Ocugen (OCGN) 10-K 22 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Mar. 20, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	HSGX
Entity Registrant Name	Histogenics Corporation
Entity Central Index Key	0001372299
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	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		94,599,601
Entity Public Float			$ 63.6

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 15,542	$ 7,081
Marketable securities		900
Prepaid expenses and other current assets	858	194
Total current assets	16,400	8,175
Property and equipment, net	141	2,723
Other assets	750
Restricted cash	137	137
Total assets	17,428	11,035
Current liabilities:
Accounts payable	1,590	776
Accrued expenses	1,000	2,705
Current portion of deferred rent	45	35
Current portion of deferred lease incentive	238	111
Current portion of equipment loan		178
Total current liabilities	2,873	3,805
Accrued expenses due to Intrexon Corporation	1,125	3,040
Deferred revenue	10,000
Deferred rent	351	280
Deferred lease incentive	1,025	499
Warrant liability	2,512	14,679
Total liabilities	17,886	22,303
Commitments and contingencies (Note 7)
Convertible preferred stock and stockholders’ equity (deficit):
Convertible preferred stock, $0.01 par value; 30,000 shares authorized, 400.4910 and 4,605.6533 shares issued and outstanding at December 31, 2018 and 2017, respectively
Common stock, $0.01 par value; 100,000,000 shares authorized, 62,025,398 and 24,571,029 shares issued and outstanding at December 31, 2018 and 2017, respectively	513	159
Additional paid-in capital	215,859	196,760
Accumulated deficit	(216,830)	(208,187)
Total stockholders’ equity (deficit)	(458)	(11,268)
Total liabilities and stockholders’ equity (deficit)	$ 17,428	$ 11,035

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Convertible preferred stock, shares authorized	30,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	62,025,398	24,571,029
Common stock, shares outstanding	62,025,398	24,571,029
Series A Convertible Preferred Stock [Member]
Convertible preferred stock, par value	$ 0.01	$ 0.01
Convertible preferred stock, shares authorized	30,000	30,000
Convertible preferred stock, shares issued	400.4910	4,605.6533
Convertible preferred stock, shares outstanding	400.4910	4,605.6533

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Revenue	$ 0	$ 0
Operating expenses:
Research and development	15,634	15,566
General and administrative	10,204	9,384
Loss due to asset impairment	4,270
Total operating expenses	30,108	24,950
Loss from operations	(30,108)	(24,950)
Other income (expense):
Interest income (expense), net	163	134
Other income (expense), net	(106)	(116)
Gain due to extinguishment of liability	1,540
Warrant expense	(733)
Change in fair value of warrant liability	20,601	(1,482)
Total other income (expense), net	21,465	(1,464)
Net loss	(8,643)	(26,414)
Loss attributable to common stockholders—basic	(8,522)	(22,499)
Loss attributable to common stockholders—diluted	$ (29,123)	$ (22,499)
Loss per common share—basic	$ (0.23)	$ (0.99)
Loss per common share—diluted	$ (0.79)	$ (0.99)
Weighted-average shares used to compute loss per common share—basic	36,398,450	22,669,819
Weighted-average shares used to compute loss per common share—diluted	37,090,197	22,669,819

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Restricted Stock [Member]
Beginning Balance at Dec. 31, 2016	$ 13,567		$ 159	$ 195,181	$ (181,773)
Beginning Balance, Shares at Dec. 31, 2016		13,416
Beginning Balance, Shares at Dec. 31, 2016			20,645,723			1,889
Stock-based compensation expense	1,573			1,573
Exercise of common stock options	6			6
Exercise of common stock options, Shares			7,497
Vesting of restricted stock, Shares			1,889			(1,889)
Conversion of Series A convertible preferred stock, Shares		(8,811)	3,915,920
Net loss	(26,414)				(26,414)
Ending Balance at Dec. 31, 2017	(11,268)		$ 159	196,760	(208,187)
Ending Balance, Shares at Dec. 31, 2017		4,605
Ending Balance, Shares at Dec. 31, 2017			24,571,029
Stock-based compensation expense	1,625			1,625
Exercise of common stock options	$ 2			2
Exercise of common stock options, Shares	919		919
Exercise of warrants	$ 1			1
Exercise of warrants, Shares			104,092
Issuance of common stock, net	17,825		$ 354	17,471
Issuance of common stock net, shares			35,480,397
Conversion of Series A convertible preferred stock, Shares		(4,205)	1,868,961
Net loss	(8,643)				(8,643)
Ending Balance at Dec. 31, 2018	$ (458)		$ 513	$ 215,859	$ (216,830)
Ending Balance, Shares at Dec. 31, 2018		400
Ending Balance, Shares at Dec. 31, 2018			62,025,398

Consolidated Statements of Co_2

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Common stock, par value	$ 0.01	$ 0.01
Restricted Stock [Member]
Common stock, par value	0.01	0.01
Common Stock [Member]
Common stock, par value	0.01	0.01
Series A Convertible Preferred Stock [Member]
Temporary equity, par value	$ 0.01	$ 0.01

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (8,643)	$ (26,414)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	450	1,534
Amortization of discount of investments		54
Deferred revenue	10,000
Deferred rent and lease incentive	734	(543)
Stock-based compensation	1,625	1,573
Warrant expense	733
Change in warrant liability	(20,601)	1,482
Loss due to asset impairment	4,270
Gain on extinguishment of liability due to Intrexon Corporation	(1,540)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(664)	(21)
Other long term assets	(750)
Accounts payable	689	(849)
Accounts payable due to Intrexon Corporation		(360)
Accrued expenses due to Intrexon Corporation	(375)
Accrued expenses	(1,705)	524
Net cash used in operating activities	(15,777)	(23,020)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(2,013)	(276)
Proceeds from maturities of marketable securities	900	7,050
Purchases of marketable securities		(8,004)
Net cash used in investing activities	(1,113)	(1,230)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of issuance costs	25,526
Repayments on equipment term loan	(178)	(583)
Proceeds from exercise of stock options and warrants	3	6
Net cash provided by (used in) financing activities	25,351	(577)
Net increase (decrease) in cash and cash equivalents	8,461	(24,827)
Cash and cash equivalents and restricted cash —Beginning of period	7,218	32,045
Cash and cash equivalents and restricted cash —End of period	15,679	7,218
Supplemental Disclosure of Non-Cash Items:
Purchases of property and equipment in accounts payable	125
Public offering costs in accounts payable	99
Supplemental Disclosure of Cash Flow information:
Cash paid for taxes	105	197
Cash paid for interest	$ 1	$ 30

