Athersys, Inc / New (ATHXQ) 10-K 25 Mar 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 19, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
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	false
Entity Public Float			$ 464.4
Entity Common Stock, Shares Outstanding		215,244,507
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 2021 annual meeting of stockholders.
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0001368148

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 51,546	$ 35,041
Prepaid expenses and other	2,926	1,185
Total current assets	54,561	37,171
Property and equipment, net	3,155	2,882
Deposits and other	1,998	1,613
Total assets	59,714	41,666
Current liabilities:
Accrued compensation and related benefits	1,779	773
Accrued clinical trial related costs	6,870	1,160
Accrued expenses and other	1,198	723
Total current liabilities	22,954	12,837
Other long-term liabilities	197	220
Stockholders’ equity:
Preferred stock, at stated value; 10,000,000 shares authorized, and no shares issued and outstanding at December 31, 2020 and 2019	0	0
Common stock, $0.001 par value; 300,000,000 shares authorized; 201,973,582 and 159,791,585 shares issued and outstanding at December 31, 2020 and 2019, respectively	202	160
Additional paid-in capital	527,549	440,735
Accumulated deficit	(496,389)	(417,624)
Total stockholders’ equity	31,362	23,271
Total liabilities and stockholders’ equity	59,714	41,666
Consolidated entity, excluding related party
Current liabilities:
Accounts payable	11,337	9,048
Healios
Current assets:
Accounts receivable from Healios	89	945
Current liabilities:
Accounts payable	1,705	1,068
Deferred revenue - Healios	65	65
Advance from Healios	$ 5,201	$ 5,338

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
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)	300,000,000	300,000,000
Common stock, shares issued (in shares)	201,973,582	159,791,585
Common stock, shares outstanding (in shares)	201,973,582	159,791,585

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Grant revenue	$ 8	$ 116	$ 554
Total revenues	1,440	5,633	24,291
Costs and expenses
Research and development (including stock compensation expense of $3,351, $2,217 and $1,609 in 2020, 2019 and 2018, respectively)	62,994	39,045	38,656
General and administrative (including stock compensation expense of $4,028, $2,634 and $2,240 in 2020, 2019 and 2018, respectively)	15,888	11,378	10,442
Depreciation	890	698	855
Total costs and expenses	79,772	51,121	49,953
Gain from insurance proceeds, net	0	0	617
Loss from operations	(78,332)	(45,488)	(25,045)
Other (expense) income, net	(433)	906	762
Net loss and comprehensive loss	$ (78,765)	$ (44,582)	$ (24,283)
Net loss per common share, basic and diluted (in dollars per share)	$ (0.42)	$ (0.29)	$ (0.18)
Weighted average shares outstanding, basic and diluted (in shares)	187,472	151,696	136,641
Royalty and other contract revenue
Revenues
Revenues	$ 0	$ 0	$ 1,461
Healios | Contract revenue from Healios
Revenues
Revenues	$ 1,432	$ 5,517	$ 22,276

Consolidated Statements of Op_2

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock compensation expense	$ 7,400	$ 4,900	$ 3,800
Research and development
Stock compensation expense	3,351	2,217	1,609
General and administrative
Stock compensation expense	$ 4,028	$ 2,634	$ 2,240

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated DeficitCumulative Effect, Period of Adoption, Adjustment	Consolidated entity, excluding related party	Consolidated entity, excluding related partyCommon Stock	Consolidated entity, excluding related partyAdditional Paid-in Capital	Healios	HealiosCommon Stock	HealiosAdditional Paid-in Capital
Preferred stock shares, beginning balance (in shares) at Dec. 31, 2017			0
Beginning balance at Dec. 31, 2017	$ 23,376	$ 1,871	$ 0	$ 122	$ 373,884	$ (350,630)	$ 1,871
Common stock, beginning balance (in shares) at Dec. 31, 2017				122,077,453
Stock-based compensation	3,849				3,849
Issuance of warrant to Healios at fair value	1,080				1,080
Issuance of common stock, net of issuance costs (in shares)									9,658,582			12,000,000
Issuance of common stock, net of issuance costs								$ 16,628	$ 9	$ 16,619	$ 20,995	$ 12	$ 20,983
Issuance of common stock under equity compensation plans (in shares)				556,704
Issuance of common stock under equity compensation plans	(400)			$ 1	(401)
Net and comprehensive loss	(24,283)					(24,283)
Preferred stock shares, ending balance (in shares) at Dec. 31, 2018			0
Ending balance at Dec. 31, 2018	43,116		$ 0	$ 144	416,014	(373,042)
Common stock, ending balance (in shares) at Dec. 31, 2018				144,292,739
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		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			159,791,585
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	$ 37	$ 72,745	$ 7,574	$ 4	$ 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

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net loss	$ (78,765)	$ (44,582)	$ (24,283)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	890	698	855
Stock-based compensation	7,379	4,851	3,849
Discount on revenue from issuance of warrant	0	0	1,080
Stock-based patent license and settlement expense	0	0	315
Gain from insurance proceeds, net	0	0	(617)
Changes in operating assets and liabilities:
Prepaid expenses, deposits and other	(2,126)	1,102	(1,022)
Net cash used in operating activities	(61,810)	(35,326)	(13,350)
Investing activities
Proceeds from insurance, net	0	0	617
Purchases of equipment	(1,162)	(579)	(1,532)
Net cash used in investing activities	(1,162)	(579)	(915)
Financing activities
Shares retained for withholding tax payments on stock-based awards	(879)	(424)	(402)
Net cash provided by financing activities	79,477	19,887	36,008
Increase (Decrease) in cash and cash equivalents	16,505	(16,018)	21,743
Cash and cash equivalents at beginning of year	35,041	51,059	29,316
Cash and cash equivalents at end of year	51,546	35,041	51,059
Healios
Changes in operating assets and liabilities:
Accounts receivable from Healios	856	3,783	(4,545)
Accounts payable to Healios	637	1,068	0
Advance from Healios	(137)	199	4,889
Deferred revenue	0	(609)	2,110
Financing activities
Proceeds from issuance of common stock, net	7,574	0	20,995
Consolidated entity, excluding related party
Changes in operating assets and liabilities:
Accounts payable and accrued expenses	9,456	(1,836)	4,269
Deferred revenue	0	0	(250)
Financing activities
Proceeds from issuance of common stock, net	$ 72,782	$ 20,311	$ 15,415

Background

Background	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Background	Background We are a biotechnology company focused in the field of regenerative medicine and operate 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 have incurred losses since our inception in 1995 and had an accumulated deficit of $496.4 million at December 31, 2020, and we will not commence sales of our clinical product candidates until they receive regulatory approval for commercialization. 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. At December 31, 2020, we had available cash and cash equivalents of $51.5 million. In April 2020, we completed an underwritten public offering of common stock, which generated net proceeds of approximately of $53.7 million. Also, in March 2020, HEALIOS K.K. (“Healios”), our collaborator in Japan and largest stockholder, elected to exercise a warrant in full, generating proceeds to us of approximately $7.0 million. We believe that these recent proceeds, available proceeds from our existing equity facility, potential delays in certain non-core programs, and our ability to defer certain spending will enable us to meet our obligations as they come due at least for the next year from the date of the issuance of these consolidated financial statements. Importantly, we are approaching near-term milestones and clinical trial results, including the results of two Healios’ clinical trials, followed by the results of our MASTERS-2 clinical trial, which we would expect to 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 outcome of these milestones and clinical trial results, we may accelerate, defer or stage the timing of 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, the sale of equity securities from time to time including through our equity facility and grant-funding opportunities.

