Histogen (HSTO) 10-K 9 Mar 23 2022 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Mar. 08, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	FY
Entity Registrant Name	Histogen Inc.
Entity Central Index Key	0001383701
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock, $0.0001 par value
Trading Symbol	HSTO
Security Exchange Name	NASDAQ
Entity Incorporation, State or Country Code	DE
Entity Address, Address Line One	10655 Sorrento Valley Road
Entity Address, Address Line Two	Suite 200
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92121
City Area Code	(858)
Local Phone Number	526-3100
Entity File Number	001-36003
Entity Tax Identification Number	20-3183915
Entity Common Stock, Shares Outstanding		4,271,759
Entity Public Float			$ 5.4
Document Annual Report	true
Document Transition Report	false
Auditor Firm ID	199
Auditor Name	Mayer Hoffman McCann P.C.
Auditor Location	San Diego, California
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE The following documents are incorporated by reference into the following parts of the Annual Report on Form 10-K: Certain information required in Part III of this Annual Report on Form 10-K is incorporated from the Registrant’s Proxy Statement for the 2023 Annual Meeting of Stockholders.

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Current assets
Cash and cash equivalents	$ 12,109	$ 18,685
Restricted cash	400	400
Accounts receivable, net	99	165
Prepaid and other current assets	848	2,359
Total current assets	13,456	21,609
Property and equipment, net	436	399
Right-of-use asset	4,658	4,432
Other assets	523	805
Total assets	19,073	27,245
Current liabilities
Accounts payable	382	1,393
Accrued liabilities	595	791
Current portion of lease liabilities	238	127
Current portion of deferred revenue	19	19
Total current liabilities	1,234	2,330
Lease liabilities, non-current	4,379	4,617
Deferred revenue, non-current	79	98
Finance lease liability, non-current	5	14
Total liabilities	5,697	7,059
Commitments and contingencies (Note 9)
Stockholders’ equity
Preferred stock, $0.0001 par value; 10,000,000 shares authorized at December 31, 2022 and 2021; no shares issued and outstanding at December 31, 2022 and 2021
Common stock, $0.0001 par value; 200,000,000 shares authorized at December 31, 2022 and 2021; 4,271,759 and 2,497,450 shares issued and outstanding at December 31, 2022 and 2021, respectively	5	5
Additional paid-in capital	102,673	98,839
Accumulated deficit	(88,273)	(77,652)
Total Histogen Inc. stockholders’ equity	14,405	21,192
Noncontrolling interest	(1,029)	(1,006)
Total equity	13,376	20,186
Total liabilities and stockholders’ equity	$ 19,073	$ 27,245

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	4,271,759	2,497,450
Common stock, shares outstanding	4,271,759	2,497,450
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Revenue
Total revenue	$ 3,769	$ 1,032
Operating expense
Research and development	5,021	8,473
General and administrative	9,391	7,796
Total operating expense	14,412	16,489
Loss from operations	(10,643)	(15,457)
Other income (expense)
Interest expense, net	(1)	(10)
Other income, net		458
Net loss	(10,644)	(15,009)
Loss attributable to noncontrolling interest	23	59
Deemed dividend - accretion of discount and redemption feature of redeemable convertible preferred stock	(488)
Net loss available to common stockholders	$ (11,109)	$ (14,950)
Net loss per share available to common stockholders, basic	$ (3.46)	$ (7.79)
Net loss per share available to common stockholders, diluted	$ (3.46)	$ (7.79)
Weighted-average number of common shares outstanding used to compute net loss per share, basic	3,211,139	1,918,176
Weighted-average number of common shares outstanding used to compute net loss per share, diluted	3,211,139	1,918,176
Product [Member]
Revenue
Total revenue		$ 892
Operating expense
Cost of product revenue		220
License [Member]
Revenue
Total revenue	$ 3,769	27
Grant [Member]
Revenue
Total revenue	$ 0	$ 113

CONSOLIDATED STATEMENTS OF REDE

CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Total Histogen Inc. Stockholders' Deficit [Member]	Noncontrolling Interest [Member]
Beginning balance at Dec. 31, 2020	$ 6,913		$ 1	$ 70,561	$ (62,702)	$ 7,860	$ (947)
Beginning balance, shares at Dec. 31, 2020			751,537
Issuance of common stock, net of issuance costs	20,738		$ 3	20,735		20,738
Issuance of common stock, net of issuance costs, shares			1,410,600
Issuance of common stock upon net exercise of warrants	6,840		$ 1	6,839		6,840
Issuance of common stock upon net exercise of warrants, shares			336,030
Repurchase of common stock, shares			(717)
Stock-based compensation expense	704			704		704
Net loss	(15,009)				(14,950)	(14,950)	(59)
Ending balance at Dec. 31, 2021	20,186		$ 5	98,839	(77,652)	21,192	(1,006)
Ending balance, shares at Dec. 31, 2021			2,497,450
Issuance of redeemable convertible preferred stock (mezzanine equity), net of issuance costs, shares		5,000
Issuance of redeemable convertible preferred stock (mezzanine equity), net of issuance costs		$ 4,177
Accretion of issuance costs, discount and redemption feature of redeemable convertible preferred stock	(1,073)	$ 1,073		(1,073)		(1,073)
Redemption of redeemable convertible preferred stock, shares		(5,000)
Redemption of redeemable convertible preferred stock		$ (5,250)
Issuance of common stock, net of issuance costs	4,405			4,405		4,405
Issuance of common stock, net of issuance costs, shares			1,774,309
Stock-based compensation expense	502			502		502
Net loss	(10,644)				(10,621)	(10,621)	(23)
Ending balance at Dec. 31, 2022	$ 13,376		$ 5	$ 102,673	$ (88,273)	$ 14,405	$ (1,029)
Ending balance, shares at Dec. 31, 2022			4,271,759

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Cash flows from operating activities
Net loss	$ (10,644)	$ (15,009)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	140	97
Stock-based compensation	502	704
Forgiveness of the Payroll Protection Program Loan		(467)
Loss on disposal of property and equipment		17
Write-off of cell bank material	61
Changes in operating assets and liabilities:
Accounts receivable	66	(21)
Inventories		239
Prepaid expenses and other current assets	1,119	(1,176)
Other assets	221	1,187
Accounts payable	(1,011)	854
Accrued liabilities	(196)	(799)
Right-of-use asset and lease liabilities, net	78	(111)
Deferred revenue	(19)	(47)
Net cash used in operating activities	(9,683)	(14,532)
Cash flows from investing activities
Cash paid for property and equipment	(216)	(241)
Net cash used in investing activities	(216)	(241)
Cash flows from financing activities
Proceeds from the issuance of common stock, net of issuance costs	4,405	20,738
Repayment of finance lease obligations	(9)	(9)
Issuance costs for redeemable convertible preferred stock	(585)
Redemption payment for redeemable convertible preferred stock	(488)
Settlement of forward purchase contract		(290)
Payment on financing of insurance premiums		(193)
Proceeds from the exercise of warrants		6,839
Net cash provided by financing activities	3,323	27,085
Net increase (decrease) in cash, cash equivalents and restricted cash	(6,576)	12,312
Cash, cash equivalents and restricted cash, beginning of period	19,085	6,773
Cash, cash equivalents and restricted cash, end of period	12,509	19,085
Reconciliation of cash, cash equivalents and restricted cash to the consolidated balance sheets
Cash and cash equivalents	12,109	18,685
Restricted cash	400	400
Total cash, cash equivalents and restricted cash	12,509	19,085
Supplemental disclosure of cash flow information
Cash paid for interest	1	6
Noncash investing and financing activities
Issuance of redeemable convertible preferred stock, proceeds were held in escrow until redemption	4,762
Redemption payment of redeemable convertible preferred stock from escrow	(4,762)
Fair value of warrants issued to Placement Agent	$ 283	$ 590

Organization and Nature of Oper

Organization and Nature of Operations	12 Months Ended
	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Nature of Operations	1. Organization and Nature of Operations Description of Business Histogen Inc. (the “Company,” “Histogen,” “we,” or the “combined company”), formerly known as Conatus Pharmaceuticals Inc. (“Conatus”), was incorporated in the state of Delaware on July 13, 2005. The Company is a clinical-stage therapeutics company initially focused on developing potential first-in-class clinical and preclinical small molecule pan-caspase and caspase selective inhibitors that protect the body’s natural process to restore immune function. Merger between Private Histogen and Conatus Pharmaceuticals Inc. and Name Change On January 28, 2020, the Company, then operating as Conatus, entered into an Agreement and Plan of Merger and Reorganization, as amended (the “Merger Agreement”), with privately-held Histogen, Inc. (“Private Histogen”) and Chinook Merger Sub, Inc., a wholly-owned subsidiary of the Company (“Merger Sub”). Under the Merger Agreement, Merger Sub merged with and into Private Histogen, with Private Histogen surviving as a wholly-owned subsidiary of the Company (the “Merger”). On May 26, 2020, the Merger was completed. Conatus changed its name to Histogen Inc., and Private Histogen, which remains as a wholly-owned subsidiary of the Company, changed its name to Histogen Therapeutics Inc. On May 27, 2020, the combined company’s common stock began trading on The Nasdaq Capital Market under the ticker symbol “HSTO”. Reverse Stock Split On June 2, 2022, the Company’s Board of Directors approved a one-for- twenty reverse stock split of its then outstanding common stock (the “Reverse Stock Split”) with any fractional shares resulting from the Reserve Stock Split rounded down to the next whole share of common stock. The par value and the authorized shares of the common stock were not adjusted as a result of the Reverse Stock Split. All references to share and per share amounts for all periods presented in the consolidated financial statements have been retrospectively restated to reflect this Reverse Stock Split. Additionally, all rights to receive shares of common stock under outstanding warrants, options, and restricted stock units (“RSUs”) were adjusted to give effect of the reverse stock split. Furthermore, remaining shares of common stock available for future issuance under stock-based payment award plans and employee stock purchase plans were adjusted to give effect to the Reverse Stock Split. Liquidity and Going Concern Uncertainty The Company has incurred operating losses and negative cash flows from operations and had an accumulated deficit of $ 88.3 million as of December 31, 2022. The Company expects operating losses and negative cash flows from operations to continue for the foreseeable future. As of December 31, 2022 , the Company had $ 12.1 million in cash and cash equivalents, which will not be sufficient to sustain its operations. The Company has not yet established ongoing sources of revenues sufficient to cover its operating costs and will need to continue to raise additional capital to support its future operating activities, including progression of its development programs, preparation for potential commercialization, and other operating costs. Management’s plans with regard to these matters include entering into a combination of additional debt or equity financing arrangements, strategic partnerships, collaboration and licensing arrangements, or other similar arrangements. There can be no assurance that the Company will be able to obtain additional financing on terms acceptable to the Company, on a timely basis or at all. The consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. Based on the current business plan and operating budget, there is substantial doubt about the Company’s ability to continue as a going concern within one year from the date the consolidated financial statements are issued. The consolidated financial statements do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classification of liabilities that may result from the outcome of this uncertainty.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation The consolidated financial statements include the accounts of the Company and its controlled subsidiaries, including Histogen Therapeutics, Inc., and have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”). All intercompany balances and transactions have been eliminated upon consolidation. The Company acquired Centro De Investigacion de Medicina Regenerativa, S.A. de C.V. (“CIMRESA”), a company in Mexico, during 2018 to facilitate a potential clinical development program for HST-001, or hair stimulating complex (“HSC”). This is a wholly-owned subsidiary intended to pursue registration with the COFEPRIS (Mexico equivalent to Food and Drug Administration). CIMRESA had no operational or financial activity for the years ended December 31, 2022 and 2021. The Company holds a majority interest in Adaptive Biologix, Inc. (“AB”, formerly Histogen Oncology, LLC). AB was formed to develop and market applications for the treatment of cancer. The Company consolidates AB into its consolidated financial statements. 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, liabilities and the disclosure of contingent assets and liabilities and contingencies at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the periods presented. Management believes that these estimates and assumptions are reasonable, however, actual results may differ and could have a material effect on future results of operations and financial position. Though the impact of the COVID-19 pandemic to our business and operating results presents additional uncertainty, the Company continues to use the best information available to them in their significant accounting estimates. Significant estimates and assumptions include the useful lives of property and equipment, discount rates used in recognizing contracts containing leases, unrecognized tax benefits, volatility used for stock-based compensation option pricing, and best estimate of standalone selling price of revenue deliverables. Actual results may materially differ from those estimates. Variable Interest Entities The Company determined that AB is a variable interest entity (“VIE”) and that the Company is its primary beneficiary. The Company holds greater than 50 % of the shares and has the authority to manage the business and affairs of the VIE. AB’s other shareholder does not have a controlling interest. A VIE is typically an entity for which the Company has less than a 100 % equity interest but controls the decision making over the business and affairs of the entity, directs the decisions driving the economic performance of such entity and participates in the profit and losses of such an entity. The Company weighed both quantitative and qualitative information about the different risks and reward characteristics of each entity and the significance of that entity to the consolidating group in the aggregate. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker, the Interim Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with an original maturity date of ninety days or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking, money market accounts and brokerage accounts. The Company’s current restricted cash consists of cash held as collateral for a letter of credit issued as a security deposit for the lease of the Company’s headquarters and is required to be held throughout the lease term. Risks and Uncertainties Credit Risk At certain times throughout the year, the Company may maintain deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash balances due to the financial position of the depository institutions in which those deposits are held. Customer Risk During the years ended December 31, 2022 and 2021 , one customer accounted for 100 % and 88 % of total revenues, respectively. Accounts receivable from the customer was $ 0 at both December 31, 2022 and 2021. COVID-19 The cumulative effect of the COVID-19 outbreak and associated disruptions have had, and may continue to have, an adverse impact on the Company’s business and its results of operations. The full impact of the COVID-19 outbreak continues to evolve as of the date these consolidated financial statements were available to be issued and will depend on future developments that are highly uncertain and unpredictable, including efficacy and adoption of vaccines, future resurgences of the virus and its variants, the imposition of governmental lockdowns, and quarantine and physical distancing requirements. As such, it is uncertain as to the full magnitude that the pandemic will have on the Company’s financial condition, liquidity, and future results of operations. Accounts Receivable Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts, if any. Management considers all accounts receivable to be fully collectible as of December 31, 2022 and 2021 , and accordingly, no provision for doubtful accounts was recorded. Property and Equipment Property and equipment are reported net of accumulated depreciation and amortization and are comprised of office furniture and equipment, lab and manufacturing equipment, and leasehold improvements. Ordinary maintenance and repairs are charged to expense, while expenditures that extend the physical or economic life of the assets are capitalized. Furniture and all equipment are depreciated over their estimated useful lives, or five years , using the straight-line method. Software is amortized over its estimated useful lives, or three years , using the straight-line method. Leasehold improvements are amortized over their estimated useful lives and limited by the remaining term of the building lease, using the straight-line method. Valuation of Long-Lived Assets Long-lived assets to be held and used, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. As of December 31, 2022 and 2021, the Company has no t recognized any impairment to long-lived assets. Forward Purchase Contract In 2011, Private Histogen contracted for research services from EPS Global Research Pte. Ltd. (“EPS”) to conduct clinical trials and compile data from a study that took place in 2011 and 2013. The unpaid amount due for the services was approximately $ 0.3 million. In 2017, Private Histogen and EPS entered into a Debt Settlement and Conversion Agreement (“Settlement Agreement”) whereby Private Histogen paid $ 50 thousand and issued EPS 717 shares of Series D convertible preferred stock. The Company was required to repurchase the shares at the greater of the remaining balance due of approximately $ 0.3 million and the market price of the shares at the time of repurchase, but in no event later than December 31, 2021. The Company had the sole option to repurchase the shares (which were converted from Series D convertible preferred stock into shares of common stock upon the Merger) at any time on or before December 31, 2021. On December 16, 2021, the Company repurchased from EPS 717 shares of common stock in exchange for a cash payment of approximately $ 0.3 million. The repurchased shares were recorded as treasury stock and retired as of December 31, 2021. As of December 31, 2021, all amounts due to EPS under the Settlement Agreement have been paid. Fair Value Measurements ASC 820, Fair Value Measurements , defines fair value, establishes a framework for measuring fair value under generally accepted accounting principles and enhances disclosures about fair value measurements. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: • Level 1 — Observable inputs such as quoted price (unadjusted) for identical instruments in active markets. • Level 2 — Observable inputs such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, or model derived valuations whose significant inputs are observable. • Level 3 — Unobservable inputs that reflect the reporting entity’s own assumptions. At December 31, 2022 and 2021, management believes the carrying amount of financial instruments consisting of cash, cash equivalents, restricted cash, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to the short-term nature of those instruments. Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the accompanying consolidated financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources, including unrealized gains and losses on investments and foreign currency translation adjustments. Net loss and comprehensive loss were the same for all periods presented. Revenue Recognition Product and License Revenue The Company records revenue in accordance with ASC 606, Revenue from Contracts with Customers , whereby revenue is recognized when a customer obtains control of promised goods or services in an amount that reflects the consideration expected to be received in exchange for those goods or services. A five-step model is used to achieve the core principle: (1) identify the customer contract, (2) identify the contract’s performance obligations, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations and (5) recognize revenue when or as a performance obligation is satisfied. The Company applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. Shipping charges billed to customers are included in product revenue and the related shipping costs are included in cost of product revenue. The Company applies the revenue recognition standard, including the use of any practical expedients, consistently to contracts with similar characteristics and in similar circumstances (Refer to Note 5 for further information). Grant Awards In March 2017, the National Science Foundation (“NSF”), a government agency, awarded the Company a research and development grant to develop a novel wound dressing for infection control and tissue regeneration. The Company has concluded this government grant is not within the scope of ASC 606, as government entities generally do not meet the definition of a “customer” as defined by ASC 606. Payments received under the grant are considered conditional, non-exchange contributions under the scope of ASC 958-605, Not-for-Profit Entities – Revenue Recognition , and are recorded as grant revenue in the period in which such conditions are satisfied. In reaching the determination that such payments should be recorded as revenue, management considered a number of factors, including whether the Company is a principal under the arrangement, and whether the arrangement is significant to, and part of, the Company’s ongoing operations. In September 2020, the Company was approved for a grant award from the U.S. Department of Defense (“DoD”) in the amount of approximately $ 2.0 million to partially fund the Company’s Phase 1/2 clinical trial of HST-003 for regeneration of cartilage in the knee. The Company applies International Accounting Standard (“IAS”) 20, Accounting for Government Grants and Disclosure of Government Assistance , by analogy as there is no existing authoritative guidance under GAAP. Under the terms of the award, the DoD will reimburse the Company for certain allowable costs. The period of performance for the grant award substantially expires in September 2025 and is subject to annual and quarterly reporting requirements. As the DoD grant is a cost-type (reimbursement) grant, the Company must incur program expenses in accordance with the Statement of Work and approved budget in order to be reimbursed by the DoD. The Company will recognize funding received from the grant award as a reduction of research and development expenses in the period in which qualifying expenses have been incurred, as the Company is reasonably assured that the expenses will be reimbursed and the funding is collectible. For the years ended December 31, 2022 and 2021, qualifying expenses totaling $ 0.6 million and $ 0.7 million, respectively, were incurred with a corresponding reduction of research and development expenses related to the award. As of December 31, 2022 and 2021, $ 0.1 million and $ 0.2 million, respectively, was included within accounts receivable on the consolidated balance sheets related to the award. Cost of Product Revenue Cost of product revenue represents direct and indirect costs incurred to bring the product to saleable condition. Research and Development Expenses All research and development costs are charged to expense as incurred. Research and development expenses primarily include (i) payroll and related costs associated with research and development performed, (ii) costs related to clinical and preclinical testing of the Company’s technologies under development, and (iii) other research and development costs including allocations of facility costs, net of reimbursable research and development costs incurred under the DoD grant. General and Administrative Expenses General and administrative expenses represent personnel costs for employees involved in general corporate functions, including finance, accounting, legal and human resources, among others. Additional costs included within general and administrative expenses consist of professional fees for legal (including patent costs), audit and other consulting services, travel and entertainment, recruiting, allocated facility and general information technology costs, depreciation and amortization, and other general corporate overhead expenses. Patent Costs The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included as a component of general and administrative expenses in the accompanying consolidated statements of operations. Income Taxes Income taxes are accounted for under the asset and liability method. Deferred income taxes are recorded for temporary differences between consolidated financial statement carrying amounts and the tax basis of assets and liabilities. Deferred tax assets and liabilities reflect the tax rates expected to be in effect for the years in which the differences are expected to reverse. No income tax expense or benefit was recorded for the years ended December 31, 2022 and 2021, due to the full valuation allowance on the Company’s net deferred tax assets. A valuation allowance is provided if it is more likely than not that some or all the deferred tax assets will not be realized. The Company also follows the provisions of accounting for uncertainty in income taxes which prescribes a model for the recognition and measurement of a tax position taken or expected to be taken in a tax return, and provides guidance on derecognition, classification, interest and penalties, disclosure and transition. The Company’s policy is to recognize interest or penalties related to income tax matters in income tax expense. Interest and penalties related to income tax matters were not material for the periods presented. Net Loss Per Share Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted 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 and potentially dilutive securities outstanding for the period. For the years ended December 31, 2022 and 2021, diluted net loss per share attributable to common stockholders is equal to basic net loss per share attributable to common stockholders as common stock equivalent shares from stock options and warrants were anti-dilutive. The following table sets forth outstanding potentially dilutive shares that have been excluded from the calculation of diluted net loss per share attributable to common stockholders because of their anti-dilutive effect (in common stock equivalents): Years Ended December 31, 2022 2021 Common stock options issued and outstanding 118,166 116,311 Warrants to purchase common stock 4,876,639 1,186,307 Total anti-dilutive shares 4,994,805 1,302,618 Common Stock Valuations Prior to the Merger, Private Histogen was required to periodically estimate the fair value of common stock with the assistance of an independent third-party valuation expert when issuing stock options and computing its estimated stock-based compensation expense. The assumptions underlying these valuations represented management’s best estimates, which involved inherent uncertainties and the application of significant levels of management judgment. In order to determine the fair value, Private Histogen considered, among other things, contemporaneous valuations of its common stock, business, financial condition and results of operations, including related industry trends affecting its operations; the likelihood of achieving various liquidity events; the lack of marketability of its common stock; the market performance of comparable publicly traded companies; and U.S. and global economic and capital market conditions. Stock-Based Compensation Service-Based Awards The Company recognizes stock-based compensation expense for service-based stock options and restricted stock units (“RSUs”) over the requisite service period on a straight-line basis. Employee and director stock-based compensation for service-based stock options is measured based on estimated fair value as of the grant date using the Black-Scholes option pricing model. The Company estimates the fair value of RSUs based on the closing price of the Company’s common stock on the date of issuance. The Company uses the following assumptions for estimating fair value of service-based option grants: Fair Value of Common Stock – The fair value of common stock underlying the option grant is determined based on observable market prices of the Company’s common stock. Expected Volatility – Volatility is a measure of the amount by which the Company’s share price has historically fluctuated or is expected to fluctuate (i.e., expected volatility) during a period. Due to the lack of an adequate history of a public market for the trading of the Company’s common stock and a lack of adequate company-specific historical and implied volatility data, volatility has been estimated and based on the historical volatility of a group of similar companies that are publicly traded. For these analyses, the Company has selected companies with comparable characteristics, including enterprise value, risk profiles, and position within the industry, and with historical share price information sufficient to meet the expected term of the stock-based awards. Expected Term – This is the period of time during which the options are expected to remain unexercised. Options have a maximum contractual term of ten years. The Company estimates the expected term of stock options using the “simplified method”, whereby the expected term equals the average of the vesting term and the original contractual term of the underlying option. Risk-Free Interest Rate – This is the observed yield on zero-coupon U.S. Treasury securities, as of the day each option is granted, with a term that most closely resembles the expected term of the option. Expected Forfeiture Rate – Forfeitures are recognized as they occur. Performance-Based Options Stock-based compensation expense for performance-based options is recognized based on amortizing the fair market value as of the grant date over the periods during which the achievement of the performance is probable. Performance-based options require certain performance conditions to be achieved in order for these options to vest. These options vest on the date of achievement of the performance condition. Market-Based Options Stock-based compensation expense for market-based options is recognized on a straight-line basis over the derived service period, regardless of whether the market condition is satisfied. Market-based options subject to market-based performance targets require achievement of the performance target in order for these options to vest. The Company estimates the fair value of market-based options as of the grant date and expected term using a Monte Carlo simulation that incorporates option-pricing inputs covering the period from the grant date through the end of the derived service period. Recently Adopted Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40) (“ASU 2020-06”). This new guidance is intended to simplify the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts on an entity’s own equity. Entities may adopt ASU 2020-06 using either a partial retrospective or fully retrospective method of transition. This ASU is effective for public business entities for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years, with early adoption permitted. The Company adopted ASU 2020-06 on January 1, 2022, utilizing the modified retrospective method. The adoption of this standard did not result in an adjustment and did not have a material impact on the Company’s consolidated financial statements or related disclosures. In May 2021, the FASB issued ASU No. 2021-04, Earnings Per Share (Topic 260), Debt — Modifications and Extinguishments (Subtopic 470-50), Compensation — Stock Compensation (Topic 718), and Derivatives and Hedging — Contracts in Entity’s Own Equity (Subtopic 815-40): Issuer’s Accounting for Certain Modifications or Exchanges of Freestanding Equity-Classified Written Call Options (“ASU 2021-04”). The amendments in ASU 2021-04 provide guidance to clarify and reduce diversity in an issuer’s accounting for modifications or exchanges of freestanding equity-classified written call options (for example, warrants) that remain equity classified after modification or exchange. The accounting standard update is effective for fiscal years beginning after December 15, 2021. On January 1, 2022, the Company adopted ASU 2021-04. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements or related disclosures. In November 2021, the FASB issued ASU No. 2021-10, Government Assistance (Topic 832): Disclosure by Business Entities about Government Assistance (“ASU 2021-10”), which improves the transparency of government assistance received by certain business entities by requiring the disclosure of (1) the types of government assistance received; (2) the accounting for such assistance, and (3) the effect of the assistance on the business entity’s financial statements. ASU 2021-10 is effective for fiscal years beginning after December 15, 2021, with early adoption permitted. The Company adopted ASU 2021-10 on January 1, 2022. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements or related disclosures.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Property and Equipment	3. Property and Equipment Property and equipment, net, consisted of the following (in thousands): December 31, 2022 2021 Lab and manufacturing equipment $ 937 $ 943 Office furniture and equipment 225 42 Software 48 48 Total 1,210 1,033 Less: accumulated depreciation and amortization ( 774 ) ( 634 ) Property and equipment, net $ 436 $ 399 Depreciation and amortization expense was approximately $ 0.1 million for the years ended December 31, 2022 and 2021 . During the year ended December 31, 2021, the Company disposed of approximately $ 1.4 million in property and equipment that had been depreciated and amortized in full and had an immaterial impact on the accompanying consolidated statements of operations.

