifically related to the security, among other factors. The Company also evaluated whether it intended to sell the security and whether it was more likely than not that the Company would be required to sell the security before recovering its amortized cost basis. The Company determined no portion of the unrealized losses relate to a credit loss. There have been no impairments of the Company’s assets measured and carried at fair value during the year ended December 31, 2023 .

Other Balance Sheet Details

Other Balance Sheet Details	12 Months Ended
	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Other Balance Sheet Details	5. Other Balance Sheet Details Property and Equipment Property and equipment, net consisted of the following (in thousands): December 31, 2023 2022 Computer equipment $ 103 $ - Furniture and equipment 377 11 Leasehold improvements 11,964 378 Lab equipment 2,116 — Construction in progress 338 5,198 Total property and equipment, at cost 14,898 5,587 Less accumulated depreciation 880 1 Property and equipment, net $ 14,018 $ 5,586 Depreciation expense for the year ended December 31, 2023 was $ 0.9 million. Depreciation expense for the year ended December 31, 2022 was not material. Accrued Expenses Accrued expenses consisted of the following (in thousands): December 31, 2023 2022 Accrued external research and development costs $ 12,665 $ 3,510 Accrued payroll and payroll-related costs 5,233 4,018 Accrued professional costs 498 307 Other 157 375 Total accrued expenses $ 18,553 $ 8,210 Cash, Cash Equivalents and Restricted Cash The following table provides a reconciliation of cash, cash equivalents and restricted cash recorded within the accompanying consolidated balance sheets that sum to the amounts shown in the consolidated statements of cash flows (in thousands): December 31, 2023 2022 Cash and cash equivalents $ 216,678 $ 279,401 Restricted cash 1,631 1,631 Total cash, cash equivalents and restricted cash $ 218,309 $ 281,032

Leases

Leases	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Leases	6. Leases Operating Leases In August 2021, the Company entered into a five-year noncancelable operating lease for a facility in Switzerland, which it determined was an operating lease at the inception of the lease contract. The lease commencement date occurred in September 2021 when the Company gained access to the facility. The Company is obligated to make monthly rental payments that periodically escalate during the lease term and is subject to additional charges for common area maintenance and other costs. The Company has an option to extend the lease for a period of five years which the Company is not reasonably certain to exercise. In March 2022, the Company entered into a lease for office and laboratory space located in Boston, Massachusetts (as amended, the “Boston Lease”), which it determined was an operating lease at the inception of the lease contract. The Boston Lease commenced in April 2022 with base rental payments beginning in January 2023. The Boston Lease includes certain tenant improvement allowances for the reimbursement of up to $ 6.3 million of costs incurred by the Company, and an optio n for the Company to extend the lease for a period of five years , which the Company is not reasonably certain to exercise. The Company determined that it owns the leasehold improvements related to the Boston Lease and, as such, reflected the $ 6.3 million lease incentive as a reduction of the rental payments used to measure the operating lease liability, and, in turn, the operating lease right-of-use asset as of the lease commencement date in April 2022. Between the lease commencement date and December 31, 2023 , the Company recorded increases of $ 6.0 million to the operating lease liability as and when such lease incentives were received from the landlord. Under the terms of the Boston Lease, the Company provided the lessor with an irrevocable standby letter of credit secured by restricted cash in the amount of $ 1.6 million. The following table summarizes operating lease expense for the year ended December 31, 2023 (in thousands): Year Ended 2023 2022 Lease expense: Operating lease expense $ 3,115 $ 2,351 The Company incurred an immaterial amount of expense related to short-term leases and variable lease costs during the years ended December 31, 2023 and December 31, 2022. The following table summarizes the lease term and discount rate for operating leases: December 31, 2023 2022 Other information: Weighted-average remaining lease term 9.00 9.96 Weighted-average discount rate 7.4 % 7.4 % As there was not an implicit rate within the leases, management estimated the incremental borrowing rate based on the rate of interest the Company would have to pay to borrow a similar amount on a collateralized basis over a similar term as well as by using a set of peer companies' incremental borrowing rates. The following table summarizes the cash paid for amounts included in the measurement of lease liabilities (in thousands): December 31, Cash paid for amounts included in the measurement of operating lease liabilities (operating cash flows) $ 3,487 At December 31, 2023, the future minimum noncancelable operating lease payments were as follows (in thousands): December 31, Years ending December 31: 2024 3,589 2025 3,692 2026 3,787 2027 3,860 2028 3,974 Thereafter 17,101 Total undiscounted operating lease payments 36,003 Present value adjustment ( 9,703 ) Tenant improvement reimbursements ( 351 ) Operating lease liability 25,949 Less current portion of operating lease liability 3,118 Operating lease liability, net of current portion $ 22,831

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	7. Related Party Transactions Frazier Life Sciences X, L.P. or its affiliates ("Frazier") is a principal stockholder of the Company and is represented on the Company’s board of directors. From January 8, 2019 (inception) to December 31, 2023, the Company and Frazier reimbursed each other for various goods and services, including personnel related expenses, travel, insurance, facilities and other various overhead and administrative expenses. As of December 31, 2022 , the Company had outstanding amounts due to Frazier of $ 6,000 related to these shared operating expenses. For the year ended December 31, 2022 , the Company incurred $ 40,000 of shared operating expenses. For the year ended December 31, 2023 , the Company did no t incur any shared operating expenses related to Frazier. As described in Note 9, the Company borrowed amounts from Frazier in connection with various convertible note financings. For the year ended December 31, 2022 , the Company recognized a $ 13.2 million change in fair value of convertible promissory notes in connection with convertible promissory notes issued to Frazier. For the year ended December 31, 2022 , the Company recognized $ 0.7 million of interest expense in connection with convertible promissory notes issued to Frazier. The convertible promissory notes automatically converted into 10,672,138 shares of the Company's common stock immediately prior to the completion of the IPO. In connection with the Takeda License (as defined and described in Note 8), Takeda became a related party stockholder with representation on the Company’s board of directors. The Company and Takeda are party to a TSA (as defined and described in Note 8) under which the Company is obligated to pay Takeda for certain services, including pass-through costs, related to research and development and regulatory assistance services, oversight and management of ongoing clinical and research studies, and maintenance of third-party vendor contracts. For the years ended December 31, 2023 and 2022, the Company incurred $ 0.4 million and $ 2.4 million, respectively, of research and development expenses for Takeda’s services. As of December 31, 2023 and 2022, the Company had $ 33,000 and $ 0.3 million, respectively, of accounts payable and accrued expenses due to Takeda. See Note 8 for further information regarding the Company’s related party transactions with Takeda.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies License Agreement On July 2, 2021, the Company entered into a license agreement with Takeda pursuant to which it was granted an exclusive sublicensable, royalty-bearing license (the “Takeda License”) to develop and commercialize HIL-214 pharmaceutical products for all human uses on a worldwide basis outside of Japan (the “Territory”). The Company will be responsible, at its own cost, for the development, manufacture and commercialization of HIL-214 products in the Territory, and the Company will integrate certain Japan development activities into its development activities at its own cost. The Company is obligated to use commercially reasonable efforts to develop and commercialize HIL-214 products in the Territory, and to seek regulatory approval for such products throughout the world. In consideration of the Takeda License, the Company (i) paid Takeda $ 2.5 million in cash, (ii) issued Takeda 840,500 shares of its common stock at a fair value of $ 4.4 million, (iii) issued Takeda a warrant (the “Takeda Warrant”) to purchase 5,883,500 shares of its common stock at an exercise price of $ 0.0000595 per share, which was fully exercised in November 2022, and (iv) issued Takeda a warrant right (the “Takeda Warrant Right”) to receive an additional common stock warrant should Takeda’s fully-diluted ownership of the Company, including the Takeda Warrant, represent less than a certain specified percentage of the fully-diluted capitalization, including shares issuable upon conversion of outstanding convertible promissory notes, calculated immediately prior to the earlier of the closing of the Company’s IPO or a change of control transaction, at an initial fair value of $ 34,000 . In addition, the Company is obligated to pay Takeda an aggregate of $ 2.5 million upon the release of certain drug product and the completion of certain regulatory activities, which payment was made in March 2022, $ 7.5 million upon the achievement of a specified development milestone, up to an aggregate of $ 150.0 million in sales milestones upon the achievement of specified annual sales levels of HIL-214 products in the Territory, and tiered high single-digit to low-teen percentage royalties on net sales of HIL-214 products in the Territory, subject to specified offsets and reductions. Takeda has agreed to pay the Company tiered mid-single digit to low-double digit percentage royalties on net sales of HIL-214 products in Japan, subject to specified offsets and reductions. Royalties will be payable, on a product-by-product and country-by-country basis from the first commercial sale of such product in such country, until the latest of expiration of the licensed patents covering the applicable product, expiration of regulatory exclusivity in such country, or 20 years following first commercial sale of such product in such country. The obligations related to contingent payments are recognized in the accompanying consolidated financial statements when the contingency is resolved and the consideration is paid or becomes payable. As of December 31, 2023, none of the remaining contingent payments were due or payable. Absent early termination, the Takeda License expires on a country-by-country and product-by-product basis upon the expiration of the applicable royalty term with respect to each product in each country, as applicable, or in its entirety upon the expiration of the royalty term with respect to the last product commercialized in the last country. The Company may terminate the Takeda License upon six months’ prior written notice. The Company and Takeda may terminate the Takeda License in the case of the other party’s insolvency, or upon prior written notice within a specified time period for the other party’s material uncured breach. Takeda may terminate the Takeda License if the Company challenges licensed patents, or assists any third-party in challenging such patents. The acquisition of the Takeda License has been accounted for as an asset acquisition as substantially all of the fair value is concentrated in a group of similar assets. In March 2022, the Company paid Takeda an aggregate $ 2.5 million contingent payment upon the release of certain drug products and the completion of certain regulatory activities, which have no alternative future use, and was recorded as in-process research and development in the Company’s consolidated statement of operations for the year ended December 31, 2022. The Company did no t make any milestone payments to Takeda during the year ended December 31, 2023. Transitional Services Agreement with Takeda As contemplated by the Takeda License, on December 17, 2021, the Company entered into a Transitional Services Agreement (“TSA”) with Takeda under which the Company will be obligated to pay Takeda for certain services, including pass-through costs, related to research and development and regulatory assistance services, oversight and management of ongoing clinical and research studies, and maintenance of third party vendor contracts. The TSA and related activities are considered related party transactions. Unless earlier terminated under its terms, the TSA will remain in effect until all transitional services are completed. The Company may terminate the provision of any or all services under the TSA upon certain written notice. The Company and Takeda may terminate the TSA in the case of the other party’s insolvency, or upon prior written notice within a specified time period for the other party’s material uncured breach. Takeda may terminate the TSA for non-payment and, in certain circumstances, upon a change of control of the Company. Contingencies In the event the Company becomes subject to claims or suits arising in the ordinary course of business, the Company would accrue a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated.

