Athersys, Inc / New (ATHXQ) 10-K 15 Mar 22 2021 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Mar. 09, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-33876
Entity Registrant Name	ATHERSYS, INC / NEW
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-4864095
Entity Address, Address Line One	3201 Carnegie Avenue,
Entity Address, City or Town	Cleveland,
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	44115-2634
City Area Code	216
Local Phone Number	431-9900
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	ATHX
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	true
Entity Public Float			$ 185.1
Entity Common Stock, Shares Outstanding		243,980,180
Documents Incorporated by Reference	Part III of this Annual Report on Form 10-K incorporates by reference certain information from the registrant’s definitive proxy statement with respect to the 2022 annual meeting of stockholders.
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Central Index Key	0001368148

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2021
Audit Information [Abstract]
Auditor Name	Ernst & Young LLP
Auditor Location	Cleveland, Ohio
Auditor Firm ID	42

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 37,407	$ 51,546
Prepaid expenses and other	4,206	2,926
Total current assets	46,027	54,561
Operating right-of-use assets, net	8,960	648
Property and equipment, net	3,692	3,155
Deposits and other	1,505	1,350
Total assets	60,184	59,714
Current liabilities:
Operating lease liabilities, current	1,011	480
Accrued compensation and related benefits	4,133	1,779
Accrued clinical trial related costs	3,773	6,870
Accrued expenses and other	704	718
Total current liabilities	29,861	22,954
Operating lease liabilities, non-current	8,755	197
Stockholders’ equity:
Preferred stock, at stated value; 10,000,000 shares authorized, and no shares issued and outstanding at December 31, 2021 and 2020	0	0
Common stock, $0.001 par value; 600,000,000 shares authorized, and 242,844,180 issued and outstanding at December 31, 2021 and 300,000,000 shares authorized, and 201,973,582 shares issued and outstanding at December 31, 2020	243	202
Additional paid-in capital	599,470	527,549
Accumulated deficit	(583,344)	(496,389)
Total stockholders’ equity	16,369	31,362
Total liabilities and stockholders’ equity	60,184	59,714
Healios
Current assets:
Accounts receivable from Healios	1,414	89
Unbilled accounts receivable from Healios	3,000	0
Current liabilities:
Accounts payable	1,119	1,705
Deferred revenue - Healios	3,340	65
Advance from Healios	5,199	5,201
Consolidated entity, excluding related party
Current liabilities:
Accounts payable	$ 15,781	$ 11,337

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Stockholders’ equity:
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	600,000,000	300,000,000
Common stock, shares issued (in shares)	242,844,180	201,973,582
Common stock, shares outstanding (in shares)	242,844,180	201,973,582

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues
Grant revenue	$ 0	$ 8	$ 116
Total revenues	5,514	1,440	5,633
Costs and expenses
Research and development (including stock compensation expense of $3,642, $3,351 and $2,217 in 2021, 2020 and 2019, respectively)	71,080	62,994	39,045
General and administrative (including stock compensation expense of $4,914, $4,028 and $2,634 in 2021, 2020 and 2019, respectively)	20,065	15,888	11,378
Depreciation	1,427	890	698
Total costs and expenses	92,572	79,772	51,121
Loss from operations	(87,058)	(78,332)	(45,488)
Other income (expense), net	103	(433)	906
Net loss and comprehensive loss	$ (86,955)	$ (78,765)	$ (44,582)
Net loss per common share, basic (in dollars per share)	$ (0.39)	$ (0.42)	$ (0.29)
Net loss per common share, diluted (in dollars per share)	$ (0.39)	$ (0.42)	$ (0.29)
Weighted average shares outstanding, basic (in shares)	224,274	187,472	151,696
Weighted average shares outstanding, diluted (in shares)	224,274	187,472	151,696
Healios
Revenues
Contract revenue from Healios	$ 5,514	$ 1,432	$ 5,517

Consolidated Statements of Op_2

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock-based compensation expense	$ 8,600	$ 7,400	$ 4,900
Research and development
Stock-based compensation expense	3,642	3,351	2,217
General and administrative
Stock-based compensation expense	$ 4,914	$ 4,028	$ 2,634

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Consolidated entity, excluding related party	Healios	Preferred Stock	Common Stock	Common StockConsolidated entity, excluding related party	Common StockHealios	Additional Paid-in Capital	Additional Paid-in CapitalConsolidated entity, excluding related party	Additional Paid-in CapitalHealios	Accumulated Deficit
Preferred stock shares, beginning balance (in shares) at Dec. 31, 2018				0
Beginning balance at Dec. 31, 2018	$ 43,116			$ 0	$ 144			$ 416,014			$ (373,042)
Common stock, beginning balance (in shares) at Dec. 31, 2018					144,292,739
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	4,851							4,851
Issuance of common stock, net of issuance costs (in shares)						14,825,000
Issuance of common stock, net of issuance costs		$ 20,284				$ 15			$ 20,269
Issuance of common stock under equity compensation plans (in shares)					673,846
Issuance of common stock under equity compensation plans	(398)				$ 1			(399)
Net and comprehensive loss	(44,582)										(44,582)
Preferred stock shares, ending balance (in shares) at Dec. 31, 2019				0
Ending balance at Dec. 31, 2019	23,271			$ 0	$ 160			440,735			(417,624)
Common stock, ending balance (in shares) at Dec. 31, 2019					159,791,585
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	7,379							7,379
Issuance of common stock, net of issuance costs (in shares)						37,012,500	4,310,526
Issuance of common stock, net of issuance costs		72,782	$ 7,574			$ 37	$ 4		72,745	$ 7,570
Issuance of common stock under equity compensation plans (in shares)					858,971
Issuance of common stock under equity compensation plans	(879)				$ 1			(880)
Net and comprehensive loss	$ (78,765)										(78,765)
Preferred stock shares, ending balance (in shares) at Dec. 31, 2020	0			0
Ending balance at Dec. 31, 2020	$ 31,362			$ 0	$ 202			527,549			(496,389)
Common stock, ending balance (in shares) at Dec. 31, 2020	201,973,582				201,973,582
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	$ 8,556							8,556
Issuance of common stock, net of issuance costs (in shares)						40,031,000
Issuance of common stock, net of issuance costs		$ 64,263				$ 40			$ 64,223
Issuance of common stock under equity compensation plans (in shares)					839,598
Issuance of common stock under equity compensation plans	(857)				$ 1			(858)
Net and comprehensive loss	$ (86,955)										(86,955)
Preferred stock shares, ending balance (in shares) at Dec. 31, 2021	0			0
Ending balance at Dec. 31, 2021	$ 16,369			$ 0	$ 243			$ 599,470			$ (583,344)
Common stock, ending balance (in shares) at Dec. 31, 2021	242,844,180				242,844,180

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating activities
Net loss	$ (86,955)	$ (78,765)	$ (44,582)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,427	890	698
Stock-based compensation	8,556	7,379	4,851
Operating right-of-use assets, net	235	0	0
Changes in operating assets and liabilities:
Prepaid expenses, deposits and other	(1,605)	(2,126)	1,102
Net cash used in operating activities	(76,185)	(61,810)	(35,326)
Investing activities
Purchases of equipment	(1,360)	(1,162)	(579)
Net cash used in investing activities	(1,360)	(1,162)	(579)
Financing activities
Shares retained for withholding tax payments on stock-based awards	(857)	(879)	(424)
Net cash provided by financing activities	63,406	79,477	19,887
(Decrease) Increase in cash and cash equivalents	(14,139)	16,505	(16,018)
Cash and cash equivalents at beginning of year	51,546	35,041	51,059
Cash and cash equivalents at end of year	37,407	51,546	35,041
Non-cash investing activities:
Right-of-use assets obtained in exchange for lease liabilities	9,162	0	0
Healios
Changes in operating assets and liabilities:
Accounts receivable from Healios - billed and unbilled	(4,325)	856	3,783
Accounts payable to Healios	(586)	637	1,068
Deferred revenue - Healios	3,275	0	(609)
Advance from Healios	(2)	(137)	199
Financing activities
Proceeds from issuance of common stock, net	0	7,574	0
Consolidated entity, excluding related party
Changes in operating assets and liabilities:
Accounts payable, accrued expenses and other	3,795	9,456	(1,836)
Financing activities
Proceeds from issuance of common stock, net	$ 64,263	$ 72,782	$ 20,311

Background

Background	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Background	Background Athersys, Inc., including its consolidated subsidiaries (collectively, “we,” “us,” “Athersys,” and the “Company”) is a biotechnology company focused in the field of regenerative medicine and operates in one business segment. Our operations consist of research, clinical development, manufacturing and manufacturing process development activities, and our most advanced program is in a pivotal Phase 3 clinical trial. We expect that the the results of the TREASURE study, the clinical trial of our partner in Japan, HEALIOS K.K. (“Healios”), followed by the results of our MASTERS-2 clinical trial, will have a significant impact, favorable or unfavorable, on our ability to access capital from potential third-party commercial partners or the equity capital markets. Depending on the nature of these results, we may accelerate or may delay certain programs. In the longer term, we will have to continue to generate additional capital to meet our needs until we would become cash flow positive as a result of the sales of our clinical products, if they are approved for marketing. Such capital would come from new and existing collaborations and the related license fees, milestones and potential royalties and the sale of equity securities from time to time including through our equity facility and grant-funding opportunities. Healios Framework Agreement On August 5, 2021, we expanded our partnership with Healios by entering into the Comprehensive Framework Agreement for Commercial Manufacturing and Ongoing Support (the “Framework Agreement”) to optimize and better align the collaboration structure to drive therapeutic reach and commercial success in Japan for the MultiStem product following potential regulatory approval. The Framework Agreement provides for planned investment by Healios in certain manufacturing preparation activities. We have agreed to defer certain milestone payments and potentially adjust royalty payments during the initial commercial launch period. Refer to Note F, Collaborative Arrangements and Revenue Recognition , for additional information. On February 16, 2021, the Company, Healios and Dr. Hardy TS Kagimoto, the Chairman and Chief Executive Officer of Healios and a member of our board of directors (the “Board”), entered into a cooperation agreement (the “Cooperation Agreement”). The Cooperation Agreement provided for the parties’ cooperation on certain commercial matters, including a commitment to work in good faith to finalize negotiations on all aspects of their supply, manufacturing, information provision and regulatory support relationship. The Cooperation Agreement also provided for, among related matters, the dismissal with prejudice of the complaint filed by Dr. Kagimoto against the Company seeking the inspection of the Company’s books and records in the Court of Chancery of the State of Delaware on November 21, 2020 (the “Section 220 Litigation”). Pursuant to the Cooperation Agreement, in April 2021, we reimbursed Healios and Dr. Kagimoto for reasonable out-of-pocket fees and expenses, including legal expenses, incurred in connection with the Section 220 Litigation, which were not to exceed $0.5 million in the aggregate. In connection with the execution of the Framework Agreement, certain issues as contemplated by the Cooperation Agreement were resolved and the Cooperation Agreement was amended to extend certain customary standstill provisions until the conclusion of our 2023 annual meeting of stockholders. Retention Program In the first quarter of 2021, we entered into retention letter agreements (“Retention Agreements”) with our executive officers and certain other employees in leadership positions. Each Retention Agreement provides for, among other things, a cash retention bonus and a stock option award, each with vesting tied to continued employment. The cash retention bonuses generally represent a percentage of the employee’s annual compensation and generally vest in full if employed on May 1, 2022. The stock option awards generally vest one-third on May 1, 2022 with the remainder vesting on May 1, 2023 and include a provision for accelerated vesting upon termination without cause. The total stock compensation expense related to the stock option awards is approximately $2.7 million and is being expensed ratably over the vesting period. In April 2021, we expanded the retention program to all then-current employees of the Company, providing for a cash retention bonus with vesting also tied to continued employment through May 1, 2022. The total cash retention bonus is approximately $2.5 million, which is being expensed ratably over the respective vesting periods. Chief Executive Officer Separation Letter Agreement Effective February 15, 2021, Dr. Gil Van Bokkelen resigned from his position as the Company’s Chief Executive Officer and Chairman of the Board. In connection with his resignation, the Company and Dr. Van Bokkelen entered into a separation letter agreement (the “Separation Letter”) entitling him to severance payments and benefits with an aggregate value of approximately $1.0 million payable in installments over an 18-month period, and providing for a total lump sum payment of approximately $0.2 million. At December 31, 2021, we recorded a liability in the amount of $0.4 million, which represents the remaining installments payable to Dr. Van Bokkelen. The lump sum payment was made to Dr. Van Bokkelen in March 2021. The related expense is recorded in general and administrative expense on the consolidated statements of operations and comprehensive loss. The terms of the Separation Letter also provided for the accelerated vesting of Dr. Van Bokkelen’s outstanding restricted stock units (“RSUs”) and the modification of his stock option awards by providing for accelerated vesting of his unvested stock options and the extension of time during which certain vested stock options can be exercised. In the first quarter of 2021, following the evaluation of the modification, we recorded stock compensation expense of approximately $1.4 million related to the accelerated vesting of Dr. Van Bokkelen’s stock options and $0.9 million related to the accelerated vesting of his RSUs.