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business	1. NATURE OF BUSINESS Organization Histogenics Corporation (the “Company”) was incorporated under the laws of the Commonwealth of Massachusetts on June 28, 2000 and has its principal operations in Waltham, Massachusetts. In 2006, the Company’s board of directors approved a corporate reorganization pursuant to which the Company incorporated as a Delaware corporation. The Company historically focused on the development of restorative cell therapies (RCTs). RCTs refer to a new class of products that are designed to offer patients rapid-onset pain relief and restored function through the repair of damaged or worn tissue. The Company’s lead product, NeoCart ® On May 13, 2011, the Company completed the acquisition of ProChon Biotech Ltd. (“ProChon”), a privately-held biotechnology company focused on modulating the fibroblast growth factor system for consideration of $2.2 million to enable it to create more effective solutions for tissue regeneration. ProChon’s products combine cell regeneration technologies with proprietary growth factors and biocompatible scaffolds to restore injured or chronically damaged tissues. The acquisition led to the initial recognition of goodwill, which was subsequently written off in 2011, and intangible assets including IPR&D and a licensing agreement which were fully impaired in 2016 as discussed in Note 2. On September 29, 2016, the Company closed a private placement of common stock, preferred stock and warrants, contemplated by a securities purchase agreement dated September 15, 2016, with certain institutional and accredited investors. The net proceeds after deducting placement agent fees and other transaction-related expenses were $27.6 million. See Note 8, Capital Stock, for further discussion of the private placement. In January 2018, the Company closed a registered direct offering where the Company issued 2,691,494 shares of In March 2018, the Company entered into an equity distribution agreement (“ATM Agreement”) with Canaccord Genuity Inc. (“Canaccord”), pursuant to which the Company may, from time to time, sell shares of its common stock having an aggregate offering price of up to $10.0 million (the “Shares”) through Canaccord, as sales agent. During the year ended December 31, 2018, the Company sold an aggregate of 6,633,903 shares of common stock and received $4.5 million after deducting commissions related to the ATM Agreement and other offering costs. In October 2018, the Company closed an underwritten public offering of 26,155,000 shares of its common stock and warrants to purchase up to 19,616,250 shares of common stock, at a combined purchase price of $0.65 per share of common stock and accompanying warrant. The gross proceeds to Histogenics from this offering were $17.0 million, before deducting underwriting discounts and commissions, and offering expenses payable by the Company. The warrants are exercisable immediately upon issuance at a price of $0.70 per share of common stock and have a term of five years commencing on the date of issuance. Since its inception, the Company has devoted substantially all of its efforts to product development, recruiting management and technical staff, raising capital, starting up production and building infrastructure and has not yet generated product revenues. Expenses have primarily been for research and development and related administrative costs. The Company is subject to a number of risks including the successful development of therapeutics, the ability to obtain adequate financing, the ability to obtain FDA approval and reimbursement for any products we may develop, protection of intellectual property, fluctuations in operating results, dependence on key personnel and collaborative partners, rapid technological changes inherent in the target markets of any products the Company may develop, the introduction of substitute products and competition from larger companies. Liquidity The consolidated financial statements have been prepared on a going-concern basis, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. As shown in the accompanying consolidated financial statements, the Company has incurred losses and cash flow deficits from operations since inception, resulting in an accumulated deficit at December 31, 2018 of $216.8 million. The Company has financed operations to date primarily through public and private placements of equity securities, and borrowings under debt agreements. The Company anticipates that it will continue to incur net losses for the foreseeable future. The Company believes that its existing cash, cash equivalents and marketable securities will only be sufficient to fund its projected cash needs into the middle of 2019. Accordingly, these factors, among others, raise substantial doubt about the Company’s ability to continue as a going concern. To meet future capital needs, the Company would need to raise additional capital through debt or equity financing or other strategic transactions. The failure of the Company to obtain sufficient funds on commercially acceptable terms when needed will have a material adverse effect on the Company’s business, results of operations and financial condition. The forecast of cash resources is forward-looking information that involves risks and uncertainties, and the actual amount of our expenses could vary materially and adversely as a result of a number of factors. The Company has based its estimates on assumptions that may prove to be wrong, and the Company’s expenses could prove to be significantly higher than it currently anticipates.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Accounting The consolidated financial statements are prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The consolidated financial statements include the accounts of Histogenics Corporation and its wholly-owned subsidiaries, ProChon and Histogenics Securities Corporation. All significant intercompany accounts and transactions are eliminated in consolidation. Use of Estimates The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the valuation of equity awards, warrant liability, recoverability of deferred tax assets, estimated useful lives of fixed assets. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions on an ongoing basis. The Company recorded in 2018 a loss on impairment of fixed assets. See Note 5 Property and Equipment. The Company’s actual results may differ from these estimates under different assumptions or conditions. Foreign Currency Translation The Company’s consolidated financial statements are prepared in U.S. dollars. The Company’s foreign subsidiary uses the U.S. dollar as its functional and reporting currency, as management determined that the U.S. dollar is the primary currency of the economic environment in which the subsidiary operates. When transactions are required to be paid in the local currency of the foreign subsidiary, any resulting foreign currency transaction gain or loss is recorded as a component of “Other income (expense), net” in the consolidated statements of operations. Segment and Geographic Information Operating segments are defined as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker (“CODM”) or decision-making group in making decisions regarding resource allocation and assessing performance. The Company operates in two geographic regions: the United States (Massachusetts) and Israel (Tel Aviv) and views its operations as two operating segments: Histogenics Corporation (United States) and ProChon (Israel) as the CODM reviews separate discrete financial information in making decisions regarding resource allocations and assessing performance. Operating segments that have similar economic characteristics can be aggregated. As the nature of the products, customers, and methods to distribute products are the same and the nature of the regulatory environment, the production processes and historical and estimated future margins are similar, the two operating segments have been aggregated into one reporting segment as they have similar economic characteristics. Fair Value Measurements The carrying amounts reported in the Company’s consolidated financial statements for cash and cash equivalents, accounts payable, equipment loan, and accrued liabilities approximate their respective fair values because of the short-term nature of these accounts. Fair value is defined as the price that would be received if selling an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Fair value should be based on the assumptions that market participants would use when pricing an asset or liability and is based on a fair value hierarchy that prioritizes the information used to develop those assumptions. Fair value measurements should be disclosed separately by level within the fair value hierarchy. For assets and liabilities recorded at fair value, it is the Company’s policy to maximize the use of observable inputs (quoted prices in active markets) and minimize the use of unobservable inputs (Company assumptions) when developing fair value measurements, in accordance with established fair value hierarchy. Fair value measurements for assets and liabilities where there exists limited or no observable market data are based primarily upon estimates, and often are calculated based on the economic and competitive environment, the characteristics of the asset or liability and other factors. Therefore, the results cannot be determined with precision and may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there may be inherent weaknesses in any valuation technique, and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the results of current or future values. Additionally, from time to time, the Company may be required to record at fair value other assets on a nonrecurring basis, such as assets held for sale and certain other assets. These nonrecurring fair value adjustments typically involve application of lower-of-cost-or-market accounting or write-downs of individual assets. The fair value hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets (Level 1), and the lowest priority to unobservable inputs (Level 3). The Company’s financial assets are classified within the fair value hierarchy based on the lowest level of inputs that is significant to the fair value measurement. The three levels of the fair value hierarchy, and its applicability to the Company’s financial assets, are described below. Level 1 : Unadjusted quoted prices in active markets that are accessible at the measurement date of identical, unrestricted assets. Level 2 : Quoted prices for similar assets, or inputs that are observable, either directly or indirectly, for substantially the full term through corroboration with observable market data. Level 2 includes investments valued at quoted prices adjusted for legal or contractual restrictions specific to the security. Level 3 : Pricing inputs are unobservable for the assets, that is, inputs that reflect the reporting entity’s own assumptions about the assumptions market participants would use in pricing the assets. Level 3 includes private investments that are supported by little or no market activity. Level 3 valuations are for instruments that are not traded in active markets or are subject to transfer restrictions and may be adjusted to reflect illiquidity and/or non-transferability, with such adjustment generally based on available market evidence. In the absence of such evidence, management’s best estimate is used. An adjustment to the pricing method used within either Level 1 or Level 2 inputs could generate a fair value measurement that effectively falls in a lower level in the hierarchy. The Company had no assets or liabilities classified as Level 1 or Level 2 as of December 31, 2018 and 2017 other than the money market fund described in the “Cash and Cash Equivalents” section and the asset-backed securities in the “Marketable securities” section below. There were no material re-measurements of fair value with respect to financial assets and liabilities, during the periods presented, other than those assets and liabilities that are measured at fair value on a recurring basis. The Company’s only assets or liabilities classified as level 3 are the warrants issued in connection with the September 2016 private placement and the October 2018 underwritten public offering. The fair value of the warrants issued in connection with the September 2016 private placement was determined using a Monte Carlo simulation model. This model incorporated several assumptions at each valuation date including: the price of the Company’s common stock on the date of valuation, the historical volatility of the price of the Company’s common stock, the remaining contractual term of the warrant and estimates of the probability of a fundamental transaction occurring. The fair value of the warrants issued in connection with the October 2018 underwritten public offering was determined using the Black Scholes model. See Note 8, Capital Stock, for further discussion of the private placement and underwritten public offering. Description Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (in thousands) December 31, 2018 Assets: Cash Equivalents Money market funds 9,711 9,711 — — Liabilities: Warrant liability 2,512 — — 2,512 December 31, 2017 Assets: Cash Equivalents Money market funds 5,547 5,547 — — Marketable securities: Asset-backed securities 900 — 900 — Liabilities: Warrant liability 14,679 — — 14,679 The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs: As of December 31, 2018 (in thousands) Beginning balance, January 1, 2018 $ 14,679 Issuance of warrants 8,434 Change in fair value of warrant liability (20,601 ) Ending balance $ 2,512 Cash and Cash Equivalents Cash and cash equivalents include cash in readily available checking and savings accounts and money market funds. The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents. Marketable Securities The Company classifies marketable securities with a remaining maturity when purchased of greater than three months as available for sale. The Company considers all available for sale securities, including those with maturity dates beyond 12 months, as available to support current operational liquidity needs and therefore classifies all securities including those with maturity dates beyond 90 days at the date of purchase as current assets within the consolidated balance sheets. Available for sale securities are maintained by the Company’s investment managers and may consist of commercial paper, high-grade corporate notes, U.S. Treasury securities, U.S. government agency securities, and certificates of deposit. Available for sale securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity (deficit) until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the instrument. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary” and, if so, marks the investment to market through a charge to the Company’s consolidated statement of operations and comprehensive loss. The Company did not hold any available for sale securities prior to the first quarter of 2017. The amortized cost of available for sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. At December 31, 2018, the balance in the Company’s accumulated other comprehensive loss was composed solely of activity related to the Company’s available for sale marketable securities. The aggregate fair value of available for sale securities held by the Company for less than twelve months as of December 31, 2017 was $0.9 million which matured in 2018. The Company did not hold any available for sale securities and there were no sales of such during the year ended December 31, 2018. The Company determined that there was no material change in the credit risk of any of its investments. As a result, the Company determined it did not hold any investments with any other-than-temporary impairment as of December 31, 2017. The weighted average maturity of the Company’s portfolio was less than one month at December 31, 2017. Concentration of Credit Risk Financial instruments, which potentially subject the Company to significant concentration of credit risk, consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. The Company has no financial instruments with off-balance sheet risk of loss. Property and Equipment Property and equipment are recorded at historical cost. Costs for capital assets not yet placed into service are capitalized as construction in progress, and are depreciated in accordance with the below guidelines once placed into service. Maintenance and repair costs are expensed as incurred. Costs which materially improve or extend the lives of existing assets are capitalized. The Company provides for depreciation and amortization using the straight-line method over the estimated useful lives of the assets, which are as follows: Asset Category Estimated Useful Lives Office equipment 3 to 5 years Laboratory equipment 3 to 5 years Leasehold improvements Shorter of the remaining lease term or useful life Upon retirement or sale, the cost of assets disposed and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recorded in the consolidated statements of operations. Impairment of Long-Lived Assets Long-lived assets consist primarily of property and equipment and identifiable intangible assets. When impairment indicators exist, the Company’s management evaluates long-lived assets for potential impairment. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. In 2018 a triggering event caused an impairment of the Company’s property and equipment. The triggering event related to the Company’s announcement that the NeoCart program was discontinued and the subsequent 73% reduction in stock price. An impairment loss of $4.3 million was recognized in earnings. See Note 5 Property and Equipment. Restricted Cash Restricted cash represents cash held in a depository account at a financial institution to collateralize a conditional stand-by letter of credit related to the Company’s Lexington, Massachusetts facility lease agreement. Restricted cash is reported as non-current unless the restrictions are expected to be released in the next twelve months. Deferred Rent Deferred rent consists of the difference between cash payments and the recognition of rent expense on a straight-line basis for the facilities the Company occupies. The Company’s leases for its Waltham, Massachusetts and Lexington, Massachusetts facilities provide for fixed increases in minimum annual rental payments. The total amount of rental payments due over each lease term is being charged to rent expense ratably over the life of each lease, respectively. Financial Instruments Indexed to and Potentially Settled in the Company’s Common Stock The Company evaluates all financial instruments issued in connection with its equity offerings when determining the proper accounting treatment for such instruments in the Company’s financial statements. The Company considers a number of generally accepted accounting principles under U.S. GAAP to determine such treatment and evaluates the features of the instrument to determine the appropriate accounting treatment. The Company utilizes the Probability Weighted Expected Return Method (“PWERM”), Option Pricing Model (“OM”) or other appropriate methods to determine the fair value of its derivative financial instruments, such as the warrant liability. For financial instruments indexed to and potentially settled in the Company’s common stock that are determined to be classified as liabilities on the consolidated balance sheet, changes in fair value are recorded as a gain or loss in the Company’s consolidated statement of operations with the corresponding amount recorded as an adjustment to the liability on its consolidated balance sheet. Revenue Recognition In May 2014, the Financial Accounting Standards Board (the “FASB”) issued a new standard related to revenue recognition, Accounting Standard Update Revenue is recognized when, or as, performance obligations are satisfied, which occurs when control of the promised products or services is transferred to customers. Revenue is measured as the amount of consideration the Company expects to receive in exchange for transferring products or services to a customer (“transaction price”). To the extent that the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing the most likely amount method. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Estimates of variable consideration and determination of whether to include estimated amounts in the transaction price are based largely on an assessment of the Company’s anticipated performance and all information (historical, current and forecasted) that is reasonably available. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation based on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The Company’s revenues are generated primarily through collaborative research, development and commercialization agreements. The terms of these agreements may contain multiple promises which may include: (i) licenses to the Company’s technology; (ii) services related to the transfer and update of know-how; and (iii) manufacturing supply services. Payments to the Company under these arrangements typically include one or more of the following: non-refundable upfront license fees; milestone payments; royalties on future product sales; and fees for manufacturing supply services. None of the Company's contracts as of December 31, 2018 contained a significant financing component. The Company assesses the promises to determine if they are distinct performance obligations. Once the performance obligations are determined, the transaction price is allocated based on a relative standalone selling price basis. Milestone payments and royalties are typically considered variable consideration at the outset of the contract and are recognized in the transaction price either upon occurrence or when the constraint of a probable reversal is no longer applicable. Collaboration Revenue While no revenue has been recognized as of December 31, 2018, the Company has collaboration and license agreements with strategic partners for the development and commercialization of product candidates. The collaboration and license agreements are within the scope of Accounting Standards Codification (ASC 606) Revenue from Contracts with Customers. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under the agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for the arrangement, the Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include market conditions, reimbursement rates for personnel costs, development timelines and probabilities of regulatory success. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Manufacturing Supply Services: If the promise to supply products for clinical and/or commercial development are determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from the fees allocated to the supply when or as the supply is transferred to the customer, generally upon delivery to the customer. If the promise to supply products for clinical and/or commercial development are not determined to be distinct from the other performance obligations identified in the arrangement, the Company utilizes judgement to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue, including amounts from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service and revenue is recognized in the period in which the milestone is achieved. If the milestone payment is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the Company evaluates the milestone to determine whether the milestone is considered probable of being reached and estimates the amount to be included in the transaction price using either the most likely amount or the expected value method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall allocation. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration and other revenues and earnings in the period of adjustment. Royalties: For arrangements that include sales-based or usage-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of: (i) when the related sales occur; or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). License and Collaboration Arrangements MEDINET Co., Ltd. In December 2017 the Company entered into the License and Commercialization Agreement (the “License Agreement”) with MEDINET Co., Ltd. (“MEDINET”) to grant MEDINET a license under certain patents, patent applications, know-how, and technology to develop and commercialize certain therapeutic products to replace or repair damaged, worn, or defective cartilage. In exchange for the license, MEDINET agreed to pay the Company an non-refundable upfront cash payment of $10.0 million which was received in January 2018. As of December 31, 2018, the contract with MEDINET was wholly unperformed. MEDINET also agreed to pay the Company tiered royalties, at percentages ranging from the low single digits to low double digits, of net sales of MEDINET products governed by the License Agreement. The Company is eligible to receive up to ¥330 million ($3.0 million as of December 31, 2018) in development milestone payments, $1.0 million and ¥720 million ($6.5 million as of December 31, 2018) in regulatory payments and up to an aggregate of ¥7,100 million ($64.3 million as of December 31, 2018) for the achievement of certain commercial milestones related to the sales of MEDINET products governed by the License Agreement. The Company assessed the promised goods and services to determine if they are distinct. Due to the unique nature of the clinical manufacturing services, there are no third-party vendors from which MEDINET can obtain such services from currently. The Company expects to be the only vendor capable of providing the commercial manufacturing services for a period of at least one to two years, which is approximately the estimated length of the clinical trial period in Japan. After this point, if the Company were to transfer to a third-party its technology and know-how related to the commercial manufacturing services that third-party vendor would be capable of providing the commercial manufacturing services, and therefore MEDINET would be able to choose whether to utilize the Company or another vendor for such services. The Company determined that the option to obtain to commercial manufacturing services does not represent a material right, as the fees charged to MEDINET by the Company are expected to approximate the fair market value for manufacturing services. As noted, with the assistance of the Company, third-party vendors could have the capability to perform such services by this time, and the Company expects the contract value to approximate the market price. Due to MEDINET’s limitations in obtaining the clinical manufacturing services from a third-party, as well as MEDINET’s limited ability to obtain the benefits of the licensed intellectual property without the clinical manufacturing services, the licensed intellectual property and clinical manufacturing services are determined to be a combined performance obligation. Based on this assessment, the Company determined that the promised goods and services do not have standalone value and are highly interrelated. Accordingly, the promised goods and services represent one performance obligation. Based on the assessment of the combined performance obligation, the Company determined that the predominant promise in the arrangement is the transfer of the license and associated knowhow which are expected to occur over the length of the clinical trial. The Company determined that MEDINET will be simultaneously receiving and consuming the benefits of the Company’s performance of the clinical trial. Therefore, the revenue associated with the combined performance obligation will be recognized over time. In determining the correct measure of progress to use when recognizing revenue over time, the Company assessed whether an input or output based measure of progress would be appropriate. The Company determined that an output based measure of progress would be appropriate to use when recognizing revenue associated with the combined performance obligation. The Company will recognize revenue based on the clinical manufacturing services completed to date. At the outset of the clinical trial in Japan to be conducted by MEDINET, the Company will have quantifiable estimates of total clinical candidates, and therefore, of total estimated performance. The Company will recognize revenue based on performance completed to date, as evidenced by the estimated number of clinical trial enrollees. The Company expects to provide the clinical manufacturing services to MEDINET over an estimated period of two years. Therefore, the estimated two-year clinical manufacturing period is the appropriate timing of revenue recognition for the combined performance obligation. Revenue will be recognized using the output method, as the clinical manufacturing services are delivered, over the estimated two-year year proportional performance service period. Upon the conclusion of the clinical manufacturing period, the Company expects other third-party vendors to have the capabilities to provide similar services. At this point, the license would effectively become a distinct performance obligation, with no remaining undelivered obligations. Therefore, the Company determined that the up-front payment associated with the licensed intellectual property should be fully recognized by the conclusion of the clinical manufacturing service period. Upon conclusion of the clinical manufacturing service period, the Company will have no remaining performance obligations, and MEDINET will be able to obtain commercial manufacturing services from other vendors. At contract inception, the Company determined that the $10.0 million non-refundable upfront amount constituted the entirety of the consideration to be included in the transaction price as the development, regulatory, and commercial milestones represent variable consideration and were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensees’ efforts. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. The Company also determined that consideration associated with the clinical trials, which are payable by MEDINET on per-patient basis represent variable consideration, will be included in the transaction price upon occurrence, or once the associated clinical manufacturing service(s) for the patient are concluded. The upfront transaction price of $10.0 million will be recognized over a period of approximately two-years, commencing at the start of the clinical trial which, in management’s judgement represents the Company’s best estimate of the period of performance for satisfying the performance obligation of supply of clinical trial materials and transfer of license to MEDINET. Management has included $10.0 as non-current based on the feedback from the FDA and subsequent suspension of the NeoCart program. MEDINET relies on Company’s NeoCart product to supply clinical trial patients. MEDINET has suspended development of its clinical trial. Management will reevaluate that estimate at each reporting period. Revenue is being recognized using the output method, as the clinical manufacturing services are delivered, over the estimated two year proportional performance clinical manufacturing period. Transaction Price Allocated to Future Performance Obligations Remaining performance obligations represents the transaction price

Loss Per Common Share

Loss Per Common Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Loss Per Common Share	3. LOSS PER COMMON SHARE Basic and diluted loss per common share are calculated as follows: For the Year Ended 2018 2017 (In thousands, except share and per share data) Numerator: Net loss $ (8,643 ) $ (26,414 ) Net Loss attributable to Series A Preferred Stock (a) (121 ) (3,915 ) Numerator for basic EPS - loss attributable to common stockholders $ (8,522 ) $ (22,499 ) Effect of dilutive securities: Deduct change in fair value of warrant liability $ (20,601 ) $ — Numerator for diluted EPS - loss attributable to common stockholders after assumed conversions $ (29,123 ) $ (22,499 ) Denominator: Weighted-average number of common shares used in loss per share—basic 36,398,450 22,669,819 Effect of dilutive securities: Nonparticipating warrants 691,747 — Denominator for diluted EPS - adjusted weighted average shares 37,090,197 22,669,819 Loss per share—basic $ (0.23 ) $ (0.99 ) Loss per share—diluted $ (0.79 ) $ (0.99 ) (a) The Series A Preferred Stock participates in income and losses The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares outstanding, as they would be anti-dilutive (in common stock equivalent shares): As of December 31, 2018 2017 Unvested restricted stock and options to purchase common stock 3,339,471 2,158,348 Series A preferred stock unconverted 177,996 2,046,957 Warrants exercisable into common stock — 13,633,070

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	4. PREPAID EXPENSES AND OTHER CURRENT ASSETS Prepaid expenses and other current assets consisted of the following: As of December 31, 2018 2017 (in thousands) Insurance 686 72 Other current assets 172 122 Prepaid expenses and other current assets $ 858 $ 194

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Property and Equipment	5. PROPERTY AND EQUIPMENT Property and equipment consisted of the following: December 31, December 31, 2018 2017 (in thousands) Office equipment $ 266 $ 279 Laboratory equipment 4,561 4,565 Leasehold improvements 5,504 7,712 Construction in progress — 990 Software 96 96 Total property and equipment 10,427 13,642 Less: accumulated depreciation (10,286 ) (10,919 ) Property and equipment, net $ 141 $ 2,723 Depreciation expense related to property and equipment amounted to $0.5 million and $1.5 million for the years ended December 31, 2018 and 2017, respectively. For year ended December 31, 2018 the company deemed the value of its property and equipment to be impaired based on the triggering event that occurred in December 2018. In connection with the impairment, the Company reduced the net book value of its property and equipment to an estimated fair value which was calculated based on the present value of expected future cash flows from these assets. As a result, the Company incurred a charge of $4.3 million that was recorded in the Statement of Operations.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued Expenses	6. ACCRUED EXPENSES Accrued expenses consisted of the following: As of December 31, 2018 2017 (in thousands) Accrued compensation $ 514 $ 1,671 Accrued audit fees 159 133 Accrued license fees 90 70 Accrued clinical expenses 86 199 Accrued other 151 632 Total accrued expenses $ 1,000 $ 2,705

