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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Mar. 13, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
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	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		28,687,412
Entity Public Float			$ 14.9

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 7,081	$ 31,908
Marketable securities	900
Prepaid expenses and other current assets	194	173
Total current assets	8,175	32,081
Property and equipment, net	2,723	3,860
Restricted cash	137	137
Total assets	11,035	36,078
Current liabilities:
Accounts payable	776	1,588
Accounts payable due to Intrexon Corporation		360
Accrued expenses	2,705	2,097
Current portion of deferred rent	35	136
Current portion of deferred lease incentive	111	407
Current portion of equipment loan	178	583
Total current liabilities	3,805	5,171
Accrued expenses due to Intrexon Corporation	3,040	3,040
Deferred rent, long-term	280	315
Deferred lease incentive, long-term	499	610
Equipment loan, long-term		178
Warrant liability	14,679	13,197
Total liabilities	22,303	22,511
Commitments and contingencies (Note 7)
Convertible preferred stock and stockholders’ equity (deficit):
Convertible preferred stock, $0.01 par value; 30,000 shares authorized, 4,605.6533 and 13,416.4734 shares issued and outstanding at December 31, 2017 and 2016, respectively
Common stock, $0.01 par value; 100,000,000 shares authorized, 24,571,029 and 20,647,612 shares issued and outstanding at December 31, 2017 and 2016, respectively	159	159
Additional paid-in capital	196,760	195,181
Accumulated deficit	(208,187)	(181,773)
Total stockholders’ equity (deficit)	(11,268)	13,567
Total liabilities and stockholders’ equity (deficit)	$ 11,035	$ 36,078

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
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	24,571,029	20,647,612
Common stock, shares outstanding	24,571,029	20,647,612
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	4,605.6533	13,416.4734
Convertible preferred stock, shares outstanding	4,605.6533	13,416.4734

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Revenue	$ 0	$ 0
Operating expenses:
Research and development	15,566	21,577
General and administrative	9,384	8,530
Impairment of intangible asset		200
Total operating expenses	24,950	30,307
Loss from operations	(24,950)	(30,307)
Other income (expense):
Interest Income (expense), net	134	(60)
Other expense, net	(116)	(248)
Warrant expense		(3,100)
Change in fair value of warrant liability	(1,482)	17,507
Total other income (expense), net	(1,464)	14,099
Net loss	(26,414)	(16,208)
Loss attributable to common stockholders—basic	(22,499)	(13,863)
Loss attributable to common stockholders—diluted	$ (22,499)	$ (31,370)
Loss per common share—basic	$ (0.99)	$ (0.97)
Loss per common share—diluted	$ (0.99)	$ (2.18)
Weighted-average shares used to compute loss per common share—basic	22,669,819	14,256,954
Weighted-average shares used to compute loss per common share—diluted	22,669,819	14,389,192

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, 2015	$ 28,198		$ 132	$ 193,631	$ (165,565)
Beginning Balance, Shares at Dec. 31, 2015			13,268,280			5,190
Stock-based compensation expense	1,548			1,548
Exercise of common stock options	3		$ 1	2
Exercise of common stock options, Shares			3,685
Vesting of restricted stock, Shares			3,301			(3,301)
Issuance of common stock related to private placement	26		$ 26
Issuance of common stock related to private placement, Shares			2,596,059
Issuance of Series A convertible preferred stock, Shares		24,159
Conversion of Series A convertible preferred stock, Shares		(10,743)	4,774,398
Net loss	(16,208)				(16,208)
Ending Balance at Dec. 31, 2016	13,567		$ 159	195,181	(181,773)
Ending Balance, Shares at Dec. 31, 2016		13,416
Ending 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		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

Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
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 Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (26,414)	$ (16,208)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,534	1,673
Amortization of discount of investments	54
Deferred rent and lease incentive	(543)	(533)
Impairment of intangible asset		200
Stock-based compensation	1,573	1,548
Change in fair value of warrant	1,482	(17,507)
Warrant expense in connection with private placement		3,100
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(21)	148
Accrued expenses due to Intrexon Corporation		1,494
Accounts payable	(849)	(435)
Accounts payable due to Intrexon Corporation	(360)	131
Accrued expenses	524	653
Net cash used in operating activities	(23,020)	(25,736)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(276)	(320)
Proceeds from maturities of marketable securities	7,050
Purchases of marketable securities	(8,004)
Net cash used in investing activities	(1,230)	(320)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, preferred stock, and warrants in connection with private placement, net of issuance costs		27,630
Repayments on equipment term loan	(583)	(583)
Proceeds from exercise of stock options	6	2
Net cash provided by financing activities	(577)	27,049
Net increase (decrease) in cash and cash equivalents	(24,827)	993
Cash and cash equivalents—Beginning of period	31,908	30,915
Cash and cash equivalents—End of period	7,081	31,908
Supplemental Disclosure of Non-Cash Items:
Fair market value of private placement warrants at issuance		30,704
Supplemental Disclosure of Cash Flow information:
Cash paid for taxes	197	257
Cash paid for interest	$ 30	$ 66

Nature of Business

12 Months Ended

Dec. 31, 2017

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 is a leader in the development of restorative cell therapies (“RCTs”). RCTs refer to a new class of products the Company is developing that are designed to offer patients rapid-onset pain relief and restored function through the repair of damaged or worn tissue. NeoCart, the Company’s lead investigational product, is an innovative cell therapy that utilizes various aspects of the Company’s RCT technology platform to treat tissue injury in the field of orthopedics, specifically cartilage damage in the knee. NeoCart is designed to rebuild a patient’s own knee cartilage to treat pain at the source, improve function and potentially prevent a patient’s progression to osteoarthritis. NeoCart is one of the most rigorously studied restorative cell therapies for orthopedic use and is currently in a 249 patient, Phase 3 clinical trial in the United States (the “U.S.”) under a special protocol assessment with the U.S. Food and Drug Administration (the “FDA”). Patient enrollment in this trial is complete with top-line, one-year superiority data expected in the third quarter of 2018, with a potential Biologics License Application (“BLA”) submission expected in the third quarter of 2018, subject to successful Phase 3 clinical trial results

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 was $27.6 million. See Note 8, Capital Stock, for further discussion of the private placement.

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 from its planned principal operations. Expenses have primarily been for research and development and related administrative costs.

The Company is subject to a number of risks. The developmental nature of its activities is such that significant inherent risks exist in the Company’s operations. Principal among these risks are the successful development of therapeutics, successfully enrolling patients in its clinical trials in a timely manner, ability to obtain adequate financing, obtaining regulatory approval for any of its product candidates in any jurisdiction, obtaining adequate reimbursement rates for any of its approved product candidates, compliance with government regulations, protection of proprietary therapeutics, fluctuations in operating results, dependence on key personnel and collaborative partners, adoption of the Company’s products by the physician community, rapid technological changes inherent in the markets targeted, 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, 2017 of $208.2 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 next several years. The Company believes that its existing cash, cash equivalents and marketable securities will only be sufficient to fund its projected cash needs into the fourth quarter of 2018. Accordingly, these factors, among others, raise substantial doubt about the Company’s ability to continue as a going concern. The Company will require additional capital to commercialize NeoCart, if approved, and for the future development of its existing product candidates. To meet its capital needs, the Company intends to raise additional capital through debt or equity financing or other strategic transactions. However, any such financing may not be on favorable terms or available to the Company. 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 Accounting Policies

12 Months Ended

Dec. 31, 2017

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.

