HilleVax (HLVX) 10-K 17 Mar 23 2022 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Mar. 13, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Document Fiscal Year Focus	2022
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
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		39,252,128
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	75 State Street
Entity Address, Address Line Two	Suite 100 - #9995
Entity Address City Or Town	Boston
Entity Address State Or Province	MA
Entity Address Postal Zip Code	02109
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			$ 227.8
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 2023 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, 2022 , 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, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 279,401	$ 124,566
Prepaid expenses and other current assets	11,212	141
Total current assets	290,613	124,707
Property and equipment, net	5,586	42
Operating lease right-of-use assets	19,359	189
Restricted cash	1,631
Other assets	22	2,221
Total assets	317,211	127,159
Current liabilities:
Accounts payable (includes related party amounts of $141 and $22, respectively)	4,744	1,024
Accrued expenses (includes related party amounts of $140 and $4,911, respectively)	8,210	9,164
Accrued interest (includes related party amounts of $0 and $723, respectively)	55	2,821
Convertible promissory notes payable at fair value (includes related party amounts of $0 and $40,580, respectively)		158,276
Current portion of operating lease liability	37	32
Warrant liabilities - related party		56,445
Total current liabilities	13,046	227,762
Operating lease liability, net of current portion	21,569	153
Long-term debt, net of debt discount	14,792
Other long-term liabilities	575	1
Total liabilities	49,982	227,916
Commitments and contingencies (Note 7)
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; authorized shares- 50,000,000 and 0 at December 31, 2022 and December 31, 2021, respectively; no shares issued and outstanding at December 31, 2022 and December 31, 2021
Common stock, $0.0001 par value; authorized shares- 500,000,000 and 50,000,000 at December 31, 2022 and December 31, 2021, respectively; issued shares- 39,240,746 and 9,225,321 at December 31, 2022 and December 31, 2021, respectively; outstanding shares- 37,656,037 and 6,599,886 at December 31, 2022 and December 31, 2021, respectively	4	1
Additional paid-in capital	532,499	4,426
Accumulated other comprehensive loss	(281)
Accumulated deficit	(264,993)	(105,184)
Total stockholders' equity (deficit)	267,229	(100,757)
Total liabilities and stockholders' equity (deficit)	$ 317,211	$ 127,159

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Preferred stock par value	$ 0.0001	$ 0.0001
Preferred stock shares authorized	50,000,000	0
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	50,000,000
Common stock shares issued	39,240,746	9,225,321
Common stock shares outstanding	37,656,037	6,599,886
Accounts Payable
Related party amounts	$ 141	$ 22
Accrued Expenses
Related party amounts	140	4,911
Accrued Interest
Related party amounts	0	723
Convertible Promissory Notes Payable
Related party amounts	$ 0	$ 40,580

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating expenses:
Research and development (includes related party amounts of $2,426 and $4,926, respectively)	$ 45,908	$ 10,014
In-process research and development - related party	2,500	37,656
General and administrative (includes related party amounts of $40 and $619, respectively)	16,705	5,756
Total operating expenses	65,113	53,426
Loss from operating ,Total	(65,113)	(53,426)
Other income (expense):
Interest income	3,875
Interest expense (includes related party amounts of $(717) and $(740), respectively)	(3,414)	(2,844)
Change in fair value of convertible promissory notes (includes related party amounts of $(13,196) and $(6,258), respectively)	(51,469)	(20,204)
Change in fair value of warrant liabilities - related party	(43,575)	(25,911)
Other income (expense)	(113)	(23)
Total other income (expense)	(94,696)	(48,982)
Net loss	(159,809)	(102,408)
Other comprehensive loss:
Pension and other postemployment benefits	(281)
Total comprehensive loss	$ (160,090)	$ (102,408)
Net loss per share, basic	$ (5.89)	$ (18.22)
Net loss per share, diluted	$ (5.89)	$ (18.22)
Weighted-average shares of common stock outstanding, basic	27,147,314	5,619,182
Weighted-average shares of common stock outstanding, diluted	27,147,314	5,619,182

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) (Unaudited) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Statement [Abstract]
Related party expenses	$ 2,426	$ 4,926
General and administrative, related party	40	619
Interest expense, related party	717	740
Change in fair value of convertible promissory notes, related party	$ 13,196	$ 6,258

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Deficit (Unaudited) - USD ($) $ in Thousands	Total	License agreement	Initial Public Offering	Common Stock	Common Stock License agreement	Common Stock Initial Public Offering	Additional Paid-in Capital	Additional Paid-in Capital License agreement	Additional Paid-in Capital Initial Public Offering	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance at Dec. 31, 2020	$ (2,773)						$ 3				$ (2,776)
Beginning Balance, Shares at Dec. 31, 2020				4,759,968
Issuance of common stock	1	$ 4,357		$ 1				$ 4,357
Issuance of common stock, Shares				1,606,815	840,500
Vesting restrictions placed on previously issued and outstanding common stock	(1)						(1)
Vesting restrictions placed on previously issued and outstanding common stock, Shares				(2,332,386)
Vesting of restricted shares, Shares				1,724,989
Stock - based compensation	67						67
Net loss	(102,408)										(102,408)
Ending Balance at Dec. 31, 2021	(100,757)			$ 1			4,426				(105,184)
Ending 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 stock purchase plan	173						173
Issuance of common stock under stock purchase plan, 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

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Stockholders' Deficit (Unaudited) (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, 2022	Dec. 31, 2021
Cash flows from operating activities
Net loss	$ (159,809)	$ (102,408)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1	3
Stock-based compensation	3,003	67
Change in fair value of convertible promissory notes (includes related party amounts of $13,196 and $6,258, respectively)	51,469	20,204
Change in fair value of warrant liabilities - related party	43,575	25,911
Non-cash lease costs	2,251	(4)
Amortization of debt discount	292
Issuance of PIK interest debt	87
Acquired in-process research and development - related party	2,500	37,656
Loss on disposal of property and equipment	42
Changes in operating assets and liabilities:
Prepaid expenses and other current assets (includes related party amounts of $0 and $48, respectively)	(11,071)	(116)
Accounts payable, accrued expenses and other long-term liabilities (includes related party amounts of $(4,652) and $4,803, respectively)	2,819	8,548
Accrued interest (includes related party amounts of $717 and $746, respectively)	2,852	2,844
Net cash used in operating activities	(61,989)	(7,295)
Cash flows from investing activities
Cash paid for purchased in-process research and development	(2,500)	(2,763)
Purchases of property and equipment	(4,014)	(45)
Net cash used in investing activities	(6,514)	(2,808)
Cash flows from financing activities
Proceeds from issuance of common stock		1
Proceeds from issuance of common stock in initial public offering	230,006
Payment of initial public offering costs	(19,702)	(789)
Proceeds from issuance of long-term debt, net of issuance costs	14,665
Proceeds from issuance of convertible promissory notes		135,000
Net cash provided by financing activities	224,969	134,212
Net increase in cash, cash equivalents and restricted cash	156,466	124,109
Cash and, cash equivalents and restricted cash-beginning of period	124,566	457
Cash, cash equivalents and restricted cash-end of period	281,032	124,566
Supplemental disclosure of cash flow information
Cash paid for interest	193
Supplemental disclosure of noncash investing and financing activities
Accrued interest exchanged for convertible promissory notes		47
Operating lease	20,317	180
Issuance of Takeda Warrants in connection with Takeda License		30,534
Issuance of common stock in connection with Takeda License		4,357
Unpaid initial public offering costs		$ 1,409
Unpaid property and equipment purchases	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	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, 2022	Dec. 31, 2021
Statement Of Cash Flows [Abstract]
Change in fair value of convertible promissory notes, related party	$ 13,196	$ 6,258
Related parties prepaid expenses and other assets current	0	48
Related parties accounts payable, accrued expenses and other long-term liabilities	(4,652)	4,803
Related parties accrued interest	$ 717	$ 746

