Tectonic Therapeutic (TECX) S-1 19 Jul 24 IPO registration Financial data

Cover Page

Cover Page	3 Months Ended
	Mar. 31, 2024
Document Information [Line Items]
Document Type	S-1
Amendment Flag	false
Entity Registrant Name	Tectonic Therapeutic, Inc.
Entity Central Index Key	0001681087
Entity Incorporation, State or Country Code	DE
Entity Primary SIC Number	2836
Entity Tax Identification Number	81-0710585
Entity Address, Address Line One	490 Arsenal Way
Entity Address, Address Line Two	Suite 210
Entity Address, City or Town	Watertown
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02472
City Area Code	339
Local Phone Number	666-3320
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Business Contact [Member]
Document Information [Line Items]
Contact Personnel Name	Daniel Lochner
Entity Address, Address Line One	490 Arsenal Way
Entity Address, Address Line Two	Suite 210
Entity Address, City or Town	Watertown
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02472
City Area Code	339
Local Phone Number	666-3320

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 18,748	$ 28,769	$ 35,966
Prepaid expenses and other current assets	1,810	2,115	1,076
Total current assets	20,558	30,884	37,042
Property, equipment and improvements, net	2,864	3,122	3,608
Finance right-of-use assets, net	1,323	1,437	2,159
Operating right-of-use assets	2,375	2,669	3,787
Deferred offering costs	3,444	669
Restricted cash	587	587	587
Other assets	4	31	26
Total assets	31,155	39,399	47,209
Current liabilities:
Accounts payable	2,563	409	574
Accrued expenses and other current liabilities	11,048	8,141	5,814
SAFE liabilities	32,590	30,515
Operating lease liability - current portion	1,388	1,348	950
Finance lease liability - current portion	475	475	499
Total current liabilities	48,064	40,888	7,837
Operating lease liability - net of current portion	1,280	1,644	2,992
Finance lease liability - net of current portion	758	876	1,351
Other noncurrent liabilities			56
Total liabilities	50,102	43,408	12,236
Commitments and contingencies (Note 6)
Convertible preferred stock	80,627	80,627	80,627
Stockholders' Deficit
Common stock
Additional paid-in capital	6,304	5,979	2,127
Accumulated other comprehensive loss	(53)	(11)
Accumulated deficit	(105,825)	(90,604)	(47,781)
Total stockholders' deficit	(99,574)	(84,636)	(45,654)
Total liabilities, convertible preferred stock and stockholders' deficit	$ 31,155	$ 39,399	$ 47,209

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Preferred stock, authorized	6,825,483	6,825,483	6,825,483
Preferred stock, issued	6,825,483	6,825,483	6,825,483
Preferred stock, outstanding	6,825,483	6,825,483	6,825,483
Temporary Equity, Liquidation Preference	$ 87,459	$ 87,459	$ 87,459
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, authorized	11,947,558	11,947,558	11,947,558
Common stock, issued	2,637,120	2,634,246	2,525,771
Common stock, outstanding	2,637,120	2,634,246	2,525,771
Convertible Preferred Stock [Member]
Preferred stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred stock, authorized	6,825,483	6,825,483	6,825,483
Preferred stock, issued	6,825,483	6,825,483	6,825,483
Preferred stock, outstanding	6,825,483	6,825,483	6,825,483
Temporary Equity, Liquidation Preference	$ 87,459	$ 87,459	$ 87,459

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and other Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Operating expenses:
Research and development	$ 10,818	$ 12,985	$ 36,966	$ 25,654
General and administrative	2,150	1,546	7,682	7,176
Total operating expenses	12,968	14,531	44,648	32,830
Loss from operations	(12,968)	(14,531)	(44,648)	(32,830)
Other income (expense), net:
Change in fair value of preferred stock tranche liability				643
Loss on issuance of SAFEs			(255)
Change in fair value of SAFE liabilities	(2,075)		1,255
Interest income	256	128	581	149
Interest expense	(31)	(42)	(152)	(144)
Other income (expense)	(403)		396	2
Total other (expense) income, net	(2,253)	86	1,825	650
Loss before provision for income taxes			(42,823)	(32,180)
Net loss	$ (15,221)	$ (14,445)	$ (42,823)	$ (32,180)
Net loss per share attributable to common stockholders, basic	$ (5.83)	$ (6.5)	$ (18.04)	$ (16.34)
Net loss per share attributable to common stockholders, diluted	$ (5.83)	$ (6.5)	$ (18.04)	$ (16.34)
Weighted-average common shares outstanding, basic	2,608,740	2,222,800	2,373,674	1,969,418
Weighted-average common shares outstanding, diluted	2,608,740	2,222,800	2,373,674	1,969,418
Other comprehensive loss:
Foreign currency translation adjustment	$ (50)		$ (11)
Comprehensive loss	$ (15,271)	$ (14,445)	$ (42,834)	$ (32,180)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Convertible Preferred Stock [Member] Preferred Stock [Member]
Beginning balance at Dec. 31, 2021	$ (14,960)		$ 641		$ (15,601)	$ 42,610
Beginning balance (in shares) at Dec. 31, 2021		2,297,901				3,941,829
Exercise of stock options	4		4
Exercise of stock options (in shares)		3,233
Stock-based compensation expense	1,119		1,119
Issuance of common stock	363		363			$ 38,017
Issuance of common stock (in shares)		227,486				2,883,654
Repurchase of common stock (in shares)		(2,849)
Net loss	(32,180)				(32,180)
Ending balance at Dec. 31, 2022	(45,654)		2,127		(47,781)	$ 80,627
Ending balance (in shares) at Dec. 31, 2022		2,525,771				6,825,483
Exercise of stock options	1		1
Exercise of stock options (in shares)		1,285
Stock-based compensation expense	275		275
Net loss	(14,445)				(14,445)
Ending balance at Mar. 31, 2023	(59,823)		2,403		(62,226)	$ 80,627
Ending balance (in shares) at Mar. 31, 2023		2,527,056				6,825,483
Beginning balance at Dec. 31, 2022	(45,654)		2,127		(47,781)	$ 80,627
Beginning balance (in shares) at Dec. 31, 2022		2,525,771				6,825,483
Exercise of stock options	$ 121		121
Exercise of stock options (in shares)	108,475	108,475
Stock-based compensation expense	$ 1,121		1,121
Contribution from related party investors related to SAFEs	2,610		2,610
Foreign currency translation adjustment	(11)			$ (11)
Net loss	(42,823)				(42,823)
Ending balance at Dec. 31, 2023	(84,636)		5,979	(11)	(90,604)	$ 80,627
Ending balance (in shares) at Dec. 31, 2023		2,634,246				6,825,483
Exercise of stock options	$ 4		4
Exercise of stock options (in shares)	2,874	2,874
Stock-based compensation expense	$ 321		321
Foreign currency translation adjustment	(42)			(42)
Net loss	(15,221)				(15,221)
Ending balance at Mar. 31, 2024	$ (99,574)		$ 6,304	$ (53)	$ (105,825)	$ 80,627
Ending balance (in shares) at Mar. 31, 2024		2,637,120				6,825,483

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Deficit (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2022
Net of issuance costs	$ 554	$ 12

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net loss	$ (15,221)	$ (14,445)	$ (42,823)	$ (32,180)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	377	364	1,478	1,006
Stock-based compensation expense	321	275	1,121	1,119
Loss on fixed asset disposal			9
Loss on issuance of SAFEs			255
Non-cash lease expense	294	274	1,118	862
Non-cash issuance of common stock for the exchange of license				363
Change in fair value of preferred stock tranche liability				(643)
Change in fair value of SAFE liabilities	2,075		(1,255)
Change in operating assets and liabilities:
Prepaid expenses and other current assets	289	(335)	(1,019)	(376)
Other non-current assets	24	(20)	(5)	(14)
Accounts payable	1,510	1,039	(165)	(1,234)
Accrued expenses and other current liabilities	1,382	2,326	1,611	4,509
Operating lease liabilities	(324)	(293)	(950)	(1,105)
Other non-current liabilities			(56)	56
Net cash used in operating activities	(9,273)	(10,815)	(40,681)	(27,637)
Cash flows from investing activities:
Purchase of property, equipment and improvements	(4)	(136)	(279)	(2,088)
Net cash used in investing activities	(4)	(136)	(279)	(2,088)
Cash flows from financing activities:
Proceeds from the issuance of SAFEs			34,125
Proceeds from issuance of convertible preferred stock - net of issuance costs				38,017
Payment for deferred offering costs	(554)			(12)
Proceeds from exercise of common stock options	4	1	121	4
Repayment of finance lease obligations	(118)	(144)	(499)	(393)
Net cash used in financing activities	(668)	(143)	33,747	37,628
Effect of exchange rate changes on cash and cash equivalents	(76)		16
Net decrease in cash and cash equivalents and restricted cash	(10,021)	(11,094)	(7,197)	7,903
Cash and cash equivalents and restricted cash as of beginning of period	29,356	36,553	36,553	28,650
Cash and cash equivalents and restricted cash as of end of period	19,335	25,459	29,356	36,553
Components of cash, cash equivalents and restricted cash:
Cash and cash equivalents	18,748	24,872	28,769	35,966
Restricted cash	587	587	587	587
Total cash, cash equivalents and restricted cash	19,335	25,459	29,356	36,553
Supplemental disclosure of non-cash financing activities:
Purchase of equipment through finance leases			234	1,340
Deferred offering costs included in accrued expenses and other current liabilities	1,576		669
Supplemental disclosure of cash flow information:
Cash paid for interest	$ 31	$ 42	$ 152	$ 144

