Histogen (HSTO) 10-Q 13 May 21 2021 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2021	May 06, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Trading Symbol	HSTO
Entity Registrant Name	Histogen Inc.
Entity Central Index Key	0001383701
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock, $0.0001 par value
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		35,751,957
Document Quarterly Report	true
Document Transition Report	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 21,743	$ 6,763
Restricted cash	10	10
Accounts receivable, net	188	144
Inventories	61	300
Prepaid and other assets	906	1,183
Total current assets	22,908	8,400
Property and equipment, net	248	271
Right-of-use assets	4,491	4,411
Other assets	1,166	1,931
Total assets	28,813	15,013
Current liabilities:
Accounts payable	496	539
Accrued liabilities	1,148	1,880
Current portion of lease liabilities	157	28
Payroll protection program loan, current	156	97
Financed insurance premiums, current		193
Current portion of deferred revenue	19	48
Total current liabilities	1,976	2,785
Payroll protection program loan, non-current	310	369
Lease liabilities, non-current	4,763	4,806
Noncurrent portion of deferred revenue	113	118
Other liabilities	20	22
Total liabilities	7,182	8,100
Commitments and contingencies (Note 10)
Stockholders’ Equity (Deficit)
Preferred stock, $0.0001 par value; 10,000,000 shares authorized at March 31, 2021 and December 31, 2020; no shares issued and outstanding at March 31, 2021 and December 31, 2020
Common stock, $0.0001 par value; 200,000,000 shares authorized at March 31, 2021 and December 31, 2020; 35,744,457 and 15,030,757 shares issued and outstanding at March 30, 2021 and December 31, 2020, respectively	4	1
Additional paid-in capital	89,554	70,561
Accumulated deficit	(66,972)	(62,702)
Total Histogen Inc. stockholders’ equity (deficit)	22,586	7,860
Noncontrolling interest	(955)	(947)
Total equity (deficit)	21,631	6,913
Total liabilities and stockholders’ equity (deficit)	$ 28,813	$ 15,013

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
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
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	35,744,457	15,030,757
Common stock, shares outstanding	35,744,457	15,030,757

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues:
Total revenues	$ 431,000	$ 978,000
Operating expenses:
Research and development	2,153,000	1,391,000
General and administrative	2,331,000	1,183,000
Total operating expenses	4,704,000	2,832,000
Loss from operations	(4,273,000)	(1,854,000)
Other income (expense):
Interest income (expense), net	(5,000)
Total other income (expense)	(5,000)
Net loss	(4,278,000)	(1,854,000)
Net loss attributable to noncontrolling interest	8,000	10,000
Net loss attributable to common stockholders	$ (4,270,000)	$ (1,844,000)
Net loss per share available to common stockholders, basic and diluted	$ (0.14)	$ (0.55)
Weighted-average number of common shares outstanding used to compute net loss per share, basic and diluted	31,571,676	3,343,357
Product [Member]
Revenues:
Total revenues	$ 306,000
Operating expenses:
Cost of Revenue	220,000	$ 161,000
Grant [Member]
Revenues:
Total revenues	113,000
License [Member]
Revenues:
Total revenues	$ 12,000	867,000
Professional Services [Member]
Revenues:
Total revenues		111,000
Operating expenses:
Cost of Revenue		$ 97,000

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	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, 2019	$ (37,968)			$ 6,864	$ (43,933)	$ (37,069)	$ (899)
Beginning balance, shares at Dec. 31, 2019		5,046,154
Beginning balance at Dec. 31, 2019		$ 39,070
Beginning balance, shares at Dec. 31, 2019			3,343,357
Share-based compensation expense	101			101		101
Net loss	(1,854)				(1,844)	(1,844)	(10)
Ending balance at Mar. 31, 2020	(39,721)			6,965	(45,777)	(38,812)	(909)
Ending balance, shares at Mar. 31, 2020		5,046,154
Ending balance at Mar. 31, 2020		$ 39,070
Ending balance, shares at Mar. 31, 2020			3,343,357
Beginning balance at Dec. 31, 2020	6,913		$ 1	70,561	(62,702)	7,860	(947)
Beginning balance, shares at Dec. 31, 2020			15,030,757
Issuance of common stock, net of issuance costs	11,955		$ 2	11,953		11,955
Issuance of common stock, net of issuance costs, shares			14,000,000
Issuance of common stock for warrant exercises	6,832		$ 1	6,831		6,832
Issuance of common stock for warrant exercises, shares			6,713,700
Share-based compensation expense	209			209		209
Net loss	(4,278)				(4,270)	(4,270)	(8)
Ending balance at Mar. 31, 2021	$ 21,631		$ 4	$ 89,554	$ (66,972)	$ 22,586	$ (955)
Ending balance, shares at Mar. 31, 2021			35,744,457

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Cash flows from operating activities
Net loss	$ (4,278)	$ (1,854)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	23	28
Stock-based compensation	209	101
Write-off of inventory		161
Changes in operating assets and liabilities:
Accounts receivable	(44)	(12)
Inventories	239	(277)
Prepaid expenses and other assets	1,042	88
Accounts payable	(43)	337
Accrued liabilities	(732)	336
Right-of-use asset and lease liabilities, net	6	54
Deferred revenue	(34)	133
Net cash (used in) operating activities	(3,612)	(905)
Cash flows from investing activities
Cash paid for acquisition related costs		(401)
Net cash (used in) investing activities		(401)
Cash flows from financing activities
Proceeds from sales of common stock, net of issuance costs	11,955
Proceeds from the exercise of warrants	6,832
Payments on financing of insurance premiums	(193)
Repayment of finance lease obligations	(2)	(2)
Net cash (used in) provided by financing activities	18,592	(2)
Net increase (decrease) in cash, cash equivalents and restricted cash	14,980	(1,308)
Cash, cash equivalents and restricted cash, beginning of period	6,773	2,075	$ 2,075
Cash, cash equivalents and restricted cash, end of period	21,753	767	6,773
Reconciliation of cash, cash equivalents and restricted cash to the consolidated balance sheets
Cash and cash equivalents	21,743	507	$ 6,763
Restricted cash	10	260
Total cash, cash equivalents and restricted cash	$ 21,753	767
Noncash investing and financing activities
Right-of-use asset obtained in exchange for operating lease liability		4,481
Acquisition related costs included in accounts payable		$ 482