Reclassifications

The Company has reclassified certain prior period amounts to conform to the current period presentation. The amounts reclassified impact Accounts Payable and Accounts Payable due to Intrexon Corporation (“Intrexon”) for the year ended December 31, 2016. These reclassifications have no effect on the previously reported net loss.

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 and intangible 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’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. The fair value hierarchy gives the highest priority to quoted prices in active markets (observable inputs) and the lowest priority to the Company’s assumptions (unobservable inputs). 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 and minimize the use of unobservable inputs 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, 2017 and 2016 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. Other than the warrants issued in connection with the private placement transaction which closed on September 29, 2016, the Company had no assets or liabilities classified as Level 3 as of December 31, 2017 and 2016. Transfers are calculated on values as of the transfer date. There were no transfers between Levels 1, 2 and 3 during the twelve months ended December 31, 2017 and 2016.

The fair value of the warrants 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. See Note 8, Capital Stock, for further discussion of the private placement.

Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
	(in thousands)
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
December 31, 2016
Assets:
Money market funds		30,318		30,318		-		-
Liabilities:
Warrant liability		13,197		-		-		13,197

The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs:

	As of December 31, 2017
	(in thousands)
Beginning balance, January 1, 2017	$	13,197
Change in fair value of warrant liability		1,482
Ending balance	$	14,679

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 following table summarizes the available for sale securities held at December 31, 2017:

			Unrealized		Unrealized
Description	Amortized Cost		Gains		Losses		Fair Value
			(in thousands)
Asset-backed securities	$	900	$	-	$	-	$	900
Total	$	900	$	-	$	-	$	900

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, 2017, 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. There were no sales of available for sale securities during the year ended December 31, 2017.

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. 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 will be 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. While the Company’s current and historical operating losses and negative cash flows are indicators of impairment, management believes that future cash flows to be received support the carrying value of its long-lived assets.

Impairments, if any, are recognized in earnings. An impairment loss would be recognized in an amount equal to the excess of the carrying amount over the undiscounted expected future cash flows.

Intangible Asset

The Company’s intangible asset consists of acquired in-process research and development (“IPR&D”) obtained through the acquisition of ProChon. IPR&D represents the fair value assigned to research and development assets that have not been completed at the date of acquisition. The value assigned to acquired IPR&D is determined by estimating the costs to develop the acquired technology into commercially viable products, estimating the resulting revenue from the projects, and discounting the net cash flows to present value. The revenue and costs projections used to value acquired IPR&D were adjusted based on the probability of success of developing a new product. Additionally, the projections considered the relevant market sizes and growth factors, expected trends in technology and the nature and expected timing of new product introductions by the Company and its competitors. The rates utilized to discount the net cash flows to their present value were commensurate with the stage of development of the projects and uncertainties in the economic estimates used in the projections described above.

IPR&D is considered an indefinite-lived intangible asset and is assessed for impairment annually or more frequently if impairment indicators exist. When performing the impairment assessment, the Company first assesses qualitative factors to determine whether it is necessary to recalculate the fair value of its acquired IPR&D. If the Company believes, as a result of the qualitative assessment, that it is more likely than not that the fair value of acquired IPR&D is less than its carrying amount, it calculates the fair value using the same methodology as described above. If the carrying value of the Company’s acquired IPR&D exceeds its fair value, then an impairment charge is taken and the intangible asset is written-down to its fair value. During the fourth quarter the Company deemed the value of the IPR&D to be zero for the year ended December 31, 2016 as it had no plans to advance the technology or use it in any future clinical development activities. The result was a write-off of $0.2 million for the year ended December 31, 2016. The Company performed its annual impairment test of its IPR&D as of December 31, 2016 using an income approach, including a discount rate of 13%, applied to probability-adjusted after-tax cash flows. The Company believes that the assumptions are representative of those a market participant would use in estimating the fair value of the IPR&D.

Intangible asset, net of accumulated impairment charges, are summarized as follows:

	As of December 31, 2017							As of December 31, 2016
	Cost		Accumulated Impairment			Net Book Value		Cost		Accumulated Impairment			Net Book Value
	(in thousands)							(in thousands)
IPR&D	$	630	$	(630	)	$	-	$	630	$	(630	)	$	-
	$	630	$	(630	)	$	-	$	630	$	(630	)	$	-

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 facility and its Lexington, Massachusetts facility 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 (“ASU”) No. 2014-09, Revenue from Contracts with Customers. This new accounting standard will replace most current U.S. GAAP guidance on this topic and eliminate most industry-specific guidance. It provides a unified model to determine when and how revenue is recognized. The core principle is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration for which the entity expects to be entitled in exchange for those goods or services. Entities may adopt the new standard either retrospectively to all periods presented in the financial statements (the full retrospective method) or as a cumulative-effect adjustment as of the date of adoption (modified retrospective method) in the year of adoption without applying to comparative years’ financial statements. Further, in August 2015, the FASB issued ASU No. 2015-14, Revenue from Contracts with Customers: Deferral of the Effective Date, to defer the effective adoption date by one year to December 15, 2017 for annual reporting periods beginning after that date and permitted early adoption of the standard, but not before fiscal years beginning after the original effective date of December 15, 2016. The Company elected to early adopt the guidance in 2017 using the modified retrospective method.

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 sale; and fees for manufacturing supply services. None of the Company's contracts as of December 31, 2017 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, 2017, the Company expects to generate its revenue through 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.

In December 2017 the Company entered into the License and Commercialization Agreement (the “License Agreement”) with MEDINET Co. (“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 upfront cash payment of $10.0 million which the Company had not received as of December 2017. As of December 31, 2017, 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 ($2.9 million as of December 31, 2017) in development milestone payments, $1.0 million and ¥720 million ($7.4 million as of December 31, 2017)in regulatory payments and up to an aggregate of ¥7,100 million ($62.8 million as of December 31, 2017) 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 end of the clinical trial period. 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 a 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 for such services or another vendor. 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 that 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 expected to be 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 trials 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 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, 2017, the aggregate amount of the transaction price allocated to 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, 2017 and 2016, respectively. The Company expects to recognize revenue on approximately 25% and 100% of the remaining performance obligations over the next 12 months and 13 to 21 months, respectively.

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. Refer to Note 14, Related Parties for further details on all terms, conditions and exceptions of this collaboration.

License Agreements

Costs associated with licenses of technology are expensed as incurred and are included in research and development expenses.

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

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 2016 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.

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.

Earnings (Loss) per Common Share

Earnings (loss) per common share is calculated using the two-class method, which is an earnings allocation formula that determines earnings (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 earnings (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 earnings (loss) per share if their effect is antidilutive.