Description of Business

Description of Business	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	1. DESCRIPTION OF BUSINESS Business Tectonic Therapeutic, Inc. (“Company”) is a biotechnology company focused on the discovery and development of therapeutic proteins and antibodies that modulate the activity of G-protein ™ June 5, 2019 Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive pre-clinical The Company’s proprietary GEODe ™ Liquidity and Going Concern As of March 31, 2024, the Company had an accumulated deficit of $105.8 million and has incurred losses and negative cash flows from operations since inception, including a net loss of $15.2 million for the three months ended March 31, 2024. To date, the Company has financed its operations primarily through the issuance of common stock, convertible preferred stock, convertible promissory notes and Simple Agreements for Future Equity (“SAFEs”). The Company has devoted substantially all of its financial resources and efforts to business planning, conducting research and development, recruiting management and technical staff, and raising capital. Management expects that the Company’s operating losses and negative cash flows will continue for the foreseeable future as it continues to develop its product candidates. As the Company continues to develop its proprietary platform and potential product candidates, it will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. It may never achieve profitability, and unless and until it does, it will continue to need to raise additional capital to fund its operations. On June 20, 2024, the Company completed a merger with AVROBIO, Inc. (“AVROBIO”) pursuant to which the Company received $77.3 million of cash from AVROBIO and completed the sale of $96.6 million of common stock (see Note 14). Management believes that its current cash on hand along with the cash received from the closing of the merger agreement are sufficient to fund the Company’s planned operations for at least one year from the date of issuance of these unaudited condensed consolidated financial statements.	1. DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION Business Tectonic Therapeutic, Inc. (“Company”) is a biotechnology company focused on the discovery and development of therapeutic proteins and antibodies that modulate the activity of G-protein ™ June 5, 2019 Risks and Uncertainties The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive pre-clinical The Company’s proprietary GEODe ™ Liquidity and Going Concern As of December 31, 2023, the Company had an accumulated deficit of $90.6 million and has incurred losses and negative cash flows from operations since inception, including a net loss of $42.8 million for the year ended December 31, 2023. To date, the Company has financed its operations primarily through the issuance of convertible preferred stock, convertible promissory notes and Simple Agreements for Future Equity (“SAFEs”). The Company has devoted substantially all of its financial resources and efforts to business planning, conducting research and development, recruiting management and technical staff, and raising capital. Management expects that the Company’s operating losses and negative cash flows will continue for the foreseeable future as it continues to develop its product candidates. As the Company continues to develop its proprietary platform and potential product candidates, it will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. It may never achieve profitability, and unless and until it does, it will continue to need to raise additional capital to fund its operations. The Company is seeking to complete a planned reverse merger with AVROBIO, Inc. (“AVROBIO”) (see Note 14). In the event the Company does not complete the reverse merger, the Company plans to seek additional funding through private equity financings, debt financings or other capital sources, including collaboration agreements, strategic alliances and licensing arrangements. The Company may not be able to obtain financing on acceptable terms, or at all. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. Management believes that the Company’s cash and cash equivalents of $28.8 million The Company intends to fund future operations through private and potentially public equity financings, debt financings, collaboration agreements, strategic alliances and licensing arrangements. The availability of sufficient funding to alleviate the conditions that raise substantial doubt are not within management’s control and cannot be assessed as being probable of occurring. If the Company is unable to obtain adequate financing, management will evaluate alternatives, which may include a delay, reduction or elimination of research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect future business prospects, and the ability to continue operations.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying unaudited interim condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”) and the rules and regulations of the Securities and Exchange Commission (“SEC”). Any reference in these notes to applicable guidance is meant to refer to GAAP, as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). In the opinion of the Company, the accompanying unaudited condensed consolidated financial statements contain all adjustments, consisting of only normal recurring adjustments, necessary for a fair presentation of its financial position and its results of operations, changes in convertible preferred stock and stockholders’ deficit and cash flows. The information as of December 31, 2023 included in the unaudited interim condensed consolidated balance sheets was derived from audited annual consolidated financial statements but does not contain all of the footnote disclosures from the audited annual consolidated financial statements. These unaudited interim condensed consolidated financial statements should be read in conjunction with the audited annual consolidated financial statements as of and for the years ended December 31, 2023 and 2022. Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements, and the reported amounts of expenses during the reporting periods. Significant items subject to such estimates and assumptions include the contract research accruals, stock-based compensation expense, the fair value of the Company’s common stock, the income tax valuation allowance, and the fair value determination of the SAFEs. Management’s estimates are based on historical experience and various other assumptions that it believes are reasonable under the circumstances. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Principles of Consolidation The condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB, or other standard setting bodies and are adopted by the Company as of the specified effective dates. Unless otherwise discussed, the impact of recently issued standards that are not yet effective are not anticipated to have a material impact on the Company’s condensed consolidated financial statements upon adoption. Recently Adopted Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, 470-20) 815-40): 2020-06”). 2020-06 paid-in 2020-06 2020-06 Recently Issued Accounting Pronouncements Not Yet Adopted In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting 2023-07”), 2023-07, 2023-07 2023-07 2023-07 In December 2023, the FASB issued ASU No. 2023-09, Income Taxes 2023-09”), 2023-09, 2023-09 2023-09	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to GAAP, as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). Principles of Consolidation The consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting periods. Significant items subject to such estimates and assumptions include the contract research accruals, stock-based compensation expense, the fair value of the Company’s common stock, the income tax valuation allowance, the fair value determination of the SAFEs and the preferred stock tranche liability settled in 2022. Management’s estimates are based on historical experience and various other assumptions that it believes are reasonable under the circumstances. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates. Foreign Currency The functional currency of the Company’s wholly-owned foreign subsidiary in Australia is Australian Dollars. Accounts and transactions denominated in currencies other than an entity’s functional currency are remeasured into the functional currency using the appropriate foreign exchange rate in accordance with FASB ASC Topic 830, Foreign Currency Matters. from transactions denominated in foreign currencies are recorded in the statements of operations and comprehensive loss as other income or expenses. The financial statements of the Australian subsidiary will be translated into the Company’s U.S. dollar reporting currency at each reporting date, and the translation adjustments will be recognized as an unrealized gain or loss within the cumulative translation adjustment. Segment Information The Company considered the Company’s organizational structure and the information regularly reviewed and evaluated by the Company’s chief operating decision maker (“CODM”) when deciding how to allocate resources and assess performance. The Company has determined that its CODM is its Chief Executive Officer. The CODM reviews the financial information on a consolidated basis for purposes of evaluating financial performance and allocating resources. On the basis of this factor, the Company determined that it operates and manages its business as a single Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less when purchased to be cash equivalents. As of December 31, 2023, cash equivalents were comprised primarily of money market funds. Restricted Cash The Company classifies all cash whose use is limited by contractual provisions as restricted cash. Restricted cash arises from the requirement for the Company to maintain cash of $0.6 million as collateral in connection with a letter of credit issued with the corporate headquarters and lab space lease agreement entered into on November 19, 2020 and may not access these funds until after the expiration of the initial lease term on December 31, 2025. The Company has classified the certificate of deposits collateralizing the letter of credits issued as a security deposit as restricted cash in the noncurrent asset section of the balance sheets. Deferred Offering Costs Deferred offering costs consist of direct legal, accounting and other fees and costs directly attributable to the Company’s proposed Merger (see Note 14). The Company capitalized deferred offering costs incurred prior to the close of the Merger which are included in deferred offering costs within the consolidated balance sheet as of December 31, 2023. The deferred offering costs were $0.7 million as of December 31, 2023. Concentrations of Credit Risk and Off-Balance Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. Periodically, the Company maintains deposits in accredited financial institutions in excess of governmental insured limits. The Company deposits its cash and cash equivalents in financial institutions that it believes have a high credit quality and have not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships. Property, Equipment and Improvements Property, equipment and improvements are stated at cost less accumulated depreciation. Depreciation is calculated using the straight-line method over the estimated useful life of each asset. Construction in process is capitalized and once the asset is operational, the Company will commence depreciation of the asset. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recognized. Expenditures for major renewals and improvements that extend the useful life of the asset are capitalized as part of the asset. Expenditures for repairs and maintenance are expensed as incurred. The estimated useful lives for property and equipment are as follows: Estimated Useful Life Laboratory equipment 5 years Furniture and office equipment 5 years Computer equipment 3 years Leasehold improvements Shorter of the lease term or 10 years Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist primarily of property, equipment and improvements, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. The carrying amount of a long-lived asset is not recoverable if it exceeds the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the asset. If the carrying amount of the asset is not recoverable, an impairment will be recognized and measured as the amount by which the carrying amount of the asset exceeds its fair value. No impairments were identified during the years ended December 31, 2023 and 2022. Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Market participants are independent buyers or sellers in the principal (or most advantageous) market for the asset or liability. Fair value measurements are categorized into a three-tier hierarchy on the basis of the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). The three levels of the fair value hierarchy are as follows: • Level 1 • Level 2 • Level 3 Financial instruments are categorized in their entirety in the same level of the fair value hierarchy as the lowest level input that is significant to the entire fair value measurement. Research and Development Expenses Research and development costs are expensed as incurred. Research and development expenses consist primarily of costs incurred for the development of the proprietary platform and product candidates and include (1) expenses incurred under agreements with third parties and contract research organizations (“CROs”), (2) costs to acquire and develop supplies for research, (3) salaries and related costs, including stock-based compensation, (4) depreciation and other facility-related and overhead expenses, (5) licensing and license maintenance fees incurred under license option and license agreements where no alternative future use exists, and (6) costs related to compliance with regulatory requirements. The Company recognizes external research and development costs based on an evaluation of the progress to completion of specific tasks using information provided from the Company’s contracted service providers. Prepaid and Accrued Research and Development Costs Substantial portions of the Company’s research are performed by third-party laboratories, CROs and other vendors. These vendors generally bill monthly for services performed, or bill based upon milestone achievement. The Company accrues expenses based upon estimates of percentage of work completed and the contract milestones remaining. On occasion, the Company is obligated to make upfront payments upon execution of research and development agreements. Advance payments, including nonrefundable amounts, for goods or services that will be used or rendered for future research and development activities are capitalized as prepaid expenses until such goods are delivered or the related services are performed. The Company estimates the period over which such services will be performed based on the terms of the agreements as well as the level of effort to be expended in each period. Since inception, the Company has not experienced any material differences between the actual and estimated timing of performance or level of effort. Leases Effective January 1, 2022, the Company adopted ASC Topic 842, Leases On January 1, 2022, the Company recorded operating lease liabilities and their corresponding right-of-use For leases entered into after January 1, 2022, the Company applies the guidance in ASC 842, and determines whether an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company classifies a lease at the lease commencement date, when control of the underlying asset is transferred from the lessor to the lessee, as an operating or finance lease and records a ROU asset and a lease liability on the consolidated balance sheet for any lease with a lease term greater than twelve months. The Company has elected the practical expedient to not recognize leases with a lease term of twelve months or less on the balance sheet (“short-term leases”) and will recognize lease payments for such short-term leases as an expense on a straight-line basis. The Company enters into contracts that contain both lease and non-lease Non-lease non-lease For lease arrangements in which the Company is a lessee, finance and operating ROU assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term determined using the discount rate implicit in the lease if readily determinable. When the rate implicit in the lease is not readily determinable, the Company utilizes its IBR, which is determined on the basis of information that is available at the lease commencement date. ROU assets are further adjusted for items such as initial direct costs, prepaid rent, or lease incentives. Operating lease costs are expensed using the straight-line method as an operating expense over the lease term unless the operating lease ROU asset has been impaired. The Company’s lease terms may include options to extend the lease when it is reasonably certain that the Company will exercise that option. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated between (i) a portion that is recorded as interest expense and (ii) a portion that reduces the finance lease liability associated with the lease. Simple Agreements for Future Equity SAFE instruments do not represent legal form debt (i.e., no creditor rights), but allow for redemption based upon certain triggering events that are outside of the control of the Company. The Company accounts for a SAFE as a liability at fair value on a recurring basis. Triggering events include an equity financing, public listing transaction, change of control or dissolution. Changes in the liability’s fair value are recognized in the Company’s statements of operations and comprehensive loss. Convertible Preferred Stock The Company classifies convertible preferred stock outside of stockholders’ deficit on the consolidated balance sheets as it is redeemable upon the occurrence of a Deemed Liquidation Event, as defined below, that is not strictly within the Company’s control. The issuance of convertible preferred stock is recorded at the issuance price less any amounts allocated to freestanding liabilities associated with the issuance and related allocable issuance costs. The carrying values of the convertible preferred stock have not been adjusted to their liquidation preferences because it is not considered probable that a Deemed Liquidation Event will occur and make such stock redeemable. Stock-Based Compensation The Company measures and records the expense related to stock-based payment awards based on the fair value of those awards as determined on the date of grant. The Company recognizes stock-based compensation expense over the requisite service period of the individual grant, which is generally equal to the vesting period, using the straight-line method. For stock options with performance conditions, the Company records stock-based compensation expense when it is deemed probable that the performance condition will be met. The Company uses the Black-Scholes-Merton (“BSM”) option-pricing model to determine the fair value of stock options. The BSM option-pricing model requires the use of assumptions to determine the fair value of the stock options. The fair value of the shares of common stock underlying stock options has historically been determined by the Board of Directors (“Board”), with input from management and contemporaneous third-party valuations, as there was no public market for the common stock. Given the absence of a public market for the Company’s common stock, and in accordance with the American Institute of Certified Public Accountants Practice Aid, Valuation of Privately Held Company Equity Securities Issued as Compensation, the Board exercised reasonable judgment and considered numerous objective and subjective factors to determine the best estimate of the fair value of the Company’s common stock at each stock option grant date. The Company calculates the fair value of stock options granted by using the BSM option-pricing model with the following assumptions: Expected Volatility Expected Term Risk-Free Interest Rate zero-coupon Dividend Yield Forfeitures The purchase price of restricted common stock granted to founders, employees and consultants is the estimated fair value on the grant date and is subject to various vesting schedules. Unvested restricted common stock are subject to repurchase rights held by the Company at the original issuance price in the event the restricted common stockholders’ service to the Company is terminated either voluntarily or involuntarily. The associated liability is classified in accrued expenses and other current liabilities in the consolidated balance sheets. The balance of this liability as of December 31, 2023 and 2022 is immaterial. All stock-based compensation expense is recorded in research and development expense or general and administrative expense in the consolidated statements of operations and comprehensive loss, on the basis of the respective employee and nonemployee’s role within the Company. Income Taxes The Company accounts for income taxes under the asset and liability method under ASC Topic 740, Income Taxes The Company recognizes deferred tax assets to the extent that it believes that these assets are more likely than not to be realized. In making such a determination, the Company considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning The Company records uncertain tax positions in accordance with ASC 740 on the basis of a two-step more-likely-than-not Related Party Transactions Related parties are directly or indirectly related to the Company, through one or more intermediaries and are in control, controlled by, or under common control with the Company. Related parties also include principal owners of the Company, its management, members of the immediate families of principal owners of the Company and its management, and other parties with which the Company may transact with if one party controls or can significantly influence the management or operating policies of the other to an extent that one of the transacting parties might be prevented from fully pursuing its own separate interests. The Board reviews and approves transactions with directors, officers and holders of 5% or more of the Company’s voting securities and their affiliates or their family members. The material facts as to the related party’s relationship or interest in the transaction are disclosed to the Board prior to its consideration of such transaction, and the transaction is not considered approved by the Board unless a majority of the directors who are not interested in the transaction approve the transaction. Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ deficit that result from transactions and economic events other than those with stockholders. The comprehensive loss for the Company equals its net loss plus changes in foreign currency translation for all periods presented. Net Loss per Share The Company applies the two-class two-class two-class Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, excluding potentially dilutive common shares. Diluted net loss per share attributable to common stockholders is computed by adjusting net loss attributable to common stockholders to reallocate earnings based on the potential impact of dilutive securities. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, including potential dilutive common shares. For purposes of this calculation, the Company’s outstanding convertible preferred stock, stock options, unvested restricted common stock and the SAFEs are considered potential dilutive common shares. The Company generated a net loss for each of the years presented. Accordingly, basic and diluted net loss per share attributable to common stockholders are the same because the inclusion of the potentially dilutive securities would be anti-dilutive. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB, or other standard setting bodies and are adopted by the Company as of the specified effective dates. Unless otherwise discussed, the impact of recently issued standards that are not yet effective are not anticipated to have a material impact on the Company’s consolidated financial statements upon adoption. Recently Issued Accounting Pronouncement Not Yet Adopted In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) 815-40): (“ASU 2020-06”). ASU 2020-06 paid-in ASU 2020-06 ASU 2020-06 ASU 2020-06 In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting 2023-07”), 2023-07, 2023-07 2023-07 2023-07 In December 2023, the FASB issued ASU No. 2023-09, Income Taxes 2023-09”), 2023-09, 2023-09 2023-09

Fair Value Measurements

Fair Value Measurements	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. FAIR VALUE MEASUREMENTS The following tables present information about financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): March 31, 2024 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 17,213 $ —  $ —  $ 17,213 $ 17,213 $ —  $ —  $ 17,213 Liabilities: SAFE liabilities $ —  $ —  $ 32,590 $ 32,590 $ —  $ —  $ 32,590 $ 32,590 December 31, 2023 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 27,278 $ —  $ —  $ 27,278 $ 27,278 $ —  $ —  $ 27,278 Liabilities: SAFE liabilities $ —  $ —  $ 30,515 $ 30,515 $ —  $ —  $ 30,515 $ 30,515 As of March 31, 2024 and December 31, 2023, the Company’s cash equivalents, which were invested in money market funds, were valued based on Level 1 inputs. SAFE Liabilities From October through December 2023, the Company entered into multiple SAFE agreements with certain existing investors and received $34.1 million (see Note 13). The SAFE liabilities are included within the Level 3 fair value hierarchy. The SAFE liabilities were valued using a probability weighted scenario analysis and discount rates derived by application of the build-up The valuations of the SAFE liabilities as of March 31, 2024 and December 31, 2023, were determined based on a probability-weighted scenario analysis that assumed the probabilities of the occurrence of an equity financing, public listing transaction and dissolution to be 10.0%, 87.5% and 2.5% respectively. The estimated time to redemption used in the March 31, 2024 valuation was two months for an equity financing and dissolution and one month for a public listing transaction. The estimated time to redemption used in the December 31, 2023 valuation was five months for an equity financing and dissolution and four months for a public listing transaction. The valuations used a discount rate of 30.2% to approximate the cost of equity, which was derived from application of a build-up date, and adjustments to reflect market risk, a small stock premium, and a selected company-specific risk premium. The valuation of the SAFE liabilities at the October issuance date was determined using the same methodology; however, the discount rate was 30.9% due to the higher risk-free rate at the valuation date. In October 2023, the probabilities of the occurrence of an equity financing, public listing transaction and dissolution used were 87.5%, 10.0%, and 2.5%, respectively. The estimated time to redemption used was 1.5 months for an equity financing and 5.5 months for a public listing transaction and dissolution. The following table presents activity for the SAFE liabilities that were measured at fair value using significant unobservable Level 3 inputs during the three months ended March 31, 2024 and the year ended December 31, 2023 (in thousands): SAFE Liabilities Balance as of January 1, 2023 $ —  Initial fair value recognition 31,515 Loss on issuance 255 Fair value adjustments (1,255 ) Balance as of December 31, 2023 30,515 Fair value adjustments 2,075 Balance as of March 31, 2024 $ 32,590	3. FAIR VALUE MEASUREMENTS The following tables present information about financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): December 31, 2023 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 27,278 $ —  $ —  $ 27,278 $ 27,278 $ —  $ —  $ 27,278 Liabilities: SAFE liabilities $ —  $ —  $ 30,515 $ 30,515 $ —  $ —  $ 30,515 $ 30,515 December 31, 2022 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 33,640 $ —  $ —  $ 33,640 $ 33,640 $ —  $ —  $ 33,640 As of December 31, 2023 and 2022, the Company’s cash equivalents, which were invested in money market funds, were valued based on Level 1 inputs. SAFE Liabilities From October through December 2023, the Company entered into multiple SAFE agreements with certain existing investors and received $34.1 million (see Note 13). The SAFE liabilities are included within the Level 3 fair value hierarchy. The SAFE liabilities were valued using a probability weighted scenario analysis and discount rates derived by application of the build-up The valuation of the SAFE liabilities as of December 31, 2023, was determined based on a probability-weighted scenario analysis that assumed the probabilities of the occurrence of an equity financing, public listing transaction and dissolution to be 10.0%, 87.5% and 2.5% respectively. The estimated time to redemption used was five months for an equity financing and dissolution and four months for a public listing transaction. The valuation used a discount rate of 30.2% to approximate the cost of equity, which was derived from application of a build-up adjustments to reflect market risk, a small stock premium, and a selected company-specific risk premium. The valuation of the SAFE liabilities at the October issuance date was determined using the same methodology; however, the discount rate was 30.9% due the higher risk-free rate at the valuation date. In October 2023, the probabilities of the occurrence of an equity financing, public listing transaction and dissolution used were 87.5%, 10.0%, and 2.5%, respectively. The estimated time to redemption used was 1.5 months for an equity financing and 5.5 months for a public listing transaction and dissolution. Valuation of Preferred Stock Tranche Liability The fair value of the preferred stock tranche liability was based on significant inputs not observable in the market and is a Level 3 measurement within the fair value hierarchy. The valuations were made using Black-Scholes-Merton pricing model with inputs based on certain subjective assumptions, including (a) estimated conversion dates, (b) expected stock price volatility, (c) a risk-free interest rates and (d) implied debt yields. The fair value of the preferred stock tranche liability was determined at the issuance of the Preferred Stock, as defined below, in 2021 and re-measured The following table presents activity for the preferred stock tranche liability and the SAFE liabilities that were measured at fair value using significant unobservable Level 3 inputs during the years ended December 31, 2023 and 2022 (in thousands): Preferred Stock SAFE Liabilities Balance as of January 1, 2022 $ 643 $ —  Fair value adjustments (643 ) —  Balance as of December 31, 2022 —  —  Initial fair value recognition —  31,515 Loss on issuance —  255 Fair value adjustments —  (1,255 ) Balance as of December 31, 2023 $ —  $ 30,515 There were no transfers between the Level 1, Level 2 or Level 3 categories during the years ended December 31, 2023 and 2022.

Property, Equipment and Improve

Property, Equipment and Improvements, Net	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Property, Equipment and Improvements, Net	4. PROPERTY, EQUIPMENT AND IMPROVEMENTS, NET Property, equipment and improvements, net is comprised of the following (in thousands): March 31, December 31, Laboratory equipment $ 4,548 $ 4,510 Furniture and office equipment 244 244 Computer equipment 165 161 Construction in progress —  38 Leasehold improvements 25 25 4,982 4,978 Less: accumulated depreciation (2,118 ) (1,856 ) Property and equipment, net $ 2,864 $ 3,122 Depreciation expense was $0.3 million and $0.2 million during the three months ended March 31, 2024 and 2023 and was recorded as follows (in thousands): Three Months Ended March 31, 2024 2023 General and administrative $ 4 $ 4 Research and development 258 226 $ 262 $ 230 These amounts are exclusive of amortization related to finance lease assets of $0.1 million during the three months ended March 31, 2024 and 2023.	4. PROPERTY, EQUIPMENT AND IMPROVEMENTS, NET Property, equipment and improvements, net is comprised of the following (in thousands): December 31, 2023 2022 Laboratory equipment $ 4,510 $ 4,018 Furniture and office equipment 244 244 Computer equipment 161 149 Construction in progress 38 49 Leasehold improvements 25 25 4,978 4,485 Less: accumulated depreciation (1,856 ) (877 ) Property and equipment, net $ 3,122 $ 3,608 Depreciation expense was $1.0 million and $0.6 million and was recorded as follows (in thousands): Year Ended 2023 2022 General and administrative $ 17 $ 12 Research and development 973 635 $ 990 $ 647 These amounts are exclusive of amortization related to finance lease and capital lease assets of $0.5 million and $ 0.3

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	5. ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities is comprised of the following (in thousands): March 31, December 31, Employee compensation related costs $ 3,769 $ 2,840 Accrued office and laboratory costs 141 211 Accrued contract research organization fees 3,207 2,298 Accrued contract development and manufacturing organization fees 604 660 Accrued professional fees 2,935 1,798 Other current liabilities 392 334 $ 11,048 $ 8,141	5. ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses and other current liabilities is comprised of the following (in thousands): December 31, 2023 2022 Employee compensation related costs $ 2,840 $ 2,158 Accrued office and laboratory costs 211 481 Accrued contract research organization fees 2,298 1,345 Accrued contract development and manufacturing organization fees 660 842 Accrued professional fees 1,798 489 Other current liabilities 334 499 $ 8,141 $ 5,814