Organization

Organization	12 Months Ended
	Dec. 31, 2022
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. Initial Public Offering On May 3, 2022, the Company completed its initial public offering ("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 (see Note 9). Liquidity and Capital Resources From inception to December 31, 2022, 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, 2022, the Company has funded its operations through the issuance of convertible promissory notes, commercial bank debt and the sale of common stock in its IPO which closed in May 2022. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business, and do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or amounts and classification of liabilities. 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, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The Company, North Bridge V and YamadaCo III were entities under the common control of Frazier Life Sciences X, L.P. or its affiliates (“Frazier”) as a result of, among others, Frazier’s: (i) ownership of a majority of the outstanding capital stock of each of the companies, (ii) financing of each of the companies, (iii) control of board of directors of each of the companies, and (iv) management of each of the companies. As the merged entities were under common control, the financial statements prior to the Merger report the financial position, results of operations and cash flows of these merged companies. The financial statements also include, subsequent to its formation in May 2021, the accounts of HilleVax GmbH, a wholly-owned subsidiary formed in Zurich, Switzerland. The functional currency of both the Company 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 unaudited 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 unaudited consolidated financial statements relate to accruals for research and development expenses, and 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 earnings 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 5). Concentrations of Credit Risk Financial instruments that potentially subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents 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 (generally 3 years). 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, 2022 . 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 and employee stock purchase rights, recognized on a straight-line basis over the requisite service period for stock options 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 year ended December 31, 2022, comprehensive loss included gains and losses on the Company's pension benefit obligation. For the year ended December 31, 2021, the Company’s comprehensive loss was the same as its reported net loss. 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 included 5,883,500 shares of common stock under the Takeda Warrant, prior to exercise, in the calculation of basic weighted-average common shares outstanding from the time the Takeda Warrant became exercisable upon the Company’s IPO because the Takeda Warrant is exercisable for minimal consideration. The Company has excluded weighted-average unvested shares of 2,080,038 shares and 2,694,011 shares from the basic weighted-average number of common shares outstanding for the years ended December 31, 2022 and 2021, respectively. See Note 9 for further information regarding these share restrictions. 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, contingently issuable shares under the Company's employee stock purchase plan, and common stock warrants. 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, 2022 2021 Common stock options 2,111,989 — Common stock warrants — 5,883,500 Unvested common stock 1,584,709 2,625,435 ESPP shares 4,420 — Total potentially dilutive shares 3,701,118 8,508,935 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 There were no recently adopted accounting standards which would have a material impact on the Company's financial statements. Recently Issued Accounting Pronouncements The Company assesses the adoption impacts of recently issued accounting standards by the Financial Accounting Standards Board or other standard setting bodies on the Company's consolidated financial statements as well as material updates to previous assessments, if any. Although there were several other new accounting pronouncements issued or proposed by the FASB, the Company does not believe any of those accounting pronouncements have had or will have a material impact on its financial position or operating results.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The carrying amounts of the Company’s financial instruments, including cash, cash equivalents and restricted cash, classified within the Level 1 designation discussed in Note 2, 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 information about the Company's liabilities measured at fair value on a recurring basis as of December 31, 2022 and December 31, 2021 (in thousands): Fair Value Measurements at Total Quoted Prices in Significant Significant As of December 31, 2022: Warrant liabilities $ — $ — $ — $ — Convertible promissory notes — — — — Total $ — $ — $ — $ — As of December 31, 2021: Warrant liabilities $ 56,445 $ — $ — $ 56,445 Convertible promissory notes 158,276 — — 158,276 Total $ 214,721 $ — $ — $ 214,721 The Company has no financial assets measured at fair value on a recurring basis. 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. The warrant liabilities consisted of an issued and outstanding common stock warrant (the “Takeda Warrant”) and a right to receive an additional common stock warrant (the “Takeda Warrant Right”, and together with the Takeda Warrant, the “Takeda Warrants”) issued to Takeda Vaccines, Inc. (“Takeda”) in connection with a July 2021 license agreement. The Takeda Warrants were accounted for as liabilities at fair value as they did not meet all the conditions for equity classification due to (i) insufficient authorized shares for the Takeda Warrant and (ii) the Takeda Warrant Right is not indexed to the Company’s own stock. As a result of the Company increasing its authorized shares of common stock (see Note 9) in the second quarter of 2022, the Takeda Warrant met the requirements to be equity classified, and the Company reclassified the fair value of the Takeda Warrant to stockholders' equity. The Takeda Warrant was exercised in November 2022 for the purchase of 5,883,500 shares of the Company's common stock at an exercise price of $ 0.0000595 per share. The Takeda Warrant Right expired upon the closing of the Company's IPO without effect to the financial statements since no fair value was allocated to it at that time. Prior to the reclassification to stockholders' equity, the fair value of the Takeda Warrants was derived from the model used to estimate the fair value of the Company’s common stock and, upon reclassification, the fair value was based on the Company's IPO price. The Company issued convertible promissory notes to Frazier (the “Frazier Notes”) from April 2019 to July 2021 and issued unsecured convertible promissory notes in August 2021 (the “August 2021 Notes”) to investors including Frazier. The Company elected the fair value option for each of its convertible promissory note issuances due to certain embedded features within the notes. Prior to conversion, the fair value of the Frazier Notes and the August 2021 Notes was estimated using a scenario-based analysis that estimated the fair value of the convertible promissory notes based on the probability-weighted present value of expected future investment returns, considering possible outcomes available to the noteholders, including various IPO, settlement, equity financing, corporate transactions and dissolution scenarios. The Frazier Notes were exchanged for August 2021 Notes in August 2021. The principal and accrued interest of the August 2021 Notes automatically converted into shares of the Company's common stock immediately prior to the completion of the IPO (see Note 8). The conversion date fair value of the August 2021 Notes was reclassified to stockholders' equity and was estimated using the Company's publicly traded closing price on the date the notes were converted to common stock. Prior to their reclassification to stockholders' equity in connection with the IPO, the Company adjusted the carrying value of its warrant liabilities and convertible promissory notes to their estimated fair value at each reporting date, with any related increases or decreases in the fair value recorded as change in fair value of warrant liabilities and as change in fair value of convertible promissory notes, respectively, in the consolidated statements of operations. The following table summarizes information about the significant unobservable inputs used in the fair value measurements for the Takeda Warrants and the August 2021 Notes as of December 31, 2021: Liability Key Unobservable Inputs Range Takeda Warrants Transaction prices per share $ 11.83 - $ 12.54 Estimated time to liquidity 0.20 - 1.75 years Discount rate 20 % August 2021 Notes Estimated time to liquidity 0.20 - 1.75 years Volatility 80 % - 100 % Discount rate 19 % - 20 % Risk-free interest rate 0.1 % - 0.7 % There are significant judgments, assumptions and estimates inherent in the determination of the fair value of each of the instruments described above. These include determination of a valuation method and selection of the possible outcomes available to the Company, including the determination of timing and expected future investment returns for such scenarios. The related judgments, assumptions and estimates are highly interrelated and changes in any one assumption could necessitate changes in another. In particular, any changes in the probability of a particular outcome would require a related change to the probability of another outcome. The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands): Warrant Convertible Balance at December 31, 2021 $ 56,445 $ 158,276 Change in fair value 43,575 51,469 Reclass Takeda Warrant into equity ( 100,020 ) — Conversion of August 2021 Notes into common shares upon IPO (excluding accrued interest of $ 5,619 ) — ( 209,745 ) Balance at December 31, 2022 $ — $ —