Accounting Policies

Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Accounting Policies	Accounting Policies Accounting Standards Adopted On January 1, 2019 we adopted Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2016-02, Leases (“Topic 842”), which requires lessees to recognize a right-of-use asset (“ROU asset”) and lease liability on their consolidated balance sheets related to the rights and obligations created by most leases, while continuing to recognize expense on their consolidated statements of income over the lease term. We transitioned to Topic 842 using the modified retrospective transition option on its effective date, January 1, 2019, and elected the package of practical expedients permitted under the transition guidance. Utilizing the practical expedients, we did not reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases, or (iii) initial direct costs for any existing leases. The adoption of the standard resulted in recording ROU assets and lease liabilities of $1.0 million at the date of adoption. The adoption did not have a material impact on our consolidated statements of operations and comprehensive loss or consolidated statements of cash flows and as a result, there was no cumulative-effect adjustment. Comparative periods for the year ended December 31, 2018 in the consolidated statements of operations and comprehensive loss reflect the former lease accounting guidance and the required comparative disclosures are included in Note J. In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software: Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract (“ASU 2018-15”). ASU 2018-15 requires implementation costs incurred by customers in cloud computing arrangements (i.e., hosting arrangements) to be capitalized under the same premises of authoritative guidance for internal-use software and deferred over the non-cancelable term of the cloud computing arrangements plus any optional renewal periods that are reasonably certain to be exercised by the customer or for which the exercise is controlled by the service provider. We adopted this standard on a prospective basis effective January 1, 2020, and the adoption of this standard had no impact on our consolidated financial statements in the year of adoption. Accounting Standards Not Yet 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. Depending on the amendment, adoption may be applied on the retrospective, modified retrospective or prospective basis. We are currently evaluating the impact of adopting this standard on our consolidated financial statements and disclosure. 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 the milestones in the Healios arrangement are generally related to development and commercial milestone achievement by Healios, we have not included any of the Healios milestones in the estimated transaction price of the Healios arrangement, since they would be constrained, as a significant reversal of revenue could result in future periods. Refer to Note E 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 before customer payment is received are included in contract assets, with those amounts that are unconditional being included in accounts receivable. Grant proceeds received in advance of our performance under the grant is included in deferred revenue. Generally, deferred revenue and contract assets or liabilities are classified as current assets or liabilities, as opposed to non-current. 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 to sixty days of invoicing. 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, 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, 2020, 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 2020, and we recorded sublicense fees of $0.1 million and $0.6 million in research and development expenses in the consolidated statements of operations and comprehensive loss in the years ended December 31, 2019 and 2018, respectively. Long-Lived Assets Equipment is stated at acquired cost less accumulated depreciation. 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. Leases 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 ROU assets and lease liabilities until such payments are no longer variable. We do not separate lease and non-lease components for all other 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. Our ROU assets are included within deposits and other, and the associated lease liabilities are included in accrued expenses and other and other long-term liabilities We had no finance leases, residual value guarantees, restrictive covenants, subleases or sale leaseback transactions at December 31, 2020 and 2019. All ROU assets are periodically reviewed for impairment losses. Refer to Note J for further information. Proceeds from Insurance In 2018, we received the final insurance proceeds, net of associated expenses, in the amount of $0.6 million related to flood damage to our facility. 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 at December 31, 2020 and 2019. Refer to Note F for a discussion of the warrant issued in 2018 to Healios (the “Healios Warrant”), which was accounted for as an equity instrument. 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, 2020 and 2019, our accounts receivable are primarily 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 We recognize stock-based compensation expense on the straight-line method and use a Black-Scholes option-pricing model to estimate the fair value of option awards. The expected term of options granted represent the period of time that option grants are expected to be outstanding. 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. Subsequent to the modification date, the Company’s 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. We determine volatility by using our historical stock volatility. We account for forfeitures as they occur. 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, although the 2018 awards vest over a three-year period. Refer to Note G for additional information. Annual stock option awards to employees typically vest over a four-year period, although the 2018 awards vest over a three-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 the Company’s stock options granted: December 31, 2020 2019 2018 Volatility 72.2 % 71.1 % 70.8 % Risk-free interest rate 0.6 % 2.0 % 2.8 % Expected life of option 5.7 years 6.2 years 6.0 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, 2020 and 2019. 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 2019 and 2018 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, 2020 2019 2018 Stock options 18,150,409 13,975,671 10,955,508 Restricted stock units 2,374,006 2,032,180 1,656,688 Warrants — 4,000,000 18,500,000 20,524,415 20,007,851 31,112,196

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Property and Equipment, net	Property and Equipment, net December 31, Property and equipment consists of (in thousands): 2020 2019 Laboratory equipment $ 9,225 $ 8,008 Office equipment and leasehold improvements 3,336 3,191 Process development equipment not yet in service 294 574 12,855 11,773 Accumulated depreciation (9,700) (8,891) $ 3,155 $ 2,882 During 2020 and 2019, we disposed of approximately $0.1 million of obsolete laboratory equipment, office equipment and leasehold improvements in each year, all of which were fully depreciated.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2020
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.