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. COMMITMENTS AND CONTINGENCIES Leases The Company’s commitments under its operating and finance leases are described in Note 7. Harvard Agreement In July 2020, the Company entered into an agreement with the President and Fellows of Harvard College (“Harvard”), for an option fee in the low five digits, whereby Harvard granted the Company an exclusive option to negotiate a worldwide, exclusive, royalty-bearing license under Harvard’s interest in the patent rights covering certain technology that was developed by Harvard. In October 2021, the Company exercised the option and on February 10, 2022, entered into a license agreement (“License Agreement”) with Harvard to conduct research and development activities using certain materials, technology and patent rights owned by Harvard, with the intent to develop, obtain regulatory approval for, and commercialize products. The License Agreement will remain in effect until the expiration of the last valid claim within the patent rights covering a product developed under the License Agreement or the termination of the License Agreement. Management concluded that the acquisition of patents and materials received under the License Agreement represents an asset acquisition of an in-progress As consideration for the License Agreement, the Company agreed to pay Harvard a non-refundable The Company also will be responsible for payment of (1) annual maintenance fees ranging from the low five digits to the low six digits during the term of the License Agreement (through the first commercial sale of a royalty-bearing product); (2) royalty payments as a percentage in the low single digits of the annual net sales that the Company generates from products that utilize the license technology (“Licensed Products”) and royalty payments as a percentage in the low single digits of the annual net sales that the Company generates from know-how (“Know-How 10-20% non-royalty know-how country-by-country product-by-product Know-How Know-How Alloy Therapeutics License Agreement On November 29, 2021, the Company executed a license agreement with Alloy Therapeutics, LLC (“ATX”), whereby the Company will use ATX technology for the purpose of preclinical development, clinical development and commercialization of potential product candidates, for an initial period of three years, with an option to extend the term for an additional two years. The Company will pay ATX a non-refundable non-creditable During the three months ended March 31, 2024 and 2023, the Company paid $0.1 million and $0 to ATX, respectively. Adimab Agreement On May 1, 2023, the Company entered into a discovery agreement with Adimab, LLC (“Adimab”), an antibody discovery company, whereby the Company and Adimab are collaborating on human antibody discovery in accordance with an agreed upon research program. The Company paid an upfront technology access fee totaling $20,000 upon execution of the agreement. The Company also will be responsible for payment of (1) quarterly funding equal to 100% of the actual full-time employee (“FTE”) expended by Adimab in the performance of its obligations in accordance with the agreed upon research program at an annual rate of $0.4 million per FTE (subject to annual consumer price index increases) per the agreement, (2) delivery fees equal to $0.1 million upon both Adimab’s initial delivery of sequences or physical materials and completion pursuant to the research program (initial and completion fees payable once per target for a total of up to $0.4 million), (3) a non-creditable, non-refundable information discovered during the research program, (4) development milestone payments for the movement of certain product candidates thought clinical trials, which range in the low seven digits, and (5) royalty payments based on the annual net sales that the Company generates from products that utilize Adimab technology. The Company has the right to terminate the agreement if certain criteria are met. As of March 31, 2024, the Company recorded $0.1 million of costs associated with the FTEs in accrued expenses and other current liabilities and $0.1 million of discovery delivery fees in accounts payable. Indemnification Agreements In accordance with the Company’s amended and restated certificate of incorporation (“ARCOI”) and certain indemnification agreements, the Company indemnifies certain officers and directors for specified events or occurrences, subject to certain limits, in which the officer or director is or was serving at the Company’s request in such capacity. The Company enters into certain types of contracts that contingently requires it to indemnify various parties against claims from third parties. These contracts primarily relate to (i) the Company’s bylaws, under which it must indemnify directors and executive officers, and may indemnify other officers and employees, for liabilities arising out of their relationship with the Company, (ii) contracts under which it must indemnify directors and certain officers and consultants for liabilities arising out of their relationship, and (iii) procurement, service or license agreements under which the Company may be required to indemnify vendors, service providers or licensees for certain claims, including claims that may be brought against them arising from the Company’s acts or omissions with respect to the its products, technology, intellectual property or services. From time to time, the Company may receive indemnification claims under these contracts in the normal course of business. In the event that one or more of these matters were to result in a claim against the Company, an adverse outcome, including a judgment or settlement, may cause a material adverse effect on future business, operating results or financial condition. It is not possible to estimate the maximum amount potentially payable under these contracts since there is no history of prior indemnification claims and the unique facts and circumstances involved in each particular claim will be determinative. As of March 31, 2024 and December 31, 2023, the Company did not have any liabilities or other commitments related to indemnification claims.	6. COMMITMENTS AND CONTINGENCIES Leases The Company’s commitments under its operating and finance leases are described in Note 7. University of Texas Research Agreement The Company executed a research agreement with the University of Texas, whereby the Company and the University of Texas are conducting joint research activities in accordance with an agreed upon research program. An upfront fee of $25,000 was paid upon execution of the agreement in 2020, with the remaining balance due in two payments of $37,500 each. The first payment was due upon the completion of the joint research activities and the second due upon the receipt of the final research report by the Company. The agreement was terminated on June 30, 2022. During the year ended December 31, 2022, the Company did not pay any amounts to the University of Texas under this agreement because the joint research activities were not completed before the research agreement terminated. Harvard Agreement In July 2020, the Company entered into an agreement with the President and Fellows of Harvard College (“Harvard”), for an option fee in the low five digits, whereby Harvard granted the Company an exclusive option to negotiate a worldwide, exclusive, royalty-bearing license under Harvard’s interest in the patent rights covering certain technology that was developed by Harvard. In October 2021, the Company exercised the option and on February 10, 2022, entered into a license agreement (“License Agreement”) with Harvard to conduct research and development activities using certain materials, technology and patent rights owned by Harvard, with the intent to develop, obtain regulatory approval for, and commercialize products. The License Agreement will remain in effect until the expiration of the last valid claim within the patent rights covering a product developed under the License Agreement or the termination of the License Agreement. Management concluded that the acquisition of patents and materials received under the License Agreement represents an asset acquisition of an in-progress As consideration for the License Agreement, the Company agreed to pay Harvard a non-refundable The Company also will be responsible for payment of (1) annual maintenance fees ranging from the low five digits to the low six digits during the term of the License Agreement (through the first commercial sale of a royalty-bearing product); (2) royalty payments as a percentage in the low single digits of the annual net sales that the Company generates from products that utilize the license technology (“Licensed Products”) and royalty payments as a percentage in the low single digits of the annual net sales that the Company generates from know-how (“Know-How 10-20% non-royalty know-how country-by-country product-by-product Know-How Know-How Alloy Therapeutics License Agreement On November 29, 2021, the Company executed a license agreement with Alloy Therapeutics, LLC (“ATX”), whereby the Company will use ATX technology for the purpose of preclinical development, clinical development and commercialization of potential product candidates, for an initial period of three years, with an option to extend the term for an additional two years. The Company will pay ATX a non-refundable non-creditable will be responsible to pay ATX commercial payments in the low seven digits per year during the first six years of commercial sales, amounting to an amount in the high eight digits in total commercial payments under the license agreement. During the years ended December 31, 2023 and 2022, the Company paid $0.1 million and zero to ATX, respectively. Adimab Agreement On May 1, 2023, the Company entered into a discovery agreement with Adimab, LLC (“Adimab”), an antibody discovery company, whereby the Company and Adimab are collaborating on human antibody discovery in accordance with an agreed upon research program. The Company paid an upfront technology access fee totaling $20,000 upon execution of the agreement. The Company also will be responsible for payment of (1) quarterly funding equal to 100% of the actual full-time employee (“FTE”) expended by Adimab in the performance of its obligations in accordance with the agreed upon research program at an annual rate of $0.4 million per FTE (subject to annual consumer price index increases) per the agreement, (2) delivery fees equal to $0.1 million upon both Adimab’s initial delivery of sequences or physical materials and completion pursuant to the research program (initial and completion fees payable once per target for a total of up to $0.4 million), (3) a non-creditable, non-refundable Indemnification Agreements In accordance with the Company’s amended and restated certificate of incorporation (“ARCOI”) and certain indemnification agreements, the Company indemnifies certain officers and directors for specified events or occurrences, subject to certain limits, in which the officer or director is or was serving at the Company’s request in such capacity. The Company enters into certain types of contracts that contingently requires it to indemnify various parties against claims from third parties. These contracts primarily relate to (i) the Company’s bylaws, under which it must indemnify directors and executive officers, and may indemnify other officers and employees, for liabilities arising out of their relationship with the Company, (ii) contracts under which it must indemnify directors and certain officers and consultants for liabilities arising out of their relationship, and (iii) procurement, service or license agreements under which the Company may be required to indemnify vendors, service providers or licensees for certain claims, including claims that may be brought against them arising from the Company’s acts or omissions with respect to the its products, technology, intellectual property or services. From time to time, the Company may receive indemnification claims under these contracts in the normal course of business. In the event that one or more of these matters were to result in a claim against the Company, an adverse outcome, including a judgment or settlement, may cause a material adverse effect on future business, operating results or financial condition. It is not possible to estimate the maximum amount potentially payable under these contracts since there is no history of prior indemnification claims and the unique facts and circumstances involved in each particular claim will be determinative. As of December 31, 2023 and 2022, the Company did not have any liabilities or other commitments related to indemnification claims.

Leases

Leases	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Leases	7. LEASES The Company has entered into operating leases for office and laboratory facilities and financing leases for laboratory equipment used in research and development activities. The remaining lease terms for its leases range from two years to four years. These leases often include options to extend the term of the lease. When it is reasonably certain that the option will be exercised, the impact of the renewal term is included in the lease term for purposes of determining total future lease payments and measuring the ROU asset and lease liability. The Company is not reasonably certain to exercise any available renewal options, which are therefore excluded from the measurement of leases. The Company applies the short-term lease policy election for its real estate and equipment leases, which allows it to exclude from recognition leases with an original term of twelve months or less. In November 2020, the Company executed a facilities lease agreement to occupy 18,768 square feet of office and laboratory space, that was subsequently amended on April 21, 2022. The lease requires the Company to pay fixed base rent, which is included in the measurement of the lease, as well as its proportionate share of the facilities operating expenses which are treated as variable lease costs based on the Company’s election to combine lease and associated non-lease measurement of the lease. The lease expires on January 31, 2026, and contains a five-year renewal option exercisable by the Company which is not included in the measurement of the lease. In April 2021, the Company entered into an agreement to sublease a portion of its facility lease to a related party (see Note 13) in exchange for $28,333 per month. The sublease agreement was an operating lease with a term of 18 The following table sets forth information about lease costs for the three months ended March 31, 2024 and 2023 (in thousands): Three Months Ended Finance lease cost 2024 2023 Amortization of ROU assets $ 114 $ 134 Interest on lease liabilities 31 42 Operating lease cost 351 351 Short-term lease cost 176 150 Variable lease cost 249 206 Total lease costs $ 921 $ 883 The following table sets forth information about the Company’s leases for the three months ended March 31, 2024 and 2023 (in thousands): Three Months Ended Cash paid for amounts included in the measurement of lease 2024 2023 Finance leases - financing cash flows $ 118 $ 144 Finance leases - operating cash flows 31 42 Operating leases - operating cash flows 381 370 Weighted-average remaining lease terms (in years) Finance leases 2.99 3.97 Operating leases 1.84 2.84 Weighted-average discount rate Finance leases 9.65 % 9.54 % Operating leases 8.25 % 8.25 % The following table presents the maturity of the Company’s finance and operating lease liabilities for the three months ended March 31, 2024 (in thousands): Year ended December 31, Finance Leases Operating Leases 2024 (remaining) $ 434 $ 1,154 2025 552 1,580 2026 363 132 2027 44 —  2028 —  —  Thereafter —  —  Total lease payments 1,393 2,866 Less: interest (160 ) (198 ) Total lease liabilities $ 1,233 $ 2,668	7. LEASES The Company has entered into operating leases for office and laboratory facilities and financing leases for laboratory equipment used in research and development activities. The remaining lease terms for its leases range from two years to four years. These leases often include options to extend the term of the lease. When it is reasonably certain that the option will be exercised, the impact of the renewal term is included in the lease term for purposes of determining total future lease payments and measuring the ROU asset and lease liability. The Company is not reasonably certain to exercise any available renewal options, which are therefore excluded from the measurement of leases. The Company applies the short-term lease policy election for its real estate and equipment leases, which allows it to exclude from recognition leases with an original term of twelve months or less. In November 2020, the Company executed a facilities lease agreement to occupy 18,768 square feet of office and laboratory space, that was subsequently amended on April 21, 2022. The lease requires the Company to pay fixed base rent, which is included in the measurement of the lease, as well as its proportionate share of the facilities operating expenses which are treated as variable lease costs based on the Company’s election to combine lease and associated non-lease In April 2021, the Company entered into an agreement to sublease a portion of its facility lease to a related party (see Note 13) in exchange for $28,333 per month. The sublease agreement was an operating lease with a term of 18 During 2022, the Company entered into four additional finance leases that resulted in an increase of $1.3 million in ROU assets, inclusive of lease payments made prior to commencement, and $1.3 million in related lease liabilities. The following table sets forth information about lease costs for the years ended December 31, 2023 and 2022 (in thousands): Year Ended Finance lease cost 2023 2022 Amortization of ROU assets $ 488 $ 359 Interest on lease liabilities 151 106 Operating lease cost 1,404 1,404 Short-term lease cost 749 389 Variable lease cost 786 907 Sublease income —  (253 ) Total lease costs $ 3,578 $ 2,912 The following table sets forth information about the Company’s leases for the years ended December 31, 2023 and 2022 (in thousands): Year Ended Cash paid for amounts included in the measurement of lease liabilities 2023 2022 Finance leases - financing cash flows $ 499 $ 393 Finance leases - operating cash flows 151 106 Operating leases - operating cash flows 1,235 1,470 ROU assets obtained in exchange for lease liabilities Finance leases —  1,340 Weighted-average remaining lease terms (in years) Finance leases 3.23 4.19 Operating leases 2.09 3.09 Weighted-average discount rate Finance leases 9.62 % 9.49 % Operating leases 8.25 % 8.25 % The following table presents the maturity of the Company’s finance and operating lease liabilities for the year ended December 31, 2023 (in thousands): Year ended December 31, Finance Leases Operating Leases 2024 $ 583 $ 1,534 2025 552 1,580 2026 363 132 2027 44 —  2028 —  —  Thereafter —  —  Total lease payments 1,542 3,246 Less: interest (191 ) (254 ) Total lease liabilities $ 1,351 $ 2,992