Other Balance Sheet Details

Other Balance Sheet Details	12 Months Ended
	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Other Balance Sheet Details	4. Other Balance Sheet Details Property and Equipment Property and equipment, net consisted of the following (in thousands): December 31, 2022 2021 Furniture and equipment $ 11 $ 45 Leasehold improvements 378 — Construction in progress 5,198 — Total property and equipment, at cost 5,587 45 Less accumulated depreciation 1 3 Property and equipment, net $ 5,586 $ 42 Depreciation expense for the years ended December 31, 2022 and 2021 was not material. Accrued Expenses Accrued expenses consisted of the following (in thousands): December 31, 2022 2021 Accrued external research and development costs $ 3,510 $ 6,425 Accrued payroll and payroll-related costs 4,018 1,010 Other 682 1,729 Total accrued expenses $ 8,210 $ 9,164 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, 2022 2021 Cash and cash equivalents $ 279,401 $ 124,566 Restricted cash 1,631 — Total cash, cash equivalents and restricted cash $ 281,032 $ 124,566

Leases

Leases	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Leases	5. 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 (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. As of December 31, 2022 , the Company has not yet incurred any leasehold improvement costs that were paid for by the lessor. The Company expects to receive all tenant improvement reimbursements during the year ending December 31, 2023. 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 during the year ended December 31, 2022 (in thousands): Year Ended 2022 Lease expense: Operating lease expense $ 2,351 The Company incurred an immaterial amount of expense related to short-term leases during the year ended December 31, 2022 . Operating lease expense was no t material for the year ended December 31, 2021. The following table summarizes the lease term and discount rate for operating leases: Year Ended 2022 2021 Other information: Weighted-average remaining lease term 9.96 4.75 Weighted-average discount rate 7.4 % 6.0 % 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) $ 101 At December 31, 2022, the future minimum noncancelable operating lease payments were as follows (in thousands): December 31, Years ending December 31: 2023 $ 3,483 2024 3,584 2025 3,688 2026 3,784 2027 3,860 Thereafter 21,075 Total undiscounted operating lease payments 39,474 Present value adjustment ( 11,950 ) Tenant improvement reimbursements ( 5,918 ) Operating lease liability 21,606 Less current portion of operating lease liability 37 Operating lease liability, net of current portion $ 21,569

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2022
Related Party Transactions [Abstract]
Related Party Transactions	. Related Party Transactions 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, 2022, 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 and 2021, the Company had outstanding amounts due to Frazier of $ 6,000 and $ 22,000 , respectively, related to these shared operating expenses. For the years ended December 31, 2022 and 2021 , the Company incurred $ 40,000 and $ 0.6 million, respectively, of shared operating expenses. As described in Note 8, the Company borrowed amounts from Frazier in connection with various convertible note financings. For the years ended December 31, 2022 and 2021 , the Company recognized a $ 13.2 million and $ 6.3 million, respectively, change in fair value of convertible promissory notes in connection with convertible promissory notes issued to Frazier. For each of the years ended December 31, 2022 and 2021 , the Company recognized $ 0.7 million of interest expense in connection with convertible promissory notes issued to Frazier. In connection with the Takeda License (as defined and described in Note 7), 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 7) 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, 2022 and 2021, the Company incurred $ 2.4 million and $ 4.9 million, respectively, of research and development expenses for Takeda’s services. As of December 31, 2022 and 2021, the Company had $ 0.3 million and $ 4.9 million, respectively, of accounts payable and accrued expenses due to Takeda. See Note 7 for further information regarding the Company’s related party transactions with Takeda.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2022
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	. 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, 2022, none of the 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. The $ 37.7 million fair value (including $ 0.3 million of transaction costs ) of the consideration paid for these research and development assets, which have no alternative future use, was recorded as in-process research and development in the Company’s consolidated statement of operations for the year ended December 31, 2021. 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. 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. 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 matching contributions for the year ended December 31, 2022 were not material. 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, 2022
Debt Disclosure [Abstract]
Convertible Promissory Notes and Long-Term Debt	. 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 . As of December 31, 2021, the outstanding principal balance of the August 2021 Notes was $ 139.5 million. 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 years ended December 31, 2022 and 2021 , the Company recognized a $ 51.5 million and $ 20.2 million, respectively, change in fair value of convertible promissory notes. For each of the years ended December 31, 2022 and 2021 , the Company 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 $ 15,000 Accumulated PIK interest 87 Total principal (including PIK interest) 15,087 Unamortized debt discount ( 295 ) Long-term debt, net of debt discount $ 14,792 On April 18, 2022, the Company entered into a Loan and Security Agreement (“Loan Agreement”) with Hercules Capital, Inc. (“Hercules”), as administrative and collateral agent, and the lenders party thereto¸ providing for term loans (“Term Loans”) of up to $ 75.0 million in the aggregate. As of December 31, 2022, the Company had borrowed $1 5.0 million pursuant to the Loan Agreement and has the right to borrow up to an additional $ 15.0 million through June 30, 2023 (collectively, “Term Loan 1”). The Company also has the right to borrow up to $ 20.0 million through June 30, 2023 (“Term Loan 2”). In addition, the Company has the right to borrow $ 25.0 million through March 31, 2024 (“Term Loan 3”), provided that on or prior to March 31, 2023, (i) the Company has announced that the planned Phase 2b clinical trial evaluating the safety, immunogenicity, and efficacy of HIL-214 in infants (“HIL-214 Vaccine Trial”) will continue without material adverse modification after completion of the planned interim safety and immunogenicity analysis on the first 200 evaluable subjects in the HIL-214 Vaccine Trial, and (ii) the Company has announced the completion of subject enrollment for the HIL-214 Vaccine Trial, which shall involve the enrollment of approximately 3,000 or more subjects. 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 the Company’s 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, 2022), 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, (x) the conditions to Term Loan 3 have been satisfied and (y) the Company has reasonably determined that (i) the HIL-214 Vaccine Trial has achieved the protocol-specified primary efficacy endpoint and (ii) HIL-214 has demonstrated acceptable safety results in the HIL-214 Vaccine 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, in each case 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) $ 2.1 million and (ii) 7.15 % of the original principal amount of the Term Loans (which is $ 2.1 million as of December 31, 2022). 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 2.00 % 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. During the year ended December 31, 2022, the Company has recognized interest expense of $ 0.6 million related to the Term Loans using the effective interest method. Included in such expense was $ 0.3 million, related to accretion of the final payment fee to other long-term liabilities, $ 0.1 million of PIK interest, $ 0.2 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, 2022 are as follows (in thousands): December 31, Years ending December 31: 2023 $ 902 2024 967 2025 5,063 2026 7,982 2027 7,405 Total principal payments, interest payments and final payment fee 22,319 Less: interest, PIK interest and final payment fee ( 7,232 ) Long-term debt $ 15,087