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 the Monte Carlo simulation 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.

Recent Accounting Pronouncements

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 March 2016, the FASB issued ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Shared-Based Payment Accounting. This standard provides guidance on accounting for employee share-based payments. This guidance addresses several aspects of the accounting for share-based payment award transactions, including: (a) income tax consequences; (b) classification of awards as either equity or liabilities; and (c) classification on the statement of cash flows. This standard will be effective for fiscal years beginning after December 15, 2016, including interim periods within those fiscal years. The Company has concluded that this guidance has no material impact on the presentation of its results of operations, financial position and disclosures.

In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements—Going Concern (Subtopic 2015-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. This guidance addresses management’s responsibility in evaluating whether there is substantial doubt about a company’s ability to continue as a going concern and to provide related footnote disclosures. The guidance is effective for fiscal years ending after December 15, 2016 and for interim periods within those fiscal years. The Company adopted this guidance in the fourth quarter of 2016 and made the relevant disclosures in the consolidated financial statements and related footnotes.

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 2, Revenue Recognition.

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 for annual periods beginning after December 15, 2017, and for interim periods and annual periods thereafter. 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 November 2016, the FASB issued guidance that requires restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the total beginning and ending amounts for the periods shown on the statement of cash flows. The new standard is effective for the Company on January 1, 2018 using a retrospective transition method to each period presented. Early adoption is permitted. We are currently evaluating the timing of our adoption and the expected impact that this standard could have on our consolidated financial statements and related disclosures.

In February 2016, the FASB, issued ASU No. 2016-02, Leases (Topic 842). The ASU 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 is currently evaluating the impact that the adoption of ASU 2016-02 will have on the Company’s consolidated financial statements or related disclosures.

Loss Per Common Share

12 Months Ended

Dec. 31, 2017

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
	2017			2016
	(In thousands, except share and per share data)
Numerator:
Net loss	$	(26,414	)	$	(16,208	)
Net Loss attributable to Series A Preferred Stock (a)		(3,915	)		(2,345	)
Numerator for basic EPS - Earnings (loss) attributable to common stockholders	$	(22,499	)	$	(13,863	)
Effect of dilutive securities:
Deduct change in fair value of warrant liability	$	-		$	(17,507	)
Numerator for diluted EPS - Earnings (loss) attributable to common stockholders after assumed conversions	$	(22,499	)	$	(31,370	)
Denominator:
Weighted-average number of common shares used in earnings (loss) per share - basic		22,669,819			14,256,954
Effect of dilutive securities:
Nonparticipating warrants		-			132,238
Denominator for diluted EPS - adjusted weighted average shares		22,669,819			14,389,192
Earnings (loss) per share - basic	$	(0.99	)	$	(0.97	)
Earnings (loss) per share - diluted	$	(0.99	)	$	(2.18	)

(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,
	2017		2016
Unvested restricted stock and options to purchase common stock		2,158,348		1,578,905
Series A preferred stock unconverted		2,046,957		5,962,817
Warrants exercisable into common stock		13,633,070		166,403

Prepaid Expenses and Other Current Assets

12 Months Ended

Dec. 31, 2017

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,
	2017		2016
	(in thousands)
Deposits	$	10	$	10
Insurance		72		95
Other current assets		112		68
Prepaid expenses and other current assets	$	194	$	173

Property and Equipment

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Property and Equipment

5.	PROPERTY AND EQUIPMENT

Property and equipment consisted of the following:

	December 31,			December 31,
	2017			2016
	(in thousands)
Office equipment	$	279		$	266
Laboratory equipment		4,565			4,443
Leasehold improvements		7,712			7,683
Construction in progress		990			759
Software		96			96
Total property and equipment		13,642			13,247
Less: accumulated depreciation		(10,919	)		(9,387	)
Property and equipment, net	$	2,723		$	3,860

Depreciation expense related to property and equipment amounted to $1.5 million and $1.7 million for the years ended December 31, 2017 and 2016, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2017

Payables And Accruals [Abstract]

Accrued Expenses

6.	ACCRUED EXPENSES

Accrued expenses consisted of the following:

	As of December 31,
	2017		2016
	(in thousands)
Accrued compensation	$	1,671	$	1,402
Accrued clinical expenses		199		187
Accrued other		835		508
Total accrued expenses	$	2,705	$	2,097

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

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. The Company’s wholly-owned subsidiary, ProChon, leased a facility in Woburn, Massachusetts which expired in 2016 and was not renewed.

Aggregate minimum annual lease commitments of the Company under its non-cancellable operating leases as of December 31, 2017, are as follows:

For the Year Ended December 31,
	(in thousands)
2018	$	1,798
2019		1,845
2020		1,892
2021		1,941
2022		1,991
Thereafter		3,188
Total minimum lease payments	$	12,655

Rent expense under operating lease agreements amounted to $1.0 million and $1.0 million for the years ended December 31, 2017 and 2016, 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, 2017, 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, 2017, 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.

Honeycomb License

In March 2013, the Company entered into a license agreement with Koken Co., Ltd. (“Koken”) and paid a fee for a non-exclusive, non-transferable and non-sublicensable right to use its know-how related to the process for manufacturing atelocollagen honeycomb sponge materials, which is used in scaffolds (the “Honeycomb License Agreement”). Under the terms of the Honeycomb License Agreement, future commitments will be based on the amount of materials supplied to the Company and may vary from period to period over the term of the agreement.

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, 2017, 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.

The OCS Agreement

In connection with its research and development, the Company received grants from the Office of Chief Scientist of the Ministry of Industry and Trade in Israel (“OCS”) in the aggregate of $1.1 million for funding the fibroblast growth factor (“FGF”) program. In consideration for this grant, the Company is committed to pay royalties at a rate of 3% to 5% of the sales of sponsored products developed using the grant money, up to the amount of the participation payments received. The Company committed to pay up to 100% of grants received plus interest according to the LIBOR interest rate if the sponsored product is produced in Israel. If the manufacturing of the sponsored product takes place outside of Israel, the royalties can increase up to, but no more than, 300% of grants received plus interest based on the LIBOR interest rate, depending on the percentage of the manufacturing of sponsored product that takes place outside of Israel.

Engineering Agreement

The Company entered into an agreement with a development corporation to purchase a multi-unit bioreactor system. Pursuant to the agreement, as of December 31, 2017, the Company made total payments in an aggregate amount of $0.6 million of which $0.2 million was made in 2016 after acceptance of the final product. There are no additional payments due under this agreement.

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. In February 2017, the Company entered into an amendment with the Supplier. Pursuant to the amendment, the Company agreed to pay the Supplier approximately $0.1 million in exchange for eliminating the minimum annual order of material and/or services and any other amounts due Supplier. The payment of $0.1 million will be made over the 18 months following the date of the amendment. As of December 31, 2017, the Company has paid $30 thousand under the terms of the amendment. The remaining amount of $70 thousand is expected to be paid over the next 6 months.

