Athersys, Inc / New (ATHXQ) 10-K 16 Mar 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 13, 2020	Jun. 28, 2019
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	ATHERSYS, INC / NEW
Entity Central Index Key	0001368148
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		164,146,585
Entity Public Float			$ 218.6

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 35,041	$ 51,059
Prepaid expenses and other	1,168	1,791
Total current assets	37,171	57,840
Equipment, net	2,882	3,002
Deposits and other	1,613	888
Total assets	41,666	61,730
Current liabilities:
Accrued compensation and related benefits	773	1,901
Accrued clinical trial related costs	1,160	1,276
Accrued expenses	723	461
Total current liabilities	12,837	15,475
Other long-term liabilities	220	0
Stockholders’ equity:
Preferred stock, at stated value; 10,000,000 shares authorized, and no shares issued and outstanding at December 31, 2019 and 2018	0	0
Common stock, $0.001 par value; 300,000,000 shares authorized; 159,791,585 and 144,292,739 shares issued and outstanding at December 31, 2019 and 2018, respectively	160	144
Additional paid-in capital	440,735	416,014
Accumulated deficit	(417,624)	(373,042)
Total stockholders’ equity	23,271	43,116
Total liabilities and stockholders’ equity	41,666	61,730
Consolidated entity, excluding related party
Current assets:
Accounts receivable	17	262
Current liabilities:
Accounts payable	9,048	9,163
Healios
Current assets:
Accounts receivable	945	1,108
Unbilled accounts receivable from Healios	0	3,620
Current liabilities:
Accounts payable	1,068	0
Deposit from Healios	0	2,000
Deferred revenue - Healios	65	674
Advance from Healios	$ 5,338	$ 3,139

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
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)	159,791,585	144,292,739
Common stock, shares outstanding (in shares)	159,791,585	144,292,739

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues
Revenues	$ 5,633	$ 24,291	$ 3,708
Costs and expenses
Research and development (including stock compensation expense of $2,217, $1,609 and $1,232 in 2019, 2018 and 2017, respectively)	39,045	38,656	27,841
General and administrative (including stock compensation expense of $2,634, $2,240 and $1,812 in 2019, 2018 and 2017, respectively)	11,378	10,442	8,466
Depreciation	698	855	684
Total costs and expenses	51,121	49,953	36,991
Gain from insurance proceeds, net	0	617	0
Loss from operations	(45,488)	(25,045)	(33,283)
Income from change in fair value of warrants, net	0	0	728
Other income, net	906	762	314
Net loss and comprehensive loss	$ (44,582)	$ (24,283)	$ (32,241)
Net loss per common share, basic and diluted (in dollars per share)	$ (0.29)	$ (0.18)	$ (0.29)
Weighted average shares outstanding, basic and diluted (in shares)	151,696	136,641	112,053
Royalty and other contract revenue
Revenues
Revenues	$ 0	$ 1,461	$ 1,925
Grant revenue
Revenues
Revenues	116	554	865
Healios | Contract revenue
Revenues
Revenues	$ 5,517	$ 22,276	$ 918

Consolidated Statements of Op_2

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock compensation expense	$ 4,900	$ 3,800	$ 3,000
Research and Development
Stock compensation expense	2,217	1,609	1,232
General and Administrative
Stock compensation expense	$ 2,634	$ 2,240	$ 1,812

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	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, 2016		0
Common stock, beginning balance (in shares) at Dec. 31, 2016			86,629,302
Beginning balance at Dec. 31, 2016	$ 11,181	$ 0	$ 87	$ 329,373	$ (318,279)
Stock-based compensation	3,154			3,154
Issuance of common stock from warrant exercises (in shares)			1,843,363
Issuance of common stock from warrant exercises	1,862		$ 2	1,860
Issuance of common stock, net of issuance costs (in shares)							33,172,300
Issuance of common stock, net of issuance costs						$ 39,813	$ 33	$ 39,780
Issuance of common stock under equity compensation plans (in shares)			432,488
Issuance of common stock under equity compensation plans	(283)			(283)
Net and comprehensive loss	(32,241)				(32,241)
Preferred stock shares, ending balance (in shares) at Dec. 31, 2017		0
Common stock, ending balance (in shares) at Dec. 31, 2017			122,077,453
Ending balance at Dec. 31, 2017	23,376	$ 0	$ 122	373,884	(350,630)
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	0
Common stock, ending balance (in shares) at Dec. 31, 2018	144,292,739		144,292,739
Ending balance at Dec. 31, 2018	$ 43,116	$ 0	$ 144	416,014	(373,042)
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
Common stock, ending balance (in shares) at Dec. 31, 2019	159,791,585		159,791,585
Ending balance at Dec. 31, 2019	$ 23,271	$ 0	$ 160	$ 440,735	$ (417,624)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (9,923)	$ (12,956)	$ (11,321)	$ (10,155)	$ (44,582)	$ (24,283)	$ (32,241)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation					698	855	684
Stock-based compensation					4,851	3,849	3,044
Discount on revenue from issuance of warrant					0	1,080	0
Other					0	0	(22)
Stock–based patent license and settlement expense					0	315	3,150
Gain from insurance proceeds, net					0	(617)	0	$ (700)
Change in fair value of warrant liabilities					0	0	(728)
Changes in operating assets and liabilities:
Prepaid expenses and other					857	(1,346)	(206)
Net cash used in operating activities					(35,326)	(13,350)	(24,018)
Investing activities
Proceeds from insurance, net					0	617	0
Purchases of equipment					(579)	(1,532)	(285)
Net cash used in investing activities					(579)	(915)	(285)
Financing activities
Proceeds from exercise of warrants					0	0	1,862
Shares retained for withholding tax payments on stock-based awards					(424)	(402)	(283)
Net cash provided by financing activities					19,887	36,008	38,866
(Decrease) increase in cash and cash equivalents					(16,018)	21,743	14,563
Cash and cash equivalents at beginning of year		$ 51,059		$ 29,316	51,059	29,316	14,753
Cash and cash equivalents at end of year	$ 35,041		$ 51,059		35,041	51,059	29,316	$ 14,753
Consolidated entity, excluding related party
Changes in operating assets and liabilities:
Accounts receivable					245	324	12
Accounts payable and accrued expenses					(1,836)	4,269	1,537
Deferred revenue					0	(250)	771
Financing activities
Proceeds from issuance of common stock, net					20,311	15,415	37,287
Healios
Changes in operating assets and liabilities:
Accounts receivable					3,783	(4,545)	(153)
Accounts payable to Healios					1,068	0	0
Advances and deposits from Healios					199	4,889	134
Deferred revenue					(609)	2,110	0
Financing activities
Proceeds from issuance of common stock, net					$ 0	$ 20,995	$ 0