Going Concern

Going Concern	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Going Concern	Going ConcernWe have prepared our consolidated financial statements on a going concern basis, which assumes that we will realize our assets and satisfy our liabilities in the normal course of business. However, we have incurred net losses since our inception in 1995 and have negative operating cash flows. These factors, among others, raise substantial doubt about our ability to continue as a going concern within one year after the date that these financial statements are issued.At December 31, 2021, we had cash and cash equivalents of $37.4 million. We will require significant additional capital to continue our research and development programs, including progressing our clinical product candidates to potential commercialization and preparing for commercial-scale manufacturing and sales. The accompanying consolidated financial statements do not include any adjustments to reflect the possible future effect on the recoverability and classification of assets or the amounts and classification of liabilities that may result from the outcome of the uncertainty concerning our ability to continue as a going concern. Management plans to raise additional capital through the use of our equity purchase agreement with Aspire Capital Fund, LLC (“Aspire Capital”) and, depending on market conditions, through equity offerings. We are entitled to a new milestone payment from Healios in the amount of $3.0 million by June 2022. Additionally, management has the ability to defer certain spending and potentially defer and delay certain non-core programs. While management believes this plan to generate additional funds will alleviate the conditions that raise substantial doubt, these plans are not entirely within its control and cannot be assessed as being probable of occurring. For the foreseeable future, our ability to continue our operations is dependent upon the ability to obtain additional capital.

Accounting Policies

Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Accounting Policies	Accounting Policies Accounting Standards Adopted In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes , which simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The ASU is effective for fiscal years beginning after December 15, 2020. We adopted this ASU prospectively as of January 1, 2021 and the adoption of this ASU did not have a material impact on our consolidated financial statements and disclosures. Accounting Standards Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments (Topic 326) . This ASU replaces the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. Subsequent to issuing ASU 2016-13, the FASB issued ASU 2019-10, Financial Instruments - Credit Losses (Topic 326): Effective Dates , delaying the effective date for smaller reporting companies until January 2023. We are currently evaluating the potential impact of adoption of this standard on our consolidated financial statements and disclosures, and we do not intend to early adopt. Principles of Consolidation The consolidated financial statements include our accounts and results of operations and those of our wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates. Reclassification Certain reclassifications of prior period presentations have been made to conform to the current period presentation. Revenue Recognition Our license and collaboration agreements may contain multiple elements, including license and technology access fees, research and development funding, product supply revenue, service revenue, cost-sharing, milestones and royalties. The deliverables under our arrangements are evaluated under FASB Accounting Standards Codification No. 606 (“Topic 606”) which requires an entity to recognize revenue in a manner that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Milestone Payments Topic 606 does not contain guidance specific to milestone payments, but rather requires potential milestone payments to be considered in accordance with the overall model of Topic 606. As a result, revenues from contingent milestone payments are recognized based on an assessment of the probability of milestone achievement and the likelihood of a significant reversal of such milestone revenue at each reporting date. This assessment may result in recognizing milestone revenue before the milestone event has been achieved. Since milestone payments in the Healios arrangement are generally related to development and commercial milestone achievement by Healios, we only include milestones that are unconditionally entitled to in the estimated transaction price of the Healios arrangement. Conditional or contingent milestones are constrained to the extent that a significant reversal of revenue could result in future periods. Refer to Note F, Collaborative Arrangements and Revenue Recognition, for further information. Grant Revenue Grant revenue, which is not within the scope of Topic 606 for our grant arrangements, consists of funding under cost reimbursement programs primarily from federal and non-profit foundation sources for qualified research and development activities performed by us, and as such, are not based on estimates that are susceptible to change. Such amounts are invoiced and recorded as revenue as grant-funded activities are performed, with any advance funding recorded as deferred revenue until the activities are performed. Royalty Revenue We generate royalty revenue from the sale of licensed products by our licensees. Royalty revenue is recognized upon the later to occur of (i) achievement of the collaborator’s underlying sales and (ii) satisfaction of any performance obligation(s) related to these sales, in each case assuming the license to our intellectual property is deemed to be the predominant item to which the sales-based royalties relate. Contractual Right to Consideration and Deferred Revenue Amounts included in deferred revenue or contract assets are determined at the contract level, and for our Healios arrangement, such amounts are included in a contract asset or liability depending on the overall status of the arrangement. Amounts received from customers or collaborators in advance of our performance of services or other deliverables are included in deferred revenue, while amounts for performance of services or other deliverables in excess of the customer payment received are included in contract assets, with those accounts that are unconditional and billed being included in accounts receivable separate from contract assets. Grant proceeds received in advance of our performance under the grant is included in deferred revenue. Cash and Cash Equivalents We consider all highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash equivalents are primarily invested in money market funds. The carrying amount of our cash equivalents approximates fair value due to the short maturity of the investments. Research and Development Research and development expenditures, which consist primarily of costs associated with clinical trials, preclinical research, clinical product manufacturing and process development for manufacturing, personnel, legal fees resulting from intellectual property application and maintenance processes, and laboratory supply and reagent costs, including direct and allocated overhead expenses, are charged to expense as incurred. Clinical Trial Costs Clinical trial costs are accrued based on work performed by outside contractors that manage and perform the trials, and those that manufacture the investigational product. We obtain initial estimates of total costs based on enrollment of subjects, trial duration, project management estimates, manufacturing estimates, patient treatment costs and other activities. Actual costs may be charged to us and recognized as the tasks are completed by the contractor or, alternatively, may be invoiced in accordance with agreed-upon payment schedules and recognized based on estimates of work completed to date. Accrued clinical trial costs may be subject to revisions as clinical trials progress, and any revisions are recorded in the period in which the facts that give rise to the revisions become known. Royalty Payments and Sublicense Fees We are required to make royalty payments to certain parties based on our product sales under license agreements. No royalties were recorded during the year ended December 31, 2021, since we have not yet generated sales revenue. We are also required to record sublicense fees from time-to-time in connection with license fees from collaborators and clinical and commercial milestone achievement. Sublicenses fees were not significant in 2021 and 2020, and we recorded sublicense fees of $0.1 million in research and development expenses in the consolidated statements of operations and comprehensive loss in the year ended December 31, 2019. Long-Lived Assets Property and equipment is stated at acquired cost net of depreciation and amortization. Laboratory and office equipment are depreciated on the straight-line basis over the estimated useful lives ( three Long-lived assets are evaluated for impairment when events or changes in circumstances indicate that the carrying amount of the asset or related group of assets may not be recoverable. If the expected future undiscounted cash flows are less than the carrying amount of the asset or related group of assets, an impairment loss is recognized at that time. Measurement of impairment may be based upon appraisal, market value of similar assets or discounted cash flows. Leasing Arrangements We lease equipment, buildings and office space under operating lease arrangements. We have various supply agreements with third-party manufacturers, which involve the lease of manufacturing facilities and equipment, as defined in Topic 842. We have elected to separate lease and non-lease components for these arrangements. These manufacturing agreements have variable lease payments, which typically become binding once certain manufacturing milestones are achieved, and as such, are not included in right-of-use (“ROU”) assets and lease liabilities until such payments are no longer variable. We do not separate lease and non-lease components for all other currently existing asset classes. We apply the short-term lease exemption to all qualified lease agreements. The short-term lease exemption allows for the non-recognition of ROU assets and lease liabilities for leases with a term of twelve months or less. We determine if an arrangement is or contains a lease at contract inception and exercise judgment and apply certain assumptions when determining the discount rate, lease term and lease payments. Generally, we do not have knowledge of the discount rate implicit in the lease and, therefore, in most cases we use the incremental borrowing rate to compute the present value of future lease payments. The incremental borrowing rate is determined based on lease term and leased asset, and is adjusted for the impacts of collateral. The lease term includes the non-cancelable period of the lease plus any additional periods covered by an option to extend that we are reasonably certain to exercise, or an option to extend that is controlled by the lessor. Lease expense for lease payments is recognized on a straight-line basis over the lease term. Payments for certain lease agreements are adjusted annually for changes in an index or rate. We had no finance leases, residual value guarantees, restrictive covenants, subleases or sale leaseback transactions at December 31, 2021 and 2020. All ROU assets are periodically reviewed for impairment losses. Refer to Note K, Leasing Arrangements , for further information. Patent Costs and Rights Costs of applying for, prosecuting and maintaining patents and patent rights are expensed as incurred. We have filed for broad intellectual property protection on our proprietary technologies and have numerous United States and international patents and patent applications related to our technologies. Warrants We account for common stock warrants as either liabilities or as equity instruments depending on the specific terms of the warrant agreements. Generally, warrants are classified as liabilities, as opposed to equity, if the agreement includes the potential for a cash settlement or an adjustment to the exercise price, and warrant liabilities are recorded at their fair values at each balance sheet date. We had no warrant liabilities or warrant equity instruments recorded in the consolidated financial statements at December 31, 2021 and 2020. Refer to Note G, Capitalization and Warrant Instruments , for a discussion of common stock warrants issued to Healios in 2021. Concentration of Credit Risk Our accounts receivable are generally comprised of amounts due from collaborators and granting authorities and are subject to concentration of credit risk due to the absence of a large number of customers. At December 31, 2021 and 2020, our accounts receivable are due from Healios. We do not typically require collateral from our customers. Legal Matters We evaluate the development of legal matters on a regular basis and accrue a liability when we believe a loss is probable and the amounts can be reasonably estimated. Stock-Based Compensation Compensation expense related to stock options granted is measured at the grant date based on the estimated fair value of the award and is recognized using the straight-line method over the requisite service period, for awards without performance conditions. We determine the estimated fair value of each stock option on the date of grant using the Black-Scholes option-pricing model. The expected term of stock options granted represent the period of time that stock option grants are expected to be outstanding. The risk-free interest rate is based on the U.S. Treasury yield for a period consistent with the expected term of the stock option at the time of the grant. We determine volatility by using our historical stock volatility. We account for forfeitures as they occur. We have never paid or declared dividends or paid dividends on our common stock and have no plans to do so in the foreseeable future. Changes in these assumptions may lead to variability with respect to the amount of stock compensation expense we recognize related to stock options. Stock-based compensation for an award with a performance condition is recognized when the achievement of such performance condition is determined to be probable. If the outcome of such performance condition is not determined to be probable or is not met, no compensation expense is recognized. Prior to June 2020, we used the “simplified” method to calculate the expected term of option grants. In June 2020, we modified our stock option awards for all then-current employees and directors by providing an extension to the period of time during which vested stock options can be exercised. The extension to the period of time during which stock options can be exercised also applies to all stock options granted after June 2020. Subsequent to the modification date, our stock options no longer qualify to use the “simplified” method, and the expected term of our option grants is determined based on the historical experience and patterns, as well as current trends as previously described. The fair value of our restricted stock units is equal to the closing price of our common stock on the date of grant and is expensed over the vesting period on a straight-line basis. Restricted stock units typically vest over a four-year period. Refer to Note H, Stock-Based Compensation , for additional information. Stock option awards to employees typically vest over a four-year period, have an exercise price equal to the fair market value of a share of common stock on the grant date and have a contractual term of 10 years. The following weighted-average input assumptions were used in determining the fair value of our stock options granted: December 31, 2021 2020 2019 Volatility 75.2 % 72.2 % 71.1 % Risk-free interest rate 0.8 % 0.6 % 2.0 % Expected life of option 5.4 years 5.7 years 6.2 years Expected dividend yield 0.0 % 0.0 % 0.0 % Income Taxes Deferred tax liabilities and assets are determined based on the differences between the financial reporting and tax basis of assets and liabilities and are measured using the tax rate and laws currently in effect. We evaluate our deferred income taxes to determine if a valuation allowance should be established against the deferred tax assets or if the valuation allowance should be reduced based on consideration of all available evidence, both positive and negative, using a “more likely than not” standard. We had no liability for uncertain income tax positions as of December 31, 2021 and 2020. Our policy is to recognize potential accrued interest and penalties related to the liability for uncertain tax benefits, if applicable, in income tax expense. Net operating loss and credit carryforwards since inception remain open to examination by taxing authorities and will for a period post utilization. Net Loss per Share Basic and diluted net loss per share have been computed using the weighted-average number of shares of common stock outstanding during the period. We have outstanding options and restricted stock units and, in 2021 and 2019, had outstanding warrants that were not used in the calculation of diluted net loss per share because to do so would be antidilutive. The following instruments, were excluded from the calculation of diluted net loss per share because their effects would be antidilutive: Years ended December 31, 2021 2020 2019 Stock options 23,043,035 18,150,409 13,975,671 Restricted stock units 1,985,057 2,374,006 2,032,180 Warrants — — 4,000,000 25,028,092 20,524,415 20,007,851 We issued 10,000,000 common stock warrants to Healios in 2021 which are excluded from the calculation of diluted net loss per share, as the underlying performance condition associated with each warrant has not been satisfied and is not yet considered probable at the end of the reporting period. Refer to Note G. Capitalization and Warrant Instruments , for a discussion of the common stock warrants issued to Healios in 2021.