Collaborative Arrangements and

Collaborative Arrangements and Revenue Recognition	12 Months Ended
	Dec. 31, 2020
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 at that time included acute respiratory distress syndrome (“ARDS”) and another indication in the orthopedic area, and all indications for the organ bud program. In accordance with the First License Agreement, in addition to potential royalties and milestones, we received a nonrefundable up-front cash payment of $15 million, and if expanded at Healios’ election, Healios would pay an additional $10 million cash payment. Healios exercised its option to expand the collaboration in June 2018, as described below. 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 and the transfer of technology to a contract manufacturer in Japan to produce product for Healios’ use. 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. Healios’ cost-share payments may be creditable, as defined, against milestone payments that may become due under the First License Agreement and a sales milestone would be increased, or such payments may be repaid by us at our election. 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. Certain services referenced in the Memorandum resulted in disputed payment obligations, which have not been reflected within the December 31, 2020 consolidated balance sheets and consolidated statement of operations and comprehensive loss because, at December 31, 2020, we had not reached agreement with Healios and the activity did not meet the requirements for accounting under Topic 606. Our agreement to work in good faith with Healios as quickly as possible on all aspects of product supply and manufacturing services referred to in Note L includes seeking to resolve issues regarding these disputed activities. In March 2018, we entered into a letter of intent (“LOI”) with Healios outlining the terms for a potential expansion of the relationship with Healios beyond that contemplated by the First License Agreement, to include, among other things, the exercise of its option to license the ARDS field in Japan and the organ bud program on a global basis, a worldwide exclusive license for use of MultiStem product to treat certain ophthalmological indications, and an exclusive option to a license to develop and commercialize certain MultiStem treatments in China. In connection with the LOI, in March 2018, Healios purchased 12,000,000 shares of our common stock and the Healios Warrant for $21.1 million, or approximately $1.76 per share. In June 2018, Healios exercised its option to expand the collaboration to include ARDS and expand organ bud as contemplated by the First License Agreement, 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 all indications, Healios is responsible for the costs of clinical development in its licensed territories, and we provide manufacturing services to Healios. For the rights granted to Healios under the CEA, Healios paid us a nonrefundable, up-front cash payment of $10.0 million to exercise its option to license ARDS and expand its license for organ bud, as contemplated by the First License Agreement, and paid an additional $10.0 million for the other license rights in installments. Healios may elect to credit up to $10.0 million against milestone payments that may become due under the First License Agreement, as expanded to include ARDS, with limitations on amounts that may be credited to earlier milestone payments versus later milestone payments. 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; and we have a time-limited right of first negotiation for commercialization of an organ bud product in North America. 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 F. 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) services to transfer technology to a contract manufacturer on Healios’ behalf. It was determined that these performance obligations were both capable of being distinct and distinct within the context of the contract. We develop assumptions that require judgment to determine the standalone selling price in order to account for our collaborative agreements, as these assumptions typically include probabilities of obtaining marketing approval for the product candidates, estimated timing of commercialization, estimated future cash flows from potential product sales of our product candidates, estimating the cost and markup of providing product supply and technical services, and appropriate discount rates. 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 is driven off the underlying cost per dose over the entire life of the agreement and is subject to variability as those costs change. We estimate the cost per dose for the life of the contract taking into consideration historical experience of our contract manufacturers and anticipated changes to production yields and other factors. 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 technology transfer services are satisfied over time, and we recognize revenue in proportion to the contractual services provided. For performance obligations satisfied at a point in time (i.e., product supply), we recognize revenue upon delivery. The remaining transaction price for the performance obligations that were not yet delivered is not significant at December 31, 2020. At December 31, 2020, the contract liability included in Deferred Revenue - Healios on the consolidated balance sheets, is properly classified as a current liability since the rights to consideration are expected to be satisfied, in all material respects, within one year. We included as a reduction of the transaction price of the licenses granted in the June 2018 expansion, the value of a portion of the Healios Warrant that was issued in March 2018 in connection with the then-proposed expansion under a letter of intent. Under the agreements in the June 2018 expansion that included an amendment to the Healios Warrant, 4,000,000 shares (“Warrant Shares”) became exercisable, and as a result, $1.1 million of the $5.3 million initial warrant valuation was recorded in June 2018 as a reduction of revenue. In accordance with the June 2018 amendment to the Healios Warrant, the remaining 16,000,000 shares would not be exercisable until the execution of an option for a license in China, and the remaining $4.2 million of the Healios Warrant was reversed against additional paid-in-capital. See Note F. Also, see Note B regarding our revenue recognition policies. 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 December 31, 2020 Twelve months ended December 31, 2019 Twelve months ended December 31, 2018 Point in Time Over Time Point in Time Over Time Point in Time Over Time Contract revenue from Healios: License fee revenue $ — $ — $ 1,624 $ — $ 17,682 $ — Product supply revenue 1,432 — 2,167 — 1,445 — Service revenue — — — 1,726 — 3,149 Other contract revenue — — — — 251 — Total disaggregated revenues $ 1,432 $ — $ 3,791 $ 1,726 $ 19,378 $ 3,149