Background

Background	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Background	Background We are an international biotechnology company focused in the field of regenerative medicine and operate in one business segment. Our operations consist of research, preclinical development and clinical development activities, and our most advanced program is in Phase 3 clinical development. We have incurred losses since our inception in 1995 and had an accumulated deficit of $417.6 million at December 31, 2019 , 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 commercialization and preparing for commercial-scale manufacturing and sales. At December 31, 2019 , we had available cash and cash equivalents of $35.0 million . We believe that these funds, expected cash receipts primarily attributed to our collaboration with HEALIOS K.K. (“Healios”), 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. Furthermore, we are actively pursuing new collaborative opportunities and other potential sources of funding, which could reduce the current level of usage of our equity facility and potentially accelerate certain costs. If sufficient capital is available, we would plan to accelerate our clinical activity and preparation for regulatory application, approval and commercialization, including commercial manufacturing. Importantly, we are approaching near-term milestones, including the results of 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, for example. Depending on the outcome of these milestones, we may accelerate or may delay certain programs. In the longer term, we will have to continue to generate additional capital to meet our needs until we would become cash flow positive as a result of the sales of our clinical products, if they are approved for marketing. Such capital would come from new and existing collaborations and the related license fees, milestones and potential royalties, 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, 2019
Accounting Policies [Abstract]
Accounting Policies	B. Accounting Policies 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. 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. As further described below, on January 1, 2018, we adopted Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (“Topic 606”), to account for revenue. The deliverables under our arrangements are evaluated under 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. Other than for our collaboration with Healios that has remaining deliverables, as of the date of adoption of Topic 606 on January 1, 2018, we had recognized the full amount of license fees under our collaboration agreements as contract revenue under the prior guidance associated with multiple-element arrangements, since the performance periods for our multiple element arrangements had concluded. The events triggering any future contingent milestone payments from these arrangements were determined to be non-substantive and revenue will be recognized in the period that the triggering event occurs, and the remaining potential commercial milestones will be recognized when earned. 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. Unbilled Accounts Receivable We record amounts that are due to us under contractual arrangements for which invoicing has not yet occurred if our performance has concluded for the billable activity, and we have the unconditional right to the consideration, but such amounts have not yet been billed. The remaining transaction price for the performance obligations that were not yet delivered was not significant at December 31, 2019. At December 31, 2018, unbilled accounts receivable from Healios was $3.6 million , which includes $2.5 million of license fees that were paid to us by Healios in the first quarter of 2019 related to the expansion of our arrangement described in Note E . The remainder of the unbilled accounts receivable on the consolidated balance sheets at December 31, 2018 relates to manufacturing technology transfer services performed that were not yet billed to Healios. 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 or due are included in contract assets, with those amounts that are unconditional being included in either accounts receivable or unbilled 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 obligations, as opposed to non-current. Deposit from Healios Included in the deposit from Healios at December 31, 2018 is a $2.0 million payment received from Healios to extend the period of its exclusive right to negotiate for an option to expand its license to develop and commercialize certain disease indications in China. These nonrefundable proceeds will be creditable against potential milestone payments under the existing Healios licenses. The exclusive right of negotiation period expired on June 30, 2019. Advances from Healios The clinical trial supply agreement with Healios was amended in July 2017 to clarify a cost-sharing arrangement associated with our supply of clinical product for Healios' ischemic stroke trial in Japan. The proceeds from Healios for clinical supply that relate specifically to the cost-sharing arrangement may (i) result in a decrease in the amount we receive from Healios upon the achievement of certain milestones and an increase to a commercial milestone or (ii) be repaid at our election. While the amendment to the supply agreement resulted in a revision to the terms associated with the product supply, namely the cost of product supply, the revision did not affect any of the performance obligations under the overall arrangement. The proceeds from Healios that relate specifically to the cost-sharing arrangement for Healios’ ischemic stroke study in Japan are recognized as a non-current advance from Healios until the related milestones are achieved or such amounts are repaid to Healios at our election. No revenue has been recognized yet related to this advance. Recently Adopted Accounting Standards In May 2014, the Financial Accounting Standards Board ("FASB") issued guidance codified in ASC 606, Revenue Recognition - Revenue from Contracts with Customers ("Topic 606"), which amends the guidance in former ASC 605, Revenue Recognition . The core principle of Topic 606 is that an entity should recognize revenue to depict 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 good or services. We adopted Topic 606 utilizing the modified retrospective transition method applied to contracts that were not complete as of January 1, 2018. We evaluated all of our arrangements on a contract-by-contract basis, identifying all of the performance obligations, including those that are contingent. For our contracts with customers that contain multiple performance obligations, we account for the individual performance obligations separately when they are both capable of being distinct, whereby the customer can benefit from the service either on its own or together with other resources that are readily available from third parties or from us, and are distinct in the context of the contract, whereby the transfer of the services is separately identifiable from other promises in the contract. Under the new standard, we assessed whether licenses granted under our collaboration and license agreements were distinct in the context of the agreement from other performance obligations and functional when granted. After considering the relative selling prices of the contract elements and the allocation of revenue thereto, we recognized a cumulative effect adjustment of $1.9 million as an adjustment to the opening balance of our December 31, 2018 accumulated deficit primarily related to a contract asset since the revenue permitted to be recognized at inception was not limited to the cash proceeds received as of that time, which was a requirement of the previous guidance. We concluded that the new guidance resulted in revisions to accounting for our arrangement with Healios, only, since our other collaborations had no remaining performance obligations and potential contingent receipts would be constrained. Notes E and F further describe our arrangement with Healios. The comparative information for fiscal year ended December 31, 2017 has not been restated and continues to be reported under the accounting standards in effect for those periods. In January 2019 we adopted ASU 2016-02, Leases ("Topic 842"), which requires lessees to put most leases with a term greater than 12 months on their balance sheets, but recognize expenses on their statement of operations in a manner similar to current accounting practice. Under the guidance, lessees initially recognize a lease liability for the obligation to make lease payments and a right-of-use (“ROU”) asset for the right to use the underlying asset for the lease term. The lease liability is measured at the present value of the lease payments over the lease term. The ROU asset is measured at the lease liability amount, adjusted for lease prepayments, lease incentives received and the lessee’s initial direct costs. The guidance is effective for the annual and interim periods beginning after December 15, 2018. The impact of adoption to our consolidated financial statements is further discussed in Note J . 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. Cash used in investing activities excluded $0.1 million of accrued capital expenditures in 2018. 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 three-year period ended December 31, 2019 , 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, of which $0.1 million and $0.6 million were recorded as research and development expenses in the Consolidated Statements of Operations 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 to ten years ). Leasehold improvements are amortized over the shorter of the lease term or estimated useful life. 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, 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. Proceeds from Insurance In 2016, our facility sustained flood damage representing both an unusual and infrequent event, and we recognized a net insurance recovery gain of $0.7 million in 2016 that was reported as a separate component of our loss from operations. An additional $0.6 million of insurance proceeds, net of associated expenses, were received in 2018, concluding the insurance claim. Proceeds from insurance settlements, except for those directly related to investing or financing activities, were recognized as cash inflows from operating activities. Since the majority of the damage from the flood was to fully depreciated leasehold improvements, the amount of losses was less than the amount of the insurance proceeds received. 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, 2019 and 2018. Refer to Note F for a warrant issued in 2018 to Healios (the “Healios Warrant”), which is 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, 2019 and 2018, most of our accounts receivable are due from Healios. We do not typically require collateral from our customers. 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. 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. We use the “simplified” method to calculate the expected life of option grants given our limited history of exercise activity and determine volatility by using our historical stock volatility. 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. Options may be exercised for cash or by a cashless exercise that is permitted under certain conditions. In the event of a cashless exercise, we retain the number of shares equivalent to the exercise cost based on the market value at the time of exercise and issue the net number of shares to the holder. We recognize income tax benefits and deficiencies as income tax expense or benefit in the consolidated statement of operations and the tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. We also recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. Excess tax benefits are classified along with other income tax cash flows as an operating activity in the consolidated statement of cash flows. Regarding forfeitures, we account for them when they occur. All the aforementioned estimates and assumptions are evaluated on a quarterly basis and may change as facts and circumstances warrant. Changes in these assumptions can materially affect the estimate of the fair value of our share-based payments and the related amount recognized in our financial statements. Annual stock-based 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: December 31, 2019 2018 2017 Volatility 71.1 % 70.8 % 71.2 % Risk-free interest rate 2.0 % 2.8 % 2.0 % Expected life of option 6.2 years 6.0 years 6.2 years Expected dividend yield 0.0 % 0.0 % 0.0 % Income Taxes Deferred tax liabilities and assets are determined based on the differences between the financial reporting and tax basis of assets and liabilities and are measured using the tax rate and laws currently in effect. We evaluate our deferred income taxes to determine if a valuation allowance should be established against the deferred tax assets or if the valuation allowance should be reduced based on consideration of all available evidence, both positive and negative, using a “more likely than not” standard. We had no liability for uncertain income tax positions as of December 31, 2019 and 2018 . 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. For each reporting period in which we have outstanding warrants, we evaluate the income from such warrant liabilities and consider whether it results in a potentially dilutive effect to net loss per share. There were no such dilutive effects from warrant liabilities for each of the periods ended December 31, 2019 , 2018 and 2017 . We have outstanding options, restricted stock units and 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, 2019 2018 2017 Stock options 13,975,671 10,955,508 8,919,113 Restricted stock units 2,032,180 1,656,688 1,648,986 Warrants 4,000,000 18,500,000 — 20,007,851 31,112,196 10,568,099 Recently Issued Accounting Standards In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes . The ASU simplifies the accounting for income taxes, changes the accounting for certain income tax transactions, and other minor changes. This guidance is effective for fiscal years beginning after December 15, 2020, including interim periods, with early adoption permitted. We are currently assessing the impact that this ASU will have on our consolidated financial statements and disclosures. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (“Topic 808”): Clarifying the Interaction between Topic 808 and Topic 606 . The amendments in this update make targeted improvements to generally accepted accounting principles (“GAAP”) for collaborative arrangements as follows: clarify that certain transactions between collaborative arrangement participants should be accounted for as revenue under Topic 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in Topic 606 should be applied, including recognition, measurement, presentation, and disclosure requirements; add unit-of-account guidance in Topic 808 to align with the guidance in Topic 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of Topic 606; and require that in a transaction with a collaborative arrangement participant that is not directly related to sales to third parties, presenting the transaction together with revenue recognized under Topic 606 is precluded if the collaborative arrangement participant is not a customer. The provisions of ASU 2018-18 are effective for years beginning after December 15, 2019. We are currently evaluating the impact of this clarifying guidance. 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 noncancellable term of the cloud computing arrangements plus any option renewal periods that are reasonably certain to be exercised by the customer or for which the exercise is controlled by the service provider. The guidance is effective for the annual and interim periods beginning after December 15, 2019, with early adoption permitted. Entities can choose to adopt prospectively or retrospectively. We will adopt the standard effective January 1, 2020 prospectively and are currently evaluating the potential impact on our consolidated financial statements. 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.