Description of Business, Basis

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of Business, Basis of Presentation and Summary of Significant Accounting Policies	1. Description of Business, Basis of Presentation and Summary of Significant Accounting Policies Description of Business Histogen Inc. (the “Company,” “Histogen,” “we,” or the “combined company”), formerly known as Conatus Pharmaceuticals Inc. (“Conatus”) clinical-stage therapeutics company focused on developing potential first-in-class restorative therapeutics that ignite the body’s natural process to repair and maintain healthy biological function. The therapeutics are designed for aesthetic and therapeutic applications based upon the Company’s unique technology that utilizes proteins and growth factors produced by hypoxia-induced multipotent cells. The Company has a portfolio of product candidates derived from one core technology process without using embryonic stem cells or animal components. The Company’s product candidates are covered by patented technologies which focus on replacing and regenerating tissues in the body. The Company currently has two product candidates in development which utilizes our proprietary technology platform intended to potentially address what we believe to be underserved, multibillion-dollar global markets, HST-001, a treatment for hair loss, HST-003, a treatment for joint cartilage repair. In addition, we retained development and commercialization rights to emricasan, an asset previously developed by Conatus Pharmaceuticals Inc. (“Conatus”), which is being jointly developed with our collaboration partner, Amerimmune, for the potential treatment of COVID-19. 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”. Except as otherwise indicated, references herein to “Histogen,” the “Company,” “we,” or the “combined company”, refer to Histogen Inc. on a post-Merger basis, and the term “Private Histogen” refers to the business of privately-held Histogen Inc., prior to completion of the Merger. References to Conatus refer to Conatus Pharmaceuticals Inc. prior to completion of the Merger. Pursuant to the terms of the Merger Agreement, each outstanding share of Private Histogen common stock outstanding immediately prior to the closing of the Merger was converted into approximately 0.14342 shares of Company common stock (the “Exchange Ratio”), after taking into account the Reverse Stock Split, as defined below. Immediately prior to the closing of the Merger, all shares of Private Histogen preferred stock then outstanding were exchanged into shares of common stock of Private Histogen. In addition, all outstanding options exercisable for common stock of Private Histogen and warrants exercisable for common stock of Private Histogen became options and warrants exercisable for the same number of shares of common stock of the Company multiplied by the Exchange Ratio. Immediately following the Merger, stockholders of Private Histogen owned approximately 71.3% of the outstanding common stock of the combined company. The transaction was accounted for as a reverse asset acquisition in accordance with generally accepted accounting principles in the United States of America (“GAAP”). Under this method of accounting, Private Histogen was deemed to be the accounting acquirer for financial reporting purposes. This determination was primarily based on the facts that, immediately following the Merger: (i) Private Histogen’s stockholders owned a substantial majority of the voting rights in the combined company, (ii) Private Histogen designated a majority of the members of the initial board of directors of the combined company, and (iii) Private Histogen’s senior management holds all key positions in the senior management of the combined company. As a result, as of the closing date of the Merger, the net assets of the Company were recorded at their acquisition-date relative fair values in the accompanying condensed consolidated financial statements of the Company and the reported operating results prior to the Merger are those of Private Histogen. Reverse Stock Split and Exchange Ratio On May 26, 2020, in connection with, and prior to the completion of, the Merger, the Company effected a one-for-ten reverse stock split of its then outstanding common stock (the “Reverse Stock Split”). The par value and the authorized shares of the common stock were not adjusted as a result of the Reverse Stock Split. All of the Company’s issued and outstanding common stock have been retroactively adjusted to reflect this Reverse Stock Split for all periods presented. All issued and outstanding Private Histogen common stock, convertible preferred stock, options and warrants prior to the effective date of the Merger have been retroactively adjusted to reflect the Exchange Ratio for all periods presented. Liquidity and Going Concern From inception and through March 31, 2021 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, government funding, strategic partnerships, collaboration and licensing arrangements, or other similar arrangements. In addition, the Company may fund its losses from operations through the common stock purchase agreement the Company entered into with Lincoln Park in July 2020, for the purchase of up to $10.0 million of the Company’s common stock over the 24 month period of the purchase agreement, $8.5 million of which remains available for sale as of the date (See Note 9), subject to limitations on the amount of securities the Company may sell under its effective registration statement on Form S-3 within any 12 month period. The condensed 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. Basis of Presentation and Principles of Consolidation The condensed 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 hair stimulating complex (“HSC”). This is a wholly-owned subsidiary intended to pursue registration with the COFEPRIS (Mexico equivalent to FDA). CIMRESA had no operational or financial activity for the three months ended March 31, 2021 and 2020. 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 condensed consolidated financial statements. Unaudited Interim Financial Information The unaudited condensed consolidated financial statements for the three months ended March 31, 2021 and 2020 have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC) and Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and the disclosure of contingent assets and liabilities and contingencies at the date of the condensed 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, we continue to use the best information available to us in our critical 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, reserves for excess or obsolete inventory, stock-based compensation, 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. On January 12, 2018, AB was converted into a traditional C corporation, a Delaware corporation, under a Plan of Conversion agreement between the Company and the other member of the limited liability company, Wylde, LLC (“Wylde”). The entity structure change eliminated some of the special rights Wylde had under the LLC charter and gave the Company more control over the voting rights under the new corporate structure. The Plan of Conversion called for 3,800,000 common stock shares of AB to be issued to the Company and Wylde in proportion to their interest in the LLC immediately before the agreement was executed. Contemporaneously, the Company offered to purchase, and Wylde agreed to sell, 100,000 of the AB common shares for $1.00 per share for a total price of $0.1 million. The completion of this transaction among the stockholders of AB resulted in Histogen owning 2,600,000 common shares or approximately 68% of AB. 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 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 the issuer of its credit card accounts. 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 three months ended March 31, 2021 and 2020, one customer accounted for 72% and 100% of total revenues, respectively. Accounts receivable from the customer was $11 thousand and $0.1 million at March 31, 2021 and December 31, 2020, respectively. COVID-19 On January 30, 2020, the World Health Organization (“WHO”) announced a global health emergency because of a new strain of coronavirus originating in Wuhan, China (the “COVID-19 outbreak”) and the risks to the international community as the virus spreads globally beyond its point of origin. In March 2020, the WHO classified the COVID-19 outbreak as a pandemic, based on the rapid increase in exposure globally. The full impact of the COVID-19 outbreak continues to evolve as of the date these condensed consolidated financial statements were available to be issued. 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. Management is actively monitoring the situation on its financial condition, liquidity, operations, customers, suppliers, industry, and workforce. Given the daily evolution of the COVID-19 outbreak and the response to curb its spread, the Company is not able to estimate the effects of the COVID-19 outbreak to its results of operations, financial condition, or liquidity for fiscal year 202 1 . On March 27, 2020, President Trump signed into law the Coronavirus Aid, Relief and Economic Security Act (the “CARES Act”). The CARES Act, among other things, includes provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations, increased limitations on qualified charitable contributions and technical corrections to tax depreciation methods for qualified improvement property. The Company continues to examine the impact that the CARES Act may have on its business. Currently, the Company is unable to determine the impact that the CARES Act will have on its financial condition, results of operations, or liquidity. The CARES Act also appropriated funds for the U.S. Small Business Administration Paycheck Protection Program (“PPP”) loans that are forgivable in certain situations to promote continued employment, as well as Economic Injury Disaster Loans to provide liquidity to small businesses harmed by COVID-19. Refer to Note 8 – Paycheck Protection Program Loan for further information. Accounts Receivable Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. The allowance is based on an analysis of historical bad debt, current receivables aging and expected future write-offs of uncollectible accounts, as well as an assessment of specific identifiable accounts considered at risk or uncollectible. Additions to the allowance for doubtful accounts include provisions for bad debt and deductions from the allowance for doubtful accounts include customer write-offs. Provision for doubtful accounts was not material for all periods presented. Inventories Inventories, consisting of raw materials, work in process, and finished goods, are valued at the lower of cost (first-in, first-out method) or net realizable value. The Company writes down excess and obsolete inventory to its estimated net realizable value based on management’s review of inventories on hand compared to estimated future usage and sales, shelf-life and assumptions about the likelihood of obsolescence. The cost components of work in process and finished goods inventories include raw materials, direct labor and an allocation of the Company’s overhead. 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. 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 March 31, 2021, the Company has not recognized any impairment to long-lived assets. Forward Purchase Contract In late 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. On January 26, 2017, Private Histogen and EPS entered into a Debt Settlement and Conversion Agreement (“Settlement Agreement”) whereby Private Histogen paid $50 thousand and issued EPS 14,342 shares of Series D convertible preferred stock. The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $ 0.3 million The Settlement Agreement was treated as debt subject to Accounting Standards Codification (“ASC”) 470, Debt Distinguishing Liabilities from Equity The Company determined the fair value of the liability to be approximately $0.3 million which is the value as if the repurchase commitment was exercised immediately. As of March 31, 2021 and December 31, 2020, the fair value of the EPS forward contract remained at approximately $0.3 million and is included in other liabilities in the accompanying condensed consolidated balance sheets. Comprehensive Income (Loss) The Company is required to report all components of comprehensive income (loss), including net income (loss), in the accompanying condensed consolidated financial statements in the period in which they are recognized. Comprehensive income (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 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 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 planned Phase 1/2 clinical trial of HST-003 for regeneration of cartilage in the knee. 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 three months ended March 3 1 , 202 1 , q ualifying expenses totaling $ million have been incurred with a corresponding reduction of research and development expenses related to the award . At March 31, 2021 , $ million remains in accounts receivable within the condensed consolidated balance sheets with respect to the DoD grant . Professional Services Revenue The Company recognizes revenue for professional services which are based upon negotiated rates with the counterparty. Professional services fees are recognized as revenue over time when the underlying services are performed, in accordance with ASC 606, and none of the revenue recognized to date is refundable. Cost of Product Revenue Cost of product revenue represents direct and indirect costs incurred to bring the product to saleable condition. Cost of Professional Services Revenue Cost of professional services revenue represents the Company’s costs for full-time employee equivalents and actual out-of-pocket costs. 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. Acquired In-Process Research and Development Expense The Company has acquired and may continue to acquire the rights to drug candidates in various stages of development. The up-front payments to acquire a drug candidate are immediately expensed as acquired in-process research and development, provided that the drug candidate has not obtained regulatory approval for marketing and, absent obtaining such approval, have no alternative future use. 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 in general and administrative expenses consist of professional fees for legal (including patent costs), audit and other consulting services, travel and entertainment, charitable contributions, 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 in general and administrative expenses in the accompanying condensed 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 three months ended March 31, 2021 and 2020, 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 attributable to common stockholders Potentially dilutive common shares consist of shares issuable from warrants, stock options, and convertible preferred stock. Potentially dilutive common shares issuable upon vesting of stock options and warrants are determined using the average share price for each period under the treasury stock method. In periods of net losses, we exclude all potentially dilutive common shares from the computation of diluted net loss per share for the periods as the effect would be anti-dilutive. For both three-month periods ended March 31, 2021 and 2020, diluted net loss per share attributable to common stockholders is equal to the 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): March 31, 2021 March 31, 2020 Outstanding stock options 2,672,963 1,308,409 Convertible preferred stock — 5,046,154 Warrants to purchase common stock 10,009,456 3,585 Total 12,682,419 6,358,148 Common Stock Valuations Prior to the Merger, the Company 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, the Company considered, among other things, contemporaneous valuations of the Company’s common stock, the Company’s 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 the Company’s common stock; the market performance of comparable publicly traded companies; and U.S. and global economic and capital market conditions. Stock-Based Compensation Stock Options The Company recognizes stock-based compensation expense over the requisite service period on a straight-line basis. Employee and director stock-based compensation for stock options is measured based on estimated fair value as of the grant date, using the Black-Scholes option pricing model, in calculating the fair value of option grants as of the grant date. The Company uses the following assumptions for estimating fair value of 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. The expected volatility as of the grant date is estimated and based on the historical volatility of a group of similar companies that are publicly traded. The risk-free interest rate is based on the yield on zero-coupon U.S. Treasury securities, as of the day the option is granted, with a term that most closely resembles the expected term of the option. Recently Issued Accounting Pronouncements None Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. ASU 2019-12 also improves the consistent application, and the simplification, of other areas of Topic 740 by clarifying and amending existing guidance. ASU 2019-12 is effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years, with early adoption permitted. The adoption of this standard did not have a material impact on the Company’s condensed consolidated financial statements or related disclosures.