Balance Sheet Details

Balance Sheet Details	12 Months Ended
	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Details	. Balance Sheet Details Prepaid and other current assets consist of the following (in thousands): December 31, 2022 2021 Insurance $ 626 $ 691 Tenant improvement reimbursement receivable — 1,057 Prepaid rent 81 132 Pre-clinical and clinical related expenses 64 158 Prepaid materials — 138 Other 77 183 Total $ 848 $ 2,359 Other assets consist of the following (in thousands): December 31, 2022 2021 Insurance $ 513 $ 732 Cell bank material — 61 Other 10 12 Total $ 523 $ 805 Accrued liabilities consist of the following (in thousands): December 31, 2022 2021 Current portion of finance lease liabilities $ 9 $ 9 Accrued compensation 160 346 Clinical study related expenses 150 103 Legal fees 44 144 Accrued franchise tax 162 18 Other 70 171 Total $ 595 $ 791

Revenue

Revenue	12 Months Ended
	Dec. 31, 2022
Revenue from Contract with Customer [Abstract]
Revenue	5. Revenue The following is a summary description of the material revenue arrangements, including arrangements that generated revenues during the years ended December 31, 2022 and 2021. Allergan License Agreements 2017 Allergan Amendment In 2017, the Company entered into a series of agreements (collectively, the “2017 Allergan Agreement”), which ultimately transferred Suneva Medical, Inc.’s license and supply rights of Histogen’s cell conditioned medium (“CCM”) skin care ingredient in the medical aesthetics market to Allergan Sales LLC (“Allergan”) and granted Allergan an exclusive, royalty-free, perpetual, irrevocable, non-terminable and transferable license, including the right to sublicense to third parties, to use the Company’s CCM skin care ingredient in the medical aesthetics market. The 2017 Allergan Agreement also obligated the Company to deliver CCM to Allergan (the “Supply of CCM to Allergan”) in the future as well as share with Allergan any potential future improvements to the Company’s CCM skin care ingredients identified through the Company’s research and development efforts (“Potential Future Improvements”). In consideration for the execution of the agreements, the Company received a cash payment of $ 11.0 million and a potential additional payment of $ 5.5 million if Allergan’s net sales of products containing the Company’s CCM skin care ingredient exceeds $ 60.0 million in any calendar year through December 31, 2027. 2019 Allergan Amendment In March 2019, the Company entered into a separate agreement with Allergan (the “2019 Allergan Amendment”) to amend the 2017 Allergan Agreement in exchange for a one-time payment of $ 7.5 million to the Company. The agreement broadened Allergan’s license rights, expanding Allergan’s access to certain sales channels where its products incorporating the CCM ingredient can be sold. Specifically, the license was broadened to provide Allergan the exclusive right to sell through the “Amazon Professional” website, or any website or digital platform owned or licensed by Allergan or under the Allergan brand name, and non-exclusive rights to sell on other websites and through brick-and-mortar medical spas and wellness centers (excluding websites and brick-and-mortar stores of luxury brands). The Company evaluated the 2019 Allergan Amendment under ASC 606 and concluded that Allergan continues to be a customer and that the expanded license is distinct from the 2017 Allergan Agreement. The Company determined the expanded license under the 2019 Allergan Amendment to be functional intellectual property as Allergan has the right to utilize the Company’s CCM skin care ingredient, and that ingredient is functional to Allergan at the time the Company transferred the expanded license. The standalone selling price of the expanded license was not readily observable since the Company has not yet established a price for this expanded license and the expanded license has not been sold on a standalone basis to any customer. The Company accounted for the 2019 Allergan Amendment as a modification to the 2017 Allergan Agreement. The contract modification was accounted for as if the 2017 Allergan Agreement had been terminated and the new contract included the expanded license as well as the remaining performance obligations that arose from the 2017 Allergan Agreement related to the Supply of CCM to Allergan and Potential Future Improvements. The total transaction price for the new contract included the $ 7.5 million from the 2019 Allergan Amendment as well as the amounts deferred as of the 2019 Allergan Amendment execution date for each the Supply of CCM to Allergan and Potential Future Improvements. The standalone selling price for the Supply of CCM to Allergan was determined based on comparable sales transactions. The standalone selling price of the Potential Future Improvements was estimated at the fully burdened rate of research and development employees cost plus a commercially reasonable markup. The amount of the total transaction price allocated to the expanded license was determined using the residual approach, as a result of not having a standalone selling price for the expanded license; that is, the total transaction price less the standalone selling prices of the Supply of CCM to Allergan and Potential Future Improvements. Revenue related to the Supply of CCM to Allergan has been deferred and recognized at the point in time in which deliveries are completed while revenue related to the Potential Future Improvements has been deferred and amortized ratably over the remaining 9 -year life of the patent. The Supply of CCM to Allergan under the 2019 Allergan Amendment was entirely fulfilled during the year ended December 31, 2019. The $ 7.5 million residual amount of the total transaction price allocated to the expanded license was recognized as license revenue upon transfer of the license to Allergan in March 2019. 2020 Allergan Amendment In January 2020, the Company further amended the 2019 Allergan Amendment in exchange for a one-time payment of $ 1.0 million to the Company (the “2020 Allergan Amendment”). The 2020 Allergan Amendment further broadened Allergan’s exclusive and non-exclusive license rights to include products used for or in connection with microdermabrasion. In addition, the Company agreed to provide Allergan with an additional 200 kilograms of CCM (the “Additional Supply of CCM to Allergan”). The Company evaluated the 2020 Allergan Amendment under ASC 606 and concluded that Allergan continues to be a customer and that the expanded license is distinct from the 2019 Allergan Amendment. The Company determined the expanded license under the 2020 Allergan Amendment to be functional intellectual property as Allergan has the right to utilize the Company’s CCM skin care ingredient, and that ingredient is functional to Allergan at the time the Company transferred the expanded license. The standalone selling price of the expanded license was not readily observable since the Company has not yet established a price for this expanded license and the expanded license has not been sold on a standalone basis to any customer. The Company accounted for the 2020 Allergan Amendment as a modification to the 2019 Allergan Amendment (which had modified the 2017 Allergan Agreement, as noted above). The contract modification was accounted for as if the 2019 Allergan Amendment had been terminated and the new contract included the expanded license and Additional Supply of CCM to Allergan, as well as the remaining performance obligation related to Potential Future Improvements. The total transaction price for the new contract included the $ 1.0 million from the 2020 Allergan Amendment, the future payment for the Additional Supply of CCM to Allergan, as well as the amounts deferred as of the 2020 Allergan Amendment execution date for Potential Future Improvements. The standalone selling price for the Additional Supply of CCM to Allergan was determined using the observable inputs of historical comparable sales transactions, including the margin from such sales. The Company also considered its reduced expected cost of satisfying this performance obligation based on the current efficiencies within its CCM manufacturing processes. Due to significant efficiencies in the Company’s CCM manufacturing processes, the forecasted cost of CCM production has decreased, while the applied margin was determined by comparison to similar sales transactions in prior years. The standalone selling price of the Potential Future Improvements was estimated at the fully burdened rate of research and development employees cost plus a commercially reasonable markup. The amount of the total transaction price allocated to the expanded license was determined using the residual approach, as a result of not having a standalone selling price for the expanded license; that is, the total transaction price less the standalone selling prices of the Additional Supply of CCM to Allergan and Potential Future Improvements. Under the Amended and Restated License Agreement, as amended, Allergan will indemnify the Company for third party claims arising from Allergan’s breach of the agreement, negligence or willful misconduct, or the exploitation of products by Allergan or its sublicensees. The Company will indemnify Allergan for third party claims arising from the Company’s breach of the agreement, negligence or willful misconduct, or the exploitation of products by the Company prior to the effective date. Allergan may terminate the Agreement for convenience upon one business days’ notice to the Company. Revenue related to the Additional Supply of CCM to Allergan was deferred and was recognized at the point in time in which deliveries were completed. All deliveries of Additional Supply of CCM to Allergan have been completed as of March 31, 2021. As such, there is no revenue for t he year ended December 31, 2022. Revenue of $ 0.2 million related to the Potential Future Improvements has been deferred and amortized ratably over the remaining 9 -year life of the patent, for which $ 19 thousand of previously deferred revenue was recognized in revenue during each of the years ended December 31, 2022 and 2021. The $ 0.9 million residual amount of the total transaction price allocated to the expanded license was recognized as license revenue upon transfer of the license to Allergan in January 2020. In August 2021, unrelated to the Allergan Agreements, the Company agreed to a sale of CCM under a purchase order with Allergan. The CCM sold to Allergan was initially manufactured by the Company for research and development purposes in support of its product candidates. In September 2021, the Company recognized $ 0.6 million of product revenue related to the sale. The Company does not have any additional purchase orders with Allergan for fulfillment. 2022 Allergan Letter Agreement Pursuant to the 2017 Allergan Amendment, the Company had the right to a potential milestone payment of $ 5.5 million if Allergan’s net sales of products containing the Company’s CCM skin care ingredient exceeds $ 60.0 million in any calendar year through December 31, 2027. In lieu of the potential milestone payment of $ 5.5 million, the Company entered into a letter agreement on March 18, 2022 (the “Letter Agreement”) with Allergan. In consideration for the execution of the Letter Agreement, the Company received a one-time payment equal to $ 3.8 million (the “Final Payment”) in March 2022. In exchange, among other things, the Company agreed that the Final Payment represents a full and final satisfaction of all money due to the Company pursuant to the License Agreement. The Company evaluated the 2022 Allergan Letter Agreement under ASC 606 and concluded that the performance obligation has been satisfied and therefore applied point in time recognition. The Company recognized $ 3.8 million of license revenue related to the Letter Agreement during the year ended December 31, 2022. The Letter Agreement did not have an impact on the remaining performance obligation to share with Allergan any Potential Future Improvements to CCM identified through the Company’s research and development efforts. Remaining Performance Obligation and Deferred Revenue The remaining performance obligation is the Company’s obligation to share with Allergan any Potential Future Improvements to CCM identified through the Company’s research and development efforts. Deferred revenue recorded for the Potential Future Improvements was $ 0.1 million as of both December 31, 2022 and 2021. Deferred revenue is classified in current portion of deferred revenue liabilities when the Company’s obligations to provide research for Potential Future Improvements are expected to be satisfied within twelve months of the balance sheet date. The deferred revenue is recognized on a straight-line basis over the remaining life of the licensing patents into early 2028. Grant Revenue In March 2017, the National Science Foundation, a government agency, awarded the Company a research and development grant to develop a novel wound dressing for infection control and tissue regeneration. Grant revenue recognized was $ 0 and $ 0.1 million for the years ended December 31, 2022 and 2021, respectively. As of March 31, 2021, the Company had completed all obligations under the NSF development grant and, as such, no longer generates any revenues in connection with the research and development grant. Amerimmune Collaborative Development and Commercialization Agreement In October 2020, the Company entered into a Collaborative Development and Commercialization Agreement (the “Collaboration Agreement”) with Amerimmune to jointly develop emricasan for the potential treatment of COVID-19. The FDA approved an investigational new drug application (IND) to initiate a Phase 1 study of emricasan in mild COVID-19 patients to assess safety and tolerability in 2020. Under the Collaboration Agreement, Amerimmune, at its expense and in collaboration with the Company, was required to use commercially reasonable efforts to lead the development activities for emricasan. Amerimmune was responsible for conducting clinical trials and the Company agreed to provide reasonable quantities of emricasan for such purpose. Pursuant to the terms of the Collaboration Agreement, each party retained ownership of their legacy intellectual property and responsibility for ongoing patent application prosecution and maintenance costs and jointly owned any intellectual property developed during the term of the agreement. In addition, the Company granted Amerimmune an exclusive option, subject to terms and conditions including completion of a Phase 2 clinical trial by Amerimmune during the research term, to obtain an exclusive license that, if granted by us, would have allowed Amerimmune alone, or in conjunction with one or more strategic partners, to use its commercially reasonable efforts to develop, manufacture, and commercialize emricasan and other caspase modulators, including CTS-2090 and CTS-2096, and the Company would have shared the profits equally with Amerimmune. No consideration would have been transferred to the Company until profits, as defined in the Collaboration Agreement, were generated by Amerimmune from developing or commercializing products. The Company identified multiple promises to deliver goods and services, which included at the inception of the agreement: (i) a license to technology and patents, information, and know-how; (ii) supply of emricasan, and (iii) collaboration, including the Company’s participation in a Joint Development Committee and Joint Partnering Committee. At inception and through December 31, 2022, the Company has identified one performance obligation for all the deliverables under the Collaboration Agreement since the delivered elements were either not capable of being distinct or are not distinct within the context of the contract. No upfront consideration was exchanged between the parties and any consideration received would have been dependent on the successful execution of a qualifying strategic partnership, as defined, on the successful commercialization of emricasan, or upon a change in control of Amerimmune, as defined. Although the Company would have recognized revenue upon the occurrence of one of these events, no such events had occurred as of December 31, 2022. On January 19, 2022, the Company provided a notice of material breach in connection with Amerimmune’s non-performance under the Collaboration Agreement and, on March 3, 2022, filed a demand for arbitration (“Arbitration Demand”). On March 11, 2022, Judicial Arbitration and Mediation Services, Inc. (“JAMS”) issued a Notice of Commencement of Arbitration letter, confirming the commencement of the arbitration as of that date. On November 28, 2022, the Company received an Interim Award (“Interim Award”) issued by the Arbitrator presiding over the Arbitration Demand filed by the Company in the County of San Diego, against Amerimmune LLC seeking a declaratory judgment that Amerimmune has materially breached the terms of the Collaboration Agreement to jointly develop emricasan for the potential treatment of COVID-19 entered into by and between the Company and Amerimmune on October 26, 2020, and that the Company therefore was entitled to terminate the Collaboration Agreement. As affirmed by the Interim Award, the Company has terminated the Collaboration Agreement and all rights and licenses granted to Amerimmune by the Company have been terminated, and Amerimmune shall cease any and all development, manufacture and commercialization activities under the Agreement, and any and all rights granted by the Company to Amerimmune revert to the Company except any such rights that shall survive termination of the Collaboration Agreement. On January 2, 2023, the arbitrator issued the Final Award affirming the arbitration outcome set forth in the Interim Award. Amerimmune will have 100 days from the date it receives the final award to petition a court to vacate or correct the Final Award. The Company has sought to confirm the award to judgment by filing a petition to confirm award filed (refer to Note 9 for further information).