Equipment

Equipment	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Equipment	Equipment December 31, Equipment consists of (in thousands): 2019 2018 Laboratory equipment $ 8,008 $ 7,444 Office equipment and leasehold improvements 3,191 3,043 Process development equipment not yet in service 574 822 11,773 11,309 Accumulated depreciation (8,891 ) (8,307 ) $ 2,882 $ 3,002 During 2019 , we disposed of approximately $0.1 million of obsolete laboratory equipment, office equipment and leasehold improvements, all of which were fully depreciated.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2019
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. At December 31, 2019 , we had no financial assets or liabilities measured at fair value on a recurring basis. The Healios Warrant that was issued in March 2018 was measured at fair value on a nonrecurring basis and is a Level 3 equity instrument under the hierarchy. Refer to Note F regarding its valuation. Financing Arrangements We lease office and laboratory space under operating leases. The lease for our corporate offices and laboratories began in 2000 and currently expires in March 2021, with options to renew annually through March 2024. Our rent is approximately $267,000 per year and our rental rate has not changed since the lease inception in 2000. We also lease office and laboratory space for our Belgian subsidiary, which expires in July 2021. Annual rent expense is approximately $190,000 , subject to adjustments based on an inflationary index. Aggregate rent expense for the years ended December 31, 2018 and 2017 recognized prior to the adoption of Topic 842 was approximately $493,000 and $477,000 , respectively. Refer to Note J regarding our adoption of Topic 842 in January 2019 to account for our leases.

Collaborative Arrangements and

Collaborative Arrangements and Revenue Recognition	12 Months Ended
	Dec. 31, 2019
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, currently 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. We receive payments for these products and services provided to Healios. In 2017, we signed a clinical trial supply agreement for delivering the planned manufacturing services for Healios’ clinical trial in Japan treating ischemic stroke patients. 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 Healios’ TREASURE study in Japan. Healios’ cost-share payments may be creditable 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. Services to Healios under the clinical trial supply agreement are ongoing. 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. 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. Services to Healios under the technology transfer services agreement are ongoing. 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 new license rights, which has been paid in full in four quarterly installment payments of $2.5 million . The payments were received in the second, third and fourth quarters of 2018 with the final payment received in the first quarter of 2019. 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 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 reversal of previously recognized revenue could occur throughout the life of the contract, and both the likelihood and magnitude of a potential reversal of revenue are taken into consideration. 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. During our evaluation of variable consideration in the third and fourth quarters of 2019, we revised our estimated transaction price due to changes in the underlying cost per dose of the product supply occurring during the respective quarter. 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 the third quarter of 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, unrelated to the cost per dose changes, the number of doses of clinical product requested by Healios was amended in the third quarter of 2019, and our revenues were further reduced during the period. Similarly, during the third and fourth quarters of 2019, certain services related to technology transfer activities were determined to be constrained since the activity may no longer be required under the arrangement. At inception and upon each modification date, 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 modifications and any new elements from a modification to the arrangement if the conditions are not met for being treated as a separate agreement. Following the June 2018 modification, the specific performance obligations that had been delivered included the licenses, and the performance obligations that were not yet fully delivered included clinical product manufacturing services and technology transfer services that we provide to a contract manufacturer in Japan. In the third quarter of 2018, an additional modification was executed to add clinical product manufacturing services for Healios’ planned ARDS study, which resulted in a new performance obligation, creating a modification to the arrangement and remeasurement of the transaction and standalone selling prices for the undelivered elements on the modification date. 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, 2019. At December 31, 2019 , 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 investigational product for Healios for its Japan stroke clinical study 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 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. 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, 2019 Twelve months ended December 31, 2018 Point in Time Over Time Point in Time Over Time Contract revenue from Healios: License fee revenue $ 1,624 $ — $ 17,682 $ — Product supply revenue 2,167 — 1,445 — Service revenue — 1,726 — 3,149 Other contract revenue — — 251 — Total disaggregated revenues $ 3,791 $ 1,726 $ 19,378 $ 3,149