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. COMMITMENTS AND CONTINGENCIES Operating Leases The Company leases its office and research facilities in Waltham and Lexington, Massachusetts under non-cancellable operating leases. The Lexington, Massachusetts facility lease expires in June 2023. The lease provided for one extension term of five years. The Waltham, Massachusetts facility lease was extended in April 2017 with an effective date of January 2018. Under the terms of the extension, the lease will expire in December 2024 with one additional extension term of five years. Terms of the agreements generally provide for an initial rent-free period and future rent escalation, and provide that in addition to minimum lease rental payments, the Company is responsible for a pro-rata share of common area operating expenses. Aggregate minimum annual lease commitments of the Company under its non-cancellable operating leases as of December 31, 2018, are as follows: For the Year Ended December 31, (in thousands) 2019 $ 1,845 2020 1,892 2021 1,941 2022 1,991 2023 1,728 Thereafter 1,460 Total minimum lease payments $ 10,857 Rent expense under operating lease agreements amounted to $1.6 million and $1.0 million for the years ended December 31, 2018 and 2017, respectively. As an inducement to enter into the Waltham facility lease extension, the lessor agreed to provide the Company with a construction allowance of up to $0.9 million towards the total cost of tenant improvements. As an inducement to enter into its Lexington facility lease, the lessor agreed to provide the Company with a construction allowance of up to $1.0 million towards the total cost of tenant improvements. The Company has recorded these costs in the consolidated balance sheet as leasehold improvements, with the corresponding liability as deferred lease incentive. These liabilities are amortized on a straight-line basis over the term of the lease as a reduction of rent expense. License Agreements From time to time, the Company enters into various licensing agreements whereby the Company may use certain technologies in conjunction with its product research and development. Licensing agreements and the Company’s commitments under the agreements are as follows: Hydrogel License In May 2005, the Company entered into an exclusive license agreement with Angiotech Pharmaceuticals (US), Inc. for the use of certain patents, patent applications, and knowledge related to the manufacture and use of a hydrogel material in conjunction with NeoCart and certain other products (“Hydrogel License Agreement”). As of December 31, 2018, the Company has paid an aggregate $3.2 million in commercialization milestones under the terms of the Hydrogel License Agreement, which has been expensed to research and development. Under the terms of the Hydrogel License Agreement, the Company’s future commitments include: • A one-time $3.0 million payment upon approval of an eligible product by the FDA; and • Single digit royalties on the net sales of NeoCart and certain other future products. Tissue Regeneration License In April 2001, the Company entered into an exclusive license agreement with The Board of Trustees of the Leland Stanford Junior University (“Stanford University”) for the use of certain technology to develop, manufacture and sell licensed products in the field of growth and regeneration of cartilage (“Tissue Regeneration License Agreement”). The term of the Tissue Regeneration License Agreement extends to the expiration date of Stanford University’s last to expire domestic or foreign patents. As of December 31, 2018, the Company has paid an aggregate $0.8 million in patent reimbursement costs, royalty fees, and commercialization milestone payments under the terms of the Tissue Regeneration License Agreement, which have been recorded to research and development expense. Under the terms of the Tissue Regeneration License Agreement, the Company’s future commitments include: • A one-time $0.3 million payment upon approval of an eligible product by the FDA; • An annual minimum non-refundable royalty fee of $10 thousand for the life of the license that may be used to offset up to 50% of each earned royalty described below; and • Low single digit royalties on net sales. Tissue Processor Sub-License In December 2005, the Company entered into an exclusive agreement to sub-license certain technology from Purpose, Co. (“Purpose”), which is owned by a stockholder of the Company (“Sub-License Agreement”). Purpose entered into the original license agreement (“Original Agreement”) with Brigham and Women’s Hospital, Inc. (“Brigham and Women’s”) in August 2001. The Original Agreement shall remain in effect for the licensed patents owned by Brigham and Women’s unless extended or terminated as provided for in the agreement. The technology is to be used to develop, manufacture, use and sell licensed products that cultivate cell or tissue development. The Sub-License Agreement extends to the expiration date of the last to expire domestic or foreign patents covered by the agreement. As of December 31, 2018, the Company has paid an aggregate $1.0 million in royalty and sub-license payments under the terms of the Sub-License Agreement. The Sub-License Agreement was amended and restated in June 2012. Under the amended and restated agreement, the Company made Purpose the sole supplier of equipment the Company uses in its manufacturing processes, and granted Purpose distribution rights of the Company’s products for certain territories. In exchange, Purpose allowed for the use of its technology (owned or licensed) and manufactured and serviced exogenous tissue processors used by the Company. Under the terms of the agreement, as amended, Purpose granted the Company: (a) exclusive rights to all of Purpose’s technology (owned or licensed) related to the exogenous tissue processors, (b) continued supply of exogenous tissue processors during the Company’s clinical trials, and (c) rights to manufacture the exogenous tissue processors at any location the Company chooses. In exchange for such consideration, the Company granted Purpose an exclusive license in Japan for the use of all of the Company’s technology and made a payment of $0.3 million to reimburse Purpose for development costs on a next generation tissue processor. In May 2016, the Original Agreement was amended whereby the Company acquired the development and commercialization rights to NeoCart for the Japanese market from Purpose. Under the terms of the amended agreement, the Company assumes sole responsibility for and rights to the development and commercialization of NeoCart in Japan. In exchange for the transfer of development and commercialization rights, the Company will pay a success-based milestone to Purpose upon conditional approval of NeoCart in Japan, as well as commercial milestones and a low single digit royalty on Japanese sales of NeoCart, upon full approval, if any, in Japan In addition to the above, the Company’s future commitments under the terms of the Original Agreement and Sub-License Agreement include: • A minimum non-refundable annual royalty fee of $20 thousand, for the life of the license; • An additional, non-refundable annual royalty fee of $30 thousand from 2016 through 2019; • $10.2 million in potential milestone payments; and • Low single digit royalties on net sales of a licensed product. Collagen Supply Agreement In September 2015, the Company entered into an agreement with Collagen Solutions (UK) Limited (the “Supplier”) to purchase soluble collagen that meets specifications provided by the Company. The initial term of the agreement is three years and will automatically renew from year to year thereafter unless otherwise terminated with at least 180 days’ notice by either party.

Capital Stock

Capital Stock	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Capital Stock	8. CAPITAL STOCK . In October 2018, the Company closed a underwritten public offering of 26,155,000 shares of its common stock and warrants to purchase up to 19,616,250 shares of common stock, at a combined purchase price of $0.65 per share of common stock and accompanying warrant. The gross proceeds to Histogenics from this offering were $17.0 million, before deducting underwriting discounts and commissions, and offering expenses payable by the Company. The warrants are exercisable immediately upon issuance at a price of $0.70 per share of common stock and have a term of five years commencing on the date of issuance. The exercise price of the Warrants is subject to adjustment upon the occurrence of specific events, including stock dividends, stock splits, combinations and reclassifications of the Company’s Common Stock. In the event of certain fundamental transactions of the Company, a warrant holder may demand redemption of its warrant for cash in accordance with a Black-Scholes option pricing model. A fundamental transaction is defined as a merger, sale of assets, sale of the Company, recapitalization of stock and a sale of stock whereby any owner after the transaction would own greater than 50% of the outstanding common stock in the Company. The Company determined the warrants are classified as a liability on the consolidated balance sheet because of the provision whereby in a fundamental transaction (as described above), the holder can elect to receive either the amount they are entitled to on an as-if-exercised basis or an amount based on the Black-Scholes value of the warrants at the time of the fundamental transaction. At the issuance date, the warrants were recorded at the fair value of $8.4 million In March 2018, the Company entered into an equity distribution agreement (“the Equity Distribution Agreement”) with Canaccord Genuity Inc. (“Canaccord”), pursuant to which the Company may, from time to time, sell shares of its common stock having an aggregate offering price of up to $10.0 million (the “Shares”) through Canaccord, as sales agent. During the year ended December 31, 2018, the Company sold an aggregate of 6,633,903 shares of common stock and received $4.5 million after deducting commissions related to the Equity Distribution Agreement and other offering costs. In January 2018, the Company closed a registered direct offering where the Company issued 2,691,494 shares of In September 2016, the Company closed the private placement contemplated by the securities purchase agreement (the “Purchase Agreement”), dated September 15, 2016, between the Company and certain institutional and accredited investors in which the Company received gross proceeds of $30.0 million (the “Private Placement”). The net proceeds after deducting placement agent fees and other transaction-related expenses was $27.6 million. At the closing, the Company issued 2,596,059 shares of the Company’s common stock at a per share price of $2.25 and 24,158.8693 shares of the Company’s newly-created Series A Convertible Preferred Stock (“Series A Preferred Stock”), which are convertible into approximately 10,737,275 shares of common stock. As of December 31, 2018, there were 400.4910 shares of Series A Preferred Stock outstanding, which remain convertible into 177,996 shares of the Company’s common stock. As part of the Private Placement, the investors received warrants to purchase up to 13,333,334 shares of the Company’s common stock at an exercise price of $2.25 per share. The placement agent for the Private Placement, H.C. Wainwright & Co. LLC (“HCW”), and certain of its affiliates were also granted warrants to purchase 133,333 shares of the Company’s common stock at an exercise price of $2.25 per share in exchange for the services provided by HCW. The placement agent warrants were considered a financing cost of the Company and included in warrant expense within the consolidated statements of operations. The warrants include a cashless-exercise feature that may be exercised solely in the event there is no effective registration statement, or no current prospectus available for, the resale of the shares of common stock underlying the warrants as of the six-month anniversary of the closing of the Private Placement. Upon a fundamental transaction, the holders of the warrant may require the Company to purchase any unexercised warrants in an amount equal to the Black-Scholes value of the option. A fundamental transaction is defined as a merger, sale of assets, sale of the Company, recapitalization of stock and a sale of stock whereby any owner after the transaction would own greater than 50% of the outstanding common stock in the Company. The warrants became exercisable following approval of the Private Placement by our stockholders in the fourth quarter of 2016 and expire five years after the date of such stockholder approval. The Company determined the warrants are classified as a liability on the consolidated balance sheet because they contain a provision whereby in a fundamental transaction (as described above), the holder can elect to receive either the amount they are entitled to on an as-if-exercised basis or an amount based on the Black-Scholes value of the warrants at the time of the fundamental transaction. At the issuance date, the warrants were recorded at the fair value of $30.7 million. Concurrent with the closing of the Private Placement, the Company’s Certificate of Incorporation was amended by the filing of a Certificate of Designation to create the Series A Preferred Stock. The Series A Preferred Stock has a par value of $0.01 and each share is convertible into 444.44 shares of common stock, at a conversion price of $2.25 per share, at the option of the holder. The Series A Preferred Stock has no voting rights and is only entitled to dividends as declared on an as-converted basis. The Series A Preferred Stock contains no liquidation preferences or redemption rights and shares in distributions of the Company on an as-converted basis with the common stock. As part of the Private Placement, affiliates of certain members of the Company’s Board of Directors purchased an aggregate of 283,046 shares of common stock, an aggregate of 2,563.1439 shares of Series A Preferred Stock and received warrants to purchase up to 1,422,221 shares of common stock at an exercise price of $2.25 per share in the Private Placement. These amounts are included in the amounts noted above. Common Stock -100,000,000 shares authorized The holders of shares of common stock are entitled to one vote per share. The holders of shares of common stock are not entitled to receive dividends, unless declared by the Company’s board of directors out of legally available funds, if ever. Reserved for future issuance The Company has reserved for future issuance the following number of shares of common stock: As of December 31, 2018 2017 Options to purchase common stock 3,339,471 2,158,348 Common stock warrants 33,145,228 13,633,070 Total 36,484,699 15,791,418 Preferred Stock -30,000 shares authorized S eries A Convertible Preferred Stock On September 29, 2016, the Company issued 24,158.8693 shares of newly-created Series A Convertible Preferred Stock, which were convertible into approximately 10,737,275 shares of common stock at an initial conversion price of $2.25. The Series A Preferred Stock has a par value of $0.01 and each share is convertible into 444.44 shares of common stock at the option of the holder. The holders of Series A Preferred Stock have no voting rights, share in both income and losses and are only entitled to dividends as declared on an as-converted basis. The Series A Preferred Stock contains no liquidation preferences or redemption rights and shares in the distribution of the Company on an as-converted basis with the common stock. The Series A Preferred Stock shall not be converted if, after giving effect to the conversion, the holder and its affiliated persons would own beneficially more than 4.99% of our common stock (subject to adjustment up to 9.99% solely at the holder’s discretion upon 61 days’ prior notice to us or, solely as to a holder, if such limitation is waived by such holder upon execution of the private placement agreement). As of December 31, 2018, there were 400.4910 shares of Series A Preferred Stock outstanding, which remain convertible into 177,996 shares of the Company’s common stock.

Warrants

Warrants	12 Months Ended
	Dec. 31, 2018
Warrants And Rights Note Disclosure [Abstract]
Warrants	9. WARRANTS Issued Classification Warrants Outstanding Exercise Price Expiration October 2018 Liability 19,616,250 $ 0.70 October 2028 September 2016 Liability 13,466,667 2.25 November 2022 March 2015 Equity 3,699 9.75 March 2025 July 2014 Equity 6,566 7.99 July 2024 July 2012 Equity 52,046 0.01 July 2022 In the first quarter of 2019 the Company reduced the exercise price for all but 508,714 of the warrants issued in September 2016 and all of the warrants issued in October 2018. Refer to Note 15, Subsequent Events