Inventories

Inventories	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Inventories	2. Inventories Inventories consisted of the following (in thousands): March 31, 2021 December 31, 2020 Raw materials $ 61 $ 61 Work in process — 239 Total $ 61 $ 300 As of March 31, 2021 and December 31, 2020, no finished goods were included in inventories.

Property and Equipment, Net

Property and Equipment, Net	3 Months Ended
	Mar. 31, 2021
Property Plant And Equipment [Abstract]
Property and Equipment, Net	3. Property and Equipment, Net Property and equipment, net consisted of the following (in thousands): March 31, 2021 December 31, 2020 Lab and manufacturing equipment $ 1,235 $ 1,235 Leasehold improvements 845 845 Office furniture and equipment 157 157 Total 2,237 2,237 Less: accumulated depreciation and amortization (1,989 ) (1,966 ) Property and equipment, net $ 248 $ 271 Depreciation and amortization expense for the three months ended March 31, 2021 and 2020, were $23 thousand and $28 thousand, respectively.

Balance Sheet Details

Balance Sheet Details	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Details	4. Balance Sheet Details Prepaid and other current assets consisted of the following (in thousands): March 31, 2021 December 31, 2020 Insurance $ 409 $ 671 Security deposit — 77 Prepaid rent — 74 Clinical trial and study related costs 357 42 Other 140 319 Total $ 906 $ 1,183 Other assets consisted of the following (in thousands): March 31, 2021 December 31, 2020 Insurance $ 903 $ 959 Deferred offering costs — $ 708 Security deposit 250 $ 250 Other 13 14 Total $ 1,166 $ 1,931 Accrued liabilities consisted of the following (in thousands): March 31, 2021 December 31, 2020 Current portion of finance lease liabilities $ 8 $ 8 Compensation 686 639 Clinical trial and study related costs 33 226 Legal fees 73 52 Forward purchase contract 290 290 Offering costs — 602 Other 58 63 Total $ 1,148 $ 1,880

Revenues

Revenues	3 Months Ended
	Mar. 31, 2021
Revenue From Contract With Customer [Abstract]
Revenues	5. Revenues The following is a summary description of the material revenue arrangements, including arrangements that generated revenues during the three months ended March 31, 2021 and 2020. 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, Histogen 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, Histogen 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. Revenue related to the Additional Supply of CCM to Allergan has been deferred and will be recognized at the point in time in which deliveries are completed. Revenue related to the Additional Supply of CCM to Allergan was $0.3 million ($28 thousand of which was previously deferred) during the three months ended March 31, 2021. All deliveries of Additional Supply of CCM to Allergan have been completed as of March 31, 2021. Revenue related to the Potential Future Improvements has been deferred and amortized ratably over the remaining 9-year life of the patent, for which $5 thousand of previously deferred revenue was recognized in revenue during each of the three months ended March 31, 2021 and 2020. 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. 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 March 31, 2021 and December 31, 2020. Deferred revenue is classified in current liabilities when the Company’s obligations to provide research for Potential Future Improvements is expected to be satisfied within twelve months of the balance sheet date. Grant Revenue 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. Grant revenue recognized was $0.1 million for the three months ended March 31, 2021, and no grant revenue was recognized during 2020. As of March 31, 2021, the Company has completed all obligations under the NSF development grant. Professional Services Revenue The Company recognizes revenue for professional services which are based upon negotiated rates with the counterparty and are nonrefundable. Professional services fees are recognized as revenue over time as the underlying services are performed. Professional services revenue related to the Company’s assistance in establishing Allergan’s alternative manufacturing facility was zero and $0.1 million for the three months ended March 31, 2021 and 2020, respectively. Amerimmune Collaborative Development and Commercialization Agreement In October 2020, the Company entered into a Collaborative Development and Commercialization Agreement (the “Amerimmune Agreement”) with Amerimmune to jointly develop emricasan for the potential treatment of COVID-19. The FDA approved an investigation 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 Amerimmune Agreement, Amerimmune, at its expense and in collaboration with the Company, shall use commercially reasonable efforts to lead the development activities for emricasan. Amerimmune is responsible for conducting clinical trials and the Company agreed to provide reasonable quantities of emricasan for such purpose. Each party shall retain ownership of their legacy intellectual property and responsibility for ongoing patent application prosecution and maintenance costs. In addition, the Company granted Amerimmune an exclusive option, subject to certain terms and conditions, to an exclusive license to develop and commercialize emricasan throughout the world during the term of the Amerimmune Agreement. After exercise of the option, Amerimmune, alone or in conjunction with one or more strategic partners, will use its commercially reasonable efforts to develop, manufacture and commercialize emricasan and the Company will share the profits equally with Amerimmune. No consideration will be transferred to the Company until profits, as defined in the Amerimmune Agreement, are generated by Amerimmune from developing or commercializing products. The Company has identified multiple promises to deliver goods and services, which include 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 March 31, 2021, the Company has identified one performance obligation for all the deliverables under the Amerimmune Agreement since the delivered elements are 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 will be 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 will recognize revenue upon the occurrence of one of these events, no such events have occurred as of March 31, 2021.

Merger

Merger	3 Months Ended
	Mar. 31, 2021
Asset Acquisition [Abstract]
Merger	6. Merger The Merger, which closed on May 26, 2020, was accounted for as a reverse asset acquisition pursuant to Topic 805, Clarifying the Definition of a Business The total purchase price paid in the Merger has been allocated to the net assets acquired and liabilities assumed based on their fair values as of the completion of the Merger. The following summarizes the purchase price paid in the Merger (in thousands, except share and per share amounts): Number of shares of the combined organization owned by the Company’s pre-Merger stockholders 3,394,299 Multiplied by the fair value per share of Conatus common stock (1) $ 5.56 Fair value of consideration issued to effect the Merger $ 18,872 Transaction costs 1,817 Purchase price $ 20,689 (1) Based on the last reported sale price of the Company’s common stock on the Nasdaq Capital Market on May 26, 2020, the closing date of the Merger, and gives effect to the Reverse Stock Split. The allocation of the purchase price is as follows (in thousands): Cash acquired $ 12,835 Net assets acquired 710 Acquired IPR&D (2) 7,144 Purchase price $ 20,689 (2) Represents the research and development projects of Conatus which were in-process, but not yet completed. This consists primarily of Conatus’ emricasan product candidate. Current accounting standards require that the fair value of IPR&D projects acquired in an asset acquisition with no alternative future use be allocated a portion of the consideration transferred and charged to expense on the acquisition date. The acquired assets did not have outputs or employees.

PUR Settlement

PUR Settlement	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
PUR Settlement	7. 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 167,323 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 US FDA related to the Development Assets, (b) a $0.4 million commercialization milestone upon reaching gross sales (by the Company or licensee) of $0.5 million of products incorporating the Development Assets, and (c) a five percent (5%) royalty on net revenues collected by Histogen 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 ASC 450, Contingencies

Paycheck Protection Program Loa

Paycheck Protection Program Loan	3 Months Ended
	Mar. 31, 2021
Long Term Debt [Abstract]
Paycheck Protection Program Loan	8. 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, 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 twenty-four weeks 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 PPP program requirements. Final approval of the PPP loan forgiveness is subject to the approval of the Small Business Administration.