Capital Stock

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Capital Stock

8.	CAPITAL STOCK

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, 2017, there were 4,605.6533 shares of Series A Preferred Stock outstanding, which remain convertible into 2,046,957 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 and approximately $0.4 million excess of the fair value of the liability recorded for these warrants over the proceeds received was recorded as a charge to earnings in the third quarter of 2016 and is included in warrant expense within the consolidated statement of operations. In connection with the Private Placement, the Company incurred $3.1 million in warrant expense within the consolidated statements of operations.

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,
	2017		2016
Vesting of restricted stock		-		1,889
Options to purchase common stock		2,158,348		1,577,016
Common stock warrants		13,633,070		13,633,070
Total		15,791,418		15,211,975

Preferred Stock-30,000 shares authorized

Series 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).

Warrants

12 Months Ended

Dec. 31, 2017

Warrants And Rights Note Disclosure [Abstract]

Warrants

WARRANTS

Investor Warrants

In September 2016, in connection with the Private Placement, the Company issued common stock warrants to the investors to purchase up to 13,333,334 shares of our common stock at an exercise price of $2.25 per share. The warrants include a cashless-exercise feature that may be exercised solely in the event there is no effective registration statement registering, 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. 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 warrants were valued at $2.28 per share using a Monte Carlo simulation and are marked-to-market on a quarterly basis with the change in value recorded as warrant expense or income on the consolidated statements of operations.

Placement Agent Warrants

In September 2016, in connection with the Private Placement, the Company issued HCW and certain of its affiliates warrants for the purchase of 133,333 shares of common stock at an exercise price of $2.25 per share. The HCW 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 warrants were valued at $2.28 per share using a Monte Carlo simulation and are marked-to-market on a quarterly basis with the change in value recorded as warrant expense or income on the consolidated statements of operations.

Affiliates of an Advisor Warrant

On July 20, 2012, the Company issued a warrant to purchase its common stock to affiliates of an advisor. The warrant provides the holders with the right to purchase an aggregate of 161,977 shares of the Company’s common stock at a per share exercise price of $0.01. The warrants are exercisable, in whole or in part, immediately upon issuance and may be exercised on a cashless basis. The warrants expire on the tenth anniversary of issuance. The fair value of the warrants as of July 20, 2012 was estimated using the OM with the following inputs: (a) risk-free interest rate of 0.22%; (b) implied volatility of the Company’s common stock of 99%; and (c) the expected term to a liquidity event of 1.7 years. On December 3, 2014, the Company completed its IPO and warrants for 5,839 shares of common stock were surrendered and common stock was issued by the Company to Purpose, Co. for the warrant shares surrendered. As of December 31, 2017 and 2016, warrants to purchase an aggregate of 156,138 shares of the Company’s common stock at an exercise price of $0.01 are outstanding.

Equipment Line of Credit Warrant

In July 2014, the Company granted Silicon Valley Bank a warrant to purchase 6,566 shares of common stock at a per share exercise price of $7.99 as discussed in Note 10. The warrant is exercisable, in whole or in part, immediately and may be exercised on a cashless basis and expires on the tenth anniversary of issuance. The fair value of the warrant as of July 9, 2014 was estimated at $51 thousand with the following inputs: (a) risk-free interest rate of 2.58%; (b) implied volatility of the Company’s common stock of 87%; (c) the expected term of 10 years. The fair value of the warrant was recorded as a debt issuance cost with a corresponding credit to additional paid-in capital.

Consulting Agreement Warrant

In March 2015, in connection with a consulting agreement entered into for an interim chief financial officer, the Company issued a common stock warrant as compensation to the consulting firm. The warrant provides the holder with the right to purchase an aggregate of 7,398 shares of the Company’s common stock at a per share exercise price of $9.75, the closing price of the Company’s common stock on the date of issuance. The warrant vested and became exercisable in monthly installments over 24 months beginning September 30, 2015 and expires on the tenth anniversary of issuance. The warrant is equity classified and accounted for using the fair value approach. The fair value of the warrant is estimated using the Black-Scholes option pricing model and is subject to re-measurement at each reporting period until the measurement date is reached. On December 21, 2016, the Company terminated the consulting agreement resulting in the forfeiture of 50% (3,699) of the shares eligible for exercise under the warrant. The remaining 3,699 shares were vested and exercisable on December 31, 2017 and December 31, 2016.

Equipment Loan Payable

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Equipment Loan Payable

10.	EQUIPMENT LOAN PAYABLE

As of December 31, 2017 and 2016, the Company had the following outstanding borrowing obligations:

	December 31,			December 31,
	2017			2016
	(in thousands)
Silicon Valley Bank Equipment Loan Payable	$	178		$	761
Less: current portion		(178	)		(583	)
Long-term debt, net	$	-		$	178

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.

As of December 31, 2017 and 2016, $0.2 and $0.8 million respectively, of borrowings were outstanding under the line of credit and the Company was in compliance with all required covenants.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2017

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 will be 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, 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, 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 982,841 shares effective January 1, 2017. 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 51,832 shares effective January 1, 2017. 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 2017 and 2016.

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, 2016		1,577,016		$	5.95		8.4	$	71
Granted		910,950			1.74
Exercised		(7,497	)		0.76
Cancelled		(322,121	)		4.52
Outstanding at December 31, 2017		2,158,348		$	4.40		8.1	$	436
Vested and expected to vest at December 31, 2017		1,968,878		$	4.54		8.1	$	390
Exercisable at December 31, 2017		958,201		$	5.78		7.4	$	153

As of December 31, 2017 and 2016, the unrecognized compensation cost related to outstanding options was $1.4 million and $2.6 million, respectively, and is expected to be recognized as expense over approximately 1.70 years and 2.01 years, respectively. The intrinsic value of options exercised during the years ended December 31, 2017 and 2016 was $8 thousand and $10 thousand, respectively.

As of December 31, 2017, the weighted average grant date fair value of vested options was $3.92 and the weighted average grant date fair value of options outstanding was $2.72.

Additional information about the Company’s stock option activity is as follows:

	Year Ended December 31,
	2017		2016
Weighted-average grant date fair value per share of employee option grants within the year	$	1.02	$	1.26
Cash received upon exercise of options		6		3

Restricted stock awards under the 2012 and 2013 plans are summarized as follows:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2016		1,889		$	0.83
Vesting of restricted stock		(1,889	)
Unvested at December 31, 2017		-		$	-

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, 2017 and 2016. 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 $1.5 million for the years ended December 31, 2017 and 2016, respectively. Included in the table below is restricted stock-based compensation expense of $1 thousand and $2 thousand, respectively, recorded in general and administrative expense during the years ended December 31, 2017 and 2016.