Equipment Loan Payable

Equipment Loan Payable	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Equipment Loan Payable	10. EQUIPMENT LOAN PAYABLE As of December 31, 2018 and 2017, the Company had the following outstanding borrowing obligations: December 31, December 31, 2018 2017 (in thousands) Silicon Valley Bank Equipment Loan Payable $ — $ 178 Less: current portion — (178 ) Long-term debt, net $ — $ — In July 2014, the Company entered into a loan and security agreement with Silicon Valley Bank, which provided for a line of credit to finance certain equipment purchases up to an aggregate of $1.8 million through March 31, 2015. The line has been fully drawn and is payable in 36 monthly installments of principal and interest, with an annual interest rate of 2.75% plus the greater of 3.25% or the prime rate in effect at the time of each draw, as published in the Wall Street Journal. The outstanding balance on the line of credit is secured by a first priority lien over all equipment purchased using the line of credit. In accordance with the terms of the equipment line of credit, the Company issued a warrant to Silicon Valley Bank in July 2014 to purchase 6,566 shares of our common stock at an exercise price per share of $7.99. The equipment line of credit includes customary operating but non-financial covenants, including limitations on the Company’s ability to incur additional indebtedness, issue dividends, sell assets, engage in any business other than its current business, merge or consolidate with other entities, create liens on our assets, make investments, repurchase stock in certain instances, enter into transactions with affiliates, make payments on subordinated indebtedness and transfer or encumber any collateral securing the debt. The loan matured and was fully repaid in 2018.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	11. STOCK-BASED COMPENSATION Restricted Stock Awards and Stock Options The Company adopted the 2012 Equity Incentive Plan, as amended (“2012 Plan”) in July 2012 pursuant to which 609,389 shares of common stock were authorized for issuance to employees, officers, directors, consultants and advisors of the Company as of December 31, 2014. Upon the closing of the IPO on December 3, 2014, no further grants were made under the 2012 Plan as the 2013 Equity Incentive Plan (“2013 Plan”) replaced the 2012 Plan on this date. The 2012 Plan provided for the grant of incentive stock options, non-statutory stock options, rights to purchase restricted stock, stock appreciation rights, phantom stock awards and stock units. In connection with the issuance of restricted common stock, the Company maintains a repurchase right and shares of restricted common stock are released from such repurchase right over a period of time of continued service by the recipient. Recipients of incentive stock options shall be eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair value of such stock on the date of grant. Stock options generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years, unless they contain specific performance and/or market-based vesting provisions. The maximum term of stock options granted under the 2012 Plan is ten years. In determining the exercise prices for options granted, the board of directors considered the fair value of the common stock as of the measurement date. The fair value of the common stock was determined by the board of directors based on a variety of different factors, including valuations prepared by third party valuation specialists, the Company’s financial position, the status of development efforts within the Company, the composition and ability of the current scientific and management teams, the current climate in the marketplace, the illiquid nature of the Company’s common stock, any arm’s length sale of the Company’s preferred stock, the effect of the rights and preferences of the preferred stockholders, and the prospects of a liquidity event, among others. 2013 Equity Incentive Plan The Company’s board of directors adopted the 2013 Plan in November 2013 which the stockholders approved in October 2014. The 2013 Plan provides for the grant of incentive stock options, non-statutory stock options, rights to purchase restricted stock, stock appreciation rights and stock units. In connection with the issuance of restricted common stock, the Company maintains a repurchase right and shares of restricted common stock are released from such repurchase right over a period of time of continued service by the recipient. Recipients of stock options shall be eligible to purchase shares of the Company’s common stock at an exercise price equal to no less than the estimated fair value of such stock on the date of grant. Stock options generally vest 25% on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining three years, unless they contain specific performance and/or market-based vesting provisions. The maximum term of stock options granted under the 2013 Plan is ten years. In June 2016, the Company’s stockholders approved an amendment to the EIP to increase the number of shares of common stock available for issuance under the 2013 Plan by 300,000 shares and increase the number of shares of common stock automatically added to the 2013 Plan on January 1 of each year during the term of the 2013 Plan, starting with January 1, 2017 (the “EIP Amendment”). Following adoption of the EIP Amendment, the number of shares of common stock available for issuance under the 2013 Plan is subject to an automatic annual increase on the first day of the Company’s calendar year beginning in 2017 equal to the lesser of (a) 4.0% of the total number of shares of common stock outstanding on December 31 of the prior year or, (b) the number determined by the Company’s Board of Directors. Accordingly, the number of shares of common stock available for issuance under the EIP was increased by 825,904 shares on January 1, 2017 and an additional 982,841 shares on January 1, 2018. To the extent any awards under the 2013 Plan are forfeited, terminate, expire, lapse without the issuance of shares, or if the Company repurchases shares subject to awards under the 2013 Plan, those shares will again become available for issuance under the 2013 Plan. 2013 Employee Stock Purchase Plan The Company’s board of directors adopted the 2013 Employee Stock Purchase Plan (“2013 ESPP”) in November 2013 which the stockholders approved in October 2014. The 2013 ESPP became effective upon the closing of the IPO on December 3, 2014. The Company’s 2013 ESPP qualifies under Section 423 of the Internal Revenue Code of 1986, as amended (the “Code”). Under the 2013 ESPP, 103,665 shares of the Company’s common stock are authorized for issuance to eligible employees. The number of shares reserved for issuance under the 2013 ESPP is automatically increased on the first business day of each of the Company’s fiscal years, commencing in 2015, by a number equal to the lowest of (a) 51,832 shares of common stock,(b) 1% of the shares of common stock outstanding on the last business day of the prior fiscal year; or (c) the number of shares determined by the Company’s Board of Directors. Accordingly, the number of authorized shares of the Company’s common stock authorized for issuance to eligible employees under the 2013 ESPP was increased by 206,476 shares on January 1, 2017 and an additional 51,832 shares on January 1, 2018. The number of shares reserved under the 2013 ESPP will automatically be adjusted in the event of a stock split, stock dividend or a reverse stock split (including an adjustment to the per-purchase period share limit). The Company’s 2013 ESPP permits each eligible employee to purchase common stock through payroll deductions. There was no activity under the Plan in 2018 and 2017. Stock option activity under the 2012 and 2013 plans is summarized as follows: Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2017 2,158,348 $ 4.40 8.1 $ 436 Granted 4,311,090 1.21 Exercised (919 ) 2.56 Cancelled (3,129,048 ) 3.60 Outstanding at December 31, 2018 3,339,471 $ 1.03 8.1 $ - Vested and expected to vest at December 31, 2018 3,314,542 $ 1.03 8.1 $ - Exercisable at December 31, 2018 1,603,725 $ 1.37 7.1 $ - As of December 31, 2018 and 2017, the unrecognized compensation cost related to outstanding options was $2.3 million and $1.4. million, respectively, and is expected to be recognized as expense over approximately 2.50 years and 1.70 years, respectively. The intrinsic value of options exercised during the years ended December 31, 2018 and 2017 was $0 and $8 thousand, respectively. As of December 31, 2018, the weighted average grant date fair value of vested options was $0.76 and the weighted average grant date fair value of options outstanding was $0.52. Additional information about the Company’s stock option activity is as follows: Year Ended December 31, 2018 2017 Weighted-average grant date fair value per share of employee option grants within the year $ 0.59 $ 1.02 Cash received upon exercise of options 2 6 As of December 31, 2016, the unrecognized compensation cost related to restricted stock awards was $1 thousand which was recognized as expense during the year ended December 31, 2017. Stock-Based Compensation Expense The Company granted stock options to employees for the years ended December 31, 2018 and 2017. The Company estimates the fair value of stock options as of the date of grant using the Black-Scholes option pricing model and restricted stock based on the fair value of the award. Stock options and restricted stock issued to non-board member, non-employees are accounted for using the fair value approach and are subject to periodic revaluation over their vesting terms. For all periods from inception to date, stock-based compensation for all options granted and restricted stock awards are classified as research and development expense and general and administrative expense. Stock compensation expense amounted to approximately $1.6 million and $1.6 million for the years ended December 31, 2018 and 2017, respectively. Stock-based compensation is as follows: Year Ended December 31, 2018 2017 (in thousands) Research and development $ 488 $ 411 General and administrative 1,137 1,162 Total stock-based compensation expense $ 1,625 $ 1,573 The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: Year Ended December 31, 2018 2017 Risk-free interest rate 2.84 % 2.03 % Expected volatility 84.4 % 62.9 % Expected term (in years) 5.31 6.08 Expected dividend yield 0.0 % 0.0 % The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the non-employee stock option grants were as follows: Year Ended December 31, 2018 2017 Risk-free interest rate 2.57 % 1.29 % Expected volatility 88.3 % 62.3 % Expected term (in years) 6.08 6.08 Expected dividend yield 0.0 % 0.0 % Risk-free Interest Rate . The risk-free interest rate assumption is based on observed interest rates appropriate for the expected term of the stock option grants. Expected Volatility . Due to the Company’s limited operating history and lack of company-specific historical or implied volatility, the expected volatility assumption is based on historical volatilities of a peer group of similar companies whose share prices are publicly available. The peer group was developed based on companies in the biotechnology and medical device industries. Expected Term . The expected term represents the period of time that options are expected to be outstanding. Because the Company does not have historical exercise behavior, through December 31, 2018 it determined the expected life assumption using the simplified method, which is an average of the contractual term of the option and its vesting period. Expected Dividend Yield . The expected dividend yield assumption is based on the fact that the Company has never paid cash dividends and has no present intention to pay cash dividends. On October 1, 2018, the Compensation Committee of the Board of Directors approved a repricing (the “Repricing”) of 3,807,779 stock options (the “Options”) granted prior to September 1, 2018 pursuant to our 2013 Equity Incentive Plan and our 2012 Equity Incentive Plan to executive officers, employees and consultants of the Company. The Options had exercise prices between $0.75628 and $9.97 per share, which were reduced to $0.568 per share (the closing price of the Company’s common stock on The Nasdaq Capital Market on October 1, 2018). The number of shares, vesting schedules and expiration period of the Options were not altered. The impact to the Company’s financial statements in 2018 was immaterial.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	12. INCOME TAXES For the years ended December 31, 2018 and 2017, the Company did not record a current or deferred income tax expense or benefit due to current and historical losses incurred by the Company. The components of loss before income taxes were as follows: As of December 31, 2018 2017 (in thousands) U.S. $ (8,503 ) $ (26,275 ) Foreign (140 ) (140 ) Total $ (8,643 ) $ (26,415 ) A reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate to income taxes as reflected in the financial statements is as follows: As of December 31, 2018 2017 Federal income tax (benefit) at statutory rate 21.1 % 33.7 % (Increase) decrease income tax benefit resulting from: State income tax benefit, net of federal benefit 22.5 % 0.0 % Permanent differences 54.4 % (2.6 )% Net Operating Loss Limitation 0.0 % 0.0 % Federal Tax Rate change 0 % (47.2 )% R&D Credit Limitation 0.9 % 0.0 % Change in valuation allowance (98.5 )% 14.6 % Other -0.4 % 1.5 % Income tax expense (benefit) 0.0 % 0.0 % Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets and liabilities are comprised of the following: As of December 31, 2018 2017 (in thousands) Deferred tax assets: Net operating loss carryforwards $ 24,941 $ 18,540 Depreciation and amortization 4,878 4,121 Accrued expenses 141 1,484 Capitalized start-up costs 9,143 7,942 R&D credits 312 243 Other 1,155 808 Deferred tax assets before valuation allowance 40,570 33,138 Valuation allowance (40,570 ) (33,138 ) — — Deferred tax liabilities IPR&D — — Change in accounting method — — Net deferred tax assets $ — $ — The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. As of December 31, 2018 and 2017, based on the Company’s history of operating losses, the Company has concluded that it is not more likely than not that the benefit of its deferred tax assets will be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2018 and 2017. The valuation allowance decreased by $7.4 million during the year ended December 31, 2018, due primarily to net operating losses generated and capitalized expenses. The valuation allowance decreased $1.0 million during the year ended December 31, 2017, due primarily to net operating losses generated, net of the impact of a federal tax rate change of $11.5 million. In addition, the reduction in net operating losses were related to Section 382 limits as a result in a change in ownership. As of December 31, 2018 and 2017, the Company had U.S. federal NOL carryforwards of $67 million and $43.9 million respectively, which may be available to offset future income tax liabilities and expire at various dates through 2037. As of December 31, 2018 and 2017, the Company also had U.S. state NOL carryforwards of $66.9 million and $43.6 million respectively, which may be available to offset future income tax liabilities and expire at various dates through 2037. At December 31, 2018 and 2017, the Company also had $26.2 and $26.1 respectively, of foreign NOL carryforwards which may be available to offset future income tax liabilities, which carryforwards do not expire. Utilization of the NOL and research and development credit carryforwards may be subject to a substantial annual limitation due to ownership change limitations that have occurred or that could occur in the future, as required by Section 382 and Section 383 of the Code, as well as similar state and foreign provisions. These ownership changes may limit the amount of NOL and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. In general, an “ownership change” as defined by Section 382 of the Code results from a transaction or series of transactions over a three-year period resulting in an ownership change of more than 50 percentage points of the outstanding stock of a company by certain stockholders. The Company has completed a study to assess whether an ownership change has occurred or whether there have been multiple ownership changes since its formation. The results of this study indicated that the Company experienced ownership changes as defined by Section 382 of the Code. The Company has not recorded NOLs that, as a result of these restrictions, from the 2016 ownership change, will expire unused. Accordingly, the Company has recorded NOL carryforwards net of these limitations, which are approximately $52.9 million. TAX REFORM On December 22, 2017 the Tax Cuts and Jobs Act (the “TCJA”) was signed into United States law. The TCJA includes a number of changes to existing tax law, including, among other things, a permanent reduction in the federal corporate income tax rate from 34% to 21%, effective as of January 1, 2018, as well as limitation of the deduction for net operating losses to 80% of annual taxable income and elimination of net operating loss carrybacks, in each case, for losses arising in taxable years beginning after December 31, 2017 (though any such net operating losses may be carried forward indefinitely). The tax rate change resulted in (i) a reduction in the gross amount of the Company’s deferred tax assets recorded as of December 31, 2017, without an impact on the net amount of its deferred tax assets, which are recorded with a full valuation allowance, and (ii) no income tax expense or benefit being recognized as of the enactment date of the TCJA. The staff of the Securities and Exchange Commission issued Staff Accounting Bulletin No. 118 to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the TCJA. In connection with the initial analysis of the impact of the TCJA, the Company remeasured its deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which is generally 21%. The remeasurement of the Company’s deferred tax assets and liabilities was offset by a corresponding change in the valuation allowance for the year ended December 31, 2017. As a result, there was no impact to the Company’s consolidated statements of operations and comprehensive loss as a result of the reduction in tax rates. The other provisions of the TCJA did not have a material impact on the Company’s consolidated financial statements. The Company’s final determination of the TCJA impact and the remeasurement of its deferred assets and liabilities was completed prior to the deadline of one year from the enactment of the TCJA. For the year ended December 31, 2018, there were no material changes to the analysis originally performed as of December 31, 2017. The changes in the Company’s unrecognized tax benefits are summarized as follows: As of December 31, 2018 2017 (in thousands) Unrecognized tax benefit, beginning of year $ 303 $ 562 Increase (decrease) related to current year positions — (123 ) Federal rate revision — (136 ) Unrecognized tax benefit, end of year $ 303 $ 303 As of December 31, 2018 and 2017, the total amount of unrecognized tax benefits was $0.3 million and $0.3 million, respectively which, if recognized, would favorably affect the effective income tax rate in future periods. Note that liabilities for unrecognized tax benefits have been recorded to the extent that they do not exceed the Company’s available losses that are not limited as a result of ownership changes that have occurred under Section 382 of the Code. Reductions to unrecognized tax benefits for limitations on the utilization of net operating losses due to ownership changes occurring during the year has been reflected in the table as reductions based on tax positions related to the current year. The Company accrues interest and penalties related to unrecognized tax benefits as a component of its provision for income taxes. No accrued interest and penalties related to the Company’s unrecognized tax benefits has been accrued as of December 31, 2018 and 2017. The Company believes that it is reasonably possible that none of its unrecognized tax benefits, may be recognized at the end of 2018. The Company or one of its subsidiaries files income tax returns in the United States and various states and Israel. The Company is subject to U.S. federal, state and local income tax examinations by tax authorities for years 2001 through present. Carryforward attributes that were generated in earlier periods remain subject to examination to the extent the year in which they were used or will be used remains open for examination. The tax years which remain subject to examination by tax authorities in Israel, as of December 31, 2018, include years 2014 through the present.

Employee Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2018
Compensation And Retirement Disclosure [Abstract]
Employee Benefits	13. EMPLOYEE BENEFITS The Company has a defined contribution 401(k) plan for employees who are at least 21 years of age. Employees are eligible to participate in the plan beginning on the first day of the calendar quarter following their date of hire. Under the terms of the plan, employees may make voluntary contributions as a percent of compensation. No matching contributions have been made by the Company since the adoption of the 401(k) plan.