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Property and Equipment, net	Property and Equipment, net December 31, Property and equipment consists of (in thousands): 2021 2020 Laboratory equipment $ 9,352 $ 9,225 Office equipment and leasehold improvements 4,000 3,336 Process development equipment not yet in service 458 294 13,810 12,855 Accumulated depreciation and amortization (10,118) (9,700) $ 3,692 $ 3,155

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Financial Instruments	Financial Instruments Fair Value Measurements We classify the inputs used to measure fair value into the following hierarchy: Level 1 Unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 Unadjusted quoted prices in active markets for similar assets or liabilities, or unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or inputs other than quoted prices that are observable for the asset or liability. Level 3 Unobservable inputs for the asset or liability. Cash equivalents primarily consist of money market funds with overnight liquidity and no stated maturities. We classified cash equivalents as a Level 1 due to the short-term nature of these instruments and measured the fair value based on quoted prices in active markets for identical assets.

Collaborative Arrangements and

Collaborative Arrangements and Revenue Recognition	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborative Arrangements and Revenue Recognition	Collaborative Arrangements and Revenue Recognition Healios Collaboration In 2016, we entered into a license agreement (the “First License Agreement”) with Healios to develop and commercialize MultiStem cell therapy for ischemic stroke in Japan and to provide Healios with access to our proprietary MAPC technology for use in Healios’ organ bud program, initially for transplantation to treat liver disease or dysfunction. Under the terms of the First License Agreement, Healios also obtained a right to expand the scope of the collaboration to include the exclusive rights to develop and commercialize MultiStem for the treatment of two additional indications in Japan which included acute respiratory distress syndrome (“ARDS”) and another indication in the orthopedic area, and all indications for the organ bud program. Under the collaboration, Healios is responsible for the development and commercialization of the MultiStem product in the licensed territories, and we provide manufacturing services to Healios, comprising the supply of product for its clinical trials, technology transfer services and services related to commercial readiness in Japan. In 2017, we signed a clinical trial supply agreement for delivering the planned manufacturing services for Healios’ clinical trial in Japan, entitled, “ Treatment Evaluation of Acute Stroke for Using in Regenerative Cell Elements ” (“TREASURE”). The clinical trial supply agreement was amended later that year to clarify the operational elements, terms and cost-sharing arrangement associated with our supply of clinical material and certain adjustments to potential milestone payments related to the clinical product supply for TREASURE. Also in 2017, we entered into a technology transfer services agreement with Healios, in which Healios provides financial support to establish a contract manufacturer in Japan to produce product for Healios’ use. Related to the technology transfer services agreement with Healios, at the request of Healios, we entered into a manufacturing services agreement with Nikon CeLL innovation (“NCLi”), a subsidiary of Nikon Corp. and a significant Healios shareholder. At that time, we also amended the First License Agreement to confer to Healios a limited license to manufacture MultiStem if we are acquired by a third-party. The technology transfer services agreement with Healios was complete as of September 2019 and NCLi continued to provide technology transfer services to us. In the fourth quarter of 2019, the Company and Healios entered into a memorandum of understanding (the “Memorandum”) to provide additional technology transfer services. In June 2018, as contemplated by the First License Agreement, Healios exercised its option to expand the collaboration and entered into the Collaboration Expansion Agreement (“CEA”) that included new license agreements and rights that further broadened the collaboration. Under the CEA, Healios (i) expanded its First License Agreement to include ARDS in Japan, expanded the organ bud license to include all transplantation indications, and terminated Healios’ right to include a designated orthopedic indication per the First License Agreement; (ii) obtained a worldwide exclusive license, or the Ophthalmology License Agreement, for use of MultiStem product to treat certain ophthalmological indications; (iii) obtained an exclusive license in Japan (the "Combination Product License Agreement”), for use of the MultiStem product to treat diseases of the liver, kidney, pancreas and intestinal tissue through local administration of MultiStem in combination with iPSC-derived cells; (iv) obtained an exclusive, time-limited right of first negotiation (“ROFN Period”) to enter into an option for a license to develop and commercialize certain MultiStem treatments in China, which has since expired; and (v) an option for an additional non-therapeutic technology license, which has also expired. For each of the ischemic stroke indication and the ARDS indication, we may receive success-based regulatory filing and approval and sales milestones aggregating up to $225.0 million in aggregate for each indication, subject to potential milestone credits. Milestone payments are non-refundable and non-creditable towards future royalties or any other payment due from Healios. We may also receive tiered royalties on net product sales, starting in the low double digits and increasing incrementally into the high teens depending on net sales levels. For standalone products sold by Healios under the Ophthalmology License Agreement, we are entitled to receive success-based regulatory filing and approval and sales milestones aggregating up to $135.6 million and tiered royalties on net product sales in the single digits depending on net sales levels. For the combination products under the Ophthalmology License Agreement, we will be entitled to receive a low single-digit royalty, but no milestone payments. Under the Combination Product License Agreement, we are entitled to receive a low single-digit royalty on net sales of the combination product treatments, but no milestone payments. For the organ bud product, we are entitled to receive a fractional royalty percentage on net sales of the organ bud products. Under the CEA, the ROFN Period with respect to the option for a license in China was extended to June 30, 2019 in exchange for a $2.0 million payment from Healios that we received in December 2018. The extension payment will be applied as a credit against any potential milestone payments under the current licenses, subject to certain limitations. The ROFN Period expired on June 30, 2019. In connection with the entry into the CEA, we amended the terms of the Healios Warrant as addressed in Note G, Capitalization and Warrant Instruments . In August 2021, the Company and Healios entered into the Framework Agreement, which provides for clarification under and modifies the existing agreements between the parties and reframes our collaboration to set the stage for productive efforts as Healios and our collaboration move towards commercialization of MultiStem in Japan. It also provides Healios with deferral of certain milestone payments during the expensive initial commercial launch period. We will be entitled to new milestone payments in the amount of $3.0 million by June 2022 and $5.0 million upon successful completion of certain commercial manufacturing activities. Additionally, accounts payable to Healios have been reduced to $1.1 million and are due on or before December 31, 2022. In connection with the execution of the Framework Agreement, the Cooperation Agreement was amended to extend certain customary standstill provisions until the conclusion of our 2023 annual meeting of stockholders. We also issued two warrants (together, the “2021 Warrants”) to Healios in connection with the Framework Agreement to purchase up to a total of 10,000,000 shares of our common stock. The 2021 Warrants are being accounted for as consideration paid or payable to a customer according to Topic 606, Revenue from Contracts with Customers , and Topic 718, Compensation - Stock Compensation, under which the recognition of such equity instruments is required at the time that the underlying performance conditions become probable or are satisfied. As of December 31, 2021, the 2021 Warrants have not been recorded as the underlying performance conditions have not been satisfied and are not yet considered probable. Refer to Note G Capitalization and Warrant Instruments, for further information. Healios Revenue Recognition At the inception of the Healios arrangement and again each time that the arrangement has been modified, all material performance obligations were identified, which include (i) licenses to our technology, (ii) product supply services, and (iii) manufacturing services provided on Healios’ behalf. In order to determine the transaction price, in addition to the fixed payments, we estimate the amount of variable consideration utilizing the expected value or most likely amount method, depending on the facts and circumstances relative to the contract, and the estimates for variable consideration are reassessed each reporting period. We constrain, or reduce, the estimates of variable consideration if it is probable that a significant revenue reversal could occur in future periods. The pricing for certain product supply provided to Healios was driven off the underlying cost per dose over the entire life of the agreement and subject to variability as those costs change. During 2019, the price per dose from our contract manufacturers decreased for the first time under this arrangement. As such, we reduced the expected transaction price to the current estimated value and applied the reduction to the undelivered elements of the overall arrangement at the time this product supply performance obligation originated. Furthermore, the number of doses of clinical product requested by Healios was amended in 2019, and our revenues were further reduced. At inception and upon each date a modification has resulted under the Healios arrangement, once the estimated transaction price is established, amounts are allocated to each separate performance obligation on a relative standalone selling price basis. These performance obligations include any remaining, undelivered elements at the time of the modification and any new elements from a modification to the Healios arrangement as the conditions are not met for being treated as a separate agreement. For performance obligations satisfied over time, we apply an appropriate method of measuring progress each reporting period and, if necessary, adjust the estimates of performance and the related revenue recognition. Our services provided on Healios’ behalf are satisfied over time, and we recognize revenue in proportion to the contractual services provided, measured by costs incurred compared to total estimated costs. For performance obligations satisfied at a point in time (i.e., product supply), we recognize revenue upon delivery. Under the Framework Agreement, it was determined there is currently one performance obligation for services necessary for regulatory approvals, manufacturing readiness, and commercial launch in Japan. We determined the transaction price includes estimated payments for reimbursable services to be performed by us for Healios and the $3.0 million milestone payment due no later than June 2022. We allocated the total transaction price to this one performance obligation. We began recognizing revenue in the third quarter of 2021 as the services were being performed, which are now expected to be completed by the end of 2022. During our evaluation of variable consideration in the fourth quarter of 2021, we increased our estimated transaction price due to changes in the estimated cost of the reimbursable services. The remaining transaction price for the performance obligation that was not yet satisfied is $5.6 million at December 31, 2021. We recognized revenue of approximately $0.5 million for the twelve months ended December 31, 2021, and no revenue for the twelve months ended December 31, 2020 from performance obligations partially satisfied in previous periods. Accounts receivable from Healios Accounts receivable from Healios are related to our contracts and are recorded when the right to consideration is unconditional at the amount that management expects to collect. Accounts receivable from Healios do not bear interest if paid when contractually due, and payments are generally due within thirty Unbilled Accounts Receivable from Healios Unbilled accounts receivable from Healios represent amounts due to us under contractual arrangements and for which we have an unconditional right to the consideration, but which we have not yet invoiced Healios. At December 31, 2021, the unbilled accounts receivable from Healios was $3.0 million, which represents a milestone payment owed to us under the Framework Agreement for which we are entitled to receive payment by June 2022. Deferred Revenue - Healios Amounts included in deferred revenue - Healios on the consolidated balance sheets, are considered a contract liability. During the twelve months ended December 31, 2021, revenue recognized from contract liabilities as of the beginning of the respective period was $0.1 million. No revenue was recognized from contract liabilities during the twelve months ended December 31, 2020. At December 31, 2021, the contract liability included in deferred revenue - Healios, is classified as a current liability since the rights to consideration are expected to be satisfied, in all material respects, within one year. Advance from Healios In 2017, we amended the clinical trial supply agreement for the manufacturing of clinical product for TREASURE to clarify a cost-sharing arrangement. The proceeds from Healios that relate specifically to the cost-sharing arrangement may either (i) result in a reduction, as defined in the clinical trial supply agreement, in the proceeds we receive from Healios upon the achievement of two potential milestones and an increase to a commercial milestone under the First License Agreement for stroke or (ii) be repaid to Healios at our election, as defined in the clinical trial supply agreement. The cost-sharing proceeds received are recognized on the balance sheet as a non-current advance from customer until the related milestone is achieved, unless such amounts are repaid to Healios at our election, at which time, the culmination of the earnings process will be complete and revenue will be recognized. Disaggregation of Revenues We recognize license-related amounts, including upfront payments, exclusivity fees, additional disease indication fees, and development, regulatory and sales-based milestones, at a point in time when earned. Similarly, product supply revenue is recognized at a point in time, while service revenue is recognized when earned over time. The following table presents our contract revenues disaggregated by timing of revenue recognition and excludes royalty revenue (in thousands): Twelve Months Ended Twelve Months Ended Twelve Months Ended Point in Time Over Time Point in Time Over Time Point in Time Over Time Contract revenue from Healios: License fee revenue $ — $ — $ — $ — $ 1,624 $ — Product supply revenue 283 — 1,432 — 2,167 — Service revenue — 5,231 — — — 1,726 Total disaggregated revenues $ 283 $ 5,231 $ 1,432 $ — $ 3,791 $ 1,726