Stock-based compensation is as follows:

	Year Ended December 31,
	2017		2016
	(in thousands)
Research and development	$	411	$	491
General and administrative		1,162		1,057
Total stock-based compensation expense	$	1,573	$	1,548

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,
	2017			2016
Risk-free interest rate		2.03	%		1.73	%
Expected volatility		62.9	%		72.5	%
Expected term (in years)		6.08		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,
	2017			2016
Risk-free interest rate		1.29	%		1.57	%
Expected volatility		62.3	%		63.5	%
Expected term (in years)		6.08			7.0
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, 2017 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.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

12.	INCOME TAXES

For the years ended December 31, 2017 and 2016, 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,
		2017			2016
	(in thousands)
U.S.		$	(26,275	)	$	(15,838	)
Foreign			(140	)		(369	)
Total		$	(26,415	)	$	(16,207	)

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,
	2017			2016
Federal income tax (benefit) at statutory rate		33.9	%		34.0	%
(Increase) decrease income tax benefit resulting from:
Permanent differences		(2.6	)%		29.0	%
Net Operating Loss Limitation		0.0	%		(111.1	)%
Federal Tax Rate change		(47.5	)%		0.0	%
R&D Credit Limitation		0.0	%		(1.5	)%
Change in valuation allowance		14.7	%		48.7	%
Other		1.5	%		0.9	%
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,
	2017			2016
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	18,540		$	16,146
Depreciation and amortization		4,121			6,229
Accrued expenses		2,304			2,082
Capitalized start-up costs		7,942			10,037
R&D credits		243			75
Other		(12	)		-
Deferred tax assets before valuation allowance		33,138			34,569
Valuation allowance		(33,138	)		(34,569	)
		-			-
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, 2017 and 2016, 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, 2017 and 2016. 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. The valuation allowance decreased by $15.7 million during the year ended December 31, 2016, due primarily to net operating losses generated and capitalized expenses. 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, 2017 and 2016, the Company had U.S. federal NOL carryforwards of $43.9 million and $24.5 million respectively, which may be available to offset future income tax liabilities and expire at various dates through 2037. As of December 31, 2017 and 2016, the Company also had U.S. state NOL carryforwards of $43.6 million and $24.3 million respectively, which may be available to offset future income tax liabilities and expire at various dates through 2037. At December 31, 2017 and 2016, the Company also had $26.3 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 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% for federal tax purposes. The remeasurement of the Company’s deferred tax assets and liabilities was offset by a change in the valuation allowance. . Treasury is expected to issue guidance which clarifies provisions of TCJA. Additionally, state taxing agencies may issue guidance in application of the Act. The provisional amount of zero recorded as of December 31, 2017 may change as a result of additional guidance issued by one or more taxing authority.

The changes in the Company’s unrecognized tax benefits are summarized as follows:

	As of December 31,
	2017			2016
	(in thousands)
Unrecognized tax benefit, beginning of year	$	562		$	687
Increase (decrease) related to current year positions		(123	)		(125	)
Federal rate revision		(136	)		-
Unrecognized tax benefit, end of year	$	303		$	562

As of December 31, 2017 and 2016, the total amount of unrecognized tax benefits was $0.3 million and $0.6 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, 2017 and 2016. The Company believes that it is reasonably possible that none of its unrecognized tax benefits, may be recognized at the end of 2017. 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, 2017, include years 2013 through the present.

Employee Benefits

12 Months Ended

Dec. 31, 2017

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

12 Months Ended

Dec. 31, 2017

Related Parties

14.	RELATED PARTIES

Intrexon Corporation

In September 2014, the Company entered into an Exclusive Channel Collaboration agreement with Intrexon (the “Collaboration Agreement”) to use Intrexon’s proprietary technology for the development and commercialization of allogeneic cell therapeutics (the “Collaboration Products”) to treat or repair damaged articular hyaline cartilage in humans. The term of the Collaboration Agreement commenced upon the effective date, September 30, 2014, and continues until either written notice of termination is given by the Company within ninety days, or if either party creates a material breach that cannot be remedied within sixty days.

Under the terms of the Collaboration Agreement, the Company is solely responsible for the costs to develop and commercialize any Collaboration Products with the following exceptions: (i) the establishment of certain manufacturing capabilities and facilities; (ii) the cost of basic research related to Intrexon’s proprietary technology outside of costs related to the Collaboration Products; (iii) payments related to certain in-licensed third party IP; (iv) the costs of filing, prosecution and maintenance of Intrexon patents; and (v) any other costs mutually agreed upon as being the responsibility of Intrexon. As partial consideration, the Company will pay commercialization milestones totaling $12 million, if and when achieved, and sales milestones totaling $22.5 million, if and when achieved. The milestone payments are payable in cash or shares of the Company’s common stock at the option of the Company. In the event the Company is sold prior to making any of these milestone payments and the Collaboration Agreement is transferred in the sale, the milestone payments would be payable in cash. The Company is also required to make low double digit royalty payments to Intrexon on any gross profit arising from the sale of Collaboration Products and to pay an intermediate double digit percentage of any sublicensing revenue it receives.

Under the terms of the Collaboration Agreement, the Company reimburses Intrexon for 50% of the product research and development costs with the remaining 50% due after acceptance by the FDA or equivalent regulatory authority of an Investigational New Drug Application or equivalent regulatory filing of a collaboration product or upon 90 day written notice of cancellation by the Company. Total incurred expenses were $0 and $3.0 million for the year ended December 31, 2017 and 2016, respectively. The total accrued expenses due Intrexon at December 31, 2017 and December 31, 2016 was $3.0 million and $3.0 million, respectively. Amounts are reflected as current liabilities in the consolidated balance sheet as of December 31, 2016. Amounts have been reclassified to long term liabilities in the consolidated balance sheet as of December 31, 2017, as a result of a change in circumstances, including the plans for products that we are developing as a part of the Exclusive Channel Collaboration with Intrexon. These expenses were included in research and development in the consolidated statement of operations.

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, 2017 and 2016, 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

12 Months Ended

Dec. 31, 2017

Subsequent Events [Abstract]

Subsequent Events

15.	SUBSEQUENT EVENTS

On January 5, 2018, the Company received a $10 million upfront payment from MEDINET pursuant to the License Agreement entered into with MEDINET that became effective December 21, 2017.

On January 25, 2018, the Company closed an underwritten registered direct offering of 2,691,494 shares of its common stock, which included 351,064 shares sold in connection with the exercise in full by the underwriter of its option to purchase additional shares. The total net proceeds of the offering were approximately $5.9 million after deducting the underwriting discounts and commissions payable by the Company.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Accounting

Reclassifications

Use of Estimates

Foreign Currency Translation

Segment and Geographic Information

Fair Value Measurements

Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date of identical, unrestricted assets.

Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
	(in thousands)
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
December 31, 2016
Assets:
Money market funds		30,318		30,318		-		-
Liabilities:
Warrant liability		13,197		-		-		13,197

The following table provides a reconciliation of all liabilities measured at fair value using Level 3 significant unobservable inputs:

	As of December 31, 2017
	(in thousands)
Beginning balance, January 1, 2017	$	13,197
Change in fair value of warrant liability		1,482
Ending balance	$	14,679

Cash and Cash Equivalents

Marketable Securities

The following table summarizes the available for sale securities held at December 31, 2017:

			Unrealized		Unrealized
Description	Amortized Cost		Gains		Losses		Fair Value
			(in thousands)
Asset-backed securities	$	900	$	-	$	-	$	900
Total	$	900	$	-	$	-	$	900

Concentration of Credit Risk

Property and Equipment

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

Impairment of Long-Lived Assets

Impairments, if any, are recognized in earnings. An impairment loss would be recognized in an amount equal to the excess of the carrying amount over the undiscounted expected future cash flows.