Convertible Preferred Stock

Convertible Preferred Stock	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Temporary Equity Disclosure [Abstract]
Convertible preferred stock	8. CONVERTIBLE PREFERRED STOCK The Company issued Series A-1 A-1 A-2 A-2 A-3 A-3 A-4 A-4 A-1 A-2 A-3 The Preferred Stock as of March 31, 2024 and December 31, 2023 consisted of the following (in thousands, expect share and per share amounts): March 31, 2024 and December 31, 2023 Par Value Preferred Preferred Carrying Liquidation Common Stock Series A-1 $ 0.0001 4,118,120 4,118,120 $ 45,016 $ 54,308 4,118,120 Series A-2 $ 0.0001 1,649,188 1,649,188 21,654 21,749 1,649,188 Series A-3 $ 0.0001 696,516 696,516 9,187 7,348 696,516 Series A-4 $ 0.0001 361,659 361,659 4,770 4,054 361,659 6,825,483 6,825,483 $ 80,627 $ 87,459 6,825,483 Upon the issuance of each series of the Preferred Stock, the Company assessed the embedded conversion and liquidation features of the issued Preferred Stock and determined that such features did not require the Company to separately account for these features. The Preferred Stock have the following rights and privileges: Dividends The holders of the Preferred Stock are entitled to receive noncumulative dividends if and when declared by the Board at a rate of 8 Liquidation In the event of any involuntary liquidation, dissolution or winding up of the Company or Deemed Liquidation Event, holders of the Preferred Stock shall be paid out of the assets of the Company available for distribution an amount per share equal to the greater of (i) the applicable original issue price, plus any dividends declared but unpaid, or (ii) such amount per share as would have been payable had all shares of the Preferred Stock been converted into shares of common stock. If the assets available for distribution to its stockholders are insufficient to pay the holders of shares of the Preferred Stock the full amount which they shall be entitled, the holders of shares of Preferred Stock shall share ratably in any distribution in proportion to the respective amounts which would otherwise be payable if all amounts payable were paid in full. Voting On any matter presented to the stockholders of the Company for their actions or consideration at any meeting of the Company, each holder of outstanding shares of Series A-1, A-3 A-4 A-2 Redemption The Preferred Stock is conditionally redeemable upon the occurrence of a Deemed Liquidation Event. A Deemed Liquidation Event is defined as (a) a merger or consolidation (an “event”) in which the Company is a constituent party (or a subsidiary of the Company is a constituent party and the Company issues shares of its capital stock pursuant to the event), except those in which the shares Company’s stock outstanding immediately before the event continue to represent, or are converted into or exchanged for shares of capital stock that represent, immediately following the event, at least a majority, by voting power, of the capital stock of (1) the surviving or resulting corporation; or (2) if the surviving or resulting corporation is a wholly owned subsidiary of another corporation immediately following such event, the parent corporation of the surviving or resulting corporation and (b) the sale or disposition of the Company or one or more subsidiaries of the Company. Mandatory Conversion All outstanding shares of the Preferred Stock shall automatically convert into shares of common stock, at the conversion price upon either (a) the closing of the sale of shares of common stock to the public at a price of at least $39.56280 per share (subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to the common stock), in a firm-commitment underwritten initial public offering, resulting in at least $75.0 million of gross proceeds and in connection with such offering the common stock is listed for trading on the Nasdaq Stock Market’s National Market, the New York Stock Exchange or another exchange or marketplace approved by the Board of Directors, including the approval of a majority of the preferred directors or (b) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of a majority of the voting preferred stock (the “Requisite Holders”). As discussed in Note 14, all of the Company’s outstanding preferred stock converted into common stock immediately prior to the closing of the Merger. Optional Conversion Each share of the Preferred Stock shall be convertible at any time and from time to time and without the payment of additional consideration by the holder into such number of fully paid and non-assessable A-2 A-1 The conversion price for the Series A-1 A-2 A-3 A-4	8. CONVERTIBLE PREFERRED STOCK The Company issued Series A-1 A-1 A-2 A-2 A-3 A-3 A-4 A-4 Preferred Stock consisted of the following (in thousands, expect share and per share amounts): December 31, 2023 Par Value Preferred Preferred Stock Issued Carrying Liquidation Common Stock Series A-1 $ 0.0001 4,118,120 4,118,120 $ 45,016 $ 54,308 4,118,120 Series A-2 $ 0.0001 1,649,188 1,649,188 21,654 21,749 1,649,188 Series A-3 $ 0.0001 696,516 696,516 9,187 7,348 696,516 Series A-4 $ 0.0001 361,659 361,659 4,770 4,054 361,659 6,825,483 6,825,483 $ 80,627 $ 87,459 6,825,483 December 31, 2022 Par Value Preferred Preferred Stock Issued Carrying Liquidation Common Stock Series A-1 $ 0.0001 4,118,120 4,118,120 $ 45,016 $ 54,308 4,118,120 Series A-2 $ 0.0001 1,649,188 1,649,188 21,654 21,749 1,649,188 Series A-3 $ 0.0001 696,516 696,516 9,187 7,348 696,516 Series A-4 $ 0.0001 361,659 361,659 4,770 4,054 361,659 6,825,483 6,825,483 $ 80,627 $ 87,459 6,825,483 Upon the issuance of each series of the Preferred Stock, the Company assessed the embedded conversion and liquidation features of the issued Preferred Stock and determined that such features did not require the Company to separately account for these features. On September 7, 2022, the Company issued 2,446,372 shares of Series A-1 A-2 The Preferred Stock have the following rights and privileges: Dividends The holders of the Preferred Stock are entitled to receive noncumulative dividends if and when declared by the Board at a rate of 8% per annum. The Company may not declare, pay or set aside any dividends on shares of any other series of capital stock of the Company, other than dividends on common stock payable in common stock, unless the holders of the Preferred Stock first receive, or simultaneously receive, a dividend on each outstanding share of the Preferred Stock. No dividends were declared or paid during the year ended December 31, 2023 or 2022. Liquidation In the event of any involuntary liquidation, dissolution or winding up of the Company or Deemed Liquidation Event, holders of the Preferred Stock shall be paid out of the assets of the Company available for distribution an amount per share equal to the greater of (i) the applicable original issue price, plus any dividends declared but unpaid, or (ii) such amount per share as would have been payable had all shares of the Preferred Stock been converted into shares of common stock. If the assets available for distribution to its stockholders are insufficient to pay the holders of shares of the Preferred Stock the full amount which they shall be entitled, the holders of shares of Preferred Stock shall share ratably in any distribution in proportion to the respective amounts which would otherwise be payable if all amounts payable were paid in full. Voting On any matter presented to the stockholders of the Company for their actions or consideration at any meeting of the Company, each holder of outstanding shares of Series A-1, A-3 A-4 A-2 Redemption The Preferred Stock is conditionally redeemable upon the occurrence of a Deemed Liquidation Event. A Deemed Liquidation Event is defined as (a) a merger or consolidation (an “event”) in which the Company is a constituent party (or a subsidiary of the Company is a constituent party and the Company issues shares of its capital stock pursuant to the event), except those in which the shares Company’s stock outstanding immediately before the event continue to represent, or are converted into or exchanged for shares of capital stock that represent, immediately following the event, at least a majority, by voting power, of the capital stock of (1) the surviving or resulting corporation; or (2) if the surviving or resulting corporation is a wholly owned subsidiary of another corporation immediately following such event, the parent corporation of the surviving or resulting corporation and (b) the sale or disposition of the Company or one or more subsidiaries of the Company. Mandatory Conversion All outstanding shares of the Preferred Stock shall automatically convert into shares of common stock, at the conversion price upon either (a) the closing of the sale of shares of common stock to the public at a price of at least $39.56280 per share (subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to the common stock), in a firm-commitment underwritten initial public offering, resulting in at least $75.0 million of gross proceeds and in connection with such offering the common stock is listed for trading on the Nasdaq Stock Market’s National Market, the New York Stock Exchange or another exchange or marketplace approved by the Board of Directors, including the approval of a majority of the preferred directors or (b) the date and time, or the occurrence of an event, specified by vote or written consent of the holders of a majority of the voting preferred stock (the “Requisite Holders”). Additionally, shares of Series A-1 A-2 Optional Conversion Each share of the Preferred Stock shall be convertible at any time and from time to time and without the payment of additional consideration by the holder into such number of fully paid and non-assessable A-2 A-1 The conversion price for the Series A-1 A-2 A-3 A-4

Common Stock

Common Stock	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Equity [Abstract]
Common Stock	9. COMMON STOCK As of March 31, 2024, the Company’s ARCOI authorized the Company to issue up to 11,947,558 shares of $0.0001 par value common stock, of which, 2,637,120 shares were issued and outstanding. Voting, dividend and liquidation rights of the holders of common stock are subject to and qualified by the rights, powers and preferences of the holders of the Preferred Stock. Holders of common stock are entitled to one vote for each share of common stock; however, the holders of the common stock shall not be entitled to vote on any amendment to the ARCOI that relates solely to the terms of one or more outstanding series of preferred stock. The Company has included in issued and outstanding common stock shares of restricted common stock granted by the Company. As of March 31, 2024, there were 2,637,120 common shares issued and outstanding, of which 2,615,555 relate to shares of unrestricted common stock.	9. COMMON STOCK As of December 31, 2023, the Company’s ARCOI authorized the Company to issue up to 11,947,558 shares of $0.0001 par value common stock, of which, 2,634,246 shares were issued and outstanding. Voting, dividend and liquidation rights of the holders of common stock are subject to and qualified by the rights, powers and preferences of the holders of the Preferred Stock. Holders of common stock are entitled to one vote for each share of common stock; however, the holders of the common stock shall not be entitled to vote on any amendment to the ARCOI that relates solely to the terms of one or more outstanding series of preferred stock. The Company has included in issued and outstanding common stock shares of restricted common stock granted by the Company. As of December 31, 2023, there were 2,634,246 common shares issued and outstanding, of which 2,598,752 relate to shares of unrestricted common stock.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	10. STOCK-BASED COMPENSATION In June 2019, the Company adopted the 2019 Equity Incentive Plan (the “2019 Plan”), which provides employees, consultants and advisors and non-employee For incentive stock options and non-statutory A summary of the activity in the 2019 Plan for the three months ended March 31, 2024 is as follows (in thousands except share and per share amounts): Number of Weighted- Weighted-Average Aggregate Balance as of January 1, 2024 1,875,932 $ 1.66 8.2 $ 2,276 Granted —  —  Exercised (2,874 ) 1.54 $ 4 Forfeited and expired (19,558 ) 1.36 Balance as of March 31, 2024 1,853,500 $ 1.66 7.9 $ 2,242 Options vested and exercisable as of March 31, 2024 1,068,487 $ 1.34 7.3 $ 1,634 Options vested and expected to vest as of March 31, 2024 1,853,500 $ 1.66 7.9 $ 2,242 There were no options granted during the three months ended March 31, 2024. The weighted-average grant-date fair value of options granted during the three months ended March 31, 2023 was $1.34 per share. The total intrinsic value of options exercised during the three months ended March 31, 2024 and 2023 was $3,828 and $411, respectively. Forfeitures of options are recorded as incurred. Cash received from option exercises for the three months ended March 31, 2024 and 2023 was $4,420 and $0, respectively. The fair values of the options granted in the three months ended March 31, 2023 were estimated based on the BSM option pricing model, using the following assumptions: Three Months March 31, 2023 Fair value per share of underlying common stock $1.34 Expected term (in years) 5.93 Expected volatility 111.05% -111.21% Risk-free interest rate 3.65% Expected dividend yield 0% Restricted Common Stock Since 2019, the Company has granted restricted common stock to founders, employees and consultants. The purchase price of the restricted common stock is the estimated fair value on the grant date and the restricted stock is subject to various vesting schedules. Unvested restricted common stock are subject to repurchase rights held by the Company at the original issuance price in the event the restricted common stockholders’ service to the Company is terminated either voluntarily or involuntarily. As of March 31, 2024, there were 21,565 shares of unvested restricted common stock, with a repurchase liability of less than $0.1 million, that is classified in accrued expenses and other current liabilities in the accompanying condensed consolidated balance sheet. The following table summarizes restricted stock activity: Number of Unvested restricted common stock as of January 1, 2024 35,494 Granted —  Vested (13,929 ) Forfeited —  Unvested restricted common stock as of March 31, 2024 21,565 The weighted-average grant date fair value of unvested restricted common stock and restricted common stock vested and forfeited for the three months ended March 31, 2024 and 2023 was immaterial. Stock-Based Compensation Expense The Company recorded stock-based compensation expense regarding its employees and nonemployees as follows (in thousands): Three Months Ended March 31, 2024 2023 General and administrative $ 193 $ 174 Research and development 128 101 $ 321 $ 275 The Company records compensation expense on a straight-line basis over the vesting period. As of March 31, 2024, total compensation cost not yet recognized related to unvested stock options was $2.0 million, which is expected to be recognized over a weighted-average period of 2.4 years.	10. STOCK-BASED COMPENSATION In June 2019, the Company adopted the 2019 Equity Incentive Plan (the “2019 Plan”), which provides employees, consultants and advisors and non-employee For incentive stock options and non-statutory A summary of the activity in the 2019 Plan for the year ended December 31, 2023 is as follows (in thousands except share and per share amounts): Number of Weighted- Weighted-Average Aggregate Balance as of January 1, 2023 1,556,819 $ 1.32 8.7 $ 420 Granted 441,615 2.74 Exercised (108,475 ) 1.27 $ 172 Forfeited and expired (14,027 ) 1.53 Balance as of December 31, 2023 1,875,932 $ 1.66 8.2 $ 2,276 Options vested and exercisable as of December 31, 2023 972,054 $ 1.30 7.6 $ 1,525 Options vested and expected to vest as of December 31, 2023 1,875,932 $ 1.66 8.2 $ 2,276 The weighted-average grant-date fair value of options granted during the years ended December 31, 2023 and 2022 was $2.16 and $1.57 per share, respectively. The total intrinsic value of options exercised during the years ended December 31, 2023 and 2022 was $171,915 and $1,458, respectively. Cash received from option exercises for the years ended December 31, 2023 and 2022 was $111,770 and $4,105, respectively. The fair values of the options granted were estimated based on the BSM option pricing model, using the following assumptions: Year Ended 2023 2022 Fair value per share of underlying common stock $2.16 $1.57 Expected term (in years) 6.01 6.02 Expected volatility 93.44 - 111.21% 87.02 - 91.24% Risk-free interest rate 4.14% 3.01% Expected dividend yield 0% 0% Restricted Common Stock Since 2019, the Company has granted restricted common stock to founders, employees and consultants. The purchase price of the restricted common stock is the estimated fair value on the grant date and the restricted stock is subject to various vesting schedules. Unvested restricted common stock are subject to repurchase rights held by the Company at the original issuance price in the event the restricted common stockholders’ service to the Company is terminated either voluntarily or involuntarily. As of December 31, 2023, there were 35,494 unvested restricted common stock, with a repurchase liability of less than $0.1 million, that is classified in accrued expenses and other current liabilities in the accompanying consolidated balance sheet. The following table summarizes restricted stock activity: Number of Shares Unvested restricted common stock as of 312,826 Granted —  Vested (277,332 ) Forfeited —  Unvested restricted common stock as of 35,494 The weighted-average grant date fair value of unvested restricted common stock and restricted common stock vested and forfeited for the years ended December 31, 2023 and 2022 was immaterial. Stock-Based Compensation Expense The Company recorded stock-based compensation expense regarding its employees and nonemployees as follows (in thousands): Year Ended 2023 2022 General and administrative $ 705 $ 738 Research and development 416 381 $ 1,121 $ 1,119 The Company records compensation expense on a straight-line basis over the vesting period. As of December 31, 2023, total compensation cost not yet recognized related to unvested stock options was $2.4 million, which is expected to be recognized over a weighted-average period of 2.6 years.

Income Taxes

Income Taxes	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Income Taxes	11. INCOME TAXES During the three months ended March 31, 2024 and 2023, the Company recorded no income tax provision or benefit. The Company has evaluated the positive and negative evidence bearing upon its ability to realize its deferred tax assets, which primarily consist of net operating loss carryforwards. The Company has considered its history of cumulative net losses, estimated future taxable income and prudent and feasible tax planning strategies and has concluded that it is more likely than not that the Company will not realize the benefits of its deferred tax assets. As a result, as of March 31, 2024, the Company has maintained a full valuation allowance against its net deferred tax assets.	11. INCOME TAXES Income tax expense consists of the following (in thousands): Year Ended December 31, 2023 2022 Current expense (benefit): Federal $ —  $ —  State —  —  Total current expense (benefit): $ —  $ —  Deferred expense (benefit): Federal $ 11,207 $ 7,407 State 3,361 2,189 Deferred tax benefit 14,568 9,596 Less change in valuation allowance (14,568 ) (9,596 ) Total income tax expense (benefit): $ —  $ —  The components of the Company’s loss before income tax expense are compromised solely of domestic sources. The reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2023 2022 Federal statutory income tax rate 21.0 % 21.0 % State income taxes 7.8 % 6.8 % Foreign rate differential 0.1 % 0.0 % Permanent differences 1.2 % -0.3 % Equity-based compensation -0.4 % -0.6 % Preferred stock liability fair value adjustment 0.0 % 0.4 % Tax credits 4.4 % 2.5 % Change in valuation allowance -34.0 % -29.8 % Effective income tax rate 0.0 % 0.0 % Significant components of the Company’s deferred tax assets and liabilities consist of the following (in thousands): Year Ended December 31, 2023 2022 Deferred tax assets Net operating loss carryforward $ 11,392 $ 7,765 Research credits 4,336 1,579 Lease liability 817 1,575 Capitalized R&D expenses 14,595 7,027 Accruals & other 1,027 859 Total deferred tax assets 32,167 18,805 Valuation allowance (30,228 ) (15,658 ) Net deferred tax assets $ 1,939 $ 3,147 Deferred tax liabilities Depreciation $ (1,210 ) $ (1,530 ) Right of use asset (729 ) (1,617 ) Total deferred tax liabilitites (1,939 ) (3,147 ) Net deferred tax assets (liability) $ —  $ —  Future realization of the tax benefits of existing temporary differences and net operating loss (“NOL”) carryforwards ultimately depends on the existence of sufficient taxable income within the carryforward period. As of December 31, 2023 and 2022, the Company performed an evaluation to determine whether a valuation allowance was needed. The Company considered all available evidence, both positive and negative, which included the results of operations for the current and preceding years. The Company determined that it was not possible to reasonably quantify future taxable income and determined that it is more likely than not that all of the deferred tax assets will not be realized. Accordingly, the Company maintained a full valuation allowance as of December 31, 2023 and 2022. The utilization of NOLs and tax credit carryforwards to offset future taxable income may be subject to an annual limitation as a result of ownership changes that have occurred previously or may occur in the future. Under Sections 382 and 383 of the Internal Revenue Code (“IRC”) of 1986, as amended, a corporation that undergoes an ownership change may be subject to limitations on its ability to utilize its pre-change The Company’s valuation allowance increased for the year ended December 31, 2023 by $14.6 million due primarily to the generation of NOLs. As of December 31, 2023, the Company has NOL carryforwards for federal and state tax reporting purposes of $43.6 million and $35.3 million, respectively. NOL carryforwards generated after December 31, 2017 for federal tax reporting purposes of $43.6 million have an indefinite life. NOL carryforwards for state purposes of $35.3 million begin to expire in 2039. As of December 31, 2023, the Company also has federal and state research and development tax credits of $2.9 million and $1.9 million, which being to expire in 2039 and 2034, respectively. The Tax Cuts and Jobs Act resulted in significant changes to the treatment of research and developmental expenses under Section 174. For tax years beginning after December 31, 2021, taxpayers are required to capitalize and amortize all research and development expenses that are paid or incurred in connection with their trade or business. Specifically, costs for U.S. based research and development activities must be amortized over five years and costs for foreign research and development activities must be amortized over 15 years using a midyear convention. During the year ended December 31, 2023, the Company capitalized $36.2 million of research and development expenses. The Company evaluates its uncertain tax positions under ASC 740-10, The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. The earliest tax years that remain subject to examination by jurisdiction is the year ended December 31, 2020 for both federal and state. However, to the extent the Company utilizes NOLs from years ending prior to 2020, the statute remains open to the extent of the NOLs or other credits are utilized.