Capitalization and Warrant Inst

Capitalization and Warrant Instruments	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Capitalization and Warrant Instruments	Capitalization and Warrant Instruments Capitalization In June 2021, our stockholders approved an amendment to our certificate of incorporation to increase the number of shares of the Company’s authorized common stock from 300,000,000 shares to 600,000,000 shares. At December 31, 2021 and December 31, 2020, we had 600,000,000 and 300,000,000 shares of common stock, respectively, and 10,000,000 shares of undesignated preferred stock authorized. No shares of preferred stock have been issued as of December 31, 2021 and 2020. In April 2020, we completed an underwritten public offering of common stock generating net proceeds of approximately $53.7 million through the issuance of 25,587,500 shares of common stock at the offering price of $2.25 per share. The following shares, in thousands, of common stock were reserved for future issuance: December 31, 2021 2020 Stock-based compensation 28,204 29,591 Healios Warrants to purchase common stock 10,000 — 38,204 29,591 Healios Investor Rights Agreement In March 2018, we entered into an investor rights agreement (the “Investor Rights Agreement”) with Healios that governs certain of our and Healios’ rights relating to its ownership of our common stock. Under the Investor Rights Agreement, Healios is permitted to participate in certain equity issuances as a means to maintain its proportionate ownership of our common stock as of the time of such issuance. In May 2020, we entered into a purchase agreement with Healios, providing for Healios to purchase shares of our common stock in connection with certain equity issuances to Aspire Capital. Healios purchased 310,526 shares of our common stock at $1.72 per share for an aggregate purchase price of $0.5 million, in accordance with the terms of the Investor Rights Agreement. Under the Investor Rights Agreement, we further agreed that during such time as Healios beneficially owns more than 5.0% but less than 15.0% of our outstanding common stock, our Board of Directors (the “Board”) will nominate a Healios nominee suitable to us to become a member of the Board, and during such time as Healios beneficially owns 15.0% or more of our outstanding common stock, our Board will nominate two suitable Healios nominees to become members of the Board, at each annual election of directors. Healios nominated an individual to the Board, who was elected at the 2018 annual stockholders’ meeting. As a result of Healios’ investment, Healios became a related party, and the transactions with Healios are separately identified within these financial statements as related party transactions. In connection with the Framework Agreement, Healios agreed to terminate its existing right under the Investor Rights Agreement to nominate two nominees for election to the Board, if Healios beneficially owned 15.0% or more of our outstanding shares of common stock. Healios retains the right to appoint one nominee for election to the Board if Healios beneficially owns 5.0% or more of our outstanding shares of common stock. Healios Warrants In March 2018, we issued to Healios a warrant to purchase up to 20,000,000 shares of our common stock (the “2018 Warrant”). Based upon the terms of the 2018 Warrant as amended in June 2018, it was no longer exercisable for up to 16,000,000 warrant shares as of June 2019. In March 2020, Healios elected to exercise the 2018 Warrant in full, and we issued 4,000,000 shares of our common stock at an exercise price equal to the reference price of $1.76 per share, as defined in the 2018 Warrant. Proceeds of approximately $7.0 million were received in April 2020 in accordance with the terms of the 2018 Warrant. In August 2021, we issued the 2021 Warrants to purchase up to an aggregate of 10,000,000 shares of our common stock. One of the 2021 Warrants is for the purchase of up to 3,000,000 shares at an exercise price of $1.80 per share, subject to specified increases, and generally is only exercisable within 60 days of receipt of either conditional or full marketing approval from the Pharmaceuticals and Medical Devices Agency in Japan (the “PMDA”) for the intravenous administration of MultiStem to treat patients who are suffering from acute respiratory distress syndrome. The other 2021 Warrant is for the purchase of up to 7,000,000 shares at an exercise price of $2.40 per share, subject to specified increases, and generally is only exercisable within 60 days of receipt of either conditional or full marketing approval from the PMDA for the intravenous administration of MultiStem to treat patients who are suffering from ischemic stroke. The 2021 Warrants may be terminated by us under certain conditions and have an exercise cap triggered at Healios’ ownership of 19.9% of our common stock. Equity Purchase Agreement We have had equity purchase agreements in place since 2011 with Aspire Capital that provide us the ability to sell shares to Aspire Capital from time to time. Currently, we have an agreement with Aspire Capital that was entered into in June 2021 (the “2021 Equity Facility”) and includes Aspire Capital’s commitment to purchase up to an aggregate of $100.0 million of shares of our common stock over a defined timeframe. The terms of the 2021 Equity Facility are similar to the previous equity facilities with Aspire Capital, and we filed a registration statement for the resale of 40,000,000 shares of our common stock in connection with the 2021 Equity Facility. Our prior equity facility that was entered into in 2019 (the “2019 Equity Facility”) was fully utilized and terminated during the third quarter of 2021. During the years ended December 31, 2021, 2020 and 2019, we sold 40,031,000, 11,425,000 and 14,475,000 shares, respectively, to Aspire Capital at average prices of $1.61, $1.67 and $1.41 per share, respectively.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	Stock-Based Compensation Our 2019 Equity and Incentive Compensation Plan (the “EICP”) authorized at inception an aggregate of approximately 19,000,000 shares of common stock for awards to employees, directors and consultants. The EICP was approved in June 2019 and replaced our prior long-term incentive plans. The EICP authorizes the issuance of stock-based compensation in the form of stock options, stock appreciation rights, restricted stock, restricted stock units, performance shares and units, and other stock-based awards. As of December 31, 2021, a total of 8,933,420 shares (including 282,365 shares related to an expired incentive plan) of common stock have been issued under our equity incentive plans. In June 2020, we modified option awards granted under the EICP and our prior equity plans for all then-current employees and directors by providing an extension to the period of time during which vested stock options can be exercised, subject to certain tenure-related conditions being met. The modification was applied to all then-outstanding nonqualified stock option awards outstanding on the modification date and to those incentive stock options held by individuals who accepted the modification. Following evaluation of the modification of the stock option awards, we recorded stock compensation expense of $1.2 million for the incremental value of stock option awards vested prior to the modification date. The remaining incremental value of $0.5 million determined at the modification date associated with the unvested stock option awards is being recognized over the remaining vesting period of these modified stock option awards. As of December 31, 2021, a total of 3,176,331 shares were available for issuance under our EICP, and stock-based awards representing 24,028,092 shares (including 820,478 shares related to an expired incentive plan) of common stock were outstanding. Additionally, inducement stock options granted outside of our equity incentive plans to purchase 1,000,000 shares of common stock were outstanding at December 31, 2021. We recognized $8.6 million, $7.4 million and $4.9 million of stock-based compensation expense in 2021, 2020 and 2019, respectively. Stock Options The weighted average fair value of options granted in 2021, 2020 and 2019 was $1.13, $1.50 and $1.00 per share, respectively. The total fair value of options vested during 2021, 2020 and 2019 was $4.8 million, $3.5 million and $3.0 million, respectively. The total intrinsic value of options exercised was not significant during the years ended December 31, 2021 and 2019, respectively, and $0.7 million during the year ended December 31, 2020. At December 31, 2021, total unrecognized estimated compensation cost related to unvested stock options was approximately $8.6 million, which is expected to be recognized by the end of 2025 using the straight-line method. The weighted average contractual life of unvested options at December 31, 2021 was 9.0 years. The aggregate intrinsic value of fully vested and exercisable option shares and option shares expected to vest as of December 31, 2021 not significant. A summary of our stock option activity and related information is as follows: Number Weighted Outstanding January 1, 2019 10,955,508 $ 1.87 Granted 3,402,608 1.55 Exercised (48,152) 1.40 Forfeited / Expired (334,293) 2.71 Outstanding December 31, 2019 13,975,671 1.77 Granted 5,213,168 2.44 Exercised (362,351) 1.70 Forfeited / Expired (676,079) 2.32 Outstanding December 31, 2020 18,150,409 1.95 Granted 6,240,204 1.81 Exercised (89,041) 1.77 Forfeited / Expired (1,258,537) 2.21 Outstanding December 31, 2021 23,043,035 $ 1.91 Vested during 2021 3,824,722 $ 1.99 Vested and exercisable at December 31, 2021 14,808,108 $ 1.88 December 31, 2021 Options Outstanding Options Vested and Exercisable Exercise Price Number Weighted Weighted Number Weighted Weighted $1.00 - $1.55 8,005,583 5.4 years $ 1.49 6,072,826 4.1 years $ 1.45 $1.56 - $2.17 8,196,562 6.7 years $ 1.82 3,260,020 2.9 years $ 1.74 $2.19 - $3.57 6,840,890 4.4 years $ 2.51 5,475,262 3.4 years $ 2.43 23,043,035 14,808,108 Restricted Stock Units A summary of our restricted stock unit activity and related information is as follows: Number Weighted Unvested January 1, 2019 1,656,688 $ 1.93 Granted 1,350,150 1.55 Vested-common stock issued (938,311) 1.87 Forfeited (36,347) 1.69 Unvested December 31, 2019 2,032,180 1.71 Granted 1,553,671 2.76 Vested-common stock issued (1,087,718) 1.98 Forfeited (124,127) 1.95 Unvested December 31, 2020 2,374,006 2.26 Granted 1,254,399 1.63 Vested-common stock issued (1,287,383) 2.10 Forfeited (355,965) 2.31 Unvested December 31, 2021 1,985,057 $ 1.97 Vested/Issued cumulative at December 31, 2021 7,883,277 $ 1.84 The total fair value of restricted stock units vested during 2021, 2020 and 2019 was $2.7 million, $2.2 million and $1.8 million, respectively. At December 31, 2021, total unrecognized estimated compensation cost related to unvested restricted stock units was approximately $3.8 million, which is expected to be recognized by the end of 2025 using the straight-line method.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes At December 31, 2021, we had U.S. federal net operating loss and research and development tax credit carryforwards of approximately $326.3 million and $20.6 million, respectively. Included in our federal net operating loss as of December 31, 2021 are federal net operating loss carryforwards generated after 2017 of $189.7 million that have an indefinite life, but with usage limited to 80% of taxable income in any given year. The remaining federal net operating losses and tax credits will expire at various dates between 2032 and 2041. We also had foreign net operating loss carryforwards of approximately $31.7 million. Such foreign net operating loss carryforwards do not expire. We also had state and city net operating loss carryforwards aggregating approximately $118.7 million. Such state and city net operating loss carryforwards may be used to reduce future taxable income and tax liabilities and will expire at various dates between 2022 and 2041. Certain state net operating losses do not expire. The utilization of net operating loss and tax credit carryforwards generated prior to October 2012 (the “Section 382 Limited Attributes”) is substantially limited under Section 382 of the Internal Revenue Code of 1986, as amended, (the “IRC”). We generated U.S. federal net operating loss carryforwards of $289.6 million, research and development tax credits of $20.6 million, and state and local net operating loss carryforwards of $118.5 million since 2012. We will update our analysis under Section 382 prior to using these attributes. A reconciliation of the federal statutory income tax rate to our effective tax rate is as follows: Percent of Income 2021 2020 Statutory federal income tax rate 21.0 % 21.0 % State income taxes - net of federal tax benefit 1.0 % 0.9 % Other permanent differences (2.1) % (1.4) % Valuation allowances (24.8) % (25.5) % Research and development - U.S. 4.9 % 5.0 % Effective tax rate for the year — % — % Significant components of our deferred tax assets and liabilities are as follows (in thousands): December 31, 2021 2020 Deferred tax assets: Net operating loss carryforwards $ 79,473 $ 61,670 Research and development credit carryforwards 20,587 16,308 Operating lease liabilities 1,918 146 Compensation expense 3,336 2,752 Other 2,618 3,534 Total deferred tax assets before valuation allowance 107,932 84,410 Valuation allowance for deferred tax assets (106,186) (84,255) Net deferred tax assets after valuation allowance 1,746 155 Deferred tax liabilities: Right-of-use asset (1,746) (155) Total deferred tax liabilities (1,746) (155) Net deferred tax assets $ — $ — Because of our cumulative losses, substantially all the deferred tax assets have been fully offset by a valuation allowance. We have not paid income taxes for the three-year period ended December 31, 2021. We file income tax returns with the Internal Revenue Service (“IRS”) and certain other taxing jurisdictions. We are subject to income tax examinations by the IRS and by state tax authorities until the net operating losses are settled.