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Parties	14. RELATED PARTIES Purpose, Co. In June 2012, the Company entered into an agreement with Purpose, Co. to amend its previous agreements. In the previous agreements, Purpose, Co. granted the Company a perpetual license to its patents related to its exogenous tissue processor which is used in the development of the Company’s products. In exchange, the Company granted Purpose, Co. a perpetual license to all of the Company’s biotechnology and biomaterial for use in Japan. The agreement provides for Purpose, Co. to manufacture and sell machinery to the Company for cost until the Company’s products become commercially viable. The Company has also agreed to pay royalties on any third-party revenue generated using Purpose, Co.’s licensed technology. Under the June 2012 amendment, the Company received exclusive rights to all of Purpose, Co.’s technology related to the exogenous tissue processor, continued supply of exogenous tissue processors during the Company’s clinical trials, and rights to manufacture the exogenous tissue processors at any location the Company chooses. In exchange for such consideration, the Company named Purpose, Co. the sole manufacturer of equipment and also clarified the geographic territories of the exclusive license that Purpose Co. was granted for use of the Company’s technology. Also, the Company agreed to reimburse Purpose, Co. for $0.3 million of development costs on a next generation tissue processer. Refer to the discussion under Note 7, Tissue Processor Sub-License In May 2016, the Company acquired the development and commercialization rights to NeoCart for the Japanese market from Purpose, Co. Under the terms of the amended agreement, the Company assumes sole responsibility for and rights to the development and commercialization of NeoCart in Japan. In exchange for the transfer of development and commercialization rights, the Company will pay a success-based milestone to Purpose upon conditional approval of NeoCart in Japan, as well as commercial milestones and a low single digit royalty on Japanese sales of NeoCart, upon full approval, if any, in Japan. The amounts that have been paid to Purpose, Co. under this agreement were $0.1 and $0.1 million for the years ended December 31, 2018 and 2017, respectively. Board of Director Affiliates Affiliates of certain members of the Company’s Board of Directors participated in the Private Placement as described in Note 8.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	15. SUBSEQUENT EVENTS Restructuring – Effective January 23, 2019, the Board of Directors of the Company approved a restructuring plan involving reductions in headcount as part of a plan to reduce operating costs following the Company’s decision to discontinue the development of NeoCart. The positions eliminated together represent approximately 65% of the Company’s workforce, including the Company’s Chief Medical Officer and Chief Business Officer. The Company expects to substantially complete the initial restructuring efforts and record a one-time charge for severance and related expenses of approximately $1.4 million in the first quarter of 2019 Additional Restructuring – On March 14, 2019, the Board of Directors approved a further restructuring of the Company that terminated all but one of the remaining employees. The effective date of the restructuring is March 22, 2019. In connection with this additional restructuring, the Company intends to engage, Mr. Adam Gridley, its Chief Executive Officer, Mr. Stephen Kennedy, its Chief Operating Officer, along with up to four additional employees as consultants to assist with the continuing evaluation of strategic alternatives. The Company expects to substantially complete the second restructuring and record an additional one-time charge for severance and related expenses of approximately $2.2 million also in the first quarter of 2019. Warrant Amendments – In the first quarter of 2019, The Company and certain holders of the warrants issued in 2016 (the “Participating 2016 Holders”) entered into a Warrant Amendment and Exercise Agreement (the “2016 Exercise Agreement”) pursuant to which the Company agreed to reduce the exercise price of the warrants held by such Participating 2016 Holders from $2.25 to $0.01 per share (the “2016 Reduced Exercise Price”) in consideration for the exercise of the warrants held by such Participating 2016 Holders in full at the 2016 Reduced Exercise Price for cash. In connection with the exercise of the warrants by the Participating 2016 Holders, the Company received aggregate gross proceeds of approximately $0.1 million. After the full exercise of the warrants held by the Participating 2016 Holders, warrants issued in 2016 to purchase approximately 508,714 shares of the Company’s Common Stock are outstanding. Also in the first quarter of 2019, the Company reduced the exercise price of the warrants issued in 2018 from $0.70 to $0.01 per share (the “2018 Reduced Exercise Price”) and all of the holders of these warrants (the “Participating 2018 Holders”) entered into a Warrant Exercise Agreement (the “2018 Exercise Agreement”) pursuant to which in consideration for the 2018 Reduced Exercise Price, the Participating 2018 Holders agreed to exercise the warrants held by such Participating 2018 Holders in full at the 2018 Reduced Exercise Price for cash. In connection with the exercise of the warrants by the Participating 2018 Holders, the Company received aggregate gross proceeds of approximately $0.2 million.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Accounting	Basis of Accounting The consolidated financial statements are prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). The consolidated financial statements include the accounts of Histogenics Corporation and its wholly-owned subsidiaries, ProChon and Histogenics Securities Corporation. All significant intercompany accounts and transactions are eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities in the Company’s consolidated financial statements and accompanying notes. The most significant estimates in the Company’s consolidated financial statements relate to the valuation of equity awards, warrant liability, recoverability of deferred tax assets, estimated useful lives of fixed assets. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions on an ongoing basis. The Company recorded in 2018 a loss on impairment of fixed assets. See Note 5 Property and Equipment. The Company’s actual results may differ from these estimates under different assumptions or conditions.
Foreign Currency Translation	Foreign Currency Translation The Company’s consolidated financial statements are prepared in U.S. dollars. The Company’s foreign subsidiary uses the U.S. dollar as its functional and reporting currency, as management determined that the U.S. dollar is the primary currency of the economic environment in which the subsidiary operates. When transactions are required to be paid in the local currency of the foreign subsidiary, any resulting foreign currency transaction gain or loss is recorded as a component of “Other income (expense), net” in the consolidated statements of operations.
Segment and Geographic Information	Segment and Geographic Information Operating segments are defined as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker (“CODM”) or decision-making group in making decisions regarding resource allocation and assessing performance. The Company operates in two geographic regions: the United States (Massachusetts) and Israel (Tel Aviv) and views its operations as two operating segments: Histogenics Corporation (United States) and ProChon (Israel) as the CODM reviews separate discrete financial information in making decisions regarding resource allocations and assessing performance. Operating segments that have similar economic characteristics can be aggregated. As the nature of the products, customers, and methods to distribute products are the same and the nature of the regulatory environment, the production processes and historical and estimated future margins are similar, the two operating segments have been aggregated into one reporting segment as they have similar economic characteristics.
Fair Value Measurements	Fair Value Measurements The carrying amounts reported in the Company’s consolidated financial statements for cash and cash equivalents, accounts payable, equipment loan, and accrued liabilities approximate their respective fair values because of the short-term nature of these accounts. Fair value is defined as the price that would be received if selling an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Fair value should be based on the assumptions that market participants would use when pricing an asset or liability and is based on a fair value hierarchy that prioritizes the information used to develop those assumptions. Fair value measurements should be disclosed separately by level within the fair value hierarchy. For assets and liabilities recorded at fair value, it is the Company’s policy to maximize the use of observable inputs (quoted prices in active markets) and minimize the use of unobservable inputs (Company assumptions) when developing fair value measurements, in accordance with established fair value hierarchy. Fair value measurements for assets and liabilities where there exists limited or no observable market data are based primarily upon estimates, and often are calculated based on the economic and competitive environment, the characteristics of the asset or liability and other factors. Therefore, the results cannot be determined with precision and may not be realized in an actual sale or immediate settlement of the asset or liability. Additionally, there may be inherent weaknesses in any valuation technique, and changes in the underlying assumptions used, including discount rates and estimates of future cash flows, could significantly affect the results of current or future values. Additionally, from time to time, the Company may be required to record at fair value other assets on a nonrecurring basis, such as assets held for sale and certain other assets. These nonrecurring fair value adjustments typically involve application of lower-of-cost-or-market accounting or write-downs of individual assets. The fair value hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets (Level 1), and the lowest priority to unobservable inputs (Level 3). The Company’s financial assets are classified within the fair value hierarchy based on the lowest level of inputs that is significant to the fair value measurement. The three levels of the fair value hierarchy, and its applicability to the Company’s financial assets, are described below. Level 1 : Unadjusted quoted prices in active markets that are accessible at the measurement date of identical, unrestricted assets. Level 2 : Quoted prices for similar assets, or inputs that are observable, either directly or indirectly, for substantially the full term through corroboration with observable market data. Level 2 includes investments valued at quoted prices adjusted for legal or contractual restrictions specific to the security. Level 3 : Pricing inputs are unobservable for the assets, that is, inputs that reflect the reporting entity’s own assumptions about the assumptions market participants would use in pricing the assets. Level 3 includes private investments that are supported by little or no market activity. Level 3 valuations are for instruments that are not traded in active markets or are subject to transfer restrictions and may be adjusted to reflect illiquidity and/or non-transferability, with such adjustment generally based on available market evidence. In the absence of such evidence, management’s best estimate is used. An adjustment to the pricing method used within either Level 1 or Level 2 inputs could generate a fair value measurement that effectively falls in a lower level in the hierarchy. The Company had no assets or liabilities classified as Level 1 or Level 2 as of December 31, 2018 and 2017 other than the money market fund described in the “Cash and Cash Equivalents” section and the asset-backed securities in the “Marketable securities” section below. There were no material re-measurements of fair value with respect to financial assets and liabilities, during the periods presented, other than those assets and liabilities that are measured at fair value on a recurring basis. The Company’s only assets or liabilities classified as level 3 are the warrants issued in connection with the September 2016 private placement and the October 2018 underwritten public offering. The fair value of the warrants issued in connection with the September 2016 private placement was determined using a Monte Carlo simulation model. This model incorporated several assumptions at each valuation date including: the price of the Company’s common stock on the date of valuation, the historical volatility of the price of the Company’s common stock, the remaining contractual term of the warrant and estimates of the probability of a fundamental transaction occurring. The fair value of the warrants issued in connection with the October 2018 underwritten public offering was determined using the Black Scholes model. See Note 8, Capital Stock, for further discussion of the private placement and underwritten public offering. Description Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (in thousands) December 31, 2018 Assets: Cash Equivalents Money market funds 9,711 9,711 — — Liabilities: Warrant liability 2,512 — — 2,512 December 31, 2017 Assets: Cash Equivalents Money market funds 5,547 5,547 — — Marketable securities: Asset-backed securities 900 — 900 — Liabilities: Warrant liability 14,679 — — 14,679 The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs: As of December 31, 2018 (in thousands) Beginning balance, January 1, 2018 $ 14,679 Issuance of warrants 8,434 Change in fair value of warrant liability (20,601 ) Ending balance $ 2,512
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents include cash in readily available checking and savings accounts and money market funds. The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents.
Marketable Securities	Marketable Securities The Company classifies marketable securities with a remaining maturity when purchased of greater than three months as available for sale. The Company considers all available for sale securities, including those with maturity dates beyond 12 months, as available to support current operational liquidity needs and therefore classifies all securities including those with maturity dates beyond 90 days at the date of purchase as current assets within the consolidated balance sheets. Available for sale securities are maintained by the Company’s investment managers and may consist of commercial paper, high-grade corporate notes, U.S. Treasury securities, U.S. government agency securities, and certificates of deposit. Available for sale securities are carried at fair value with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ equity (deficit) until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the instrument. Realized gains and losses are determined using the specific identification method and are included in other income (expense). If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary” and, if so, marks the investment to market through a charge to the Company’s consolidated statement of operations and comprehensive loss. The Company did not hold any available for sale securities prior to the first quarter of 2017. The amortized cost of available for sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. At December 31, 2018, the balance in the Company’s accumulated other comprehensive loss was composed solely of activity related to the Company’s available for sale marketable securities. The aggregate fair value of available for sale securities held by the Company for less than twelve months as of December 31, 2017 was $0.9 million which matured in 2018. The Company did not hold any available for sale securities and there were no sales of such during the year ended December 31, 2018. The Company determined that there was no material change in the credit risk of any of its investments. As a result, the Company determined it did not hold any investments with any other-than-temporary impairment as of December 31, 2017. The weighted average maturity of the Company’s portfolio was less than one month at December 31, 2017.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments, which potentially subject the Company to significant concentration of credit risk, consist primarily of cash and cash equivalents. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. The Company has no financial instruments with off-balance sheet risk of loss.
Property and Equipment	Property and Equipment Property and equipment are recorded at historical cost. Costs for capital assets not yet placed into service are capitalized as construction in progress, and are depreciated in accordance with the below guidelines once placed into service. Maintenance and repair costs are expensed as incurred. Costs which materially improve or extend the lives of existing assets are capitalized. The Company provides for depreciation and amortization using the straight-line method over the estimated useful lives of the assets, which are as follows: Asset Category Estimated Useful Lives Office equipment 3 to 5 years Laboratory equipment 3 to 5 years Leasehold improvements Shorter of the remaining lease term or useful life Upon retirement or sale, the cost of assets disposed and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recorded in the consolidated statements of operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist primarily of property and equipment and identifiable intangible assets. When impairment indicators exist, the Company’s management evaluates long-lived assets for potential impairment. An impairment loss is recorded if and when events and circumstances indicate that assets might be impaired and the undiscounted cash flows estimated to be generated by those assets are less than the carrying amount of those assets. In 2018 a triggering event caused an impairment of the Company’s property and equipment. The triggering event related to the Company’s announcement that the NeoCart program was discontinued and the subsequent 73% reduction in stock price. An impairment loss of $4.3 million was recognized in earnings. See Note 5 Property and Equipment.
Restricted Cash	Restricted Cash Restricted cash represents cash held in a depository account at a financial institution to collateralize a conditional stand-by letter of credit related to the Company’s Lexington, Massachusetts facility lease agreement. Restricted cash is reported as non-current unless the restrictions are expected to be released in the next twelve months.
Deferred Rent	Deferred Rent Deferred rent consists of the difference between cash payments and the recognition of rent expense on a straight-line basis for the facilities the Company occupies. The Company’s leases for its Waltham, Massachusetts and Lexington, Massachusetts facilities provide for fixed increases in minimum annual rental payments. The total amount of rental payments due over each lease term is being charged to rent expense ratably over the life of each lease, respectively.
Financial Instruments Indexed to and Potentially Settled in the Company's Common Stock	Financial Instruments Indexed to and Potentially Settled in the Company’s Common Stock The Company evaluates all financial instruments issued in connection with its equity offerings when determining the proper accounting treatment for such instruments in the Company’s financial statements. The Company considers a number of generally accepted accounting principles under U.S. GAAP to determine such treatment and evaluates the features of the instrument to determine the appropriate accounting treatment. The Company utilizes the Probability Weighted Expected Return Method (“PWERM”), Option Pricing Model (“OM”) or other appropriate methods to determine the fair value of its derivative financial instruments, such as the warrant liability. For financial instruments indexed to and potentially settled in the Company’s common stock that are determined to be classified as liabilities on the consolidated balance sheet, changes in fair value are recorded as a gain or loss in the Company’s consolidated statement of operations with the corresponding amount recorded as an adjustment to the liability on its consolidated balance sheet.
Revenue Recognition	Revenue Recognition In May 2014, the Financial Accounting Standards Board (the “FASB”) issued a new standard related to revenue recognition, Accounting Standard Update Revenue is recognized when, or as, performance obligations are satisfied, which occurs when control of the promised products or services is transferred to customers. Revenue is measured as the amount of consideration the Company expects to receive in exchange for transferring products or services to a customer (“transaction price”). To the extent that the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing the most likely amount method. Variable consideration is included in the transaction price if, in the Company’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Estimates of variable consideration and determination of whether to include estimated amounts in the transaction price are based largely on an assessment of the Company’s anticipated performance and all information (historical, current and forecasted) that is reasonably available. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation based on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation. The Company’s revenues are generated primarily through collaborative research, development and commercialization agreements. The terms of these agreements may contain multiple promises which may include: (i) licenses to the Company’s technology; (ii) services related to the transfer and update of know-how; and (iii) manufacturing supply services. Payments to the Company under these arrangements typically include one or more of the following: non-refundable upfront license fees; milestone payments; royalties on future product sales; and fees for manufacturing supply services. None of the Company's contracts as of December 31, 2018 contained a significant financing component. The Company assesses the promises to determine if they are distinct performance obligations. Once the performance obligations are determined, the transaction price is allocated based on a relative standalone selling price basis. Milestone payments and royalties are typically considered variable consideration at the outset of the contract and are recognized in the transaction price either upon occurrence or when the constraint of a probable reversal is no longer applicable. Collaboration Revenue While no revenue has been recognized as of December 31, 2018, the Company has collaboration and license agreements with strategic partners for the development and commercialization of product candidates. The collaboration and license agreements are within the scope of Accounting Standards Codification (ASC 606) Revenue from Contracts with Customers. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under the agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for the arrangement, the Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include market conditions, reimbursement rates for personnel costs, development timelines and probabilities of regulatory success. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Manufacturing Supply Services: If the promise to supply products for clinical and/or commercial development are determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from the fees allocated to the supply when or as the supply is transferred to the customer, generally upon delivery to the customer. If the promise to supply products for clinical and/or commercial development are not determined to be distinct from the other performance obligations identified in the arrangement, the Company utilizes judgement to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue, including amounts from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service and revenue is recognized in the period in which the milestone is achieved. If the milestone payment is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the Company evaluates the milestone to determine whether the milestone is considered probable of being reached and estimates the amount to be included in the transaction price using either the most likely amount or the expected value method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall allocation. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration and other revenues and earnings in the period of adjustment. Royalties: For arrangements that include sales-based or usage-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of: (i) when the related sales occur; or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied).
License and Collaboration Arrangements	License and Collaboration Arrangements MEDINET Co., Ltd. In December 2017 the Company entered into the License and Commercialization Agreement (the “License Agreement”) with MEDINET Co., Ltd. (“MEDINET”) to grant MEDINET a license under certain patents, patent applications, know-how, and technology to develop and commercialize certain therapeutic products to replace or repair damaged, worn, or defective cartilage. In exchange for the license, MEDINET agreed to pay the Company an non-refundable upfront cash payment of $10.0 million which was received in January 2018. As of December 31, 2018, the contract with MEDINET was wholly unperformed. MEDINET also agreed to pay the Company tiered royalties, at percentages ranging from the low single digits to low double digits, of net sales of MEDINET products governed by the License Agreement. The Company is eligible to receive up to ¥330 million ($3.0 million as of December 31, 2018) in development milestone payments, $1.0 million and ¥720 million ($6.5 million as of December 31, 2018) in regulatory payments and up to an aggregate of ¥7,100 million ($64.3 million as of December 31, 2018) for the achievement of certain commercial milestones related to the sales of MEDINET products governed by the License Agreement. The Company assessed the promised goods and services to determine if they are distinct. Due to the unique nature of the clinical manufacturing services, there are no third-party vendors from which MEDINET can obtain such services from currently. The Company expects to be the only vendor capable of providing the commercial manufacturing services for a period of at least one to two years, which is approximately the estimated length of the clinical trial period in Japan. After this point, if the Company were to transfer to a third-party its technology and know-how related to the commercial manufacturing services that third-party vendor would be capable of providing the commercial manufacturing services, and therefore MEDINET would be able to choose whether to utilize the Company or another vendor for such services. The Company determined that the option to obtain to commercial manufacturing services does not represent a material right, as the fees charged to MEDINET by the Company are expected to approximate the fair market value for manufacturing services. As noted, with the assistance of the Company, third-party vendors could have the capability to perform such services by this time, and the Company expects the contract value to approximate the market price. Due to MEDINET’s limitations in obtaining the clinical manufacturing services from a third-party, as well as MEDINET’s limited ability to obtain the benefits of the licensed intellectual property without the clinical manufacturing services, the licensed intellectual property and clinical manufacturing services are determined to be a combined performance obligation. Based on this assessment, the Company determined that the promised goods and services do not have standalone value and are highly interrelated. Accordingly, the promised goods and services represent one performance obligation. Based on the assessment of the combined performance obligation, the Company determined that the predominant promise in the arrangement is the transfer of the license and associated knowhow which are expected to occur over the length of the clinical trial. The Company determined that MEDINET will be simultaneously receiving and consuming the benefits of the Company’s performance of the clinical trial. Therefore, the revenue associated with the combined performance obligation will be recognized over time. In determining the correct measure of progress to use when recognizing revenue over time, the Company assessed whether an input or output based measure of progress would be appropriate. The Company determined that an output based measure of progress would be appropriate to use when recognizing revenue associated with the combined performance obligation. The Company will recognize revenue based on the clinical manufacturing services completed to date. At the outset of the clinical trial in Japan to be conducted by MEDINET, the Company will have quantifiable estimates of total clinical candidates, and therefore, of total estimated performance. The Company will recognize revenue based on performance completed to date, as evidenced by the estimated number of clinical trial enrollees. The Company expects to provide the clinical manufacturing services to MEDINET over an estimated period of two years. Therefore, the estimated two-year clinical manufacturing period is the appropriate timing of revenue recognition for the combined performance obligation. Revenue will be recognized using the output method, as the clinical manufacturing services are delivered, over the estimated two-year year proportional performance service period. Upon the conclusion of the clinical manufacturing period, the Company expects other third-party vendors to have the capabilities to provide similar services. At this point, the license would effectively become a distinct performance obligation, with no remaining undelivered obligations. Therefore, the Company determined that the up-front payment associated with the licensed intellectual property should be fully recognized by the conclusion of the clinical manufacturing service period. Upon conclusion of the clinical manufacturing service period, the Company will have no remaining performance obligations, and MEDINET will be able to obtain commercial manufacturing services from other vendors. At contract inception, the Company determined that the $10.0 million non-refundable upfront amount constituted the entirety of the consideration to be included in the transaction price as the development, regulatory, and commercial milestones represent variable consideration and were fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensees’ efforts. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. The Company also determined that consideration associated with the clinical trials, which are payable by MEDINET on per-patient basis represent variable consideration, will be included in the transaction price upon occurrence, or once the associated clinical manufacturing service(s) for the patient are concluded. The upfront transaction price of $10.0 million will be recognized over a period of approximately two-years, commencing at the start of the clinical trial which, in management’s judgement represents the Company’s best estimate of the period of performance for satisfying the performance obligation of supply of clinical trial materials and transfer of license to MEDINET. Management has included $10.0 as non-current based on the feedback from the FDA and subsequent suspension of the NeoCart program. MEDINET relies on Company’s NeoCart product to supply clinical trial patients. MEDINET has suspended development of its clinical trial. Management will reevaluate that estimate at each reporting period. Revenue is being recognized using the output method, as the clinical manufacturing services are delivered, over the estimated two year proportional performance clinical manufacturing period. Transaction Price Allocated to Future Performance Obligations Remaining performance obligations represents the transaction price of contracts for which work has not been performed (or has been partially performed) and excludes unexercised contract options. As of December 31, 2018, the aggregate amount of the transaction price allocated to the remaining performance obligations was $10.0 million. The contract with MEDINET is wholly unperformed, and the Company recognized no revenue associated with the agreement during the years ended December 31, 2018 and 2017, respectively.
Research and Development Costs	Research and Development Costs Research and development costs are charged to expense as incurred. These costs include, but are not limited to: license fees related to the acquisition of in-licensed products; employee-related expenses, including salaries, benefits and travel; expenses incurred under agreements with contract research organizations and investigative sites that conduct clinical trials and preclinical studies; the cost of acquiring, developing and manufacturing clinical trial materials; facilities, depreciation and other expenses, which include direct and allocated expenses for rent and maintenance of facilities; insurance and other supplies; and costs associated with preclinical activities and regulatory operations. Costs for certain development activities, such as clinical trials, are recognized based on an evaluation of the progress to completion of specific tasks using data such as patient enrollment, clinical site activations, or information provided to the Company by its vendors with respect to their actual costs incurred. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected in the consolidated financial statements as prepaid or accrued research and development expense. Collaboration Arrangements Costs reimbursed to a collaborator for work that it performs are recorded as research and development expenses. These reimbursements can include payments for work performed, or a milestone for which a payment is due, the reimbursements or development milestone achievement are recorded as research and development expense. In September 2014, the Company entered into a collaboration agreement with Intrexon Corporation (“Intrexon”) for the development and commercialization of allogeneic cell therapeutics for the treatment or repair of damaged articular hyaline cartilage in humans, utilizing Intrexon’s proprietary technology (the “Collaboration Agreement”). Under the terms of the Collaboration Agreement, the Company is responsible for the costs of development and commercialization, with some exceptions. This agreement was terminated in December 2018. In connection with the Mutual Termination Agreement, in lieu of payment of the Accrued Expenses, the Company agreed to pay Intrexon an aggregate of up to $1.5 million, with $0.375 million paid at the time of entering into the Mutual Termination Agreement and $1.125 million payable within one year following any submission of a BLA to the FDA for NeoCart
License Agreements	License Agreements Costs associated with licenses of technology are expensed as incurred and are included in research and development expenses.
Patent Costs	Patent Costs Costs related to filing and pursuing patent applications are recorded as general and administrative expense as incurred since the recoverability of such expenditures is uncertain.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for grants of stock options and restricted stock based on their grant date fair value and recognizes compensation expense over their vesting period. The Company estimates the fair value of stock options as of the date of grant using the Black-Scholes option pricing model and restricted stock based on the fair value of the underlying common stock as determined by management or the value of the services provided, whichever is more readily determinable. Stock-based compensation expense represents the cost of the grant date fair value of employee stock option grants recognized over the requisite service period of the awards (usually the vesting period) on a straight-line basis, net of estimated forfeitures. The expense is adjusted for actual forfeitures at year end. Stock-based compensation expense recognized in the consolidated financial statements is based on awards that are ultimately expected to vest. For stock option grants with performance-based milestones, the expense is recorded over the remaining service period after the point when the achievement of the milestone is probable or the performance condition has been achieved. For stock option grants with both performance-based milestones and market conditions, expense is recorded over the derived service period after the point when the achievement of the performance-based milestone is probable or the performance condition has been achieved. The Company did not issue performance-based awards in 2018 or 2017. The Company accounts for stock options and restricted stock awards to non-employees using the fair value approach. Stock options and restricted stock awards to non-employees are subject to periodic revaluation over their vesting terms. On October 1, 2018, the Compensation Committee of the Board of Directors approved a repricing (the “Repricing”) of 3,807,779 stock options (the “Options”) granted prior to September 1, 2018 pursuant to the 2013 Equity Incentive Plan and the 2012 Equity Incentive Plan to executive officers, employees and consultants of the Company. The Options had exercise prices between $0.75628 and $9.97 per share, which were reduced to $0.568 per share (the closing price of the Company’s common stock on The Nasdaq Capital Market on October 1, 2018). The number of shares, vesting schedules and expiration period of the Options were not altered. The impact to the Company’s financial statements in 2018 was immaterial.
Income Taxes	Income Taxes The Company accounts for income taxes under the liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future, in excess of its net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more likely than not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50 percent likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability.
Loss per Common Share	Loss per Common Share Loss per common share is calculated using the two-class method, which is an earnings allocation formula that determines loss per share for the holders of the Company’s common shares and participating securities. All series of preferred stock contain participation rights in any dividend paid by the Company and are deemed to be participating securities. Earnings available to common stockholders and participating convertible redeemable preferred shares are allocated to each share on an as-converted basis as if all of the earnings for the period had been distributed. The participating securities include a contractual obligation to share in losses of the Company and are included in the calculation of net loss per share in the periods that have a net loss. Diluted earnings per share is computed using the more dilutive of (a) the two-class method, or (b) the if-converted method. The Company allocates earnings first to preferred stockholders based on dividend rights and then to common and preferred stockholders based on ownership interests. The weighted-average number of common shares included in the computation of diluted loss gives effect to all potentially dilutive common equivalent shares, including outstanding stock options, warrants, convertible redeemable preferred stock and the potential issuance of stock upon the conversion of the Company’s convertible notes. Common stock equivalent shares are excluded from the computation of diluted loss per share if their effect is antidilutive.
Warrant Accounting	Warrant Accounting As noted in Note 9, the Company classifies warrants to purchase shares of its common stock as a liability on its consolidated balance sheet if the warrant is a free-standing financial instrument that may require the Company to transfer consideration upon exercise. Each warrant of this type is initially recorded at fair value on date of grant using a Monte Carlo simulation or Black Scholes model and net of issuance costs, and is subsequently re-measured to fair value at each subsequent balance sheet date. Changes in fair value of the warrants are recognized as a component of other income (expense), net in the consolidated statement of operations. The Company will continue to adjust the liability for changes in fair value until the earlier of the exercise or expiration of the warrants. In the first quarter of 2019 the Company reduced the exercise price of all but 508,714 warrants issued in connection with the 2016 private placement and all of the warrants issued in connection with the October 2018 underwritten public offering. Refer to Note 15, Subsequent Events
Recent Accounting Pronouncements	Recent Accounting Pronouncements In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606. The amendments in this update provide guidance on whether certain transactions between collaborative arrangement participants should be accounted for with revenue under Topic 606. The guidance also provides more comparability in the presentation of revenue for certain transactions between collaborative arrangement participants. For public business entities, the amendments in this update are effective for fiscal years and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted, including adoption in any interim period, for public business entities for periods for which financial statements have not yet been issued. The Company is currently evaluating the impact that the adoption of this guidance will have on the Company’s consolidated financial statements and related disclosures. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Changes to the Disclosure Requirements for Fair Value Measurement. The amendments in this update modify the disclosure requirements on fair value measurements based on the concepts in the Concepts Statement, including the consideration of costs and benefits. In August 2018, the SEC adopted the final rule under SEC Release No. 33-10532, Disclosure Update and Simplification. This final rule amends certain disclosure requirements that are redundant, duplicative, overlapping, outdated or superseded. In addition, the amendments expand the disclosure requirements on the analysis of stockholders’ equity for interim financial statements. Under the amendments, an analysis of changes in each caption of stockholders’ equity presented in the balance sheet must be provided in a note or separate statement. The analysis should present a reconciliation of the beginning balance to the ending balance of each period for which a statement of comprehensive income is required to be filed. This final rule is effective for the Company for all filings made on or after November 5, 2018. The SEC staff clarified that the first presentation of the changes in shareholders’ equity may be included in the first Form 10-Q for the quarter that begins after the effective date of the amendments. The adoption of the final rule did not have a material impact on the Company’s consolidated financial statements. In June 2018, the FASB issued ASU No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share- Based Payment Accounting. This update is to simplify the aspects of accounting for nonemployee share-based payment transactions for acquiring goods or services from nonemployees. The amendments in this update are effective for fiscal years beginning after December 15, 2018, including interim periods within that year. The Company has concluded that this guidance has no material impact on the Company’s consolidated financial statements and related disclosures. In July 2017, the FASB issued ASU No. 2017-11, Earnings Per Share (Topic 260): Distinguishing Liabilities from Equity (Topic 480); Derivatives and Hedging (Topic 815): (PART I) Accounting for certain financial instruments with down round features. This update addresses the complexity of accounting for certain financial instruments with down round features. The guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. The Company has concluded that this guidance has no impact on the presentation of its results of operations, financial position and disclosures. In May 2017, the FASB issued ASU No. 2017-09, Compensation-Stock Compensation (Topic 718): Scope of Modification Accounting. This standard provides guidance on changes to the terms or conditions of a share-based payment award that requires an entity to apply modification accounting. The guidance is effective prospectively for annual periods beginning after December 15, 2017, and for interim periods and annual periods thereafter. The Company has concluded that this guidance has a immaterial no impact on the presentation of its results of operations, financial position and disclosures. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows: Restricted Cash (“ASU 2016-18”). The amendments in this update require that amounts generally described as restricted cash and restricted cash equivalents be included within cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 was effective January 1, 2018. As a result of adopting ASU 2016-18, the Company includes its restricted cash balance in the cash and cash equivalents reconciliation of operating, investing and financing activities. The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the statement of financial position that sum to the total of the same such amounts shown in the statement of cash flows. As of December 31, 2018 2017 (in thousands) Cash and cash equivalents $ 15,542 $ 7,081 Restricted cash 137 137 Total cash, cash equivalents, and restricted cash shown in the statement of cash flows $ 15,679 $ 7,218 In February 2016, the FASB issued ASU No. 2016-02- Leases (Topic 842). This standard requires companies to recognize on the balance sheet the assets and liabilities for the rights and obligations created by leased assets. ASU 2016-02 will be effective for the Company in the first quarter of 2019, with early adoption permitted. The Company estimates that it will recognize approximately $8 million to $10 million of right-of-use assets and corresponding lease liabilities on the balance sheet upon adoption. However, the population of contracts subject to balance sheet recognition and their initial measurement remains under evaluation; and the final impact on the balance sheet will depend on the lease portfolio as the time of adoption. The Company does not expect that adoption will have a material impact on its results of operations or statement of cash flows. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (“Topic 606”), which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. In the fourth quarter of 2017, the Company early adopted ASC 606 and this standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. The Company had only one revenue arrangement as of the adoption date. Topic 606 requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. Topic 606 provides a five-step model for determining revenue recognition for arrangements that are within the scope of the standard: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For a complete discussion of accounting for revenues, see Note 1, Summary of Significant Accounting Policies – Revenue Recognition