Debt

Debt	12 Months Ended
	Dec. 31, 2022
Debt Disclosure [Abstract]
Debt	6. Debt Paycheck Protection Program Loan In April 2020, Private Histogen applied for and received loan proceeds in the amount of $ 0.5 million (the “PPP Loan”) under the PPP as government aid for payroll, rent and utilities. The application for these funds required the Company to, in good faith, certify that the current economic uncertainty made the loan request necessary to support the ongoing operations of the Company. This certification further required the Company to take into account its current business activity and its ability to access other sources of liquidity sufficient to support ongoing operations in a manner that is not significantly detrimental to the business. The certification made by the Company did not contain any objective criteria and is subject to interpretation. Based in part on the Company’s assessment of other sources of liquidity, the uncertainty associated with future revenues created by the COVID-19 pandemic and related governmental responses, and the going concern uncertainty reflected in the Company’s consolidated financial statements as of December 31, 2019, the Company believed in good faith that it met the eligibility requirements for the PPP Loan. If, despite the good-faith belief that given the Company’s circumstances all eligibility requirements for the PPP Loan were satisfied, it is later determined that the Company had violated any applicable laws or regulations or it is otherwise determined that the Company was ineligible to receive the PPP Loan, it may be required to repay the PPP Loan in its entirety and/or be subject to additional penalties and potential liabilities. On June 5, 2020, the Paycheck Protection Program Flexibility Act was signed into law, extending the PPP Loan forgiveness period from eight weeks to 24 weeks after loan origination, extending the initial deferral period of principal and interest payments from six months to ten months after the loan forgiveness period, reducing the required amount of payroll expenditures from 75 % to 60 %, removing the prior ban on borrowers taking advantage of payroll tax deferral after loan forgiveness and allowing for the amendment of the maturity date on existing loans from two years to five years . On March 8, 2021 the Company applied for PPP loan forgiveness with its lender and subsequently received approval from the lender on April 2, 2021. The Company, in good faith, believes it maintained compliance with the requirements of the PPP. On May 21, 2021, the Small Business Administration granted its forgiveness of the PPP Loan, including principal and accrued interest, of $ 0.5 million. The gain on forgiveness is reported as a component of other income on the accompanying consolidated statement of operations.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Redeemable Convertible Preferred Stock	7. Redeemable Convertible Preferred Stock The redeemable convertible preferred stock instruments were contingently redeemable preferred stock. Each series contained redemption features, limited voting rights, dividends, and conversion terms. The convertible preferred stock was presented on the consolidated balance sheets as mezzanine equity as of March 31, 2022. All shares of redeemable convertible preferred stock were fully redeemed and are no longer outstanding as of June 30, 2022. March 2022 Offering In March 2022, the Company completed a private placement offering (the “March 2022 Offering”) of (i) 2,500 shares of the Company’s Series A Redeemable Convertible Preferred Stock, par value $ 0.0001 per share (the “Series A Preferred Stock”), and (ii) 2,500 shares of the Company’s Series B Redeemable Convertible Preferred Stock, par value $ 0.0001 per share (the “Series B Preferred Stock” and together with the Series A Preferred Stock, the “Preferred Stock”), in each case, at an offering price of $ 952.38 per share, representing a 5 % original issue discount to the stated value of $ 1,000 per share of Preferred Stock, for gross proceeds from the Offerings of approximately $ 4.76 million, before the deduction of the placement agent’s fee and other offering expenses. The shares of Series A Preferred Stock had a stated value of $ 1,000 per share and were convertible, at a conversion price of $ 20.00 per share, into 125,000 shares of common stock. The shares of Series B Preferred Stock had a stated value of $ 1,000 per share and were convertible, at a conversion price of $ 20.00 per share, into 125,000 shares of common stock. The closing occurred on March 25, 2022 . The proceeds of $ 4.76 million were held in escrow and were only permitted to be disbursed to the Company upon conversion of the Series A and Series B Preferred Stock. Since the redeemable convertible preferred stock could have been redeemed at the option of the holder, but was not mandatorily redeemable, the redeemable preferred stock was classified as mezzanine equity and initially recognized at fair value of $ 4.76 million as mezzanine equity on the accompanying statement of redeemable convertible preferred stock and stockholders' equity. The March 2022 Offering generated gross proceeds of $ 4.76 million and the Company incurred cash-based placement agent fees and other offering expenses of approximately $ 0.6 million. The proceeds were held in escrow and were only permitted to be disbursed to the Company upon conversion of the Series A and Series B Preferred Stock. The Company’s placement agent was issued compensatory warrants to purchase up to 7.0 % of the aggregate number of shares of Preferred Stock sold in the offering (on an as-converted to common stock basis), resulting in common stock warrants to purchase up to 17,501 shares of common stock, with an exercise price of 125 % of the offering price, or $ 25.00 per share, which are exercisable 6 months after issuance on or after September 25, 2022 , and expire five and a half ( 5.5 ) years following the date of issuance on September 25, 2027. The placement agent warrants, which are recorded as a component of stockholders’ equity, were valued at an aggregate of $ 34 thousand dollars using the Black Scholes option pricing model based upon the following assumptions: expected volatility of 78.90 %, risk-free interest rate of 2.40 %, expected dividend yield of 0 %, and an expected term of 5.5 years. As of December 31, 2022, the Company had 17,501 sha res of common stock reserved for issuance pursuant to the placement agent’s warrants issued by the Company in the March 2022 Offering at an exercise price of $ 25.00 per share. Voting Rights The shares of Preferred Stock had no voting rights, except that they only have the right to vote, with the holders of common stock, as a single class on a proposal to approve an amendment to our certificate of incorporation to effect a reverse stock split of our issued and outstanding common stock within a range, to be determined by our board of directors and set forth in such proposal. Each share of Series A Preferred Stock outstanding on April 14, 2022 (the “Record Date”) had a number of votes equal to the number of shares of Common Stock issuable upon conversion of such share (whether or not such shares are then convertible). Accordingly, as of the Record Date, each share of Series A Preferred Stock had 3,776 votes, which is determined by dividing $ 1,000 , the stated value of one share of Series A Preferred Stock, by $ 0.2648 , the NASDAQ Minimum Price as of the closing on March 25, 2022. The holders of the Series A Preferred Stock agreed to not transfer their shares of Series A Preferred Stock until after the Annual Meeting and to vote all shares of Series A Preferred Stock in favor of the Reverse Stock Split Proposal. Each share of Series B Preferred Stock outstanding on the Record Date entitled the holder thereof to cast 30,000 votes on the Reverse Stock Split Proposal. The holders of the Series B Preferred Stock agreed to not transfer their shares of Series B Preferred Stock until after the Annual Meeting and to vote all shares of Series B Preferred Stock in the same proportion as the aggregate shares of Common Stock and Series A Preferred Stock are voted on the Reverse Stock Split Proposal. As an example, if 70 % of the aggregate votes cast by Common Stock and Series A Preferred Stock voting on the Reverse Stock Split Proposal were voted in favor thereof and 30 % of the aggregate votes cast by Common Stock and Series A Preferred Stock voting on the Reverse Stock Split Proposal were voted against such Proposal, then 70 % of the votes entitled to be cast by Series B Preferred Stock would have been cast in favor of the proposal and 30 % of such votes would have been cast against the proposal. Dividends The holders of the redeemable convertible preferred stock were entitled to receive dividends on shares of Preferred Stock equal (on an as-if-converted-to-Common-Stock basis, disregarding for such purpose any conversion limitations hereunder) to and in the same form as dividends actually paid on shares of the Common Stock when, as and if such dividends are paid on shares of the Common Stock. No other dividends were payable on shares of Preferred Stock. Conversion Rights Each share of Preferred Stock was convertible, at any time and from time to time from and after the Reverse Stock Split Date at the option of the Holder thereof, into that number of shares of Common Stock determined by dividing the stated value per share of preferred stock by the conversion price. The shares of Series A Preferred Stock had a stated value of $ 1,000 per share and were convertible, at a conversion price of $ 20.00 per share, into 125,000 shares of common stock. The shares of Series B Preferred Stock had a stated value of $ 1,000 per share and were convertible, at a conversion price of $ 20.00 per share, into 125,000 shares of common stock. Redemption Rights Each share of Preferred Stock was redeemable after (i) the earlier of (1) the receipt of authorized stockholder approval for the reverse stock split and (2) the date that was 90 days following the Original Issue Date of March 25, 2022, and (ii) before the date that was 120 days after the Original Issue Date or July 23, 2022 (the “Redemption Period”) , each stockholder had the right to cause the Company to redeem all or part of such stockholder’s shares of Preferred Stock at a price per share equal to 105 % of the stated value of $ 1,000 per share. Between June 2, 2022, and June 29, 2022, at the request of the holders, the Company redeemed for cash proceeds totaling $ 5.25 million ($ 4.76 million payment from escrow and $ 0.5 million redemption payment by the Company), 2,500 outstanding shares of Series A Preferred Stock and 2,500 outstanding shares of Series B Preferred Stock based on the receipt of the Redemption Notices (the “Preferred Redemption”) at a price equal to 105 % of the $ 1,000 stated value per share, which represented all outstanding shares of Preferred Stock. The approximately $ 1.1 million accretion of the Series A and Series B Preferred Stock to its redemption value was recorded as a reduction to additional paid-in capital. The Company recognized a portion of the accretion as a deemed dividend related to the accretion of the discount and redemption feature of approximately $ 0.5 million upon redemption of Preferred Stock on the consolidated statement of operations. On June 30, 2022, the Company filed a Certificate of Elimination with respect to the Series A Preferred Stock and Series B Preferred Stock (the “Series A Certificate of Elimination and the Series B Certificate of Elimination”), which upon filing with the Secretary of State of the State of Delaware (“Delaware Secretary”), eliminated from all matters set forth in the Certificates of Designation of Series A and Series B Preferred Stock. As of December 31, 2022 , all shares of the Series A Preferred Stock and Series B Preferred Stock are no longer outstanding and the Company’s only remaining class of outstanding stock is its common stock, par value $ 0.0001 per share.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity Common Stock January 2021 Offering In January 2021, the Company completed an S-1 offering (the “January 2021 Offering”) of an aggregate of 580,000 shares of common stock, pre-funded warrants to purchase up to 120,000 shares of its common stock, and common stock warrants to purchase up to an aggregate of 700,000 shares of common stock. To the extent that an investor determines, at their sole discretion, that they would beneficially own in excess of the Beneficial Ownership Limitations (or as such investor may otherwise choose), in lieu of purchasing shares of Common Stock and Common Warrants, such investor could have elected to purchase Pre-Funded Warrants and Common Warrants at the Pre-Funded Purchase Price in lieu of the shares of Common Stock and Common Warrants in such a manner to result in the same aggregate purchase price being paid by such investor to the Company. The combined purchase price of one share of common stock and the accompanying common stock warrant was $ 20.00 , and the combined purchase price of one pre-funded warrant and accompanying common stock warrant was $ 19.998 . The common stock warrants are exercisable for five ( 5 ) years at an exercise price of $ 20.00 per share. The pre-funded warrants are immediately exercisable at an exercise price of $ 0.002 per share and may be exercised at any time until all of the pre-funded warrants are exercised in full. Placement agent warrants were issued to purchase up to 35,000 shares of common stock, are immediately exercisable for an exercise price of $ 25.00 per share, and are exercisable for five ( 5 ) years following the date of issuance. The Company received gross proceeds of $ 14.0 million and incurred placement agent’s fees and other offering expenses of approximately $ 1.9 million. The warrants and placement agent warrants were valued at $ 7.2 million and $ 0.3 million, respectively, using the Black-Scholes option pricing model based on the following assumptions: expected volatility 80.08 %, risk-free interest rate 0.38 %, expected dividend yield 0 %, and an expected term of 5.0 years. As of December 31, 2022, a total of 336,060 warrants issued in the January 2021 Offering to purchase shares of common stock have been exercised and the Company issued 336,060 shares of its common stock. The Company received gross proceeds of approximately $ 6.8 million. As of December 31, 2022, the Company had 387,565 shares and 11,375 shares of co mmon stock reserved for issuance pursuant to the warrants and placement agent’s warrants, respectively, issued by the Company in the January 2021 Offering, at an exercise price of $ 20.00 per share and $ 25.00 per share, respectively. June 2021 Offering In June 2021, the Company completed a registered direct offering (the “June 2021 Offering”) of an aggregate of 298,865 shares of common stock, together with accompanying warrants to purchase up to an aggregate of 239,093 shares of common stock, at a public offering price of $ 22.00 per share. The accompanying warrants permit the investor to purchase additional shares equal to 80 % of the number of shares of the Company’s common stock purchased by the investor. The warrants have an exercise price of $ 20.00 per share, are immediately exercisable, and expire five and a half ( 5.5 ) years following the date of issuance. In addition, the Company’s placement agent was issued compensatory warrants equal to 5.0 %, or 14,946 shares, of the aggregate number of common stock sold in the offering, which are immediately exercisable for an exercise price of $ 27.50 and expire five ( 5 ) years following the date of issuance on June 7, 2026. The Company received gross proceeds of $ 6.6 million and incurred cash-based placement agent fees and other offering expenses of approximately $ 0.9 million. The warrants and placement agent warrants were valued at $ 3.0 million and $ 0.2 million, respectively, using a Black-Scholes option pricing model with the following assumptions: expected volatility 81.44 % and 80.15 %, risk-free interest rate 0.88 % and 0.77 %, expected dividend yield 0 % and 0 %, and an expected term of 5.5 years or 5.0 years, respectively. As of December 31, 2022 , no warrants associated with the June 2021 Offering have been exercised. As of December 31, 2022 , the Company had 90,910 shares and 14,946 shares of common stock reserved for issuance pursuant to the warrants and placement agent’s warrants, respectively, issued by the Company in the June 2021 Offering, at an exercise price of $ 20.00 per share and $ 27.50 per share, respectively. In connection with the July 2022 Offering, the Company agreed to amend warrants, by reducing the exercise price and extending the expiration date, to purchase up to an aggregate of 148,183 shares of common stock of the Company that were originally issued to the investor in the June 2021 Offering. Refer to July 2022 Offering overview below for accounting treatment for the amended warrants. December 2021 Offering In December 2021, the Company completed a registered direct offering (the “December 2021 Offering”) of an aggregate of 411,764 shares of common stock and 411,766 warrants to purchase up to 411,766 shares of common stock, at a public offering price of $ 8.50 per share. The accompanying warrants permit the investor to purchase additional shares equal to approximately the same number of shares of the Company’s common stock purchased by the investor. The warrants have an exercise price of $ 8.50 per share, may be exercised any time on or after 6 months and one (1) day after the issuance date, and expire five and a half ( 5.5 ) years following the date of issuance. In addition, the Company’s placement agent was issued compensatory warrants equal to 5.0 %, or 20,590 shares, of the aggregate number of shares of common stock sold in the offering, which are immediately exercisable for an exercise price of $ 10.626 and expire five and a half ( 5.5 ) years following the date of issuance on June 21, 2027. The Company received gross proceeds of $ 3.5 million and incurred cash-based placement agent fees and other offering expenses of approximately $ 0.5 million. The placement agent warrants, which are recorded as a component of stockholders’ equity, were valued at an aggregate $ 0.1 million using the Black-Scholes option pricing model based on the following assumptions: expected volatility of 79.81 %, risk-free interest rate of 1.21 %, expected dividend yield of 0 % and an expected term of 5.5 years. As of December 31, 2022 , no warrants associated with the December 2021 Offering have been exercised. As of December 31, 2022 , the Company had 164,707 shares and 20,590 shares of common stock reserved for issuance pursuant to the warrants and placement agent’s warrants, respectively, issued by the Company in the December 2021 Offering, at an exercise price of $ 8.50 per share and $ 10.626 per share, respectively. In connection with the July 2022 Offering, the Company agreed to amend warrants, by reducing the exercise price and extending the expiration date, to purchase up to an aggregate of 247,059 shares of common stock of the Company that were originally issued to the investor in the December 2021 Offering. Refer to July 2022 Offering overview below for accounting treatment for the amended warrants. July 2022 Offering On July 12, 2022, the Company entered into a Securities Purchase Agreement (the “July 2022 Purchase Agreement”) with a single healthcare-focused institutional investor for the sale by the Company of (i) a pre-funded warrant to purchase up to 1,774,309 shares of Common Stock (the “Pre-Funded Warrant”), (ii) a Series A warrant to purchase up to an aggregate of 1,774,309 shares of common stock (the “Series A Warrant”), and (iii) a Series B warrant to purchase up to an aggregate of 1,774,309 shares of common stock (the “Series B Warrant,” and together with the Pre-Funded Warrant and the Series A Warrant, the “Warrants”), in a private placement offering (the “Offering”). The combined purchase price of one Pre-Funded Warrant and accompanying Series A Warrant and accompanying Series B Warrant was $ 2.818 . Subject to certain ownership limitations, the Series A Warrant became exercisable immediately after the issuance date at an exercise price equal to $ 2.568 per share of common stock, subject to adjustments as provided under the terms of the Series A Warrant, and has a term of five and a half ( 5.5 ) years from the issuance date. Subject to certain ownership limitations, the Series B Warrant became exercisable immediately after the issuance date at an exercise price equal to $ 2.568 per share of common stock, subject to adjustments as provided under the terms of the Series B Warrant, and has a term of one and a half ( 1.5 ) years from the issuance date. Subject to certain ownership limitations described in the Pre-Funded Warrant, the Pre-Funded Warrant was immediately exercisable and may be exercised at an exercise price of $ 0.0001 per share of common stock any time until all of the Pre-Funded Warrant is exercised in full. As of December 31, 2022 , the Pre-Funded Warrant to purchase up to an aggregate of 1,774,309 shares of common stock had been fully exercised and the Company issued 1,774,309 shares of common stock. The Company also agreed to amend certain warrants to purchase up to an aggregate of 447,800 shares of common stock of the Company that were issued to the investor in the private placement in November 2020, June 2021 and December 2021 with exercise prices ranging from $ 8.50 to $ 34.00 per share and expiration dates ranging from May 18, 2026 to June 21, 2027 , so that such warrants have a reduced exercise price of $ 2.568 per share and expiration date of five and a half ( 5.5 ) years following the closing of the private placement, for an additional offering price of $ 0.0316 per amended warrant. The incremental fair value resulting from the modifications to the warrants was adjusted against the gross proceeds from the offering as an equity issuance cost. The gross proceeds to the Company were approximately $ 5 million, before deducting the placement agent’s fees and other offering expenses, and excluding the proceeds, if any, from the exercise of the Series A Warrant, the Series B Warrant, and amended warrants. The Series A warrants and placement agent warrants were valued at $ 3.8 million and $ 0.2 million, respectively, using the Black-Scholes option pricing model based on the following assumptions: expected volatility 79.28 %, risk-free interest rate 3.06 %, expected dividend yield 0 %, and an expected term of 5.5 years. The Series B warrants were valued at $ 2.3 million using the Black-Scholes option pricing model based on the following assumptions: expected volatility 74.25 %, risk-free interest rate 3.16 %, expected dividend yield 0 %, and an expected term of 1.5 years. The amended warrants were valued at $ 1.0 million using the Black-Scholes option pricing model based on the following assumptions: expected volatility 79.28 %, risk-free interest rate 3.06 %, expected dividend yield 0 %, and an expected term of 5.5 years. The estimated fair value of the original warrants immediately prior to the warrant amendments was $ 0.5 million using Black-Scholes option pricing model based on the following assumptions: expected volatility ranging from 81.21 – 83.34 %, risk-free interest rates of 3.06 – 3.16 %, expected dividend yield 0 %, and an expected terms of 3.84 – 4.94 years. The warrant modifications resulted in an estimated value of $ 0.5 million, measured as the incremental fair value of the amended warrants, and was adjusted against the gross proceeds from the offering. As of December 31, 2022 , no warrants associated with the July 2022 Purchase Agreement have been exercised. As of December 31, 2022 , the Company had 3,996,418 shares and 124,202 shares of common stock reserved for issuance pursuant to the warrants and placement agent’s warrants, respectively, issued by the Company in the July 2022 Purchase Agreement, at an exercise price of $ 2.568 per share and $ 3.5225 per share, respectively. Common Stock Purchase Agreement with Lincoln Park In July 2020, the Company entered into a common stock purchase agreement (the “2020 Purchase Agreement”) with Lincoln Park which provided that, upon the terms and subject to the conditions and limitations in the 2020 Purchase Agreement, Lincoln Park was committed to purchase up to an aggregate of $ 10.0 million of shares of the Company’s common stock at the Company’s request from time to time during a 24 month period that began in July 2020 and at prices based on the market price of the Company’s common stock at the time of each sale. Upon execution of the 2020 Purchase Agreement, the Company sold 16,425 shares of common stock at $ 60.88 per share to Lincoln Park for gross proceeds of $ 1.0 million. During the year ended December 31, 2020, the Company sold an additional 15,000 shares of common stock to Lincoln Park for gross proceeds of approximately $ 0.5 million. In addition, in consideration for entering into the 2020 Purchase Agreement and concurrently with the execution of the 2020 Purchase Agreement, the Company issued 3,348 shares of its common stock to Lincoln Park. During the years ended December 31, 2022 and 2021, the Company did not sell any shares of common stock to Lincoln Park. The 2020 Purchase Agreement expired automatically pursuant to its term on August 1, 2022, and the Company did not sell any additional shares of common stock to Lincoln Park through the date of expiration of the 2020 Purchase Agreement. Common Stock Warrants In 2016, Private Histogen issued warrants to purchase common stock as consideration for settlement of prior liability claims. The warrants for the purchase of up to 180 common shares at an exercise price of $ 461.60 per share expired on July 31, 2021 . In addition, at December 31, 2022, warrants to purchase 68 shares of common stock with an exercise price of $ 1,486.00 per share remain outstanding that were issued by Conatus in connection with obtaining financing in 2016. T hese warrants expire on July 3, 2023 . See warrant discussion above in connection with the January 2021 Offering, the June 2021 Offering, the December 2021 Offering, and the July 2022 Offering. Stock-Based Compensation Equity Incentive Plans On December 18, 2017, Private Histogen established the Histogen Inc. 2017 Stock Plan (the “2017 Plan”). Under the 2017 Plan, Private Histogen was authorized to issue a maximum aggregate of 41,861 shares of common stock with adjustments for unissued or forfeited shares under the predecessor plan (the Histogen Inc. 2007 Stock Plan). In April 2019, Private Histogen amended the 2017 Plan, which increased the number of common stock available for grants by 16,336 shares. The 2017 Plan permitted the issuance of incentive stock options (“ISOs”), non-statutory stock options (“NSOs”), and Stock Purchase Rights. NSOs could be granted to employees, directors, or consultants, while ISOs could be granted only to employees. Options granted vest over a maximum period of four years and expire ten years from the date of grant. In connection with the closing of the Merger, no further awards will be made under the 2017 Plan. In May 2020, in connection with the closing of the Merger, the Company’s stockholders approved the Company’s 2020 Incentive Award Plan (the “2020 Plan”). The maximum number of shares of the Company’s common stock available for issuance under the 2020 Plan equals the sum of (a) 42,500 shares; (b) any shares of common stock of the Company which are subject to awards under the Conatus 2013 Equity Incentive Plan (the “Conatus 2013 Plan”) as of the effective date of the 2020 Plan which become available for issuance under the 2020 Plan after such date in accordance with its terms; and (c) an annual increase on the first day of each calendar year beginning with the January 1 of the calendar year following the effectiveness of the 2020 Plan and ending with the last January 1 during the initial ten-year term of the 2020 Plan, equal to the lesser of (i) five percent of the number of shares of the Company’s common stock outstanding (on an as-converted basis) on the final day of the immediately preceding calendar year, and (ii) such lesser number of shares of the Company’s common stock as determined by the Company’s board of directors. Additionally, in connection with the closing of the Merger, no further awards will be made under the Conatus 2013 Plan. As of December 31, 2022, 4,887 ful ly vested options remain outstanding under the Conatus 2013 Plan with a weighted average exercise price of $ 859.59 per share. The following summarizes activity related to the Company’s stock options under the 2017 Plan and the 2020 Plan for the year ended December 31, 2022: Options Weighted- Weighted- Aggregate Outstanding at December 31, 2021 111,418 $ 37.62 6.78 $ — Granted 67,300 4.54 Cancelled / Forfeited ( 65,439 ) 31.83 Outstanding at December 31, 2022 113,279 21.30 8.09 $ — Vested and exercisable at December 31, 2022 41,101 $ 39.60 6.54 $ — Prior Chief Executive Officer Stock Options On January 24, 2019, the Company issued 22,909 stock options to its then newly appointed Chief Executive Officer. In accordance with the original award agreement, 40 % of the options would vest immediately upon an initial public offering or 45 days following a change in control, as defined in the award agreement, while the remaining 60 % are subject to vesting, of which 25 % vest on the first anniversary of the grant date and then ratably over the remaining 36 months. On January 28, 2020, the award agreement was amended, which became effective upon the close of the Merger in May 2020, whereby the 40 % of stock options (“Liquidity Option Shares”) subject to vesting upon an initial public offering or 45 days following a change in control will now vest immediately upon meeting certain performance and market condition-based criteria. The vesting of the Liquidity Option Shares is divided into four separate tranches, each vesting 25 % of the Liquidity Option Shares, upon: (1) the closing of the proposed merger with Conatus; (2) the date that the market capitalization of the Company exceeds $ 200.0 million; (3) the date that the market capitalization of the Company exceeds $ 275.0 million, and; (4) the date that the market capitalization of the Company exceeds $ 300.0 million. Each vesting tranche represents a unique derived service period and therefore stock-based compensation expense for each vesting tranche is recognized on a straight-line basis over its respective derived service period. Additionally, in the event that the Chief Executive Officer’s employment with the Company is terminated without cause or he resigns for good reason, an additional portion of the stock options award will vest equal to the number of such options which would have vested in the 12 months following the date of such termination. On May 26, 2020, in connection with the closing of the Merger, 2,426 options of the Liquidity Option Shares became fully vested as the performance condition was achieved. In November 2021, the Company’s then President and Chief Executive Officer voluntarily resigned. No further stock-based compensation expense related to the market-based options will be recognized. As of December 31, 2022, the vested option awards expired unexercised. Board of Directors and Employee Stock Options In March 2021, in conjunction with a former Board Member’s voluntary resignation, the Company modified stock-based payment awards by accelerating the vesting of all awards that were unvested at the time of his voluntary resignation and by extending the exercise period through December 31, 2021. As a result of the modification, the Company recorded an immaterial amount of additional stock-based compensation expense during the year ended December 31, 2021. As of December 31, 2022, the awards expired unexercised. In June 2021, in conjunction with a former employees’ voluntary resignation, the Company modified stock-based payment awards by accelerating the vesting of all awards that were unvested at the time of the voluntary resignation and by extending the exercise period through August 29, 2023. Valuation of Stock Option Awards The following weighted-average assumptions were used to calculate the fair value of awards granted to employees, non-employees and directors: Years Ended December 31, 2022 2021 Expected volatility 78.95 % 78.69 % Risk-free interest rate 2.14 % 0.85 % Expected option life (in years) 6.02 6.08 Expected dividend yield —% —% Restricted Stock Units On November 8, 2021, the Company granted 23,423 restricted stock units to the Company’s Interim Chief Executive Officer, Chief Financial Officer, and Senior Vice President of Technical Operations. The fair value of the RSUs was $ 14.58 per share, which was the closing market price of the Company’s common stock on the date of grant. The RSUs vest in full upon the earlier of (1) 12 months following the grant date and (2) a change of control of the Company, as defined in the Company’s 2020 Plan, subject to continued service to the Company. Prior to RSU vesting, the Company and the RSU recipients mutually agreed to enter into RSU Cancellation Agreements such that the RSU awards shall no longer be outstanding. As of December 31, 2022, no restricted stock units remain outstanding. Stock-based Compensation Expense The compensation cost that has been included in the Company’s consolidated statements of operations for all stock-based compensation arrangements is detailed as follows (in thousands): Years Ended December 31, 2022 2021 General and administrative $ 470 $ 520 Research and development 32 184 Total $ 502 $ 704 As of December 31, 2022 , total unrecognized compensation cost related to unvested options was approximately $ 0.5 million which is expected to be recognized over a weighted-average period of 2.29 years. Common Stock Reserved for Future Issuance Common stock reserved for future issuance is as follows: December 31, 2022 2021 Common stock warrants 4,876,639 1,186,307 Common stock options issued and outstanding 118,166 116,311 Common stock available for issuance under stock plan 100,577 2,309 5,095,382 1,304,927