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	12 Months Ended
	Dec. 31, 2022
Stockholders Equity Note [Abstract]
Stockholders' Equity (Deficit)	9. Stockholders’ Equity (Deficit) 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. Common Stock From March 2021 through May 2021, the Company issued and sold an aggregate of 707,701 shares of restricted common stock outside of the 2021 Plan (defined and described below) at a purchase price of $ 0.0006303 per share to certain employees and consultants. The Company has the right, but not the obligation, to repurchase unvested shares at the original purchase price in the event the purchaser’s relationship with the Company is terminated, subject to certain limitations. The repurchase rights lapse over a four-year period, with 25 % lapsing on the first anniversary of the vesting commencement date and the remaining portion lapsing in 36 equal monthly amounts thereafter. On February 8, 2021, subsequent to the Merger, the Company issued and sold 1,606,815 shares of common stock to Frazier at $ 0.0006303 per share. On February 8, 2021, certain of the Company’s founders entered into stock restriction agreements granting the Company a repurchase right on 2,332,386 shares of fully vested common stock originally purchased in 2019 and 2020. The Company has the right, but not the obligation, to repurchase unvested shares in the event the founder’s relationship with the Company is terminated, subject to certain limitations, at $ 0.0003816 per share. The repurchase right lapsed for 583,095 shares on the effective date of the stock restriction agreements and the repurchase right for the remaining 1,749,291 shares lapses in equal monthly amounts over the following 48 -month period ending in February 2025. 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. In March 2021, the Company issued and sold an aggregate of 16,810 shares of restricted common stock under the 2021 Plan at a purchase price of $ 0.0006303 per share to certain consultants. The Company has the right, but not the obligation, to repurchase unvested shares at the original purchase price in the event the purchaser’s relationship with the Company is terminated, subject to certain limitations. The repurchase rights lapse on the first anniversary of the vesting commencement date. From February through April 2021, the Company issued 1,713,779 shares of restricted common stock to certain of its employees, consultants and directors under the 2021 Plan. The shares are subject to forfeiture restrictions under which the shares would become immediately retired in the event the stockholder’s service with the Company is terminated. The share restriction generally lapses over a four- year period, with 25 % lapsing on the first anniversary of the vesting commencement date and the remaining portion lapsing in 36 equal monthly amounts thereafter. 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 beginning in 2023 and 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, 2022, 5,192,844 shares were reserved for issuance under the 2022 Plan, of which 4,231,570 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 beginning in 2023 and 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. Stock-based compensation expense related to the ESPP for the year ended December 31, 2022 was not material. Valuation of Common Stock and Stock-Based Compensation Expense Prior to obtaining the Takeda License on July 2, 2021, the fair value of the Company’s common stock was nominal since the Company was not sufficiently capitalized and held no assets that could be used to generate future revenues. Subsequent to obtaining the Takeda License and prior to the Company's IPO, the Company estimated the fair value of its common stock using methodologies, approaches and assumptions consistent with the American Institute of Certified Public Accountants Accounting and Valuation Guide: Valuation of Privately Held Company Equity Securities Issued as Compensation (the “Practice Aid”). The Practice Aid prescribes several valuation approaches for setting the value of an enterprise, such as the cost, income and market approaches, and various methodologies for allocating the value of an enterprise to its common stock. The Company’s 2021 valuations utilized a scenario-based analysis that estimated the fair value per share based on the probability-weighted present value of expected future investment returns, considering each of the possible outcomes available to the Company, including various IPO, stay private and dissolution scenarios, and applying a discount for lack of marketability for certain equity holders. The Company considered various stay private scenarios using the income approach and allocated the indicated equity value, adjusted for the expected impact of the convertible notes, to each class of equity on a fully-diluted basis, considering option value for certain option classes. The Company also considered various IPO scenarios based on expected equity values in an IPO and allocated the indicated equity value to each class of equity on a fully-diluted basis considering the dilutive impacts of the convertible notes. Following the completion of the Company's IPO, the fair value of its 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. Since all restricted stock awards from inception were issued prior to obtaining the Takeda License on July 2, 2021, the Company has recorded no material stock-based compensation expense and has no material unrecognized stock-based compensation related to these awards. 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, 2021 727,873 $ 6.99 9.94 $ 765 Granted 1,494,384 12.42 Cancelled ( 110,268 ) 11.05 Balance at December 31, 2022 2,111,989 $ 10.62 9.33 $ 13,330 Vested and expected to vest at December 31, 2022 2,111,989 $ 10.62 9.33 $ 13,330 Exercisable at December 31, 2022 114,595 $ 7.28 8.95 $ 1,084 Stock-Based Compensation Expense The assumptions used in the Black-Scholes option pricing model to determine the fair value of stock option grants were as follows: Year Ended 2022 2021 Risk-free interest rate 1.9 %– 4.2 % 1.2 %– 1.3 % Expected volatility 83.4 %– 94.3 % 82 % Expected term (in years) 5.3 – 6.1 5.5 – 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 2022 2021 Research and development $ 1,720 $ 50 General and administrative 1,283 17 Total $ 3,003 $ 67 The weighted average grant date fair value per share of option grants for the years ended December 31, 2022 and 2021 was $ 9.41 and $ 4.88 , respectively. No stock options were exercised during the years ended December 31, 2022 or 2021. As of December 31, 2022, total unrecognized stock-based compensation cost was approximately $ 13.8 million, which is expected to be recognized over a remaining weighted-average period of approximately 3.3 years. A summary of the Company’s unvested shares is as follows: Number of Balance at December 31, 2021 2,625,435 Shares repurchased ( 81,949 ) Share vesting ( 958,777 ) Balance at December 31, 2022 1,584,709 For accounting purposes, unvested shares of common stock are considered issued, but not outstanding until they vest. As of December 31, 2022 and 2021, 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 2,111,989 Shares available for issuance under the Plans 4,231,570 Shares available for issuance under the ESPP 398,014 6,741,573