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis	The fair value of the warrants issued in connection with the September 2016 private placement was determined using a Monte Carlo simulation model. This model incorporated several assumptions at each valuation date including: the price of the Company’s common stock on the date of valuation, the historical volatility of the price of the Company’s common stock, the remaining contractual term of the warrant and estimates of the probability of a fundamental transaction occurring. The fair value of the warrants issued in connection with the October 2018 underwritten public offering was determined using the Black Scholes model. See Note 8, Capital Stock, for further discussion of the private placement and underwritten public offering. Description Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) (in thousands) December 31, 2018 Assets: Cash Equivalents Money market funds 9,711 9,711 — — Liabilities: Warrant liability 2,512 — — 2,512 December 31, 2017 Assets: Cash Equivalents Money market funds 5,547 5,547 — — Marketable securities: Asset-backed securities 900 — 900 — Liabilities: Warrant liability 14,679 — — 14,679
Schedule of Reconciliation of Liabilities Measured at Fair Value	The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs: As of December 31, 2018 (in thousands) Beginning balance, January 1, 2018 $ 14,679 Issuance of warrants 8,434 Change in fair value of warrant liability (20,601 ) Ending balance $ 2,512
Schedule of Depreciation and Amortization using Straight-line Method over Estimated Useful Lives of Assets	The Company provides for depreciation and amortization using the straight-line method over the estimated useful lives of the assets, which are as follows: Asset Category Estimated Useful Lives Office equipment 3 to 5 years Laboratory equipment 3 to 5 years Leasehold improvements Shorter of the remaining lease term or useful life
Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash within the statement of financial position that sum to the total of the same such amounts shown in the statement of cash flows. As of December 31, 2018 2017 (in thousands) Cash and cash equivalents $ 15,542 $ 7,081 Restricted cash 137 137 Total cash, cash equivalents, and restricted cash shown in the statement of cash flows $ 15,679 $ 7,218

Loss Per Common Share (Tables)

Loss Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Loss Per Common Share	Basic and diluted loss per common share are calculated as follows: For the Year Ended 2018 2017 (In thousands, except share and per share data) Numerator: Net loss $ (8,643 ) $ (26,414 ) Net Loss attributable to Series A Preferred Stock (a) (121 ) (3,915 ) Numerator for basic EPS - loss attributable to common stockholders $ (8,522 ) $ (22,499 ) Effect of dilutive securities: Deduct change in fair value of warrant liability $ (20,601 ) $ — Numerator for diluted EPS - loss attributable to common stockholders after assumed conversions $ (29,123 ) $ (22,499 ) Denominator: Weighted-average number of common shares used in loss per share—basic 36,398,450 22,669,819 Effect of dilutive securities: Nonparticipating warrants 691,747 — Denominator for diluted EPS - adjusted weighted average shares 37,090,197 22,669,819 Loss per share—basic $ (0.23 ) $ (0.99 ) Loss per share—diluted $ (0.79 ) $ (0.99 ) (a) The Series A Preferred Stock participates in income and losses
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares outstanding, as they would be anti-dilutive (in common stock equivalent shares): As of December 31, 2018 2017 Unvested restricted stock and options to purchase common stock 3,339,471 2,158,348 Series A preferred stock unconverted 177,996 2,046,957 Warrants exercisable into common stock — 13,633,070

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following: As of December 31, 2018 2017 (in thousands) Insurance 686 72 Other current assets 172 122 Prepaid expenses and other current assets $ 858 $ 194

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following: December 31, December 31, 2018 2017 (in thousands) Office equipment $ 266 $ 279 Laboratory equipment 4,561 4,565 Leasehold improvements 5,504 7,712 Construction in progress — 990 Software 96 96 Total property and equipment 10,427 13,642 Less: accumulated depreciation (10,286 ) (10,919 ) Property and equipment, net $ 141 $ 2,723

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2018
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following: As of December 31, 2018 2017 (in thousands) Accrued compensation $ 514 $ 1,671 Accrued audit fees 159 133 Accrued license fees 90 70 Accrued clinical expenses 86 199 Accrued other 151 632 Total accrued expenses $ 1,000 $ 2,705