Convertible Promissory Notes an

Convertible Promissory Notes and Long-Term Debt	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Convertible Promissory Notes and Long-Term Debt	9. Convertible Promissory Notes and Long-Term Debt Frazier Convertible Note Financings During 2019, 2020 and 2021, the Company issued the Frazier Notes for an aggregate of $ 8.5 million bearing interest at per annum rates ranging from 0.12 % to 2.52 %. An aggregate of $ 0.9 million of the Frazier Notes were issued in April, May and September of 2019 (the “2019 Frazier Notes”), an aggregate of $ 1.3 million of the Frazier Notes were issued in March, August and October of 2020 (the “2020 Frazier Notes”) and an aggregate of $ 6.3 million of Frazier Notes were issued from April to July 2021 (the “2021 Frazier Notes”). The Frazier Notes were generally scheduled to mature 12 to 18 months from the date of issuance. The Company recorded changes in the fair value of the Frazier Notes in the consolidated statements of operations. The Frazier Notes were exchanged for convertible promissory notes newly issued in connection with the August 2021 convertible note financing described below. August 2021 Convertible Note Financing On August 31, 2021, the Company entered into a note purchase agreement under which it issued the August 2021 Notes for an aggregate of $ 139.52 million. Of the August 2021 Notes, $ 103.75 million were issued to new investors, $ 25.0 million were issued to Frazier for cash and $ 10.77 million were issued to Frazier in exchange for the then outstanding principal and accrued interest on the Frazier Notes. The August 2021 Notes carried interest at a rate of 6 % per annum, compounded annually . The principal and accrued interest on the August 2021 Notes automatically converted into 10,672,138 shares of the Company's common stock immediately prior to the completion of the IPO. Of these shares, 2,736,234 were issued to Frazier. For the year ended December 31, 2022 , the Company recognized a $ 51.5 million change in fair value of convertible promissory notes and recognized $ 2.8 million of interest expense in connection with convertible promissory notes. Long-Term Debt The Company’s Term Loan consists of the following (in thousands): December 31, Long-term debt $ 25,000 Accumulated PIK interest 635 Total principal (including PIK interest) 25,635 Unamortized debt discount ( 391 ) Long-term debt, net of debt discount $ 25,244 On April 18, 2022, the Company entered into a Loan and Security Agreement (the "Existing Loan Agreement” and, as amended by the First Amendment (as defined below) the "Loan Agreement") with Hercules Capital, Inc., as administrative and collateral agent (in such capacity, "Hercules"), and the lenders from time to time party thereto (the "Lenders"), providing for term loans (“Term Loans”) of up to $ 75.0 million. Prior to June 16, 2023, the Company had borrowed $ 15.0 million in term loans under the Existing Loan Agreement and had the right thereunder to borrow (i) an additional $ 15.0 million of term loans until June 30, 2023 (“Term Loan Tranche 1”), (ii) an additional $ 20.0 million of term loans until June 30, 2023 (“Term Loan Tranche 2”), and (iii) subject to the achievement of certain clinical development milestones by the Company, an additional $ 25.0 million until March 31, 2024 (“Term Loan Tranche 3”). On June 16, 2023, the Company entered into a First Amendment to Loan and Security Agreement (the "First Amendment") with Hercules and the Lenders party thereto, which amended the Existing Loan Agreement. In connection with the First Amendment, the Company borrowed $ 10.0 million under Term Loan Tranche 1. Additionally, the First Amendment, among other things, amended the following: (i) with respect to the remaining $ 5.0 million under Term Loan Tranche 1, modified the period during which the Company may borrow thereunder to start on December 1, 2023 and end May 31, 2024 (or such earlier date if Lenders elect in their sole discretion), (ii) with respect to Term Loan Tranche 2, modified the period during which the Company may borrow thereunder to start on December 1, 2023 and end May 31, 2024 (or such earlier date if Lenders elect in their sole discretion) and (iii) with respect to Term Loan Tranche 3, (a) added as a new condition to borrow thereunder that (x) the Company’s Phase 2b clinical trial evaluating the safety, immunogenicity and efficacy of HIL-214 in infants ("NEST-IN1”) has achieved the protocol-specified primary efficacy endpoint and (y) HIL-214 has demonstrated acceptable safety results in the NEST-IN1 clinical trial, and, as a result, the Company supports the initiation of a Phase 3 registrational trial as the next immediate step in the development of HIL-214 (the “Tranche 3 Milestone”) and (b) modified the period during which the Company may borrow thereunder to start on the date the Company achieves the Tranche 3 Milestone and end on the earlier of (x) June 15, 2024 and (y) 30 days following the date the Company achieves the Tranche 3 Milestone. The First Amendment was accounted for as a debt modification; as such, the financing costs of $ 0.2 million were reflected as additional debt discount and is amortized as an adjustment to interest expense over the term of the First Amendment. On November 9, 2023, the Company entered into a Second Amendment to Loan and Security Agreement (the "Second Amendment") with Hercules and the Lenders party thereto, which amended the Existing Loan Agreement. The Second Amendment amended the following: (i) with respect to the remaining $ 5.0 million under Term Loan Tranche 1, modified the period during which the Company may borrow thereunder to start on January 1, 2024 and end July 19, 2024 (or such earlier date if Lenders elect in their sole discretion), (ii) with respect to Term Loan Tranche 2, modified the period during which the Company may borrow thereunder to start on January 1, 2024 and end July 19, 2024 (or such earlier date if Lenders elect in their sole discretion) and (iii) with respect to Term Loan Tranche 3, modified the period during which the Company may borrow thereunder to end on the earlier of (x) September 15, 2024 and (y) 30 days following the date the Company achieves the Tranche 3 Milestone. The Company did not incur any fees in connection with the Second Amendment. All Term Loans are subject to a minimum draw amount of $ 5.0 million and no event of default under the Loan Agreement having occurred and is continuing. The borrowings under the Loan Agreement are collateralized by substantially all of our assets, including intellectual property and certain other assets. The Term Loans bear (a) cash interest at a floating rate of the higher of (i) the Wall Street Journal prime rate (or 5.00 % if less) plus 1.05 %, or (ii) 4.55 % (interest rate of 6.05 % as of December 31, 2023 ), and (b) additional interest ("PIK Interest") at a per annum rate equal to 2.85 %, with such interest being added to the outstanding principal balance of the Term Loans on a monthly basis. The monthly payments consist of interest-only through June 1, 2025 or, if prior to April 30, 2025, the Company achieves the Tranche 3 Milestone, subject to reasonable verification by Hercules, through June 1, 2026. Subsequent to the interest-only period, the Term Loans will be payable in equal monthly installments of principal, plus accrued and unpaid interest, through the maturity date of May 1, 2027 . In addition, the Company is obligated to pay a final payment fee equal to the greater of (i) $ 2.145 million and (ii) 7.15 % of the original principal amount of the Term Loans (which is $ 2.1 million as of December 31, 2023 ). The final payment fee is recorded as a debt discount amortized over the life of the debt. The Company may elect to prepay all or a portion of the Term Loans prior to maturity, subject to a prepayment fee of up to 1.00 % of the then outstanding principal balance and the pro rata application of such payment to the final payment fee. After repayment, no Term Loan amounts may be borrowed again. The Loan Agreement contains certain customary affirmative and negative covenants and events of default. The affirmative covenants include, among others, covenants requiring the Company to maintain its legal existence and governmental approvals, deliver certain financial reports, maintain insurance coverage and satisfy certain requirements regarding its operating accounts. The negative covenants include, among others, limitations on the Company’s ability to incur additional indebtedness and liens, merge with other companies or consummate certain changes of control, acquire other companies or businesses, make certain investments, pay dividends, transfer or dispose of assets, amend certain material agreements, including the Takeda License, or enter into various specified transactions. Upon the occurrence of an event of default, subject to any specified cure periods, all amounts owed by the Company would begin to bear interest at a rate that is 4.00 % above the rate effective immediately before the event of default and may be declared immediately due and payable by Hercules, as collateral agent. As of December 31, 2023 , the Company had borrowed $ 25.0 million pursuant to the Loan Agreement. During the year ended December 31, 2023, the Company recognized interest expense of $ 2.4 million related to the Term Loans using the effective interest method. Included in such expense was $ 0.5 million, related to accretion of the final payment fee to other long-term liabilities, $ 0.5 million of PIK interest, $ 1.3 million of coupon interest, and an immaterial amount of debt discount amortization. Future minimum principal and interest payments, including the final payment fee, as of December 31, 2023 are as follows (in thousands): December 31, Years ending December 31: 2024 $ 1,599 2025 8,433 2026 13,303 2027 10,645 Total principal payments, interest payments and final payment fee 33,980 Less: interest, PIK interest and final payment fee ( 8,345 ) Long-term debt $ 25,635