Capitalization and Warrant Inst

Capitalization and Warrant Instruments	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Capitalization and Warrant Instruments	Capitalization and Warrant Instruments Capitalization At December 31, 2019 and December 31, 2018 , we had 300 million shares of common stock and 10.0 million shares of undesignated preferred stock authorized. No shares of preferred stock have been issued as of December 31, 2019 and 2018. The following shares, in thousands, of common stock were reserved for future issuance: December 31 2019 2018 Stock-based compensation plans 30,054 16,096 Healios Warrants to purchase common stock 4,000 18,500 34,054 34,596 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. 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, 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. The 4,000,000 Warrant Shares are exercisable at the greater of $1.76 and the Reference Price (which is generally 110% of the average closing price per share of the Company's common stock for the ten trading days ending on the trading day immediately preceding the date the Warrant is exercised). 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 exercisability of the 16,000,000 shares underlying the Healios Warrant 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, as appropriate. The current agreement with Aspire Capital was entered into in February 2018 and includes Aspire Capital’s commitment to purchase up to an aggregate of $100.0 million of shares of our common stock over a three -year period. The terms of the 2018 equity facility are similar to the previous arrangements, and we issued 450,000 shares of our common stock to Aspire Capital as a commitment fee in February 2018 and filed a registration statement for the resale of 24,700,000 shares of common stock in connection with the equity facility. Also, in connection with this equity facility, in February 2018, Aspire Capital invested $1.0 million in us at $2.00 per share of common stock. During the years ended December 31, 2019 , 2018 and 2017 , we sold 14,475,000 , 8,708,582 and 9,400,000 shares, respectively, to Aspire Capital at average prices of $1.41 , $1.78 and $1.75 per share, respectively. In the first quarter of 2020 through March 13, 2020, we generated an additional $5.5 million in proceeds from the use of our equity purchase arrangement. In November 2019, we entered into a new facility to replace the current facility, which will provide us with the ability to purchase up to an aggregate of $ 100.0 million of shares of common stock over a three -year period. The terms of the 2019 equity facility are similar to the previous arrangements, and we issued 350,000 shares of 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 new equity facility. Open Market Sale Agreement In May 2019, we entered into an open market sale agreement with Jefferies LLC ("Jefferies"), as sales agent, pursuant to which we could offer and sell, from time to time, through Jefferies, 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 will no longer be effective on March 21, 2020. Because that registration statement on Form S-3 will soon expire, the open market sale agreement with Jefferies will not be operable without additional SEC filings. We did not sell any shares of our common stock under this agreement. 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 are concluded.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-Based Compensation Our 2019 Equity and Incentive Compensation Plan (the "EICP") authorizes 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, 2019 , a total of 6,106,927 shares (including 255,656 shares related to an expired incentive plan) of common stock have been issued under our equity incentive plans. As of December 31, 2019 , a total of 14,048,065 shares were available for issuance under our EICP, and stock-based awards to purchase 16,007,851 shares (including 872,187 shares related to an expired incentive plan) of common stock were outstanding. We recognized $4.9 million , $3.8 million and $3.0 million of stock-based compensation expense in 2019 , 2018 and 2017 , respectively. Stock Options The weighted average fair value of options granted in 2019 , 2018 and 2017 was $1.00 , $1.46 and $0.95 per share, respectively. The total fair value of options vested during 2019 , 2018 and 2017 was $3.0 million , $2.5 million and $2.0 million , respectively. The total intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017 was not significant. At December 31, 2019 , total unrecognized estimated compensation cost related to unvested stock options was approximately $5.5 million , which is expected to be recognized by the end of 2023 using the straight-line method. The weighted average contractual life of unvested options at December 31, 2019 was 8.8 years . The aggregate intrinsic value of fully vested option shares and option shares expected to vest as of December 31, 2019 was not significant. A summary of our stock option activity and related information is as follows: Number of Options Weighted Average Exercise Price Outstanding January 1, 2017 9,236,228 $ 2.76 Granted 2,596,480 1.47 Exercised (136,056 ) 1.50 Forfeited / Expired (2,777,539 ) 4.76 Outstanding December 31, 2017 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 Vested during 2019 2,508,333 $ 1.88 Vested and exercisable at December 31, 2019 8,919,741 $ 1.81 December 31, 2019 Options Outstanding Options Vested and Exercisable Exercise Price Number of Options Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number of Options Weighted Average Remaining Contractual Life Weighted Average Exercise Price $1.01 – $1.55 6,832,730 8.0 years $ 1.47 3,223,605 3.2 years $ 1.42 $1.56 – $1.98 2,685,058 4.7 years $ 1.72 2,499,294 4.1 years $ 1.72 $2.06 – $3.84 4,457,883 7.2 years $ 2.26 3,196,842 5.0 years $ 2.26 13,975,671 8,919,741 Restricted Stock Units A summary of our restricted stock unit activity and related information is as follows: Number of Restricted Stock Units Weighted Average Fair Value Outstanding January 1, 2017 1,201,159 $ 1.92 Granted 1,054,720 1.46 Vested-common stock issued (571,118 ) 1.75 Forfeited / Expired (35,775 ) 1.82 Outstanding December 31, 2017 1,648,986 1.69 Granted 787,968 2.31 Vested-common stock issued (741,424 ) 1.81 Forfeited / Expired (38,842 ) 1.74 Outstanding 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 Outstanding December 31, 2019 2,032,180 $ 1.71 Vested/Issued cumulative at December 31, 2019 5,508,176 $ 1.75 The total fair value of restricted stock units vested during 2019 , 2018 and 2017 was $1.8 million , $1.3 million and $1.0 million , respectively. At December 31, 2019 , total unrecognized estimated compensation cost related to unvested restricted stock units was approximately $3.4 million , which is expected to be recognized by the end of 2023 using the straight-line method.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes At December 31, 2019 , we had U.S. federal net operating loss and research and development tax credit carryforwards of approximately $193.2 million and $12.8 million , respectively. Such operating losses and tax credits may be used to reduce future taxable income and tax liabilities and will expire at various dates between 2032 and 2039 . Additionally, as of December 31, 2019 , we had federal net operating loss carryforwards generated after 2017 of $ 56.6 million that have an indefinite life, but with usage limited to 80% of taxable income in any given year. We also had foreign net operating loss carryforwards of approximately $24.2 million . Such foreign net operating loss carryforwards do not expire. We also had state and city net operating loss carryforwards aggregating approximately $63.5 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 2020 and 2037 . 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 $156.5 million , research and development tax credits of $12.8 million , and state and local net operating loss carryforwards of $63.3 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 before Income Taxes 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % State income taxes - net of federal tax benefit 0.9 % 0.9 % Other permanent differences (2.3 )% (3.7 )% Valuation allowances (25.9 )% (29.2 )% Research and development - U.S. 6.3 % 11.0 % Effective tax rate for the year — % — % Significant components of our deferred tax assets are as follows (in thousands): December 31, 2019 2018 Net operating loss carryforwards $ 48,182 $ 38,813 Research and development credit carryforwards 12,797 9,979 Compensation expense 1,156 1,552 Other 903 1,166 Total deferred tax assets 63,038 51,510 Valuation allowance for deferred tax assets (63,038 ) (51,510 ) 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, 2019 . In December 2017, the U.S. federal government enacted legislation commonly referred to as the “Tax Cuts and Jobs Act” (the “TCJA”). The TCJA made widespread changes to the IRC, including, among other items, a reduction in the federal corporate tax rate from 35% to 21% , effective January 1, 2018. The TCJA also eliminated alternative minimum tax and the 20-year carryforward limitation for net operating losses incurred after December 31, 2017 and imposes a limit on the usage of net operating losses incurred after such date equal to 80% of taxable income in any given year. The 80% usage limit will not have an economic impact on us until our current net operating losses are either utilized or expire. The carrying value of our deferred tax assets and liabilities is determined by the enacted U.S. corporate income tax rate. Consequently, any changes in the U.S. corporate income tax rate impacts the carrying value of our deferred tax assets and liabilities. The Deemed Repatriation Transition Tax (“Transition Tax”) is a tax on previously untaxed accumulated and current earnings and profit (“E&P”) of certain of our foreign subsidiaries. To determine the amount of Transition Tax, a company must determine, in addition to other factors, the amount of post-1986 E&P of the relevant foreign subsidiaries as well as the amount of non-U.S. income tax paid on such earnings. We have an overall foreign E&P deficit and accordingly have not recorded any Transition Tax obligation. As of December 31, 2018, we have completed the accounting for all the impacts of the TCJA. We continue to evaluate the impacts of the TCJA and will consider additional guidance from the U.S. Treasury Department, Internal Revenue Service or other standard-setting bodies. However, no additional adjustments were recorded by us during the measurement period in 2018 as permitted by SEC Staff Accounting Bulletin 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act .

Profit Sharing and 401(k) Plan

Profit Sharing and 401(k) Plan	12 Months Ended
	Dec. 31, 2019
Postemployment Benefits [Abstract]
Profit Sharing and 401(k) Plan	Profit Sharing and 401(k) Plan We 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 $0.4 million , $0.5 million and $0.3 million in 2019 , 2018 and 2017 , respectively.

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases	Leases In February 2016, the FASB issued Topic 842, which requires lessees to record most leases with a term greater than 12 months on their balance sheets, but recognize expenses on their statement of operations in a manner similar to current accounting practice. Under the guidance, lessees initially recognize a lease liability for the obligation to make lease payments and a ROU asset for the right to use the underlying asset for the lease term. The lease liability is measured at the present value of the lease payments over the lease term. The ROU asset is measured at the lease liability amount, adjusted for lease prepayments, lease incentives received and the lessee’s initial direct costs. We adopted ASU 2016-02, Leases ("Topic 842") effective January 1, 2019, using the modified retrospective transition option. The adoption of the standard resulted in the recording of ROU assets, primarily consisting of operating leases of facilities and minor equipment, and lease liabilities of $1.0 million as of the commencement date. The adoption did not have a material impact on our consolidated statements of operations and comprehensive loss or cash flows related to existing leases. As a result, there was no cumulative-effect adjustment. We elected certain practical expedients as part of the adoption, which allow us to not reassess our prior conclusions about lease identification, lease classification and initial direct costs. We also elected the short-term lease recognition exemption for all leases that qualify and will not recognize ROU assets or lease liabilities for those leases. Lastly, we elected to separate lease and non-lease components only for contract manufacturing assets based on an assessment of the contract terms. We did not separate lease and non-lease components for all other existing asset classes. Most leases do not contain an implicit discount rate; therefore, we estimate our incremental borrowing rate to discount the lease payments based on information available at lease commencement. Our facilities leases contain one or more options to renew after the noncancellable term. The exercise of lease renewal options is not reasonably certain upon lease commencement and is at management's sole discretion. Our ROU assets are included within deposits and other in our consolidated balance sheet at December 31, 2019 . Associated lease liabilities are included in accrued expenses and other, and other long-term liabilities in our consolidated balance sheet at December 31, 2019 . Lease expense for lease payments is recognized on a straight-line basis over the lease term within loss from operations in the consolidated statements of operations and comprehensive loss. Payments for certain lease agreements are adjusted annually for changes in an index or rate. We had no finance leases, residual value guarantees, restrictive covenants, subleases or sale leasebacks at December 31, 2019 . As of December 31, 2019 , ROU assets and lease liabilities were each $0.7 million. The weighted-average remaining term for lease contracts was 1.6 years at December 31, 2019 , with maturities ranging from 15 months to 50 months. The weighted-average discount rate was 5.3% at December 31, 2019 . We paid $0.5 million for operating leases included in the measurement of lease liabilities during the year ended December 31, 2019 . Aside from facilities and minor equipment, 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 liabilities until such payments are no longer variable. Lease Costs The table below presents certain information related to the lease costs (in thousands) for operating leases as of December 31, 2019 : Twelve months ended December 31, 2019 Operating lease cost $ 487 Short-term lease cost 61 Variable lease cost (1) 205 Total lease cost $ 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, 2019 : 2020 $ 489 2021 198 2022 15 2023 12 2024 2 Total minimum lease payments 716 Less: amount of lease payments representing interest 30 Present value of operating lease liabilities $ 686