Capitalization and Warrant Inst

Capitalization and Warrant Instruments	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Capitalization and Warrant Instruments	Capitalization and Warrant Instruments Capitalization At both December 31, 2020 and December 31, 2019, we had 300,000,000 shares of common stock and 10,000,000 shares of undesignated preferred stock authorized. No shares of preferred stock have been issued as of December 31, 2020 and 2019. 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, 2020 2019 Stock-based compensation plans 29,591 30,054 Healios Warrants to purchase common stock — 4,000 29,591 34,054 Equity Issuance - Healios In March 2018, Healios purchased 12,000,000 shares of our common stock for $21.1 million, or approximately $1.76 per share, and the Healios Warrant to purchase up to an additional 20,000,000 shares. In connection with this investment, we entered into an Investor Rights Agreement (the "Investor Rights Agreement") that governs certain rights of Healios and us relating to Healios’ ownership of our common stock. The Investor Rights Agreement provides for customary standstill and voting obligations, transfer restrictions and registration rights for Healios. Additionally, we agree to provide notice to Healios of certain equity issuances and to allow Healios to participate in certain issuances in order maintain its proportionate ownership of our common stock as of the time of such issuance. In May 2020, we sold Healios 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. 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. At the time of the investment in March 2018, the 20,000,000 Warrant Shares would not become exercisable until the planned collaboration expansion was completed, which at the time included an option to commercialize in China. At the time of the June 2018 expansion, however, the parties had not reached agreement on the option so Athersys agreed to provide Healios with a right of first negotiation with respect to the option, and therefore, the parties bifurcated the Healios Warrant so that 4,000,000 Warrant Shares became exercisable with the June 2018 expansion and the remaining 16,000,000 Warrant Shares would become exercisable if Healios agreed to execute an option for a license in China. As of June 30, 2019, the 16,000,000 Warrant Shares were no longer exercisable and expired under the terms of the Healios Warrant, since an option in China was not executed. In March 2020, the 4,000,000 Warrant Shares were exercised at the reference price of $1.76, as defined in the Healios Warrant and proceeds of approximately $7.0 million were received in April 2020. The value of the Healios Warrant was considered as an element of compensation in the transaction price of the Healios collaboration expansion. We evaluated the various terms of the Healios Warrant and concluded that it is accounted for as an equity instrument at inception and $5.3 million was computed as the best estimate of the fair value of the Healios Warrant at the time of issuance in March 2018. The fair value was computed using a Monte Carlo simulation model that included probability-weighted estimates of potential milestone points in time that could impact the value of the Healios Warrant during its term. The fair value was recorded as additional paid-in capital in the first quarter of 2018, with the offset being included in other asset related to Healios, and the asset would be included as an element of compensation in the transaction price upon the consummation of the expansion that was proposed in March 2018 under the LOI. Upon the modification of the Healios Warrant in June 2018 in connection with the expansion of the collaboration that included the bifurcation of the Healios Warrant due to the change related to China rights, we reassessed the fair value of the Healios Warrant immediately before and after the modification using the same valuation methodology, which resulted in no incremental fair value to be recorded. The value of the 4,000,000 Warrant Shares that became exercisable upon the June 2018 expansion of $1.1 million was recorded as a reduction to the revenue recognized for the delivered licenses in June 2018. See Note E. However, since the June 2018 expansion agreements made the ability to exercise the Healios Warrant for 16,000,000 underlying shares contingent on entering into an option for a license in China, we considered the ability to apply the $4.2 million value of such Warrant Shares as an element of compensation to be constrained. Therefore, the remaining asset was reversed against additional paid-in-capital. Equity Purchase Agreement We have had equity purchase agreements in place since 2011 with Aspire Capital Fund LLC (“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 November 2019 (the “2019 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. Our prior equity facility that was entered into in 2018 (the “2018 Equity Facility”) was fully utilized and terminated during the first quarter of 2020. The terms of the 2019 Equity Facility are similar to the previous equity purchase arrangements, and we issued 350,000 shares of our common stock to Aspire Capital as a commitment fee in November 2019 and filed a registration statement for the resale of 31,000,000 shares of common stock in connection with the equity facility. The 2018 Equity Facility provided us with the ability to sell shares to Aspire Capital up to $100.0 million in aggregate. The terms of the 2018 Equity Facility are similar to the previous equity facilities with Aspire Capital, and we issued 450,000 shares of our common stock to Aspire Capital as a commitment fee in 2018 and registered for resale of 24,700,000 shares of our common stock. Also in connection with the 2018 Equity Facility, Aspire Capital invested $1.0 million to purchase 500,000 shares of common stock at $2.00 per share. During the years ended December 31, 2020, 2019 and 2018, we sold 11,425,000, 14,475,000 and 8,708,582 shares, respectively, to Aspire Capital at average prices of $1.67, $1.41 and $1.78 per share, respectively. In the first quarter of 2021, through March 19, 2021, we generated an additional $26.6 million in proceeds from the use of our equity purchase arrangement with Aspire Capital. Open Market Sale Agreement In May 2019, we entered into an open market sale agreement with a sales agent, pursuant to which we could offer and sell, from time to time, through the sales agent, shares of our common stock having an aggregate offering price of up to $50.0 million. The shares could have been offered and sold pursuant to our registration statement on Form S-3 that was declared effective by the SEC on March 21, 2017, but expired on March 21, 2020 and was no longer effective. We did not sell any shares of our common stock under this agreement and have allowed the open market sale agreement to lapse. License Agreement and Settlement In October 2017, we entered into an agreement to settle longstanding intellectual property disagreements with a third party. As part of the agreement, we were granted a worldwide, non-exclusive license, with the right to sublicense, to the other party’s patents and applications that were at the core of the intellectual property dispute, for use related to the treatment or prevention of disease or conditions using cells. In return, we agreed not to enforce our intellectual property rights against the party with respect to certain patent claims, nor to further challenge the patentability or validity of certain applications or patents. Upon execution of the license and settlement agreement in 2017, we paid $0.5 million and issued 1,000,000 shares of our common stock with a fair value of $2.3 million. In 2018, in accordance with the agreement, we paid an additional $1.0 million and we issued 500,000 additional shares of our common stock related to a patent issuance. This contingent obligation to issue 500,000 shares of common stock was originally recorded in accrued license fee expense on the consolidated balance sheets at December 31, 2017 at a fair value of $0.9 million. The actual issuance of the 500,000 shares in May 2018 was recorded at an actual fair value of $1.2 million, resulting in $0.3 million of additional paid-in-capital and research and development expense in 2018. There will be no royalty, milestone or other payments due to the third party associated with the development and commercialization of our cell therapy products. Our payment obligations have concluded.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2020
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 18,500,000 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, 2020, a total of 7,556,996 shares (including 266,932 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, first, for employees, following an employee's voluntary termination of employment or the involuntary termination of the employee's employment by the Company without cause (as defined with respect to the applicable options) and second, for directors, following a director's death or voluntary termination of service with the Company, in each case following significant tenure with the Company. Upon modification, based on tenure, employees have post-employment exercise periods from three months up to a maximum of three years, and directors have post-employment exercise periods from eighteen months up to thirty months maximum. The modification was applied to all nonqualified stock option awards outstanding on the modification date and to those incentive stock options held by individuals who accepted the modification. Stock option awards issued post-modification include the extended exercise provisions as described in this paragraph. 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 will be recognized over the remaining vesting period of these modified stock option awards. As of December 31, 2020, a total of 9,066,432 shares were available for issuance under our EICP, and stock-based awards representing 19,524,415 shares (including 845,911 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, 2020. We recognized $7.4 million, $4.9 million and $3.8 million of stock-based compensation expense in 2020, 2019 and 2018, respectively. Stock Options The weighted average fair value of options granted in 2020, 2019 and 2018 was $1.50, $1.00 and $1.46 per share, respectively. The total fair value of options vested during 2020, 2019 and 2018 was $3.5 million, $3.0 million and $2.5 million, respectively. The total intrinsic value of options exercised during the year ended December 31, 2020 was $0.7 million. The total intrinsic value of options exercised during the years ended December 31, 2019 and 2018 was not significant. At December 31, 2020, total unrecognized estimated compensation cost related to unvested stock options was approximately $9.1 million, which is expected to be recognized by the end of 2024 using the straight-line method. The weighted average contractual life of unvested options at December 31, 2020 was 8.5 years. The aggregate intrinsic value of fully vested and exercisable option shares and option shares expected to vest as of December 31, 2020 was $2.4 million. A summary of our stock option activity and related information is as follows: Number Weighted Outstanding January 1, 2018 8,919,113 $ 1.78 Granted 2,434,732 2.26 Exercised (112,484) 1.57 Forfeited / Expired (285,853) 2.62 Outstanding December 31, 2018 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 Vested during 2020 2,816,432 $ 1.98 Vested and exercisable at December 31, 2020 11,229,772 $ 1.85 December 31, 2020 Options Outstanding Options Vested and Exercisable Exercise Price Number Weighted Weighted Number Weighted Weighted $1.01 - $1.55 7,524,261 5.7 years $ 1.45 4,414,112 4.0 years $ 1.45 $1.56 - $2.19 5,289,451 3.2 years $ 1.93 4,594,032 2.4 years $ 1.93 $2.30 - $3.57 5,336,697 6.7 years $ 2.67 2,221,628 3.8 years $ 2.46 18,150,409 11,229,772 Restricted Stock Units A summary of our restricted stock unit activity and related information is as follows: Number Weighted Unvested January 1, 2018 1,648,986 $ 1.69 Granted 787,968 2.31 Vested-common stock issued (741,424) 1.81 Forfeited / Expired (38,842) 1.74 Unvested December 31, 2018 1,656,688 1.93 Granted 1,350,150 1.55 Vested-common stock issued (938,311) 1.87 Forfeited / Expired (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 / Expired (124,127) 1.95 Unvested December 31, 2020 2,374,006 $ 2.26 Vested/Issued cumulative at December 31, 2020 6,599,894 $ 1.79 The total fair value of restricted stock units vested during 2020, 2019 and 2018 was $2.2 million, $1.8 million and $1.3 million, respectively. At December 31, 2020, total unrecognized estimated compensation cost related to unvested restricted stock units was approximately $5.2 million, which is expected to be recognized by the end of 2024 using the straight-line method.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes At December 31, 2020, we had U.S. federal net operating loss and research and development tax credit carryforwards of approximately $248.0 million and $16.3 million, respectively. Included in our federal net operating loss as of December 31, 2020 are federal net operating loss carryforwards generated after 2017 of $111.4 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 2040. We also had foreign net operating loss carryforwards of approximately $30.0 million. Such foreign net operating loss carryforwards do not expire. We also had state and city net operating loss carryforwards aggregating approximately $82.5 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 2021 and 2040. 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 $211.3 million, research and development tax credits of $16.3 million, and state and local net operating loss carryforwards of $82.3 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 2020 2019 Statutory federal income tax rate 21.0 % 21.0 % State income taxes - net of federal tax benefit 0.9 % 0.9 % Other permanent differences (1.4) % (2.3) % Valuation allowances (25.5) % (25.9) % Research and development - U.S. 5.0 % 6.3 % Effective tax rate for the year — % — % Significant components of our deferred tax assets are as follows (in thousands): December 31, 2020 2019 Net operating loss carryforwards $ 61,670 $ 48,182 Research and development credit carryforwards 16,308 12,797 Compensation expense 2,752 1,156 Other 3,526 903 Total deferred tax assets 84,256 63,038 Valuation allowance for deferred tax assets (84,256) (63,038) 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, 2020. On March 27, 2020, the President signed the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”). The CARES Act includes, among other things, provisions relating to refundable payroll tax credits, deferral of certain payment requirements for the employer portion of Social Security taxes, net operating loss carryback periods and temporarily increasing the amount of net operating losses that corporations can use to offset income, etc. These provisions did not have a material impact on our operating results.

Profit Sharing and 401(k) Plan

Profit Sharing and 401(k) Plan	12 Months Ended
	Dec. 31, 2020
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 $0.5 million, $0.4 million and $0.5 million in 2020, 2019 and 2018, respectively.