Stockholders' Deficit

Stockholders' Deficit	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Stockholders’ Deficit	9. Stockholders’ Deficit Common Stock November 2020 Offering of Common Stock In November 2020, the Company completed a registered direct offering (the “November 2020 Offering”) of an aggregate of 2,522,784 shares of common stock, together with accompanying warrants to purchase up to an aggregate of 1,892,088 shares of common stock, at an offering price of $1.78375 per share and accompanying warrant. The common stock was sold in the offering with a warrant that permits the investor to purchase 75% of the number of shares of the Company’s common stock purchased by the investor. The warrants have an exercise price of $1.70 per share, are immediately exercisable, and expire five and a half (5.5) years following the date of issuance. Placement agent warrants were issued to purchase up to 126,139 shares of common stock, are immediately exercisable for an exercise price of $2.2297, and expire on November 11, 2025. The Company received gross proceeds of $4.5 million and incurred placement agent’s fees and other offering expenses of approximately $0.9 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 79.6%, risk-free interest rate of 0.41%, expected dividend yield of 0% and an expected term of 5.0 years. At March 31, 2021, no warrants associated with the November 2020 Offering have been exercised. January 2021 Offering of Common Stock In January 2021, the Company completed an S-1 offering (the “January 2021 Offering”) of an aggregate of 11,600,000 shares of common stock, prefunded warrants to purchase up to 2,400,000 shares of its common stock and common stock warrants to purchase up to an aggregate of 14,000,000 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 $1.00, and the combined purchase price of one pre-funded warrant and accompanying common stock warrant was $0.9999. The common stock warrants are exercisable for five years at an exercise price of $1.00 per share. The pre-funded warrants are immediately exercisable at an exercise price of $0.0001 per share and may be exercised at any time until all of the prefunded warrants are exercised in full. Placement agent warrants were issued to purchase up to 700,000 shares of common stock, are immediately exercisable for an exercise price of $1.25, and are exercisable for five 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 an $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 0.00% and an expected term of 5.0 years. As of March 31, 2021, a total of 6,713,700 warrants issued in the January 2021 Offering to purchase shares of common stock have been exercised and the Company issued 6,713,700 shares of its common stock. The Company received gross proceeds of approximately $6.8 million. At March 31, 2021, the Company had 7,758,800 shares and 227,500 shares of common 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 $1.00 per share and $1.25 per share, respectively. At Market Issuance Sales Agreement with Stifel, Nicolaus & Company, Incorporated Prior to the Merger, Conatus entered into an At Market Issuance Sales Agreement (the “Sales Agreement”) with Stifel, Nicolaus & Company, Incorporated (“Stifel”), pursuant to which Conatus could sell from time to time, at its option, up to an aggregate of $35.0 million of shares of its common stock through Stifel, as sales agent. In July 2020, the Company terminated the Sales Agreement with Stifel, with no shares having been issued pursuant to the Sales Agreement. 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 provides that, upon the terms and subject to the conditions and limitations in the 2020 Purchase Agreement, Lincoln Park is 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 328,516 shares of common stock at $3.04399 per share to Lincoln Park for gross proceeds of $1.0 million. During the year ended December 31, 2020, the Company sold an additional 300,000 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 66,964 shares of its common stock to Lincoln Park. During the three months ended March 31, 2021 the Company did not sell any shares of common stock to Lincoln Park and approximately $ million of common stock rema i ns available for sale under the 2020 Purchase Agreement, subject to limitations on the amount of securities the Company may sell under its effective registration statement on Form S-3 within any 12 month period. 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 3,583 common shares at an exercise price of $23.08 a share expire on July 31, 2021. The warrants remain outstanding and unexercised for the periods presented. In addition, at March 31, 2021, warrants to purchase 1,346 shares of common stock with an exercise price of $74.30 a share remain outstanding that were issued by Conatus in connection with obtaining financing in 2016. These warrants expire on July 3, 2023. As discussed above, in November 2020, in connection with the November 2020 Offering, the Company issued warrants to: (i) investors for the purchase of 1,892,088 shares of common stock. Subject to certain ownership limitations, the warrants are immediately exercisable at an exercise price equal to $1.70 per share and expire on May 16, 2026, and (ii) the placement agent for the purchase of 126,139 shares of common stock, which were immediately exercisable at an exercise price of $2.2297 per share and expire on September 11, 2025. As of March 31, 2021, no such warrants have been exercised. Also discussed above, in January 2021, in connection with the January 2021 Offering, the Company issued warrants to: (i) investors for the purchase of 14,000,000 shares of common stock. Subject to certain ownership limitations, the warrants are immediately exercisable at an exercise price equal to $1.00 per share and expire on January 5, 2026, (ii) and (iii) the placement agent for the purchase of 700,000 shares of common stock, which were immediately exercisable at an exercise price of $1.25 per share and expire on December 30, 2025. As of March 31, 2021, a total of 6,713,700 warrants issued in the January 2021 Offering to purchase shares of common stock have been exercised and the Company issued 6,713,700 shares of its common stock. The Company received gross proceeds of approximately $6.8 million. 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 837,208 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 326,711 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) 850,000 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 March 31, 2021, 116,091 fully vested options remain outstanding under the Conatus 2013 Plan with a weighted average exercise price of $37.59 per share. The following summarizes activity related to the Company’s stock options under the 2017 Plan and the 2020 Plan for the three months ended March 31, 2021: Options Outstanding Weighted- average Exercise Price Weighted- average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2020 1,592,187 $ 3.06 6.20 $ 108 Granted 1,004,100 $ 0.99 Exercised — $ — Cancelled or forfeited (39,415 ) $ 2.16 Outstanding at March 31, 2021 2,556,872 $ 2.26 7.22 $ 668 Vested and exercisable at March 31, 2021 988,565 $ 2.48 3.81 $ 362 Chief Executive Officer Stock Options On January 24, 2019, the Company issued 485,178 stock options to its 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, 48,517 options of the Liquidity Option Shares became fully vested as the performance condition was achieved. For the three months ended March 31, 2021, the Company recognized $14 thousand in compensation expense related to the market-based options, all of which is recorded in general and administrative expense in the accompanying condensed consolidated statements of operations. As of March 31, 2021, there was $0.4 million of total unrecognized compensation cost related to unvested market condition-based options. Board of Directors Stock Options During the quarter ended March 31, 2021, in conjunction with a former Board Member’s voluntary resignation, the Company modified share-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 quarter ended March 31, 2021. Valuation of Stock Option Awards The following assumptions were used to calculate the fair value of awards granted to employees, non-employees and directors: Three Months Ended March 31, 2021 2020 Expected volatility 77.8% - 80.3% 70.0 % Risk-free interest rate 0.72% - 1.17% 2.60 % Expected term (in years) 6.00 - 6.08 6.25 Expected dividend yield — % — % The compensation cost that has been included in the accompanying condensed consolidated statements of operations for all stock-based compensation arrangements is detailed as follows (in thousands): Three Months Ended March 31, 2021 2020 Cost of product revenue $ — $ 5 Research and development 32 9 General and administrative 177 87 Total $ 209 $ 101 As of March 31, 2021, total unrecognized compensation cost related to unvested options, including unvested market condition-based options, was approximately $2.0 million which is expected to be recognized over a weighted-average period of 3.66 years. Common Stock Reserved for Future Issuance Common stock reserved for future issuance is as follows: As of March 31, 2021 2020 Common stock warrants 10,009,456 3,585 Convertible preferred stock (if converted) — 5,046,154 Common stock options issued and outstanding 2,672,963 1,308,409 Common stock available for issuance under stock plans 289,179 540,178 Total 12,971,598 6,898,326

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. 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 six 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. In connection with the closing of the Merger, the Company assumed Conatus’ noncancelable operating lease agreement, as amended, for certain office space with a lease term that expired on September 30, 2020. Upon close of the Merger, the Company recognized a right-of-use asset and operating lease liability in the amount of $0.1 million and $0.2 million, respectively, related to the Conatus lease. Prior to the Merger, Conatus entered into a sub-lease agreement with a third-party to lease the whole office space for the remainder of the lease term. The Company leases certain office equipment that is classified as a finance lease. As of March 31, 2021, the weighted-average remaining term of the Company’s operating and finance lease was 10.4 years and three years, respectively. The Company recognizes r ight-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. As of March 31, 2021, 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. At March 31, 2021, f uture minimum payments of lease liabilities were as follows (in thousands): Operating Leases Finance Lease 2021(remaining 9 months) $ 554 $ 7 2022 757 10 2023 780 10 2024 803 5 2025 827 — Thereafter 5,183 — Total minimum lease payments 8,904 32 Less: imputed interest (3,984 ) (4 ) Total future minimum lease payments 4,920 28 Less: current obligations under leases (157 ) (8 ) Noncurrent lease obligations $ 4,763 $ 20 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 does not believe that any of such pending claims and legal proceedings will have a material adverse effect on its consolidated financial statements.

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 2020
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 March 31, 2021 and December 31, 2020, Lordship controlled approximately 6.6% and 16% 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. 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 and in January 2020, but continues to carry the same rights to certain payments. The Company recognized an expense to Lordship for the three months ended March 31, 2021 and 2020 of $3 thousand and $0.1 million, respectively, all of which is included in general and administrative expenses on the accompanying condensed consolidated statements of operations. As of March 31, 2021 and December 31, 2020, there was a balance of $13 thousand and $14 thousand, respectively, paid to Lordship included in other assets on the accompanying condensed consolidated balance sheet in connection with the deferral of revenue from the Allergan License Agreements. Promissory Note s In April 2020, the Company entered into two promissory notes (the “Notes”), each for $0.3 million, with two stockholders, one of which was a principal owner of the Company. The Notes carried a fixed return of $25 thousand, due upon maturity. All outstanding principal and interest were due upon the earlier of (1) June 13, 2020 or (ii) 15 days following the consummation of the Merger. In June 2020, the Notes, including principal and interest, were repaid.