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Leases In January 2020, Private Histogen entered into a long-term operating lease with San Diego Sycamore, LLC (“Sycamore”) for its headquarters that includes office and laboratory space. The lease commenced on March 1, 2020 and expires on August 31, 2031 , with no options to renew or extend. The lease was accounted for as a modification of Private Histogen’s existing lease with Sycamore as the lease agreement did not grant Private Histogen an additional right-of-use asset. The terms of the lease agreement include seven months of rent abatement at lease commencement and a tenant improvement allowance of up to $ 2.2 million. The tenant improvements are required to be permanently affixed to the leased office and laboratory space and do not constitute leasehold improvements of the Company. During the construction period of the tenant improvements, the lease agreement requires the Company to relocate its operations to a similar Sycamore property whereby monthly rent is substantially reduced for the duration of the construction period. The lease is subject to additional variable charges for common area maintenance, insurance, taxes and other operating costs. At lease commencement, the Company recognized a right-of-use asset and operating lease liability totaling approximately $ 4.5 million. The Company used a discount rate based on its estimated incremental borrowing rate to determine the right-of-use asset and operating lease liability amounts to be recognized. The Company determined its incremental borrowing rate based on the term and lease payments of the new operating lease and what it would normally pay to borrow, on a collateralized basis, over a similar term for an amount equal to the lease payments. Operating lease expense is recognized on a straight-line basis over the lease term. The terms of the lease required the Company to provide the landlord a security deposit of $ 0.3 million as collateral for a letter of credit issued to be held throughout the lease term. This security deposit is shown as restricted cash on the accompanying consolidated balance sheets. In June 2021, the Company entered into the First Amendment to Lease (the “Amendment”). Pursuant to the Amendment, among other things, the Company and Sycamore agreed (i) to substitute the temporary premises, (ii) to delay the start of construction and the timing of the Company’s relocation to the replacement temporary premises, (iii) to increase the tenant improvement allowance from $ 2.2 million to $ 2.3 million, (iv) to increase the letter of credit amount from $ 0.3 million to $ 0.4 million upon commencement of the tenant improvements, and (v) to review potential subsequent reductions to the security deposit and related letter of credit requirement at certain time intervals along the lease term provided that the Company is not in default. As a result of the modification, the lease liability was remeasured using the incremental borrowing rate at the modification date and a corresponding reduction of $ 0.3 million was recorded to both the lease liability and right-of-use-asset. During the year ended December 31, 2022, the Company completed construction of the building improvements. Due to construction delays, the tenant improvement construction period was extended by two months for which the Company was granted an incremental two-month extension of rent abatement and effectively shortened the lease term. Upon completion of the improvements, the building improvement costs in excess of the tenant improvement allowance that was funded by the Company were capitalized to the right-of-use-asset, to be amortized over the remaining lease term. As a result of the modification, the lease liability was remeasured and a corresponding increase of $ 0.4 million was recorded to both the lease liability and right-of-use-asset. The Company leases certain office equipment that is classified as a finance lease. As of December 31, 2022 , the weighted-average remaining term of the Company’s operating lease and finance lease was approximately 8.7 years and 1.5 years, respectively. The Company recognizes right-of-use assets and lease liabilities at the lease commencement date based on the present value of future minimum lease payments over the lease term. The discount rate used to determine the present value of the lease payments is the rate implicit in the lease unless that rate cannot be readily determined, in which case, the Company utilizes its incremental borrowing rate in determining the present value of the future minimum lease payments. At the inception dates of the leases, the weighted-average discount rate for the Company’s operating and finance lease was 12.2 % and 10.0 %, respectively. The Company does not record leases with an initial term of 12 months or less on the consolidated balance sheets. Expense for these short-term leases is recognized on a straight-line basis over the lease term. The Company has elected the practical expedient to combine lease and non-lease components into a single component for all classes of underlying assets. The Company’s lease assets and lease liabilities were as follows (in thousands): December 31, Balance Sheet 2022 2021 Assets Operating lease Right-of-use asset $ 4,658 $ 4,432 Finance lease Property and equipment, net 12 20 Total lease assets $ 4,670 $ 4,452 Liabilities Current Operating lease liability Current portion of lease liability $ 238 $ 127 Finance lease liability Accrued liabilities 9 9 Total current liabilities 247 136 Noncurrent Operating lease liability Noncurrent portion of lease liability 4,379 4,617 Finance lease liability Other liabilities 5 14 Total noncurrent liabilities 4,384 4,631 Total lease liabilities $ 4,631 $ 4,767 The components of lease expense were as follows (in thousands): Years Ended December 31, Statement of Operations 2022 2021 Operating lease cost: Research and development $ 597 $ 210 General and administrative 694 428 Total operating lease cost $ 1,291 $ 638 Finance lease cost: Amortization of fixed assets Property and equipment, net $ 8 $ 9 Interest on lease liabilities Interest expense 1 3 Total finance lease cost $ 9 $ 12 Supplemental cash flow information related to leases were as follows (in thousands): Years Ended December 31, 2022 2021 Cash paid for amounts included in the measurement Operating cash flows from operating lease $ ( 78 ) $ 111 Operating cash flows from finance lease 1 3 Financing cash flows from finance lease 9 9 At December 31, 2022, future minimum payments of lease liabilities were as follows (in thousands): Operating Finance 2023 $ 780 $ 10 2024 803 5 2025 827 — 2026 853 — Thereafter 4,330 — Total minimum lease payments 7,593 15 Less: imputed interest ( 2,976 ) ( 1 ) Total future minimum lease payments 4,617 14 Less: current obligations under leases ( 238 ) ( 9 ) Noncurrent lease obligations $ 4,379 $ 5 Material Contracts Pfizer Inc. In July 2010, Conatus entered into a Stock Purchase Agreement with Pfizer, pursuant to which it acquired all of the outstanding capital stock of Idun Pharmaceuticals, Inc., which was subsequently spun off to Conatus stockholders in January 2013. Under the stock purchase agreement, the Company may be required to make payments to Pfizer totaling $ 18.0 million upon the achievement of specified regulatory milestones. In accordance with authoritative guidance, amounts for the milestone payments will be recognized when it is probable that the related contingent liability has been incurred and the amount owed is reasonably estimated. No amounts for the milestone payments have been recorded during the years ended December 31, 2022 and 2021. Prior to the termination of the Collaboration Agreement with Amerimmune on November 28, 2022, the obligations pursuant to the Stock Purchase Agreement were the responsibility of our former collaboration partner, Amerimmune. In accordance with authoritative guidance, amounts for the milestone payments will be recognized when it is probable that the related contingent liability has been incurred and the amount owed is reasonably estimated. No amounts for the milestone payments have been recorded during the year ended December 31, 2022 . PUR Settlement In April 2019, Private Histogen entered into a Settlement, Release and Termination Agreement (“PUR Settlement”) with PUR Biologics, LLC and its members which terminated the License, Supply and Operating Agreements between Private Histogen and PUR, eliminated Private Histogen’s membership interest in PUR and returned all in-process research and development assets to Private Histogen (the “Development Assets”). The agreement also provided indemnifications and complete releases by and among the parties. The acquisition of the Development Assets was accounted for as an asset acquisition in accordance with ASC 805-50-50, Acquisition of Assets Rather than a Business. As consideration for the reacquisition of the Development Assets, Private Histogen compensated PUR with both equity and cash components, including 8,366 shares of Series D convertible preferred stock with a fair value of $ 1.75 million and a potential cash payout of up to $ 6.25 million (the “Cap Amount”). Private Histogen paid PUR $ 0.5 million in upfront cash, forgave approximately $ 22 thousand of accounts receivable owed by PUR to Private Histogen, and settled an outstanding payable of PUR of approximately $ 23 thousand owed to a third party. The Company is also obligated to make milestone and royalty payments, including (a) a $ 0.4 million payment upon the unconditional acceptance and approval of a New Drug Application or Pre-Market Approval Application by the FDA related to the Development Assets, (b) a $ 0.4 million commercialization milestone upon reaching gross sales (by the Company or licensee) of the $ 0.5 million of products incorporating the Development Assets, and (c) a five percent ( 5 %) royalty on net revenues collected by the Company from commercial sales (by the Company or licensee) of products incorporating the Development Assets. The aforementioned cash payments, along with any future milestone and royalty payments, are all applied against the Cap Amount. In accordance with authoritative guidance, amounts for the milestone and royalty payments will be recognized when it is probable that the related contingent liability has been incurred and the amount owed is reasonably estimated. No amounts for the milestone and royalty payments have been recorded during the years ended December 31, 2022 and 2021. Litigation and Legal Matters The Company is subject to claims and legal proceedings that arise in the ordinary course of business. Such matters are inherently uncertain, and there can be no guarantee that the outcome of any such matter will be decided favorably to the Company or that the resolution of any such matter will not have a material adverse effect upon the Company’s consolidated financial statements. The Company accrues a liability for such matters when it is probable that future expenditures will be made, and such expenditures can be reasonably estimated. As of December 31, 2022, no accruals have been made and no liability recognized related to commitments and contingencies. Employee Litigation On or about February 17, 2022, two former employees, each of whom separately resigned and terminated their employment with Histogen, filed a complaint in the Superior Court of California, County of San Diego against the Company, the Company’s Board of Directors, the Company’s former Chief Executive Officer, as well as three individuals that are currently employed by the Company. Although the complaint lists the “Histogen Board of Directors, a business entity form unknown” as a defendant, the complaint does not specifically list the names of the board members. The plaintiffs allege whistleblower status, retaliation, discrimination, unfair business practices, wrongful termination, violation of civil rights, and other California state law claims. The Company has tendered the complaint to its liability insurer and engaged outside litigation counsel, as approved by its carrier, to defend Histogen, the Board of Directors and the individuals in this matter. The Company objects to the naming of each of the defendants in this matter and denies each of the plaintiffs’ claims. The plaintiffs agreed to pre-arbitration mediation, which was conducted on May 4, 2022, as was required by the arbitration agreement executed by each of the plaintiffs. Considering that the parties did not resolve the matter through this mediation, the Company petitioned the San Diego Superior Court for an order that the matter be submitted to arbitration consistent with each of the plaintiff’s arbitration agreements. The hearing for the motion to compel arbitration was held on August 12, 2022 and the San Diego Superior Court issued a ruling to uphold the binding arbitration agreements signed by both plaintiff’s. The matter is expected to proceed to arbitration but is the responsibility of the plaintiffs to initiate the arbitration proceeding. The Company believes that our defense costs, settlement monies, damages or any other awards would be covered by our liability insurance; provided, however, insurance may not cover all claims or could exceed our insurance coverage. The Company believes that there are substantial defenses to this lawsuit, and we intend to vigorously defend against each of these claims. While this litigation matter is in the early stages, the Company believes the action is without merit. Nonetheless, the ultimate outcome is unknown at this time. Amerimmune Collaborative Development and Commercialization Agreement Arbitration On March 3, 2022, the Company filed a demand for arbitration (“Arbitration Demand”) with JAMS in the county of San Diego, against Amerimmune LLC (“Amerimmune”) seeking a declaratory judgment that Amerimmune has materially breached the Collaboration Agreement entered into by and between the Company and Amerimmune on October 26, 2020, and that the Company is therefore entitled to terminate the Collaboration Agreement in accordance with its terms. On November 28, 2022, the arbitrator issued an interim award in favor of the Company, granting the Company’s request for declaratory relief and specific performance terminating the Collaboration Agreement and denying each of Amerimmune’s counterclaims. On January 2, 2023, the arbitrator issued a final award affirming the arbitration outcome set forth in the interim award and further awarding the Company its costs in pursuing the arbitration. On February 9, 2023, the Company filed a petition in the Superior Court of California, County of San Diego, seeking to confirm the arbitration award. A hearing on the petition is currently scheduled for May 26, 2023.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes The reconciliation of income taxes computed using the statutory U.S. income tax rate and the provision is as follows (in thousands): Years Ended December 31, 2022 2021 Tax computed at federal statutory rate $ ( 2,235 ) $ ( 3,152 ) State tax, net of federal tax benefits ( 5 ) ( 908 ) Tax credits ( 368 ) ( 325 ) Valuation allowance 1,825 5,320 PPP loan forgiveness — ( 126 ) Other 783 ( 809 ) Provision for income taxes $ — $ — Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2022 2021 Deferred tax assets: Tax loss carryforward $ 19,250 $ 18,041 R&D credits and other tax credits 2,201 1,834 Stock-based compensation 132 152 Compensation 26 58 Deferred revenue 4 5 Lease liability 970 1,283 Capitalized research and development 1,992 2,607 Section 174 1,056 — Other 33 80 Total deferred tax assets 25,664 24,060 Less: valuation allowance ( 24,686 ) ( 22,861 ) Deferred tax assets, net 978 1,199 Deferred tax liability: Right-of-use assets ( 978 ) ( 1,199 ) Net deferred tax assets $ — $ — The Company records a valuation allowance against deferred tax assets to the extent that it is more likely than not that some portion, or all, the deferred tax assets will not be realized. Due to the substantial doubt related to the Company’s ability to utilize its deferred tax assets, the Company recorded a valuation allowance against the deferred tax assets. The change in the valuation allowance is an increase of $ 1.8 million and $ 5.3 million for the years ended December 31, 2022 and 2021, respectively. As of December 31, 2022 , the Company had federal and California net operating loss (“NOL”) carryforwards of approximately $ 72.0 million and $ 57.4 million, respectively. Additionally, as of December 31, 2022 , Adaptive Biologix has federal and state net operating losses of $ 0.4 million each. The Company has federal net operating loss carryforwards of $ 41.3 million that are not subject to expiration. No California NOLs expired in 2022. As of December 31, 2022 , the Company had federal and California research and development (“R&D”) credit carryforwards of approximately $ 1.7 million and $ 1.6 million, respectively. The federal R&D tax credit carryforwards will begin to expire in 2027 unless previously utilized. The California R&D credit carryforwards will carry forward indefinitely. Under Sections 382 and 383 of the Internal Revenue Code (“IRC”), substantial changes in the Company’s ownership may limit the amount of NOL and research and development credit carryforwards that could be used annually in the future to offset taxable income. The tax benefits related to future utilization of federal and state NOL carryforwards, credit carryforwards, and other deferred tax assets may be limited or lost if cumulative changes in ownership exceeds 50 % within any three-year period. The Company has not completed an IRC Section 382/383 analysis regarding the limitation of net operating loss and research and development credit carryforwards, and therefore, the ability of the Company to utilize its NOL and R&D credits is unknown. Uncertain Tax Positions The FASB ASC Topic 740, Income Taxes , addresses the determination of whether tax benefits claimed or expected to be claimed on a tax return should be recorded in the financial statements. Under ASC Topic 740-10, the Company may recognize the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authorities, based on the technical merits of the position. For fiscal years through December 31, 2022, the Company generated research and development credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development tax credit carryforwards; therefore, based on the accumulation of research and development tax credits since the Company’s inception and the Company’s uncertainty around its ability to utilize those tax credits until a study is completed, the Company has reserved a portion of those credits as an uncertain tax position as of December 31, 2022. A full valuation allowance has been provided against the Company’s research and development tax credit carryforwards and, if an adjustment were to be required, this adjustment would be offset by a corresponding reduction to the valuation allowance. The following table summarizes the activity related to our unrecognized tax benefits (in thousands): Years Ended December 31, 2022 2021 Gross unrecognized tax benefits at the beginning of $ 683 $ 561 Additions from tax positions taken in the current year 133 118 Additions from tax positions taken in prior years — 4 Reductions for tax positions from prior year — — Gross unrecognized tax benefits at end of the year $ 816 $ 683 Due to the existence of the valuation allowance, future changes in the Company’s unrecognized tax benefits will not impact the Company’s effective tax rate. The Company does not anticipate that there will be a substantial change in unrecognized tax benefits within the next twelve months. The Company has no t recognized any interest and penalties related to income taxes in the accompanying consolidated balance sheets or statements of operations. The Company is subject to taxation in the U.S. and state jurisdictions. The Company’s income tax returns for all years beginning January 1, 2018 and subsequent are still open to audit by the taxing authorities. CARES ACT On March 27, 2020, the United States enacted the Coronavirus Aid, Relief and Economic Security Act (CARES Act). The Cares Act is an emergency economic stimulus package that includes spending and tax breaks to strengthen the United States economy and fund a nationwide effort to curtail the effect of COVID-19. While the CARES Act provides sweeping tax changes in response to the COVID-19 pandemic, some of the more- significant provisions which are expected to impact the Company’s consolidated financial statements include removal of certain limitations on utilization of net operating losses, increasing the loss carryback period for certain losses to five years, and increasing the ability to deduct interest expense, as well as amending certain provisions of the previously enacted Tax Cuts and Jobs Act. Due to the loss position of the U.S. entities, many provisions of the CARES Act do not impact the Company and the CARES Act did not have an impact on the Company’s income tax provision for the years ended December 31, 2022 and 2021 .