Quarterly Financial Data (unaud

Quarterly Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2019
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, 2019 and 2018 , in thousands, except per share data: 2019 First Quarter Second Quarter Third Quarter Fourth Quarter 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 ) 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Full Year Revenues $ 1,066 $ 19,391 $ 2,321 $ 1,513 $ 24,291 Income (loss) from operations (10,262 ) 6,745 (9,976 ) (11,552 ) (25,045 ) Net income (loss) (10,155 ) 6,933 (9,740 ) (11,321 ) (24,283 ) Basic and diluted net income (loss) per common share (1) $ (0.08 ) $ 0.05 $ (0.07 ) $ (0.08 ) $ (0.18 ) (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.

Schedule II - Valuation and Qua

Schedule II - Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2019
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	Schedule II – Valuation and Qualifying Accounts (In thousands) Balance at Beginning of Year Additions Deductions Balance at End of Year Year Ended December 31, 2019 Deducted from asset accounts: Tax valuation allowances $ 51,510 $ 11,528 $ — $ 63,038 (A) Total 2019 $ 51,510 $ 11,528 $ — $ 63,038 Year Ended December 31, 2018 Deducted from asset accounts: Tax valuation allowances $ 44,829 $ 6,681 $ — $ 51,510 (A) Total 2018 $ 44,829 $ 6,681 $ — $ 51,510 Year Ended December 31, 2017 Deducted from asset accounts: Allowance for doubtful accounts-note receivable $ 376 $ — $ (376 ) $ — (B) Tax valuation allowances 54,772 — (9,943 ) 44,829 (A) Total 2017 $ 55,148 $ — $ (10,319 ) $ 44,829 (A) – Substantially all our deferred tax assets are offset by valuation allowances. (B) – Reserve on note receivable that was fully-reserved. We wrote-off the note in 2017.

Accounting Policies (Policies)