Description of Business, Basi_2

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of Business	Description of Business Histogen Inc. (the “Company,” “Histogen,” “we,” or the “combined company”), formerly known as Conatus Pharmaceuticals Inc. (“Conatus”) clinical-stage therapeutics company focused on developing potential first-in-class restorative therapeutics that ignite the body’s natural process to repair and maintain healthy biological function. The therapeutics are designed for aesthetic and therapeutic applications based upon the Company’s unique technology that utilizes proteins and growth factors produced by hypoxia-induced multipotent cells. The Company has a portfolio of product candidates derived from one core technology process without using embryonic stem cells or animal components. The Company’s product candidates are covered by patented technologies which focus on replacing and regenerating tissues in the body. The Company currently has two product candidates in development which utilizes our proprietary technology platform intended to potentially address what we believe to be underserved, multibillion-dollar global markets, HST-001, a treatment for hair loss, HST-003, a treatment for joint cartilage repair. In addition, we retained development and commercialization rights to emricasan, an asset previously developed by Conatus Pharmaceuticals Inc. (“Conatus”), which is being jointly developed with our collaboration partner, Amerimmune, for the potential treatment of COVID-19.
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”. Except as otherwise indicated, references herein to “Histogen,” the “Company,” “we,” or the “combined company”, refer to Histogen Inc. on a post-Merger basis, and the term “Private Histogen” refers to the business of privately-held Histogen Inc., prior to completion of the Merger. References to Conatus refer to Conatus Pharmaceuticals Inc. prior to completion of the Merger. Pursuant to the terms of the Merger Agreement, each outstanding share of Private Histogen common stock outstanding immediately prior to the closing of the Merger was converted into approximately 0.14342 shares of Company common stock (the “Exchange Ratio”), after taking into account the Reverse Stock Split, as defined below. Immediately prior to the closing of the Merger, all shares of Private Histogen preferred stock then outstanding were exchanged into shares of common stock of Private Histogen. In addition, all outstanding options exercisable for common stock of Private Histogen and warrants exercisable for common stock of Private Histogen became options and warrants exercisable for the same number of shares of common stock of the Company multiplied by the Exchange Ratio. Immediately following the Merger, stockholders of Private Histogen owned approximately 71.3% of the outstanding common stock of the combined company. The transaction was accounted for as a reverse asset acquisition in accordance with generally accepted accounting principles in the United States of America (“GAAP”). Under this method of accounting, Private Histogen was deemed to be the accounting acquirer for financial reporting purposes. This determination was primarily based on the facts that, immediately following the Merger: (i) Private Histogen’s stockholders owned a substantial majority of the voting rights in the combined company, (ii) Private Histogen designated a majority of the members of the initial board of directors of the combined company, and (iii) Private Histogen’s senior management holds all key positions in the senior management of the combined company. As a result, as of the closing date of the Merger, the net assets of the Company were recorded at their acquisition-date relative fair values in the accompanying condensed consolidated financial statements of the Company and the reported operating results prior to the Merger are those of Private Histogen.
Reverse Stock Split and Exchange Ratio	Reverse Stock Split and Exchange Ratio On May 26, 2020, in connection with, and prior to the completion of, the Merger, the Company effected a one-for-ten reverse stock split of its then outstanding common stock (the “Reverse Stock Split”). The par value and the authorized shares of the common stock were not adjusted as a result of the Reverse Stock Split. All of the Company’s issued and outstanding common stock have been retroactively adjusted to reflect this Reverse Stock Split for all periods presented. All issued and outstanding Private Histogen common stock, convertible preferred stock, options and warrants prior to the effective date of the Merger have been retroactively adjusted to reflect the Exchange Ratio for all periods presented.
Liquidity and Going Concern	Liquidity and Going Concern From inception and through March 31, 2021 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, government funding, strategic partnerships, collaboration and licensing arrangements, or other similar arrangements. In addition, the Company may fund its losses from operations through the common stock purchase agreement the Company entered into with Lincoln Park in July 2020, for the purchase of up to $10.0 million of the Company’s common stock over the 24 month period of the purchase agreement, $8.5 million of which remains available for sale as of the date (See Note 9), subject to limitations on the amount of securities the Company may sell under its effective registration statement on Form S-3 within any 12 month period. The condensed 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.
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The condensed 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 hair stimulating complex (“HSC”). This is a wholly-owned subsidiary intended to pursue registration with the COFEPRIS (Mexico equivalent to FDA). CIMRESA had no operational or financial activity for the three months ended March 31, 2021 and 2020. 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 condensed consolidated financial statements.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The unaudited condensed consolidated financial statements for the three months ended March 31, 2021 and 2020 have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC) and
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities and the disclosure of contingent assets and liabilities and contingencies at the date of the condensed 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, we continue to use the best information available to us in our critical 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, reserves for excess or obsolete inventory, stock-based compensation, 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. On January 12, 2018, AB was converted into a traditional C corporation, a Delaware corporation, under a Plan of Conversion agreement between the Company and the other member of the limited liability company, Wylde, LLC (“Wylde”). The entity structure change eliminated some of the special rights Wylde had under the LLC charter and gave the Company more control over the voting rights under the new corporate structure. The Plan of Conversion called for 3,800,000 common stock shares of AB to be issued to the Company and Wylde in proportion to their interest in the LLC immediately before the agreement was executed. Contemporaneously, the Company offered to purchase, and Wylde agreed to sell, 100,000 of the AB common shares for $1.00 per share for a total price of $0.1 million. The completion of this transaction among the stockholders of AB resulted in Histogen owning 2,600,000 common shares or approximately 68% of AB. 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 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 the issuer of its credit card accounts.
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 three months ended March 31, 2021 and 2020, one customer accounted for 72% and 100% of total revenues, respectively. Accounts receivable from the customer was $11 thousand and $0.1 million at March 31, 2021 and December 31, 2020, respectively. COVID-19 On January 30, 2020, the World Health Organization (“WHO”) announced a global health emergency because of a new strain of coronavirus originating in Wuhan, China (the “COVID-19 outbreak”) and the risks to the international community as the virus spreads globally beyond its point of origin. In March 2020, the WHO classified the COVID-19 outbreak as a pandemic, based on the rapid increase in exposure globally. The full impact of the COVID-19 outbreak continues to evolve as of the date these condensed consolidated financial statements were available to be issued. 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. Management is actively monitoring the situation on its financial condition, liquidity, operations, customers, suppliers, industry, and workforce. Given the daily evolution of the COVID-19 outbreak and the response to curb its spread, the Company is not able to estimate the effects of the COVID-19 outbreak to its results of operations, financial condition, or liquidity for fiscal year 202 1 . On March 27, 2020, President Trump signed into law the Coronavirus Aid, Relief and Economic Security Act (the “CARES Act”). The CARES Act, among other things, includes provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations, increased limitations on qualified charitable contributions and technical corrections to tax depreciation methods for qualified improvement property. The Company continues to examine the impact that the CARES Act may have on its business. Currently, the Company is unable to determine the impact that the CARES Act will have on its financial condition, results of operations, or liquidity. The CARES Act also appropriated funds for the U.S. Small Business Administration Paycheck Protection Program (“PPP”) loans that are forgivable in certain situations to promote continued employment, as well as Economic Injury Disaster Loans to provide liquidity to small businesses harmed by COVID-19. Refer to Note 8 – Paycheck Protection Program Loan for further information.
Accounts Receivable	Accounts Receivable Accounts receivable are generally due within 30 days and are recorded net of the allowance for doubtful accounts. The allowance is based on an analysis of historical bad debt, current receivables aging and expected future write-offs of uncollectible accounts, as well as an assessment of specific identifiable accounts considered at risk or uncollectible. Additions to the allowance for doubtful accounts include provisions for bad debt and deductions from the allowance for doubtful accounts include customer write-offs. Provision for doubtful accounts was not material for all periods presented.
Inventories	Inventories Inventories, consisting of raw materials, work in process, and finished goods, are valued at the lower of cost (first-in, first-out method) or net realizable value. The Company writes down excess and obsolete inventory to its estimated net realizable value based on management’s review of inventories on hand compared to estimated future usage and sales, shelf-life and assumptions about the likelihood of obsolescence. The cost components of work in process and finished goods inventories include raw materials, direct labor and an allocation of the Company’s overhead.
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. 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 March 31, 2021, the Company has not recognized any impairment to long-lived assets.
Forward Purchase Contract	Forward Purchase Contract In late 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. On January 26, 2017, Private Histogen and EPS entered into a Debt Settlement and Conversion Agreement (“Settlement Agreement”) whereby Private Histogen paid $50 thousand and issued EPS 14,342 shares of Series D convertible preferred stock. The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $ 0.3 million The Settlement Agreement was treated as debt subject to Accounting Standards Codification (“ASC”) 470, Debt Distinguishing Liabilities from Equity The Company determined the fair value of the liability to be approximately $0.3 million which is the value as if the repurchase commitment was exercised immediately. As of March 31, 2021 and December 31, 2020, the fair value of the EPS forward contract remained at approximately $0.3 million and is included in other liabilities in the accompanying condensed consolidated balance sheets.
Comprehensive Income (Loss)	Comprehensive Income (Loss) The Company is required to report all components of comprehensive income (loss), including net income (loss), in the accompanying condensed consolidated financial statements in the period in which they are recognized. Comprehensive income (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 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 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 planned Phase 1/2 clinical trial of HST-003 for regeneration of cartilage in the knee. 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 three months ended March 3 1 , 202 1 , q ualifying expenses totaling $ million have been incurred with a corresponding reduction of research and development expenses related to the award . At March 31, 2021 , $ million remains in accounts receivable within the condensed consolidated balance sheets with respect to the DoD grant . Professional Services Revenue The Company recognizes revenue for professional services which are based upon negotiated rates with the counterparty. Professional services fees are recognized as revenue over time when the underlying services are performed, in accordance with ASC 606, and none of the revenue recognized to date is refundable.
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.
Cost of Professional Services Revenue	Cost of Professional Services Revenue Cost of professional services revenue represents the Company’s costs for full-time employee equivalents and actual out-of-pocket costs.
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.
Acquired In-Process Research and Development Expense	Acquired In-Process Research and Development Expense The Company has acquired and may continue to acquire the rights to drug candidates in various stages of development. The up-front payments to acquire a drug candidate are immediately expensed as acquired in-process research and development, provided that the drug candidate has not obtained regulatory approval for marketing and, absent obtaining such approval, have no alternative future use.
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 in general and administrative expenses consist of professional fees for legal (including patent costs), audit and other consulting services, travel and entertainment, charitable contributions, 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 in general and administrative expenses in the accompanying condensed 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 three months ended March 31, 2021 and 2020, 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 attributable to common stockholders Potentially dilutive common shares consist of shares issuable from warrants, stock options, and convertible preferred stock. Potentially dilutive common shares issuable upon vesting of stock options and warrants are determined using the average share price for each period under the treasury stock method. In periods of net losses, we exclude all potentially dilutive common shares from the computation of diluted net loss per share for the periods as the effect would be anti-dilutive. For both three-month periods ended March 31, 2021 and 2020, diluted net loss per share attributable to common stockholders is equal to the 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): March 31, 2021 March 31, 2020 Outstanding stock options 2,672,963 1,308,409 Convertible preferred stock — 5,046,154 Warrants to purchase common stock 10,009,456 3,585 Total 12,682,419 6,358,148
Common Stock Valuations	Common Stock Valuations Prior to the Merger, the Company 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, the Company considered, among other things, contemporaneous valuations of the Company’s common stock, the Company’s 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 the Company’s 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 Stock Options The Company recognizes stock-based compensation expense over the requisite service period on a straight-line basis. Employee and director stock-based compensation for stock options is measured based on estimated fair value as of the grant date, using the Black-Scholes option pricing model, in calculating the fair value of option grants as of the grant date. The Company uses the following assumptions for estimating fair value of 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. The expected volatility as of the grant date is estimated and based on the historical volatility of a group of similar companies that are publicly traded. The risk-free interest rate is based on the yield on zero-coupon U.S. Treasury securities, as of the day the option is granted, with a term that most closely resembles the expected term of the option.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements None
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”). ASU 2019-12 simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. ASU 2019-12 also improves the consistent application, and the simplification, of other areas of Topic 740 by clarifying and amending existing guidance. ASU 2019-12 is effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years, with early adoption permitted. The adoption of this standard did not have a material impact on the Company’s condensed consolidated financial statements or related disclosures.