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2022
Related Party Transactions [Abstract]
Related Parties	11. Related Parties Lordship Lordship, with its predecessor entities along with its principal owner, Jonathan Jackson, have invested and been affiliated with Private Histogen since 2010. As of December 31, 2022 and 2021 , Lordship controlled approximately 2.8 % and 4.7 % of the Company’s outstanding voting shares, respectively, and currently holds two Board of Director seats. In November 2012, Private Histogen entered into a Strategic Relationship Success Fee Agreement with Lordship (the “Success Fee Agreement”). The Success Fee Agreement causes certain payments to be made from the Company to Lordship equal to 1 % of certain product revenues and 10 % of certain license and royalty revenues generated from our Human Multipotent Cell Conditioned Media, or CCM, and our Human Extracellular Matrix, or hECM, in connection with the Company’s biologics technology platform. The Success Fee Agreement also stipulates that if the Company engages in a merger or sale of all or substantially all (defined as 90 % or more) of its assets or equity to a third party, then the Company has the option to terminate the agreement by paying Lordship the fair market value of future payments with the minimum payment being at least equal to the most recent annual payments Lordship has received. The Success Fee Agreement was amended in August 2016, but continues to carry the same rights to certain payments. The Company recognized an expense to Lordship for the years ended December 31, 2022 and 2021 totaling $ 375 thousand and $ 10 thousand, respectively, all of which is included in general and administrative expenses on the accompanying consolidated statements of operations. As of December 31, 2022 and 2021 , there was a balance of $ 10 thousand and $ 12 thousand, respectively, paid to Lordship included as a component of other assets on the accompanying consolidated balance sheets in connection with the deferral of revenue from the Allergan license transfer agreements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The consolidated financial statements include the accounts of the Company and its controlled subsidiaries, including Histogen Therapeutics, Inc., and have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”). All intercompany balances and transactions have been eliminated upon consolidation. The Company acquired Centro De Investigacion de Medicina Regenerativa, S.A. de C.V. (“CIMRESA”), a company in Mexico, during 2018 to facilitate a potential clinical development program for HST-001, or hair stimulating complex (“HSC”). This is a wholly-owned subsidiary intended to pursue registration with the COFEPRIS (Mexico equivalent to Food and Drug Administration). CIMRESA had no operational or financial activity for the years ended December 31, 2022 and 2021. The Company holds a majority interest in Adaptive Biologix, Inc. (“AB”, formerly Histogen Oncology, LLC). AB was formed to develop and market applications for the treatment of cancer. The Company consolidates AB into its consolidated financial statements.
Use of 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, liabilities and the disclosure of contingent assets and liabilities and contingencies at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the periods presented. Management believes that these estimates and assumptions are reasonable, however, actual results may differ and could have a material effect on future results of operations and financial position. Though the impact of the COVID-19 pandemic to our business and operating results presents additional uncertainty, the Company continues to use the best information available to them in their significant accounting estimates. Significant estimates and assumptions include the useful lives of property and equipment, discount rates used in recognizing contracts containing leases, unrecognized tax benefits, volatility used for stock-based compensation option pricing, and best estimate of standalone selling price of revenue deliverables. Actual results may materially differ from those estimates.
Variable Interest Entities	Variable Interest Entities The Company determined that AB is a variable interest entity (“VIE”) and that the Company is its primary beneficiary. The Company holds greater than 50 % of the shares and has the authority to manage the business and affairs of the VIE. AB’s other shareholder does not have a controlling interest. A VIE is typically an entity for which the Company has less than a 100 % equity interest but controls the decision making over the business and affairs of the entity, directs the decisions driving the economic performance of such entity and participates in the profit and losses of such an entity. The Company weighed both quantitative and qualitative information about the different risks and reward characteristics of each entity and the significance of that entity to the consolidating group in the aggregate.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker, the Interim Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one operating segment.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments purchased with an original maturity date of ninety days or less to be cash equivalents. Cash and cash equivalents include cash in readily available checking, money market accounts and brokerage accounts. The Company’s current restricted cash consists of cash held as collateral for a letter of credit issued as a security deposit for the lease of the Company’s headquarters and is required to be held throughout the lease term.
Risks and Uncertainties	Risks and Uncertainties Credit Risk At certain times throughout the year, the Company may maintain deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and believes it is not exposed to significant risk on its cash balances due to the financial position of the depository institutions in which those deposits are held. Customer Risk During the years ended December 31, 2022 and 2021 , one customer accounted for 100 % and 88 % of total revenues, respectively. Accounts receivable from the customer was $ 0 at both December 31, 2022 and 2021. COVID-19 The cumulative effect of the COVID-19 outbreak and associated disruptions have had, and may continue to have, an adverse impact on the Company’s business and its results of operations. The full impact of the COVID-19 outbreak continues to evolve as of the date these consolidated financial statements were available to be issued and will depend on future developments that are highly uncertain and unpredictable, including efficacy and adoption of vaccines, future resurgences of the virus and its variants, the imposition of governmental lockdowns, and quarantine and physical distancing requirements. As such, it is uncertain as to the full magnitude that the pandemic will have on the Company’s financial condition, liquidity, and future results of operations.
Accounts Receivable	Accounts Receivable Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts, if any. Management considers all accounts receivable to be fully collectible as of December 31, 2022 and 2021 , and accordingly, no provision for doubtful accounts was recorded.
Property and Equipment	Property and Equipment Property and equipment are reported net of accumulated depreciation and amortization and are comprised of office furniture and equipment, lab and manufacturing equipment, and leasehold improvements. Ordinary maintenance and repairs are charged to expense, while expenditures that extend the physical or economic life of the assets are capitalized. Furniture and all equipment are depreciated over their estimated useful lives, or five years , using the straight-line method. Software is amortized over its estimated useful lives, or three years , using the straight-line method. Leasehold improvements are amortized over their estimated useful lives and limited by the remaining term of the building lease, using the straight-line method.
Valuation of Long-Lived Assets	Valuation of Long-Lived Assets Long-lived assets to be held and used, including property and equipment, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable. As of December 31, 2022 and 2021, the Company has no t recognized any impairment to long-lived assets.
Forward Purchase Contract	Forward Purchase Contract In 2011, Private Histogen contracted for research services from EPS Global Research Pte. Ltd. (“EPS”) to conduct clinical trials and compile data from a study that took place in 2011 and 2013. The unpaid amount due for the services was approximately $ 0.3 million. In 2017, Private Histogen and EPS entered into a Debt Settlement and Conversion Agreement (“Settlement Agreement”) whereby Private Histogen paid $ 50 thousand and issued EPS 717 shares of Series D convertible preferred stock. The Company was required to repurchase the shares at the greater of the remaining balance due of approximately $ 0.3 million and the market price of the shares at the time of repurchase, but in no event later than December 31, 2021. The Company had the sole option to repurchase the shares (which were converted from Series D convertible preferred stock into shares of common stock upon the Merger) at any time on or before December 31, 2021. On December 16, 2021, the Company repurchased from EPS 717 shares of common stock in exchange for a cash payment of approximately $ 0.3 million. The repurchased shares were recorded as treasury stock and retired as of December 31, 2021. As of December 31, 2021, all amounts due to EPS under the Settlement Agreement have been paid.
Fair Value Measurements	Fair Value Measurements ASC 820, Fair Value Measurements , defines fair value, establishes a framework for measuring fair value under generally accepted accounting principles and enhances disclosures about fair value measurements. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the accounting guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: • Level 1 — Observable inputs such as quoted price (unadjusted) for identical instruments in active markets. • Level 2 — Observable inputs such as quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, or model derived valuations whose significant inputs are observable. • Level 3 — Unobservable inputs that reflect the reporting entity’s own assumptions. At December 31, 2022 and 2021, management believes the carrying amount of financial instruments consisting of cash, cash equivalents, restricted cash, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values due to the short-term nature of those instruments.
Comprehensive Loss	Comprehensive Loss The Company is required to report all components of comprehensive loss, including net loss, in the accompanying consolidated financial statements in the period in which they are recognized. Comprehensive loss is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources, including unrealized gains and losses on investments and foreign currency translation adjustments. Net loss and comprehensive loss were the same for all periods presented.
Revenue Recognition	Revenue Recognition Product and License Revenue The Company records revenue in accordance with ASC 606, Revenue from Contracts with Customers , whereby revenue is recognized when a customer obtains control of promised goods or services in an amount that reflects the consideration expected to be received in exchange for those goods or services. A five-step model is used to achieve the core principle: (1) identify the customer contract, (2) identify the contract’s performance obligations, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations and (5) recognize revenue when or as a performance obligation is satisfied. The Company applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. Shipping charges billed to customers are included in product revenue and the related shipping costs are included in cost of product revenue. The Company applies the revenue recognition standard, including the use of any practical expedients, consistently to contracts with similar characteristics and in similar circumstances (Refer to Note 5 for further information). Grant Awards In March 2017, the National Science Foundation (“NSF”), a government agency, awarded the Company a research and development grant to develop a novel wound dressing for infection control and tissue regeneration. The Company has concluded this government grant is not within the scope of ASC 606, as government entities generally do not meet the definition of a “customer” as defined by ASC 606. Payments received under the grant are considered conditional, non-exchange contributions under the scope of ASC 958-605, Not-for-Profit Entities – Revenue Recognition , and are recorded as grant revenue in the period in which such conditions are satisfied. In reaching the determination that such payments should be recorded as revenue, management considered a number of factors, including whether the Company is a principal under the arrangement, and whether the arrangement is significant to, and part of, the Company’s ongoing operations. In September 2020, the Company was approved for a grant award from the U.S. Department of Defense (“DoD”) in the amount of approximately $ 2.0 million to partially fund the Company’s Phase 1/2 clinical trial of HST-003 for regeneration of cartilage in the knee. The Company applies International Accounting Standard (“IAS”) 20, Accounting for Government Grants and Disclosure of Government Assistance , by analogy as there is no existing authoritative guidance under GAAP. Under the terms of the award, the DoD will reimburse the Company for certain allowable costs. The period of performance for the grant award substantially expires in September 2025 and is subject to annual and quarterly reporting requirements. As the DoD grant is a cost-type (reimbursement) grant, the Company must incur program expenses in accordance with the Statement of Work and approved budget in order to be reimbursed by the DoD. The Company will recognize funding received from the grant award as a reduction of research and development expenses in the period in which qualifying expenses have been incurred, as the Company is reasonably assured that the expenses will be reimbursed and the funding is collectible. For the years ended December 31, 2022 and 2021, qualifying expenses totaling $ 0.6 million and $ 0.7 million, respectively, were incurred with a corresponding reduction of research and development expenses related to the award. As of December 31, 2022 and 2021, $ 0.1 million and $ 0.2 million, respectively, was included within accounts receivable on the consolidated balance sheets related to the award.
Cost of Product Revenue	Cost of Product Revenue Cost of product revenue represents direct and indirect costs incurred to bring the product to saleable condition.
Research and Development Expenses	Research and Development Expenses All research and development costs are charged to expense as incurred. Research and development expenses primarily include (i) payroll and related costs associated with research and development performed, (ii) costs related to clinical and preclinical testing of the Company’s technologies under development, and (iii) other research and development costs including allocations of facility costs, net of reimbursable research and development costs incurred under the DoD grant.
General and Administrative Expenses	General and Administrative Expenses General and administrative expenses represent personnel costs for employees involved in general corporate functions, including finance, accounting, legal and human resources, among others. Additional costs included within general and administrative expenses consist of professional fees for legal (including patent costs), audit and other consulting services, travel and entertainment, recruiting, allocated facility and general information technology costs, depreciation and amortization, and other general corporate overhead expenses.
Patent Costs	Patent Costs The Company expenses all costs as incurred in connection with patent applications (including direct application fees, and the legal and consulting expenses related to making such applications) and such costs are included as a component of general and administrative expenses in the accompanying consolidated statements of operations.
Income Taxes	Income Taxes Income taxes are accounted for under the asset and liability method. Deferred income taxes are recorded for temporary differences between consolidated financial statement carrying amounts and the tax basis of assets and liabilities. Deferred tax assets and liabilities reflect the tax rates expected to be in effect for the years in which the differences are expected to reverse. No income tax expense or benefit was recorded for the years ended December 31, 2022 and 2021, due to the full valuation allowance on the Company’s net deferred tax assets. A valuation allowance is provided if it is more likely than not that some or all the deferred tax assets will not be realized. The Company also follows the provisions of accounting for uncertainty in income taxes which prescribes a model for the recognition and measurement of a tax position taken or expected to be taken in a tax return, and provides guidance on derecognition, classification, interest and penalties, disclosure and transition. The Company’s policy is to recognize interest or penalties related to income tax matters in income tax expense. Interest and penalties related to income tax matters were not material for the periods presented.
Net Loss Per Share	Net Loss Per Share Basic net loss per share attributable to common stockholders is computed by dividing net loss attributable to common stockholders by the weighted-average common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted 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 and potentially dilutive securities outstanding for the period. For the years ended December 31, 2022 and 2021, diluted net loss per share attributable to common stockholders is equal to basic net loss per share attributable to common stockholders as common stock equivalent shares from stock options and warrants were anti-dilutive. The following table sets forth outstanding potentially dilutive shares that have been excluded from the calculation of diluted net loss per share attributable to common stockholders because of their anti-dilutive effect (in common stock equivalents): Years Ended December 31, 2022 2021 Common stock options issued and outstanding 118,166 116,311 Warrants to purchase common stock 4,876,639 1,186,307 Total anti-dilutive shares 4,994,805 1,302,618
Common Stock Valuations	Common Stock Valuations Prior to the Merger, Private Histogen was required to periodically estimate the fair value of common stock with the assistance of an independent third-party valuation expert when issuing stock options and computing its estimated stock-based compensation expense. The assumptions underlying these valuations represented management’s best estimates, which involved inherent uncertainties and the application of significant levels of management judgment. In order to determine the fair value, Private Histogen considered, among other things, contemporaneous valuations of its common stock, business, financial condition and results of operations, including related industry trends affecting its operations; the likelihood of achieving various liquidity events; the lack of marketability of its common stock; the market performance of comparable publicly traded companies; and U.S. and global economic and capital market conditions.
Stock-Based Compensation	Stock-Based Compensation Service-Based Awards The Company recognizes stock-based compensation expense for service-based stock options and restricted stock units (“RSUs”) over the requisite service period on a straight-line basis. Employee and director stock-based compensation for service-based stock options is measured based on estimated fair value as of the grant date using the Black-Scholes option pricing model. The Company estimates the fair value of RSUs based on the closing price of the Company’s common stock on the date of issuance. The Company uses the following assumptions for estimating fair value of service-based option grants: Fair Value of Common Stock – The fair value of common stock underlying the option grant is determined based on observable market prices of the Company’s common stock. Expected Volatility – Volatility is a measure of the amount by which the Company’s share price has historically fluctuated or is expected to fluctuate (i.e., expected volatility) during a period. Due to the lack of an adequate history of a public market for the trading of the Company’s common stock and a lack of adequate company-specific historical and implied volatility data, volatility has been estimated and based on the historical volatility of a group of similar companies that are publicly traded. For these analyses, the Company has selected companies with comparable characteristics, including enterprise value, risk profiles, and position within the industry, and with historical share price information sufficient to meet the expected term of the stock-based awards. Expected Term – This is the period of time during which the options are expected to remain unexercised. Options have a maximum contractual term of ten years. The Company estimates the expected term of stock options using the “simplified method”, whereby the expected term equals the average of the vesting term and the original contractual term of the underlying option. Risk-Free Interest Rate – This is the observed yield on zero-coupon U.S. Treasury securities, as of the day each option is granted, with a term that most closely resembles the expected term of the option. Expected Forfeiture Rate – Forfeitures are recognized as they occur. Performance-Based Options Stock-based compensation expense for performance-based options is recognized based on amortizing the fair market value as of the grant date over the periods during which the achievement of the performance is probable. Performance-based options require certain performance conditions to be achieved in order for these options to vest. These options vest on the date of achievement of the performance condition. Market-Based Options Stock-based compensation expense for market-based options is recognized on a straight-line basis over the derived service period, regardless of whether the market condition is satisfied. Market-based options subject to market-based performance targets require achievement of the performance target in order for these options to vest. The Company estimates the fair value of market-based options as of the grant date and expected term using a Monte Carlo simulation that incorporates option-pricing inputs covering the period from the grant date through the end of the derived service period.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2020, the FASB issued ASU No. 2020-06, Debt – Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging – Contracts in Entity’s Own Equity (Subtopic 815-40) (“ASU 2020-06”). This new guidance is intended to simplify the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts on an entity’s own equity. Entities may adopt ASU 2020-06 using either a partial retrospective or fully retrospective method of transition. This ASU is effective for public business entities for fiscal years beginning after December 15, 2021, including interim periods within those fiscal years, with early adoption permitted. The Company adopted ASU 2020-06 on January 1, 2022, utilizing the modified retrospective method. The adoption of this standard did not result in an adjustment and did not have a material impact on the Company’s consolidated financial statements or related disclosures. In May 2021, the FASB issued ASU No. 2021-04, Earnings Per Share (Topic 260), Debt — Modifications and Extinguishments (Subtopic 470-50), Compensation — Stock Compensation (Topic 718), and Derivatives and Hedging — Contracts in Entity’s Own Equity (Subtopic 815-40): Issuer’s Accounting for Certain Modifications or Exchanges of Freestanding Equity-Classified Written Call Options (“ASU 2021-04”). The amendments in ASU 2021-04 provide guidance to clarify and reduce diversity in an issuer’s accounting for modifications or exchanges of freestanding equity-classified written call options (for example, warrants) that remain equity classified after modification or exchange. The accounting standard update is effective for fiscal years beginning after December 15, 2021. On January 1, 2022, the Company adopted ASU 2021-04. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements or related disclosures. In November 2021, the FASB issued ASU No. 2021-10, Government Assistance (Topic 832): Disclosure by Business Entities about Government Assistance (“ASU 2021-10”), which improves the transparency of government assistance received by certain business entities by requiring the disclosure of (1) the types of government assistance received; (2) the accounting for such assistance, and (3) the effect of the assistance on the business entity’s financial statements. ASU 2021-10 is effective for fiscal years beginning after December 15, 2021, with early adoption permitted. The Company adopted ASU 2021-10 on January 1, 2022. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements or related disclosures.
Description of Business	Description of Business Histogen Inc. (the “Company,” “Histogen,” “we,” or the “combined company”), formerly known as Conatus Pharmaceuticals Inc. (“Conatus”), was incorporated in the state of Delaware on July 13, 2005. The Company is a clinical-stage therapeutics company initially focused on developing potential first-in-class clinical and preclinical small molecule pan-caspase and caspase selective inhibitors that protect the body’s natural process to restore immune function.
Merger between Private Histogen and Conatus Pharmaceuticals Inc. and Name Change	Merger between Private Histogen and Conatus Pharmaceuticals Inc. and Name Change On January 28, 2020, the Company, then operating as Conatus, entered into an Agreement and Plan of Merger and Reorganization, as amended (the “Merger Agreement”), with privately-held Histogen, Inc. (“Private Histogen”) and Chinook Merger Sub, Inc., a wholly-owned subsidiary of the Company (“Merger Sub”). Under the Merger Agreement, Merger Sub merged with and into Private Histogen, with Private Histogen surviving as a wholly-owned subsidiary of the Company (the “Merger”). On May 26, 2020, the Merger was completed. Conatus changed its name to Histogen Inc., and Private Histogen, which remains as a wholly-owned subsidiary of the Company, changed its name to Histogen Therapeutics Inc. On May 27, 2020, the combined company’s common stock began trading on The Nasdaq Capital Market under the ticker symbol “HSTO”.
Reverse Stock Split	Reverse Stock Split On June 2, 2022, the Company’s Board of Directors approved a one-for- twenty reverse stock split of its then outstanding common stock (the “Reverse Stock Split”) with any fractional shares resulting from the Reserve Stock Split rounded down to the next whole share of common stock. The par value and the authorized shares of the common stock were not adjusted as a result of the Reverse Stock Split. All references to share and per share amounts for all periods presented in the consolidated financial statements have been retrospectively restated to reflect this Reverse Stock Split. Additionally, all rights to receive shares of common stock under outstanding warrants, options, and restricted stock units (“RSUs”) were adjusted to give effect of the reverse stock split. Furthermore, remaining shares of common stock available for future issuance under stock-based payment award plans and employee stock purchase plans were adjusted to give effect to the Reverse Stock Split.
Liquidity and Going Concern Uncertainty	Liquidity and Going Concern Uncertainty The Company has incurred operating losses and negative cash flows from operations and had an accumulated deficit of $ 88.3 million as of December 31, 2022. The Company expects operating losses and negative cash flows from operations to continue for the foreseeable future. As of December 31, 2022 , the Company had $ 12.1 million in cash and cash equivalents, which will not be sufficient to sustain its operations. The Company has not yet established ongoing sources of revenues sufficient to cover its operating costs and will need to continue to raise additional capital to support its future operating activities, including progression of its development programs, preparation for potential commercialization, and other operating costs. Management’s plans with regard to these matters include entering into a combination of additional debt or equity financing arrangements, strategic partnerships, collaboration and licensing arrangements, or other similar arrangements. There can be no assurance that the Company will be able to obtain additional financing on terms acceptable to the Company, on a timely basis or at all. The consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. Based on the current business plan and operating budget, there is substantial doubt about the Company’s ability to continue as a going concern within one year from the date the consolidated financial statements are issued. The consolidated financial statements do not include any adjustments to reflect the possible future effects on the recoverability and classification of assets or the amounts and classification of liabilities that may result from the outcome of this uncertainty.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2022
Accounting Policies [Abstract]
Summary of Outstanding Potentially Dilutive Shares Excluded in Calculation of Diluted Net Loss Per Share	The following table sets forth outstanding potentially dilutive shares that have been excluded from the calculation of diluted net loss per share attributable to common stockholders because of their anti-dilutive effect (in common stock equivalents): Years Ended December 31, 2022 2021 Common stock options issued and outstanding 118,166 116,311 Warrants to purchase common stock 4,876,639 1,186,307 Total anti-dilutive shares 4,994,805 1,302,618