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2023
Stockholders' Equity Note [Abstract]
Stockholders' Equity	10. Stockholders’ Equity Initial Public Offering On May 3, 2022, the Company completed its IPO whereby it sold 13,529,750 shares of common stock at a public offering price of $ 17.00 per share, for net proceeds of approximately $ 209.5 million, after deducting underwriting discounts, commissions and offering costs of approximately $ 20.5 million. In connection with the Company's IPO, the Company increased the number of authorized shares of the Company's common stock and preferred stock to 500,000,000 shares and 50,000,000 shares, respectively. At-the-Market-Offering On May 12, 2023 , the Company entered into an At-the-Market Equity Offering Sales Agreement (the "Sales Agreement") with Stifel, Nicolaus & Company, Incorporated (the “Agent”), pursuant to which the Company may offer and sell shares of the Company’s common stock having an aggregate offering price of up to $ 100.0 million from time to time, in “at the market” offerings through the Agent. Sales of the shares of common stock, if any, will be made at prevailing market prices at the time of sale, or as otherwise agreed with the Agent. The Agent will receive a commission from the Company of up to 3.0 % of the gross proceeds of any shares of common stock sold under the Sales Agreement. The Company is not obligated to sell, and the Agent is not obligated to buy or sell, any shares of common stock under the Sales Agreement. As of December 31, 2023, no sales have been made pursuant to the Sales Agreement. Underwritten Public Offering On September 22, 2023, the Company completed an underwritten public offering whereby it sold 9,200,000 shares of common stock, which included the exercise in full by the underwriters of their option to purchase 1,200,000 shares, at a public offering price of $ 12.50 per share for total net proceeds of approximately $ 107.8 million, after underwriting discounts and commissions and estimated offering costs. 2021 Equity Incentive Plan On February 8, 2021, the Company’s board of directors and stockholders approved and adopted the HilleVax, Inc. 2021 Equity Incentive Plan (the “2021 Plan”). The term of the 2021 Plan is ten years from the adoption date. Under the 2021 Plan, the Company may grant stock options, restricted stock, restricted stock units, and other stock-based awards to employees, directors or consultants of the Company and its subsidiaries. The stock options granted under the plan generally vest over a four-year period from the vesting commencement date. Upon the effectiveness of the 2022 Plan defined and described below, no further grants will be made under the 2021 Plan, and any outstanding awards granted under the 2021 Plan will remain subject to the terms of the 2021 Plan and applicable award agreements. 2022 Incentive Award Plan In April 2022, the Company’s board of directors and stockholders approved the 2022 Incentive Award Plan (the “2022 Plan,” and together with the 2021 Plan, the "Plans") under which the Company may grant stock options, restricted stock, dividend equivalents, restricted stock units, stock appreciation rights, and other stock or cash-based awards to its employees, consultants and directors. The 2022 Plan became effective in connection with the Company’s IPO and will remain in effect until the tenth anniversary of its effective date, which will be April 28, 2032, unless earlier terminated by the Company’s board of directors. The number of shares of the Company's common stock initially available for issuance under awards granted pursuant to the 2022 Plan was the sum of (1) 4,900,000 shares of the Company’s common stock, plus (2) 216,849 shares remaining available for issuance under the 2021 Plan as of the effective date of the 2022 Plan, plus (3) any shares subject to outstanding awards under the 2021 Plan as of the effective date of the 2022 Plan that become available for issuance under the 2022 Plan thereafter in accordance with its terms. The number of shares initially available for issuance will be increased by an annual increase on January 1 of each calendar year ending in and including 2032 , equal to the lesser of (1) 5 % of the shares of common stock outstanding on the final day of the immediately preceding calendar year and (2) such smaller number of shares as determined by the Company’s board of directors. As of December 31, 2023, 7,197,502 shares were reserved for issuance under the 2022 Plan, of which 3,576,043 shares remained available for future issuance. 2022 Employee Stock Purchase Plan In April 2022, the Company’s board of directors and stockholders approved the 2022 Employee Stock Purchase Plan (the “2022 ESPP”). The 2022 ESPP became effective in connection with the Company’s IPO. The 2022 ESPP permits eligible employees who elect to participate in an offering under the ESPP to have up to a specified percentage of their eligible earnings withheld, subject to certain limitations, to purchase shares of common stock pursuant to the 2022 ESPP. The price of common stock purchased under the 2022 ESPP is equal to 85 % of the lower of the fair market value of the common stock on the first trading day of the offering period or the relevant purchase date. A total of 410,000 shares of the Company’s common stock was initially reserved for issuance under the 2022 ESPP. In addition, the number of shares available for issuance under the 2022 ESPP will be annually increased on January 1 of each calendar year ending in and including 2032 , by an amount equal to the lesser of (1) 1 % of the shares outstanding on the final day of the immediately preceding calendar year and (2) such smaller number of shares as is determined by the Company’s board of directors, provided that no more than 10,000,000 shares of the Company’s common stock may be issued under the 2022 ESPP. A summary of the Company’s stock option activity under the Plans is as follows (in thousands, except share and per share data): Number of Weighted Weighted Aggregate Balance at December 31, 2022 2,111,989 $ 10.62 9.33 $ 13,330 Granted 2,035,225 16.88 Exercised ( 84,554 ) 7.27 Cancelled ( 166,599 ) 11.98 Balance at December 31, 2023 3,896,061 $ 13.89 8.82 $ 11,826 Vested and expected to vest at December 31, 2023 3,896,061 $ 13.89 8.82 $ 11,826 Exercisable at December 31, 2023 884,268 $ 10.35 8.32 $ 5,219 Stock-Based Compensation Expense The fair value of common stock is based on the closing price as reported on the date of grant on the primary stock exchange on which the Company's common stock is traded. The assumptions used in the Black-Scholes option pricing model to determine the fair value of stock option grants were as follows: Year Ended 2023 2022 Risk-free interest rate 3.5 %– 4.9 % 1.9 %– 4.2 % Expected volatility 91.7 %– 95.9 % 83.4 %– 94.3 % Expected term (in years) 5.5 – 6.1 5.3 – 6.1 Expected dividend yield 0 % 0 % Risk-free interest rate . The risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant for zero coupon U.S. Treasury notes with maturities similar to the expected term of the awards. Expected volatility . Given the Company's limited historical stock price volatility data, the expected volatility assumption is based on volatilities of a peer group of similar companies whose share prices are publicly available. The peer group was developed based on companies in the biotechnology industry. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Expected term . The expected term represents the period of time that options are expected to be outstanding. Because the Company does not have historical exercise behavior, it determines the expected life assumption using the simplified method, for employees, which is an average of the contractual term of the option and its vesting period. Expected dividend yield . The Company bases the expected dividend yield assumption on the fact that it has never paid cash dividends and has no present intention to pay cash dividends and, therefore, used an expected dividend yield of zero . Stock-based compensation expense has been reported in the consolidated statements of operations as follows (in thousands): Year Ended 2023 2022 Research and development $ 6,582 $ 1,720 General and administrative 7,008 1,283 Total $ 13,590 $ 3,003 The weighted average grant date fair value per share of option grants for the years ended December 31, 2023 and 2022 was $ 13.03 and $ 4.88 , respectively. As of December 31, 2023, total unrecognized stock-based compensation cost related to stock options was approximately $ 28.9 million, which is expected to be recognized over a remaining weighted-average period of approximately 2.7 years. A summary of the Company’s unvested shares is as follows: Number of Weighted Average Grant-Date Fair Value Balance at December 31, 2022 1,584,709 $ 0.001 Shares granted 759,266 18.000 Shares forfeited ( 88,849 ) 0.001 Share vested ( 683,410 ) 0.001 Balance at December 31, 2023 1,571,716 — The Company issued shares of restricted common stock during the year ended December 31, 2023 , which consisted only of restricted stock units. The Company did no t issue any shares of restricted common stock during the year ended December 31, 2022. The weighted average grant date fair value per share of restricted common stock grants for the year ended December 31, 2023 was $ 18.00 . As of December 31, 2023, total unrecognized stock-based compensation cost related to restricted stock was approximately $ 10.3 million, which is expected to be recognized over a remaining weighted-average period of approximately 3.1 years. For accounting purposes, unvested shares of restricted common stock are not considered outstanding until they vest. As of December 31, 2023 and 2022, the Company had no material repurchase liability related to the unvested shares in the table above. Common Stock Reserved for Future Issuance Common stock reserved for future issuance consists of the following: December 31, Common stock options outstanding 3,896,061 Shares available for issuance under the Plans 3,576,043 Shares available for issuance under the ESPP 732,137 8,204,241