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Schedule of Minimum Annual Lease Commitments Under Non-Cancellable Operating Leases	Aggregate minimum annual lease commitments of the Company under its non-cancellable operating leases as of December 31, 2018, are as follows: For the Year Ended December 31, (in thousands) 2019 $ 1,845 2020 1,892 2021 1,941 2022 1,991 2023 1,728 Thereafter 1,460 Total minimum lease payments $ 10,857

Capital Stock (Tables)

Capital Stock (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Common Stock Reserved for Future Issuance	The Company has reserved for future issuance the following number of shares of common stock: As of December 31, 2018 2017 Options to purchase common stock 3,339,471 2,158,348 Common stock warrants 33,145,228 13,633,070 Total 36,484,699 15,791,418

Warrants (Tables)

Warrants (Tables)	12 Months Ended
	Dec. 31, 2018
Warrants And Rights Note Disclosure [Abstract]
Schedule of Warrants to Purchase Common Stock Outstanding	Issued Classification Warrants Outstanding Exercise Price Expiration October 2018 Liability 19,616,250 $ 0.70 October 2028 September 2016 Liability 13,466,667 2.25 November 2022 March 2015 Equity 3,699 9.75 March 2025 July 2014 Equity 6,566 7.99 July 2024 July 2012 Equity 52,046 0.01 July 2022

Equipment Loan Payable (Tables)

Equipment Loan Payable (Tables)	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Schedule of Outstanding Borrowing Obligations	As of December 31, 2018 and 2017, the Company had the following outstanding borrowing obligations: December 31, December 31, 2018 2017 (in thousands) Silicon Valley Bank Equipment Loan Payable $ — $ 178 Less: current portion — (178 ) Long-term debt, net $ — $ —

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity Under the 2012 and 2013 Plans	Stock option activity under the 2012 and 2013 plans is summarized as follows: Number of Options Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2017 2,158,348 $ 4.40 8.1 $ 436 Granted 4,311,090 1.21 Exercised (919 ) 2.56 Cancelled (3,129,048 ) 3.60 Outstanding at December 31, 2018 3,339,471 $ 1.03 8.1 $ - Vested and expected to vest at December 31, 2018 3,314,542 $ 1.03 8.1 $ - Exercisable at December 31, 2018 1,603,725 $ 1.37 7.1 $ -
Additional Information about Stock Option Activity	Additional information about the Company’s stock option activity is as follows: Year Ended December 31, 2018 2017 Weighted-average grant date fair value per share of employee option grants within the year $ 0.59 $ 1.02 Cash received upon exercise of options 2 6
Summary of Stock-Based Compensation	Stock-based compensation is as follows: Year Ended December 31, 2018 2017 (in thousands) Research and development $ 488 $ 411 General and administrative 1,137 1,162 Total stock-based compensation expense $ 1,625 $ 1,573
Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Employee Stock Option Grants	The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: Year Ended December 31, 2018 2017 Risk-free interest rate 2.84 % 2.03 % Expected volatility 84.4 % 62.9 % Expected term (in years) 5.31 6.08 Expected dividend yield 0.0 % 0.0 %
Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Non-Employee Stock Option Grants	The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the non-employee stock option grants were as follows: Year Ended December 31, 2018 2017 Risk-free interest rate 2.57 % 1.29 % Expected volatility 88.3 % 62.3 % Expected term (in years) 6.08 6.08 Expected dividend yield 0.0 % 0.0 %

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Components of Loss Before Income Taxes	The components of loss before income taxes were as follows: As of December 31, 2018 2017 (in thousands) U.S. $ (8,503 ) $ (26,275 ) Foreign (140 ) (140 ) Total $ (8,643 ) $ (26,415 )
Schedule of Reconciliation of Income Tax Expense (Benefit) Computed at Statutory Federal Income Tax Rate	A reconciliation of income tax expense (benefit) computed at the statutory federal income tax rate to income taxes as reflected in the financial statements is as follows: As of December 31, 2018 2017 Federal income tax (benefit) at statutory rate 21.1 % 33.7 % (Increase) decrease income tax benefit resulting from: State income tax benefit, net of federal benefit 22.5 % 0.0 % Permanent differences 54.4 % (2.6 )% Net Operating Loss Limitation 0.0 % 0.0 % Federal Tax Rate change 0 % (47.2 )% R&D Credit Limitation 0.9 % 0.0 % Change in valuation allowance (98.5 )% 14.6 % Other -0.4 % 1.5 % Income tax expense (benefit) 0.0 % 0.0 %
Components of Deferred Tax Assets and Liabilities	Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets and liabilities are comprised of the following: As of December 31, 2018 2017 (in thousands) Deferred tax assets: Net operating loss carryforwards $ 24,941 $ 18,540 Depreciation and amortization 4,878 4,121 Accrued expenses 141 1,484 Capitalized start-up costs 9,143 7,942 R&D credits 312 243 Other 1,155 808 Deferred tax assets before valuation allowance 40,570 33,138 Valuation allowance (40,570 ) (33,138 ) — — Deferred tax liabilities IPR&D — — Change in accounting method — — Net deferred tax assets $ — $ —
Summary of Changes In Unrecognized Tax Benefits	The changes in the Company’s unrecognized tax benefits are summarized as follows: As of December 31, 2018 2017 (in thousands) Unrecognized tax benefit, beginning of year $ 303 $ 562 Increase (decrease) related to current year positions — (123 ) Federal rate revision — (136 ) Unrecognized tax benefit, end of year $ 303 $ 303

Nature of Business - Additional

Nature of Business - Additional Information (Detail) - USD ($)	Sep. 29, 2016	May 13, 2011	Oct. 31, 2018	Jan. 31, 2018	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds of offering after deducting underwriting discounts and commissions						$ 25,526,000
Warrant exercise price						$ 2.25
Accumulated deficit						$ 216,830,000	$ 208,187,000
Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Shares issued				2,691,494		35,480,397
Common stock price per share				$ 2.35
Option to purchase additional shares				351,064
Net proceeds of offering after deducting underwriting discounts and commissions				$ 5,900,000
Private Placement [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Proceeds from issuance of common stock, preferred stock and warrants, net of issuance costs	$ 27,600,000				$ 27,600,000
Common stock price per share					$ 2.25
Class of Warrants or right to purchase common stock					13,333,334
Warrant exercise price					$ 2.25	$ 2.25
Private Placement [Member] | Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Shares issued					2,596,059
At-The-Market Sales Agreement [Member] | Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Shares issued						6,633,903
Net proceeds of offering after deducting underwriting discounts and commissions						$ 4,500,000
At-The-Market Sales Agreement [Member] | Common Stock [Member] | Maximum [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Aggregate offering price of shares						$ 10,000,000
Underwritten Public Offering [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Class of Warrants or right to purchase common stock			19,616,250
Gross proceeds from offering, before deducting underwriting discounts and commissions and offering expenses			$ 17,000,000
Warrant exercise price			$ 0.70
Warrants exercisable term			5 years
Underwritten Public Offering [Member] | Common Stock [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Shares issued			26,155,000
Underwritten Public Offering [Member] | Common Stock and Warrants [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Common stock price per share			$ 0.65
ProChon [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Business acquisition date						May 13, 2011
Consideration paid to acquisition		$ 2,200,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, ¥ in Millions	Oct. 01, 2018$ / sharesshares	Dec. 31, 2018USD ($)	Jan. 31, 2018USD ($)	Jan. 31, 2018CNY (¥)	Dec. 31, 2018USD ($)Segment$ / sharesshares	Dec. 31, 2017USD ($)shares	Mar. 31, 2019shares	Jan. 01, 2019USD ($)	Mar. 31, 2017USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments | Segment					2
Number of reporting segment | Segment					1
Transfers between Levels 1, 2 and 3		$ 0			$ 0	$ 0
Available for sale securities		$ 0			0				$ 0
Marketable securities other-than-temporary impairment						0
Aggregate fair value of available for sale securities held for less than twelve months						900,000
Sale of available for sale securities					$ 0
Percentage of reduction in stock price		73.00%			73.00%
Impairment loss					$ 4,270,000
Remaining performance obligations		$ 10,000,000			10,000,000
Accrued expenses		1,125,000			1,125,000	$ 3,040,000
Gain on extinguishment of liability					$ 1,540,000
Stock options granted | shares					4,311,090
Stock options exercise price, lower range | $ / shares					$ 0.75628
Stock options exercise price, upper range | $ / shares					$ 9.97
Stock options reduced exercise price | $ / shares	$ 0.568
Maximum percentage of recognition of tax benefits from uncertain tax positions					50.00%
Scenario, Forecast [Member] | 2016 Private Placement [Member]
Summary Of Significant Accounting Policies [Line Items]
Warrants issued | shares							508,714
Performance-based Awards [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of shares issued | shares					0	0
Stock Option Repricing [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock options reduced exercise price | $ / shares	$ 0.568
Stock Option Repricing [Member] | 2013 Equity Incentive Plan and 2012 Equity Incentive Plan [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock options granted | shares	3,807,779
Intrexon [Member]
Summary Of Significant Accounting Policies [Line Items]
Aggregate agreement terimation amount		1,500,000
Payment of termination amount		375,000
Termination amount payable subject to certain condition		1,125,000
Accrued expenses		1,125,000			$ 1,125,000
Gain on extinguishment of liability		1,500,000
MEDINET Co. [Member]
Summary Of Significant Accounting Policies [Line Items]
Non-refundable upfront cash payment under license agreement			$ 10,000,000
Royalties at percentage rates ranging					Low single digits to low double digits
Development milestone payments				¥ 330	$ 3,000,000
Regulatory payments			1,000,000	720	6,500,000
Commercial Milestones Payment				¥ 7,100	64,300,000
Non-refundable upfront amount			10,000,000
Upfront transaction price			$ 10,000,000
Upfront transaction price recognized period			2 years	2 years
Upfront transaction price noncurrent			$ 10,000,000
Remaining performance obligations		0			0	$ 0
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Weighted average of maturity portfolio						1 month
Maximum [Member] | ASU 2016-02 [Member] | Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Right-of-use assets								$ 10,000,000
Lease liability								10,000,000
Minimum [Member] | ASU 2016-02 [Member] | Subsequent Event [Member]
Summary Of Significant Accounting Policies [Line Items]
Right-of-use assets								8,000,000
Lease liability								$ 8,000,000
Quoted Prices in Active Markets (Level 1) [Member] | Fair Value Measurement Recurring [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets, fair value disclosure, recurring		0			0	$ 0
Liabilities, fair value disclosure, recurring		0			0	0
Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurement Recurring [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets, fair value disclosure, recurring		0			0	0
Liabilities, fair value disclosure, recurring		$ 0			$ 0	$ 0

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Assets:
Money market funds, fair value	$ 9,711,000	$ 5,547,000
Marketable securities, fair value	0		$ 0
Liabilities:
Warrant liability, fair value	2,512,000	14,679,000
Asset Backed Securities [Member]
Assets:
Marketable securities, fair value		900,000
Quoted Prices in Active Markets (Level 1) [Member]
Assets:
Money market funds, fair value	9,711,000	5,547,000
Significant Other Observable Inputs (Level 2) [Member] | Asset Backed Securities [Member]
Assets:
Marketable securities, fair value		900,000
Significant Unobservable Inputs (Level 3) [Member]
Liabilities:
Warrant liability, fair value	$ 2,512,000	$ 14,679,000

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Reconciliation of Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in fair value of warrant liability	$ (20,601)	$ 1,482
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	14,679
Issuance of warrants	8,434
Change in fair value of warrant liability	(20,601)
Ending balance	$ 2,512	$ 14,679

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Schedule of Depreciation and Amortization using Straight-line Method over Estimated Useful Lives of Assets (Detail)	12 Months Ended
	Dec. 31, 2018
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	Shorter of the remaining lease term or useful life
Minimum [Member] | Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Minimum [Member] | Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	3 years
Maximum [Member] | Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years
Maximum [Member] | Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	5 years

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cash and cash equivalents	$ 15,542	$ 7,081
ASU 2016-18 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cash and cash equivalents	15,542	7,081
Restricted cash	137	137
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	$ 15,679	$ 7,218

Loss Per Common Share - Schedul

Loss Per Common Share - Schedule of Basic and Diluted Loss Per Common Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Numerator:
Net loss	$ (8,643)	$ (26,414)
Net Loss attributable to Series A Preferred Stock	(121)	(3,915)
Numerator for basic EPS - loss attributable to common stockholders	(8,522)	(22,499)
Effect of dilutive securities:
Deduct change in fair value of warrant liability	(20,601)
Numerator for diluted EPS - loss attributable to common stockholders after assumed conversions	$ (29,123)	$ (22,499)
Denominator:
Weighted-average number of common shares used in loss per share—basic	36,398,450	22,669,819
Effect of dilutive securities:
Nonparticipating warrants	691,747
Denominator for diluted EPS - adjusted weighted average shares	37,090,197	22,669,819
Loss per share—basic	$ (0.23)	$ (0.99)
Loss per share—diluted	$ (0.79)	$ (0.99)

Loss Per Common Share - Sched_2

Loss Per Common Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Series A Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	177,996	2,046,957
Unvested Restricted Stock and Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	3,339,471	2,158,348
Warrants Exercisable into Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share		13,633,070

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Prepaid Expense And Other Assets Current [Abstract]
Insurance	$ 686	$ 72
Other current assets	172	122
Prepaid expenses and other current assets	$ 858	$ 194

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 10,427	$ 13,642
Less: accumulated depreciation	(10,286)	(10,919)
Property and equipment, net	141	2,723
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	266	279
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	4,561	4,565
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	5,504	7,712
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment		990
Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 96	$ 96

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 450	$ 1,534
Impairment charge	$ 4,270

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued compensation	$ 514	$ 1,671
Accrued audit fees	159	133
Accrued license fees	90	70
Accrued clinical expenses	86	199
Accrued other	151	632
Total accrued expenses	$ 1,000	$ 2,705

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended			12 Months Ended		23 Months Ended
	Feb. 28, 2017USD ($)	Sep. 30, 2015	Jun. 30, 2012USD ($)	Dec. 31, 2018USD ($)Option	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)
Loss Contingencies [Line Items]
Rent expense under operating lease agreements				$ 1,600,000	$ 1,000,000
Research and development expense				$ 15,634,000	$ 15,566,000
Collagen Supply Agreement [Member]
Loss Contingencies [Line Items]
Supplier agreement description				The initial term of the agreement is three years and will automatically renew from year to year thereafter unless otherwise terminated with at least 180 days’ notice by either party.
Initial term of the agreement		3 years
Minimum amount of material and/or services	$ 100,000
Amount paid during period for amending the agreement						$ 100,000
Amount agreed for amending minimum annual order	$ 100,000
Tissue Processor Sub License Agreement [Member]
Loss Contingencies [Line Items]
Research and development expense				$ 1,000,000
Reimbursement for development cost			$ 300,000
Additional non-refundable royalty fee				$ 30,000
Additional non-refundable royalty fee payment description				2016 through 2019
Potential milestone payments				$ 10,200,000		10,200,000
Hydrogel License Agreement [Member]
Loss Contingencies [Line Items]
Research and development expense				3,200,000
Amount to be paid upon FDA approval				3,000,000		3,000,000
Tissue Regeneration License Agreement [Member]
Loss Contingencies [Line Items]
Research and development expense				800,000
Amount to be paid upon FDA approval				$ 300,000		$ 300,000
Percentage of royalty offsetting				50.00%
Minimum [Member] | Tissue Processor Sub License Agreement [Member]
Loss Contingencies [Line Items]
Non-refundable royalty fee				$ 20,000
Minimum [Member] | Tissue Regeneration License Agreement [Member]
Loss Contingencies [Line Items]
Non-refundable royalty fee				10,000
Waltham [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Construction allowances to total cost of tenant improvements				900,000
Lexington [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Construction allowances to total cost of tenant improvements				$ 1,000,000
Massachusetts [Member] | Waltham [Member]
Loss Contingencies [Line Items]
Effective date of amended lease				Jan. 31, 2018
Lease termination date				Dec. 31, 2024
Number of additional renewal terms | Option				1
Additional operating lease term				5 years		5 years
Massachusetts [Member] | Lexington [Member]
Loss Contingencies [Line Items]
Lease expiration period				2023
Number of additional renewal terms | Option				1
Additional operating lease term				5 years		5 years