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2022
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net, consisted of the following (in thousands): December 31, 2022 2021 Lab and manufacturing equipment $ 937 $ 943 Office furniture and equipment 225 42 Software 48 48 Total 1,210 1,033 Less: accumulated depreciation and amortization ( 774 ) ( 634 ) Property and equipment, net $ 436 $ 399

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	12 Months Ended
	Dec. 31, 2022
Balance Sheet Related Disclosures [Abstract]
Summary of Prepaid and Other Current Assets	Prepaid and other current assets consist of the following (in thousands): December 31, 2022 2021 Insurance $ 626 $ 691 Tenant improvement reimbursement receivable — 1,057 Prepaid rent 81 132 Pre-clinical and clinical related expenses 64 158 Prepaid materials — 138 Other 77 183 Total $ 848 $ 2,359
Summary of Other Assets	Other assets consist of the following (in thousands): December 31, 2022 2021 Insurance $ 513 $ 732 Cell bank material — 61 Other 10 12 Total $ 523 $ 805
Summary of Accrued Liabilities	Accrued liabilities consist of the following (in thousands): December 31, 2022 2021 Current portion of finance lease liabilities $ 9 $ 9 Accrued compensation 160 346 Clinical study related expenses 150 103 Legal fees 44 144 Accrued franchise tax 162 18 Other 70 171 Total $ 595 $ 791

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2022
Equity [Abstract]
Summary of Stock Option Activity	The following summarizes activity related to the Company’s stock options under the 2017 Plan and the 2020 Plan for the year ended December 31, 2022: Options Weighted- Weighted- Aggregate Outstanding at December 31, 2021 111,418 $ 37.62 6.78 $ — Granted 67,300 4.54 Cancelled / Forfeited ( 65,439 ) 31.83 Outstanding at December 31, 2022 113,279 21.30 8.09 $ — Vested and exercisable at December 31, 2022 41,101 $ 39.60 6.54 $ —
Summary of Valuation of Stock Option Awards	The following weighted-average assumptions were used to calculate the fair value of awards granted to employees, non-employees and directors: Years Ended December 31, 2022 2021 Expected volatility 78.95 % 78.69 % Risk-free interest rate 2.14 % 0.85 % Expected option life (in years) 6.02 6.08 Expected dividend yield —% —%
Summary of Compensation Cost Included in the Company's Consolidated Statements of Operations for Stock-based Compensation Arrangements	The compensation cost that has been included in the Company’s consolidated statements of operations for all stock-based compensation arrangements is detailed as follows (in thousands): Years Ended December 31, 2022 2021 General and administrative $ 470 $ 520 Research and development 32 184 Total $ 502 $ 704
Summary of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance is as follows: December 31, 2022 2021 Common stock warrants 4,876,639 1,186,307 Common stock options issued and outstanding 118,166 116,311 Common stock available for issuance under stock plan 100,577 2,309 5,095,382 1,304,927

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
Summary of Lease Assets and Lease Liabilities	The Company’s lease assets and lease liabilities were as follows (in thousands): December 31, Balance Sheet 2022 2021 Assets Operating lease Right-of-use asset $ 4,658 $ 4,432 Finance lease Property and equipment, net 12 20 Total lease assets $ 4,670 $ 4,452 Liabilities Current Operating lease liability Current portion of lease liability $ 238 $ 127 Finance lease liability Accrued liabilities 9 9 Total current liabilities 247 136 Noncurrent Operating lease liability Noncurrent portion of lease liability 4,379 4,617 Finance lease liability Other liabilities 5 14 Total noncurrent liabilities 4,384 4,631 Total lease liabilities $ 4,631 $ 4,767
Summary of Components of Lease Expense	The components of lease expense were as follows (in thousands): Years Ended December 31, Statement of Operations 2022 2021 Operating lease cost: Research and development $ 597 $ 210 General and administrative 694 428 Total operating lease cost $ 1,291 $ 638 Finance lease cost: Amortization of fixed assets Property and equipment, net $ 8 $ 9 Interest on lease liabilities Interest expense 1 3 Total finance lease cost $ 9 $ 12
Summary of Supplemental Cash Flow Information Related to Leases	Supplemental cash flow information related to leases were as follows (in thousands): Years Ended December 31, 2022 2021 Cash paid for amounts included in the measurement Operating cash flows from operating lease $ ( 78 ) $ 111 Operating cash flows from finance lease 1 3 Financing cash flows from finance lease 9 9
Schedule of Future Minimum Payments of Lease Liabilities	At December 31, 2022, future minimum payments of lease liabilities were as follows (in thousands): Operating Finance 2023 $ 780 $ 10 2024 803 5 2025 827 — 2026 853 — Thereafter 4,330 — Total minimum lease payments 7,593 15 Less: imputed interest ( 2,976 ) ( 1 ) Total future minimum lease payments 4,617 14 Less: current obligations under leases ( 238 ) ( 9 ) Noncurrent lease obligations $ 4,379 $ 5 Material Contracts Pfizer Inc. In July 2010, Conatus entered into a Stock Purchase Agreement with Pfizer, pursuant to which it acquired all of the outstanding capital stock of Idun Pharmaceuticals, Inc., which was subsequently spun off to Conatus stockholders in January 2013. Under the stock purchase agreement, the Company may be required to make payments to Pfizer totaling $ 18.0 million upon the achievement of specified regulatory milestones. In accordance with authoritative guidance, amounts for the milestone payments will be recognized when it is probable that the related contingent liability has been incurred and the amount owed is reasonably estimated. No amounts for the milestone payments have been recorded during the years ended December 31, 2022 and 2021. Prior to the termination of the Collaboration Agreement with Amerimmune on November 28, 2022, the obligations pursuant to the Stock Purchase Agreement were the responsibility of our former collaboration partner, Amerimmune. In accordance with authoritative guidance, amounts for the milestone payments will be recognized when it is probable that the related contingent liability has been incurred and the amount owed is reasonably estimated. No amounts for the milestone payments have been recorded during the year ended December 31, 2022 .