Net Loss Per Share

Net Loss Per Share	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Earnings Per Share [Abstract]
Net Loss Per Share	12. NET LOSS PER SHARE Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended March 31, 2024 2023 Numerator: Net loss attributable to common stockholders $ (15,221 ) $ (14,445 ) Denominator: Weighted-average common shares outstanding, basic and diluted 2,608,740 2,222,800 Net loss per share attributable to common stockholders, basic and diluted $ (5.83 ) $ (6.50 ) The Company’s potential dilutive securities have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. For the three months ended March 31, 2024 and 2023, the Company excluded the following potential common shares from the computation of diluted net loss per share attributable to common stockholders for the period because including them would have had an anti-dilutive effect: Three Months Ended March 31, 2024 2023 Convertible preferred stock (as converted to common stock) 6,825,483 6,825,483 Stock options to purchase common stock 1,853,500 1,597,259 Unvested restricted common stock 21,565 294,733 SAFEs (as converted to common stock) 2,752,216 —  11,452,764 8,717,475	12. NET LOSS PER SHARE Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Year Ended 2023 2022 Numerator: Net loss attributable to common stockholders $ (42,823 ) $ (32,180 ) Denominator: Weighted-average common shares outstanding, basic and diluted 2,373,674 1,969,418 Net loss per share attributable to common stockholders, basic and diluted $ (18.04 ) $ (16.34 ) The Company’s potential dilutive securities have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted-average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. For the years ended December 31, 2023 and 2022, the Company excluded the following potential common shares from the computation of diluted net loss per share attributable to common stockholders for the period because including them would have had an anti-dilutive effect: Year Ended 2023 2022 Convertible preferred stock (as converted to common stock) 6,825,483 6,825,483 Stock options to purchase common stock 1,875,932 1,556,819 Unvested restricted common stock 35,494 312,826 SAFEs (as converted to common stock) 2,842,954 —  11,579,863 8,695,128

Related Party Transactions

Related Party Transactions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	13. RELATED PARTY TRANSACTIONS Scientific Advisory Board Member One of the Company’s co-founders License Agreement Harvard College (“Harvard”) meets the criteria of a related party resulting from the Company’s co-founders’ co-founders co-founder For the three months ended March 31, 2024 and 2023, the Company paid Harvard $0.1 and $0.1 million in cash considerations, respectively (see Note 6). Accounts payable to Harvard amounted to less than $0.1 million and $0.1 million as of March 31, 2024 and December 31, 2023, respectively. SAFE Agreements From October through December 2023, the Company entered into multiple SAFE agreements with certain existing investors and received $34.1 million representing the purchase amount. All investors are considered related parties of the Company. The SAFE agreements have no maturity date, bear no interest, and will be redeemed by the Company upon the occurrence of a triggering event, including an equity financing, public listing transaction, change of control or dissolution. Equity financing is defined as a sale of the Company’s preferred stock at a fixed valuation. In the event of an equity financing, the SAFEs will automatically be redeemed through delivery of a variable number of shares of Company preferred stock equal to the SAFE purchase amount divided by the preferred stock per share issuance price in the equity financing. In the case of the SAFE agreements issued in October 2023, a 10% discount will be applied to the per share issuance price in the equity financing in determining the number of shares of Company preferred stock issued to the investors upon redemption. Public listing transaction is defined as a direct listing, initial public offering (“IPO”) of the Company’s common stock, a reverse merger or a SPAC transaction. In any of these instances, the SAFEs will automatically be redeemed through delivery of a variable number of shares of the Company’s common stock determined by dividing the SAFE purchase amount by the offering or conversion price in the respective transaction. In the event of a change in control transaction, the SAFE investors will be entitled to receive a portion of the transaction proceeds equal to the greater of the SAFE purchase amount, payable in cash or other consideration, or the amount payable on the number of shares of the Company’s common stock equal to the SAFE purchase amount divided by the change in control conversion price, as defined in the agreement. In a dissolution event, the investor will automatically be entitled to receive a portion of the dissolution purchase amount equal to the SAFE proceeds. The SAFEs are not in the legal form of an outstanding share or debt and therefore were evaluated under ASC 480, Distinguishing Liabilities from Equity The SAFEs issued in October 2023 were recognized at their fair value of $10.4 million on the issuance date. The issuance date fair value exceeded the proceeds received by approximately $0.3 million and this difference was recognized as loss at issuance in the consolidated statement of operations and comprehensive loss. The SAFEs issued in December 2023 were recognized at their fair value of approximately $21.4 million on the issuance date. The proceeds received exceeded the issuance date fair value by approximately $2.6 million and this difference was recognized as a capital contribution from the related party investors in additional paid-in	13. RELATED PARTY TRANSACTIONS Scientific Advisory Board Member One of the Company’s co-founders License Agreement Harvard College (“Harvard”) meets the criteria of a related party resulting from the Company’s co-founders’ co-founders co-founder For the years ended December 31, 2023 and 2022, the Company paid Harvard $0.2 and $0.1 million in cash considerations, respectively (see Note 6). Accounts payable to Harvard amounted to less than $0.1 million and zero as of December 31, 2023 and 2022. Sublease Agreement The Company entered into a sublease agreement with a company controlled by the Company’s co-founders. Issuance of Preferred Stock On September 7, 2022, the Company issued 2,237,846 shares of Series A-1 A-2 key members of management, members of the Board, and certain of the Chief Executive Officer’s family members. SAFE Agreements From October through December 2023, the Company entered into multiple SAFE agreements with certain existing investors and received $34.1 million representing the purchase amount. All investors are considered related parties of the Company. The SAFE agreements have no maturity date, bear no interest, and will be redeemed by the Company upon the occurrence of a triggering event, including an equity financing, public listing transaction, change of control or dissolution. Equity financing is defined as a sale of the Company’s preferred stock at a fixed valuation. In the event of an equity financing, the SAFEs will automatically be redeemed through delivery of a variable number of shares of Company preferred stock equal to the SAFE purchase amount divided by the preferred stock per share issuance price in the equity financing. In the case of SAFE agreements issued in October 2023, a 10% discount will be applied to the per share issuance price in the equity financing in determining the number of shares of Company preferred stock issued to the investors upon redemption. Public listing transaction is defined as a direct listing, initial public offering (“IPO”) of the Company’s common stock, a reverse merger or a SPAC transaction. In any of these instances, the SAFEs will automatically be redeemed through delivery of a variable number of shares of the Company’s common stock determined by dividing the SAFE purchase amount by the offering or conversion price in the respective transaction. In the event of a change in control transaction, the SAFE investors will be entitled to receive a portion of the transaction proceeds equal to the greater of the SAFE purchase amount, payable in cash or other consideration, or the amount payable on the number of shares of the Company’s common stock equal to the SAFE purchase amount divided by the change in control conversion price, as defined in the agreement. In a dissolution event, the investor will automatically be entitled to receive a portion of the dissolution purchase amount equal to the SAFE proceeds. The SAFEs are not in the legal form of an outstanding share or debt and therefore were evaluated under ASC 480, Distinguishing Liabilities from Equity The SAFEs issued in October 2023 were recognized at their fair value of $10.4 million on the issuance date. The issuance date fair value exceeded the proceeds received by approximately $0.3 million and this difference was recognized as loss at issuance in the consolidated statement of operations and comprehensive loss. The SAFEs issued in December 2023 were recognized at their fair value of approximately $21.4 million on the issuance date. The proceeds received exceeded the issuance date fair value by approximately $2.6 million and this difference was recognized as a capital contribution from the related party investors in additional paid-in

Subsequent Events

Subsequent Events	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Subsequent Events [Abstract]
Subsequent Events	14. SUBSEQUENT EVENTS Management has evaluated subsequent events through June 20, 2024, which is the date the unaudited condensed consolidated financial statements were available to be issued, to ensure that these consolidated financial statements include appropriate disclosure of events both recognized in the consolidated financial statements and events which occurred but were not recognized in the consolidated financial statements. Merger with AVROBIO As discussed in Note 1, on January 30, 2024, the Company entered into an Agreement and Plan of Merger and Reorganization (the “Merger Agreement”) with AVROBIO, pursuant to which the subsidiaries of AVROBIO merged with and into the Company on June 20, 2024, with the Company continuing as a wholly owned subsidiary of the surviving corporation of the merger (the “Merger”). The Merger is being accounted for as a reverse recapitalization in accordance with GAAP, with AVROBIO treated as the acquired company for financial reporting purposes, and the Company treated as the accounting acquirer. Upon the closing of the Merger, each outstanding share of the Company’s common stock, including outstanding and unvested restricted stock, was converted into the right to receive a number of shares of AVROBIO’s common stock based on the Exchange Ratio, as defined in the Merger Agreement. Each outstanding and unexercised option to purchase shares of the Company’s common stock immediately prior to closing was assumed by AVROBIO and was converted into an option to purchase shares of AVROBIO common stock, with necessary adjustments to the number of shares and exercise price to reflect the Exchange Ratio. All of the Company’s restricted common stock outstanding and unvested immediately prior to the closing that was assumed by AVROBIO in the Merger remains unvested to the same extent and is subject to the same repurchase option, risk of forfeiture or other condition under any applicable restricted stock purchase agreement.  The Company’s stockholders received approximately 10,956,614 shares of AVROBIO common stock in connection with the Merger, including 11,448 shares of AVROBIO common stock subject to vesting terms, based on the number of shares of the Company’s common stock outstanding immediately prior to the Merger, including restricted stock, the number of shares of common stock issued to investors participating in the Subscription Agreements (as defined below) and SAFEs, and the Company’s convertible preferred stock outstanding immediately prior to the Merger, which was converted into shares of the Company’s common stock on a one-for-one Subscription Agreement Concurrently with the closing of the Merger, certain investors of the Company completed the purchase of 7,790,889 shares of the Company’s common stock pursuant to that certain subscription agreement dated January 30, 2024 (the “Subscription Agreement”) at a purchase price of approximately $12.40 per share for an aggregate purchase price of approximately $96.6 million. Shares of the Company’s common stock issued pursuant to the Subscription Agreements were converted into 4,163,606 shares of AVROBIO common stock at the closing of the Merger based on the exchange ratio, pursuant to the Merger Agreement.	14. SUBSEQUENT EVENTS Management has evaluated subsequent events through March 25, 2024, which is the date the consolidated financial statements were available to be issued and April 12, 2024, which is the date the consolidated financial statements were available to be re-issued, to ensure that these consolidated financial statements include appropriate disclosure of events both recognized in the consolidated financial statements and events which occurred but were not recognized in the consolidated financial statements. Proposed Merger with AVROBIO As discussed in Note 1, on January 30, 2024, the Company entered into an Agreement and Plan of Merger and Reorganization (the “Merger Agreement”) with AVROBIO, pursuant to which the subsidiaries of AVROBIO will merge with and into the Company, with the Company continuing as a wholly owned subsidiary of the surviving corporation of the merger (the “Merger”). The Merger is expected to be accounted for as a reverse recapitalization in accordance with GAAP, with AVROBIO treated as the acquired company for financial reporting purposes, and the Company treated as the accounting acquirer. Subscription Agreement Concurrently with the Merger Agreement, certain parties will enter into certain subscription agreements (the “Subscription Agreements”) with the Company to purchase, prior to the consummation of the merger, approximately 7,790,903 shares of the Company’s common stock for an aggregate purchase price of approximately $96.6 million. Shares of the Company’s common stock issued pursuant to the Subscription Agreements will be converted into shares of AVROBIO common stock at the closing of the merger based on an exchange ratio, pursuant to the Merger Agreement.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited interim condensed consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”) and the rules and regulations of the Securities and Exchange Commission (“SEC”). Any reference in these notes to applicable guidance is meant to refer to GAAP, as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). In the opinion of the Company, the accompanying unaudited condensed consolidated financial statements contain all adjustments, consisting of only normal recurring adjustments, necessary for a fair presentation of its financial position and its results of operations, changes in convertible preferred stock and stockholders’ deficit and cash flows. The information as of December 31, 2023 included in the unaudited interim condensed consolidated balance sheets was derived from audited annual consolidated financial statements but does not contain all of the footnote disclosures from the audited annual consolidated financial statements. These unaudited interim condensed consolidated financial statements should be read in conjunction with the audited annual consolidated financial statements as of and for the years ended December 31, 2023 and 2022.	Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to GAAP, as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”).
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements, and the reported amounts of expenses during the reporting periods. Significant items subject to such estimates and assumptions include the contract research accruals, stock-based compensation expense, the fair value of the Company’s common stock, the income tax valuation allowance, and the fair value determination of the SAFEs. Management’s estimates are based on historical experience and various other assumptions that it believes are reasonable under the circumstances. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting periods. Significant items subject to such estimates and assumptions include the contract research accruals, stock-based compensation expense, the fair value of the Company’s common stock, the income tax valuation allowance, the fair value determination of the SAFEs and the preferred stock tranche liability settled in 2022. Management’s estimates are based on historical experience and various other assumptions that it believes are reasonable under the circumstances. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.
Principles of Consolidation	Principles of Consolidation The condensed consolidated financial statements include the accounts of the Company and its subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Foreign Currency		Foreign Currency The functional currency of the Company’s wholly-owned foreign subsidiary in Australia is Australian Dollars. Accounts and transactions denominated in currencies other than an entity’s functional currency are remeasured into the functional currency using the appropriate foreign exchange rate in accordance with FASB ASC Topic 830, Foreign Currency Matters. from transactions denominated in foreign currencies are recorded in the statements of operations and comprehensive loss as other income or expenses. The financial statements of the Australian subsidiary will be translated into the Company’s U.S. dollar reporting currency at each reporting date, and the translation adjustments will be recognized as an unrealized gain or loss within the cumulative translation adjustment.
Segment Information		Segment Information The Company considered the Company’s organizational structure and the information regularly reviewed and evaluated by the Company’s chief operating decision maker (“CODM”) when deciding how to allocate resources and assess performance. The Company has determined that its CODM is its Chief Executive Officer. The CODM reviews the financial information on a consolidated basis for purposes of evaluating financial performance and allocating resources. On the basis of this factor, the Company determined that it operates and manages its business as a single
Cash and Cash Equivalents		Cash and Cash Equivalents The Company considers all highly liquid investments with an original maturity of three months or less when purchased to be cash equivalents. As of December 31, 2023, cash equivalents were comprised primarily of money market funds.
Restricted Cash		Restricted Cash The Company classifies all cash whose use is limited by contractual provisions as restricted cash. Restricted cash arises from the requirement for the Company to maintain cash of $0.6 million as collateral in connection with a letter of credit issued with the corporate headquarters and lab space lease agreement entered into on November 19, 2020 and may not access these funds until after the expiration of the initial lease term on December 31, 2025. The Company has classified the certificate of deposits collateralizing the letter of credits issued as a security deposit as restricted cash in the noncurrent asset section of the balance sheets.
Deferred Offering Costs		Deferred Offering Costs Deferred offering costs consist of direct legal, accounting and other fees and costs directly attributable to the Company’s proposed Merger (see Note 14). The Company capitalized deferred offering costs incurred prior to the close of the Merger which are included in deferred offering costs within the consolidated balance sheet as of December 31, 2023. The deferred offering costs were $0.7 million as of December 31, 2023.
Concentrations of Credit Risk and Off-Balance Sheet Risk		Concentrations of Credit Risk and Off-Balance Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. Periodically, the Company maintains deposits in accredited financial institutions in excess of governmental insured limits. The Company deposits its cash and cash equivalents in financial institutions that it believes have a high credit quality and have not experienced any losses on such accounts and does not believe it is exposed to any unusual credit risk beyond the normal credit risk associated with commercial banking relationships.
Property, Equipment and Improvements		Property, Equipment and Improvements Property, equipment and improvements are stated at cost less accumulated depreciation. Depreciation is calculated using the straight-line method over the estimated useful life of each asset. Construction in process is capitalized and once the asset is operational, the Company will commence depreciation of the asset. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recognized. Expenditures for major renewals and improvements that extend the useful life of the asset are capitalized as part of the asset. Expenditures for repairs and maintenance are expensed as incurred. The estimated useful lives for property and equipment are as follows: Estimated Useful Life Laboratory equipment 5 years Furniture and office equipment 5 years Computer equipment 3 years Leasehold improvements Shorter of the lease term or 10 years
Impairment of Long-Lived Assets		Impairment of Long-Lived Assets The Company evaluates its long-lived assets, which consist primarily of property, equipment and improvements, for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. The carrying amount of a long-lived asset is not recoverable if it exceeds the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the asset. If the carrying amount of the asset is not recoverable, an impairment will be recognized and measured as the amount by which the carrying amount of the asset exceeds its fair value. No impairments were identified during the years ended December 31, 2023 and 2022.
Fair Value Measurements		Fair Value Measurements Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Market participants are independent buyers or sellers in the principal (or most advantageous) market for the asset or liability. Fair value measurements are categorized into a three-tier hierarchy on the basis of the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). The three levels of the fair value hierarchy are as follows: • Level 1 • Level 2 • Level 3 Financial instruments are categorized in their entirety in the same level of the fair value hierarchy as the lowest level input that is significant to the entire fair value measurement.
Research and Development Expenses		Research and Development Expenses Research and development costs are expensed as incurred. Research and development expenses consist primarily of costs incurred for the development of the proprietary platform and product candidates and include (1) expenses incurred under agreements with third parties and contract research organizations (“CROs”), (2) costs to acquire and develop supplies for research, (3) salaries and related costs, including stock-based compensation, (4) depreciation and other facility-related and overhead expenses, (5) licensing and license maintenance fees incurred under license option and license agreements where no alternative future use exists, and (6) costs related to compliance with regulatory requirements. The Company recognizes external research and development costs based on an evaluation of the progress to completion of specific tasks using information provided from the Company’s contracted service providers.
Prepaid and Accrued Research and Development Costs		Prepaid and Accrued Research and Development Costs Substantial portions of the Company’s research are performed by third-party laboratories, CROs and other vendors. These vendors generally bill monthly for services performed, or bill based upon milestone achievement. The Company accrues expenses based upon estimates of percentage of work completed and the contract milestones remaining. On occasion, the Company is obligated to make upfront payments upon execution of research and development agreements. Advance payments, including nonrefundable amounts, for goods or services that will be used or rendered for future research and development activities are capitalized as prepaid expenses until such goods are delivered or the related services are performed. The Company estimates the period over which such services will be performed based on the terms of the agreements as well as the level of effort to be expended in each period. Since inception, the Company has not experienced any material differences between the actual and estimated timing of performance or level of effort.
Leases		Leases Effective January 1, 2022, the Company adopted ASC Topic 842, Leases On January 1, 2022, the Company recorded operating lease liabilities and their corresponding right-of-use For leases entered into after January 1, 2022, the Company applies the guidance in ASC 842, and determines whether an arrangement is or contains a lease at inception. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. The Company classifies a lease at the lease commencement date, when control of the underlying asset is transferred from the lessor to the lessee, as an operating or finance lease and records a ROU asset and a lease liability on the consolidated balance sheet for any lease with a lease term greater than twelve months. The Company has elected the practical expedient to not recognize leases with a lease term of twelve months or less on the balance sheet (“short-term leases”) and will recognize lease payments for such short-term leases as an expense on a straight-line basis. The Company enters into contracts that contain both lease and non-lease Non-lease non-lease For lease arrangements in which the Company is a lessee, finance and operating ROU assets and liabilities are recognized at the lease commencement date based on the present value of the lease payments over the lease term determined using the discount rate implicit in the lease if readily determinable. When the rate implicit in the lease is not readily determinable, the Company utilizes its IBR, which is determined on the basis of information that is available at the lease commencement date. ROU assets are further adjusted for items such as initial direct costs, prepaid rent, or lease incentives. Operating lease costs are expensed using the straight-line method as an operating expense over the lease term unless the operating lease ROU asset has been impaired. The Company’s lease terms may include options to extend the lease when it is reasonably certain that the Company will exercise that option. Finance lease assets are amortized to depreciation expense using the straight-line method over the shorter of the useful life of the related asset or the lease term. Finance lease payments are bifurcated between (i) a portion that is recorded as interest expense and (ii) a portion that reduces the finance lease liability associated with the lease.
Simple Agreements for Future Equity		Simple Agreements for Future Equity SAFE instruments do not represent legal form debt (i.e., no creditor rights), but allow for redemption based upon certain triggering events that are outside of the control of the Company. The Company accounts for a SAFE as a liability at fair value on a recurring basis. Triggering events include an equity financing, public listing transaction, change of control or dissolution. Changes in the liability’s fair value are recognized in the Company’s statements of operations and comprehensive loss.
Convertible Preferred Stock		Convertible Preferred Stock The Company classifies convertible preferred stock outside of stockholders’ deficit on the consolidated balance sheets as it is redeemable upon the occurrence of a Deemed Liquidation Event, as defined below, that is not strictly within the Company’s control. The issuance of convertible preferred stock is recorded at the issuance price less any amounts allocated to freestanding liabilities associated with the issuance and related allocable issuance costs. The carrying values of the convertible preferred stock have not been adjusted to their liquidation preferences because it is not considered probable that a Deemed Liquidation Event will occur and make such stock redeemable.
Stock-Based Compensation		Stock-Based Compensation The Company measures and records the expense related to stock-based payment awards based on the fair value of those awards as determined on the date of grant. The Company recognizes stock-based compensation expense over the requisite service period of the individual grant, which is generally equal to the vesting period, using the straight-line method. For stock options with performance conditions, the Company records stock-based compensation expense when it is deemed probable that the performance condition will be met. The Company uses the Black-Scholes-Merton (“BSM”) option-pricing model to determine the fair value of stock options. The BSM option-pricing model requires the use of assumptions to determine the fair value of the stock options. The fair value of the shares of common stock underlying stock options has historically been determined by the Board of Directors (“Board”), with input from management and contemporaneous third-party valuations, as there was no public market for the common stock. Given the absence of a public market for the Company’s common stock, and in accordance with the American Institute of Certified Public Accountants Practice Aid, Valuation of Privately Held Company Equity Securities Issued as Compensation, the Board exercised reasonable judgment and considered numerous objective and subjective factors to determine the best estimate of the fair value of the Company’s common stock at each stock option grant date. The Company calculates the fair value of stock options granted by using the BSM option-pricing model with the following assumptions: Expected Volatility Expected Term Risk-Free Interest Rate zero-coupon Dividend Yield Forfeitures The purchase price of restricted common stock granted to founders, employees and consultants is the estimated fair value on the grant date and is subject to various vesting schedules. Unvested restricted common stock are subject to repurchase rights held by the Company at the original issuance price in the event the restricted common stockholders’ service to the Company is terminated either voluntarily or involuntarily. The associated liability is classified in accrued expenses and other current liabilities in the consolidated balance sheets. The balance of this liability as of December 31, 2023 and 2022 is immaterial. All stock-based compensation expense is recorded in research and development expense or general and administrative expense in the consolidated statements of operations and comprehensive loss, on the basis of the respective employee and nonemployee’s role within the Company.
Income Taxes		Income Taxes The Company accounts for income taxes under the asset and liability method under ASC Topic 740, Income Taxes The Company recognizes deferred tax assets to the extent that it believes that these assets are more likely than not to be realized. In making such a determination, the Company considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning The Company records uncertain tax positions in accordance with ASC 740 on the basis of a two-step more-likely-than-not
Related Party Transactions		Related Party Transactions Related parties are directly or indirectly related to the Company, through one or more intermediaries and are in control, controlled by, or under common control with the Company. Related parties also include principal owners of the Company, its management, members of the immediate families of principal owners of the Company and its management, and other parties with which the Company may transact with if one party controls or can significantly influence the management or operating policies of the other to an extent that one of the transacting parties might be prevented from fully pursuing its own separate interests. The Board reviews and approves transactions with directors, officers and holders of 5% or more of the Company’s voting securities and their affiliates or their family members. The material facts as to the related party’s relationship or interest in the transaction are disclosed to the Board prior to its consideration of such transaction, and the transaction is not considered approved by the Board unless a majority of the directors who are not interested in the transaction approve the transaction.
Comprehensive Loss		Comprehensive Loss Comprehensive loss includes net loss as well as other changes in stockholders’ deficit that result from transactions and economic events other than those with stockholders. The comprehensive loss for the Company equals its net loss plus changes in foreign currency translation for all periods presented.
Net Loss per Share		Net Loss per Share The Company applies the two-class two-class two-class Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, excluding potentially dilutive common shares. Diluted net loss per share attributable to common stockholders is computed by adjusting net loss attributable to common stockholders to reallocate earnings based on the potential impact of dilutive securities. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period, including potential dilutive common shares. For purposes of this calculation, the Company’s outstanding convertible preferred stock, stock options, unvested restricted common stock and the SAFEs are considered potential dilutive common shares. The Company generated a net loss for each of the years presented. Accordingly, basic and diluted net loss per share attributable to common stockholders are the same because the inclusion of the potentially dilutive securities would be anti-dilutive.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB, or other standard setting bodies and are adopted by the Company as of the specified effective dates. Unless otherwise discussed, the impact of recently issued standards that are not yet effective are not anticipated to have a material impact on the Company’s condensed consolidated financial statements upon adoption. Recently Adopted Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, 470-20) 815-40): 2020-06”). 2020-06 paid-in 2020-06 2020-06	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB, or other standard setting bodies and are adopted by the Company as of the specified effective dates. Unless otherwise discussed, the impact of recently issued standards that are not yet effective are not anticipated to have a material impact on the Company’s consolidated financial statements upon adoption.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting 2023-07”), 2023-07, 2023-07 2023-07 2023-07 In December 2023, the FASB issued ASU No. 2023-09, Income Taxes 2023-09”), 2023-09, 2023-09 2023-09	Recently Issued Accounting Pronouncement Not Yet Adopted In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) 815-40): (“ASU 2020-06”). ASU 2020-06 paid-in ASU 2020-06 ASU 2020-06 ASU 2020-06 In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting 2023-07”), 2023-07, 2023-07 2023-07 2023-07 In December 2023, the FASB issued ASU No. 2023-09, Income Taxes 2023-09”), 2023-09, 2023-09 2023-09