Intangible Asset

Intangible asset, net of accumulated impairment charges, are summarized as follows:

	As of December 31, 2017							As of December 31, 2016
	Cost		Accumulated Impairment			Net Book Value		Cost		Accumulated Impairment			Net Book Value
	(in thousands)							(in thousands)
IPR&D	$	630	$	(630	)	$	-	$	630	$	(630	)	$	-
	$	630	$	(630	)	$	-	$	630	$	(630	)	$	-

Restricted Cash

Deferred Rent

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

Revenue Recognition

Collaboration Revenue

License and Collaboration Arrangements

MEDINET Co.

Transaction Price Allocated to Future Performance Obligations

Research and Development Costs

Collaboration Arrangements

License Agreements

Costs associated with licenses of technology are expensed as incurred and are included in research and development expenses.

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

Income Taxes

Earnings (Loss) per Common Share

Warrant Accounting

Recent Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis

Description	Total		Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
	(in thousands)
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
December 31, 2016
Assets:
Money market funds		30,318		30,318		-		-
Liabilities:
Warrant liability		13,197		-		-		13,197

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, 2017
	(in thousands)
Beginning balance, January 1, 2017	$	13,197
Change in fair value of warrant liability		1,482
Ending balance	$	14,679

Summary of Available for Sale Securities

The following table summarizes the available for sale securities held at December 31, 2017:

			Unrealized		Unrealized
Description	Amortized Cost		Gains		Losses		Fair Value
			(in thousands)
Asset-backed securities	$	900	$	-	$	-	$	900
Total	$	900	$	-	$	-	$	900

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

Summary of Intangible Assets, Net of Accumulated Impairment Charges

Intangible asset, net of accumulated impairment charges, are summarized as follows:

	As of December 31, 2017							As of December 31, 2016
	Cost		Accumulated Impairment			Net Book Value		Cost		Accumulated Impairment			Net Book Value
	(in thousands)							(in thousands)
IPR&D	$	630	$	(630	)	$	-	$	630	$	(630	)	$	-
	$	630	$	(630	)	$	-	$	630	$	(630	)	$	-

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Loss Per Common Share (Tables)

12 Months Ended

Dec. 31, 2017

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
	2017			2016
	(In thousands, except share and per share data)
Numerator:
Net loss	$	(26,414	)	$	(16,208	)
Net Loss attributable to Series A Preferred Stock (a)		(3,915	)		(2,345	)
Numerator for basic EPS - Earnings (loss) attributable to common stockholders	$	(22,499	)	$	(13,863	)
Effect of dilutive securities:
Deduct change in fair value of warrant liability	$	-		$	(17,507	)
Numerator for diluted EPS - Earnings (loss) attributable to common stockholders after assumed conversions	$	(22,499	)	$	(31,370	)
Denominator:
Weighted-average number of common shares used in earnings (loss) per share - basic		22,669,819			14,256,954
Effect of dilutive securities:
Nonparticipating warrants		-			132,238
Denominator for diluted EPS - adjusted weighted average shares		22,669,819			14,389,192
Earnings (loss) per share - basic	$	(0.99	)	$	(0.97	)
Earnings (loss) per share - diluted	$	(0.99	)	$	(2.18	)

(a)	The Series A Preferred Stock participates in income and losses

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

	As of December 31,
	2017		2016
Unvested restricted stock and options to purchase common stock		2,158,348		1,578,905
Series A preferred stock unconverted		2,046,957		5,962,817
Warrants exercisable into common stock		13,633,070		166,403

Prepaid Expenses and Other Current Assets (Tables)

12 Months Ended

Dec. 31, 2017

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,
	2017		2016
	(in thousands)
Deposits	$	10	$	10
Insurance		72		95
Other current assets		112		68
Prepaid expenses and other current assets	$	194	$	173

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consisted of the following:

	December 31,			December 31,
	2017			2016
	(in thousands)
Office equipment	$	279		$	266
Laboratory equipment		4,565			4,443
Leasehold improvements		7,712			7,683
Construction in progress		990			759
Software		96			96
Total property and equipment		13,642			13,247
Less: accumulated depreciation		(10,919	)		(9,387	)
Property and equipment, net	$	2,723		$	3,860

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2017

Payables And Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following:

	As of December 31,
	2017		2016
	(in thousands)
Accrued compensation	$	1,671	$	1,402
Accrued clinical expenses		199		187
Accrued other		835		508
Total accrued expenses	$	2,705	$	2,097

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

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, 2017, are as follows:

For the Year Ended December 31,
	(in thousands)
2018	$	1,798
2019		1,845
2020		1,892
2021		1,941
2022		1,991
Thereafter		3,188
Total minimum lease payments	$	12,655

Capital Stock (Tables)

12 Months Ended

Dec. 31, 2017

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,
	2017		2016
Vesting of restricted stock		-		1,889
Options to purchase common stock		2,158,348		1,577,016
Common stock warrants		13,633,070		13,633,070
Total		15,791,418		15,211,975

Equipment Loan Payable (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Outstanding Borrowing Obligations

As of December 31, 2017 and 2016, the Company had the following outstanding borrowing obligations:

	December 31,			December 31,
	2017			2016
	(in thousands)
Silicon Valley Bank Equipment Loan Payable	$	178		$	761
Less: current portion		(178	)		(583	)
Long-term debt, net	$	-		$	178

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

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, 2016		1,577,016		$	5.95		8.4	$	71
Granted		910,950			1.74
Exercised		(7,497	)		0.76
Cancelled		(322,121	)		4.52
Outstanding at December 31, 2017		2,158,348		$	4.40		8.1	$	436
Vested and expected to vest at December 31, 2017		1,968,878		$	4.54		8.1	$	390
Exercisable at December 31, 2017		958,201		$	5.78		7.4	$	153

Additional Information about Stock Option Activity

Additional information about the Company’s stock option activity is as follows:

	Year Ended December 31,
	2017		2016
Weighted-average grant date fair value per share of employee option grants within the year	$	1.02	$	1.26
Cash received upon exercise of options		6		3

Schedule of Restricted Stock Awards Under the 2012 and 2013 Plans

Restricted stock awards under the 2012 and 2013 plans are summarized as follows:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested at December 31, 2016		1,889		$	0.83
Vesting of restricted stock		(1,889	)
Unvested at December 31, 2017		-		$	-

Summary of Stock-Based Compensation

Stock-based compensation is as follows:

	Year Ended December 31,
	2017		2016
	(in thousands)
Research and development	$	411	$	491
General and administrative		1,162		1,057
Total stock-based compensation expense	$	1,573	$	1,548