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	Leases As of December 31, 2020 and 2019, ROU assets and lease liabilities were $0.7 million. The weighted-average remaining term for lease contracts was 1.5 years at December 31, 2020 and 1.6 years at December 31, 2019 with maturities ranging from 8 months to 38 months. The weighted-average discount rate was 5.0% at December 31, 2020 and 5.3% at December 31, 2019. We paid $0.5 million and $0.5 million for operating leases included in the measurement of lease liabilities during the year ended December 31, 2020 and 2019, respectively. Lease Costs Rent expense for the year ended December 31, 2018 recognized prior to the adoption of Topic 842 was approximately $0.5 million. The table below presents certain information related to the lease costs (in thousands) for operating leases as of December 31, 2020 and 2019: Twelve months ended December 31, 2020 2019 Operating lease cost $ 516 $ 487 Short-term lease cost 111 61 Variable lease cost (1) 1,321 205 Total lease cost $ 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, 2020: 2021 $ 503 2022 188 2023 12 2024 2 Total minimum lease payments 705 Less: amount of lease payments representing interest 27 Present value of operating lease liabilities $ 678

Quarterly Financial Data (unaud

Quarterly Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2020
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, 2020 and 2019, in thousands, except per share data: 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) 2019 First Second Third Fourth Full Year Revenues $ 1,445 $ 4,262 $ (361) $ 287 $ 5,633 Loss from operations (13,260) (9,901) (12,342) (9,985) (45,488) Net loss (12,956) (9,688) (12,015) (9,923) (44,582) Basic and diluted net loss per common share (1) $ (0.09) $ (0.06) $ (0.08) $ (0.06) $ (0.29) (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, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Healios Cooperation Agreement On February 16, 2021, the Company and Healios and Dr. Hardy TS Kagimoto entered into a cooperation agreement (the “Cooperation Agreement”). The Cooperation Agreement provides 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. Additionally, pursuant to the Cooperation Agreement, the parties agree to seek to resolve issues over disputed payment obligations for certain manufacturing activities. The Cooperation Agreement also provides 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 Delaware on November 21, 2020 (the “220 Litigation”). Pursuant to the Cooperation Agreement, the Company shall reimburse Healios and Dr. Kagimoto for reasonable out-of-pocket fees and expenses including legal expenses incurred in connection with the Section 220 Litigation, not to exceed $0.5 million in aggregate. As the amount is probable and reasonably estimable, a liability was recorded in accounts payable to Healios on the consolidated balance sheets at December 31, 2020. 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 cessation of service, 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 provides for a lump sum payment of approximately $0.2 million. The terms of the Separation Letter also provides for the accelerated vesting of his outstanding restricted stock units and stock options. Lease Agreement On January 4, 2021, we entered into an agreement to lease approximately 214,000 square feet of warehouse and office space in Ohio. The initial lease term is approximately 10 years and includes five renewal options with terms of five years each. Base annual rent for the first year is approximately $1.3 million with 2.0% annual rent escalators. Retention Program In February and March, 2021, we entered into retention letter agreements (“Retention Agreements”) with our officers and certain other employees in leadership positions. Each Retention Agreement provided 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 employees’ annual compensation and 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.

Accounting Policies (Policies)

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Accounting Standards Adopted and Not Yet Adopted	Accounting Standards Adopted On January 1, 2019 we adopted Financial Accounting Standards Board (“FASB”) Accounting Standards Update (“ASU”) 2016-02, Leases (“Topic 842”), which requires lessees to recognize a right-of-use asset (“ROU asset”) and lease liability on their consolidated balance sheets related to the rights and obligations created by most leases, while continuing to recognize expense on their consolidated statements of income over the lease term. We transitioned to Topic 842 using the modified retrospective transition option on its effective date, January 1, 2019, and elected the package of practical expedients permitted under the transition guidance. Utilizing the practical expedients, we did not reassess (i) whether any expired or existing contracts are or contain leases, (ii) the lease classification for any expired or existing leases, or (iii) initial direct costs for any existing leases. The adoption of the standard resulted in recording ROU assets and lease liabilities of $1.0 million at the date of adoption. The adoption did not have a material impact on our consolidated statements of operations and comprehensive loss or consolidated statements of cash flows and as a result, there was no cumulative-effect adjustment. Comparative periods for the year ended December 31, 2018 in the consolidated statements of operations and comprehensive loss reflect the former lease accounting guidance and the required comparative disclosures are included in Note J. In August 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software: Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract (“ASU 2018-15”). ASU 2018-15 requires implementation costs incurred by customers in cloud computing arrangements (i.e., hosting arrangements) to be capitalized under the same premises of authoritative guidance for internal-use software and deferred over the non-cancelable term of the cloud computing arrangements plus any optional renewal periods that are reasonably certain to be exercised by the customer or for which the exercise is controlled by the service provider. We adopted this standard on a prospective basis effective January 1, 2020, and the adoption of this standard had no impact on our consolidated financial statements in the year of adoption. Accounting Standards Not Yet 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. Depending on the amendment, adoption may be applied on the retrospective, modified retrospective or prospective basis. We are currently evaluating the impact of adopting this standard on our consolidated financial statements and disclosure. 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 the milestones in the Healios arrangement are generally related to development and commercial milestone achievement by Healios, we have not included any of the Healios milestones in the estimated transaction price of the Healios arrangement, since they would be constrained, as a significant reversal of revenue could result in future periods. Refer to Note E 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 before customer payment is received are included in contract assets, with those amounts that are unconditional being included in accounts receivable. Grant proceeds received in advance of our performance under the grant is included in deferred revenue. Generally, deferred revenue and contract assets or liabilities are classified as current assets or liabilities, as opposed to non-current.
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, 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 FeesWe 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, 2020, 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 2020, and w
Long-Lived Assets	Long-Lived Assets Equipment is stated at acquired cost less accumulated depreciation. 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.
Leases	Leases 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 ROU assets and lease liabilities until such payments are no longer variable. We do not separate lease and non-lease components for all other 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. Our ROU assets are included within deposits and other, and the associated lease liabilities are included in accrued expenses and other and other long-term liabilities We had no finance leases, residual value guarantees, restrictive covenants, subleases or sale leaseback transactions at December 31, 2020 and 2019. All ROU assets are periodically reviewed for impairment losses. Refer to Note J for further information.
Proceeds from Insurance	Proceeds from InsuranceIn 2018, we received the final insurance proceeds, net of associated expenses, in the amount of $0.6 million related to flood damage to our facility.
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.
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.
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, 2020 and 2019, our accounts receivable are primarily due from Healios. We do not typically require collateral from our customers.
Stock-Based Compensation	Stock-Based Compensation We recognize stock-based compensation expense on the straight-line method and use a Black-Scholes option-pricing model to estimate the fair value of option awards. The expected term of options granted represent the period of time that option grants are expected to be outstanding. 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. Subsequent to the modification date, the Company’s 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. We determine volatility by using our historical stock volatility. We account for forfeitures as they occur. 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, although the 2018 awards vest over a three-year period. Refer to Note G 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. We had no liability for uncertain income tax positions as of December 31, 2020 and 2019. 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	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.