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	10. 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 2022 2021 Tax computed at federal statutory rate $ ( 33,588 ) $ ( 21,506 ) State income taxes ( 1,366 ) ( 586 ) Change in fair value of warrant liabilities 9,249 5,441 Convertible debt 11,396 4,840 Permanent differences and other ( 354 ) 69 Change in valuation allowance 14,734 11,742 Other ( 71 ) — Provision for income taxes $ — $ — Significant components of the Company’s deferred tax assets are as follows (in thousands): December 31, 2022 2021 Deferred tax assets: Intangible assets $ 8,406 $ 8,372 Net operating loss carryforwards 6,950 2,849 Start up and organization costs 685 756 Capitalized research cost 9,337 — Lease liability 4,979 — Other, net 1,030 164 Total deferred tax assets 31,387 12,141 Valuation allowance ( 26,930 ) ( 12,141 ) Deferred tax assets, net of allowance $ 4,457 $ — Deferred tax liabilities: Right-of-use asset $ ( 4,457 ) — Total deferred tax liabilities ( 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 $ 26.9 million as of December 31, 2022 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, 2022 , the Company has federal and state net operating loss carryforwards of approximately $ 29.4 million and $ 12.4 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 has not yet conducted a study to document whether its research activities may qualify for the research and development tax credit. Such a study may result in the creation of a research and development credit carryforward; however, until a study is completed, no amount is being presented as a deferred tax asset or as an uncertain tax position. Any research and development credit carryforward identified and claimed if and when such study is complete would be offset by an adjustment to 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. As of December 31, 2022, the Company has no uncertain tax positions. 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.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2022
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.
Initial Public Offering	Initial Public Offering On May 3, 2022, the Company completed its initial public offering ("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 (see Note 9).
Liquidity and Capital Resources	Liquidity and Capital Resources From inception to December 31, 2022, 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, 2022, the Company has funded its operations through the issuance of convertible promissory notes, commercial bank debt and the sale of common stock in its IPO which closed in May 2022. The accompanying consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business, and do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or amounts and classification of liabilities. 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, North Bridge V and YamadaCo III were entities under the common control of Frazier Life Sciences X, L.P. or its affiliates (“Frazier”) as a result of, among others, Frazier’s: (i) ownership of a majority of the outstanding capital stock of each of the companies, (ii) financing of each of the companies, (iii) control of board of directors of each of the companies, and (iv) management of each of the companies. As the merged entities were under common control, the financial statements prior to the Merger report the financial position, results of operations and cash flows of these merged companies. The financial statements also include, subsequent to its formation in May 2021, the accounts of HilleVax GmbH, a wholly-owned subsidiary formed in Zurich, Switzerland. The functional currency of both the Company 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 unaudited 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 unaudited consolidated financial statements relate to accruals for research and development expenses, and 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 earnings 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 5).
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 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 (generally 3 years). 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, 2022 .
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 and employee stock purchase rights, recognized on a straight-line basis over the requisite service period for stock options 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 year ended December 31, 2022, comprehensive loss included gains and losses on the Company's pension benefit obligation. For the year ended December 31, 2021, the Company’s comprehensive loss was the same as its reported net loss.
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 included 5,883,500 shares of common stock under the Takeda Warrant, prior to exercise, in the calculation of basic weighted-average common shares outstanding from the time the Takeda Warrant became exercisable upon the Company’s IPO because the Takeda Warrant is exercisable for minimal consideration. The Company has excluded weighted-average unvested shares of 2,080,038 shares and 2,694,011 shares from the basic weighted-average number of common shares outstanding for the years ended December 31, 2022 and 2021, respectively. See Note 9 for further information regarding these share restrictions. 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, contingently issuable shares under the Company's employee stock purchase plan, and common stock warrants. 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, 2022 2021 Common stock options 2,111,989 — Common stock warrants — 5,883,500 Unvested common stock 1,584,709 2,625,435 ESPP shares 4,420 — Total potentially dilutive shares 3,701,118 8,508,935
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 There were no recently adopted accounting standards which would have a material impact on the Company's financial statements. Recently Issued Accounting Pronouncements The Company assesses the adoption impacts of recently issued accounting standards by the Financial Accounting Standards Board or other standard setting bodies on the Company's consolidated financial statements as well as material updates to previous assessments, if any. Although there were several other new accounting pronouncements issued or proposed by the FASB, the Company does not believe any of those accounting pronouncements have had or will have a material impact on its financial position or operating results.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
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, 2022 2021 Common stock options 2,111,989 — Common stock warrants — 5,883,500 Unvested common stock 1,584,709 2,625,435 ESPP shares 4,420 — Total potentially dilutive shares 3,701,118 8,508,935

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Liabilities Measured at Fair Value on Recurring Basis	The following tables present information about the Company's liabilities measured at fair value on a recurring basis as of December 31, 2022 and December 31, 2021 (in thousands): Fair Value Measurements at Total Quoted Prices in Significant Significant As of December 31, 2022: Warrant liabilities $ — $ — $ — $ — Convertible promissory notes — — — — Total $ — $ — $ — $ — As of December 31, 2021: Warrant liabilities $ 56,445 $ — $ — $ 56,445 Convertible promissory notes 158,276 — — 158,276 Total $ 214,721 $ — $ — $ 214,721
Summary of Significant Unobservable Inputs Used in Fair Value Measurements	The following table summarizes information about the significant unobservable inputs used in the fair value measurements for the Takeda Warrants and the August 2021 Notes as of December 31, 2021: Liability Key Unobservable Inputs Range Takeda Warrants Transaction prices per share $ 11.83 - $ 12.54 Estimated time to liquidity 0.20 - 1.75 years Discount rate 20 % August 2021 Notes Estimated time to liquidity 0.20 - 1.75 years Volatility 80 % - 100 % Discount rate 19 % - 20 % Risk-free interest rate 0.1 % - 0.7 %
Reconciliation of All Liabilities Measured at Fair Value Using Level 3 Significant Unobservable Inputs	The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs (in thousands): Warrant Convertible Balance at December 31, 2021 $ 56,445 $ 158,276 Change in fair value 43,575 51,469 Reclass Takeda Warrant into equity ( 100,020 ) — Conversion of August 2021 Notes into common shares upon IPO (excluding accrued interest of $ 5,619 ) — ( 209,745 ) Balance at December 31, 2022 $ — $ —

Other Balance Sheet Details (Ta

Other Balance Sheet Details (Tables)	12 Months Ended
	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Property and Equipment	Property and equipment, net consisted of the following (in thousands): December 31, 2022 2021 Furniture and equipment $ 11 $ 45 Leasehold improvements 378 — Construction in progress 5,198 — Total property and equipment, at cost 5,587 45 Less accumulated depreciation 1 3 Property and equipment, net $ 5,586 $ 42
Accrued Expenses	Accrued expenses consisted of the following (in thousands): December 31, 2022 2021 Accrued external research and development costs $ 3,510 $ 6,425 Accrued payroll and payroll-related costs 4,018 1,010 Other 682 1,729 Total accrued expenses $ 8,210 $ 9,164
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, 2022 2021 Cash and cash equivalents $ 279,401 $ 124,566 Restricted cash 1,631 — Total cash, cash equivalents and restricted cash $ 281,032 $ 124,566