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
Accounting Policies [Abstract]
Schedule of Property and Equipment Estimated Useful Life	The estimated useful lives for property and equipment are as follows: Estimated Useful Life Laboratory equipment 5 years Furniture and office equipment 5 years Computer equipment 3 years Leasehold improvements Shorter of the lease term or 10 years

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables present information about financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): March 31, 2024 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 17,213 $ —  $ —  $ 17,213 $ 17,213 $ —  $ —  $ 17,213 Liabilities: SAFE liabilities $ —  $ —  $ 32,590 $ 32,590 $ —  $ —  $ 32,590 $ 32,590 December 31, 2023 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 27,278 $ —  $ —  $ 27,278 $ 27,278 $ —  $ —  $ 27,278 Liabilities: SAFE liabilities $ —  $ —  $ 30,515 $ 30,515 $ —  $ —  $ 30,515 $ 30,515	The following tables present information about financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values (in thousands): December 31, 2023 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 27,278 $ —  $ —  $ 27,278 $ 27,278 $ —  $ —  $ 27,278 Liabilities: SAFE liabilities $ —  $ —  $ 30,515 $ 30,515 $ —  $ —  $ 30,515 $ 30,515 December 31, 2022 Level 1 Level 2 Level 3 Total Assets: Cash equivalents: Money market funds $ 33,640 $ —  $ —  $ 33,640 $ 33,640 $ —  $ —  $ 33,640
Summary of Activity for the Safe Liabilities that were Measured at Fair Value	The following table presents activity for the SAFE liabilities that were measured at fair value using significant unobservable Level 3 inputs during the three months ended March 31, 2024 and the year ended December 31, 2023 (in thousands): SAFE Liabilities Balance as of January 1, 2023 $ —  Initial fair value recognition 31,515 Loss on issuance 255 Fair value adjustments (1,255 ) Balance as of December 31, 2023 30,515 Fair value adjustments 2,075 Balance as of March 31, 2024 $ 32,590	The following table presents activity for the preferred stock tranche liability and the SAFE liabilities that were measured at fair value using significant unobservable Level 3 inputs during the years ended December 31, 2023 and 2022 (in thousands): Preferred Stock SAFE Liabilities Balance as of January 1, 2022 $ 643 $ —  Fair value adjustments (643 ) —  Balance as of December 31, 2022 —  —  Initial fair value recognition —  31,515 Loss on issuance —  255 Fair value adjustments —  (1,255 ) Balance as of December 31, 2023 $ —  $ 30,515

Property, Equipment and Impro_2

Property, Equipment and Improvements, Net (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Abstract]
Summary of Property Equipment and Improvements Net	Property, equipment and improvements, net is comprised of the following (in thousands): March 31, December 31, Laboratory equipment $ 4,548 $ 4,510 Furniture and office equipment 244 244 Computer equipment 165 161 Construction in progress —  38 Leasehold improvements 25 25 4,982 4,978 Less: accumulated depreciation (2,118 ) (1,856 ) Property and equipment, net $ 2,864 $ 3,122	Property, equipment and improvements, net is comprised of the following (in thousands): December 31, 2023 2022 Laboratory equipment $ 4,510 $ 4,018 Furniture and office equipment 244 244 Computer equipment 161 149 Construction in progress 38 49 Leasehold improvements 25 25 4,978 4,485 Less: accumulated depreciation (1,856 ) (877 ) Property and equipment, net $ 3,122 $ 3,608
Summary of Depreciation Expenses	Depreciation expense was $0.3 million and $0.2 million during the three months ended March 31, 2024 and 2023 and was recorded as follows (in thousands): Three Months Ended March 31, 2024 2023 General and administrative $ 4 $ 4 Research and development 258 226 $ 262 $ 230 These amounts are exclusive of amortization related to finance lease assets of $0.1 million during the three months ended March 31, 2024 and 2023.	Depreciation expense was $1.0 million and $0.6 million and was recorded as follows (in thousands): Year Ended 2023 2022 General and administrative $ 17 $ 12 Research and development 973 635 $ 990 $ 647

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities is comprised of the following (in thousands): March 31, December 31, Employee compensation related costs $ 3,769 $ 2,840 Accrued office and laboratory costs 141 211 Accrued contract research organization fees 3,207 2,298 Accrued contract development and manufacturing organization fees 604 660 Accrued professional fees 2,935 1,798 Other current liabilities 392 334 $ 11,048 $ 8,141	Accrued expenses and other current liabilities is comprised of the following (in thousands): December 31, 2023 2022 Employee compensation related costs $ 2,840 $ 2,158 Accrued office and laboratory costs 211 481 Accrued contract research organization fees 2,298 1,345 Accrued contract development and manufacturing organization fees 660 842 Accrued professional fees 1,798 489 Other current liabilities 334 499 $ 8,141 $ 5,814

Leases (Tables)

Leases (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Leases [Abstract]
Schedule of effect of lease costs in the company's consolidated statement of operations and comprehensive loss	The following table sets forth information about lease costs for the three months ended March 31, 2024 and 2023 (in thousands): Three Months Ended Finance lease cost 2024 2023 Amortization of ROU assets $ 114 $ 134 Interest on lease liabilities 31 42 Operating lease cost 351 351 Short-term lease cost 176 150 Variable lease cost 249 206 Total lease costs $ 921 $ 883	The following table sets forth information about lease costs for the years ended December 31, 2023 and 2022 (in thousands): Year Ended Finance lease cost 2023 2022 Amortization of ROU assets $ 488 $ 359 Interest on lease liabilities 151 106 Operating lease cost 1,404 1,404 Short-term lease cost 749 389 Variable lease cost 786 907 Sublease income —  (253 ) Total lease costs $ 3,578 $ 2,912
Schedule of information about the company's leases	The following table sets forth information about the Company’s leases for the three months ended March 31, 2024 and 2023 (in thousands): Three Months Ended Cash paid for amounts included in the measurement of lease 2024 2023 Finance leases - financing cash flows $ 118 $ 144 Finance leases - operating cash flows 31 42 Operating leases - operating cash flows 381 370 Weighted-average remaining lease terms (in years) Finance leases 2.99 3.97 Operating leases 1.84 2.84 Weighted-average discount rate Finance leases 9.65 % 9.54 % Operating leases 8.25 % 8.25 %	The following table sets forth information about the Company’s leases for the years ended December 31, 2023 and 2022 (in thousands): Year Ended Cash paid for amounts included in the measurement of lease liabilities 2023 2022 Finance leases - financing cash flows $ 499 $ 393 Finance leases - operating cash flows 151 106 Operating leases - operating cash flows 1,235 1,470 ROU assets obtained in exchange for lease liabilities Finance leases —  1,340 Weighted-average remaining lease terms (in years) Finance leases 3.23 4.19 Operating leases 2.09 3.09 Weighted-average discount rate Finance leases 9.62 % 9.49 % Operating leases 8.25 % 8.25 %
Schedule in tabular form of maturity of operating and finance leases	The following table presents the maturity of the Company’s finance and operating lease liabilities for the three months ended March 31, 2024 (in thousands): Year ended December 31, Finance Leases Operating Leases 2024 (remaining) $ 434 $ 1,154 2025 552 1,580 2026 363 132 2027 44 —  2028 —  —  Thereafter —  —  Total lease payments 1,393 2,866 Less: interest (160 ) (198 ) Total lease liabilities $ 1,233 $ 2,668	The following table presents the maturity of the Company’s finance and operating lease liabilities for the year ended December 31, 2023 (in thousands): Year ended December 31, Finance Leases Operating Leases 2024 $ 583 $ 1,534 2025 552 1,580 2026 363 132 2027 44 —  2028 —  —  Thereafter —  —  Total lease payments 1,542 3,246 Less: interest (191 ) (254 ) Total lease liabilities $ 1,351 $ 2,992

Convertible Preferred Stock (Ta

Convertible Preferred Stock (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Temporary Equity Disclosure [Abstract]
Summary of Preferred Stock	The Preferred Stock as of March 31, 2024 and December 31, 2023 consisted of the following (in thousands, expect share and per share amounts): March 31, 2024 and December 31, 2023 Par Value Preferred Preferred Carrying Liquidation Common Stock Series A-1 $ 0.0001 4,118,120 4,118,120 $ 45,016 $ 54,308 4,118,120 Series A-2 $ 0.0001 1,649,188 1,649,188 21,654 21,749 1,649,188 Series A-3 $ 0.0001 696,516 696,516 9,187 7,348 696,516 Series A-4 $ 0.0001 361,659 361,659 4,770 4,054 361,659 6,825,483 6,825,483 $ 80,627 $ 87,459 6,825,483	Preferred Stock consisted of the following (in thousands, expect share and per share amounts): December 31, 2023 Par Value Preferred Preferred Stock Issued Carrying Liquidation Common Stock Series A-1 $ 0.0001 4,118,120 4,118,120 $ 45,016 $ 54,308 4,118,120 Series A-2 $ 0.0001 1,649,188 1,649,188 21,654 21,749 1,649,188 Series A-3 $ 0.0001 696,516 696,516 9,187 7,348 696,516 Series A-4 $ 0.0001 361,659 361,659 4,770 4,054 361,659 6,825,483 6,825,483 $ 80,627 $ 87,459 6,825,483 December 31, 2022 Par Value Preferred Preferred Stock Issued Carrying Liquidation Common Stock Series A-1 $ 0.0001 4,118,120 4,118,120 $ 45,016 $ 54,308 4,118,120 Series A-2 $ 0.0001 1,649,188 1,649,188 21,654 21,749 1,649,188 Series A-3 $ 0.0001 696,516 696,516 9,187 7,348 696,516 Series A-4 $ 0.0001 361,659 361,659 4,770 4,054 361,659 6,825,483 6,825,483 $ 80,627 $ 87,459 6,825,483