Profit Sharing and 401(k) Plan

Profit Sharing and 401(k) Plan	12 Months Ended
	Dec. 31, 2021
Postemployment Benefits [Abstract]
Profit Sharing and 401(k) Plan	Profit Sharing and 401(k) PlanWe have a profit sharing and 401(k) plan that covers substantially all employees and allows for discretionary contributions by us. We make employer contributions to this plan, and the expense was approximately $0.6 million, $0.5 million and $0.4 million in 2021, 2020 and 2019, respectively.

Leasing Arrangements

Leasing Arrangements	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Leasing Arrangements	Leasing Arrangements As of December 31, 2021, ROU assets were $9.0 million and lease liabilities were $9.8 million. As of December 31, 2020 and 2019, ROU assets were $0.6 million and $0.7 million, and lease liabilities were $0.7 million and $0.7 million, respectively. The weighted-average remaining term for lease contracts was 8.9 years at December 31, 2021, 1.5 years at December 31, 2020 and 1.6 years at December 31, 2019. As of December 31, 2021, maturities ranged from 15 months to 114 months. The weighted-average discount rate was 8.8% at December 31, 2021, 5.0% at December 31, 2020, and 5.3% at December 31, 2019. We paid $1.3 million, $0.5 million and $0.5 million for operating leases included in the measurement of lease liabilities during the year ended December 31, 2021, 2020 and 2019, respectively. Warehouse Lease Agreement In January 2021, we entered into an operating lease agreement to lease approximately 214,000 square feet of warehouse and office space. The initial lease term is approximately ten years and includes five renewal options with terms of five years each. The lease commenced on May 1, 2021, upon us taking control of the warehouse and office space on that date. Base annual rent for the first year is approximately $1.3 million with 2.0% annual rent escalators. As of the lease commencement date, the right-of-use asset and corresponding operating lease liability was approximately $9.2 million, which represented the present value of remaining lease payments over the initial lease term, using an incremental borrowing rate of 9.0%. The terms of the lease agreement also include an allowance in the amount of $0.7 million for the cost of construction of office and laboratory space, some of which was completed as of December 31, 2021. We are also obligated to pay certain variable expenses separately from the base rent, including utilities, real estate taxes and common area maintenance. Such costs and have been excluded from the calculation of the right-of-use asset and corresponding operating lease liability and are being expensed in the period they are incurred. Lease Costs The table below presents certain information related to the lease costs (in thousands) for operating leases as of December 31, 2021, 2020 and 2019: Twelve months ended December 31, 2021 2020 2019 Operating lease cost $ 1,458 $ 516 $ 487 Short-term lease cost 134 111 61 Variable lease cost (1) 7,113 1,321 205 Total lease cost $ 8,705 $ 1,948 $ 753 (1) Includes lease components from our third-party manufacturing agreements. Undiscounted Cash Flows The following table summarizes future maturities (in thousands) for operating lease liabilities as of December 31, 2021: 2022 $ 1,927 2023 1,566 2024 1,390 2025 1,404 2026 1,432 2027 and beyond 6,803 Total minimum lease payments 14,522 Less: amount of lease payments representing interest 4,756 Present value of operating lease liabilities $ 9,766

Quarterly Financial Data (unaud

Quarterly Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2021
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data (unaudited)	Quarterly Financial Data (unaudited) The following table presents quarterly data for the years ended December 31, 2021 and 2020, in thousands, except per share data: 2021 First Second Third Fourth Full Year Revenues $ — $ — $ 4,792 $ 722 $ 5,514 Loss from operations (26,589) (22,572) (16,222) (21,675) (87,058) Net loss (26,468) (22,599) (16,177) (21,711) (86,955) Basic and diluted net loss per common share (1) $ (0.13) $ (0.10) $ (0.07) $ (0.09) $ (0.39) 2020 First Second Third Fourth Full Year Revenues $ — $ 84 $ 86 $ 1,270 $ 1,440 Loss from operations (15,759) (18,337) (22,318) (21,918) (78,332) Net loss (15,644) (18,372) (22,543) (22,206) (78,765) Basic and diluted net loss per common share (1) $ (0.10) $ (0.10) $ (0.11) $ (0.11) $ (0.42) (1) Due to the effect of quarterly changes to outstanding shares of common stock and weightings, the annual loss per share will not necessarily equal the sum of the respective quarters.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent EventsOn January 20, 2022, we announced that the Board appointed Daniel A. Camardo to the Board and also named Mr. Camardo as the Company’s Chief Executive Officer, each effective as of February 14, 2022. In connection with Mr. Camardo’s appointment to Chief Executive Officer, the Company and Mr. Camardo entered into an employment agreement (“the Employment Agreement”). The Employment Agreement provides for an initial annual base salary of $0.6 million, a cash signing bonus of $0.3 million and annual cash incentive compensation with a target opportunity equal to 60% of Mr. Camardo’s annual base salary subject to Company performance, as well as participation in our equity award program, severance and other standard employment benefits. As an inducement to Mr. Camardo’s acceptance of employment with us, Mr. Camardo was granted an initial equity award that is intended to be an inducement award (“the Inducement Award”) of a stock option award to purchase 10,000,000 shares of our common stock at a per share exercise price of $0.86. With regard to 4,000,000 shares, vesting of the Inducement Award will occur over a four-year period, with 25% of such portion of the award generally vesting on the first anniversary of the grant date and the remainder generally vesting monthly in substantially equal installments over the remaining 36 months. With regard to 6,000,000 shares, vesting of the Inducement Award will generally occur upon achievement of certain Company milestones, including FDA manufacturing process and marketing approvals, cumulative product sales, and business development and fundraising activities, as and when reasonably evaluated and determined by the Board in its sole discretion. The Inducement Award has up to a 10-year term.

Accounting Policies (Policies)