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2022
Leases [Abstract]
Schedule of Operating Lease Expense	The following table summarizes operating lease expense during the year ended December 31, 2022 (in thousands): Year Ended 2022 Lease expense: Operating lease expense $ 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: Year Ended 2022 2021 Other information: Weighted-average remaining lease term 9.96 4.75 Weighted-average discount rate 7.4 % 6.0 %
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) $ 101
Schedule of Future Minimum Noncancelable Operating Lease Payments	At December 31, 2022, the future minimum noncancelable operating lease payments were as follows (in thousands): December 31, Years ending December 31: 2023 $ 3,483 2024 3,584 2025 3,688 2026 3,784 2027 3,860 Thereafter 21,075 Total undiscounted operating lease payments 39,474 Present value adjustment ( 11,950 ) Tenant improvement reimbursements ( 5,918 ) Operating lease liability 21,606 Less current portion of operating lease liability 37 Operating lease liability, net of current portion $ 21,569

Convertible Promissory Notes _2

Convertible Promissory Notes and Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Schedule of Term Loan	The Company’s Term Loan consists of the following (in thousands): December 31, Long-term debt $ 15,000 Accumulated PIK interest 87 Total principal (including PIK interest) 15,087 Unamortized debt discount ( 295 ) Long-term debt, net of debt discount $ 14,792
Schedule of Future Minimum Principal and Interest Payments	Future minimum principal and interest payments, including the final payment fee, as of December 31, 2022 are as follows (in thousands): December 31, Years ending December 31: 2023 $ 902 2024 967 2025 5,063 2026 7,982 2027 7,405 Total principal payments, interest payments and final payment fee 22,319 Less: interest, PIK interest and final payment fee ( 7,232 ) Long-term debt $ 15,087

Stockholder's Equity (Deficit)

Stockholder's Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2022
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, 2021 727,873 $ 6.99 9.94 $ 765 Granted 1,494,384 12.42 Cancelled ( 110,268 ) 11.05 Balance at December 31, 2022 2,111,989 $ 10.62 9.33 $ 13,330 Vested and expected to vest at December 31, 2022 2,111,989 $ 10.62 9.33 $ 13,330 Exercisable at December 31, 2022 114,595 $ 7.28 8.95 $ 1,084
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 2022 2021 Risk-free interest rate 1.9 %– 4.2 % 1.2 %– 1.3 % Expected volatility 83.4 %– 94.3 % 82 % Expected term (in years) 5.3 – 6.1 5.5 – 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 2022 2021 Research and development $ 1,720 $ 50 General and administrative 1,283 17 Total $ 3,003 $ 67
Summary of Unvested Shares	A summary of the Company’s unvested shares is as follows: Number of Balance at December 31, 2021 2,625,435 Shares repurchased ( 81,949 ) Share vesting ( 958,777 ) Balance at December 31, 2022 1,584,709
Schedule of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance consists of the following: December 31, Common stock options outstanding 2,111,989 Shares available for issuance under the Plans 4,231,570 Shares available for issuance under the ESPP 398,014 6,741,573

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022
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 2022 2021 Tax computed at federal statutory rate $ ( 33,588 ) $ ( 21,506 ) State income taxes ( 1,366 ) ( 586 ) Change in fair value of warrant liabilities 9,249 5,441 Convertible debt 11,396 4,840 Permanent differences and other ( 354 ) 69 Change in valuation allowance 14,734 11,742 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, 2022 2021 Deferred tax assets: Intangible assets $ 8,406 $ 8,372 Net operating loss carryforwards 6,950 2,849 Start up and organization costs 685 756 Capitalized research cost 9,337 — Lease liability 4,979 — Other, net 1,030 164 Total deferred tax assets 31,387 12,141 Valuation allowance ( 26,930 ) ( 12,141 ) Deferred tax assets, net of allowance $ 4,457 $ — Deferred tax liabilities: Right-of-use asset $ ( 4,457 ) — Total deferred tax liabilities ( 4,457 ) — Net deferred tax assets $ — $ —

Organization - Additional Infor

Organization - Additional Information (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	May 03, 2022 USD ($) $ / shares shares	Apr. 22, 2022 shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 shares
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Forward split of shares		1.681
Common stock shares authorized | shares		50,000,000	500,000,000	50,000,000
Sale of common stock | shares	13,529,750
Public offering price per share | $ / shares	$ 17
Net proceeds from initial public offering | $	$ 209,500		$ 230,006
Underwriting discounts, commissions and offering costs | $	$ 20,500

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2022 Segment shares	Dec. 31, 2021 shares
Summary of Significant Accounting Policies [Line Item]
Number of operating segment | Segment	1
Basic weighted- average common shares outstanding	27,147,314	5,619,182
Weighted-average unvested shares excluded from computation of earnings per share amount	2,080,038	2,694,011
Initial Public Offering
Summary of Significant Accounting Policies [Line Item]
Basic weighted- average common shares outstanding	5,883,500

Summary of Significant Accoun_5

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, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	3,701,118	8,508,935
Common Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	2,111,989
Common Stock Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount		5,883,500
Unvested common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	1,584,709	2,625,435
ESPP shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount	4,420

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details)	12 Months Ended
	Dec. 31, 2022 USD ($) $ / shares shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchase of common stock upon exercise of outstanding warrant | shares	5,883,500
Transaction prices per share | $ / shares	$ 0.0000595
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	$ 0
Non-Recurring
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 Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring $ in Thousands	Dec. 31, 2021 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	$ 214,721
Warrant Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	56,445
Convertible Promissory Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	158,276
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	214,721
Significant Unobservable Inputs (Level 3) | Warrant Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	56,445
Significant Unobservable Inputs (Level 3) | Convertible Promissory Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value	$ 158,276

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Significant Unobservable Inputs Used in Fair Value Measurements (Details)	12 Months Ended
	Dec. 31, 2021 $ / shares	Dec. 31, 2022 $ / shares
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Transaction prices per share		$ 0.0000595
Takeda Warrants | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants measurement input	20
Takeda Warrants | Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Transaction prices per share	$ 11.83
Estimated time to liquidity	2 months 12 days
Takeda Warrants | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Transaction prices per share	$ 12.54
Estimated time to liquidity	1 year 9 months
August 2021 Notes | Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Estimated time to liquidity	2 months 12 days
August 2021 Notes | Minimum | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes measurement input	19
August 2021 Notes | Minimum | Volatility
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes measurement input	80
August 2021 Notes | Minimum | Risk-Free Interest Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes measurement input	0.1
August 2021 Notes | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Estimated time to liquidity	1 year 9 months
August 2021 Notes | Maximum | Discount Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes measurement input	20
August 2021 Notes | Maximum | Volatility
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes measurement input	100
August 2021 Notes | Maximum | Risk-Free Interest Rate
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Notes measurement input	0.7