Pension and Other Postretiremen

Pension and Other Postretirement Benefit Plans	12 Months Ended
	Dec. 31, 2023
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefit Plans	11. Pension and Other Postretirement Benefit Plans 401(k) Plan The Company established a defined-contribution plan under Section 401(k) of the Internal Revenue Code (the 401(k) Plan). The 401(k) Plan covers all eligible employees who meet defined minimum age and service requirements and allows participants to defer a portion of their annual compensation on a pre-tax basis. Beginning November 2022, the Company made matching contributions equal to 100 % of the employee’s contributions, subject to a maximum of 4 % of eligible compensation. The Company made matching contributions of $ 0.6 million during the year ended December 31, 2023. The matching contributions for the year ended December 31, 2022 were not material. Pension Plan The Company sponsors a defined benefit pension plan covering eligible employees in Switzerland. Under the defined benefit pension plan, the Company and certain of its employees with annual earnings in excess of government determined amounts are required to make contributions into a fund managed by an independent investment fiduciary. Employer contributions must be in an amount at least equal to the employee’s contribution. Under U.S. GAAP, the Company is required to recognize the overfunded or underfunded status of a defined benefit pension and other postretirement plan as an asset or liability in its consolidated balance sheets and to recognize changes in that funded status in the year in which the changes occur through the changes in the pension and other postemployment benefits line on the consolidated statements of operations and comprehensive loss. The Company is also required to measure the funded status of a plan as of the date of its fiscal year-end for which consolidated financial statements are presented. The following table sets forth the projected benefit obligation, fair value of plan assets, and the funded status of the Company’s plan as of December 31, 2023 and 2022 (in thousands): December 31, 2023 2022 Change in benefit obligation Benefit obligation at beginning of year $ 2,051 $ 1,017 Prior service cost 47 — Service cost 246 120 Interest cost 60 6 Contributions paid by plan participants 169 92 Benefits deposited 1,692 692 Actuarial loss 598 114 Exchange rate adjustments 393 10 Benefit obligation at end of year 5,256 2,051 Fair value of plan assets at end of year 4,414 1,739 Funded status - deficit $ ( 842 ) $ ( 312 ) The accumulated benefit obligation as of December 31, 2023 and 2022 was $ 5.1 million and $ 2.0 million respectively. The components of net periodic benefit cost recognized in operating expense in the consolidated statements of operations and comprehensive loss and other amounts recognized in adjustment to pension liability in the consolidated statements of operations and comprehensive loss for the year ended December 31, 2023 and 2022 were as follows (in thousands): December 31, 2023 2022 Service cost $ 246 $ 120 Interest cost 60 6 Expected return on plan assets ( 72 ) ( 33 ) Amortization of net loss 7 — Total recognized in operating expense 241 93 Adjustment to pension liability 620 281 Total recognized other comprehensive loss 620 281 Total costs recognized in consolidated comprehensive loss $ 861 $ 374 The weighted average actuarial assumptions used to determine net periodic benefit cost for the years ended December 31, 2023 and 2022 were as follows: December 31, 2023 2022 Discount rate 1.5 % 1.9 % Inflation rate 1.0 % 1.0 % Expected rate of return on plan assets 3.0 % 2.5 % Rate of compensation increase 1.0 % 1.0 % The demographic assumptions, including mortality and disability rates, used to determine the net periodic benefit costs for the years ended December 31, 2023 and 2022 were based on the LPP/BVG 2020 tables. As of December 31, 2023, the pension plan benefits expected to be paid over the next ten years are as follows (in thousands): December 31, Years ending December 31: 2024 $ 5 2025 10 2026 14 2027 19 2028 24 2029-2033 200 Total expected benefits to be paid $ 272 The Company made contributions to the pension plan of approximately $ 0.4 million and $ 0.2 million during the year ended December 31, 2023 and 2022 , respectively. The Company anticipates making contributions at similar levels during the next fiscal year.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes A reconciliation between the provision for income taxes and income taxes computed using the U.S. federal statutory corporate tax rate is as follows (in thousands): Year Ended 2023 2022 Tax computed at federal statutory rate $ ( 25,927 ) $ ( 33,588 ) State income taxes ( 1,291 ) ( 1,366 ) Change in fair value of warrant liabilities — 9,249 Convertible debt — 11,396 Permanent differences and other 997 ( 354 ) Research and development credits ( 2,838 ) — Effect of rate change on deferred tax assets and liabilities 1,455 — Change in valuation allowance 27,604 14,734 Other — ( 71 ) Provision for income taxes $ — $ — Significant components of the Company’s deferred tax assets are as follows (in thousands): December 31, 2023 2022 Deferred tax assets: Intangible assets $ 7,315 $ 8,406 Net operating loss carryforwards 10,323 6,950 Start up and organization costs 596 685 Capitalized research cost 27,564 9,337 Lease liability 5,654 4,979 Share based compensation 2,166 — Tax credit carryforwards 3,577 — Other, net 1,236 1,030 Total deferred tax assets 58,431 31,387 Valuation allowance ( 54,491 ) ( 26,930 ) Deferred tax assets, net of allowance $ 3,940 $ 4,457 Deferred tax liabilities: Right-of-use asset $ ( 3,940 ) $ ( 4,457 ) Total deferred tax liabilities ( 3,940 ) ( 4,457 ) Net deferred tax assets $ — $ — The Company has established a valuation allowance against its deferred tax assets due to the uncertainty surrounding the realization of such assets. The Company periodically evaluates the recoverability of the deferred tax assets. At such time as it is determined that it is more likely than not that deferred tax assets are realizable, the valuation allowance will be reduced. The Company has recorded a full valuation allowance of $ 54.5 million as of December 31, 2023 as it cannot conclude that it is more likely than not that the deferred tax assets will be realized primarily due to the generation of pre-tax book losses from its inception. As of December 31, 2023, the Company has federal and state net operating loss carryforwards of approximately $ 47.8 million and $ 36.5 million, respectively. As a result of the Tax Cuts and Jobs Act of 2017, for U.S. federal income tax purposes, net operating losses generated after December 31, 2017 can be carried forward indefinitely, but are limited to 80 % utilization against future taxable income each year. The state net operating loss carryforwards begin to expire in 2041 . Pursuant to Internal Revenue Code Sections 382 and 383, annual use of the Company’s net operating loss may be limited in the event a cumulative change in ownership of more than 50 % occurs within a three-year period. The Company has not completed an ownership change analysis pursuant to IRS Section 382. If ownership changes have occurred or occur in the future, the amount of remaining tax attribute carryforwards available to offset taxable income and income tax expense in future years may be restricted or eliminated. If eliminated, the related asset would be removed from deferred tax assets with a corresponding reduction in the valuation allowance. The Company recognizes liabilities for uncertain tax positions based on a two-step process. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained on audit, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount that is more than 50% likely of being realized upon settlement. While the Company believes that it has appropriate support for the positions taken on its tax returns, the Company regularly assesses the potential outcome of examinations by tax authorities in determining the adequacy of its provision for income taxes. The following table summarizes the activity related to the Company's gross unrecognized tax benefits (in thousands): Year Ended 2023 2022 Beginning Balance $ — $ — Increases (decreases) related to prior year tax positions 177 — Increases related to current year tax positions 782 — Ending Balance $ 959 $ — As of December 31, 2023, the Company has gross unrecognized tax benefits of $ 959,000 , none of which would affect the effective tax rate due to a full valuation allowance. The Company does not anticipate any significant changes in its unrecognized tax benefits over the next twelve months. The Company's policy is to recognize the interest expense and/or penalties related to income tax matters as a component of income tax expense. The Company has no accrual for interest or penalties on its balance sheet at December 31, 2023, and has not recognized interest and/or penalties in its statement of operations for the year ended December 31, 2023. The Company is subject to taxation in the United States, Switzerland, and various states. The Company is not currently under examination by any taxing authorities. Due to the carryover of tax attributes, the statute of limitations is currently open for tax years since inception. The Company’s policy is to recognize interest and penalties related to income tax matters as a component of income tax expense. The Company has not recognized interest or penalties in its consolidated statements of operations since inception.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	13. Subsequent Events License Agreement On January 8, 2024, the Company entered into an exclusive license agreement with Chengdu Kanghua Biological Products Co., Ltd. ("Kangh"), for rights to Kangh’s hexavalent virus-like particle vaccine candidate for norovirus (the "Kangh License"), referred to by the Company as HIL-216, outside of Greater China. In consideration of the Kangh License, the Company will pay an upfront amount of $ 15.0 million with the potential for additional payments of up to $ 255.5 million upon achieving certain development and sales milestones. Kangh is also eligible to receive a single-digit tiered royalty on net sales outside of Greater China. At-the-Market-Offering The Company sold 1,016,950 shares of its common stock under its Sales Agreement for its at-the-market offering program subsequent to December 31, 2023 through March 20, 2024 for aggregate gross cash proceeds of $ 15.0 million, before deducting commission fees and offering expenses payable by the Company.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Forward Stock Split	Forward Stock Split On April 22, 2022, the Company effected a 1.681 -for-1 forward split of shares of the Company’s common stock (the “Forward Stock Split”). The par value of the common stock was not adjusted as a result of the Forward Stock Split and the authorized shares were increased to 50,000,000 shares of common stock in connection with the Forward Stock Split. The accompanying financial statements and notes to the financial statements give retroactive effect to the Forward Stock Split for all periods presented, unless otherwise indicated.
Liquidity and Capital Resources	Liquidity and Capital Resources From inception to December 31, 2023, the Company has devoted substantially all of its efforts to organizing and staffing the Company, business planning, raising capital, in-licensing its initial vaccine candidate, HIL-214, preparing for and managing its clinical trials of HIL-214, and providing other general and administrative support for these operations. The Company has a limited operating history, has never generated any revenue, and the sales and income potential of its business is unproven. The Company has incurred net losses and negative cash flows from operating activities since its inception and expects to continue to incur net losses into the foreseeable future as it continues the development and potential commercialization of HIL-214. From inception to December 31, 2023 , the Company has funded its operations through the issuance of convertible promissory notes, commercial bank debt, the sale of 13,529,750 shares of common stock for net proceeds of approximately $ 209.5 million in its initial public offering ("IPO") which closed in May 2022, and the sale of 9,200,000 shares of common stock for net proceeds of approximately $ 107.8 million in its underwritten public offering which closed in September 2023 (see Note 10). The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern. Management is required to perform a two-step analysis over the Company’s ability to continue as a going concern. Management must first evaluate whether there are conditions and events that raise substantial doubt about the Company’s ability to continue as a going concern (Step 1). If management concludes that substantial doubt is raised, management is also required to consider whether its plans alleviate that doubt (Step 2). Management believes that it has sufficient working capital on hand to fund operations through at least the next twelve months from the date these financial statements were issued. There can be no assurance that the Company will be successful in acquiring additional funding, if needed, that the Company’s projections of its future working capital needs will prove accurate, or that any additional funding would be sufficient to continue operations in future years.
Basis of Presentation	Basis of Presentation The Company's financial statements include the accounts of HilleVax Security Corporation, a wholly-owned subsidiary formed in Massachusetts, and HilleVax GmbH, a wholly-owned subsidiary formed in Zurich, Switzerland. The functional currency of the Company, HilleVax Security Corporation and HilleVax GmbH is the U.S. dollar. The Company’s assets and liabilities that are not denominated in the functional currency are remeasured into U.S. dollars at foreign currency exchange rates in effect at the balance sheet date except for nonmonetary assets, which are remeasured at historical foreign currency exchange rates in effect at the date of transaction. Net realized and unrealized gains and losses from foreign currency transactions and remeasurement are reported in other income (expense), in the consolidated statements of operations and were not material for the periods presented. All intercompany transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The Company’s consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to accruals for research and development expenses, and prior to the Company's IPO, the valuation of convertible promissory notes, warrant liabilities and various other equity instruments. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results could differ materially from those estimates and assumptions.
Fair Value Option	Fair Value Option As permitted under Accounting Standards Codification (“ASC”) 825, Financial Instruments , (“ASC 825”), the Company has elected the fair value option to account for its convertible promissory notes issued through May 2022, when the convertible promissory notes converted into equity in connection with the Company's IPO. In accordance with ASC 825, the Company recorded these convertible promissory notes at fair value with changes in fair value recorded in the consolidated statements of operations. As a result of applying the fair value option, direct costs and fees related to the convertible promissory notes were recognized in the statement of operations as incurred and not deferred.
Fair Value Measurements	Fair Value Measurements The accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or non-recurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets. Level 2: Inputs, other than the quoted prices in active markets that are observable either directly or indirectly. Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less when purchased to be cash equivalents. Cash and cash equivalents include cash in readily available checking accounts and money market funds.
Restricted Cash	Restricted Cash Restricted cash consists of a money market account securing a standby letter of credit issued in connection with the Company’s Boston Lease (as defined and described in Note 6).
Marketable Securities	Marketable Securities Marketable securities represent holdings of available-for-sale marketable debt securities in accordance with the Company’s investment policy. The Company has classified its investments with maturities beyond one year as current, based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. Investments in marketable securities are recorded at fair value, with any unrealized gains and losses reported within accumulated other comprehensive income (loss) as a separate component of stockholders’ equity (deficit) until realized, a determination is made that an other-than-temporary decline in market value has occurred or until the security has experienced a credit loss. The amortized cost of debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization and accretion, together with interest on securities sold, is determined based on the specific identification method and any realized gains or losses on the sale of investments are reflected as a component of other income (expense).
Concentrations of Credit Risk	Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities, and restricted cash. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are stated at cost and depreciated on a straight-line basis over the estimated useful life of the related assets as follows: Estimated Useful Life Computer equipment 3 years Lab equipment 5 years Furniture and fixtures 5 years Leasehold improvements 3 – 10 years or term of lease Repairs and maintenance costs are charged to expense as incurred.
Leases	Leases At the inception of a contractual arrangement, the Company determines whether the contract contains a lease by assessing whether there is an identified asset and whether the contract conveys the right to control the use of the identified asset in exchange for consideration over a period of time. Lease terms are determined at the commencement date by considering whether renewal options and termination options are reasonably assured of exercise. For its long-term operating leases, the Company recognizes a lease liability and a right-of-use (“ROU”) asset on its balance sheet and recognizes lease expense on a straight-line basis over the lease term. The lease liability is determined as the present value of future lease payments, reduced by any reimbursements for tenant improvements, using the discount rate implicit in the lease or, if the implicit rate is not readily determinable, an estimate of the Company’s incremental borrowing rate. The ROU asset is based on the lease liability, adjusted for any prepaid or deferred rent, and reduced by any reimbursements for tenant improvements. The Company aggregates all lease and non-lease components for each class of underlying assets into a single lease component and variable charges for common area maintenance and other variable costs are recognized as expense as incurred. The Company has elected to not recognize a lease liability or ROU asset in connection with short-term operating leases and recognizes lease expense for short-term operating leases on a straight-line basis over the lease term. The Company does not have any financing leases.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, such as property and equipment, for impairment whenever events or changes in circumstances indicate the carrying amount of an asset may not be recoverable. Recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset to the future undiscounted net cash flows expected to be generated by the asset. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds the fair value of the assets. Fair value would be assessed using discounted cash flows or other appropriate measures of fair value. The Company has not recognized any impairment losses through December 31, 2023 .
Research and Development Expenses and Accruals	Research and Development Expenses and Accruals All research and development costs are expensed in the period incurred and consist primarily of salaries, payroll taxes, employee benefits, stock-based compensation charges for those individuals involved in research and development efforts, external research and development costs incurred under agreements with contract research organizations and consultants to conduct and support the Company’s clinical trials of HIL-214. The Company has entered into various research and development contracts with clinical research organizations, clinical manufacturing organizations and other companies. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and payments made in advance of performance are reflected in the accompanying balance sheets as prepaid expenses. The Company records accruals for estimated costs incurred for ongoing research and development activities. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the services, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the prepaid or accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates.
In-Process Research and Development	In-Process Research and Development The Company evaluates whether acquired intangible assets are a business under applicable accounting standards. Additionally, the Company evaluates whether the acquired assets have a future alternative use. Intangible assets that do not have future alternative use are considered acquired in-process research and development. When the acquired in-process research and development assets are not part of a business combination, the value of the consideration paid is expensed on the acquisition date.
Patent Costs	Patent Costs Costs related to filing and pursuing patent applications are recorded as general and administrative expenses and expensed as incurred since recoverability of such expenditures is uncertain.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense represents the cost of the grant date fair value of equity awards, primarily consisting of stock options, restricted common stock, and employee stock purchase rights, recognized on a straight-line basis over the requisite service period for stock options and restricted common stock, and over the respective offering period for employee stock purchase plan rights. The Company recognizes forfeitures as they occur.
Benefit plans	Benefit plans The Company has established a defined contribution savings plan for its employees in the United States under Section 401(k) of the Internal Revenue Code, and a defined benefits plan for its employees outside of the United States. The defined benefits plan is valued by an independent actuary using the projected unit credit method. The liabilities correspond to the projected benefit obligations of which the discounted net present value is calculated based on years of employment, expected salary increase, and pension adjustments. The Company reviews its actuarial assumptions on an annual basis and makes modifications to the assumptions based on current rates and trends. This plan is recognized under ASC 715, Compensation - Retirement Benefits .
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the consolidated statements of operations in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (i) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (ii) for those tax positions that meet the more-likely-than-not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense in the consolidated statements of operations. Any accrued interest and penalties are included within the related tax liability in the consolidated balance sheets. The Company did not recognize any interest or penalties during the periods presented.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. For the years ended December 31, 2023 and December 31, 2022 , comprehensive loss included losses on the Company's pension benefit obligation and unrealized losses on marketable securities.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker in making decisions on how to allocate resources and assess performance. The Company views its operations and manages its business as one operating segment.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the consolidated net loss by the weighted-average number of common shares outstanding for the period, without consideration for potentially dilutive securities. The Company has excluded weighted-average unvested shares of 1,232,828 shares and 2,080,038 shares from the basic weighted-average number of common shares outstanding for the years ended December 31, 2023 and 2022, respectively. Diluted net loss per share is computed by dividing the consolidated net loss by the weighted-average number of common shares and dilutive common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Potentially dilutive common stock equivalents are comprised of unvested common stock, common stock options, and contingently issuable shares under the Company's employee stock purchase plan. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as inclusion of the potentially dilutive common stock equivalents would be antidilutive. Potentially dilutive securities not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows (in common stock equivalent shares): December 31, 2023 2022 Common stock options 3,896,061 2,111,989 Unvested common stock 1,571,716 1,584,709 ESPP shares 8,473 4,420 Total potentially dilutive shares 5,476,250 3,701,118
Emerging Growth Company Status	Emerging Growth Company Status The Company is an emerging growth company, as defined in the Jumpstart Our Business Startups Act of 2012 (“JOBS Act”). Under the JOBS Act, emerging growth companies can delay adopting new or revised accounting standards issued subsequent to the enactment of the JOBS Act until such time as those standards apply to private companies. The Company has irrevocably elected to avail itself of this exemption from new or revised accounting standards and, therefore, will not be subject to the same new or revised accounting standards as other public companies that are not emerging growth companies.
Recently Adopted/Issued Accounting Standards/Pronouncements	Recently Adopted Accounting Standards In June 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2016-13, Financial Instruments – Credit Losses (Topic 326), to provide financial statement users with more decision-useful information about the expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. To achieve this objective, the amendments in Topic 326 replace the incurred loss impairment methodology in current U.S. GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. We adopted Topic 326 on January 1, 2023 . The adoption did no t have a material impact on our consolidated financial statements’. Recently Issued Accounting Pronouncements In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280) . The amendments in this update expand segment disclosure requirements, including new segment disclosure requirements for entities with a single reportable segment among other disclosure requirements. This update is effective for fiscal years beginning after December 15, 2023, and interim periods within fiscal years beginning after December 15, 2024. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740) . The amendments in this update expand income tax disclosure requirements, including additional information pertaining to the rate reconciliation, income taxes paid, and other disclosures. This update is effective for annual periods beginning after December 15, 2024. The adoption of this standard is not expected to have a material impact on the Company’s consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Schedule of Estimated Useful Life of the Related assets	Property and equipment are stated at cost and depreciated on a straight-line basis over the estimated useful life of the related assets as follows: Estimated Useful Life Computer equipment 3 years Lab equipment 5 years Furniture and fixtures 5 years Leasehold improvements 3 – 10 years or term of lease
Schedule of Potentially Dilutive Securities Not Included in the Calculation of Diluted Net Loss Per Share	Potentially dilutive securities not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows (in common stock equivalent shares): December 31, 2023 2022 Common stock options 3,896,061 2,111,989 Unvested common stock 1,571,716 1,584,709 ESPP shares 8,473 4,420 Total potentially dilutive shares 5,476,250 3,701,118