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,
	2017			2016
Risk-free interest rate		2.03	%		1.73	%
Expected volatility		62.9	%		72.5	%
Expected term (in years)		6.08		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,
	2017			2016
Risk-free interest rate		1.29	%		1.57	%
Expected volatility		62.3	%		63.5	%
Expected term (in years)		6.08			7.0
Expected dividend yield		0.0	%		0.0	%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Components of Loss Before Income Taxes

The components of loss before income taxes were as follows:

		As of December 31,
		2017			2016
	(in thousands)
U.S.		$	(26,275	)	$	(15,838	)
Foreign			(140	)		(369	)
Total		$	(26,415	)	$	(16,207	)

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,
	2017			2016
Federal income tax (benefit) at statutory rate		33.9	%		34.0	%
(Increase) decrease income tax benefit resulting from:
Permanent differences		(2.6	)%		29.0	%
Net Operating Loss Limitation		0.0	%		(111.1	)%
Federal Tax Rate change		(47.5	)%		0.0	%
R&D Credit Limitation		0.0	%		(1.5	)%
Change in valuation allowance		14.7	%		48.7	%
Other		1.5	%		0.9	%
Income tax expense (benefit)		0.0	%		0.0	%

Components of Deferred Tax Assets and Liabilities

	As of December 31,
	2017			2016
	(in thousands)
Deferred tax assets:
Net operating loss carryforwards	$	18,540		$	16,146
Depreciation and amortization		4,121			6,229
Accrued expenses		2,304			2,082
Capitalized start-up costs		7,942			10,037
R&D credits		243			75
Other		(12	)		-
Deferred tax assets before valuation allowance		33,138			34,569
Valuation allowance		(33,138	)		(34,569	)
		-			-
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,
	2017			2016
	(in thousands)
Unrecognized tax benefit, beginning of year	$	562		$	687
Increase (decrease) related to current year positions		(123	)		(125	)
Federal rate revision		(136	)		-
Unrecognized tax benefit, end of year	$	303		$	562

Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands			12 Months Ended
	Sep. 29, 2016	May 13, 2011	Dec. 31, 2017	Dec. 31, 2016
Nature Of Business And Basis Of Presentation [Line Items]
Proceeds from issuance of issuance of common stock, preferred stock and warrants, net of issuance costs	$ 27,600			$ 27,630
Accumulated deficit			$ 208,187	$ 181,773
ProChon [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Business acquisition date			May 13, 2011
Consideration paid to acquisition		$ 2,200

Summary of Significant Accounting Policies - Additional Information (Detail) ¥ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CNY (¥)	Dec. 31, 2017 USD ($) Segment shares	Dec. 31, 2016 USD ($)
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	900,000		900,000	0
Sale of available for sale securities			0
Marketable securities other-than-temporary impairment			0
Aggregate fair value of available for sale securities held for less than twelve months	900,000		900,000
Impairment of intangible asset				$ 200,000
Discount rate				13.00%
Remaining performance obligations	10,000,000		$ 10,000,000
Remaining performance obligation explanation			Expects to recognize revenue on approximately 25% and 100% of the remaining performance obligations over the next 12 months and 13 to 21 months, respectively.
Percentage of recognize revenue			0.25
Percentage of recognize revenue			1.00
Remaining performance obligation expected period			12 months
Maximum percentage of recognition of tax benefits from uncertain tax positions			50.00%
Performance-based Awards [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of shares issued \| shares			0
MEDINET Co. [Member]
Summary Of Significant Accounting Policies [Line Items]
Upfront cash payment under license agreement	$ 10,000,000
Royalties at percentage rates ranging	Low single digits to low double digits	Low single digits to low double digits
Development milestone payments		¥ 330	$ 2,900,000
Regulatory payments	$ 1,000,000	720	7,400,000
Commercial Milestones Payment		¥ 7,100	62,800,000
Non-refundable upfront amount	10,000,000
Upfront transaction price	$ 10,000,000
Upfront transaction price recognized period	2 years	2 years
Remaining performance obligations	$ 0		$ 0	$ 0
IPR&D [Member]
Summary Of Significant Accounting Policies [Line Items]
Impairment of intangible asset				200,000
Net Book Value				0
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Weighted average of maturity portfolio			1 month
Remaining performance obligation expected period			21 months
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Remaining performance obligation expected period			13 months
Quoted Prices in Active Markets (Level 1) [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]
Summary Of Significant Accounting Policies [Line Items]
Assets, fair value disclosure, recurring	0		0	0
Liabilities, fair value disclosure, recurring	0		0	0
Significant Unobservable Inputs (Level 3) [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 Accounting Policies - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Warrant Liability [Member]
Liabilities:
Liabilities, fair value	$ 14,679	$ 13,197
Money Market Funds [Member]
Assets:
Assets, fair value	5,547	30,318
Marketable Securities [Member] \| Asset Backed Securities [Member]
Assets:
Assets, fair value	900
Quoted Prices in Active Markets (Level 1) [Member] \| Money Market Funds [Member]
Assets:
Assets, fair value	5,547	30,318
Significant Other Observable Inputs (Level 2) [Member] \| Marketable Securities [Member] \| Asset Backed Securities [Member]
Assets:
Assets, fair value	900
Significant Unobservable Inputs (Level 3) [Member] \| Warrant Liability [Member]
Liabilities:
Liabilities, fair value	$ 14,679	$ 13,197

Summary of Significant Accounting Policies - Schedule of Reconciliation of Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in fair value of warrant liability	$ 1,482	$ (17,507)
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	13,197
Change in fair value of warrant liability	1,482
Ending balance	$ 14,679	$ 13,197

Summary of Significant Accounting Policies - Summary of Available for Sale Securities (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 900,000
Fair Value	900,000	$ 0
Asset Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	900,000
Fair Value	$ 900,000

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, 2017
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 Accounting Policies - Summary of Intangible Assets, Net of Accumulated Impairment Charges (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Cost	$ 630,000	$ 630,000
Accumulated Impairment	(630,000)	(630,000)
IPR&D [Member]
Finite-Lived Intangible Assets [Line Items]
Cost	630,000	630,000
Accumulated Impairment	$ (630,000)	(630,000)
Net Book Value		$ 0

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, 2017	Dec. 31, 2016
Numerator:
Net loss	$ (26,414)	$ (16,208)
Net Loss attributable to Series A Preferred Stock	(3,915)	(2,345)
Numerator for basic EPS - Earnings (loss) attributable to common stockholders	(22,499)	(13,863)
Effect of dilutive securities:
Change in fair value of warrant liability	1,482	(17,507)
Numerator for diluted EPS - Earnings (loss) attributable to common stockholders after assumed conversions	$ (22,499)	$ (31,370)
Denominator:
Weighted-average number of common shares used in earnings (loss) per share - basic	22,669,819	14,256,954
Effect of dilutive securities:
Nonparticipating warrants		132,238
Denominator for diluted EPS - adjusted weighted average shares	22,669,819	14,389,192
Earnings (loss) per share - basic	$ (0.99)	$ (0.97)
Earnings (loss) per share - diluted	$ (0.99)	$ (2.18)

Loss Per Common Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
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	2,046,957	5,962,817
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	2,158,348	1,578,905
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	166,403