Fair Value Measurements - Sum_3

Fair Value Measurements - Summary of Reconciliation of All Liabilities Measured at Fair Value Using Level 3 Significant Unobservable Inputs (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Reclass Takeda Warrant into equity	$ (100,020)
Warrant Liabilities
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at December 31, 2021	56,445
Change in fair value	43,575
Reclass Takeda Warrant into equity	(100,020)
Convertible Promissory Notes
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at December 31, 2021	158,276
Change in fair value	51,469
Conversion of August 2021 Notes into common shares upon IPO (excluding accrued interest of $5,619)	$ (209,745)

Fair Value Measurements - Recon

Fair Value Measurements - Reconciliation of All liabilities Measured At Fair Value Using Level 3 Significant Unobservable Inputs (in thousands) (Parenthetical) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
August 2021 Notes
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Debt instrument accrued interest	$ 5,619

Other Balance Sheet Details - S

Other Balance Sheet Details - Summary of Components of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 5,587	$ 45
Less accumulated depreciation	1	3
Property, Plant and Equipment, Net, Total	5,586	42
Furniture and equipment
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	11	$ 45
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	378
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 5,198

Other Balance Sheet Details -_2

Other Balance Sheet Details - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Accrued external research and development costs	$ 3,510	$ 6,425
Accrued payroll and payroll-related costs	4,018	1,010
Other	682	1,729
Total accrued expenses	$ 8,210	$ 9,164

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, 2022	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Cash and cash equivalents	$ 279,401	$ 124,566
Restricted cash	1,631
Total cash, cash equivalents and restricted cash	$ 281,032	$ 124,566	$ 457

Leases - Additional Information

Leases - Additional Information (Details) - USD ($)	1 Months Ended		12 Months Ended
	Mar. 31, 2022	Aug. 31, 2021	Dec. 31, 2022	Dec. 31, 2021
Lessee, Lease, Description [Line Items]
Operating lease expense			$ 2,351,000	$ 0
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
Maximum lessee operating lease tenant improvement allowances for reimbursement cost			$ 6,300,000
Irrevocable standby letter of credit secured by restricted cash amount			$ 1,600,000

Leases - Schedule of Operating

Leases - Schedule of Operating Lease Expense (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Lease expense:
Operating lease expense	$ 2,351,000	$ 0

Leases - Schedule of Weighted A

Leases - Schedule of Weighted Average Lease Term and Discount Rate for Operating Lease (Details)	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
Weighted-average remaining lease term	9 years 11 months 15 days	4 years 9 months
Weighted-average discount rate	7.40%	6%

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, 2022 USD ($)
Leases [Abstract]
Cash paid for amounts included in the measurement of operating lease liabilities (operating cash flows)	$ 101

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Noncancelable Operating Lease Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Leases [Abstract]
2023	$ 3,483
2024	3,584
2025	3,688
2026	3,784
2027	3,860
Thereafter	21,075
Total undiscounted operating lease payments	39,474
Present value adjustment	(11,950)
Tenant improvement reimbursements	(5,918)
Operating lease liability	21,606
Less current portion of operating lease liability	37	$ 32
Operating lease liability, net of current portion	$ 21,569	$ 153

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Change in fair value of convertible promissory notes	$ 51,469,000	$ 20,204,000
Accounts payable and accrued expenses	8,210,000	9,164,000
Frazier
Related Party Transaction [Line Items]
Due to related parties	6,000	22,000
Shared operating expenses	40,000	600,000
Change in fair value of convertible promissory notes	13,200,000	6,300,000
Interest Expense	700,000	700,000
Takeda | TSA
Related Party Transaction [Line Items]
Research and development expenses	2,400,000	4,900,000
Accounts payable and accrued expenses	$ 300,000	$ 4,900,000

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, 2022	Dec. 31, 2021
Commitments And Contingencies Disclosure [Line Items]
Purchase of common stock upon exercise of outstanding warrant				5,883,500
Transaction prices per share				$ 0.0000595
Common stock shares issued				39,240,746	9,225,321
Issuance of common stock in connection with Takeda License					$ 4,357,000
Matching contribution				the Company made matching contributions equal to 100% of the employee’s contributions, subject to a maximum of 4% of eligible compensation. The matching contributions for the year ended December 31, 2022 were not material.
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
Contingent payment recorded as in-process research and development	$ 2,500,000		$ 2,500,000		37,700,000
Common stock shares issued	840,500
Issuance of common stock in connection with Takeda License	$ 4.4
Promissory notes initial fair value	34,000,000
Development Milestones	7,500,000
Sales Milestones	$ 150,000,000
Transaction costs					$ 300,000
Research and Development Asset Acquired Other than through Business Combination, Writeoff, Statement of Income or Comprehensive Income [Extensible Enumeration]					Research and Development in Process with Related Party

Convertible Promissory Notes _3

Convertible Promissory Notes and Long-Term Debt - Additional Information (Details) - USD ($)			12 Months Ended
	Apr. 18, 2022	Aug. 31, 2021	Dec. 31, 2022	Dec. 31, 2021
Convertible Promissory Notes [Line Items]
Convertible promissory notes, outstanding principal balance				$ 158,276,000
Change in fair value of convertible promissory notes			$ 51,469,000	$ 20,204,000
Debt instrument, carrying amount			15,000,000
PIK interest			87,000
Amortization of debt discount			$ 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
Term Loan
Convertible Promissory Notes [Line Items]
Interest expense			$ 600,000
Debt instrument, accretion of final payment fee			300,000
PIK interest			100,000
Debt instrument, coupon interest			$ 200,000
Term Loan | Loan Agreement
Convertible Promissory Notes [Line Items]
Debt instrument, interest rate	4.55%		6.05%
Debt instrument, carrying amount	$ 75,000,000
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, (x) the conditions to Term Loan 3 have been satisfied and (y) the Company has reasonably determined that (i) the HIL-214 Vaccine Trial has achieved the protocol-specified primary efficacy endpoint and (ii) HIL-214 has demonstrated acceptable safety results in the HIL-214 Vaccine 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, in each case 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	$ 2,100,000		$ 2,100,000
Percentage of original principal amount payable	7.15%
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	2%
Term Loan | Prime Rate | Loan Agreement
Convertible Promissory Notes [Line Items]
Debt instrument, basis spread on variable rate	1.05%
Term Loan 1 | Loan Agreement
Convertible Promissory Notes [Line Items]
Debt instrument, amount borrowed	$ 5,000,000
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
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	$ 2,800,000
Convertible promissory notes, outstanding principal balance				139,500,000
Change in fair value of convertible promissory notes			51,500,000	$ 20,200,000
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 | Maximum
Convertible Promissory Notes [Line Items]
Debt instrument, available credit under loan agreement			15,000,000
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, 2022 USD ($)
Debt Disclosure [Abstract]
Long-term debt	$ 15,000
Accumulated PIK interest	87
Total principal (including PIK interest)	15,087
Unamortized debt discount	(295)
Long-term debt, net of debt discount	$ 14,792

Convertible Promissory Notes _5

Convertible Promissory Notes and Long-Term Debt - Schedule of Future Minimum Principal and Interest Payments (Details) $ in Thousands	Dec. 31, 2022 USD ($)
Debt Disclosure [Abstract]
2023	$ 902
2024	967
2025	5,063
2026	7,982
2027	7,405
Total principal payments, interest payments and final payment fee	22,319
Less: interest, PIK interest and final payment fee	(7,232)
Long-term debt	$ 15,087