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]
Summary of the activity in the 2019 Plan	A summary of the activity in the 2019 Plan for the three months ended March 31, 2024 is as follows (in thousands except share and per share amounts): Number of Weighted- Weighted-Average Aggregate Balance as of January 1, 2024 1,875,932 $ 1.66 8.2 $ 2,276 Granted —  —  Exercised (2,874 ) 1.54 $ 4 Forfeited and expired (19,558 ) 1.36 Balance as of March 31, 2024 1,853,500 $ 1.66 7.9 $ 2,242 Options vested and exercisable as of March 31, 2024 1,068,487 $ 1.34 7.3 $ 1,634 Options vested and expected to vest as of March 31, 2024 1,853,500 $ 1.66 7.9 $ 2,242	A summary of the activity in the 2019 Plan for the year ended December 31, 2023 is as follows (in thousands except share and per share amounts): Number of Weighted- Weighted-Average Aggregate Balance as of January 1, 2023 1,556,819 $ 1.32 8.7 $ 420 Granted 441,615 2.74 Exercised (108,475 ) 1.27 $ 172 Forfeited and expired (14,027 ) 1.53 Balance as of December 31, 2023 1,875,932 $ 1.66 8.2 $ 2,276 Options vested and exercisable as of December 31, 2023 972,054 $ 1.30 7.6 $ 1,525 Options vested and expected to vest as of December 31, 2023 1,875,932 $ 1.66 8.2 $ 2,276
Summary of Fair Values of the Options Granted	The fair values of the options granted in the three months ended March 31, 2023 were estimated based on the BSM option pricing model, using the following assumptions: Three Months March 31, 2023 Fair value per share of underlying common stock $1.34 Expected term (in years) 5.93 Expected volatility 111.05% -111.21% Risk-free interest rate 3.65% Expected dividend yield 0%	The fair values of the options granted were estimated based on the BSM option pricing model, using the following assumptions: Year Ended 2023 2022 Fair value per share of underlying common stock $2.16 $1.57 Expected term (in years) 6.01 6.02 Expected volatility 93.44 - 111.21% 87.02 - 91.24% Risk-free interest rate 4.14% 3.01% Expected dividend yield 0% 0%
Summary of Restricted Stock Activity	The following table summarizes restricted stock activity: Number of Unvested restricted common stock as of January 1, 2024 35,494 Granted —  Vested (13,929 ) Forfeited —  Unvested restricted common stock as of March 31, 2024 21,565	The following table summarizes restricted stock activity: Number of Shares Unvested restricted common stock as of 312,826 Granted —  Vested (277,332 ) Forfeited —  Unvested restricted common stock as of 35,494
Summary of Stock Based Compensation Expense Regarding its Employees and Nonemployees	The Company recorded stock-based compensation expense regarding its employees and nonemployees as follows (in thousands): Three Months Ended March 31, 2024 2023 General and administrative $ 193 $ 174 Research and development 128 101 $ 321 $ 275	The Company recorded stock-based compensation expense regarding its employees and nonemployees as follows (in thousands): Year Ended 2023 2022 General and administrative $ 705 $ 738 Research and development 416 381 $ 1,121 $ 1,119

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Summary of components of income tax expense (benefit)	Income tax expense consists of the following (in thousands): Year Ended December 31, 2023 2022 Current expense (benefit): Federal $ —  $ —  State —  —  Total current expense (benefit): $ —  $ —  Deferred expense (benefit): Federal $ 11,207 $ 7,407 State 3,361 2,189 Deferred tax benefit 14,568 9,596 Less change in valuation allowance (14,568 ) (9,596 ) Total income tax expense (benefit): $ —  $ —
Summary of reconciliation of income tax expense (benefit)	The components of the Company’s loss before income tax expense are compromised solely of domestic sources. The reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows: Year Ended December 31, 2023 2022 Federal statutory income tax rate 21.0 % 21.0 % State income taxes 7.8 % 6.8 % Foreign rate differential 0.1 % 0.0 % Permanent differences 1.2 % -0.3 % Equity-based compensation -0.4 % -0.6 % Preferred stock liability fair value adjustment 0.0 % 0.4 % Tax credits 4.4 % 2.5 % Change in valuation allowance -34.0 % -29.8 % Effective income tax rate 0.0 % 0.0 %
Summary of deferred tax assets and liabilities	Significant components of the Company’s deferred tax assets and liabilities consist of the following (in thousands): Year Ended December 31, 2023 2022 Deferred tax assets Net operating loss carryforward $ 11,392 $ 7,765 Research credits 4,336 1,579 Lease liability 817 1,575 Capitalized R&D expenses 14,595 7,027 Accruals & other 1,027 859 Total deferred tax assets 32,167 18,805 Valuation allowance (30,228 ) (15,658 ) Net deferred tax assets $ 1,939 $ 3,147 Deferred tax liabilities Depreciation $ (1,210 ) $ (1,530 ) Right of use asset (729 ) (1,617 ) Total deferred tax liabilitites (1,939 ) (3,147 ) Net deferred tax assets (liability) $ —  $ —

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Earnings Per Share [Abstract]
Summary of Basic and Diluted Earnings Per Share	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Three Months Ended March 31, 2024 2023 Numerator: Net loss attributable to common stockholders $ (15,221 ) $ (14,445 ) Denominator: Weighted-average common shares outstanding, basic and diluted 2,608,740 2,222,800 Net loss per share attributable to common stockholders, basic and diluted $ (5.83 ) $ (6.50 )	Basic and diluted net loss per share attributable to common stockholders was calculated as follows (in thousands, except share and per share amounts): Year Ended 2023 2022 Numerator: Net loss attributable to common stockholders $ (42,823 ) $ (32,180 ) Denominator: Weighted-average common shares outstanding, basic and diluted 2,373,674 1,969,418 Net loss per share attributable to common stockholders, basic and diluted $ (18.04 ) $ (16.34 )
Summary of Diluted Net Loss Per Share Attributable to Common Stockholders	the following potential common shares from the computation of diluted net loss per share attributable to common stockholders for the period because including them would have had an anti-dilutive effect: Three Months Ended March 31, 2024 2023 Convertible preferred stock (as converted to common stock) 6,825,483 6,825,483 Stock options to purchase common stock 1,853,500 1,597,259 Unvested restricted common stock 21,565 294,733 SAFEs (as converted to common stock) 2,752,216 —  11,452,764 8,717,475	the Company excluded the following potential common shares from the computation of diluted net loss per share attributable to common stockholders for the period because including them would have had an anti-dilutive effect: Year Ended 2023 2022 Convertible preferred stock (as converted to common stock) 6,825,483 6,825,483 Stock options to purchase common stock 1,875,932 1,556,819 Unvested restricted common stock 35,494 312,826 SAFEs (as converted to common stock) 2,842,954 —  11,579,863 8,695,128

Description of Business - Addit

Description of Business - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Jun. 20, 2024
Nature Of Operations [Line Items]
Entity Incorporation, Date of Incorporation	Jun. 05, 2019		Jun. 05, 2019
Retained Earnings (Accumulated Deficit)	$ (105,825)		$ (90,604)	$ (47,781)
Net loss	(15,221)	$ (14,445)	(42,823)	(32,180)
Cash and cash equivalents	$ 18,748	$ 24,872	$ 28,769	$ 35,966
AVROBIO, Inc [Member] | Subscription Agreement [Member]
Nature Of Operations [Line Items]
Cash received for sale of common stock for merger					$ 77,300
Sale of common stock for merger					$ 96,600

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Number of operating segments | Segment	1
Cash collateral for borrowed securities	$ 600
Lease expiration date	Dec. 31, 2025
Deferred offering costs	$ 700
Impairment of long-lived assets to be disposed of	$ 0	$ 0
Minimum [Member] | Directors, officers and holders [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Equity method investment, ownership percentage	5%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Life (Detail)	12 Months Ended
	Dec. 31, 2023
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life	5 years
Furniture and office equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life	5 years
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life	3 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment estimated useful life	10 years
Property and equipment estimated useful life	Shorter of the lease term

Fair Value Measurement - Additi

Fair Value Measurement - Additional Information (Detail) - USD ($) $ in Thousands			1 Months Ended	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Oct. 31, 2023	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proceeds from simple agreement for future equity				$ 34,100
Fair Value, measurement with unobservable inputs reconciliation, recurring basis, liability, transfers, net					$ 0	$ 0
Simple Agreements for Future Equity [Member] | Equity Financing [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments subject to mandatory redemption redemption period					1 month 15 days
Simple Agreements for Future Equity [Member] | Public Listing Transaction [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments subject to mandatory redemption redemption period					5 months 15 days
Simple Agreements for Future Equity [Member] | Dissolution [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments subject to mandatory redemption redemption period					5 months 15 days
Simple Agreements for Future Equity [Member] | Probability Weighted Scenario Analysis [Member] | Equity Financing [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing assets and servicing liabilities at fair value, assumptions used to estimate fair value, prepayment speed	10%	10%	87.50%
Simple Agreements for Future Equity [Member] | Probability Weighted Scenario Analysis [Member] | Public Listing Transaction [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing assets and servicing liabilities at fair value, assumptions used to estimate fair value, prepayment speed	87.50%	87.50%	10%
Simple Agreements for Future Equity [Member] | Probability Weighted Scenario Analysis [Member] | Dissolution [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing assets and servicing liabilities at fair value, assumptions used to estimate fair value, prepayment speed	2.50%	2.50%	2.50%
Simple Agreements for Future Equity [Member] | Application of Build Up Method [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing assets and servicing liabilities at fair value, assumptions used to estimate fair value, discount rate	30.20%	30.20%
Simple Agreements for Future Equity [Member] | Due to Higher Risk Free Rate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Servicing assets and servicing liabilities at fair value, assumptions used to estimate fair value, discount rate	30.90%	30.90%

Fair Value Measurement - Summar

Fair Value Measurement - Summary of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Assets:
Assets	$ 17,213	$ 27,278	$ 33,640
Liabilities:
Liabilities	32,590	30,515
SAFE Liabilities [Member]
Liabilities:
Liabilities	32,590	30,515
Money Market Funds [Member] | Cash Equivalents [Member]
Assets:
Assets	17,213	27,278	33,640
Fair Value, Inputs, Level 1 [Member]
Assets:
Assets	17,213	27,278	33,640
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member] | Cash Equivalents [Member]
Assets:
Assets	17,213	27,278	$ 33,640
Fair Value, Inputs, Level 3 [Member]
Liabilities:
Liabilities	32,590	30,515
Fair Value, Inputs, Level 3 [Member] | SAFE Liabilities [Member]
Liabilities:
Liabilities	$ 32,590	$ 30,515

Fair Value Measurement - Summ_2

Fair Value Measurement - Summary of Activity for the Safe Liabilities that were Measured at Fair Value (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Preferred Stock Tranche Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening Balance			$ 643
Fair value adjustments			$ (643)
SAFE Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening Balance	$ 30,515
Initial fair value recognition		$ 31,515
Loss on issuance		255
Fair value adjustments	2,075	(1,255)
Ending Balance	$ 32,590	$ 30,515

Property, Equipment and Impro_3

Property, Equipment and Improvements, Net - Summary of Depreciation Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Depreciation	$ 262	$ 230	$ 990	$ 647
General and administrative [Member]
Property, Plant and Equipment [Line Items]
Depreciation	4	4	17	12
Research and development [Member]
Property, Plant and Equipment [Line Items]
Depreciation	$ 258	$ 226	$ 973	$ 635

Property, Equipment and Impro_4

Property, Equipment and Improvements, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Depreciation	$ 262	$ 230	$ 990	$ 647
Finance lease right-of-use asset amortization	$ 114	$ 134	$ 488	$ 359

Property, Equipment and Impro_5

Property, Equipment and Improvements, Net - Summary of Property Equipment and Improvements Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 4,982	$ 4,978	$ 4,485
Less: accumulated depreciation	(2,118)	(1,856)	(877)
Property and equipment, net	2,864	3,122	3,608
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	4,548	4,510	4,018
Furniture and office equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	244	244	244
Computer equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	165	161	149
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment gross		38	49
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment gross	$ 25	$ 25	$ 25

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Employee compensation related costs	$ 3,769	$ 2,840	$ 2,158
Accrued office and laboratory costs	141	211	481
Accrued contract research organization fees	3,207	2,298	1,345
Accrued contract development and manufacturing organization fees	604	660	842
Accrued professional fees	2,935	1,798	489
Other current liabilities	392	334	499
Total	$ 11,048	$ 8,141	$ 5,814

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)

3 Months Ended

12 Months Ended

Jun. 20, 2024

May 01, 2023

Mar. 31, 2024

Mar. 31, 2023

Dec. 31, 2023

May 31, 2023

Dec. 31, 2022

Jul. 02, 2024

Jul. 02, 2023

Jul. 02, 2022

Feb. 10, 2022

Nov. 29, 2021

Other Commitments [Line Items]

Accounts payable and accrued liabilities, current

$ 11,048,000

$ 8,141,000

$ 5,814,000

Indemnification Agreement [Member]

Other Commitments [Line Items]

Other commitment

0

0

0

License Agreement [Member] | Harvard [Member]

Other Commitments [Line Items]

Non refundable license fee amount

$ 170,000

Due to related party

$ 100,000

$ 100,000

$ 100,000

License Agreement [Member] | Harvard [Member] | License [Member] | Maximum [Member]

Other Commitments [Line Items]

Percentage of non royalty income received

20%

20%

License Agreement [Member] | Harvard [Member] | License [Member] | Minimum [Member]

Other Commitments [Line Items]

Percentage of non royalty income received

10%

10%

License Agreement [Member] | Harvard [Member] | First Installment [Member]

Other Commitments [Line Items]

Payment of non refundable license fee amount

$ 56,666

License Agreement [Member] | Harvard [Member] | Second Installment [Member]

Other Commitments [Line Items]

Payment of non refundable license fee amount

$ 56,666

License Agreement [Member] | Harvard [Member] | Third Installment [Member]

Other Commitments [Line Items]

Payment of non refundable license fee amount

$ 56,668

License Agreement [Member] | Harvard [Member] | Common Stock [Member]

Other Commitments [Line Items]

Non refundable license fee shares

227,486

Non refundable license fee shares fair value

400,000

License Agreement [Member] | Alloy Therapeutics, LLC [Member]

Other Commitments [Line Items]

Non refundable and non creditable annul fee

$ 100,000

$ 100,000

Milestone payment

4,800,000

$ 4,800,000

Milestone fees

$ 100,000

$ 0

100,000

$ 0

Discovery Agreement [Member] | Adimab, LLC [Member]

Other Commitments [Line Items]

Non refundable license fee shares fair value

$ 500,000

Non refundable and non creditable annul fee

$ 500,000

Payment of upfront technology access fee

$ 20,000

Percentage of actual full time employee performance

100%

Annual rate of performance obligation per full time employee

$ 400,000

Delivery fees

100,000

100,000

Target range of initial and completion fees payable

400,000

Accounts payable and accrued liabilities, current

$ 100,000

$ 100,000

Research Agreement [Member]

Other Commitments [Line Items]

Payment upfront fees

$ 25,000

Research Agreement [Member] | Payment One [Member]

Other Commitments [Line Items]

Upfront fees due

37,500

Research Agreement [Member] | Payment Two [Member]

Other Commitments [Line Items]

Upfront fees due

$ 37,500

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands		1 Months Ended		12 Months Ended
	Apr. 01, 2021 USD ($)	Apr. 30, 2021 USD ($)	Nov. 30, 2020 ft²	Dec. 31, 2022 USD ($)	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Finance lease payments prior to commencement				$ 1,300
Finance lease payments related to lease liabilities				$ 1,300
Operating Lease for Office and Laboratory Spaces [Member]
Lessee, Lease, Description [Line Items]
Area of real estate | ft²			18,768
Operating lease date of expiry			Jan. 31, 2026
Operating lease renewal term			5 years
Operating Sublease With Related Party [Member]
Lessee, Lease, Description [Line Items]
Operating lease sublease income per month	$ 28,333	$ 28,333
Maximum [Member] | Operating Lease for Office and Laboratory Spaces [Member]
Lessee, Lease, Description [Line Items]
Operating lease remaining lease term					4 years
Maximum [Member] | Finance Lease for Laboratory and Equipment [Member]
Lessee, Lease, Description [Line Items]
Finance lease remaining lease term					4 years
Minimum [Member] | Operating Lease for Office and Laboratory Spaces [Member]
Lessee, Lease, Description [Line Items]
Operating lease remaining lease term					2 years
Minimum [Member] | Finance Lease for Laboratory and Equipment [Member]
Lessee, Lease, Description [Line Items]
Finance lease remaining lease term					2 years

Leases - Schedule of Effect of

Leases - Schedule of Effect of Lease Costs in the Company's Consolidated Statement of Operations and Comprehensive Loss (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Finance Lease Costs [Abstract]
Amortization of ROU assets	$ 114	$ 134	$ 488	$ 359
Interest on lease liabilities	31	42	151	106
Operating lease cost	351	351	1,404	1,404
Short-term lease cost	176	150	749	389
Variable lease cost	249	206	786	907
Sublease income			0	(253)
Total lease costs	$ 921	$ 883	$ 3,578	$ 2,912