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Minimum Annual Lease Commitments Under Non-Cancellable Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2019	$ 1,845
2020	1,892
2021	1,941
2022	1,991
2023	1,728
Thereafter	1,460
Total minimum lease payments	$ 10,857

Capital Stock - Additional Info

Capital Stock - Additional Information (Detail) - USD ($)	Sep. 29, 2016	Oct. 31, 2018	Jan. 31, 2018	Sep. 30, 2016	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Class of Warrants or right to purchase common stock, exercise price					$ 2.25
Minimum percentage of outstanding common stock					50.00%
Fair value of warrants					$ 8,400,000
Proceeds from issuance of common stock					$ 25,526,000
Common stock, shares authorized					100,000,000	100,000,000
Preferred stock, shares authorized					30,000
Minimum threshold percentage of beneficial common stock interest	4.99%
Maximum threshold percentage of beneficial common stock interest on holder's discretion	9.99%
Convertible preferred stock, terms of conversion					The Series A Preferred Stock shall not be converted if, after giving effect to the conversion, the holder and its affiliated persons would own beneficially more than 4.99% of our common stock (subject to adjustment up to 9.99% solely at the holder’s discretion upon 61 days’ prior notice to us or, solely as to a holder, if such limitation is waived by such holder upon execution of the private placement agreement).
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued	24,158.8693
Convertible preferred stock, shares outstanding					400.4910
Conversion of preferred stock in to common stock, preferred stock converted	10,737,275				444.44
Preferred stock par value					$ 0.01
Common Stock [Member]
Class of Stock [Line Items]
Shares issued			2,691,494		35,480,397
Common stock price per share			$ 2.35
Proceeds from issuance of common stock			$ 5,900,000
Common Stock [Member] | Series A Preferred Stock [Member]
Class of Stock [Line Items]
Conversion of preferred stock in to common stock, preferred stock converted					177,996
Underwritten Public Offering [Member]
Class of Stock [Line Items]
Class of Warrants or right to purchase common stock		19,616,250
Gross proceeds from offering, before deducting underwriting discounts and commissions and offering expenses		$ 17,000,000
Class of Warrants or right to purchase common stock, exercise price		$ 0.70
Warrants exercisable term		5 years
Underwritten Public Offering [Member] | Common Stock [Member]
Class of Stock [Line Items]
Shares issued		26,155,000
Underwritten Public Offering [Member] | Common Stock and Warrants [Member]
Class of Stock [Line Items]
Common stock price per share		$ 0.65
The Equity Distribution Agreement [Member] | Common Stock [Member]
Class of Stock [Line Items]
Shares issued					6,633,903
Proceeds from issuance of common stock					$ 4,500,000
The Equity Distribution Agreement [Member] | Common Stock [Member] | Maximum [Member]
Class of Stock [Line Items]
Aggregate offering price of shares					$ 10,000,000
Underwriter Option [Member]
Class of Stock [Line Items]
Shares issued			351,064
Private Placement [Member]
Class of Stock [Line Items]
Class of Warrants or right to purchase common stock				13,333,334
Common stock price per share				$ 2.25
Class of Warrants or right to purchase common stock, exercise price				$ 2.25	$ 2.25
Minimum percentage of outstanding common stock					50.00%
Fair value of warrants					$ 30,700,000
Gross proceeds from issuance of common stock, preferred stock and warrants				$ 30,000,000
Proceeds from issuance of common stock, preferred stock and warrants, net of issuance costs	$ 27,600,000			$ 27,600,000
Conversion of preferred stock in to common stock, preferred stock converted				10,737,275	444.44
Warrants granted to placement agent				133,333
Warrants granted to placement agent, exercise price				$ 2.25
Warrants expiry period					5 years
Warrants exercisable period					6 months
Preferred stock par value					$ 0.01
Private Placement [Member] | Members of Board of Directors [Member]
Class of Stock [Line Items]
Class of Warrants or right to purchase common stock					1,422,221
Class of Warrants or right to purchase common stock, exercise price					$ 2.25
Private Placement [Member] | Series A Preferred Stock [Member]
Class of Stock [Line Items]
Shares issued				24,158.8693
Convertible preferred stock, shares outstanding					400.4910
Private Placement [Member] | Series A Preferred Stock [Member] | Members of Board of Directors [Member]
Class of Stock [Line Items]
Shares issued					2,563.1439
Private Placement [Member] | Common Stock [Member]
Class of Stock [Line Items]
Shares issued				2,596,059
Private Placement [Member] | Common Stock [Member] | Members of Board of Directors [Member]
Class of Stock [Line Items]
Shares issued					283,046
Private Placement [Member] | Common Stock [Member] | Series A Preferred Stock [Member]
Class of Stock [Line Items]
Conversion of preferred stock in to common stock, preferred stock converted					177,996

Capital Stock - Schedule of Com

Capital Stock - Schedule of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock reserved for future issuance	36,484,699	15,791,418
Warrants Exercisable into Common Stock [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance	33,145,228	13,633,070
Stock Options [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance	3,339,471	2,158,348

Warrants - Schedule of Warrants

Warrants - Schedule of Warrants to Purchase Common Stock Outstanding (Detail)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Class of Warrant or Right [Line Items]
Exercise Price	$ 2.25
Warrants Issued October 2018 [Member]
Class of Warrant or Right [Line Items]
Issued	2018-10
Warrants Outstanding | shares	19,616,250
Exercise Price	$ 0.70
Expiration	2028-10
Warrants Issued September 2016 [Member]
Class of Warrant or Right [Line Items]
Issued	2016-09
Warrants Outstanding | shares	13,466,667
Exercise Price	$ 2.25
Expiration	2022-11
Warrants Issued March 2015 [Member]
Class of Warrant or Right [Line Items]
Issued	2015-03
Warrants Outstanding | shares	3,699
Exercise Price	$ 9.75
Expiration	2025-03
Warrants Issued July 2014 [Member]
Class of Warrant or Right [Line Items]
Issued	2014-07
Warrants Outstanding | shares	6,566
Exercise Price	$ 7.99
Expiration	2024-07
Warrants Issued July 2012 [Member]
Class of Warrant or Right [Line Items]
Issued	2012-07
Warrants Outstanding | shares	52,046
Exercise Price	$ 0.01
Expiration	2022-07

Warrants - Additional Informati

Warrants - Additional Information (Detail)	Mar. 31, 2019shares
Scenario, Forecast [Member] | 2016 Private Placement [Member]
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock	508,714

Equipment Loan Payable - Schedu

Equipment Loan Payable - Schedule of Outstanding Borrowing Obligations (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Debt Instrument [Line Items]
Less: current portion	$ (178)
Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Total debt	$ 178

Equipment Loan Payable - Additi

Equipment Loan Payable - Additional Information (Detail) - USD ($)	1 Months Ended
	Jul. 31, 2014	Dec. 31, 2018
Class of Warrant or Right [Line Items]
Exercise Price		$ 2.25
Silicon Valley Bank [Member]
Class of Warrant or Right [Line Items]
Amount of loan to purchase equipment	$ 1,800,000
Line of credit facility, interest rate, stated percentage	3.25%
Bank loan and security agreement, repayment period	36 months
Warrants Outstanding	6,566
Exercise Price	$ 7.99
Silicon Valley Bank [Member] | Prime Rate [Member]
Class of Warrant or Right [Line Items]
Amount of loan bears interest basis spread on variable rate	2.75%

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	Oct. 01, 2018	Jan. 01, 2018	Jan. 01, 2017	Jun. 16, 2016	Dec. 03, 2014	Oct. 31, 2014	Jul. 31, 2012	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to outstanding options								$ 2,300,000	$ 1,400,000
Intrinsic value of options exercised								$ 0	8,000
Weighted average grant date fair value of vested options								$ 0.76
Weighted average grant date fair value of options outstanding								$ 0.52
Stock-based compensation expense								$ 1,625,000	$ 1,573,000
Stock options granted								4,311,090
Stock options exercise price, lower range								$ 0.75628
Stock options exercise price, upper range								$ 9.97
Stock options reduced exercise price	$ 0.568
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, recognition period								2 years 6 months	1 year 8 months 12 days
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to restricted stock awards										$ 1,000
Stock-based compensation expense									$ 1,000
Stock Option Repricing [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options reduced exercise price	$ 0.568
2012 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance											609,389
Stock options vesting period							3 years
Term of stock options granted							10 years
2012 Equity Incentive Plan [Member] | First Anniversary of Original Vesting Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage							25.00%
2013 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting period						3 years
Term of stock options granted						10 years
2013 Equity Incentive Plan [Member] | EIP Amendment [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in authorized shares of common stock amount		982,841	825,904	300,000
Increase in authorized shares, percentage of common stock outstanding						4.00%
2013 Equity Incentive Plan [Member] | First Anniversary of Original Vesting Date [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options vesting percentage						25.00%
2013 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for issuance					103,665
Increase in authorized shares of common stock amount		51,832	206,476		51,832
Increase in authorized shares, percentage of common stock outstanding					1.00%
2013 Equity Incentive Plan and 2012 Equity Incentive Plan [Member] | Stock Option Repricing [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted	3,807,779

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity Under the 2012 and 2013 Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding Beginning Balance	2,158,348
Number of Options, Granted	4,311,090
Number of Options, Exercised	(919)
Number of Options, Cancelled	(3,129,048)
Number of Options, Outstanding Ending Balance	3,339,471	2,158,348
Number of Options, Vested and expected to vest outstanding	3,314,542
Number of Options, Exercisable	1,603,725
Weighted Average Exercise Price, Outstanding Beginning Balance	$ 4.40
Weighted Average Exercise Price, Granted	1.21
Weighted Average Exercise Price, Exercised	2.56
Weighted Average Exercise Price, Cancelled	3.60
Weighted Average Exercise Price, Outstanding Ending Balance	1.03	$ 4.40
Weighted Average Exercise Price, Vested and expected to vest outstanding	1.03
Weighted Average Exercise Price, Exercisable	$ 1.37
Weighted Average Remaining Contractual Term, Outstanding	8 years 1 month 6 days	8 years 1 month 6 days
Weighted Average Remaining Contractual Term, Vested and expected to vest outstanding	8 years 1 month 6 days
Weighted Average Remaining Contractual Term, Exercisable	7 years 1 month 6 days
Aggregate Intrinsic Value, Outstanding		$ 436

Stock-Based Compensation - Ad_2

Stock-Based Compensation - Additional Information about Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted-average grant date fair value per share of employee option grants within the year	$ 0.59	$ 1.02
Cash received upon exercise of options	$ 2	$ 6

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Stock-Based Compensation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,625	$ 1,573
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	488	411
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,137	$ 1,162

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Employee Stock Option Grants (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Risk-free interest rate	2.84%	2.03%
Expected volatility	84.40%	62.90%
Expected term (in years)	5 years 3 months 21 days	6 years 29 days
Expected dividend yield	0.00%	0.00%

Stock-Based Compensation - Su_4

Stock-Based Compensation - Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Non-Employee Stock Option Grants (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share Based Goods And Nonemployee Services Transaction [Abstract]
Risk-free interest rate	2.57%	1.29%
Expected volatility	88.30%	62.30%
Expected term (in years)	6 years 29 days	6 years 29 days
Expected dividend yield	0.00%	0.00%

Income Taxes - Components of Lo

Income Taxes - Components of Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S.	$ (8,503)	$ (26,275)
Foreign	(140)	(140)
Total	$ (8,643)	$ (26,415)

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Income Tax Expense (Benefit) Computed at Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal income tax (benefit) at statutory rate	21.10%	33.70%
(Increase) decrease income tax benefit resulting from:
State income tax benefit, net of federal benefit	22.50%	0.00%
Permanent differences	54.40%	(2.60%)
Net Operating Loss Limitation	0.00%	0.00%
Federal Tax Rate change	0.00%	(47.20%)
R&D Credit Limitation	0.90%	0.00%
Change in valuation allowance	(98.50%)	14.60%
Other	(0.40%)	1.50%
Income tax expense (benefit)	0.00%	0.00%

Income Taxes - Components of De

Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 24,941	$ 18,540
Depreciation and amortization	4,878	4,121
Accrued expenses	141	1,484
Capitalized start-up costs	9,143	7,942
R&D credits	312	243
Other	1,155	808
Deferred tax assets before valuation allowance	40,570	33,138
Valuation allowance	$ (40,570)	$ (33,138)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes Disclosure [Line Items]
Decrease in valuation allowance	$ (7,400,000)	$ (1,000,000)
Impact of a federal tax rate change		$ 11,500,000
NOL carry forwards, net of limitations	$ 52,900,000
Federal corporate income tax rate	21.10%	33.70%
Tax cuts and jobs act of 2017, deduction for net operating losses percentage of taxable income	80.00%
Income tax expense or benefit	$ 0
Unrecognized tax benefits	303,000	$ 303,000	$ 562,000
Accrued interest and penalties related to unrecognized tax benefits	0	0
Interest and penalties related to uncertain tax benefits	$ 0	0
Unrecognized tax benefits may be recognized by the end of 2018		0
Income tax examination description	The Company is subject to U.S. federal, state and local income tax examinations by tax authorities for years 2001 through present. Carryforward attributes that were generated in earlier periods remain subject to examination to the extent the year in which they were used or will be used remains open for examination. The tax years which remain subject to examination by tax authorities in Israel, as of December 31, 2018, include years 2014 through the present.
U.S. Federal [Member]
Income Taxes Disclosure [Line Items]
NOL carryforwards	$ 67,000,000	43,900,000
NOL carryforwards, expiration date	Dec. 31, 2037
U.S. State [Member]
Income Taxes Disclosure [Line Items]
NOL carryforwards	$ 66,900,000	43,600,000
NOL carryforwards, expiration date	Dec. 31, 2037
Foreign [Member]
Income Taxes Disclosure [Line Items]
NOL carryforwards	$ 26.2	$ 26.1

Income Taxes - Summary of Chang

Income Taxes - Summary of Changes In Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Unrecognized tax benefit, beginning of year	$ 303	$ 562
Increase (decrease) related to current year positions	0	(123)
Federal rate revision	0	(136)
Unrecognized tax benefit, end of year	$ 303	$ 303

Employee Benefits - Additional

Employee Benefits - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018USD ($)
Defined Contribution Plan Disclosure [Line Items]
Defined benefit plan contribution by employer	$ 0
Minimum [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan eligibility years of age for employees	21 years

Related Parties - Additional In

Related Parties - Additional Information (Detail) - Purpose, Co. [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2012
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement for development cost, amount			$ 0.3
Reimbursement for development cost, paid	$ 0.1	$ 0.1

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) $ / shares in Units, $ in Millions	Mar. 14, 2019	Jan. 23, 2019	Mar. 31, 2019USD ($)$ / sharesshares	Mar. 22, 2019Employee	Dec. 31, 2018$ / shares
Subsequent Event [Line Items]
Warrant exercise price					$ 2.25
Warrants Issued September 2016 [Member]
Subsequent Event [Line Items]
Warrant exercise price					2.25
Warrants Issued September 2016 [Member] | 2016 Exercise Agreement [Member]
Subsequent Event [Line Items]
Warrant exercise price					2.25
Warrants Issued October 2018 [Member]
Subsequent Event [Line Items]
Warrant exercise price					0.70
Warrants Issued October 2018 [Member] | 2018 Exercise Agreement [Member]
Subsequent Event [Line Items]
Warrant exercise price					$ 0.70
Subsequent Event [Member]
Subsequent Event [Line Items]
Percentage of workforce positions eliminated		65.00%
Effective date of restructuring	Mar. 22, 2019
Scenario, Forecast [Member]
Subsequent Event [Line Items]
One-time charge for severance and related expenses | $			$ 1.4
Maximum number of additional consultants employees to assist with continuing evaluation of strategic alternatives | Employee				4
Scenario, Forecast [Member] | Warrants Issued September 2016 [Member] | 2016 Exercise Agreement [Member]
Subsequent Event [Line Items]
Warrant exercise price			$ 0.01
Proceeds from warrant exercises | $			$ 0.1
Class of Warrants or right to purchase common stock | shares			508,714
Scenario, Forecast [Member] | Warrants Issued October 2018 [Member] | 2018 Exercise Agreement [Member]
Subsequent Event [Line Items]
Warrant exercise price			$ 0.01
Proceeds from warrant exercises | $			$ 0.2
Scenario, Forecast [Member] | Additional Second Restructuring [Member]
Subsequent Event [Line Items]
One-time charge for severance and related expenses | $			$ 2.2