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
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.
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. As further described below, on January 1, 2018, we adopted Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (“Topic 606”), to account for revenue. The deliverables under our arrangements are evaluated under 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. Other than for our collaboration with Healios that has remaining deliverables, as of the date of adoption of Topic 606 on January 1, 2018, we had recognized the full amount of license fees under our collaboration agreements as contract revenue under the prior guidance associated with multiple-element arrangements, since the performance periods for our multiple element arrangements had concluded. The events triggering any future contingent milestone payments from these arrangements were determined to be non-substantive and revenue will be recognized in the period that the triggering event occurs, and the remaining potential commercial milestones will be recognized when earned. 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. Unbilled Accounts Receivable We record amounts that are due to us under contractual arrangements for which invoicing has not yet occurred if our performance has concluded for the billable activity, and we have the unconditional right to the consideration, but such amounts have not yet been billed. The remaining transaction price for the performance obligations that were not yet delivered was not significant at December 31, 2019. At December 31, 2018, unbilled accounts receivable from Healios was $3.6 million , which includes $2.5 million of license fees that were paid to us by Healios in the first quarter of 2019 related to the expansion of our arrangement described in Note E . The remainder of the unbilled accounts receivable on the consolidated balance sheets at December 31, 2018 relates to manufacturing technology transfer services performed that were not yet billed to Healios. 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 or due are included in contract assets, with those amounts that are unconditional being included in either accounts receivable or unbilled 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 obligations, as opposed to non-current. Deposit from Healios Included in the deposit from Healios at December 31, 2018 is a $2.0 million payment received from Healios to extend the period of its exclusive right to negotiate for an option to expand its license to develop and commercialize certain disease indications in China. These nonrefundable proceeds will be creditable against potential milestone payments under the existing Healios licenses. The exclusive right of negotiation period expired on June 30, 2019. Advances from Healios The clinical trial supply agreement with Healios was amended in July 2017 to clarify a cost-sharing arrangement associated with our supply of clinical product for Healios' ischemic stroke trial in Japan. The proceeds from Healios for clinical supply that relate specifically to the cost-sharing arrangement may (i) result in a decrease in the amount we receive from Healios upon the achievement of certain milestones and an increase to a commercial milestone or (ii) be repaid at our election. While the amendment to the supply agreement resulted in a revision to the terms associated with the product supply, namely the cost of product supply, the revision did not affect any of the performance obligations under the overall arrangement. The proceeds from Healios that relate specifically to the cost-sharing arrangement for Healios’ ischemic stroke study in Japan are recognized as a non-current advance from Healios until the related milestones are achieved or such amounts are repaid to Healios at our election. No revenue has been recognized yet related to this advance. Recently Adopted Accounting Standards In May 2014, the Financial Accounting Standards Board ("FASB") issued guidance codified in ASC 606, Revenue Recognition - Revenue from Contracts with Customers ("Topic 606"), which amends the guidance in former ASC 605, Revenue Recognition . The core principle of Topic 606 is that an entity should recognize revenue to depict 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 good or services. We adopted Topic 606 utilizing the modified retrospective transition method applied to contracts that were not complete as of January 1, 2018. We evaluated all of our arrangements on a contract-by-contract basis, identifying all of the performance obligations, including those that are contingent. For our contracts with customers that contain multiple performance obligations, we account for the individual performance obligations separately when they are both capable of being distinct, whereby the customer can benefit from the service either on its own or together with other resources that are readily available from third parties or from us, and are distinct in the context of the contract, whereby the transfer of the services is separately identifiable from other promises in the contract. Under the new standard, we assessed whether licenses granted under our collaboration and license agreements were distinct in the context of the agreement from other performance obligations and functional when granted. After considering the relative selling prices of the contract elements and the allocation of revenue thereto, we recognized a cumulative effect adjustment of $1.9 million as an adjustment to the opening balance of our December 31, 2018 accumulated deficit primarily related to a contract asset since the revenue permitted to be recognized at inception was not limited to the cash proceeds received as of that time, which was a requirement of the previous guidance. We concluded that the new guidance resulted in revisions to accounting for our arrangement with Healios, only, since our other collaborations had no remaining performance obligations and potential contingent receipts would be constrained. Notes E and F further describe our arrangement with Healios. The comparative information for fiscal year ended December 31, 2017 has not been restated and continues to be reported under the accounting standards in effect for those periods.
Leases	In January 2019 we adopted ASU 2016-02, Leases ("Topic 842"), which requires lessees to put most leases with a term greater than 12 months on their balance sheets, but recognize expenses on their statement of operations in a manner similar to current accounting practice. Under the guidance, lessees initially recognize a lease liability for the obligation to make lease payments and a right-of-use (“ROU”) asset for the right to use the underlying asset for the lease term. The lease liability is measured at the present value of the lease payments over the lease term. The ROU asset is measured at the lease liability amount, adjusted for lease prepayments, lease incentives received and the lessee’s initial direct costs. The guidance is effective for the annual and interim periods beginning after December 15, 2018. The impact of adoption to our consolidated financial statements is further discussed in Note J . In February 2016, the FASB issued Topic 842, which requires lessees to record most leases with a term greater than 12 months on their balance sheets, but recognize expenses on their statement of operations in a manner similar to current accounting practice. Under the guidance, lessees initially recognize a lease liability for the obligation to make lease payments and a ROU asset for the right to use the underlying asset for the lease term. The lease liability is measured at the present value of the lease payments over the lease term. The ROU asset is measured at the lease liability amount, adjusted for lease prepayments, lease incentives received and the lessee’s initial direct costs. We adopted ASU 2016-02, Leases ("Topic 842") effective January 1, 2019, using the modified retrospective transition option. The adoption of the standard resulted in the recording of ROU assets, primarily consisting of operating leases of facilities and minor equipment, and lease liabilities of $1.0 million as of the commencement date. The adoption did not have a material impact on our consolidated statements of operations and comprehensive loss or cash flows related to existing leases. As a result, there was no cumulative-effect adjustment. We elected certain practical expedients as part of the adoption, which allow us to not reassess our prior conclusions about lease identification, lease classification and initial direct costs. We also elected the short-term lease recognition exemption for all leases that qualify and will not recognize ROU assets or lease liabilities for those leases. Lastly, we elected to separate lease and non-lease components only for contract manufacturing assets based on an assessment of the contract terms. We did not separate lease and non-lease components for all other existing asset classes. Most leases do not contain an implicit discount rate; therefore, we estimate our incremental borrowing rate to discount the lease payments based on information available at lease commencement. Our facilities leases contain one or more options to renew after the noncancellable term. The exercise of lease renewal options is not reasonably certain upon lease commencement and is at management's sole discretion. Our ROU assets are included within deposits and other in our consolidated balance sheet at December 31, 2019 . Associated lease liabilities are included in accrued expenses and other, and other long-term liabilities in our consolidated balance sheet at December 31, 2019 . Lease expense for lease payments is recognized on a straight-line basis over the lease term within loss from operations in the consolidated statements of operations and comprehensive loss. Payments for certain lease agreements are adjusted annually for changes in an index or rate. We had no finance leases, residual value guarantees, restrictive covenants, subleases or sale leasebacks at December 31, 2019 . As of December 31, 2019 , ROU assets and lease liabilities were each $0.7 million. The weighted-average remaining term for lease contracts was 1.6 years at December 31, 2019 , with maturities ranging from 15 months to 50 months. The weighted-average discount rate was 5.3% at December 31, 2019 . We paid $0.5 million for operating leases included in the measurement of lease liabilities during the year ended December 31, 2019 . Aside from facilities and minor equipment, 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 liabilities until such payments are no longer variable.
Cash and Cash Equivalents	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 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 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 three-year period ended December 31, 2019 , 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, of which $0.1 million and $0.6 million were recorded as research and development expenses in the Consolidated Statements of Operations in the years ended December 31, 2019 and 2018 , respectively.
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 to ten years ). Leasehold improvements are amortized over the shorter of the lease term or estimated useful life. 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, 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.
Proceeds from Insurance	Proceeds from Insurance In 2016, our facility sustained flood damage representing both an unusual and infrequent event, and we recognized a net insurance recovery gain of $0.7 million in 2016 that was reported as a separate component of our loss from operations. An additional $0.6 million of insurance proceeds, net of associated expenses, were received in 2018, concluding the insurance claim. Proceeds from insurance settlements, except for those directly related to investing or financing activities, were recognized as cash inflows from operating activities. Since the majority of the damage from the flood was to fully depreciated leasehold improvements, the amount of losses was less than the amount of the insurance proceeds received.
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	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.
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, 2019 and 2018, most of our accounts receivable are due from Healios. We do not typically require collateral from our customers.
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.
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. We use the “simplified” method to calculate the expected life of option grants given our limited history of exercise activity and determine volatility by using our historical stock volatility. 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. Options may be exercised for cash or by a cashless exercise that is permitted under certain conditions. In the event of a cashless exercise, we retain the number of shares equivalent to the exercise cost based on the market value at the time of exercise and issue the net number of shares to the holder. We recognize income tax benefits and deficiencies as income tax expense or benefit in the consolidated statement of operations and the tax effects of exercised or vested awards are treated as discrete items in the reporting period in which they occur. We also recognize excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. Excess tax benefits are classified along with other income tax cash flows as an operating activity in the consolidated statement of cash flows. Regarding forfeitures, we account for them when they occur. All the aforementioned estimates and assumptions are evaluated on a quarterly basis and may change as facts and circumstances warrant. Changes in these assumptions can materially affect the estimate of the fair value of our share-based payments and the related amount recognized in our financial statements. Annual stock-based 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.
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, 2019 and 2018 . 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 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.
Recently Issued Accounting Standards	Recently Issued Accounting Standards In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes . The ASU simplifies the accounting for income taxes, changes the accounting for certain income tax transactions, and other minor changes. This guidance is effective for fiscal years beginning after December 15, 2020, including interim periods, with early adoption permitted. We are currently assessing the impact that this ASU will have on our consolidated financial statements and disclosures. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (“Topic 808”): Clarifying the Interaction between Topic 808 and Topic 606 . The amendments in this update make targeted improvements to generally accepted accounting principles (“GAAP”) for collaborative arrangements as follows: clarify that certain transactions between collaborative arrangement participants should be accounted for as revenue under Topic 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all the guidance in Topic 606 should be applied, including recognition, measurement, presentation, and disclosure requirements; add unit-of-account guidance in Topic 808 to align with the guidance in Topic 606 (that is, a distinct good or service) when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of Topic 606; and require that in a transaction with a collaborative arrangement participant that is not directly related to sales to third parties, presenting the transaction together with revenue recognized under Topic 606 is precluded if the collaborative arrangement participant is not a customer. The provisions of ASU 2018-18 are effective for years beginning after December 15, 2019. We are currently evaluating the impact of this clarifying guidance. 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 noncancellable term of the cloud computing arrangements plus any option renewal periods that are reasonably certain to be exercised by the customer or for which the exercise is controlled by the service provider. The guidance is effective for the annual and interim periods beginning after December 15, 2019, with early adoption permitted. Entities can choose to adopt prospectively or retrospectively. We will adopt the standard effective January 1, 2020 prospectively and are currently evaluating the potential impact on our consolidated financial statements. 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.
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. At December 31, 2019 , we had no financial assets or liabilities measured at fair value on a recurring basis. The Healios Warrant that was issued in March 2018 was measured at fair value on a nonrecurring basis and is a Level 3 equity instrument under the hierarchy. Refer to Note F regarding its valuation.

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
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: December 31, 2019 2018 2017 Volatility 71.1 % 70.8 % 71.2 % Risk-free interest rate 2.0 % 2.8 % 2.0 % Expected life of option 6.2 years 6.0 years 6.2 years Expected dividend yield 0.0 % 0.0 % 0.0 %
Instruments Excluded from Calculation of Diluted Net Loss Per Share	The following instruments, were excluded from the calculation of diluted net loss per share because their effects would be antidilutive: Years ended December 31, 2019 2018 2017 Stock options 13,975,671 10,955,508 8,919,113 Restricted stock units 2,032,180 1,656,688 1,648,986 Warrants 4,000,000 18,500,000 — 20,007,851 31,112,196 10,568,099

Equipment (Tables)

Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Equipment	December 31, Equipment consists of (in thousands): 2019 2018 Laboratory equipment $ 8,008 $ 7,444 Office equipment and leasehold improvements 3,191 3,043 Process development equipment not yet in service 574 822 11,773 11,309 Accumulated depreciation (8,891 ) (8,307 ) $ 2,882 $ 3,002

Collaborative Arrangements an_2

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

Capitalization and Warrant In_2

Capitalization and Warrant Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Common Stock Shares Reserved for Future Issuance	The following shares, in thousands, of common stock were reserved for future issuance: December 31 2019 2018 Stock-based compensation plans 30,054 16,096 Healios Warrants to purchase common stock 4,000 18,500 34,054 34,596