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Summary of Reconciliation of Income Taxes Computed using Statutory U.S. Income Tax Rate and Provision	The reconciliation of income taxes computed using the statutory U.S. income tax rate and the provision is as follows (in thousands): Years Ended December 31, 2022 2021 Tax computed at federal statutory rate $ ( 2,235 ) $ ( 3,152 ) State tax, net of federal tax benefits ( 5 ) ( 908 ) Tax credits ( 368 ) ( 325 ) Valuation allowance 1,825 5,320 PPP loan forgiveness — ( 126 ) Other 783 ( 809 ) Provision for income taxes $ — $ —
Components of Company's Deferred Tax Assets	Significant components of the Company’s net deferred tax assets are as follows (in thousands): Years Ended December 31, 2022 2021 Deferred tax assets: Tax loss carryforward $ 19,250 $ 18,041 R&D credits and other tax credits 2,201 1,834 Stock-based compensation 132 152 Compensation 26 58 Deferred revenue 4 5 Lease liability 970 1,283 Capitalized research and development 1,992 2,607 Section 174 1,056 — Other 33 80 Total deferred tax assets 25,664 24,060 Less: valuation allowance ( 24,686 ) ( 22,861 ) Deferred tax assets, net 978 1,199 Deferred tax liability: Right-of-use assets ( 978 ) ( 1,199 ) Net deferred tax assets $ — $ —
Summary of Activity Related to Unrecognized Tax Benefits	The following table summarizes the activity related to our unrecognized tax benefits (in thousands): Years Ended December 31, 2022 2021 Gross unrecognized tax benefits at the beginning of $ 683 $ 561 Additions from tax positions taken in the current year 133 118 Additions from tax positions taken in prior years — 4 Reductions for tax positions from prior year — — Gross unrecognized tax benefits at end of the year $ 816 $ 683

Organization and Nature of Op_2

Organization and Nature of Operations - Additional Information (Detail) $ in Thousands		12 Months Ended
	Jun. 02, 2022	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Description of Organization and Nature of Operations [Line Items]
Reverse stock split description		one-for-twenty
Reverse stock split conversion ratio	0.20
Accumulated deficit		$ (88,273)	$ (77,652)
Cash and cash equivalents		$ 12,109	$ 18,685

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)		1 Months Ended	12 Months Ended
	Dec. 16, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Dec. 31, 2022 USD ($) Segment shares	Dec. 31, 2021 USD ($) shares	Jan. 26, 2017 USD ($) shares
Summary Of Significant Accounting Policies [Line Items]
Percentage ownership not considered variable interest entity			100%
Number of operating segment | Segment			1
Impairment to long-lived assets			$ 0	$ 0
EPS unpaid services			$ 300,000
Shares issued | shares			0	0
Income tax expense benefit			$ 0	$ 0
U.S. Department of Defense ("DoD") [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable from customer			100,000	200,000
Grant funding obtained		$ 2,000,000
Grant award expiration period		2025-09
Qualifying expenses incurred			$ 600,000	700,000
Furniture and All Equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets			5 years
Software [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets			3 years
Customer Concentration Risk | One Customer [Member]
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable from customer			$ 0	$ 0
Revenue Benchmark | Customer Concentration Risk | One Customer [Member]
Summary Of Significant Accounting Policies [Line Items]
Percentage of revenues			100%	88%
Settlement Agreement [Member]
Summary Of Significant Accounting Policies [Line Items]
Variable interest entity, ownership percentage			50%
Cash paid					$ 50,000
Share repurchases, description			The Company was required to repurchase the shares at the greater of the remaining balance due of approximately $0.3 million and the market price of the shares at the time of repurchase, but in no event later than December 31, 2021. The Company had the sole option to repurchase the shares (which were converted from Series D convertible preferred stock into shares of common stock upon the Merger) at any time on or before December 31, 2021.
Share repurchases, value	$ 300,000			$ 300,000
Repurchase of common stock in cash | shares	717
Settlement Agreement [Member] | Series D Convertible Preferred Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Shares issued | shares					717

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Shares Excluded in Calculation of Diluted Net Loss Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	4,994,805	1,302,618
Common stock options issued and outstanding [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	118,166	116,311
Warrants to purchase common stock [Member] | Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	4,876,639	1,186,307

Inventories - Additional Inform

Inventories - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Inventory [Line Items]
Write-off of inventory	$ 61
Cell bank inventory		$ 61

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,210	$ 1,033
Less: accumulated depreciation and amortization	(774)	(634)
Property and equipment, net	436	399
Lab and Manufacturing Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	937	943
Office Furniture and Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	225	42
Software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 48	$ 48

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 140	$ 97
Property and equipment disposed		$ 1,400

Balance Sheet Details - Summary

Balance Sheet Details - Summary of Prepaid and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Insurance	$ 626	$ 691
Tenant improvement reimbursement receivable		1,057
Prepaid rent	81	132
Pre-clinical and clinical related expenses	64	158
Prepaid materials		138
Other	77	183
Total	$ 848	$ 2,359

Balance Sheet Details - Summa_2

Balance Sheet Details - Summary of Other Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Insurance	$ 513	$ 732
Cell bank material		61
Other	10	12
Total	$ 523	$ 805

Balance Sheet Details - Summa_3

Balance Sheet Details - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Current portion of finance lease liabilities	$ 9	$ 9
Accrued compensation	160	346
Clinical study related expenses	150	103
Legal fees	44	144
Accrued franchise tax	162	18
Other	70	171
Total	$ 595	$ 791

Revenue - Additional Informatio

Revenue - Additional Information (Detail)	1 Months Ended					12 Months Ended
	Mar. 31, 2022 USD ($)	Sep. 30, 2021 USD ($)	Jan. 31, 2020 USD ($) kg	Mar. 31, 2019 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Disaggregation of Revenue [Line Items]
Revenue						$ 3,769,000	$ 1,032,000
Deferred revenue						100,000	100,000
2017 Allergan Agreement [Member]
Disaggregation of Revenue [Line Items]
Cash payment received					$ 11,000,000
Potential additional payments					5,500,000
2019 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
One-time payment				$ 7,500,000
Remaining life of the patent				9 years
2020 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
Remaining life of the patent			9 years
Revenue		$ 600,000				0
Up front payment received			$ 1,000,000
Additional quantity of product to be supplied | kg			200
Revenue related to Potential Future Improvements			$ 200,000
Revenue recognized						19,000	19,000
2022 Allergan Letter Agreement [Member]
Disaggregation of Revenue [Line Items]
Potential milestone payment					5,500,000
Potential milestone payment recognized	$ 3,800,000
Product [Member]
Disaggregation of Revenue [Line Items]
Revenue							892,000
Product [Member] | 2017 Allergan Agreement [Member] | Minimum [Member]
Disaggregation of Revenue [Line Items]
Sales target for additional potential payment payout					60,000,000
Product [Member] | 2022 Allergan Letter Agreement [Member] | Minimum [Member]
Disaggregation of Revenue [Line Items]
Sales target for potential milestone payment					$ 60,000,000
License [Member]
Disaggregation of Revenue [Line Items]
Revenue						3,769,000	27,000
License [Member] | 2019 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
Revenue				$ 7,500,000
License [Member] | 2020 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
Revenue			$ 900,000
License [Member] | 2022 Allergan Letter Agreement [Member]
Disaggregation of Revenue [Line Items]
Revenue						3,800,000
Grant [Member]
Disaggregation of Revenue [Line Items]
Revenue						$ 0	$ 113,000

Debt - Additional Information (

Debt - Additional Information (Detail) - Paycheck Protection Program [Member] - USD ($) $ in Millions				1 Months Ended
	May 21, 2021	Jun. 05, 2020	Jun. 04, 2020	Apr. 30, 2020
Debt Instrument [Line Items]
Loan proceeds received				$ 0.5
Loan forgiveness period		168 days	56 days
Deferral period of principal and interest payments extended term		10 months	6 months
Required amount of payroll expenditures, percentage		60%	75%
Existing loans maturity period		5 years	2 years
Other Income [Member]
Debt Instrument [Line Items]
Loan forgiveness amount	$ 0.5

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock - Additional Information (Details) $ / shares in Units, $ in Thousands		1 Months Ended			12 Months Ended
	Apr. 14, 2022 Vote $ / shares	Jun. 29, 2022 USD ($) $ / shares shares	Mar. 31, 2022 USD ($) $ / shares shares	Jul. 31, 2020 shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2016 $ / shares
Redeemable Convertible Preferred Stock [Line Items]
Issuance of common stock, net of issuance costs, shares | shares				3,348
Preferred stock, stated value per share					$ 0.0001	$ 0.0001
Proceeds from the issuance of common stock, net of issuance costs | $					$ 4,405	$ 20,738
Expected volatility					78.95%	78.69%
Risk-free interest rate					2.14%	0.85%
Expected term					6 years 7 days	6 years 29 days
Common stock reserved for issuance | shares					5,095,382	1,304,927
Redemption payment by the Company | $					$ 488
Common stock, par value					$ 0.0001	$ 0.0001
March 2022 Offering [Member]
Redeemable Convertible Preferred Stock [Line Items]
Offering price per share			$ 25
Warrant purchase percentage			7%
Warrants to purchase common stock | shares			17,501
Exercise price percentage			125%
Warrants exercisable expiration period			5 years 6 months
Warrant issuance date			Sep. 25, 2022
Common stock reserved for issuance | shares					17,501
Exercise price of warrant per share			$ 25
March 2022 Offering [Member] | Black-Scholes Option Pricing Model [Member]
Redeemable Convertible Preferred Stock [Line Items]
Aggregate value of warrants | $			$ 34
March 2022 Offering [Member] | Placement Agent Warrants [Member] | Black-Scholes Option Pricing Model [Member]
Redeemable Convertible Preferred Stock [Line Items]
Expected volatility			78.90%
Risk-free interest rate			2.40%
Expected dividend yield			0%
Expected term			5 years 6 months
Preferred Stock [Member]
Redeemable Convertible Preferred Stock [Line Items]
Preferred stock, stated value per share		$ 1,000			$ 1,000
Proceeds from the issuance of common stock, net of issuance costs | $		$ 5,250
Proceeds held in escrow | $		$ 4,760
Preferred Stock, Redemption Terms					(i) the earlier of (1) the receipt of authorized stockholder approval for the reverse stock split and (2) the date that was 90 days following the Original Issue Date of March 25, 2022, and (ii) before the date that was 120 days after the Original Issue Date or July 23, 2022 (the “Redemption Period”)
Preferred stock redemption percentage of stated value per share		105%			105%
Redemption payment by the Company | $		$ 500
Accretion of Preferred Stock to its redemption value recorded as a reduction to additional paid-in capital. | $		1,100
Deemed dividend related to the accretion of the discount and redemption feature | $		$ 500
Preferred Stock [Member] | March 2022 Offering [Member]
Redeemable Convertible Preferred Stock [Line Items]
Preferred stock, stated value per share			$ 1,000
Percentage of original issue discount			5%
Proceeds from the issuance of common stock, net of issuance costs | $			$ 4,760
Closing date			Mar. 25, 2022
Proceeds held in escrow | $			$ 4,760
Fair value recognized | $			4,760
Placement agent's fees and other offering expenses | $			$ 600
Common Stock [Member]
Redeemable Convertible Preferred Stock [Line Items]
Issuance of common stock, net of issuance costs, shares | shares					1,774,309	1,410,600
Exercise price of warrant per share					$ 1,486		$ 461.60
Series A Redeemable Convertible Preferred Stock [Member] | Preferred Stock [Member] | March 2022 Offering [Member]
Redeemable Convertible Preferred Stock [Line Items]
Issuance of common stock, net of issuance costs, shares | shares			2,500
Preferred stock, stated value per share			$ 0.0001
Offering price per share			$ 952.38
Series A Preferred Stock [Member]
Redeemable Convertible Preferred Stock [Line Items]
Preferred stock, stated value per share	$ 1,000				1,000
Conversion price per share					$ 20
Number of votes per each share | Vote	3,776
Preferred stock, NASDAQ minimum price	$ 0.2648
Preferred stock, voting rights description					Each share of Series A Preferred Stock outstanding on April 14, 2022 (the “Record Date”) had a number of votes equal to the number of shares of Common Stock issuable upon conversion of such share (whether or not such shares are then convertible). Accordingly, as of the Record Date, each share of Series A Preferred Stock had 3,776 votes, which is determined by dividing $1,000, the stated value of one share of Series A Preferred Stock, by $0.2648, the NASDAQ Minimum Price as of the closing on March 25, 2022. The holders of the Series A Preferred Stock agreed to not transfer their shares of Series A Preferred Stock until after the Annual Meeting and to vote all shares of Series A Preferred Stock in favor of the Reverse Stock Split Proposal.
Series A Preferred Stock [Member] | Preferred Stock [Member]
Redeemable Convertible Preferred Stock [Line Items]
Preferred stock redeemed | shares		2,500
Redeemable convertible preferred stock, shares outstanding | shares					0
Series A Preferred Stock [Member] | Preferred Stock [Member] | March 2022 Offering [Member]
Redeemable Convertible Preferred Stock [Line Items]
Issuance of common stock, net of issuance costs, shares | shares			125,000
Preferred stock, stated value per share			$ 1,000
Conversion price per share			$ 20
Series A Preferred Stock [Member] | Common Stock [Member]
Redeemable Convertible Preferred Stock [Line Items]
Percentage of aggregate votes cast on reverse stock split voted in favor thereof	70%
Percentage of aggregate votes cast on reverse stock split voted against	30%
Convertible preferred stock conversion in to common stock | shares					125,000
Series B Redeemable Convertible Preferred Stock [Member] | Preferred Stock [Member] | March 2022 Offering [Member]
Redeemable Convertible Preferred Stock [Line Items]
Issuance of common stock, net of issuance costs, shares | shares			2,500
Preferred stock, stated value per share			$ 0.0001
Offering price per share			$ 952.38
Series B Preferred Stock [Member]
Redeemable Convertible Preferred Stock [Line Items]
Preferred stock, stated value per share					$ 1,000
Conversion price per share					$ 20
Preferred stock, voting rights description					Each share of Series B Preferred Stock outstanding on the Record Date entitled the holder thereof to cast 30,000 votes on the Reverse Stock Split Proposal. The holders of the Series B Preferred Stock agreed to not transfer their shares of Series B Preferred Stock until after the Annual Meeting and to vote all shares of Series B Preferred Stock in the same proportion as the aggregate shares of Common Stock and Series A Preferred Stock are voted on the Reverse Stock Split Proposal.
Number of votes on reverse stock split | Vote	30,000
Series B Preferred Stock [Member] | Preferred Stock [Member]
Redeemable Convertible Preferred Stock [Line Items]
Preferred stock redeemed | shares		2,500
Redeemable convertible preferred stock, shares outstanding | shares					0
Series B Preferred Stock [Member] | Preferred Stock [Member] | March 2022 Offering [Member]
Redeemable Convertible Preferred Stock [Line Items]
Issuance of common stock, net of issuance costs, shares | shares			125,000
Preferred stock, stated value per share			$ 1,000
Conversion price per share			$ 20
Series B Preferred Stock [Member] | Common Stock [Member]
Redeemable Convertible Preferred Stock [Line Items]
Percentage of aggregate votes cast on reverse stock split voted in favor thereof	70%
Percentage of aggregate votes cast on reverse stock split voted against	30%
Convertible preferred stock conversion in to common stock | shares					125,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)

1 Months Ended

12 Months Ended

Jul. 12, 2022

Nov. 08, 2021

May 26, 2020

Jan. 28, 2020

Jan. 24, 2019

Dec. 31, 2021

Jun. 30, 2021

Jan. 31, 2021

Jul. 31, 2020

May 31, 2020

Apr. 30, 2019

Dec. 31, 2022

Dec. 31, 2021

Dec. 31, 2020

Nov. 30, 2020

Dec. 18, 2017

Dec. 31, 2016

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs, shares

3,348

Proceeds from the issuance of common stock, net of issuance costs

$ 4,405,000

$ 20,738,000

Expected volatility

78.95%

78.69%

Risk-free interest rate

2.14%

0.85%

Expected term

6 years 7 days

6 years 29 days

Common stock reserved for issuance

1,304,927

5,095,382

1,304,927

Warrants to purchase common stock

1,186,307

4,876,639

1,186,307

Warrant expiration date

Jul. 03, 2023

Percentage of outstanding shares of common stock

5%

Vesting term

The RSUs vest in full upon the earlier of (1) 12 months following the grant date and (2) a change of control of the Company, as defined in the Company’s 2020 Plan, subject to continued service to the Company. Prior to RSU vesting, the Company and the RSU recipients mutually agreed to enter into RSU Cancellation Agreements such that the RSU awards shall no longer be outstanding. As of December 31, 2022, no restricted stock units remain outstanding.

Stock-based total compensation expense

$ 502,000

$ 704,000

Unrecognized compensation expense

$ 500,000

Weighted-average vesting term

2 years 3 months 14 days

Liquidity Option Shares [Member]

Class Of Stock [Line Items]

Vesting period

12 months

Number of fully vested options

2,426

Vesting percentage

25%

Vesting term

The vesting of the Liquidity Option Shares is divided into four separate tranches, each vesting 25% of the Liquidity Option Shares, upon: (1) the closing of the proposed merger with Conatus; (2) the date that the market capitalization of the Company exceeds $200.0 million; (3) the date that the market capitalization of the Company exceeds $275.0 million, and; (4) the date that the market capitalization of the Company exceeds $300.0 million. Each vesting tranche represents a unique derived service period and therefore stock-based compensation expense for each vesting tranche is recognized on a straight-line basis over its respective derived service period. Additionally, in the event that the Chief Executive Officer’s employment with the Company is terminated without cause or he resigns for good reason, an additional portion of the stock options award will vest equal to the number of such options which would have vested in the 12 months following the date of such termination.

Liquidity Option Shares [Member] | Share-based Payment Arrangement, Tranche One [Member]

Class Of Stock [Line Items]

Vesting percentage

40%

Liquidity Option Shares [Member] | Share-based Payment Arrangement, Tranche Two [Member]

Class Of Stock [Line Items]

Minimum market capitalization amount required for vesting

$ 200,000,000

Liquidity Option Shares [Member] | Share-based Payment Arrangement, Tranche Three [Member]

Class Of Stock [Line Items]

Minimum market capitalization amount required for vesting

275,000,000

Liquidity Option Shares [Member] | Share-based Payment Arrangement, Tranche Four [Member]

Class Of Stock [Line Items]

Minimum market capitalization amount required for vesting

$ 300,000,000

Market-Based Options [Member]

Class Of Stock [Line Items]

Stock-based total compensation expense

$ 0

Restricted Stock Units [Member]

Class Of Stock [Line Items]

Number of restricted stock units outstanding

0

Number of restricted stock units granted

23,423

Fair value per share

$ 14.58

Chief Executive Officer [Member] | Stock Options [Member]

Class Of Stock [Line Items]

Vesting period

36 months

Stock options issued

22,909

Vesting term

In accordance with the original award agreement, 40% of the options would vest immediately upon an initial public offering or 45 days following a change in control, as defined in the award agreement, while the remaining 60% are subject to vesting, of which 25% vest on the first anniversary of the grant date and then ratably over the remaining 36 months.