Description of Business, Basi_3

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [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): March 31, 2021 March 31, 2020 Outstanding stock options 2,672,963 1,308,409 Convertible preferred stock — 5,046,154 Warrants to purchase common stock 10,009,456 3,585 Total 12,682,419 6,358,148

Inventories (Tables)

Inventories (Tables)	3 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Components of Inventories	Inventories consisted of the following (in thousands): March 31, 2021 December 31, 2020 Raw materials $ 61 $ 61 Work in process — 239 Total $ 61 $ 300

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	3 Months Ended
	Mar. 31, 2021
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following (in thousands): March 31, 2021 December 31, 2020 Lab and manufacturing equipment $ 1,235 $ 1,235 Leasehold improvements 845 845 Office furniture and equipment 157 157 Total 2,237 2,237 Less: accumulated depreciation and amortization (1,989 ) (1,966 ) Property and equipment, net $ 248 $ 271

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	3 Months Ended
	Mar. 31, 2021
Balance Sheet Related Disclosures [Abstract]
Summary of Prepaid and Other Current Assets	Prepaid and other current assets consisted of the following (in thousands): March 31, 2021 December 31, 2020 Insurance $ 409 $ 671 Security deposit — 77 Prepaid rent — 74 Clinical trial and study related costs 357 42 Other 140 319 Total $ 906 $ 1,183
Summary of Other Assets	Other assets consisted of the following (in thousands): March 31, 2021 December 31, 2020 Insurance $ 903 $ 959 Deferred offering costs — $ 708 Security deposit 250 $ 250 Other 13 14 Total $ 1,166 $ 1,931
Summary of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): March 31, 2021 December 31, 2020 Current portion of finance lease liabilities $ 8 $ 8 Compensation 686 639 Clinical trial and study related costs 33 226 Legal fees 73 52 Forward purchase contract 290 290 Offering costs — 602 Other 58 63 Total $ 1,148 $ 1,880

Merger (Tables)

Merger (Tables)	3 Months Ended
	Mar. 31, 2021
Asset Acquisition [Abstract]
Summary of Purchase Price Paid in Merger	The following summarizes the purchase price paid in the Merger (in thousands, except share and per share amounts): Number of shares of the combined organization owned by the Company’s pre-Merger stockholders 3,394,299 Multiplied by the fair value per share of Conatus common stock (1) $ 5.56 Fair value of consideration issued to effect the Merger $ 18,872 Transaction costs 1,817 Purchase price $ 20,689 (1) Based on the last reported sale price of the Company’s common stock on the Nasdaq Capital Market on May 26, 2020, the closing date of the Merger, and gives effect to the Reverse Stock Split.
Summary of Allocation of Purchase Price	The allocation of the purchase price is as follows (in thousands): Cash acquired $ 12,835 Net assets acquired 710 Acquired IPR&D (2) 7,144 Purchase price $ 20,689 (2) Represents the research and development projects of Conatus which were in-process, but not yet completed. This consists primarily of Conatus’ emricasan product candidate. Current accounting standards require that the fair value of IPR&D projects acquired in an asset acquisition with no alternative future use be allocated a portion of the consideration transferred and charged to expense on the acquisition date. The acquired assets did not have outputs or employees.

Stockholders' Deficit (Tables)

Stockholders' Deficit (Tables)	3 Months Ended
	Mar. 31, 2021
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 three months ended March 31, 2021: Options Outstanding Weighted- average Exercise Price Weighted- average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2020 1,592,187 $ 3.06 6.20 $ 108 Granted 1,004,100 $ 0.99 Exercised — $ — Cancelled or forfeited (39,415 ) $ 2.16 Outstanding at March 31, 2021 2,556,872 $ 2.26 7.22 $ 668 Vested and exercisable at March 31, 2021 988,565 $ 2.48 3.81 $ 362
Summary of Valuation of Stock Option Awards	The following assumptions were used to calculate the fair value of awards granted to employees, non-employees and directors: Three Months Ended March 31, 2021 2020 Expected volatility 77.8% - 80.3% 70.0 % Risk-free interest rate 0.72% - 1.17% 2.60 % Expected term (in years) 6.00 - 6.08 6.25 Expected dividend yield — % — %
Summary of Compensation Cost Included in Condensed Consolidated Statements of Operations for Stock-based Compensation Arrangements	The compensation cost that has been included in the accompanying condensed consolidated statements of operations for all stock-based compensation arrangements is detailed as follows (in thousands): Three Months Ended March 31, 2021 2020 Cost of product revenue $ — $ 5 Research and development 32 9 General and administrative 177 87 Total $ 209 $ 101
Summary of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance is as follows: As of March 31, 2021 2020 Common stock warrants 10,009,456 3,585 Convertible preferred stock (if converted) — 5,046,154 Common stock options issued and outstanding 2,672,963 1,308,409 Common stock available for issuance under stock plans 289,179 540,178 Total 12,971,598 6,898,326

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Payments of Lease Liabilities	At March 31, 2021, f uture minimum payments of lease liabilities were as follows (in thousands): Operating Leases Finance Lease 2021(remaining 9 months) $ 554 $ 7 2022 757 10 2023 780 10 2024 803 5 2025 827 — Thereafter 5,183 — Total minimum lease payments 8,904 32 Less: imputed interest (3,984 ) (4 ) Total future minimum lease payments 4,920 28 Less: current obligations under leases (157 ) (8 ) Noncurrent lease obligations $ 4,763 $ 20

Description of Business, Basi_4

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail)	May 26, 2020	Jan. 28, 2020shares	Jan. 26, 2017USD ($)shares	Sep. 30, 2020USD ($)	Jul. 31, 2020USD ($)	Mar. 31, 2021USD ($)Segmentshares	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)shares	Jan. 12, 2018USD ($)$ / sharesshares
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Reverse stock split description						one-for-ten
Reverse stock split conversion ratio	0.1
Accumulated deficit						$ (66,972,000)		$ (62,702,000)
Cash and cash equivalents						$ 21,743,000	$ 507,000	$ 6,763,000
Percentage ownership not considered variable interest entity						100.00%
Number of operating segment | Segment						1
Impairment to long-lived assets						$ 0
EPS unpaid services						$ 300,000
Shares issued | shares						0		0
Fair value of liability						$ 300,000		$ 300,000
Income tax expense benefit						0	$ 0
Expected contractual term							6 years 3 months
U.S. Department of Defense (“DoD”) [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Accounts receivable from customer						200,000
Grant funding obtained				$ 2,000,000
Grant award expiration period				2025-09
Qualifying expenses incurred						$ 200,000
Settlement Agreement [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cash paid			$ 50,000
Share repurchases, description						The Company is required to repurchase the shares at the higher of the remaining balance due, approximately $0.3 million at March 31, 2021 and December 31, 2020, or the market price of the shares at the time of repurchase, but no later than December 31, 2021. The Company has the sole option to initiate the timing of the repurchase of the shares (which were converted into shares of common stock upon the Merger) before the deadline date.
Share repurchases, value						$ 300,000		300,000
Gain (Loss) on extinguishment of the original liability			$ 0
Series D Convertible Preferred Stock [Member] | Settlement Agreement [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Shares issued | shares			14,342
Customer Concentration Risk | One Customer [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Accounts receivable from customer						$ 11,000		$ 100,000
Revenue Benchmark | Customer Concentration Risk | One Customer [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of revenues						72.00%	100.00%
Minimum [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Expected contractual term						6 years
Maximum [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives of the assets						5 years
Expected contractual term						6 years 29 days
Maximum [Member] | Stock Options [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Expected contractual term						10 years
Variable Interest Entity ("VIE")
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Variable interest entity, ownership percentage						68.00%
Variable interest entity common stock shares owned | shares						2,600,000
Variable Interest Entity ("VIE") | Plan of Conversion Agreement [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of common shares specified in Plan of Conversion | shares									3,800,000
Number of AB common shares purchased | shares									100,000
Price per Share Purchase Price of AB common shares | $ / shares									$ 1
Aggregate Purchase Price of AB common shares									$ 100,000
Variable Interest Entity ("VIE") | Minimum [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Variable interest entity, ownership percentage						50.00%
Common Stock Purchase Agreement with Lincoln Park [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Common stock shares maximum committed purchase amount					$ 10,000,000
Remaining available for sale common stock shares maximum committed purchase amount					$ 8,500,000	$ 8,500,000
Long-term purchase commitment, period					24 months
Private Histogen [Member]
Description Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Exchange Ratio in reverse merger | shares		0.14342
Histogen stockholders' ownership interests post Merger		71.30%