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Option Activity and Related Information	A summary of our stock option activity and related information is as follows: Number of Options Weighted Average Exercise Price Outstanding January 1, 2017 9,236,228 $ 2.76 Granted 2,596,480 1.47 Exercised (136,056 ) 1.50 Forfeited / Expired (2,777,539 ) 4.76 Outstanding December 31, 2017 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 Vested during 2019 2,508,333 $ 1.88 Vested and exercisable at December 31, 2019 8,919,741 $ 1.81
Summarizes Information Concerning Options Outstanding and Options Vested and Exercisable	December 31, 2019 Options Outstanding Options Vested and Exercisable Exercise Price Number of Options Weighted Average Remaining Contractual Life Weighted Average Exercise Price Number of Options Weighted Average Remaining Contractual Life Weighted Average Exercise Price $1.01 – $1.55 6,832,730 8.0 years $ 1.47 3,223,605 3.2 years $ 1.42 $1.56 – $1.98 2,685,058 4.7 years $ 1.72 2,499,294 4.1 years $ 1.72 $2.06 – $3.84 4,457,883 7.2 years $ 2.26 3,196,842 5.0 years $ 2.26 13,975,671 8,919,741
Summary of Restricted Stock Unit Activity and Related Information	A summary of our restricted stock unit activity and related information is as follows: Number of Restricted Stock Units Weighted Average Fair Value Outstanding January 1, 2017 1,201,159 $ 1.92 Granted 1,054,720 1.46 Vested-common stock issued (571,118 ) 1.75 Forfeited / Expired (35,775 ) 1.82 Outstanding December 31, 2017 1,648,986 1.69 Granted 787,968 2.31 Vested-common stock issued (741,424 ) 1.81 Forfeited / Expired (38,842 ) 1.74 Outstanding 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 Outstanding December 31, 2019 2,032,180 $ 1.71 Vested/Issued cumulative at December 31, 2019 5,508,176 $ 1.75

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
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 before Income Taxes 2019 2018 Statutory federal income tax rate 21.0 % 21.0 % State income taxes - net of federal tax benefit 0.9 % 0.9 % Other permanent differences (2.3 )% (3.7 )% Valuation allowances (25.9 )% (29.2 )% Research and development - U.S. 6.3 % 11.0 % 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, 2019 2018 Net operating loss carryforwards $ 48,182 $ 38,813 Research and development credit carryforwards 12,797 9,979 Compensation expense 1,156 1,552 Other 903 1,166 Total deferred tax assets 63,038 51,510 Valuation allowance for deferred tax assets (63,038 ) (51,510 ) Net deferred tax assets $ — $ —

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 : Twelve months ended December 31, 2019 Operating lease cost $ 487 Short-term lease cost 61 Variable lease cost (1) 205 Total lease cost $ 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, 2019 : 2020 $ 489 2021 198 2022 15 2023 12 2024 2 Total minimum lease payments 716 Less: amount of lease payments representing interest 30 Present value of operating lease liabilities $ 686

Quarterly Financial Data (una_2

Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	The following table presents quarterly data for the years ended December 31, 2019 and 2018 , in thousands, except per share data: 2019 First Quarter Second Quarter Third Quarter Fourth Quarter 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 ) 2018 First Quarter Second Quarter Third Quarter Fourth Quarter Full Year Revenues $ 1,066 $ 19,391 $ 2,321 $ 1,513 $ 24,291 Income (loss) from operations (10,262 ) 6,745 (9,976 ) (11,552 ) (25,045 ) Net income (loss) (10,155 ) 6,933 (9,740 ) (11,321 ) (24,283 ) Basic and diluted net income (loss) per common share (1) $ (0.08 ) $ 0.05 $ (0.07 ) $ (0.08 ) $ (0.18 ) (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	12 Months Ended
	Dec. 31, 2019USD ($)Segment	Dec. 31, 2018USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of business segments | Segment	1
Accumulated deficit	$ 417,624	$ 373,042
Cash and cash equivalents	$ 35,041	$ 51,059

Accounting Policies - Additiona

Accounting Policies - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2019	Jan. 01, 2018	Jan. 01, 2017
Significant Accounting Policies [Line Items]
Revenue recognized related to the advance from Healios	$ 0
Cumulative effect of accounting change						$ 1,871,000	$ (110,000)
Accrued capital expenditures		$ 100,000
Payments for royalties	0	0	$ 0
Sublicense fees	100,000	600,000
Gain from insurance proceeds, net	0	617,000	0	$ 700,000
Warrant liabilities	$ 0	0
Contractual term	10 years
Liability for uncertain income tax	$ 0	0
Dilutive effects from warrant liabilities	$ 0	0	$ 0
Healios
Significant Accounting Policies [Line Items]
Unbilled accounts receivable from Healios		3,600,000
Deposit from Healios		$ 2,000,000
Minimum
Significant Accounting Policies [Line Items]
Estimated useful life of long-lived assets	3 years
Annual stock-based awards vesting period		3 years
Maximum
Significant Accounting Policies [Line Items]
Estimated useful life of long-lived assets	10 years
Annual stock-based awards vesting period	4 years
License | Healios
Significant Accounting Policies [Line Items]
Unbilled accounts receivable from Healios					$ 2,500,000
Retained Earnings
Significant Accounting Policies [Line Items]
Cumulative effect of accounting change						1,871,000	$ (110,000)
Retained Earnings | ASU 2014-09
Significant Accounting Policies [Line Items]
Cumulative effect of accounting change						$ 1,900,000

Accounting Policies - Fair Valu

Accounting Policies - Fair Value of Stock-Based Compensation Awards (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Volatility	71.10%	70.80%	71.20%
Risk-free interest rate	2.00%	2.80%	2.00%
Expected life of option	6 years 2 months 12 days	6 years	6 years 2 months 12 days
Expected dividend yield	0.00%	0.00%	0.00%

Accounting Policies - Instrumen

Accounting Policies - Instruments Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	20,007,851	31,112,196	10,568,099
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	13,975,671	10,955,508	8,919,113
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	2,032,180	1,656,688	1,648,986
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	4,000,000	18,500,000	0

Equipment - Equipment (Details)

Equipment - Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Equipment, gross	$ 11,773	$ 11,309
Accumulated depreciation	(8,891)	(8,307)
Equipment, net	2,882	3,002
Laboratory equipment
Property, Plant and Equipment [Line Items]
Equipment, gross	8,008	7,444
Office equipment and leasehold improvements
Property, Plant and Equipment [Line Items]
Equipment, gross	3,191	3,043
Process development equipment not yet in service
Property, Plant and Equipment [Line Items]
Equipment, gross	$ 574	$ 822

Equipment - Additional Informat

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

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Rent	$ 267,000
Aggregate rent expense		$ 493,000	$ 477,000
Belgium
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Rent	190,000
Fair Value Measurements, Recurring Basis
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Financial assets measured at fair value on recurring basis	0
Financial liabilities measured at fair value on recurring basis	$ 0

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 ($)	Jun. 30, 2018USD ($)Installmentshares	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 public offering (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
License and services revenue payment number of installments | Installment		4
License and services revenue payment installment amount due per quarter		$ 2.5
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
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, 2019	Dec. 31, 2018
Point in Time
Disaggregation of Revenue [Line Items]
Revenues	$ 3,791	$ 19,378
Point in Time | Other contract revenue
Disaggregation of Revenue [Line Items]
Revenues	0	251
Point in Time | Healios | License fee revenue
Disaggregation of Revenue [Line Items]
Revenues	1,624	17,682
Point in Time | Healios | Product supply revenue
Disaggregation of Revenue [Line Items]
Revenues	2,167	1,445
Point in Time | Healios | Service revenue
Disaggregation of Revenue [Line Items]
Revenues	0	0
Over Time
Disaggregation of Revenue [Line Items]
Revenues	1,726	3,149
Over Time | Other contract revenue
Disaggregation of Revenue [Line Items]
Revenues	0	0
Over Time | Healios | License fee revenue
Disaggregation of Revenue [Line Items]
Revenues	0	0
Over Time | Healios | Product supply revenue
Disaggregation of Revenue [Line Items]
Revenues	0	0
Over Time | Healios | Service revenue
Disaggregation of Revenue [Line Items]
Revenues	$ 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

2 Months Ended

12 Months Ended

Nov. 30, 2019

May 31, 2019

Jun. 30, 2018

May 31, 2018

Mar. 31, 2018

Feb. 28, 2018

Oct. 31, 2017

Mar. 13, 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

Warrants exercised, percentage of average closing price per share for ten business days

110.00%

Payment to acquire intellectual property rights

$ 0.5

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

500,000

500,000

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

Class of Warrant or Right [Line Items]

Common stock share issued in public offering (in shares)

14,475,000

8,708,582

9,400,000

Equity purchase agreement, value

$ 100

$ 100

Equity purchase agreement, term

3 years

3 years

Common stock issued as commitment fees (in shares)

350,000

450,000

Common stock registered for resale (in shares)

31,000,000

24,700,000

Net proceeds through issuance of common stock

$ 1

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

$ 2

$ 1.41

$ 1.78

$ 1.75

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 public offering (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