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Accounting Standards Adopted and Accounting Standards Not Yet Adopted	Accounting Standards Adopted In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740) - Simplifying the Accounting for Income Taxes , which simplifies the accounting for income taxes by removing certain exceptions to the general principles in Topic 740. The ASU is effective for fiscal years beginning after December 15, 2020. We adopted this ASU prospectively as of January 1, 2021 and the adoption of this ASU did not have a material impact on our consolidated financial statements and disclosures. Accounting Standards Not Yet Adopted In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments (Topic 326) . This ASU replaces the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses and requires consideration of a broader range of reasonable and supportable information to inform credit loss estimates. Subsequent to issuing ASU 2016-13, the FASB issued ASU 2019-10, Financial Instruments - Credit Losses (Topic 326): Effective Dates , delaying the effective date for smaller reporting companies until January 2023. We are currently evaluating the potential impact of adoption of this standard on our consolidated financial statements and disclosures, and we do not intend to early adopt.
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include our accounts and results of operations and those of our wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from those estimates.
Reclassification	ReclassificationCertain reclassifications of prior period presentations have been made to conform to the current period presentation.
Revenue Recognition	Revenue Recognition Our license and collaboration agreements may contain multiple elements, including license and technology access fees, research and development funding, product supply revenue, service revenue, cost-sharing, milestones and royalties. The deliverables under our arrangements are evaluated under FASB Accounting Standards Codification No. 606 (“Topic 606”) which requires an entity to recognize revenue in a manner that depicts the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. Milestone Payments Topic 606 does not contain guidance specific to milestone payments, but rather requires potential milestone payments to be considered in accordance with the overall model of Topic 606. As a result, revenues from contingent milestone payments are recognized based on an assessment of the probability of milestone achievement and the likelihood of a significant reversal of such milestone revenue at each reporting date. This assessment may result in recognizing milestone revenue before the milestone event has been achieved. Since milestone payments in the Healios arrangement are generally related to development and commercial milestone achievement by Healios, we only include milestones that are unconditionally entitled to in the estimated transaction price of the Healios arrangement. Conditional or contingent milestones are constrained to the extent that a significant reversal of revenue could result in future periods. Refer to Note F, Collaborative Arrangements and Revenue Recognition, for further information. Grant Revenue Grant revenue, which is not within the scope of Topic 606 for our grant arrangements, consists of funding under cost reimbursement programs primarily from federal and non-profit foundation sources for qualified research and development activities performed by us, and as such, are not based on estimates that are susceptible to change. Such amounts are invoiced and recorded as revenue as grant-funded activities are performed, with any advance funding recorded as deferred revenue until the activities are performed. Royalty Revenue We generate royalty revenue from the sale of licensed products by our licensees. Royalty revenue is recognized upon the later to occur of (i) achievement of the collaborator’s underlying sales and (ii) satisfaction of any performance obligation(s) related to these sales, in each case assuming the license to our intellectual property is deemed to be the predominant item to which the sales-based royalties relate. Contractual Right to Consideration and Deferred Revenue
Cash and Cash Equivalents	Cash and Cash EquivalentsWe consider all highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash equivalents are primarily invested in money market funds. The carrying amount of our cash equivalents approximates fair value due to the short maturity of the investments.
Research and Development	Research and Development Research and development expenditures, which consist primarily of costs associated with clinical trials, preclinical research, clinical product manufacturing and process development for manufacturing, personnel, legal fees resulting from intellectual property application and maintenance processes, and laboratory supply and reagent costs, including direct and allocated overhead expenses, are charged to expense as incurred.
Clinical Trial Costs	Clinical Trial Costs Clinical trial costs are accrued based on work performed by outside contractors that manage and perform the trials, and those that manufacture the investigational product. We obtain initial estimates of total costs based on enrollment of subjects, trial duration, project management estimates, manufacturing estimates, patient treatment costs and other activities. Actual costs may be charged to us and recognized as the tasks are completed by the contractor or, alternatively, may be invoiced in accordance with agreed-upon payment schedules and recognized based on estimates of work completed to date. Accrued clinical trial costs may be subject to revisions as clinical trials progress, and any revisions are recorded in the period in which the facts that give rise to the revisions become known.
Royalty Payments and Sublicense Fees	Royalty Payments and Sublicense Fees We are required to make royalty payments to certain parties based on our product sales under license agreements. No royalties were recorded during the year ended December 31, 2021, since we have not yet generated sales revenue. We are also required to record sublicense fees from time-to-time in connection with license fees from collaborators and clinical and commercial milestone achievement. Sublicenses fees were not significant in 2021 and 2020, and we recorded sublicense fees of $0.1 million in research and development expenses in the consolidated statements of operations and comprehensive loss in the year ended December 31, 2019.
Long-Lived Assets	Long-Lived Assets Property and equipment is stated at acquired cost net of depreciation and amortization. Laboratory and office equipment are depreciated on the straight-line basis over the estimated useful lives ( three Long-lived assets are evaluated for impairment when events or changes in circumstances indicate that the carrying amount of the asset or related group of assets may not be recoverable. If the expected future undiscounted cash flows are less than the carrying amount of the asset or related group of assets, an impairment loss is recognized at that time. Measurement of impairment may be based upon appraisal, market value of similar assets or discounted cash flows.
Leasing Arrangements	Leasing Arrangements We lease equipment, buildings and office space under operating lease arrangements. We have various supply agreements with third-party manufacturers, which involve the lease of manufacturing facilities and equipment, as defined in Topic 842. We have elected to separate lease and non-lease components for these arrangements. These manufacturing agreements have variable lease payments, which typically become binding once certain manufacturing milestones are achieved, and as such, are not included in right-of-use (“ROU”) assets and lease liabilities until such payments are no longer variable. We do not separate lease and non-lease components for all other currently existing asset classes. We apply the short-term lease exemption to all qualified lease agreements. The short-term lease exemption allows for the non-recognition of ROU assets and lease liabilities for leases with a term of twelve months or less. We determine if an arrangement is or contains a lease at contract inception and exercise judgment and apply certain assumptions when determining the discount rate, lease term and lease payments. Generally, we do not have knowledge of the discount rate implicit in the lease and, therefore, in most cases we use the incremental borrowing rate to compute the present value of future lease payments. The incremental borrowing rate is determined based on lease term and leased asset, and is adjusted for the impacts of collateral. The lease term includes the non-cancelable period of the lease plus any additional periods covered by an option to extend that we are reasonably certain to exercise, or an option to extend that is controlled by the lessor. Lease expense for lease payments is recognized on a straight-line basis over the lease term. Payments for certain lease agreements are adjusted annually for changes in an index or rate. We had no finance leases, residual value guarantees, restrictive covenants, subleases or sale leaseback transactions at December 31, 2021 and 2020. All ROU assets are periodically reviewed for impairment losses. Refer to Note K, Leasing Arrangements , for further information.
Patent Costs and Rights	Patent Costs and Rights Costs of applying for, prosecuting and maintaining patents and patent rights are expensed as incurred. We have filed for broad intellectual property protection on our proprietary technologies and have numerous United States and international patents and patent applications related to our technologies.
Warrants	WarrantsWe account for common stock warrants as either liabilities or as equity instruments depending on the specific terms of the warrant agreements. Generally, warrants are classified as liabilities, as opposed to equity, if the agreement includes the potential for a cash settlement or an adjustment to the exercise price, and warrant liabilities are recorded at their fair values at each balance sheet date.
Concentration of Credit Risk	Concentration of Credit Risk Our accounts receivable are generally comprised of amounts due from collaborators and granting authorities and are subject to concentration of credit risk due to the absence of a large number of customers. At December 31, 2021 and 2020, our accounts receivable are due from Healios. We do not typically require collateral from our customers.
Legal Matters	Legal MattersWe evaluate the development of legal matters on a regular basis and accrue a liability when we believe a loss is probable and the amounts can be reasonably estimated.
Stock-Based Compensation	Stock-Based Compensation Compensation expense related to stock options granted is measured at the grant date based on the estimated fair value of the award and is recognized using the straight-line method over the requisite service period, for awards without performance conditions. We determine the estimated fair value of each stock option on the date of grant using the Black-Scholes option-pricing model. The expected term of stock options granted represent the period of time that stock option grants are expected to be outstanding. The risk-free interest rate is based on the U.S. Treasury yield for a period consistent with the expected term of the stock option at the time of the grant. We determine volatility by using our historical stock volatility. We account for forfeitures as they occur. We have never paid or declared dividends or paid dividends on our common stock and have no plans to do so in the foreseeable future. Changes in these assumptions may lead to variability with respect to the amount of stock compensation expense we recognize related to stock options. Stock-based compensation for an award with a performance condition is recognized when the achievement of such performance condition is determined to be probable. If the outcome of such performance condition is not determined to be probable or is not met, no compensation expense is recognized. Prior to June 2020, we used the “simplified” method to calculate the expected term of option grants. In June 2020, we modified our stock option awards for all then-current employees and directors by providing an extension to the period of time during which vested stock options can be exercised. The extension to the period of time during which stock options can be exercised also applies to all stock options granted after June 2020. Subsequent to the modification date, our stock options no longer qualify to use the “simplified” method, and the expected term of our option grants is determined based on the historical experience and patterns, as well as current trends as previously described. The fair value of our restricted stock units is equal to the closing price of our common stock on the date of grant and is expensed over the vesting period on a straight-line basis. Restricted stock units typically vest over a four-year period. Refer to Note H, Stock-Based Compensation , for additional information.
Income Taxes	Income Taxes Deferred tax liabilities and assets are determined based on the differences between the financial reporting and tax basis of assets and liabilities and are measured using the tax rate and laws currently in effect. We evaluate our deferred income taxes to determine if a valuation allowance should be established against the deferred tax assets or if the valuation allowance should be reduced based on consideration of all available evidence, both positive and negative, using a “more likely than not” standard.
Net Loss per Share	Net Loss per ShareBasic and diluted net loss per share have been computed using the weighted-average number of shares of common stock outstanding during the period.
Fair Value Measurements	Fair Value Measurements We classify the inputs used to measure fair value into the following hierarchy: Level 1 Unadjusted quoted prices in active markets for identical assets or liabilities. Level 2 Unadjusted quoted prices in active markets for similar assets or liabilities, or unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or inputs other than quoted prices that are observable for the asset or liability. Level 3 Unobservable inputs for the asset or liability. Cash equivalents primarily consist of money market funds with overnight liquidity and no stated maturities. We classified cash equivalents as a Level 1 due to the short-term nature of these instruments and measured the fair value based on quoted prices in active markets for identical assets.

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Fair Value of Stock-Based Compensation Awards	The following weighted-average input assumptions were used in determining the fair value of our stock options granted: December 31, 2021 2020 2019 Volatility 75.2 % 72.2 % 71.1 % Risk-free interest rate 0.8 % 0.6 % 2.0 % Expected life of option 5.4 years 5.7 years 6.2 years Expected dividend yield 0.0 % 0.0 % 0.0 %
Instruments Excluded from Calculation of Diluted Net Loss Per Share	The following instruments, were excluded from the calculation of diluted net loss per share because their effects would be antidilutive: Years ended December 31, 2021 2020 2019 Stock options 23,043,035 18,150,409 13,975,671 Restricted stock units 1,985,057 2,374,006 2,032,180 Warrants — — 4,000,000 25,028,092 20,524,415 20,007,851

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2021
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, net	December 31, Property and equipment consists of (in thousands): 2021 2020 Laboratory equipment $ 9,352 $ 9,225 Office equipment and leasehold improvements 4,000 3,336 Process development equipment not yet in service 458 294 13,810 12,855 Accumulated depreciation and amortization (10,118) (9,700) $ 3,692 $ 3,155

Collaborative Arrangements an_2

Collaborative Arrangements and Revenue Recognition (Tables)	12 Months Ended
	Dec. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Disaggregation of Revenue	The following table presents our contract revenues disaggregated by timing of revenue recognition and excludes royalty revenue (in thousands): Twelve Months Ended Twelve Months Ended Twelve Months Ended Point in Time Over Time Point in Time Over Time Point in Time Over Time Contract revenue from Healios: License fee revenue $ — $ — $ — $ — $ 1,624 $ — Product supply revenue 283 — 1,432 — 2,167 — Service revenue — 5,231 — — — 1,726 Total disaggregated revenues $ 283 $ 5,231 $ 1,432 $ — $ 3,791 $ 1,726

Capitalization and Warrant In_2

Capitalization and Warrant Instruments (Tables)	12 Months Ended
	Dec. 31, 2021
Equity [Abstract]
Common Stock Shares Reserved for Future Issuance	The following shares, in thousands, of common stock were reserved for future issuance: December 31, 2021 2020 Stock-based compensation 28,204 29,591 Healios Warrants to purchase common stock 10,000 — 38,204 29,591

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Summary of Stock Option Activity and Related Information	A summary of our stock option activity and related information is as follows: Number Weighted Outstanding January 1, 2019 10,955,508 $ 1.87 Granted 3,402,608 1.55 Exercised (48,152) 1.40 Forfeited / Expired (334,293) 2.71 Outstanding December 31, 2019 13,975,671 1.77 Granted 5,213,168 2.44 Exercised (362,351) 1.70 Forfeited / Expired (676,079) 2.32 Outstanding December 31, 2020 18,150,409 1.95 Granted 6,240,204 1.81 Exercised (89,041) 1.77 Forfeited / Expired (1,258,537) 2.21 Outstanding December 31, 2021 23,043,035 $ 1.91 Vested during 2021 3,824,722 $ 1.99 Vested and exercisable at December 31, 2021 14,808,108 $ 1.88
Summarizes Information Concerning Options Outstanding and Options Vested and Exercisable	December 31, 2021 Options Outstanding Options Vested and Exercisable Exercise Price Number Weighted Weighted Number Weighted Weighted $1.00 - $1.55 8,005,583 5.4 years $ 1.49 6,072,826 4.1 years $ 1.45 $1.56 - $2.17 8,196,562 6.7 years $ 1.82 3,260,020 2.9 years $ 1.74 $2.19 - $3.57 6,840,890 4.4 years $ 2.51 5,475,262 3.4 years $ 2.43 23,043,035 14,808,108
Summary of Restricted Stock Unit Activity and Related Information	A summary of our restricted stock unit activity and related information is as follows: Number Weighted Unvested January 1, 2019 1,656,688 $ 1.93 Granted 1,350,150 1.55 Vested-common stock issued (938,311) 1.87 Forfeited (36,347) 1.69 Unvested December 31, 2019 2,032,180 1.71 Granted 1,553,671 2.76 Vested-common stock issued (1,087,718) 1.98 Forfeited (124,127) 1.95 Unvested December 31, 2020 2,374,006 2.26 Granted 1,254,399 1.63 Vested-common stock issued (1,287,383) 2.10 Forfeited (355,965) 2.31 Unvested December 31, 2021 1,985,057 $ 1.97 Vested/Issued cumulative at December 31, 2021 7,883,277 $ 1.84