Description of Business, Basi_5

Description of Business, Basis of Presentation and Summary of Significant Accounting Policies - Summary of Outstanding Potentially Dilutive Shares Excluded in Calculation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	12,682,419	6,358,148
Outstanding Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	2,672,963	1,308,409
Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities		5,046,154
Warrants to purchase common stock [Member] | Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding potentially dilutive securities	10,009,456	3,585

Inventories - Components of Inv

Inventories - Components of Inventories (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Raw materials	$ 61	$ 61
Work in process		239
Total	$ 61	$ 300

Inventories - Additional Inform

Inventories - Additional Information (Detail) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Inventory Disclosure [Abstract]
Inventory, Finished goods	$ 0	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 2,237	$ 2,237
Less: accumulated depreciation and amortization	(1,989)	(1,966)
Property and equipment, net	248	271
Lab and Manufacturing Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,235	1,235
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	845	845
Office Furniture and Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 157	$ 157

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 23	$ 28

Balance Sheet Details - Summary

Balance Sheet Details - Summary of Prepaid and Other Current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Insurance	$ 409	$ 671
Security deposit		77
Prepaid rent		74
Clinical trial and study related costs	357	42
Other	140	319
Total	$ 906	$ 1,183

Balance Sheet Details - Summa_2

Balance Sheet Details - Summary of Other Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Insurance	$ 903	$ 959
Deferred offering costs		708
Security deposit	250	250
Other	13	14
Total	$ 1,166	$ 1,931

Balance Sheet Details - Summa_3

Balance Sheet Details - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Current portion of finance lease liabilities	$ 8	$ 8
Compensation	686	639
Clinical trial and study related costs	33	226
Legal fees	73	52
Forward purchase contract	290	290
Offering costs		602
Other	58	63
Total	$ 1,148	$ 1,880

Revenues - Additional Informati

Revenues - Additional Information (Detail)	1 Months Ended			3 Months Ended		12 Months Ended
	Jan. 31, 2020USD ($)kg	Mar. 31, 2019USD ($)	Dec. 31, 2017USD ($)	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)
Disaggregation of Revenue [Line Items]
Revenue				$ 431,000	$ 978,000
Deferred revenue				100,000		$ 100,000
Product [Member]
Disaggregation of Revenue [Line Items]
Revenue				306,000
License [Member]
Disaggregation of Revenue [Line Items]
Revenue				12,000	867,000
Grant [Member]
Disaggregation of Revenue [Line Items]
Revenue				113,000		$ 0
Professional Services Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue				0	100,000
2017 Allergan Agreement [Member]
Disaggregation of Revenue [Line Items]
Cash payment received			$ 11,000,000
Potential additional payments			5,500,000
2017 Allergan Agreement [Member] | Product [Member] | Minimum [Member]
Disaggregation of Revenue [Line Items]
Sales target for additional potential payment payout			$ 60,000,000
2019 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
One-time payment		$ 7,500,000
Remaining life of the patent		9 years
2019 Allergan Amendment Agreement [Member] | License [Member]
Disaggregation of Revenue [Line Items]
Revenue		$ 7,500,000
2020 Allergan Amendment Agreement [Member]
Disaggregation of Revenue [Line Items]
Remaining life of the patent	9 years
Revenue				300,000
Up front payment received	$ 1,000,000
Additional quantity of product to be supplied | kg	200
Deferred revenue				28,000
Revenue recognized				$ 5,000	$ 5,000
2020 Allergan Amendment Agreement [Member] | License [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 900,000

Merger - Additional Information

Merger - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021
Asset Acquisition [Abstract]
Closing date of Merger	May 26, 2020

Merger - Summary of Purchase Pr

Merger - Summary of Purchase Price Paid in Merger (Detail) $ / shares in Units, $ in Thousands	May 26, 2020USD ($)$ / sharesshares
Asset Acquisition [Abstract]
Number of shares of the combined organization owned by the Company’s pre-Merger stockholders | shares	3,394,299
Multiplied by the fair value per share of Conatus common stock | $ / shares	$ 5.56	[1]
Fair value of consideration issued to effect the Merger	$ 18,872
Transaction costs	1,817
Purchase price	$ 20,689
[1]	Based on the last reported sale price of the Company’s common stock on the Nasdaq Capital Market on May 26, 2020, the closing date of the Merger, and gives effect to the Reverse Stock Split.

Merger - Summary of Allocation

Merger - Summary of Allocation of Purchase Price (Detail) $ in Thousands	May 26, 2020USD ($)
Asset Acquisition [Abstract]
Cash acquired	$ 12,835
Net assets acquired	710
Acquired IPR&D	7,144	[1]
Purchase price	$ 20,689
[1]	Represents the research and development projects of Conatus which were in-process, but not yet completed. This consists primarily of Conatus’ emricasan product candidate. Current accounting standards require that the fair value of IPR&D projects acquired in an asset acquisition with no alternative future use be allocated a portion of the consideration transferred and charged to expense on the acquisition date. The acquired assets did not have outputs or employees.

PUR Settlement - Additional Inf

PUR Settlement - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Apr. 30, 2019	Mar. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
Issuance of common stock for Lordship Indemnification		$ 11,955,000
Payment for milestone		0	$ 0
Payments for royalties		$ 0	$ 0
PUR Biologics, LLC [Member]
Loss Contingencies [Line Items]
Upfront cash paid	$ 500,000
Amount forgiven	22,000
Repayments of outstanding payable assumed	23,000
Development Assets [Member]
Loss Contingencies [Line Items]
Milestone and royalty payment obligations	$ 400,000
Percentage of royalties on net sales	5.00%
Development Assets [Member] | Commercialization Milestone [Member]
Loss Contingencies [Line Items]
Milestone and royalty payment obligations	$ 400,000
Development Assets [Member] | Product [Member] | Estimated Sales [Member]
Loss Contingencies [Line Items]
Revenue target for milestone achievement	500,000
Development Assets [Member] | PUR Biologics, LLC [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Potential cash payout	$ 6,250,000
Series D Convertible Preferred Stock [Member] | Development Assets [Member] | PUR Biologics, LLC [Member]
Loss Contingencies [Line Items]
Issuance of common stock for Lordship Indemnification, shares	167,323
Issuance of common stock for Lordship Indemnification	$ 1,750,000

Paycheck Protection Program L_2

Paycheck Protection Program Loan - Additional Information (Detail) - Paycheck Protection Program [Member] - USD ($) $ in Millions	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	60.00%	75.00%
Existing loans maturity period	5 years	2 years

Stockholders' Deficit - Additio

Stockholders' Deficit - Additional information (Details) - USD ($)

May 26, 2020

Jan. 28, 2020

Jan. 24, 2019

Jan. 31, 2021

Nov. 30, 2020

Jul. 31, 2020

May 31, 2020

Apr. 30, 2019

Mar. 31, 2021

Mar. 31, 2020

Dec. 31, 2020

Dec. 18, 2017

Dec. 31, 2016

Class Of Stock [Line Items]

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

$ 11,955,000

Expected volatility

70.00%

Risk-free interest rate

2.60%

Expected contractual term

6 years 3 months

Common stock reserved for issuance

12,971,598

6,898,326

Warrants to purchase common stock

10,009,456

3,585

Stock-based total compensation expense

$ 209,000

$ 101,000

Unrecognized compensation expense

$ 2,000,000

Weighted-average vesting term

3 years 7 months 28 days

General and Administrative Expense [Member]

Class Of Stock [Line Items]

Stock-based total compensation expense

$ 177,000

$ 87,000

Liquidity Option Shares [Member]

Class Of Stock [Line Items]

Vesting period

12 months

Number of fully vested options

48,517

Vesting percentage

25.00%

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

40.00%

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

Performance and Market-Based Options [Member] | General and Administrative Expense [Member]

Class Of Stock [Line Items]

Stock-based total compensation expense

$ 14,000

Market Condition-Based Options [Member]

Class Of Stock [Line Items]

Unrecognized compensation expense

$ 400,000

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

Class Of Stock [Line Items]

Vesting period

36 months

Stock options issued

485,178

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

40.00%

Remaining vesting percentage

25.00%

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

Class Of Stock [Line Items]

Vesting percentage

60.00%

2017 Plan [Member]

Class Of Stock [Line Items]

Number of common stock shares authorized to issue

837,208

Increase in number of common stock available for grant

326,711

Vesting period

4 years

Expiration period

10 years

Stock options issued

0

2020 Stock Plan [Member]

Class Of Stock [Line Items]

Number of common stock shares authorized to issue

850,000

Expiration period

10 years

Percentage of outstanding shares of common stock

5.00%

Conatus 2013 Plan [Member]

Class Of Stock [Line Items]

Stock options issued

0

Number of fully vested options

116,091

Weighted average exercise price of fully vested options

$ 37.59

Maximum [Member]

Class Of Stock [Line Items]