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Fair Value of Stock-Based Compensation Awards	The following weighted-average input assumptions were used in determining the fair value of the Company’s stock options granted: December 31, 2020 2019 2018 Volatility 72.2 % 71.1 % 70.8 % Risk-free interest rate 0.6 % 2.0 % 2.8 % Expected life of option 5.7 years 6.2 years 6.0 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, 2020 2019 2018 Stock options 18,150,409 13,975,671 10,955,508 Restricted stock units 2,374,006 2,032,180 1,656,688 Warrants — 4,000,000 18,500,000 20,524,415 20,007,851 31,112,196

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, net	December 31, Property and equipment consists of (in thousands): 2020 2019 Laboratory equipment $ 9,225 $ 8,008 Office equipment and leasehold improvements 3,336 3,191 Process development equipment not yet in service 294 574 12,855 11,773 Accumulated depreciation (9,700) (8,891) $ 3,155 $ 2,882

Collaborative Arrangements an_2

Collaborative Arrangements and Revenue Recognition (Tables)	12 Months Ended
	Dec. 31, 2020
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 December 31, 2020 Twelve months ended December 31, 2019 Twelve months ended December 31, 2018 Point in Time Over Time Point in Time Over Time Point in Time Over Time Contract revenue from Healios: License fee revenue $ — $ — $ 1,624 $ — $ 17,682 $ — Product supply revenue 1,432 — 2,167 — 1,445 — Service revenue — — — 1,726 — 3,149 Other contract revenue — — — — 251 — Total disaggregated revenues $ 1,432 $ — $ 3,791 $ 1,726 $ 19,378 $ 3,149

Capitalization and Warrant In_2

Capitalization and Warrant Instruments (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Common Stock Shares Reserved for Future Issuance	The following shares, in thousands, of common stock were reserved for future issuance: December 31, 2020 2019 Stock-based compensation plans 29,591 30,054 Healios Warrants to purchase common stock — 4,000 29,591 34,054

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2018 8,919,113 $ 1.78 Granted 2,434,732 2.26 Exercised (112,484) 1.57 Forfeited / Expired (285,853) 2.62 Outstanding December 31, 2018 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 Vested during 2020 2,816,432 $ 1.98 Vested and exercisable at December 31, 2020 11,229,772 $ 1.85
Summarizes Information Concerning Options Outstanding and Options Vested and Exercisable	December 31, 2020 Options Outstanding Options Vested and Exercisable Exercise Price Number Weighted Weighted Number Weighted Weighted $1.01 - $1.55 7,524,261 5.7 years $ 1.45 4,414,112 4.0 years $ 1.45 $1.56 - $2.19 5,289,451 3.2 years $ 1.93 4,594,032 2.4 years $ 1.93 $2.30 - $3.57 5,336,697 6.7 years $ 2.67 2,221,628 3.8 years $ 2.46 18,150,409 11,229,772
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, 2018 1,648,986 $ 1.69 Granted 787,968 2.31 Vested-common stock issued (741,424) 1.81 Forfeited / Expired (38,842) 1.74 Unvested December 31, 2018 1,656,688 1.93 Granted 1,350,150 1.55 Vested-common stock issued (938,311) 1.87 Forfeited / Expired (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 / Expired (124,127) 1.95 Unvested December 31, 2020 2,374,006 $ 2.26 Vested/Issued cumulative at December 31, 2020 6,599,894 $ 1.79

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
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 2020 2019 Statutory federal income tax rate 21.0 % 21.0 % State income taxes - net of federal tax benefit 0.9 % 0.9 % Other permanent differences (1.4) % (2.3) % Valuation allowances (25.5) % (25.9) % Research and development - U.S. 5.0 % 6.3 % Effective tax rate for the year — % — %
Components of Deferred Tax Assets	Significant components of our deferred tax assets are as follows (in thousands): December 31, 2020 2019 Net operating loss carryforwards $ 61,670 $ 48,182 Research and development credit carryforwards 16,308 12,797 Compensation expense 2,752 1,156 Other 3,526 903 Total deferred tax assets 84,256 63,038 Valuation allowance for deferred tax assets (84,256) (63,038) Net deferred tax assets $ — $ —

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 and 2019: Twelve months ended December 31, 2020 2019 Operating lease cost $ 516 $ 487 Short-term lease cost 111 61 Variable lease cost (1) 1,321 205 Total lease cost $ 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, 2020: 2021 $ 503 2022 188 2023 12 2024 2 Total minimum lease payments 705 Less: amount of lease payments representing interest 27 Present value of operating lease liabilities $ 678

Quarterly Financial Data (una_2

Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	The following table presents quarterly data for the years ended December 31, 2020 and 2019, in thousands, except per share data: 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) 2019 First Second Third Fourth Full Year Revenues $ 1,445 $ 4,262 $ (361) $ 287 $ 5,633 Loss from operations (13,260) (9,901) (12,342) (9,985) (45,488) Net loss (12,956) (9,688) (12,015) (9,923) (44,582) Basic and diluted net loss per common share (1) $ (0.09) $ (0.06) $ (0.08) $ (0.06) $ (0.29) (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 (Detail) $ in Thousands	1 Months Ended		12 Months Ended
	Apr. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)segment	Dec. 31, 2019USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of business segments | segment			1
Accumulated deficit			$ 496,389	$ 417,624
Cash and cash equivalents			$ 51,546	$ 35,041
Healios
Class of Stock [Line Items]
Proceeds from exercise of warrant	$ 7,000	$ 7,000
Public Stock Offering
Class of Stock [Line Items]
Net proceeds from public offering	$ 53,700

Accounting Policies - Additiona

Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Significant Accounting Policies [Line Items]
Right-of-use assets	$ 700,000	$ 700,000
Lease liabilities	678,000	700,000
Payments for royalties	$ 0
Sublicense fees		$ 100,000	$ 600,000
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Deposits and other	Deposits and other
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued expenses and other	Accrued expenses and other
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other long-term liabilities	Other long-term liabilities
Gain from insurance proceeds, net	$ 0	$ 0	$ 617,000
Warrant liabilities	$ 0	0
Annual stock-based awards vesting period (in years)	4 years
Contractual term (in years)	10 years
Liability for uncertain income tax	$ 0	$ 0
2018 Awards
Significant Accounting Policies [Line Items]
Annual stock-based awards vesting period (in years)	3 years
RSUs
Significant Accounting Policies [Line Items]
Annual stock-based awards vesting period (in years)	4 years
RSUs | 2018 Awards
Significant Accounting Policies [Line Items]
Annual stock-based awards vesting period (in years)	3 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
ASU 2016-02
Significant Accounting Policies [Line Items]
Right-of-use assets				$ 1,000,000
Lease liabilities				$ 1,000,000

Accounting Policies - Fair Valu

Accounting Policies - Fair Value of Stock-Based Compensation Awards (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Volatility	72.20%	71.10%	70.80%
Risk-free interest rate	0.60%	2.00%	2.80%
Expected life of option (in years)	5 years 8 months 12 days	6 years 2 months 12 days	6 years
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, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	20,524,415	20,007,851	31,112,196
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	18,150,409	13,975,671	10,955,508
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	2,374,006	2,032,180	1,656,688
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	0	4,000,000	18,500,000

Property and Equipment, net - S

Property and Equipment, net - Schedule of Property and Equipment, net (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 12,855	$ 11,773
Accumulated depreciation	(9,700)	(8,891)
Property and equipment, net	3,155	2,882
Laboratory equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,225	8,008
Office equipment and leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,336	3,191
Process development equipment not yet in service
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 294	$ 574

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Disposal of obsolete equipment	$ 0.1	$ 0.1