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on Recurring Basis	The following tables present the Company's fair value hierarchy for its assets that are measured at fair value on a recurring basis and indicate the level within the fair value hierarchy of the valuation techniques the Company utilized to determine such fair value (in thousands): Fair Value Measurements at Total Quoted Prices in Significant Significant Cash equivalents Money market funds $ 209,659 $ 209,659 $ — $ — Marketable securities: U.S. treasury notes 43,050 43,050 — — U.S government agency bonds 43,755 — 43,755 — Total $ 296,464 $ 252,709 $ 43,755 $ — Fair Value Measurements at Total Quoted Prices in Significant Significant Cash equivalents Money market funds $ 277,043 $ 277,043 $ — $ — Total $ 277,043 $ 277,043 $ — $ —

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2023
Investments, Debt and Equity Securities [Abstract]
Schedule of Fair Value of Available-For-Sale Marketable Debt Securities	As of December 31, 2023, the fair value of available-for-sale marketable debt securities by type of security was as follows (in thousands): December 31, 2023 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Marketable securities: U.S. treasury notes $ 43,036 $ 16 $ ( 2 ) $ 43,050 U.S. government agency bonds 43,775 4 ( 24 ) 43,755 Total $ 86,811 $ 20 $ ( 26 ) $ 86,805

Other Balance Sheet Details (Ta

Other Balance Sheet Details (Tables)	12 Months Ended
	Dec. 31, 2023
Balance Sheet Related Disclosures [Abstract]
Property and Equipment	Property and equipment, net consisted of the following (in thousands): December 31, 2023 2022 Computer equipment $ 103 $ - Furniture and equipment 377 11 Leasehold improvements 11,964 378 Lab equipment 2,116 — Construction in progress 338 5,198 Total property and equipment, at cost 14,898 5,587 Less accumulated depreciation 880 1 Property and equipment, net $ 14,018 $ 5,586
Accrued Expenses	Accrued expenses consisted of the following (in thousands): December 31, 2023 2022 Accrued external research and development costs $ 12,665 $ 3,510 Accrued payroll and payroll-related costs 5,233 4,018 Accrued professional costs 498 307 Other 157 375 Total accrued expenses $ 18,553 $ 8,210
Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash recorded within the accompanying consolidated balance sheets that sum to the amounts shown in the consolidated statements of cash flows (in thousands): December 31, 2023 2022 Cash and cash equivalents $ 216,678 $ 279,401 Restricted cash 1,631 1,631 Total cash, cash equivalents and restricted cash $ 218,309 $ 281,032

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2023
Leases [Abstract]
Schedule of Operating Lease Expense	The following table summarizes operating lease expense for the year ended December 31, 2023 (in thousands): Year Ended 2023 2022 Lease expense: Operating lease expense $ 3,115 $ 2,351
Schedule of Weighted Average Lease Term and Discount Rate for Operating Lease	The following table summarizes the lease term and discount rate for operating leases: December 31, 2023 2022 Other information: Weighted-average remaining lease term 9.00 9.96 Weighted-average discount rate 7.4 % 7.4 %
Summary of Cash Paid for Amounts Included in Measurement of Lease Liabilities	The following table summarizes the cash paid for amounts included in the measurement of lease liabilities (in thousands): December 31, Cash paid for amounts included in the measurement of operating lease liabilities (operating cash flows) $ 3,487
Schedule of Future Minimum Noncancelable Operating Lease Payments	At December 31, 2023, the future minimum noncancelable operating lease payments were as follows (in thousands): December 31, Years ending December 31: 2024 3,589 2025 3,692 2026 3,787 2027 3,860 2028 3,974 Thereafter 17,101 Total undiscounted operating lease payments 36,003 Present value adjustment ( 9,703 ) Tenant improvement reimbursements ( 351 ) Operating lease liability 25,949 Less current portion of operating lease liability 3,118 Operating lease liability, net of current portion $ 22,831