Fair value of the warrant

$ 4.2

$ 5.3

License | Healios

Class of Warrant or Right [Line Items]

Increase (decrease) in revenue from issuance of warrant

$ (1.1)

Subsequent Event | Aspire Capital

Class of Warrant or Right [Line Items]

Net proceeds through issuance of common stock

$ 5.5

Capitalization and Warrant In_4

Capitalization and Warrant Instruments - Common Stock Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares reserved for future issuance (in shares)	34,054,158	34,596,000
Stock-based compensation plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares reserved for future issuance (in shares)	30,054,158	16,096,000
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)	4,000,000	18,500,000

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4.9	$ 3.8	$ 3
Weighted average fair value of options granted (in dollars per share)	$ 1	$ 1.46	$ 0.95
Total fair value of options vested	$ 3	$ 2.5	$ 2
Total unrecognized estimated compensation cost	$ 5.5
Weighted average contractual life of unvested options	8 years 9 months 1 day
Restricted stock vested	$ 1.8	$ 1.3	$ 1
Estimated compensation cost of unvested restricted stock	$ 3.4
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	6,106,927
Shares available for issuance (in shares)	14,048,065
Shares of common stock outstanding (in shares)	16,007,851
Expired Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares issued (in shares	255,656
Shares of common stock outstanding (in shares)	872,187

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning Balance (in shares)	10,955,508	8,919,113	9,236,228
Granted (in shares)	3,402,608	2,434,732	2,596,480
Exercised (in shares)	(48,152)	(112,484)	(136,056)
Forfeited / Expired (in shares)	(334,293)	(285,853)	(2,777,539)
Ending Balance (in shares)	13,975,671	10,955,508	8,919,113
Vested during current period (in shares)	2,508,333
Vested and exercisable at period end (in shares)	8,919,741
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning Balance (in dollars per share)	$ 1.87	$ 1.78	$ 2.76
Granted (in dollars per share)	1.55	2.26	1.47
Exercised (in dollars per share)	1.40	1.57	1.50
Forfeited / Expired (in dollars per share)	2.71	2.62	4.76
Ending Balance (in dollars per share)	1.77	$ 1.87	$ 1.78
Vested during current period (in dollars per share)	1.88
Vested and exercisable at period end (in dollars per share)	$ 1.81

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summarizes Information Concerning Options Outstanding and Options Vested and Exercisable (Details)	12 Months Ended
	Dec. 31, 2019$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of options (in shares) | shares	13,975,671
Number of options (in shares) | shares	8,919,741
$1.01 – $1.55
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
Number of options (in shares) | shares	6,832,730
Weighted Average Remaining Contractual Life	7 years 11 months 29 days
Weighted average exercise price (in dollars per share)	$ 1.47
Number of options (in shares) | shares	3,223,605
Weighted Average Remaining Contractual Life	3 years 2 months 7 days
Weighted average exercise price (in dollars per share)	$ 1.42
$1.56 – $1.98
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)	$ 1.98
Number of options (in shares) | shares	2,685,058
Weighted Average Remaining Contractual Life	4 years 8 months 22 days
Weighted average exercise price (in dollars per share)	$ 1.72
Number of options (in shares) | shares	2,499,294
Weighted Average Remaining Contractual Life	4 years 1 month 10 days
Weighted average exercise price (in dollars per share)	$ 1.72
$2.06 – $3.84
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price lower range (in dollars per share)	2.06
Exercise price upper range (in dollars per share)	$ 3.84
Number of options (in shares) | shares	4,457,883
Weighted Average Remaining Contractual Life	7 years 2 months 26 days
Weighted average exercise price (in dollars per share)	$ 2.26
Number of options (in shares) | shares	3,196,842
Weighted Average Remaining Contractual Life	4 years 11 months 13 days
Weighted average exercise price (in dollars per share)	$ 2.26

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (in shares)	1,656,688	1,648,986	1,201,159
Granted (in shares)	1,350,150	787,968	1,054,720
Vested-common stock issued (in shares)	(938,311)	(741,424)	(571,118)
Forfeited / Expired (in shares)	(36,347)	(38,842)	(35,775)
Ending balance (in shares)	2,032,180	1,656,688	1,648,986
Vested/Issued cumulative at period end (in shares)	5,508,176
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning Balance (in dollars per share)	$ 1.93	$ 1.69	$ 1.92
Granted (in dollars per share)	1.55	2.31	1.46
Vested-common stock issued (in dollars per share)	1.87	1.81	1.75
Forfeited / Expired (in dollars per share)	1.69	1.74	1.82
Ending Balance (in dollars per share)	1.71	$ 1.93	$ 1.69
Vested/Issued cumulative at period end (in dollars per share)	$ 1.75

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Income tax paid	$ 0	$ 0	$ 0
U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	193,200,000
Research and development tax credit	12,800,000
Foreign
Income Taxes [Line Items]
Net operating loss carryforwards	24,200,000
State and City
Income Taxes [Line Items]
Net operating loss carryforwards	63,500,000
Subject To Annual Limitations | U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	56,600,000
Not Subject To Annual Limitations | U.S. Federal
Income Taxes [Line Items]
Net operating loss carryforwards	156,500,000
Research and development tax credit	12,800,000
Not Subject To Annual Limitations | State and City
Income Taxes [Line Items]
Net operating loss carryforwards	$ 63,300,000

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, 2019	Dec. 31, 2018
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	(2.30%)	(3.70%)
Valuation allowances	(25.90%)	(29.20%)
Research and development - U.S.	6.30%	11.00%
Effective tax rate for the year	0.00%	0.00%

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 48,182	$ 38,813
Research and development credit carryforwards	12,797	9,979
Compensation expense	1,156	1,552
Other	903	1,166
Total deferred tax assets	63,038	51,510
Valuation allowance for deferred tax assets	(63,038)	(51,510)
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, 2019	Dec. 31, 2018	Dec. 31, 2017
Postemployment Benefits [Abstract]
Employer contribution for profit sharing plan	$ 0.4	$ 0.5	$ 0.3

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Right-of-use assets	$ 700
Lease liabilities	$ 686
Weighted average remaining lease term	1 year 7 months 5 days
Weighted average discount rate (percent)	5.30%
Payment for operating leases	$ 500
Minimum
Lessee, Lease, Description [Line Items]
Lease term	15 months
Maximum
Lessee, Lease, Description [Line Items]
Lease term	50 months
ASU 2016-02
Lessee, Lease, Description [Line Items]
Right-of-use assets		$ 1,000
Lease liabilities		$ 1,000

Leases - Components of Lease Co

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

Leases - Future Minimum Lease P

Leases - Future Minimum Lease Payments for Operating Leases (Details) $ in Thousands	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 489
2021	198
2022	15
2023	12
2024	2
Total minimum lease payments	716
Less: amount of lease payments representing interest	30
Present value of operating lease liabilities	$ 686

Quarterly Financial Data (una_3

Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 287	$ (361)	$ 4,262	$ 1,445	$ 1,513	$ 2,321	$ 19,391	$ 1,066	$ 5,633	$ 24,291	$ 3,708
Income (loss) from operations	(9,985)	(12,342)	(9,901)	(13,260)	(11,552)	(9,976)	6,745	(10,262)	(45,488)	(25,045)	(33,283)
Net income (loss)	$ (9,923)	$ (12,015)	$ (9,688)	$ (12,956)	$ (11,321)	$ (9,740)	$ 6,933	$ (10,155)	$ (44,582)	$ (24,283)	$ (32,241)
Basic and diluted net loss per common share (in dollars per share)	$ (0.06)	$ (0.08)	$ (0.06)	$ (0.09)	$ (0.08)	$ (0.07)	$ 0.05	$ (0.08)	$ (0.29)	$ (0.18)	$ (0.29)

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 51,510	$ 44,829	$ 55,148
Additions	11,528	6,681	0
Deductions	0	0	(10,319)
Balance at End of Year	63,038	51,510	44,829
Allowance for doubtful accounts-note receivable
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year		0	376
Additions			0
Deductions			(376)
Balance at End of Year			0
Tax valuation allowances
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	51,510	44,829	54,772
Additions	11,528	6,681	0
Deductions	0	0	(9,943)
Balance at End of Year	$ 63,038	$ 51,510	$ 44,829