Leases - Schedule of Informatio

Leases - Schedule of Information About the Company's Leases (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Cash Paid for Amounts included in the Measurement of Lease Liabilities [Abstract]
Finance leases - financing cash flows	$ 118	$ 144	$ 499	$ 393
Finance leases - operating cash flows	31	42	151	106
Operating leases - operating cash flows	$ 381	$ 370	$ 1,235	1,470
ROU assets obtained in exchange for lease liabilities
Finance leases				$ 1,340
Weighted-average remaining lease terms (in years)
Finance leases	2 years 11 months 26 days	3 years 11 months 19 days	3 years 2 months 23 days	4 years 2 months 8 days
Operating leases	1 year 10 months 2 days	2 years 10 months 2 days	2 years 1 month 2 days	3 years 1 month 2 days
Weighted-average discount rate
Finance leases	9.65%	9.54%	9.62%	9.49%
Operating leases	8.25%	8.25%	8.25%	8.25%

Leases - Schedule in Tabular Fo

Leases - Schedule in Tabular Form of Maturity of Operating and Finance Leases (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Leases [Abstract]
2024 (remaining)	$ 434
2024/2025	552	$ 583
2025/2026	363	552
2026/2027	44	363
2027/2028		44
Total lease payments	1,393	1,542
Less: interest	(160)	(191)
Total lease liabilities	1,233	1,351
2024 (remaining)	1,154
2024/2025	1,580	1,534
2025/2026	132	1,580
2026/2027		132
Total lease payments	2,866	3,246
Less: interest	(198)	(254)
Total lease liabilities	$ 2,668	$ 2,992

Convertible Preferred Stock - S

Convertible Preferred Stock - Summary of Preferred Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Temporary Equity [Line Items]
Preferred Stock Authorized	6,825,483	6,825,483	6,825,483
Preferred Stock Issued	6,825,483	6,825,483	6,825,483
Preferred Stock Outstanding	6,825,483	6,825,483	6,825,483
Carrying Value	$ 80,627	$ 80,627	$ 80,627
Liquidation Preference	$ 87,459	$ 87,459	$ 87,459
Common Stock Issuable Upon Conversion	6,825,483	6,825,483	6,825,483
Series A-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Par Value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred Stock Authorized	4,118,120	4,118,120	4,118,120
Preferred Stock Issued	4,118,120	4,118,120	4,118,120
Preferred Stock Outstanding	4,118,120	4,118,120	4,118,120
Carrying Value	$ 45,016	$ 45,016	$ 45,016
Liquidation Preference	$ 54,308	$ 54,308	$ 54,308
Common Stock Issuable Upon Conversion	4,118,120	4,118,120	4,118,120
Series A-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Par Value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred Stock Authorized	1,649,188	1,649,188	1,649,188
Preferred Stock Issued	1,649,188	1,649,188	1,649,188
Preferred Stock Outstanding	1,649,188	1,649,188	1,649,188
Carrying Value	$ 21,654	$ 21,654	$ 21,654
Liquidation Preference	$ 21,749	$ 21,749	$ 21,749
Common Stock Issuable Upon Conversion	1,649,188	1,649,188	1,649,188
Series A-3 Preferred Stock [Member]
Temporary Equity [Line Items]
Par Value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred Stock Authorized	696,516	696,516	696,516
Preferred Stock Issued	696,516	696,516	696,516
Preferred Stock Outstanding	696,516	696,516	696,516
Carrying Value	$ 9,187	$ 9,187	$ 9,187
Liquidation Preference	$ 7,348	$ 7,348	$ 7,348
Common Stock Issuable Upon Conversion	696,516	696,516	696,516
Series A-4 Preferred Stock [Member]
Temporary Equity [Line Items]
Par Value	$ 0.0001	$ 0.0001	$ 0.0001
Preferred Stock Authorized	361,659	361,659	361,659
Preferred Stock Issued	361,659	361,659	361,659
Preferred Stock Outstanding	361,659	361,659	361,659
Carrying Value	$ 4,770	$ 4,770	$ 4,770
Liquidation Preference	$ 4,054	$ 4,054	$ 4,054
Common Stock Issuable Upon Conversion	361,659	361,659	361,659

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended	12 Months Ended
	Sep. 07, 2022	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Temporary Equity [Line Items]
Temporary equity dividend rate percentage		8%	8%
Temporary equity aggregate dividend		$ 0	$ 0	$ 0
Temporary equity mandatory conversion price per share		$ 39.5628	$ 39.5628
Estimated proceeds from firm underwritten public offering minimum		$ 75,000	$ 75,000
Preferred stock, issued		6,825,483	6,825,483	6,825,483
Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity, par value	$ 38,000
Payments of stock issuance costs	$ 11,966
Series A-1 and Series A-2 Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity conversion price per share optional conversion		$ 13.1876	$ 13.1876
Series A-3 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity conversion price per share optional conversion		$ 10.55008	$ 10.55008
Preferred stock, issued		696,516	696,516	696,516
Preferred stock, par value		$ 0.0001	$ 0.0001	$ 0.0001
Series A-4 Preferred Stock [Member]
Temporary Equity [Line Items]
Temporary equity conversion price per share optional conversion		$ 11.20946	$ 11.20946
Preferred stock, issued		361,659	361,659	361,659
Preferred stock, par value		$ 0.0001	$ 0.0001	$ 0.0001
Series A-1 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, issued		4,118,120	4,118,120	4,118,120
Preferred stock, par value		$ 0.0001	$ 0.0001	$ 0.0001
Series A-1 Preferred Stock [Member] | Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, issued	2,446,372
Preferred stock, par value	$ 13.1876
Series A-2 Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, issued		1,649,188	1,649,188	1,649,188
Preferred stock, par value		$ 0.0001	$ 0.0001	$ 0.0001
Series A-2 Preferred Stock [Member] | Redeemable Convertible Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, issued	437,282
Preferred stock, par value	$ 13.1876

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - $ / shares	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Common stock, authorized	11,947,558	11,947,558	11,947,558
Common stock, par value	$ 0.0001	$ 0.0001	$ 0.0001
Common stock, issued	2,637,120	2,634,246	2,525,771
Common stock, outstanding	2,637,120	2,634,246	2,525,771
Unrestricted Common Stock [Member]
Class of Stock [Line Items]
Common stock, outstanding	2,615,555	2,598,752

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		12 Months Ended
	Mar. 31, 2024	Jun. 30, 2019	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation by share based award vesting period		4 years
Share based compensation by share based award expiration period		10 years
Share based compensation by share based award equity instruments other than options unvested and outstanding unrecognized compensation	$ 2,000		$ 2,000		$ 2,400
Share-based payment arrangement, nonvested award, cost not yet recognized, period for recognition	2 years 4 months 24 days				2 years 7 months 6 days
Granted, Number of Shares					441,615
Aggregate intrinsic value of options exercised			4		$ 172
Proceeds from the exercise of stock options			$ 4	$ 1	$ 121	$ 4
Restricted Stock Units (RSUs) [Member]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation by share based award equity instruments other than options non vested	21,565		21,565		35,494	312,826
2019 Equity Incentive Plan [Member]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Number of common shares that may be issued under the plan		1,991,264
Options Granted, Weighted-average grant-date fair value			$ 1.34		$ 2.16	$ 1.57
Granted, Number of Shares			0
Aggregate intrinsic value of options exercised			$ 3,828	411	$ 171,915	$ 1,458
Proceeds from the exercise of stock options			$ 4,420	$ 0	$ 111,770	$ 4,105
2019 Equity Incentive Plan [Member] | Incentive And Non Statutory Stock Options [Member]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation by share based award purchase price of common stock percent		100%
2019 Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Maximum [Member]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share based compensation by share based award equity instruments other than options non vested	21,565		21,565		35,494
Share based compensation by share based award equity instruments other than options equity repurchase liability current	$ 100		$ 100		$ 100

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of the activity in the 2019 Plan (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]
Opening Balance, Number of Shares	1,875,932	1,556,819
Granted, Number of Shares		441,615
Exercised, Number of Shares	(2,874)	(108,475)
Forfeited and expired, Number of Shares	(19,558)	(14,027)
Closing Balance, Number of Shares	1,853,500	1,875,932	1,556,819
Options vested and exercisable, Number of Shares	1,068,487	972,054
Options vested and expected to vest, Number of Shares	1,853,500	1,875,932
Opening Balance, Weighted- Average Exercise Price	$ 1.66	$ 1.32
Granted, Weighted- Average Exercise Price		2.74
Exercised, Weighted- Average Exercise Price	1.54	1.27
Forfeited and expired, Weighted- Average Exercise Price	1.36	1.53
Closing Balance, Weighted- Average Exercise Price	1.66	1.66	$ 1.32
Options vested and exercisable, Weighted- Average Exercise Price	1.34	1.3
Options vested and expected to vest, Weighted- Average Exercise Price	$ 1.66	$ 1.66
Weighted-Average Remaining Contractual Term (Years)	7 years 10 months 24 days	8 years 2 months 12 days	8 years 8 months 12 days
Options vested and exercisable, Weighted-Average Remaining Contractual Term (Years)	7 years 3 months 18 days	7 years 7 months 6 days
Options vested and expected to vest, Weighted-Average Remaining Contractual Term (Years)	7 years 10 months 24 days	8 years 2 months 12 days
Opening Balance, Aggregate Intrinsic Value	$ 2,276	$ 420
Exercised, Aggregate Intrinsic Value	4	172
Ending Balance, Aggregate Intrinsic Value	2,242	2,276	$ 420
Options vested and exercisable, Aggregate Intrinsic Value	1,634	1,525
Options vested and expected to vest, Aggregate Intrinsic Value	$ 2,242	$ 2,276

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Fair Values of the Options Granted (Detail) - $ / shares	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Fair value per share of underlying common stock	$ 1.34	$ 2.16	$ 1.57
Expected term (in years)	5 years 11 months 4 days	6 years 3 days	6 years 7 days
Expected volatility ,Minimum	111.05%	93.44%	87.02%
Expected volatility ,Maximum	111.21%	111.21%	91.24%
Risk-free interest rate	3.65%	4.14%	3.01%
Expected dividend yield	0%	0%	0%

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted Common Stock [Member] - shares	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unvested restricted common stock as of January 1, 2024	35,494	312,826
Vested	(13,929)	(277,332)
Unvested restricted common stock as of March 31, 2024	21,565	35,494

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Stock Based Compensation Expense Regarding its Employees and Nonemployees (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-Based Payment Arrangement, Expense	$ 321	$ 275	$ 1,121	$ 1,119
General and administrative [Member]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-Based Payment Arrangement, Expense	193	174	705	738
Research and development [Member]
Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Share-Based Payment Arrangement, Expense	$ 128	$ 101	$ 416	$ 381

Income Taxes - Summary of Compo

Income Taxes - Summary of Components of Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Deferred expense (benefit):
Federal			$ 11,207	$ 7,407
State			3,361	2,189
Deferred tax benefit			14,568	9,596
Less change in valuation allowance			(14,568)	(9,596)
Total income tax expense (benefit):	$ 0	$ 0	$ 0	$ 0

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Income Tax Expense (Benefit) (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21%	21%
State income taxes	7.80%	6.80%
Foreign rate differential	0.10%	0%
Permanent differences	1.20%	(0.30%)
Equity-based compensation	(0.40%)	(0.60%)
Preferred stock liability fair value adjustment	0%	0.40%
Tax credits	4.40%	2.50%
Change in valuation allowance	(34.00%)	(29.80%)
Effective income tax rate	0%	0%

Income Taxes - Summary of Defer

Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets
Net operating loss carryforward	$ 11,392	$ 7,765
Research credits	4,336	1,579
Lease liability	817	1,575
Capitalized R&D expenses	14,595	7,027
Accruals & other	1,027	859
Total deferred tax assets	32,167	18,805
Valuation allowance	(30,228)	(15,658)
Net deferred tax assets	1,939	3,147
Deferred tax liabilities
Depreciation	(1,210)	(1,530)
Right of use asset	(729)	(1,617)
Total deferred tax liabilitites	(1,939)	(3,147)
Net deferred tax assets (liability)	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Income Taxes [Line Items]
Income tax expense benefit	$ 0	$ 0	$ 0	$ 0
Description of change of ownership position			An ownership change is defined as a cumulative change of 50% or more in the ownership positions of certain stockholders during a rolling three-year period.
Operating loss carryforwards, valuation allowance			$ 14,600
Research and development expenses			36,200
Research Tax Credit Carryforward [Member]
Income Taxes [Line Items]
Tax credit carryforward, amount			$ 2,900
Tax credit expiration year			2039 years
Development [Member]
Income Taxes [Line Items]
Tax credit carryforward, amount			$ 1,900
Tax credit expiration year			2034 years
Foreign Tax Authority [Member]
Income Taxes [Line Items]
Operating loss carryforwards			$ 43,600
Amortization term of research and development activities				15 years
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Operating loss carryforwards			$ 35,300
Operating loss carryforwards expiration year			2039 years
UNITED STATES
Income Taxes [Line Items]
Amortization term of research and development activities				5 years

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Net Income (Loss) Attributable to Parent [Abstract]
Net loss attributable to common stockholders, basic	$ (15,221)	$ (14,445)	$ (42,823)	$ (32,180)
Net loss attributable to common stockholders, diluted	$ (15,221)	$ (14,445)	$ (42,823)	$ (32,180)
Weighted-average common shares outstanding, basic	2,608,740	2,222,800	2,373,674	1,969,418
Weighted-average common shares outstanding, diluted	2,608,740	2,222,800	2,373,674	1,969,418
Net loss per share attributable to common stockholders, basic	$ (5.83)	$ (6.5)	$ (18.04)	$ (16.34)
Net loss per share attributable to common stockholders, diluted	$ (5.83)	$ (6.5)	$ (18.04)	$ (16.34)

Net Loss Per Share - Summary _2

Net Loss Per Share - Summary of Diluted Net Loss Per Share Attributable to Common Stockholders (Detail) - shares	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	11,452,764	8,717,475	11,579,863	8,695,128
Convertible preferred stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	6,825,483	6,825,483	6,825,483	6,825,483
Stock options to purchase common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	1,853,500	1,597,259	1,875,932	1,556,819
Unvested restricted common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	21,565	294,733	35,494	312,826
SAFEs [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share amount	2,752,216		2,842,954

Related Party Transactions - A

Related Party Transactions - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended			12 Months Ended
	Dec. 31, 2023	Oct. 31, 2023	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Oct. 01, 2023	Sep. 07, 2022
Related Party Transaction [Line Items]
Accounts payable current	$ 409		$ 2,563	$ 409		$ 409	$ 574
Sublease income						0	253
Proceeds from (repayments of) related party debt						$ 0	$ 0
Temporary equity, shares issued	6,825,483		6,825,483	6,825,483		6,825,483	6,825,483
Series A-1 Preferred Stock [Member]
Related Party Transaction [Line Items]
Temporary equity, shares issued	4,118,120		4,118,120	4,118,120		4,118,120	4,118,120
Series A-1 Preferred Stock [Member] | Convertible preferred stock [Member]
Related Party Transaction [Line Items]
Temporary equity, shares issued									2,446,372
Series A-2 Preferred Stock [Member]
Related Party Transaction [Line Items]
Temporary equity, shares issued	1,649,188		1,649,188	1,649,188		1,649,188	1,649,188
Series A-2 Preferred Stock [Member] | Convertible preferred stock [Member]
Related Party Transaction [Line Items]
Temporary equity, shares issued									437,282
Related Party [Member] | Series A-1 Preferred Stock [Member] | Convertible preferred stock [Member]
Related Party Transaction [Line Items]
Temporary equity, shares issued									2,237,846
Related Party [Member] | Series A-2 Preferred Stock [Member] | Convertible preferred stock [Member]
Related Party Transaction [Line Items]
Temporary equity, shares issued									437,282
Member of the Scientific Advisory Board [Member] | Advisory Services Agreement [Member]
Related Party Transaction [Line Items]
Other payables current	$ 0		$ 0	$ 0	$ 0	$ 0	$ 0
Member of the Scientific Advisory Board [Member] | Advisory Services Agreement [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Professional fees			100		100	100	100
Harvard College [Member] | License Agreement [Member]
Related Party Transaction [Line Items]
License fees incurred			100		100	200	100
Harvard College [Member] | License Agreement [Member] | Maximum [Member]
Related Party Transaction [Line Items]
Accounts payable current	100		100	100	$ 100	100	$ 0
Related Party Investors [Member] | Simple Agreement For Future Equity [Member]
Related Party Transaction [Line Items]
Proceeds from financial instrument subject to mandatory redemption				34,100
Percentage of eligible discount of the issue of instruments		10%						10%
Fair value measurement with unobservable inputs reconciliation recurring basis liability issues	21,400	$ 10,400		10,400
Fair value measurement with unobservable inputs reconciliation recurring basis liability gain loss included in earnings	2,600	$ 300
Fair value measurement with unobservable input recnciliation basis liability value	$ 30,500		$ 32,600	$ 30,500		$ 30,500

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] - USD ($) $ / shares in Units, $ in Millions	Jun. 20, 2024	Jan. 30, 2024
Subscription Agreement [Member]
Subsequent Event [Line Items]
Stock issued during the period shares new issues	7,790,889	7,790,903
Sale of stock issue price per share	$ 12.4
Proceeds from the issuance of common stock	$ 96.6	$ 96.6
Avorbio Common Stock [Member]
Subsequent Event [Line Items]
Stock issued during the period shares reverse recapitalization	10,956,614
Stock shares issued during the period subject to reverse recapitalization	11,448
Stock issued during the period shares new issues converted pursuant to reverse recapitalization	4,163,606