Convertible Promissory Notes _2

Convertible Promissory Notes and Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2023
Debt Disclosure [Abstract]
Schedule of Term Loan	The Company’s Term Loan consists of the following (in thousands): December 31, Long-term debt $ 25,000 Accumulated PIK interest 635 Total principal (including PIK interest) 25,635 Unamortized debt discount ( 391 ) Long-term debt, net of debt discount $ 25,244
Schedule of Future Minimum Principal and Interest Payments	Future minimum principal and interest payments, including the final payment fee, as of December 31, 2023 are as follows (in thousands): December 31, Years ending December 31: 2024 $ 1,599 2025 8,433 2026 13,303 2027 10,645 Total principal payments, interest payments and final payment fee 33,980 Less: interest, PIK interest and final payment fee ( 8,345 ) Long-term debt $ 25,635

Stockholder's Equity (Tables)

Stockholder's Equity (Tables)	12 Months Ended
	Dec. 31, 2023
Stockholders' Equity Note [Abstract]
Summary of Stock Option Activity	A summary of the Company’s stock option activity under the Plans is as follows (in thousands, except share and per share data): Number of Weighted Weighted Aggregate Balance at December 31, 2022 2,111,989 $ 10.62 9.33 $ 13,330 Granted 2,035,225 16.88 Exercised ( 84,554 ) 7.27 Cancelled ( 166,599 ) 11.98 Balance at December 31, 2023 3,896,061 $ 13.89 8.82 $ 11,826 Vested and expected to vest at December 31, 2023 3,896,061 $ 13.89 8.82 $ 11,826 Exercisable at December 31, 2023 884,268 $ 10.35 8.32 $ 5,219
Summary of Assumptions used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option Grants	The assumptions used in the Black-Scholes option pricing model to determine the fair value of stock option grants were as follows: Year Ended 2023 2022 Risk-free interest rate 3.5 %– 4.9 % 1.9 %– 4.2 % Expected volatility 91.7 %– 95.9 % 83.4 %– 94.3 % Expected term (in years) 5.5 – 6.1 5.3 – 6.1 Expected dividend yield 0 % 0 %
Schedule of Stock-based Compensation Expense	Stock-based compensation expense has been reported in the consolidated statements of operations as follows (in thousands): Year Ended 2023 2022 Research and development $ 6,582 $ 1,720 General and administrative 7,008 1,283 Total $ 13,590 $ 3,003
Summary of Unvested Shares	A summary of the Company’s unvested shares is as follows: Number of Weighted Average Grant-Date Fair Value Balance at December 31, 2022 1,584,709 $ 0.001 Shares granted 759,266 18.000 Shares forfeited ( 88,849 ) 0.001 Share vested ( 683,410 ) 0.001 Balance at December 31, 2023 1,571,716 —
Schedule of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance consists of the following: December 31, Common stock options outstanding 3,896,061 Shares available for issuance under the Plans 3,576,043 Shares available for issuance under the ESPP 732,137 8,204,241

Pension and Other Postretirem_2

Pension and Other Postretirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2023
Retirement Benefits [Abstract]
Schedule of the Projected Benefit Obligation, Fair Value of Plan Assets, and the Funded Status	The following table sets forth the projected benefit obligation, fair value of plan assets, and the funded status of the Company’s plan as of December 31, 2023 and 2022 (in thousands): December 31, 2023 2022 Change in benefit obligation Benefit obligation at beginning of year $ 2,051 $ 1,017 Prior service cost 47 — Service cost 246 120 Interest cost 60 6 Contributions paid by plan participants 169 92 Benefits deposited 1,692 692 Actuarial loss 598 114 Exchange rate adjustments 393 10 Benefit obligation at end of year 5,256 2,051 Fair value of plan assets at end of year 4,414 1,739 Funded status - deficit $ ( 842 ) $ ( 312 )
Summary of Components of Net Periodic Benefit Cost	The components of net periodic benefit cost recognized in operating expense in the consolidated statements of operations and comprehensive loss and other amounts recognized in adjustment to pension liability in the consolidated statements of operations and comprehensive loss for the year ended December 31, 2023 and 2022 were as follows (in thousands): December 31, 2023 2022 Service cost $ 246 $ 120 Interest cost 60 6 Expected return on plan assets ( 72 ) ( 33 ) Amortization of net loss 7 — Total recognized in operating expense 241 93 Adjustment to pension liability 620 281 Total recognized other comprehensive loss 620 281 Total costs recognized in consolidated comprehensive loss $ 861 $ 374
Schedule of Weighted Average Actuarial Assumptions used to Determine Net Periodic Benefit Cost	The weighted average actuarial assumptions used to determine net periodic benefit cost for the years ended December 31, 2023 and 2022 were as follows: December 31, 2023 2022 Discount rate 1.5 % 1.9 % Inflation rate 1.0 % 1.0 % Expected rate of return on plan assets 3.0 % 2.5 % Rate of compensation increase 1.0 % 1.0 %
Schedule of Pension Plan Benefits Expected to be Paid	As of December 31, 2023, the pension plan benefits expected to be paid over the next ten years are as follows (in thousands): December 31, Years ending December 31: 2024 $ 5 2025 10 2026 14 2027 19 2028 24 2029-2033 200 Total expected benefits to be paid $ 272

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Schedule of Provision for Income Taxes and Income Taxes U.S. Federal Statutory Corporate Tax Rate	A reconciliation between the provision for income taxes and income taxes computed using the U.S. federal statutory corporate tax rate is as follows (in thousands): Year Ended 2023 2022 Tax computed at federal statutory rate $ ( 25,927 ) $ ( 33,588 ) State income taxes ( 1,291 ) ( 1,366 ) Change in fair value of warrant liabilities — 9,249 Convertible debt — 11,396 Permanent differences and other 997 ( 354 ) Research and development credits ( 2,838 ) — Effect of rate change on deferred tax assets and liabilities 1,455 — Change in valuation allowance 27,604 14,734 Other — ( 71 ) Provision for income taxes $ — $ —
Schedule of Deferred Tax Assets	Significant components of the Company’s deferred tax assets are as follows (in thousands): December 31, 2023 2022 Deferred tax assets: Intangible assets $ 7,315 $ 8,406 Net operating loss carryforwards 10,323 6,950 Start up and organization costs 596 685 Capitalized research cost 27,564 9,337 Lease liability 5,654 4,979 Share based compensation 2,166 — Tax credit carryforwards 3,577 — Other, net 1,236 1,030 Total deferred tax assets 58,431 31,387 Valuation allowance ( 54,491 ) ( 26,930 ) Deferred tax assets, net of allowance $ 3,940 $ 4,457 Deferred tax liabilities: Right-of-use asset $ ( 3,940 ) $ ( 4,457 ) Total deferred tax liabilities ( 3,940 ) ( 4,457 ) Net deferred tax assets $ — $ —
Schedule of Unrecognized Tax Benefits	The following table summarizes the activity related to the Company's gross unrecognized tax benefits (in thousands): Year Ended 2023 2022 Beginning Balance $ — $ — Increases (decreases) related to prior year tax positions 177 — Increases related to current year tax positions 782 — Ending Balance $ 959 $ —

Organization - Additional Infor

Organization - Additional Information (Details) $ in Thousands			12 Months Ended	41 Months Ended	60 Months Ended
	May 03, 2022 USD ($) shares	Apr. 22, 2022 shares	Dec. 31, 2022 USD ($) shares	May 31, 2022 USD ($) shares	Dec. 31, 2023 USD ($) shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Forward split of shares		1.681
Common stock shares authorized		50,000,000	500,000,000		500,000,000
Sale of common stock				13,529,750
Net proceeds from initial public offering | $			$ 230,006
Initial Public Offering
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Common stock shares authorized	500,000,000
Sale of common stock	13,529,750
Net proceeds from initial public offering | $	$ 209,500			$ 209,500
Underwritten public offering
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Sale of common stock					9,200,000
Net proceeds from common stock | $					$ 107,800

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 Segment shares	Dec. 31, 2022 shares
Summary of Significant Accounting Policies [Line Item]
Number of operating segment | Segment	1
Weighted-average unvested shares excluded from computation of earnings per share amount | shares	1,232,828	2,080,038
ASU 2016-13
Summary of Significant Accounting Policies [Line Item]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Jan. 01, 2023
Change in accounting principle, accounting standards update, immaterial effect	true

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Estimated Useful Life of the Related Assets (Details)	Dec. 31, 2023
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Lab equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated Useful Life	5 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	us-gaap:UsefulLifeTermOfLeaseMember
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	3 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life	10 years

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Potential Dilutive Securities Not Included in the Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	5,476,250	3,701,118
Common Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	3,896,061	2,111,989
Unvested common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,571,716	1,584,709
ESPP shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	8,473	4,420

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - Non-Recurring	12 Months Ended
	Dec. 31, 2023 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-financial assets at fair value	$ 0
Non-financial liabilities at fair value	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	$ 296,464	$ 277,043
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	209,659	277,043
U.S. Treasury Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	43,050
U.S Government Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	43,755
Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	252,709	277,043
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	209,659	$ 277,043
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	43,050
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	43,755
Significant Other Observable Inputs (Level 2) | U.S Government Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	$ 43,755

Marketable Securities - Schedul

Marketable Securities - Schedule of Fair Value of Available-For-Sale Marketable Debt Securities (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	$ 86,811,000
Gross Unrealized Gains	20,000
Gross Unrealized Losses	(26,000)
Fair Value	86,805,000	$ 0
U.S. Treasury Notes
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	43,036,000
Gross Unrealized Gains	16,000
Gross Unrealized Losses	(2,000)
Fair Value	43,050,000
U.S. Government Agency Bonds
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost	43,775,000
Gross Unrealized Gains	4,000
Gross Unrealized Losses	(24,000)
Fair Value	$ 43,755,000

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Marketable debt securities	$ 86,805,000	$ 0
Impairment of assets measured and carried at fair value	$ 0

Other Balance Sheet Details - S

Other Balance Sheet Details - Summary of Components of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 14,898	$ 5,587
Less accumulated depreciation	880	1
Property, Plant and Equipment, Net, Total	14,018	5,586
Computer equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	103
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	377	11
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	11,964	378
Lab equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	2,116
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 338	$ 5,198

Other Balance Sheet Details - A

Other Balance Sheet Details - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Other Balance Sheet Details [Abstract]
Depreciation expense	$ 879	$ 1

Other Balance Sheet Details -_2

Other Balance Sheet Details - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Accrued external research and development costs	$ 12,665	$ 3,510
Accrued payroll and payroll-related costs	5,233	4,018
Accrued professional costs	498	307
Other	157	375
Total accrued expenses	$ 18,553	$ 8,210

Other Balance Sheet Details -_3

Other Balance Sheet Details - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Cash and cash equivalents	$ 216,678	$ 279,401
Restricted cash	1,631	1,631
Total cash, cash equivalents and restricted cash	$ 218,309	$ 281,032	$ 124,566