Chief Executive Officer [Member] | Stock Options [Member] | Share-based Payment Arrangement, Tranche One [Member]

Class Of Stock [Line Items]

Vesting percentage

40%

Remaining vesting percentage

25%

Chief Executive Officer [Member] | Stock Options [Member] | Share-based Payment Arrangement, Tranche Two [Member]

Class Of Stock [Line Items]

Vesting percentage

60%

2017 Plan [Member]

Class Of Stock [Line Items]

Number of common stock shares authorized to issue

41,861

Increase in number of common stock available for grant

16,336

Vesting period

4 years

Expiration period

10 years

2020 Stock Plan [Member]

Class Of Stock [Line Items]

Number of common stock shares authorized to issue

42,500

Expiration period

10 years

Conatus 2013 Plan [Member]

Class Of Stock [Line Items]

Stock options issued

0

Number of fully vested options

4,887

Weighted average exercise price of fully vested options

$ 859.59

July 2022 Offering [Member]

Class Of Stock [Line Items]

Proceeds from the issuance of common stock, net of issuance costs

$ 5,000,000

Combined purchase price of one share of common stock and accompanying warrant

$ 2.818

July 2022 Offering [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Gross proceeds from offering of warrants

$ 500,000

July 2022 Offering [Member] | Pre-funded Warrants [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

1,774,309

Exercise price of warrant per share

$ 0.0001

July 2022 Offering [Member] | Series A Warrant [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

1,774,309

Exercise price of warrant per share

$ 2.568

July 2022 Offering [Member] | Series B Warrant [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

1,774,309

Exercise price of warrant per share

$ 2.568

July 2022 Offering [Member] | Series A Warrants and Placement Agent Warrants [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Expected volatility

79.28%

Risk-free interest rate

3.06%

Expected dividend yield

0%

Expected term

5 years 6 months

July 2022 Offering [Member] | Series B Warrants and Placement Agent Warrants [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Expected volatility

74.25%

Risk-free interest rate

3.16%

Expected dividend yield

0%

Warrant exercisable period

1 year 6 months

Common Stock Purchase Agreement with Lincoln Park [Member]

Class Of Stock [Line Items]

Proceeds from the issuance of common stock, net of issuance costs

$ 1,000,000

$ 500,000

Aggregate dollar value of share purchase commitment

$ 10,000,000

Long-term purchase commitment, period

24 months

Number of common stock shares sold

16,425

15,000

Sale of common stock price per share

$ 60.88

Common Stock [Member]

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs, shares

1,774,309

1,410,600

Exercise price of warrant per share

$ 1,486

$ 461.60

Warrants to purchase common stock

68

Warrant expiration date

Jul. 31, 2021

Common Stock [Member] | December 2021 Offering [Member]

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs, shares

411,764

Warrants to purchase common stock

411,766

247,059

411,766

Offering price per share

$ 8.50

$ 8.50

Exercise price of warrant per share

$ 8.50

$ 8.50

$ 8.50

Warrants exercisable expiration period

5 years 6 months

Warrants exercised

0

Common stock reserved for issuance

164,707

Common Stock [Member] | Maximum [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

180

Common Stock [Member] | Black-Scholes Option Pricing Model [Member] | December 2021 Offering [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 100,000

$ 100,000

Expected volatility

79.81%

Risk-free interest rate

1.21%

Expected dividend yield

0%

Expected term

5 years 6 months

Common Stock [Member] | Placement Agent Warrants [Member] | December 2021 Offering [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

20,590

20,590

Percentage of warrant coverage

5%

Exercise price of warrant per share

$ 10.626

$ 10.626

$ 10.626

Warrants exercisable expiration period

5 years 6 months

Proceeds from the issuance of common stock, net of issuance costs

$ 3,500,000

Placement agent's fees and other offering expenses

$ 500,000

Common stock reserved for issuance

20,590

Common Stock [Member] | January 2021 Offering [Member]

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs, shares

336,060

Exercise price of warrant per share

$ 20

Proceeds from the issuance of common stock, net of issuance costs

$ 14,000,000

$ 6,800,000

Placement agent's fees and other offering expenses

$ 1,900,000

Common stock reserved for issuance

387,565

Issuance of common stock for warrant exercises, shares

336,060

Common Stock [Member] | January 2021 Offering [Member] | Public Offering of Common Stock [Member]

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs, shares

580,000

Warrants to purchase common stock

700,000

Exercise price of warrant per share

$ 20

Number of prefunded warrants to be issued

120,000

Combined purchase price of one share of common stock and accompanying warrant

$ 20

Combined purchase price of one pre-funded warrant and accompanying warrant

$ 19.998

Warrant exercisable period

5 years

Common Stock [Member] | January 2021 Offering [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 7,200,000

Common Stock [Member] | January 2021 Offering [Member] | Placement Agent Warrants [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

35,000

Exercise price of warrant per share

$ 25

$ 25

Common stock reserved for issuance

11,375

Warrant exercisable period

5 years

Common Stock [Member] | January 2021 Offering [Member] | Placement Agent Warrants [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 300,000

Expected volatility

80.08%

Risk-free interest rate

0.38%

Expected dividend yield

0%

Expected term

5 years

Common Stock [Member] | January 2021 Offering [Member] | Pre-funded Warrants [Member] | Public Offering of Common Stock [Member]

Class Of Stock [Line Items]

Exercise price of warrant per share

$ 0.002

Common Stock [Member] | June 2021 Offering [Member]

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs, shares

298,865

Warrants to purchase common stock

239,093

148,183

Offering price per share

$ 22

Percentage of warrant coverage

80%

Exercise price of warrant per share

$ 20

$ 20

Warrants exercisable expiration period

5 years 6 months

Warrants exercised

0

Common stock reserved for issuance

90,910

Common Stock [Member] | June 2021 Offering [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 3,000,000

Expected volatility

81.44%

Risk-free interest rate

0.88%

Expected dividend yield

0%

Expected term

5 years 6 months

Common Stock [Member] | June 2021 Offering [Member] | Placement Agent Warrants [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

14,946

Percentage of warrant coverage

5%

Exercise price of warrant per share

$ 27.50

$ 27.50

Warrants exercisable expiration period

5 years

Proceeds from the issuance of common stock, net of issuance costs

$ 6,600,000

Placement agent's fees and other offering expenses

900,000

Common stock reserved for issuance

14,946

Common Stock [Member] | June 2021 Offering [Member] | Placement Agent Warrants [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 200,000

Expected volatility

80.15%

Risk-free interest rate

0.77%

Expected dividend yield

0%

Expected term

5 years

Common Stock [Member] | July 2022 Offering [Member]

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs, shares

1,774,309

Exercise price of warrant per share

$ 2.568

Warrants exercised

0

Common stock reserved for issuance

3,996,418

Common Stock [Member] | July 2022 Offering [Member] | Private Placement [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

447,800

447,800

447,800

447,800

Offering price per share

$ 0.0316

Exercise price of warrant per share

$ 2.568

Warrant exercisable period

5 years 6 months

Common Stock [Member] | July 2022 Offering [Member] | Private Placement [Member] | Maximum [Member]

Class Of Stock [Line Items]

Exercise price of warrant per share

$ 34

$ 34

$ 34

$ 34

Warrant expiration date

Jun. 21, 2027

Common Stock [Member] | July 2022 Offering [Member] | Private Placement [Member] | Minimum [Member]

Class Of Stock [Line Items]

Exercise price of warrant per share

$ 8.50

$ 8.50

$ 8.50

$ 8.50

Warrant expiration date

May 18, 2026

Common Stock [Member] | July 2022 Offering [Member] | Placement Agent Warrants [Member]

Class Of Stock [Line Items]

Exercise price of warrant per share

$ 3.5225

Common stock reserved for issuance

124,202

Common Stock [Member] | July 2022 Offering [Member] | Placement Agent Warrants [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 200,000

Common Stock [Member] | July 2022 Offering [Member] | Pre-funded Warrants [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

1,774,309

Common Stock [Member] | July 2022 Offering [Member] | Series A Warrant [Member]

Class Of Stock [Line Items]

Warrants exercisable expiration period

5 years 6 months

Common Stock [Member] | July 2022 Offering [Member] | Series A Warrant [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 3,800,000

Common Stock [Member] | July 2022 Offering [Member] | Series B Warrant [Member]

Class Of Stock [Line Items]

Warrants exercisable expiration period

1 year 6 months

Common Stock [Member] | July 2022 Offering [Member] | Series B Warrants and Placement Agent Warrants [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 2,300,000

Amended Warrants [Member] | July 2022 Offering [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 1,000,000

Expected volatility

79.28%

Risk-free interest rate

3.06%

Expected dividend yield

0%

Expected term

5 years 6 months

Estimated Fair Value of Original Warrants Immediately Prior to Warrants Amendments [Member] | July 2022 Offering [Member] | Black-Scholes Option Pricing Model [Member] | Maximum [Member]

Class Of Stock [Line Items]

Expected volatility

83.34%

Risk-free interest rate

3.16%

Expected term

4 years 11 months 8 days

Estimated Fair Value of Original Warrants Immediately Prior to Warrants Amendments [Member] | July 2022 Offering [Member] | Black-Scholes Option Pricing Model [Member] | Minimum [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 500,000

Expected volatility

81.21%

Risk-free interest rate

3.06%

Expected dividend yield

0%

Expected term

3 years 10 months 2 days

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Stock Option Activity (Details) - 2017 and 2020 Plan [Member] - $ / shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Beginning balance	111,418
Number of Options, Granted	67,300
Number of Options, Cancelled / Forfeited	(65,439)
Number of Options, Ending balance	113,279	111,418
Number of Options, Vested and exercisable	41,101
Weighted-Average Exercise Price, Beginning balance	$ 37.62
Weighted-Average Exercise Price, Granted	4.54
Weighted-Average Exercise Price, Cancelled / Forfeited	31.83
Weighted-Average Exercise Price, Ending balance	21.30	$ 37.62
Weighted-Average Exercise Price, Vested and exercisable	$ 39.60
Weighted-Average Remaining Contractual Term Outstanding	8 years 1 month 2 days	6 years 9 months 10 days
Weighted-Average Remaining Contractual Term Outstanding, Vested and exercisable	6 years 6 months 14 days

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Valuation of Stock Option Awards (Detail)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected volatility	78.95%	78.69%
Risk-free interest rate	2.14%	0.85%
Expected option life (in years)	6 years 7 days	6 years 29 days

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Compensation Cost Included in the Company's Consolidated Statements of Operations for Stock-based Compensation Arrangements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	$ 502	$ 704
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	470	520
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	$ 32	$ 184

Stockholders' Equity - Summar_4

Stockholders' Equity - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2022	Dec. 31, 2021
Class Of Stock [Line Items]
Common stock warrants	4,876,639	1,186,307
Common stock available for issuance under stock plan	100,577	2,309
Total	5,095,382	1,304,927
Common Stock [Member]
Class Of Stock [Line Items]
Common stock warrants	68
Common stock options issued and outstanding	118,166	116,311

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended		12 Months Ended
	Jul. 31, 2020	Apr. 30, 2019	Dec. 31, 2022	Dec. 31, 2021	Mar. 01, 2020	Jul. 31, 2010
Operating Leased Assets [Line Items]
Lease commencement date			Mar. 01, 2020
Lease expiration date			Aug. 31, 2031
Lessee, operating lease, existence of option to extend			false
Rent abatement term			7 months
Tenant improvement allowance on modified lease			$ 2,200,000
Right-of-use asset			4,658,000	$ 4,432,000	$ 4,500,000
Operating lease liability			$ 4,617,000		$ 4,500,000
Operating lease remaining term			8 years 8 months 12 days
Finance lease remaining term			1 year 6 months
Operating lease weighted-average discount rate					12.20%
Finance lease weighted-average discount rate					10%
Issuance of preferred stock, shares	3,348
Issuance of preferred stock, value			$ 4,405,000	20,738,000
Accrued liabilities			0
Litigation and legal liability			0
Common Stock Purchase Agreement with Pfizer Inc. [Member]
Operating Leased Assets [Line Items]
Payment to related party						$ 18,000,000
Payment for milestone			0	0
Collaboration Agreement with Amerimmune [Member]
Operating Leased Assets [Line Items]
Payment for milestone			0
PUR Biologics, LLC [Member]
Operating Leased Assets [Line Items]
Upfront cash paid		$ 500,000
Amount forgiven		22,000
Repayments of outstanding payable assumed		23,000
Development Assets [Member]
Operating Leased Assets [Line Items]
Milestone and royalty payment obligations		$ 400,000
Percentage of royalties on net sales		5%
Development Assets [Member] | Commercialization Milestone [Member]
Operating Leased Assets [Line Items]
Milestone and royalty payment obligations		$ 400,000
Development Assets [Member] | Product [Member] | Estimated Sales [Member]
Operating Leased Assets [Line Items]
Revenue target for milestone achievement		$ 500,000
Series D Convertible Preferred Stock [Member] | Development Assets [Member] | PUR Biologics, LLC [Member]
Operating Leased Assets [Line Items]
Issuance of preferred stock, shares		8,366
Issuance of preferred stock, value		$ 1,750,000
Contingent Liability [Member]
Operating Leased Assets [Line Items]
Payment for milestone			$ 0	$ 0
Building Improvements [Member]
Operating Leased Assets [Line Items]
Extension of rent abatement			2 months
Increase (decrease) in operating lease liability			$ 400,000
Increase (decrease) in right-of-use-asset			400,000
Amendment [Member]
Operating Leased Assets [Line Items]
Tenant improvement allowance on modified lease			2,300,000
Increase (decrease) in operating lease liability			300,000
Increase (decrease) in right-of-use-asset			300,000
Letter of Credit [Member]
Operating Leased Assets [Line Items]
Security deposit			300,000
Letter of credit			300,000
Letter of Credit [Member] | Amendment [Member]
Operating Leased Assets [Line Items]
Letter of credit			400,000
Maximum [Member]
Operating Leased Assets [Line Items]
Tenant improvement allowance on modified lease			$ 2,200,000
Maximum [Member] | Development Assets [Member] | PUR Biologics, LLC [Member]
Operating Leased Assets [Line Items]
Potential cash payout		$ 6.25

Commitments and Contingencies_2

Commitments and Contingencies -Summary of Lease Assets and Lease Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Mar. 01, 2020
Leases [Abstract]
Right-of-use asset	$ 4,658	$ 4,432	$ 4,500
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Right-of-use asset	Right-of-use asset
Finance lease	$ 12	$ 20
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Property and equipment, net	Property and equipment, net
Total lease assets	$ 4,670	$ 4,452
Operating lease liability	$ 238	$ 127
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Operating lease liability	Operating lease liability
Finance lease liability	$ 9	$ 9
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued liabilities	Accrued liabilities
Total current liabilities	$ 247	$ 136
Operating lease liability	$ 4,379	$ 4,617
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Operating lease liability	Operating lease liability
Finance lease liability	$ 5	$ 14
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Finance lease liability	Finance lease liability
Total noncurrent liabilities	$ 4,384	$ 4,631
Total lease liabilities	$ 4,631	$ 4,767

Commitments and Contingencies_3

Commitments and Contingencies -Summary of Components of Lease Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Leases [Line Items]
Operating lease cost	$ 1,291	$ 638
Amortization of fixed assets	8	9
Interest on lease liabilities	1	3
Total finance lease cost	9	12
Research and Development [Member]
Leases [Line Items]
Operating lease cost	597	210
General and Administrative [Member]
Leases [Line Items]
Operating lease cost	$ 694	$ 428

Commitments and Contingencies_4

Commitments and Contingencies - Summary of Supplemental Cash Flow Information Related to Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating lease	$ (78)	$ 111
Operating cash flows from finance lease	1	3
Financing cash flows from finance lease	$ 9	$ 9

Commitments and Contingencies_5

Commitments and Contingencies - Schedule of Future Minimum Payments of Lease Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Mar. 01, 2020
Operating Lease
2023	$ 780
2024	803
2025	827
2026	853
Thereafter	4,330
Total minimum lease payments	7,593
Less: imputed interest	(2,976)
Total future minimum lease payments	4,617		$ 4,500
Less: current obligations under leases	(238)	$ (127)
Lease liabilities, non-current	4,379	4,617
Finance Lease
2023	10
2024	5
Total minimum lease payments	15
Less: imputed interest	(1)
Total future minimum lease payments	14
Less: current obligations under leases	(9)	(9)
Finance lease liability, non-current	$ 5	$ 14

Income Taxes - Summary of Recon

Income Taxes - Summary of Reconciliation of Income Taxes Computed using Statutory U.S. Income Tax Rate and Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Expense (Benefit), Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax computed at federal statutory rate	$ (2,235)	$ (3,152)
State tax, net of federal tax benefits	(5)	(908)
Tax credits	(368)	(325)
Valuation allowance	1,825	5,320
PPP loan forgiveness		(126)
Other	783	(809)
Provision for income taxes	$ 0	$ 0

Income Taxes - Components of Co

Income Taxes - Components of Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Tax loss carryforward	$ 19,250	$ 18,041
R&D credits and other tax credits	2,201	1,834
Stock-based compensation	132	152
Compensation	26	58
Deferred revenue	4	5
Lease liability	970	1,283
Capitalized research and development	1,992	2,607
Section 174	1,056
Other	33	80
Total deferred tax assets	25,664	24,060
Less: valuation allowance	(24,686)	(22,861)
Deferred tax assets, net	978	1,199
Deferred tax liability:
Right-of-use assets	$ (978)	$ (1,199)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Operating Loss Carryforwards [Line Items]
Deferred tax asset, change in valuation allowance amount	$ 1,800,000	$ 5,300,000
Cumulative change in ownership percentage	50%
Period for cumulative change in ownership percentage	3 years
Recognized interest or penalties on income tax	$ 0	$ 0
Federal [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	72,000,000
Operating loss carryforwards	41,300,000
Research credit carryforwards	$ 1,700,000
Research credit carryforwards expiration year	2027
Federal [Member] | Adaptive Biologix, Inc. [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 400,000
California [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	57,400,000
Operating loss carryforwards, expired	0
Research credit carryforwards	1,600,000
California [Member] | Adaptive Biologix, Inc. [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 400,000

Income Taxes - Summary of Activ

Income Taxes - Summary of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits at the beginning of the year	$ 683	$ 561
Additions from tax positions taken in the current year	133	118
Additions from tax positions taken in prior years		4
Reductions for tax positions from prior year		0
Gross unrecognized tax benefits at end of the year	$ 816	$ 683

Related Parties - Additional In

Related Parties - Additional Information (Detail) - Lordship Ventures Histogen Holdings LLC [Member] - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2012	Dec. 31, 2022	Dec. 31, 2021
Related Party Transaction [Line Items]
Percentage of outstanding voting shares controlled		2.80%	4.70%
Success Fee Agreement [Member]
Related Party Transaction [Line Items]
Minimum percentage of asset or equity engaged in merger or sale transaction	90%
Related party expense recognized		$ 375	$ 10
Allergan License Agreements [Member]
Related Party Transaction [Line Items]
Amount due to related parties		$ 10	$ 12
Private Histogen [Member] | Success Fee Agreement [Member]
Related Party Transaction [Line Items]
Description of related party transaction		In November 2012, Private Histogen entered into a Strategic Relationship Success Fee Agreement with Lordship (the “Success Fee Agreement”). The Success Fee Agreement causes certain payments to be made from the Company to Lordship equal to 1% of certain product revenues and 10% of certain license and royalty revenues generated from our Human Multipotent Cell Conditioned Media, or CCM, and our Human Extracellular Matrix, or hECM, in connection with the Company’s biologics technology platform. The Success Fee Agreement also stipulates that if the Company engages in a merger or sale of all or substantially all (defined as 90% or more) of its assets or equity to a third party, then the Company has the option to terminate the agreement by paying Lordship the fair market value of future payments with the minimum payment being at least equal to the most recent annual payments Lordship has received.
Private Histogen [Member] | Success Fee Agreement [Member] | Product Revenue [Member]
Related Party Transaction [Line Items]
Success fee percentage to be paid on certain product revenues	1%
Private Histogen [Member] | Success Fee Agreement [Member] | License and Royalty Revenue [Member]
Related Party Transaction [Line Items]
Success fee percentage to be paid on certain license and royalty revenues	10%