Expected contractual term

6 years 29 days

Maximum [Member] | Stock Options [Member]

Class Of Stock [Line Items]

Expected contractual term

10 years

Minimum [Member]

Class Of Stock [Line Items]

Expected contractual term

6 years

Sales Agreement with Stifel [Member]

Class Of Stock [Line Items]

Number of shares sold under sales agreement

0

Sales Agreement with Stifel [Member] | Maximum [Member]

Class Of Stock [Line Items]

Aggregate value of common shares that can be sold

$ 35,000,000

Common Stock Purchase Agreement with Lincoln Park [Member]

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs/Lordship Indemnification, shares

66,964

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

328,516

300,000

Sale of common stock price per share

$ 3.04399

Remaining available for sale common stock shares maximum committed purchase amount

$ 8,500,000

$ 8,500,000

Common Stock [Member]

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs/Lordship Indemnification, shares

14,000,000

Exercise price of warrant per share

$ 74.30

$ 23.08

Warrants to purchase common stock

1,346

Warrant expiration date

Jul. 3, 2023

Jul. 31, 2021

Common Stock [Member] | Maximum [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

3,583

Common Stock [Member] | November 2020 Offering Common Stock [Member]

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs/Lordship Indemnification, shares

2,522,784

Warrants to purchase common stock

1,892,088

Offering price per share

$ 1.78375

Percentage of warrant coverage

75.00%

Exercise price of warrant per share

$ 1.70

Warrants exercisable expiration period

5 years 6 months

Warrants exercised

0

Common Stock [Member] | November 2020 Offering Common Stock [Member] | Placement Agent Warrants [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

126,139

Exercise price of warrant per share

$ 2.2297

Warrant expiration date

Nov. 11, 2025

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

$ 4,500,000

Placement agent's fees and other offering expenses

900,000

Common Stock [Member] | November 2020 Offering Common Stock [Member] | Placement Agent Warrants [Member] | Black-Scholes Option Pricing Model [Member]

Class Of Stock [Line Items]

Aggregate value of warrants

$ 100,000

Expected volatility

79.60%

Risk-free interest rate

0.41%

Expected dividend yield

0.00%

Expected contractual term

5 years

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

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs/Lordship Indemnification, shares

6,713,700

Warrants to purchase common stock

6,713,700

Exercise price of warrant per share

$ 1

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

7,758,800

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

Class Of Stock [Line Items]

Issuance of common stock, net of issuance costs/Lordship Indemnification, shares

11,600,000

Warrants to purchase common stock

14,000,000

Exercise price of warrant per share

$ 1

Number of prefunded warrants to be issued

2,400,000

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

$ 1

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

$ 0.9999

Warrant exercisable period

5 years

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

Class Of Stock [Line Items]

Warrants to purchase common stock

700,000

Exercise price of warrant per share

$ 1.25

$ 1.25

Warrant exercisable period

5 years

Common stock reserved for issuance

227,500

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

0.00%

Expected contractual term

5 years

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

Class Of Stock [Line Items]

Exercise price of warrant per share

$ 0.0001

Common Stock [Member] | November 2020 Offering [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

1,892,088

Exercise price of warrant per share

$ 1.70

Warrant expiration date

May 16, 2026

Common Stock [Member] | November 2020 Offering [Member] | Placement Agent Warrants [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

126,139

Exercise price of warrant per share

$ 2.2297

Number of common stock warrants exercised

0

Common Stock [Member] | January Two Thousand Twenty One Offerings

Class Of Stock [Line Items]

Warrants to purchase common stock

14,000,000

6,713,700

Exercise price of warrant per share

$ 1

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

$ 6,800,000

Warrant expiration date

Jan. 5, 2026

Common Stock [Member] | January Two Thousand Twenty One Offerings | Placement Agent Warrants [Member]

Class Of Stock [Line Items]

Warrants to purchase common stock

700,000

Exercise price of warrant per share

$ 1.25

Stockholders' Deficit - Summary

Stockholders' Deficit - Summary of Stock Option Activity (Details) - 2017 and 2020 Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of Options, Beginning balance	1,592,187
Number of Options, Granted	1,004,100
Number of Options, Cancelled or forfeited	(39,415)
Number of Options, Ending balance	2,556,872	1,592,187
Number of Options, Vested and exercisable	988,565
Weighted-Average Exercise Price, Beginning balance	$ 3.06
Weighted-Average Exercise Price, Granted	0.99
Weighted-Average Exercise Price, Cancelled or forfeited	2.16
Weighted-Average Exercise Price, Ending balance	2.26	$ 3.06
Weighted-Average Exercise Price, Vested and exercisable	$ 2.48
Weighted-Average Remaining Contractual Term Outstanding	7 years 2 months 19 days	6 years 2 months 12 days
Weighted-Average Remaining Contractual Term Outstanding, Vested and exercisable	3 years 9 months 21 days
Aggregate Intrinsic Value Outstanding	$ 668	$ 108
Aggregate Intrinsic Value, Vested and exercisable	$ 362

Stockholders' Deficit - Summa_2

Stockholders' Deficit - Summary of Valuation of Stock Option Awards (Details)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility		70.00%
Expected volatility, minimum	77.80%
Expected volatility, maximum	80.30%
Risk-free interest rate		2.60%
Risk-free interest rate, minimum	0.72%
Risk-free interest rate, maximum	1.17%
Expected term (in years)		6 years 3 months
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 29 days

Stockholders' Deficit - Summa_3

Stockholders' Deficit - Summary of Compensation Cost Included in Condensed Consolidated Statements of Operations for Stock-based Compensation Arrangements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	$ 209	$ 101
Cost of Product Revenue [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost		5
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	32	9
General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Compensation cost	$ 177	$ 87

Stockholders' Deficit - Summa_4

Stockholders' Deficit - Summary of Common Stock Reserved for Future Issuance (Detail) - shares	Mar. 31, 2021	Mar. 31, 2020
Class Of Stock [Line Items]
Common stock warrants	10,009,456	3,585
Convertible preferred stock (if converted)		5,046,154
Common stock available for issuance under stock plans	289,179	540,178
Total	12,971,598	6,898,326
Common Stock [Member]
Class Of Stock [Line Items]
Common stock warrants	1,346
Common stock options issued and outstanding	2,672,963	1,308,409

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 01, 2020
Operating Leased Assets [Line Items]
Lease commencement date	Mar. 1, 2020
Lease expiration date	Aug. 31, 2031
Lessee, operating lease, existence of option to extend	false
Rent abatement term	6 months
Right-of-use asset	$ 4,491	$ 4,411	$ 4,500
Operating lease liability	$ 4,920		$ 4,500
Security deposit		$ 77
Operating lease remaining term	10 years 4 months 24 days
Finance lease remaining term	3 years
Operating lease weighted-average discount rate	12.20%
Finance lease weighted-average discount rate	10.00%
Conatus Pharmaceuticals Inc [Member]
Operating Leased Assets [Line Items]
Right-of-use asset	$ 100
Operating lease liability	$ 200
Office Space [Member]
Operating Leased Assets [Line Items]
Lease expiration date	Sep. 30, 2020
Letter of Credit [Member]
Operating Leased Assets [Line Items]
Security deposit	$ 300
Maximum [Member]
Operating Leased Assets [Line Items]
Tenant improvement allowance on modified lease	$ 2,200

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Payments of Lease Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 01, 2020
Operating Lease
2021(remaining 9 months)	$ 554
2022	757
2023	780
2024	803
2025	827
Thereafter	5,183
Total minimum lease payments	8,904
Less: imputed interest	(3,984)
Total future minimum lease payments	4,920		$ 4,500
Less: current obligations under leases	(157)	$ (28)
Noncurrent lease obligations	4,763	4,806
Finance Lease
2021(remaining 9 months)	7
2022	10
2023	10
2024	5
Total minimum lease payments	32
Less: imputed interest	(4)
Total future minimum lease payments	28
Less: current obligations under leases	(8)	$ (8)
Noncurrent lease obligations	$ 20

Related Parties - Additional In

Related Parties - Additional Information (Detail) $ in Thousands	1 Months Ended		3 Months Ended		12 Months Ended
	Apr. 30, 2020USD ($)PromissorynoteStockholder	Nov. 30, 2012	Mar. 31, 2021USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)
Related Party Transaction [Line Items]
Number of promissory notes | Promissorynote	2
Promissory Note [Member]
Related Party Transaction [Line Items]
Debt instrument, face amount	$ 300
Number of stockholders | Stockholder	2
Debt instrument interest amount	$ 25
Debt instrument, maturity date	Jun. 13, 2020
Number of days post merger that amounts are due	15 days
Lordship Ventures Histogen Holdings LLC [Member]
Related Party Transaction [Line Items]
Percentage of outstanding voting shares controlled			6.60%		16.00%
Lordship Ventures Histogen Holdings LLC [Member] | Success Fee Agreement [Member]
Related Party Transaction [Line Items]
Minimum percentage of asset or equity engaged in merger or sale transaction		90.00%
Related party expense recognized			$ 3	$ 100
Lordship Ventures Histogen Holdings LLC [Member] | Allergan License Agreements [Member]
Related Party Transaction [Line Items]
Amount due to related parties			$ 13		$ 14
Lordship Ventures Histogen Holdings LLC [Member] | 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. 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.
Lordship Ventures Histogen Holdings LLC [Member] | 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		1.00%
Lordship Ventures Histogen Holdings LLC [Member] | 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		10.00%