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Mar. 31, 2022	Aug. 31, 2021	Dec. 31, 2023
Switzerland
Lessee, Lease, Description [Line Items]
Operating lease term		5 years
Operating lease option to extend			The Company has an option to extend the lease for a period of five years which the Company is not reasonably certain to exercise.
Operating lease, existence of option to extend [true false]		true
Operating lease renewal term		5 years
Boston, Massachusetts
Lessee, Lease, Description [Line Items]
Operating lease option to extend			an option for the Company to extend the lease for a period of five years
Operating lease, existence of option to extend [true false]	true
Operating lease renewal term	5 years
Increase in operating lease liability			$ 6
Maximum lessee operating lease tenant improvement allowances for reimbursement cost			6.3
Lease incentive			6.3
Irrevocable standby letter of credit secured by restricted cash amount			$ 1.6

Leases - Schedule of Operating

Leases - Schedule of Operating Lease Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Lease expense:
Operating lease expense	$ 3,115	$ 2,351

Leases - Schedule of Weighted A

Leases - Schedule of Weighted Average Lease Term and Discount Rate for Operating Lease (Details)	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
Weighted-average remaining lease term	9 years	9 years 11 months 15 days
Weighted-average discount rate	7.40%	7.40%

Leases - Schedule of Cash Paid

Leases - Schedule of Cash Paid for Amounts Included in the Measurement of Lease Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Leases [Abstract]
Cash paid for amounts included in the measurement of operating lease liabilities (operating cash flows)	$ 3,487

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Noncancelable Operating Lease Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
2024	$ 3,589
2025	3,692
2026	3,787
2027	3,860
2028	3,974
Thereafter	17,101
Total undiscounted operating lease payments	36,003
Present value adjustment	(9,703)
Tenant improvement reimbursements	(351)
Operating lease liability	25,949
Less current portion of operating lease liability	3,118	$ 37
Operating lease liability, net of current portion	$ 22,831	$ 21,569

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Change in fair value of convertible promissory notes			$ 51,469,000
Accounts payable and accrued expenses		$ 18,553,000	8,210,000
August 2021 Notes | Common Stock
Related Party Transaction [Line Items]
Debt instrument conversion, common stock shares issued	10,672,138			10,672,138
Frazier
Related Party Transaction [Line Items]
Shared operating expenses		0	40,000
Change in fair value of convertible promissory notes			13,200,000
Interest Expense			700,000
Due to related parties			6,000
Takeda | TSA
Related Party Transaction [Line Items]
Research and development expenses		400,000	2,400,000
Accounts payable and accrued expenses		$ 33,000	$ 300,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($)		1 Months Ended		12 Months Ended
	Jul. 02, 2021	Nov. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Commitments And Contingencies Disclosure [Line Items]
Cash paid for purchased in-process research and development					$ 2,500,000
Common stock shares issued				48,497,853	39,240,746
Percentage Of employee's contributions		100%
Percentage of maximum eligible compensation		4%
Takeda
Commitments And Contingencies Disclosure [Line Items]
Purchase of common stock upon exercise of outstanding warrant	5,883,500
Transaction prices per share	$ 0.0000595
Cash paid for purchased in-process research and development	$ 2,500,000		$ 2,500,000
Common stock shares issued	840,500
Issuance of common stock in connection with Takeda License	$ 4,400,000
Promissory notes initial fair value	34,000
Development Milestones	7,500,000
Sales Milestones	$ 150,000,000
License agreement milestone payments				$ 0

Convertible Promissory Notes _3

Convertible Promissory Notes and Long-Term Debt - Additional Information (Details) - USD ($)				3 Months Ended	12 Months Ended			14 Months Ended
	Jun. 16, 2023	Apr. 18, 2022	Aug. 31, 2021	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jun. 15, 2023	Nov. 09, 2023
Convertible Promissory Notes [Line Items]
Change in fair value of convertible promissory notes						$ 51,469,000
Debt instrument, carrying amount					$ 25,000,000
Debt instrument, amount borrowed					25,635,000
PIK interest					548,000	87,000
Amortization of debt discount					$ 567,000	292,000
Minimum
Convertible Promissory Notes [Line Items]
Notes issuance, maturity period					12 months
Maximum
Convertible Promissory Notes [Line Items]
Notes issuance, maturity period					18 months
Loan Agreement
Convertible Promissory Notes [Line Items]
Debt instrument, amount borrowed					$ 25,000,000
Term Loan
Convertible Promissory Notes [Line Items]
Interest expense					2,400,000
Debt instrument, accretion of final payment fee					500,000
PIK interest					500,000
Debt instrument, coupon interest					$ 1,300,000
Term Loan | Loan Agreement
Convertible Promissory Notes [Line Items]
Debt instrument, interest rate		4.55%			6.05%
Debt instrument, maximum borrowing capacity		$ 75,000,000
Debt instrument, amount borrowed								$ 15,000,000
Debt instrument, minimum draw amount									$ 5,000,000
Debt instrument, basis spread on variable rate		5%
Debt instrument, interest rate per annum		2.85%
Debt instrument, payment terms		The monthly payments consist of interest-only through June 1, 2025 or, if prior to April 30, 2025, the Company achieves the Tranche 3 Milestone, subject to reasonable verification by Hercules, through June 1, 2026. Subsequent to the interest-only period, the Term Loans will be payable in equal monthly installments of principal, plus accrued and unpaid interest, through the maturity date of May 1, 2027.
Debt instrument, maturity date		May 01, 2027
Debt instrument, final payment fee		$ 2,145,000			$ 2,100,000
Percentage of original principal amount payable		7.15%
Financing costs					200,000
Percentage of interest upon event of default		4%
Term Loan | Loan Agreement | Maximum
Convertible Promissory Notes [Line Items]
Percentage of prepayment fee on outstanding principal balance		1%
Term Loan | Prime Rate | Loan Agreement
Convertible Promissory Notes [Line Items]
Debt instrument, basis spread on variable rate		1.05%
Frazier
Convertible Promissory Notes [Line Items]
Aggregate amount					$ 8,500,000
Frazier | Minimum
Convertible Promissory Notes [Line Items]
Bearing interest					0.12%
Frazier | Maximum
Convertible Promissory Notes [Line Items]
Bearing interest					2.52%
2019 Frazier Notes
Convertible Promissory Notes [Line Items]
Aggregate amount					$ 900,000
2020 Frazier Notes
Convertible Promissory Notes [Line Items]
Aggregate amount					1,300,000
2021 Frazier Notes
Convertible Promissory Notes [Line Items]
Aggregate amount					$ 6,300,000
August 2021 Notes | Common Stock
Convertible Promissory Notes [Line Items]
Debt instrument conversion, common stock shares issued				10,672,138			10,672,138
August 2021 Notes | Frazier Life Sciences X, L.P. | Common Stock
Convertible Promissory Notes [Line Items]
Debt instrument conversion, common stock shares issued				2,736,234
August 2021 Notes | Note Purchase Agreement
Convertible Promissory Notes [Line Items]
Aggregate amount			$ 139,520,000
Debt instrument, interest rate			6%
Debt instrument, frequency of periodic payment					annually
Interest expense						2,800,000
Change in fair value of convertible promissory notes						$ 51,500,000
August 2021 Notes | Note Purchase Agreement | New Investors
Convertible Promissory Notes [Line Items]
Aggregate amount			$ 103,750,000
August 2021 Notes | Note Purchase Agreement | Frazier Life Sciences X, L.P.
Convertible Promissory Notes [Line Items]
Aggregate amount			10,770,000
Cash proceeds from issuance of convertible notes			$ 25,000,000
Term Loan 1 Borrowing through June 30, 2023 | Term Loan 1 | Loan Agreement
Convertible Promissory Notes [Line Items]
Debt instrument, amount borrowed	$ 10,000,000
Term Loan 1 Borrowing through June 30, 2023 | Term Loan 1 | Loan Agreement | Maximum
Convertible Promissory Notes [Line Items]
Debt instrument, available credit under loan agreement								15,000,000
Term Loan 1 Borrowing December 1, 2023 through May 31, 2024 | Term Loan 1 | Loan Agreement | Maximum
Convertible Promissory Notes [Line Items]
Debt instrument, available credit under loan agreement	$ 5,000,000
Term Loan 1 Borrowing January 1, 2024 through July 19, 2024 | Term Loan 1 | Loan Agreement | Maximum
Convertible Promissory Notes [Line Items]
Debt instrument, available credit under loan agreement									$ 5,000,000
Term Loan 2 Borrowing through June 30, 2023 | Term Loan 2 | Loan Agreement | Maximum
Convertible Promissory Notes [Line Items]
Debt instrument, available credit under loan agreement								20,000,000
Term Loan 3 Borrowing through March 31, 2024 | Term Loan 3 | Loan Agreement | Maximum
Convertible Promissory Notes [Line Items]
Debt instrument, available credit under loan agreement								$ 25,000,000

Convertible Promissory Notes _4

Convertible Promissory Notes and Long-Term Debt - Schedule of Term Loan (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Debt Disclosure [Abstract]
Long-term debt	$ 25,000
Accumulated PIK interest	635
Total principal (including PIK interest)	25,635
Unamortized debt discount	(391)
Long-term debt, net of debt discount	$ 25,244

Convertible Promissory Notes _5

Convertible Promissory Notes and Long-Term Debt - Schedule of Future Minimum Principal and Interest Payments (Details) $ in Thousands	Dec. 31, 2023 USD ($)
Debt Disclosure [Abstract]
2024	$ 1,599
2025	8,433
2026	13,303
2027	10,645
Total principal payments, interest payments and final payment fee	33,980
Less: interest, PIK interest and final payment fee	(8,345)
Long-term debt	$ 25,635