Collaborative Arrangements an_3

Collaborative Arrangements and Revenue Recognition - Additional Information (Details) $ / shares in Units, $ in Millions	1 Months Ended			12 Months Ended
	Dec. 31, 2018USD ($)	Jun. 30, 2018USD ($)shares	Mar. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017milestone	Dec. 31, 2016USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Number of first warrant shares (in shares) | shares		4,000,000
Healios
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront cash payments received					$ 15
Potential payment for rights to additional indications including ARDS					$ 10
Common stock share issued (in shares) | shares			12,000,000
Shares of common stock issued, value			$ 21.1
Common stock issued, price per share (in dollars per share) | $ / shares			$ 1.76
Potential near-term payment received	$ 2	$ 10
Additional payment from Healios		10
Expected credit to future milestone payment		10
Fair value of the warrant		$ 4.2	$ 5.3
Remaining exercisable warrants (in shares) | shares		16,000,000
Healios | Regulatory and Sales Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue from approvals and milestones		$ 225
Number of future milestones achieved | milestone				2
Healios | License fee revenue
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Increase (decrease) in revenue		(1.1)
Ophthalmology License Agreement | Regulatory and Sales Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential revenue from approvals and milestones		$ 135.6

Collaborative Arrangements an_4

Collaborative Arrangements and Revenue Recognition - Summary of Revenues Disaggregated by Recognition at Point in Time and Over Time (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Point in Time
Disaggregation of Revenue [Line Items]
Revenues	$ 1,432	$ 3,791	$ 19,378
Point in Time | Other contract revenue
Disaggregation of Revenue [Line Items]
Revenues	0	0	251
Point in Time | Healios | License fee revenue
Disaggregation of Revenue [Line Items]
Revenues	0	1,624	17,682
Point in Time | Healios | Product supply revenue
Disaggregation of Revenue [Line Items]
Revenues	1,432	2,167	1,445
Point in Time | Healios | Service revenue
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Over Time
Disaggregation of Revenue [Line Items]
Revenues	0	1,726	3,149
Over Time | Other contract revenue
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Over Time | Healios | License fee revenue
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Over Time | Healios | Product supply revenue
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Over Time | Healios | Service revenue
Disaggregation of Revenue [Line Items]
Revenues	$ 0	$ 1,726	$ 3,149

Capitalization and Warrant In_3

Capitalization and Warrant Instruments - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions

1 Months Ended

3 Months Ended

12 Months Ended

May 31, 2020

Apr. 30, 2020

Mar. 31, 2020

Nov. 30, 2019

May 31, 2019

Jun. 30, 2018

May 31, 2018

Mar. 31, 2018

Oct. 31, 2017

Mar. 19, 2021

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Jun. 30, 2019

Class of Warrant or Right [Line Items]

Common stock, shares authorized (in shares)

300,000,000

300,000,000

Preferred stock, shares authorized (in shares)

10,000,000

10,000,000

Preferred stock, shares issued (in shares)

0

0

Number of first warrant shares (in shares)

4,000,000

Payment to acquire intellectual property rights

$ 0.5

Additional shares issuable upon issuance of intellectual property rights (in shares)

500,000

500,000

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

Accrued License Fees | Cash Obligation

Class of Warrant or Right [Line Items]

Payment to acquire intellectual property rights

$ 1

Intellectual Property

Class of Warrant or Right [Line Items]

Stock issued during period, shares, issued for intellectual property rights (in shares)

1,000,000

Stock issued during period, amount, issued for intellectual property rights

$ 2.3

Increase in fair value of stock issued

$ 0.3

Intellectual Property | Accrued License Fees | Contingent Obligation

Class of Warrant or Right [Line Items]

Stock issued during period, amount, issued for intellectual property rights

$ 0.9

Aspire Capital | Equity Purchase Agreement

Class of Warrant or Right [Line Items]

Common stock share issued (in shares)

11,425,000

14,475,000

8,708,582

Issuance of common stock per share (in dollars per share)

$ 1.67

$ 1.41

$ 1.78

Aspire Capital | 2019 Equity Facility

Class of Warrant or Right [Line Items]

Equity purchase agreement, value

$ 100

Common stock issued as commitment fees (in shares)

350,000

Common stock registered for resale (in shares)

31,000,000

Aspire Capital | 2018 Equity Facility

Class of Warrant or Right [Line Items]

Common stock share issued (in shares)

500,000

Equity purchase agreement, value

$ 100

Common stock issued as commitment fees (in shares)

450,000

Common stock registered for resale (in shares)

24,700,000

Net proceeds through issuance of common stock

$ 1

Issuance of common stock per share (in dollars per share)

$ 2

Jefferies

Class of Warrant or Right [Line Items]

Open market sale agreement, value

$ 50

Additional Paid-in Capital | Intellectual Property

Class of Warrant or Right [Line Items]

Stock issued during period, amount, issued for intellectual property rights

$ 1.2

Healios

Class of Warrant or Right [Line Items]

Common stock share issued (in shares)

12,000,000

Shares of common stock issued, value

$ 21.1

Common stock issued, price per share (in dollars per share)

$ 1.76

$ 1.76

Warrants issued to purchase additional shares of common stock (in shares)

20,000,000

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%

Remaining exercisable warrants (in shares)

16,000,000

Expired warrants (in shares)

16,000,000

Common stock issued upon exercise of warrant (in shares)

4,000,000

Proceeds from exercise of warrant

$ 7

$ 7

Fair value of the warrant

$ 4.2

$ 5.3

Healios | Securities Purchase Agreement

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

License fee revenue | Healios

Class of Warrant or Right [Line Items]

Increase (decrease) in revenue from issuance of warrant

$ (1.1)

Subsequent Event | Aspire Capital | Equity Purchase Agreement

Class of Warrant or Right [Line Items]

Net proceeds through issuance of common stock

$ 26.6

Capitalization and Warrant In_4

Capitalization and Warrant Instruments - Common Stock Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares reserved for future issuance (in shares)	29,591,000	34,054,000
Stock-based compensation plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares reserved for future issuance (in shares)	29,591,000	30,054,000
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)	0	4,000,000

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense			$ 7.4	$ 4.9	$ 3.8
Total unrecognized compensation cost			$ 9.1
Weighted average fair value of options granted (in dollars per share)			$ 1.50	$ 1	$ 1.46
Total fair value of options vested			$ 3.5	$ 3	$ 2.5
Total intrinsic value of options exercised			$ 0.7	0	0
Weighted average contractual life of unvested options (in years)			8 years 6 months
Aggregate intrinsic value of fully vested and exercisable option shares and option shares expected to vest			$ 2.4
Restricted stock vested			2.2	$ 1.8	$ 1.3
Estimated compensation cost of unvested restricted stock			$ 5.2
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)				18,500,000
Common stock shares issued (in shares)			7,556,996
Shares available for issuance (in shares)			9,066,432
Shares of common stock outstanding (in shares)			19,524,415
2019 Equity and Incentive Compensation Plan | Minimum | Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Post-employment exercise period (in years and months)	3 months
2019 Equity and Incentive Compensation Plan | Minimum | Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Post-employment exercise period (in years and months)	18 months
2019 Equity and Incentive Compensation Plan | Maximum | Employee
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Post-employment exercise period (in years and months)	3 years
2019 Equity and Incentive Compensation Plan | Maximum | Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Post-employment exercise period (in years and months)	30 months
Expired Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares issued (in shares)			266,932
Shares of common stock outstanding (in shares)			845,911
2019 Equity And Incentive Compensation Plan, Modification
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 1.2
Total unrecognized compensation cost	$ 0.5	$ 0.5
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, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Options
Beginning Balance (in shares)	13,975,671	10,955,508	8,919,113
Granted (in shares)	5,213,168	3,402,608	2,434,732
Exercised (in shares)	(362,351)	(48,152)	(112,484)
Forfeited / Expired (in shares)	(676,079)	(334,293)	(285,853)
Ending Balance (in shares)	18,150,409	13,975,671	10,955,508
Vested during current period (in shares)	2,816,432
Vested and exercisable at period end (in shares)	11,229,772
Weighted Average Exercise Price
Beginning Balance (in dollars per share)	$ 1.77	$ 1.87	$ 1.78
Granted (in dollars per share)	2.44	1.55	2.26
Exercised (in dollars per share)	1.70	1.40	1.57
Forfeited / Expired (in dollars per share)	2.32	2.71	2.62
Ending Balance (in dollars per share)	1.95	$ 1.77	$ 1.87
Vested during current period (in dollars per share)	1.98
Vested and exercisable at period end (in dollars per share)	$ 1.85