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of Reconciliation of Federal Statutory Income Tax Rate to Effective Tax Rate	A reconciliation of the federal statutory income tax rate to our effective tax rate is as follows: Percent of Income 2021 2020 Statutory federal income tax rate 21.0 % 21.0 % State income taxes - net of federal tax benefit 1.0 % 0.9 % Other permanent differences (2.1) % (1.4) % Valuation allowances (24.8) % (25.5) % Research and development - U.S. 4.9 % 5.0 % Effective tax rate for the year — % — %
Components of Deferred Tax Assets	Significant components of our deferred tax assets and liabilities are as follows (in thousands): December 31, 2021 2020 Deferred tax assets: Net operating loss carryforwards $ 79,473 $ 61,670 Research and development credit carryforwards 20,587 16,308 Operating lease liabilities 1,918 146 Compensation expense 3,336 2,752 Other 2,618 3,534 Total deferred tax assets before valuation allowance 107,932 84,410 Valuation allowance for deferred tax assets (106,186) (84,255) Net deferred tax assets after valuation allowance 1,746 155 Deferred tax liabilities: Right-of-use asset (1,746) (155) Total deferred tax liabilities (1,746) (155) Net deferred tax assets $ — $ —

Leasing Arrangements (Tables)

Leasing Arrangements (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Components of Lease Costs	The table below presents certain information related to the lease costs (in thousands) for operating leases as of December 31, 2021, 2020 and 2019: Twelve months ended December 31, 2021 2020 2019 Operating lease cost $ 1,458 $ 516 $ 487 Short-term lease cost 134 111 61 Variable lease cost (1) 7,113 1,321 205 Total lease cost $ 8,705 $ 1,948 $ 753 (1) Includes lease components from our third-party manufacturing agreements.
Future Minimum Lease Payments for Operating Leases	The following table summarizes future maturities (in thousands) for operating lease liabilities as of December 31, 2021: 2022 $ 1,927 2023 1,566 2024 1,390 2025 1,404 2026 1,432 2027 and beyond 6,803 Total minimum lease payments 14,522 Less: amount of lease payments representing interest 4,756 Present value of operating lease liabilities $ 9,766

Quarterly Financial Data (una_2

Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2021
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	The following table presents quarterly data for the years ended December 31, 2021 and 2020, in thousands, except per share data: 2021 First Second Third Fourth Full Year Revenues $ — $ — $ 4,792 $ 722 $ 5,514 Loss from operations (26,589) (22,572) (16,222) (21,675) (87,058) Net loss (26,468) (22,599) (16,177) (21,711) (86,955) Basic and diluted net loss per common share (1) $ (0.13) $ (0.10) $ (0.07) $ (0.09) $ (0.39) 2020 First Second Third Fourth Full Year Revenues $ — $ 84 $ 86 $ 1,270 $ 1,440 Loss from operations (15,759) (18,337) (22,318) (21,918) (78,332) Net loss (15,644) (18,372) (22,543) (22,206) (78,765) Basic and diluted net loss per common share (1) $ (0.10) $ (0.10) $ (0.11) $ (0.11) $ (0.42) (1) Due to the effect of quarterly changes to outstanding shares of common stock and weightings, the annual loss per share will not necessarily equal the sum of the respective quarters.

Background - Additional Informa

Background - Additional Information (Details) $ in Millions	Feb. 16, 2021USD ($)	Feb. 15, 2021USD ($)	Mar. 31, 2021USD ($)	Dec. 31, 2021USD ($)segment	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Apr. 30, 2021USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of business segments | segment				1
Class of Stock [Line Items]
Unrecognized compensation cost of unvested stock awards				$ 8.6
Stock-based compensation expense				8.6	$ 7.4	$ 4.9
Deferred Bonus
Class of Stock [Line Items]
Unrecognized compensation cost of unvested stock awards			$ 2.7
Deferred Bonus | Tranche One
Class of Stock [Line Items]
Award vesting percentage			33.33%
Deferred Bonus | Tranche Two
Class of Stock [Line Items]
Award vesting percentage			66.67%
Additional Employees | Deferred Bonus
Class of Stock [Line Items]
Cash retention bonus granted							$ 2.5
Former Chief Executive Officer
Class of Stock [Line Items]
Severance payments and benefits		$ 1
Severance payments and benefits, period (in months)		18 months
Lump sum payment		$ 0.2		$ 0.4
Former Chief Executive Officer | Stock options
Class of Stock [Line Items]
Stock-based compensation expense			$ 1.4
Former Chief Executive Officer | RSUs
Class of Stock [Line Items]
Stock-based compensation expense			$ 0.9
Section 220 Litigation | Maximum | Pending Litigation
Class of Stock [Line Items]
Fees and expenses sought by plaintiff	$ 0.5

Going Concern (Details)

Going Concern (Details) - USD ($) $ in Thousands	1 Months Ended
	Aug. 31, 2021	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies And General Information [Line Items]
Cash and cash equivalents		$ 37,407	$ 51,546
Healios Framework Agreement
Accounting Policies And General Information [Line Items]
Potential revenue from milestones	$ 3,000

Accounting Policies - Additiona

Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Aug. 31, 2021	Mar. 31, 2018
Significant Accounting Policies [Line Items]
Payments for royalties	$ 0
Sublicense fees	100,000	$ 100,000
Warrant liabilities	$ 0	0
Awards vesting period (in years)	4 years
Award expiration period (in years)	10 years
Liability for uncertain income tax	$ 0	$ 0
Shares called by warrants (in shares)			10,000,000	20,000,000
RSUs
Significant Accounting Policies [Line Items]
Awards vesting period (in years)	4 years
Minimum
Significant Accounting Policies [Line Items]
Estimated useful life of long-lived assets (in years)	3 years
Maximum
Significant Accounting Policies [Line Items]
Estimated useful life of long-lived assets (in years)	10 years

Accounting Policies - Fair Valu

Accounting Policies - Fair Value of Stock-Based Compensation Awards (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Volatility	75.20%	72.20%	71.10%
Risk-free interest rate	0.80%	0.60%	2.00%
Expected life of option (in years)	5 years 4 months 24 days	5 years 8 months 12 days	6 years 2 months 12 days
Expected dividend yield	0.00%	0.00%	0.00%

Accounting Policies - Instrumen

Accounting Policies - Instruments Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	25,028,092	20,524,415	20,007,851
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	23,043,035	18,150,409	13,975,671
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	1,985,057	2,374,006	2,032,180
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)	0	0	4,000,000

Property and Equipment, net - S

Property and Equipment, net - Schedule of Property and Equipment, net (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 13,810	$ 12,855
Accumulated depreciation and amortization	(10,118)	(9,700)
Property and equipment, net	3,692	3,155
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,352	9,225
Office equipment and leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,000	3,336
Process development equipment not yet in service
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 458	$ 294

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Disposal of obsolete equipment		$ 1	$ 0.1
Accelerated depreciation	$ 0.5

Collaborative Arrangements an_3

Collaborative Arrangements and Revenue Recognition - Additional Information (Details)	1 Months Ended			12 Months Ended
	Aug. 31, 2021USD ($)shares	Dec. 31, 2018USD ($)	Jun. 30, 2018USD ($)	Dec. 31, 2021USD ($)performanceObligation	Dec. 31, 2020USD ($)	Dec. 31, 2017milestone	Mar. 31, 2018shares
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Shares called by warrants (in shares) | shares	10,000,000						20,000,000
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accounts receivable, payments due within period of invoicing				30 days
Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accounts receivable, payments due within period of invoicing				45 days
Healios
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential near-term payment received		$ 2,000,000
Revenue recognized related to the advance from Healios				$ 100,000	$ 0
Healios | Regulatory and Sales Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue from approvals and milestones			$ 225,000,000
Number of future milestones achieved | milestone						2
Ophthalmology License Agreement | Regulatory and Sales Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue from approvals and milestones			$ 135,600,000
Healios Framework Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue from milestones	$ 3,000,000
Potential revenue from completion of certain manufacturing activities	5,000,000
Accounts payable to Healios, non-current	$ 1,100,000
Warrants issued (in shares) | shares	2
Shares called by warrants (in shares) | shares	10,000,000
Number of material performance obligations | performanceObligation				1
Remaining performance obligation amount				$ 5,600,000
Revenue recognized from performance obligations satisfied in previous periods				500,000	$ 0
Unbilled accounts receivable from Healios				$ 3,000,000

Collaborative Arrangements an_4

Collaborative Arrangements and Revenue Recognition - Summary of Revenues Disaggregated by Recognition at Point in Time and Over Time (Details) - Healios - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Point in Time
Disaggregation of Revenue [Line Items]
Total disaggregated revenues	$ 283	$ 1,432	$ 3,791
Point in Time | License fee revenue
Disaggregation of Revenue [Line Items]
Total disaggregated revenues	0	0	1,624
Point in Time | Product supply revenue
Disaggregation of Revenue [Line Items]
Total disaggregated revenues	283	1,432	2,167
Point in Time | Service revenue
Disaggregation of Revenue [Line Items]
Total disaggregated revenues	0	0	0
Over Time
Disaggregation of Revenue [Line Items]
Total disaggregated revenues	5,231	0	1,726
Over Time | License fee revenue
Disaggregation of Revenue [Line Items]
Total disaggregated revenues	0	0	0
Over Time | Product supply revenue
Disaggregation of Revenue [Line Items]
Total disaggregated revenues	0	0	0
Over Time | Service revenue
Disaggregation of Revenue [Line Items]
Total disaggregated revenues	$ 5,231	$ 0	$ 1,726

Capitalization and Warrant In_3

Capitalization and Warrant Instruments - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended						12 Months Ended
	Aug. 31, 2021	May 31, 2020	Apr. 30, 2020	Mar. 31, 2020	Nov. 30, 2019	Mar. 31, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2021	May 31, 2021
Class of Warrant or Right [Line Items]
Common stock, shares authorized (in shares)							600,000,000	300,000,000		600,000,000	300,000,000
Preferred stock, shares authorized (in shares)							10,000,000	10,000,000
Preferred stock, shares issued (in shares)							0	0
Shares called by warrants (in shares)	10,000,000					20,000,000
Remaining exercisable warrants (in shares)						16,000,000
Aspire Capital
Class of Warrant or Right [Line Items]
Equity purchase agreement, value					$ 100
Common stock registered for resale (in shares)										40,000,000
Warrant One
Class of Warrant or Right [Line Items]
Shares called by warrants (in shares)	3,000,000
Exercise price of warrant (in dollars per share)	$ 1.80
Exercise period (in days)	60 days
Warrant Two
Class of Warrant or Right [Line Items]
Shares called by warrants (in shares)	7,000,000
Exercise price of warrant (in dollars per share)	$ 2.40
Exercise period (in days)	60 days
Healios
Class of Warrant or Right [Line Items]
Minimum ownership percentage in outstanding common stock for board seat						5.00%
Minimum ownership percentage in outstanding common stock for two board seats						15.00%
Common stock issued upon exercise of warrant (in shares)				4,000,000
Common stock issued, price per share (in dollars per share)				$ 1.76
Proceeds from exercise of warrant			$ 7
Ownership percentage in common stock for exercise cap to be triggered	19.90%
Public Stock Offering
Class of Warrant or Right [Line Items]
Net proceeds from public offering			$ 53.7
Shares issued and sold (in shares)			25,587,500
Offering price (in dollars per share)			$ 2.25
Securities Purchase Agreement | Healios
Class of Warrant or Right [Line Items]
Net proceeds from public offering		$ 0.5
Shares issued and sold (in shares)		310,526
Offering price (in dollars per share)		$ 1.72
Equity Purchase Agreement | Aspire Capital
Class of Warrant or Right [Line Items]
Common stock share issued (in shares)							40,031,000	11,425,000	14,475,000
Issuance of common stock per share (in dollars per share)							$ 1.61	$ 1.67	$ 1.41