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended		3 Months Ended		12 Months Ended
	May 03, 2022	Feb. 08, 2021	Apr. 30, 2022	Mar. 31, 2021	May 31, 2021	Apr. 30, 2021	Dec. 31, 2022	Dec. 31, 2021	Apr. 22, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield							0%	0%
Weighted average grant date fair value per share of option grants							$ 9.41	$ 4.88
Common Stock Shares Issued							39,240,746	9,225,321
Stock options exercised							0	0
Total unrecognized stock-based compensation cost							$ 13,800
Total unrecognized stock-based compensation cost expected to be recognized over remaining weighted-average period							3 years 3 months 18 days
Sale of common stock	13,529,750
Public offering price per share	$ 17
Net proceeds from initial public offering	$ 209,500						$ 230,006
Underwriting discounts, commissions and offering costs	$ 20,500
Increase in number of authorized shares of common stock							500,000,000	50,000,000	50,000,000
Increase in number of authorized shares of preferred stock							50,000,000	0
Shares reserved for issuance							6,741,573
Initial Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Sale of common stock	13,529,750
Public offering price per share	$ 17
Net proceeds from initial public offering	$ 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
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting restrictions placed on previously issued and outstanding common stock, Shares								2,332,386
Sale of common stock								1,606,815
Common Stock | Initial Public Offering
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Sale of common stock							13,529,750
Common Stock | Certain Employees and Consultants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Repurchase rights lapse description							The repurchase rights lapse over a four-year period, with 25% lapsing on the first anniversary of the vesting commencement date and the remaining portion lapsing in 36 equal monthly amounts thereafter.
Repurchase rights lapse period					4 years
Repurchase percentage lapsing on the first anniversary of the vesting commencement date					25%
Remaining repurchase portion lapsing					36 months
Sale of common stock					707,701
Public offering price per share					$ 0.0006303
Common Stock | Founders
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Remaining repurchase portion lapsing							48 months
Vesting restrictions placed on previously issued and outstanding common stock, Shares		2,332,386
Accelerated Share Repurchases, Initial Price Paid Per Share		$ 0.0003816
Common stock shares issued restrictions have lapsed		583,095					1,749,291
Frazier
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Sale of common stock		1,606,815
Public offering price per share		$ 0.0006303
2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Plan term							ten years
Vesting period							4 years
Repurchase rights lapse description							The share restriction generally lapses over a four- year period, with 25% lapsing on the first anniversary of the vesting commencement date and the remaining portion lapsing in 36 equal monthly amounts thereafter.
Repurchase rights lapse period							4 years
Repurchase percentage lapsing on the first anniversary of the vesting commencement date							25%
Remaining repurchase portion lapsing							36 months
Sale of common stock				16,810		1,713,779
Public offering price per share				$ 0.0006303
Shares reserved for issuance							4,231,570
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							5,192,844
Number of shares remained available for issuance under awards granted			4,900,000				4,231,570
Shares issuance, ending year			2032
Percentage of shares issued from outstanding number of shares			5%
Shares issuance, beginning year			2023
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							398,014
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%
Shares issuance, beginning year			2023

Stockholders' Equity (Deficit_2

Stockholders' Equity (Deficit) - Summary of Stock Option Activity (Details) - Plans - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of outstanding options, Beginning balance	727,873
Number of outstanding options, Granted	1,494,384
Number of outstanding options, Cancelled	(110,268)
Number of outstanding options, Ending Balance	2,111,989	727,873
Number of outstanding options, Vested and expected to vest at December 31, 2022	2,111,989
Number of outstanding options, Exercisable at December 31, 2022	114,595
Weighted average exercise price, Beginning balance	$ 6.99
Weighted average exercise price, Granted	12.42
Weighted average exercise price, Cancelled	11.05
Weighted average exercise price, Ending balance	10.62	$ 6.99
Weighted average exercise price, Vested and expected to vest at December 31, 2022	10.62
Weighted average exercise price, Exercisable at December 31, 2022	$ 7.28
Weighted-average remaining contractual term (in years)	9 years 3 months 29 days	9 years 11 months 8 days
Weighted-average remaining contractual term (in years), Vested and expected to vest at December 31, 2022	9 years 3 months 29 days
Weighted-average remaining contractual term (in years) Exercisable at December 31, 2022	8 years 11 months 12 days
Aggregate intrinsic value	$ 13,330	$ 765
Aggregate intrinsic value, Vested and expected to vest at December 31, 2022	13,330
Aggregate intrinsic value, Exercisable at December 31, 2022	$ 1,084

Stockholders' Equity (Deficit_3

Stockholders' Equity (Deficit) - Summary of Assumptions used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option Grants (Details)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	1.90%	1.20%
Risk-free interest rate, maximum	4.20%	1.30%
Expected volatility		82%
Expected volatility, minimum	83.40%
Expected volatility, maximum	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 3 months 18 days	5 years 6 months
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 (Deficit_4

Stockholders' Equity (Deficit) - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 3,003	$ 67
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	1,720	50
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total	$ 1,283	$ 17

Stockholders' Equity (Deficit)-

Stockholders' Equity (Deficit)- Summary of Unvested Shares (Details)	12 Months Ended
	Dec. 31, 2022 shares
Stockholders Equity Note [Abstract]
Number of unvested shares, Beginning balance	2,625,435
Shares repurchased	(81,949)
Number of unvested shares, Shares vesting	(958,777)
Number of unvested shares, Ending balance	1,584,709

Stockholders' Equity (Deficit_5

Stockholders' Equity (Deficit) - Schedule of Common Stock Reserved for Future Issuance (Details)	Dec. 31, 2022 shares
Class Of Stock [Line Items]
Common stock reserved for future issuance	6,741,573
Common Stock Options
Class Of Stock [Line Items]
Common stock reserved for future issuance	2,111,989
Shares Available for Issuance Under the 2021 Plan
Class Of Stock [Line Items]
Common stock reserved for future issuance	4,231,570
Shares available for issuance under the ESPP
Class Of Stock [Line Items]
Common stock reserved for future issuance	398,014

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, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Tax computed at federal statutory rate	$ (33,588)	$ (21,506)
State income taxes	(1,366)	(586)
Change in fair value of warrant liabilities	9,249	5,441
Convertible debt	11,396	4,840
Permanent differences and other	(354)	69
Change in valuation allowance	14,734	$ 11,742
Other	$ (71)

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Intangible assets	$ 8,406	$ 8,372
Net operating loss carryforwards	6,950	2,849
Start up and organization costs	685	756
Capitalized research cost	9,337
Lease liability	4,979
Other, net	1,030	164
Total deferred tax assets	31,387	12,141
Valuation allowance	(26,930)	$ (12,141)
Deferred tax assets, net of allowance	4,457
Deferred tax liabilities:
Right-of-use asset	(4,457)
Total deferred tax liabilities	$ (4,457)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 26,930,000	$ 12,141,000
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.
Uncertain tax positions	$ 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	$ 29,400,000
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 12,400,000