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summarizes Information Concerning Options Outstanding and Options Vested and Exercisable (Details)	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Options Outstanding
Number of options (in shares) | shares	18,150,409
Options Vested and Exercisable
Number of options (in shares) | shares	11,229,772
Range One
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price lower range (in dollars per share)	$ 1.01
Exercise price upper range (in dollars per share)	$ 1.55
Options Outstanding
Number of options (in shares) | shares	7,524,261
Weighted Average Remaining Contractual Life	5 years 8 months 12 days
Weighted average exercise price (in dollars per share)	$ 1.45
Options Vested and Exercisable
Number of options (in shares) | shares	4,414,112
Weighted Average Remaining Contractual Life	4 years
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)	$ 2.19
Options Outstanding
Number of options (in shares) | shares	5,289,451
Weighted Average Remaining Contractual Life	3 years 2 months 12 days
Weighted average exercise price (in dollars per share)	$ 1.93
Options Vested and Exercisable
Number of options (in shares) | shares	4,594,032
Weighted Average Remaining Contractual Life	2 years 4 months 24 days
Weighted average exercise price (in dollars per share)	$ 1.93
Range Three
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price lower range (in dollars per share)	2.30
Exercise price upper range (in dollars per share)	$ 3.57
Options Outstanding
Number of options (in shares) | shares	5,336,697
Weighted Average Remaining Contractual Life	6 years 8 months 12 days
Weighted average exercise price (in dollars per share)	$ 2.67
Options Vested and Exercisable
Number of options (in shares) | shares	2,221,628
Weighted Average Remaining Contractual Life	3 years 9 months 18 days
Weighted average exercise price (in dollars per share)	$ 2.46

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, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Restricted Stock Units
Beginning balance (in shares)	2,032,180	1,656,688	1,648,986
Granted (in shares)	1,553,671	1,350,150	787,968
Vested-common stock issued (in shares)	(1,087,718)	(938,311)	(741,424)
Forfeited / Expired (in shares)	(124,127)	(36,347)	(38,842)
Ending balance (in shares)	2,374,006	2,032,180	1,656,688
Vested/Issued cumulative at period end (in shares)	6,599,894
Weighted Average Fair Value
Beginning Balance (in dollars per share)	$ 1.71	$ 1.93	$ 1.69
Granted (in dollars per share)	2.76	1.55	2.31
Vested-common stock issued (in dollars per share)	1.98	1.87	1.81
Forfeited / Expired (in dollars per share)	1.95	1.69	1.74
Ending Balance (in dollars per share)	2.26	$ 1.71	$ 1.93
Vested/Issued cumulative at period end (in dollars per share)	$ 1.79

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes [Line Items]
Income tax paid	$ 0	$ 0	$ 0
U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	248,000,000
Research and development tax credit	16,300,000
Foreign
Income Taxes [Line Items]
Net operating loss carryforwards	30,000,000
State and City
Income Taxes [Line Items]
Net operating loss carryforwards	82,500,000
Subject To Annual Limitations | U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	111,400,000
Not Subject To Annual Limitations | U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	211,300,000
Research and development tax credit	16,300,000
Not Subject To Annual Limitations | State and City
Income Taxes [Line Items]
Net operating loss carryforwards	$ 82,300,000

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, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Statutory federal income tax rate	21.00%	21.00%
State income taxes - net of federal tax benefit	0.90%	0.90%
Other permanent differences	(1.40%)	(2.30%)
Valuation allowances	(25.50%)	(25.90%)
Research and development - U.S.	5.00%	6.30%
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, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 61,670	$ 48,182
Research and development credit carryforwards	16,308	12,797
Compensation expense	2,752	1,156
Other	3,526	903
Total deferred tax assets	84,256	63,038
Valuation allowance for deferred tax assets	(84,256)	(63,038)
Net deferred tax assets	$ 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, 2020	Dec. 31, 2019	Dec. 31, 2018
Postemployment Benefits [Abstract]
Employer contribution for profit sharing plan	$ 0.5	$ 0.4	$ 0.5

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Right-of-use assets	$ 700	$ 700
Lease liabilities	$ 678	$ 700
Weighted average remaining lease term (in years)	1 year 6 months	1 year 7 months 6 days
Weighted average discount rate (percent)	5.00%	5.30%
Payment for operating leases	$ 500	$ 500
Rent expense			$ 500
Minimum
Lessee, Lease, Description [Line Items]
Lease term (in months)	8 months
Maximum
Lessee, Lease, Description [Line Items]
Lease term (in months)	38 months

Leases - Components of Lease Co

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

Leases - Future Minimum Lease P

Leases - Future Minimum Lease Payments for Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2021	$ 503
2022	188
2023	12
2024	2
Total minimum lease payments	705
Less: amount of lease payments representing interest	27
Present value of operating lease liabilities	$ 678	$ 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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 1,270	$ 86	$ 84	$ 0	$ 287	$ (361)	$ 4,262	$ 1,445	$ 1,440	$ 5,633	$ 24,291
Loss from operations	(21,918)	(22,318)	(18,337)	(15,759)	(9,985)	(12,342)	(9,901)	(13,260)	(78,332)	(45,488)	(25,045)
Net loss	$ (22,206)	$ (22,543)	$ (18,372)	$ (15,644)	$ (9,923)	$ (12,015)	$ (9,688)	$ (12,956)	$ (78,765)	$ (44,582)	$ (24,283)
Basic and diluted net loss per common share (in dollars per share)	$ (0.11)	$ (0.11)	$ (0.10)	$ (0.10)	$ (0.06)	$ (0.08)	$ (0.06)	$ (0.09)	$ (0.42)	$ (0.29)	$ (0.18)

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) $ in Thousands	Feb. 16, 2021USD ($)	Feb. 15, 2021USD ($)	Jan. 04, 2021USD ($)ft²renewalOption	Mar. 25, 2021	Dec. 31, 2020USD ($)
Subsequent Event [Line Items]
Payment due for base annual rent in first year					$ 503
Maximum
Subsequent Event [Line Items]
Lease term (in years)					38 months
Subsequent Event | Warehouse and office space
Subsequent Event [Line Items]
Number of square feet leased | ft²			214,000
Lease term (in years)			10 years
Number of renewal options | renewalOption			5
Renewal term (in years)			5 years
Payment due for base annual rent in first year			$ 1,300
Annual rent escalators (as a percent)			2.00%
Subsequent Event | Former Chief Executive Officer
Subsequent Event [Line Items]
Severance payments and benefits		$ 1,000
Severance payments and benefits, period (in months)		18 months
Lump sum payment		$ 200
Subsequent Event | Officers and Certain Other Employees in Leadership Positions | Tranche One | Stock options
Subsequent Event [Line Items]
Retention stock option award vesting rights (as a percent)				33.33%
Subsequent Event | Pending Litigation | Maximum | 220 Litigation
Subsequent Event [Line Items]
Fees and expenses sought by plaintiff	$ 500