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands				1 Months Ended	12 Months Ended		41 Months Ended
	Sep. 22, 2023	May 12, 2023	May 03, 2022	Apr. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	May 31, 2022	Apr. 22, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield					0%	0%
Number of issued shares of restricted common stock grants					759,266	0
Weighted Average Grant-Date Fair Value, Shares granted					$ 18
Total unrecognized stock-based compensation cost related to restricted stock					$ 10,300
Weighted average grant date fair value per share of option grants					$ 13.03	$ 4.88
Total unrecognized stock-based compensation cost related to stock options					$ 28,900
Sale of common stock							13,529,750
Net proceeds from initial public offering						$ 230,006
Increase in number of authorized shares of common stock					500,000,000	500,000,000		50,000,000
Increase in number of authorized shares of preferred stock					50,000,000	50,000,000
Shares reserved for issuance					8,204,241
Sales Agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Sales agreement date		May 12, 2023
Maximum commission percentage on gross proceeds of shares of common stock sold		3%
Maximum | Sales Agreement
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Agreegate offering price		$ 100,000
Common Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized stock-based compensation cost expected to be recognized over remaining weighted-average period					2 years 8 months 12 days
Shares reserved for issuance					3,896,061
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized stock-based compensation cost expected to be recognized over remaining weighted-average period					3 years 1 month 6 days
Initial Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Agreegate offering price						$ 209,515
Sale of common stock			13,529,750
Public offering price per share			$ 17
Net proceeds from initial public offering			$ 209,500				$ 209,500
Underwriting discounts, commissions and offering costs			$ 20,500
Increase in number of authorized shares of common stock			500,000,000
Increase in number of authorized shares of preferred stock			50,000,000
Underwritten Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Agreegate offering price					$ 107,790
Net proceeds after deducting underwriters commission	$ 107,800
Sale of common stock	9,200,000
Public offering price per share	$ 12.5
Common Stock | Initial Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Agreegate offering price						$ 1
Sale of common stock						13,529,750
Common Stock | Underwritten Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Agreegate offering price					$ 1
Sale of common stock	1,200,000				9,200,000
2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan term					ten years
Vesting period					4 years
Shares reserved for issuance					3,576,043
Number of shares remained available for issuance under awards granted				216,849
2022 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan term					The 2022 Plan became effective in connection with the Company’s IPO and will remain in effect until the tenth anniversary of its effective date, which will be April 28, 2032, unless earlier terminated by the Company’s board of directors. The number of shares of the Company's common stock initially available for issuance under awards granted pursuant to the 2022 Plan was the sum of (1) 4,900,000 shares of the Company’s common stock, plus (2) 216,849 shares remaining available for issuance under the 2021 Plan as of the effective date of the 2022 Plan, plus (3) any shares subject to outstanding awards under the 2021 Plan as of the effective date of the 2022 Plan that become available for issuance under the 2022 Plan thereafter in accordance with its terms.
Shares reserved for issuance					7,197,502
Number of shares remained available for issuance under awards granted				4,900,000	3,576,043
Shares issuance, ending year				2032
Percentage of shares issued from outstanding number of shares				5%
2022 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance				410,000
Shares reserved for issuance					732,137
Maximum number of shares that may be authorized in accordance with plan				10,000,000
Shares issuance, ending year				2032
Percentage of shares issued from outstanding number of shares				1%
Purchase price of common stock, percent				85%

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Option Activity (Details) - Plans - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding options, Beginning balance	2,111,989
Number of outstanding options, Granted	2,035,225
Number of outstanding options, Exercised	(84,554)
Number of outstanding options, Cancelled	(166,599)
Number of outstanding options, Ending Balance	3,896,061	2,111,989
Number of outstanding options, Vested and expected to vest at December 31, 2023	3,896,061
Number of outstanding options, Exercisable at December 31, 2023	884,268
Weighted average exercise price, Beginning balance	$ 10.62
Weighted average exercise price, Granted	16.88
Weighted average exercise price, Exercised	7.27
Weighted average exercise price, Cancelled	11.98
Weighted average exercise price, Ending balance	13.89	$ 10.62
Weighted average exercise price, Vested and expected to vest at December 31, 2023	13.89
Weighted average exercise price, Exercisable at December 31, 2023	$ 10.35
Weighted-average remaining contractual term (in years)	8 years 9 months 25 days	9 years 3 months 29 days
Weighted-average remaining contractual term (in years), Vested and expected to vest at December 31, 2023	8 years 9 months 25 days
Weighted-average remaining contractual term (in years) Exercisable at December 31, 2023	8 years 3 months 25 days
Aggregate intrinsic value	$ 11,826	$ 13,330
Aggregate intrinsic value, Vested and expected to vest at December 31, 2023	11,826
Aggregate intrinsic value, Exercisable at December 31, 2023	$ 5,219

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Assumptions used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option Grants (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	3.50%	1.90%
Risk-free interest rate, maximum	4.90%	4.20%
Expected volatility, minimum	91.70%	83.40%
Expected volatility, maximum	95.90%	94.30%
Expected dividend yield	0%	0%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 3 months 18 days
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 13,590	$ 3,003
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	6,582	1,720
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 7,008	$ 1,283

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Unvested Shares (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Stockholders' Equity Note [Abstract]
Number of unvested shares, Beginning balance	1,584,709
Number of unvested shares, Shares granted	759,266	0
Number of unvested shares, Shares forfeited	(88,849)
Number of unvested shares, Shares vested	(683,410)
Number of unvested shares, Ending balance	1,571,716	1,584,709
Weighted Average Grant-Date Fair Value, Beginning balance	$ 0.001
Weighted Average Grant-Date Fair Value, Shares granted	18
Weighted Average Grant-Date Fair Value, Shares forfeited	0.001
Weighted Average Grant-Date Fair Value, Shares vested	$ 0.001

Stockholders' Equity - Schedu_2

Stockholders' Equity - Schedule of Common Stock Reserved for Future Issuance (Details)	Dec. 31, 2023 shares
Class Of Stock [Line Items]
Common stock reserved for future issuance	8,204,241
Common Stock Options
Class Of Stock [Line Items]
Common stock reserved for future issuance	3,896,061
Shares Available for Issuance Under the 2021 Plan
Class Of Stock [Line Items]
Common stock reserved for future issuance	3,576,043
Shares available for issuance under the ESPP
Class Of Stock [Line Items]
Common stock reserved for future issuance	732,137

Pension and Other Postretirem_3

Pension and Other Postretirement Benefit Plans - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2022	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Percentage Of employee's contributions	100%
Percentage of maximum eligible compensation	4%
Matching contributions made		$ 0.6
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Matching contributions made		0.4	$ 0.2
Accumulated benefit obligation		$ 5.1	$ 2

Pension and Other Postretirem_4

Pension and Other Postretirement Benefit Plans - Schedule of the Projected Benefit Obligation, Fair Value of Plan Assets, and the Funded Status (Details) - Pension Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 2,051	$ 1,017
Prior service cost	47
Service cost	246	120
Interest cost	60	6
Contributions paid by plan participants	169	92
Benefits deposited	1,692	692
Actuarial loss	598	114
Exchange rate adjustments	393	10
Benefit obligation at end of year	5,256	2,051
Fair value of plan assets at end of year	4,414	1,739
Funded status - deficit	$ (842)	$ (312)

Pension and Other Postretirem_5

Pension and Other Postretirement Benefit Plans - Summary of Components of Net Periodic Benefit Cost (Details) - Pension Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 246	$ 120
Interest cost	60	6
Expected return on plan assets	(72)	(33)
Amortization of net loss	7
Total recognized in operating expense	241	93
Adjustment to pension liability	620	281
Total recognized other comprehensive loss	620	281
Total costs recognized in consolidated comprehensive loss	$ 861	$ 374

Pension and Other Postretirem_6

Pension and Other Postretirement Benefit Plans - Schedule of Weighted Average Actuarial Assumptions used to Determine Net Periodic Benefit Cost (Details) - Pension Plan	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Discount rate	1.50%	1.90%
Inflation rate	1%	1%
Expected rate of return on plan assets	3%	2.50%
Rate of compensation increase	1%	1%

Pension and Other Postretirem_7

Pension and Other Postretirement Benefit Plans - Schedule of Pension Plan Benefits Expected to be Paid (Details) - Pension Plan $ in Thousands	Dec. 31, 2023 USD ($)
Defined Benefit Plan Disclosure [Line Items]
2024	$ 5
2025	10
2026	14
2027	19
2028	24
2029-2033	200
Total expected benefits to be paid	$ 272

Income Taxes - Schedule of Prov

Income Taxes - Schedule of Provision for Income Taxes and Income Taxes U.S. Federal Statutory Corporate Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Tax computed at federal statutory rate	$ (25,927)	$ (33,588)
State income taxes	(1,291)	(1,366)
Change in fair value of warrant liabilities		9,249
Convertible debt		11,396
Permanent differences and other	997	(354)
Research and development credits	(2,838)
Effect of rate change on deferred tax assets and liabilities	1,455
Change in valuation allowance	$ 27,604	14,734
Other		$ (71)

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Intangible assets	$ 7,315	$ 8,406
Net operating loss carryforwards	10,323	6,950
Start up and organization costs	596	685
Capitalized research cost	27,564	9,337
Lease liability	5,654	4,979
Share based compensation	2,166
Tax credit carryforwards	3,577
Other, net	1,236	1,030
Total deferred tax assets	58,431	31,387
Valuation allowance	(54,491)	(26,930)
Deferred tax assets, net of allowance	3,940	4,457
Deferred tax liabilities:
Right-of-use asset	(3,940)	(4,457)
Total deferred tax liabilities	$ (3,940)	$ (4,457)

Income Taxes - Schedule of Unre

Income Taxes - Schedule of Unrecognized Tax Benefits (Details)	12 Months Ended
	Dec. 31, 2023 USD ($)
Income Tax Disclosure [Abstract]
Beginning Balance	$ 0
Increases (decreases) related to prior year tax positions	177,000
Increases related to current year tax positions	782,000
Ending Balance	$ 959,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 54,491,000	$ 26,930,000
Net operating losses limitation percentage of taxable income	80%
Net operating loss carryforwards , expiration year	2041
Net operating loss carryforward, description	Pursuant to Internal Revenue Code Sections 382 and 383, annual use of the Company’s net operating loss may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period.
Gross unrecognized tax benefits	$ 959,000	$ 0
Accrual for interest or penalties	$ 0
Maximum
Operating Loss Carryforwards [Line Items]
Net operating losses limitation of cumulative ownership percentage of taxable income	50%
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 47,800,000
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 36,500,000

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($)			1 Months Ended	41 Months Ended
	Jan. 08, 2024	May 12, 2023	Mar. 20, 2024	May 31, 2022
Subsequent Event [Line Items]
Issuance of common stock, Shares				13,529,750
Sales Agreement
Subsequent Event [Line Items]
Sales agreement date		May 12, 2023
Maximum | Sales Agreement
Subsequent Event [Line Items]
Agreegate offering price		$ 100,000,000
Subsequent Events | Sales Agreement
Subsequent Event [Line Items]
Gross proceeds from common stock			$ 15,000,000
Subsequent Events | Sales Agreement | Common Stock
Subsequent Event [Line Items]
Issuance of common stock, Shares			1,016,950
Subsequent Events | Exclusive License Agreement | Kangh
Subsequent Event [Line Items]
Upfront payment	$ 15,000,000
Subsequent Events | Maximum | Exclusive License Agreement | Kangh
Subsequent Event [Line Items]
Development and sales milestones	$ 255,500,000