Capitalization and Warrant In_4

Capitalization and Warrant Instruments - Common Stock Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares reserved for future issuance (in shares)	38,204,000	29,591,000
Stock-based compensation
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares reserved for future issuance (in shares)	28,204,000	29,591,000
Healios Warrants to purchase common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares reserved for future issuance (in shares)	10,000,000	0

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 8,600,000	$ 7,400,000	$ 4,900,000
Total unrecognized compensation cost		$ 8,600,000
Weighted average fair value of options granted (in dollars per share)		$ 1.13	$ 1.50	$ 1
Total fair value of options vested		$ 4,800,000	$ 3,500,000	$ 3,000,000
Total intrinsic value of options exercised		$ 0	700,000
Weighted average contractual life of unvested options (in years)		9 years
Restricted stock vested		$ 2,700,000	$ 2,200,000	$ 1,800,000
Estimated compensation cost of unvested restricted stock		$ 3,800,000
2019 Equity and Incentive Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock authorized for equity incentive plan (in shares)				19,000,000
Common stock shares issued (in shares)		8,933,420
Shares available for issuance (in shares)		3,176,331
Shares of common stock outstanding (in shares)		24,028,092
Expired Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares issued (in shares)		282,365
Shares of common stock outstanding (in shares)		820,478
2019 Equity And Incentive Compensation Plan, Modification
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,200,000
Total unrecognized compensation cost	$ 500,000
Inducement Awards Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock outstanding (in shares)		1,000,000

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Number of Options
Beginning Balance (in shares)	18,150,409	13,975,671	10,955,508
Granted (in shares)	6,240,204	5,213,168	3,402,608
Exercised (in shares)	(89,041)	(362,351)	(48,152)
Forfeited / Expired (in shares)	(1,258,537)	(676,079)	(334,293)
Ending Balance (in shares)	23,043,035	18,150,409	13,975,671
Vested during current period (in shares)	3,824,722
Vested and exercisable at period end (in shares)	14,808,108
Weighted Average Exercise Price
Beginning Balance (in dollars per share)	$ 1.95	$ 1.77	$ 1.87
Granted (in dollars per share)	1.81	2.44	1.55
Exercised (in dollars per share)	1.77	1.70	1.40
Forfeited / Expired (in dollars per share)	2.21	2.32	2.71
Ending Balance (in dollars per share)	1.91	$ 1.95	$ 1.77
Vested during current period (in dollars per share)	1.99
Vested and exercisable at period end (in dollars per share)	$ 1.88

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summarizes Information Concerning Options Outstanding and Options Vested and Exercisable (Details)	12 Months Ended
	Dec. 31, 2021$ / sharesshares
Options Outstanding
Number of options (in shares) | shares	23,043,035
Options Vested and Exercisable
Number of options (in shares) | shares	14,808,108
Range One
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price lower range (in dollars per share)	$ 1
Exercise price upper range (in dollars per share)	$ 1.55
Options Outstanding
Number of options (in shares) | shares	8,005,583
Weighted Average Remaining Contractual Life	5 years 4 months 24 days
Weighted average exercise price (in dollars per share)	$ 1.49
Options Vested and Exercisable
Number of options (in shares) | shares	6,072,826
Weighted Average Remaining Contractual Life	4 years 1 month 6 days
Weighted average exercise price (in dollars per share)	$ 1.45
Range Two
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price lower range (in dollars per share)	1.56
Exercise price upper range (in dollars per share)	$ 2.17
Options Outstanding
Number of options (in shares) | shares	8,196,562
Weighted Average Remaining Contractual Life	6 years 8 months 12 days
Weighted average exercise price (in dollars per share)	$ 1.82
Options Vested and Exercisable
Number of options (in shares) | shares	3,260,020
Weighted Average Remaining Contractual Life	2 years 10 months 24 days
Weighted average exercise price (in dollars per share)	$ 1.74
Range Three
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price lower range (in dollars per share)	2.19
Exercise price upper range (in dollars per share)	$ 3.57
Options Outstanding
Number of options (in shares) | shares	6,840,890
Weighted Average Remaining Contractual Life	4 years 4 months 24 days
Weighted average exercise price (in dollars per share)	$ 2.51
Options Vested and Exercisable
Number of options (in shares) | shares	5,475,262
Weighted Average Remaining Contractual Life	3 years 4 months 24 days
Weighted average exercise price (in dollars per share)	$ 2.43

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Restricted Stock Unit Activity and Related Information (Details) - RSUs - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Number of Restricted Stock Units
Beginning balance (in shares)	2,374,006	2,032,180	1,656,688
Granted (in shares)	1,254,399	1,553,671	1,350,150
Vested-common stock issued (in shares)	(1,287,383)	(1,087,718)	(938,311)
Forfeited (in shares)	(355,965)	(124,127)	(36,347)
Ending balance (in shares)	1,985,057	2,374,006	2,032,180
Vested/Issued cumulative at period end (in shares)	7,883,277
Weighted Average Fair Value
Beginning balance (in dollars per share)	$ 2.26	$ 1.71	$ 1.93
Granted (in dollars per share)	1.63	2.76	1.55
Vested-common stock issued (in dollars per share)	2.10	1.98	1.87
Forfeited (in dollars per share)	2.31	1.95	1.69
Ending balance (in dollars per share)	1.97	$ 2.26	$ 1.71
Vested/Issued cumulative at period end (in dollars per share)	$ 1.84

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Income tax paid	$ 0	$ 0	$ 0
U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	326,300,000
Research and development tax credit	20,600,000
U.S. Federal | Subject To Annual Limitations
Income Taxes [Line Items]
Net operating loss carryforwards	189,700,000
U.S. Federal | Not Subject To Annual Limitations
Income Taxes [Line Items]
Net operating loss carryforwards	289,600,000
Research and development tax credit	20,600,000
Foreign
Income Taxes [Line Items]
Net operating loss carryforwards	31,700,000
State and City
Income Taxes [Line Items]
Net operating loss carryforwards	118,700,000
State and City | Not Subject To Annual Limitations
Income Taxes [Line Items]
Net operating loss carryforwards	$ 118,500,000

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Federal Statutory Income Tax Rate to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	21.00%	21.00%
State income taxes - net of federal tax benefit	1.00%	0.90%
Other permanent differences	(2.10%)	(1.40%)
Valuation allowances	(24.80%)	(25.50%)
Research and development - U.S.	4.90%	5.00%
Effective tax rate for the year	0.00%	0.00%

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryforwards	$ 79,473	$ 61,670
Research and development credit carryforwards	20,587	16,308
Operating lease liabilities	1,918	146
Compensation expense	3,336	2,752
Other	2,618	3,534
Total deferred tax assets before valuation allowance	107,932	84,410
Valuation allowance for deferred tax assets	(106,186)	(84,255)
Net deferred tax assets after valuation allowance	1,746	155
Deferred tax liabilities:
Right-of-use asset	(1,746)	(155)
Total deferred tax liabilities	(1,746)	(155)
Net deferred tax assets after valuation allowance	$ 0	$ 0

Profit Sharing and 401(k) Plan

Profit Sharing and 401(k) Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Postemployment Benefits [Abstract]
Employer contribution for profit sharing plan	$ 0.6	$ 0.5	$ 0.4

Leasing Arrangements - Addition

Leasing Arrangements - Additional Information (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2021USD ($)ft²renewalOption	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	May 01, 2021USD ($)
Lessee, Lease, Description [Line Items]
Operating right-of-use assets, net		$ 8,960	$ 648	$ 700
Lease liabilities		$ 9,766	$ 700	$ 700
Weighted average remaining lease term (in years)		8 years 10 months 24 days	1 year 6 months	1 year 7 months 6 days
Weighted average discount rate (percent)		8.80%	5.00%	5.30%
Payment for operating leases		$ 1,300	$ 500	$ 500
Payment due for base annual rent in first year		$ 1,927
Warehouse and office space
Lessee, Lease, Description [Line Items]
Operating right-of-use assets, net					$ 9,200
Lease liabilities					$ 9,200
Lease term (in months)	10 years
Number of square feet leased | ft²	214,000
Number of renewal options | renewalOption	5
Renewal term (in years)	5 years
Payment due for base annual rent in first year	$ 1,300
Retention stock option award vesting rights (as a percent)	2.00%
Borrowing rate					9.00%
Allowance					$ 700
Minimum
Lessee, Lease, Description [Line Items]
Lease term (in months)		15 months
Maximum
Lessee, Lease, Description [Line Items]
Lease term (in months)		114 months

Leasing Arrangements - Componen

Leasing Arrangements - Components of Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 1,458	$ 516	$ 487
Short-term lease cost	134	111	61
Variable lease cost	7,113	1,321	205
Total lease cost	$ 8,705	$ 1,948	$ 753

Leasing Arrangements - Future M

Leasing Arrangements - Future Minimum Lease Payments for Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2022	$ 1,927
2023	1,566
2024	1,390
2025	1,404
2026	1,432
2027 and beyond	6,803
Total minimum lease payments	14,522
Less: amount of lease payments representing interest	4,756
Present value of operating lease liabilities	$ 9,766	$ 700	$ 700

Quarterly Financial Data (una_3

Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 722	$ 4,792	$ 0	$ 0	$ 1,270	$ 86	$ 84	$ 0	$ 5,514	$ 1,440	$ 5,633
Loss from operations	(21,675)	(16,222)	(22,572)	(26,589)	(21,918)	(22,318)	(18,337)	(15,759)	(87,058)	(78,332)	(45,488)
Net loss	$ (21,711)	$ (16,177)	$ (22,599)	$ (26,468)	$ (22,206)	$ (22,543)	$ (18,372)	$ (15,644)	$ (86,955)	$ (78,765)	$ (44,582)
Net loss per common share, basic (in dollars per share)	$ (0.09)	$ (0.07)	$ (0.10)	$ (0.13)	$ (0.11)	$ (0.11)	$ (0.10)	$ (0.10)	$ (0.39)	$ (0.42)	$ (0.29)
Net loss per common share, diluted (in dollars per share)	$ (0.09)	$ (0.07)	$ (0.10)	$ (0.13)	$ (0.11)	$ (0.11)	$ (0.10)	$ (0.10)	$ (0.39)	$ (0.42)	$ (0.29)

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Jan. 20, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Granted (in shares)		6,240,204	5,213,168	3,402,608
Awards vesting period (in years)		4 years
Award expiration period (in years)		10 years
Subsequent Event | Chief Executive Officer
Subsequent Event [Line Items]
Initial annual base salary	$ 0.6
Cash signing bonus	$ 0.3
Cash incentive compensation, percentage of annual base salary	60.00%
Subsequent Event | Chief Executive Officer | The Inducement Award
Subsequent Event [Line Items]
Granted (in shares)	10,000,000
Award exercise price (in dollars per share)	$ 0.86
Award expiration period (in years)	10 years
Subsequent Event | Chief Executive Officer | The Inducement Award, Four-Year Vesting
Subsequent Event [Line Items]
Granted (in shares)	4,000,000
Awards vesting period (in years)	4 years
Subsequent Event | Chief Executive Officer | The Inducement Award, Four-Year Vesting | Tranche One
Subsequent Event [Line Items]
Award vesting percentage	25.00%
Subsequent Event | Chief Executive Officer | The Inducement Award, Four-Year Vesting | Tranche Two
Subsequent Event [Line Items]
Awards vesting period (in years)	36 months
Subsequent Event | Chief Executive Officer | The Inducement Award, Performance Based Vesting
Subsequent Event [Line Items]
Granted (in shares)	6,000,000