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Prepaid Expense And Other Assets Current [Abstract]
Deposits	$ 10	$ 10
Insurance	72	95
Other current assets	112	68
Prepaid expenses and other current assets	$ 194	$ 173

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 13,642	$ 13,247
Less: accumulated depreciation	(10,919)	(9,387)
Property and equipment, net	2,723	3,860
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	279	266
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	4,565	4,443
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	7,712	7,683
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	990	759
Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 96	$ 96

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Depreciation expense	$ 1,534	$ 1,673

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables And Accruals [Abstract]
Accrued compensation	$ 1,671	$ 1,402
Accrued clinical expenses	199	187
Accrued other	835	508
Total accrued expenses	$ 2,705	$ 2,097

Commitments and Contingencies - Additional Information (Detail)	1 Months Ended			12 Months Ended
	Feb. 28, 2017 USD ($)	Sep. 30, 2015	Jun. 30, 2012 USD ($)	Dec. 31, 2017 USD ($) Option	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Rent expense under operating lease agreements				$ 1,000,000	$ 1,000,000
Research and development expense				15,566,000	21,577,000
Engineering Agreement [Member]
Loss Contingencies [Line Items]
Amount paid to suppliers				600,000	$ 200,000
Additional payments due				0
Collagen Supply Agreement [Member]
Loss Contingencies [Line Items]
Amount paid during period for amending the agreement				$ 70,000
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				$ 30,000
Amount agreed for amending minimum annual order	$ 100,000
OCS Agreement [Member]
Loss Contingencies [Line Items]
Accrued and received grants, aggregate				1,100,000
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
Hydrogel License Agreement [Member]
Loss Contingencies [Line Items]
Research and development expense				3,200,000
Amount paid during period for amending the agreement				3,000,000
Tissue Regeneration License Agreement [Member]
Loss Contingencies [Line Items]
Research and development expense				800,000
Amount paid during period for amending the agreement				$ 300,000
Percentage of royalty offsetting				50.00%
Maximum [Member] \| OCS Agreement [Member]
Loss Contingencies [Line Items]
Royalties payment, rate				5.00%
Royalty payment percentage as percentage of grant received				300.00%
Minimum [Member] \| OCS Agreement [Member]
Loss Contingencies [Line Items]
Royalties payment, rate				3.00%
Royalty payment percentage as percentage of grant received				100.00%
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
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

Commitments and Contingencies - Schedule of Minimum Annual Lease Commitments Under Non-Cancellable Operating Leases (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Operating Leases Future Minimum Payments Due [Abstract]
2018	$ 1,798
2019	1,845
2020	1,892
2021	1,941
2022	1,991
Thereafter	3,188
Total minimum lease payments	$ 12,655

Capital Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Sep. 29, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Proceeds from issuance of issuance of common stock, preferred stock and warrants, net of issuance costs	$ 27,600			$ 27,630
Class of Warrants or right to purchase common stock, exercise price			$ 2.25
Warrant expense				$ 3,100
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]
Number of shares issued	24,158.8693
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]
Number of shares issued				2,596,059
Private Placement [Member]
Class of Stock [Line Items]
Gross proceeds from issuance of common stock, preferred stock and warrants		$ 30,000
Proceeds from issuance of issuance of common stock, preferred stock and warrants, net of issuance costs		$ 27,600
Common stock price per share		$ 2.25
Conversion of preferred stock in to common stock, preferred stock converted		10,737,275	2,046,957
Class of Warrants or right to purchase common stock		13,333,334
Class of Warrants or right to purchase common stock, exercise price		$ 2.25	$ 2.25
Warrants granted to placement agent		133,333
Warrants granted to placement agent, exercise price		$ 2.25
Minimum percentage of outstanding common stock			50.00%
Warrants expiry period			5 years
Warrants exercisable period			6 months
Fair value of warrants			$ 30,700
Excess fair value of warrant liability			400
Warrant expense			$ 3,100
Preferred stock par value			$ 0.01
Preferred stock converted into common stock			444.44
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]
Number of shares issued		24,158.8693
Convertible preferred stock, shares outstanding			4,605.6533
Private Placement [Member] \| Series A Preferred Stock [Member] \| Members of Board of Directors [Member]
Class of Stock [Line Items]
Number of shares issued			2,563.1439
Private Placement [Member] \| Common Stock [Member]
Class of Stock [Line Items]
Number of shares issued		2,596,059
Private Placement [Member] \| Common Stock [Member] \| Members of Board of Directors [Member]
Class of Stock [Line Items]
Number of shares issued			283,046

Capital Stock - Schedule of Common Stock Reserved for Future Issuance (Detail) - shares	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Common stock reserved for future issuance	15,791,418	15,211,975
Warrants Exercisable into Common Stock [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance	13,633,070	13,633,070
Restricted Stock [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance		1,889
Stock Options [Member]
Class of Stock [Line Items]
Common stock reserved for future issuance	2,158,348	1,577,016

Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended	9 Months Ended	12 Months Ended
	Dec. 21, 2016	Dec. 03, 2014	Jul. 09, 2014	Jul. 20, 2012	Jul. 31, 2014	Sep. 30, 2015	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Mar. 31, 2015
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock, exercise price							$ 2.25
Silicon Valley Bank [Member]
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock					6,566
Class of Warrants or right to purchase common stock, exercise price					$ 7.99
Warrants expiry period					10 years
Fair value of the warrants, risk free interest rate			2.58%
Fair value of the warrants, implied volatility			87.00%
Fair value of the warrants, expected term to liquidity			10 years
Fair value of warrants			$ 51
Investor Warrants [Member]
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock									13,333,334
Class of Warrants or right to purchase common stock, exercise price									$ 2.25
Warrants exercisable period							6 months
Warrants expiry period							5 years
Warrant expense							$ 2.28
Placement Agent Warrant [Member]
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock									133,333
Class of Warrants or right to purchase common stock, exercise price									$ 2.25
Warrants expiry period							5 years
Warrant expense							$ 2.28
Affiliates Of Advisor Warrant [Member]
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock				161,977			156,138	156,138
Class of Warrants or right to purchase common stock, exercise price				$ 0.01			$ 0.01	$ 0.01
Warrants expiry period				10 years
Surrender of warrant to satisfy related liability		5,839
Fair value of the warrants, risk free interest rate				0.22%
Fair value of the warrants, implied volatility				99.00%
Fair value of the warrants, expected term to liquidity				1 year 8 months 12 days
Consulting Agreement Warrant [Member]
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock										7,398
Class of Warrants or right to purchase common stock, exercise price										$ 9.75
Warrants exercisable period						24 months
Warrants expiry period						10 years
Warrants, forfeiture	(3,699)
Warrants vested and exercisable							3,699	3,699
Warrants, percentage of forfeiture	50.00%

Equipment Loan Payable - Schedule of Outstanding Borrowing Obligations (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Less: current portion	$ (178)	$ (583)
Long-term debt, net		178
Silicon Valley Bank [Member]
Debt Instrument [Line Items]
Total debt	$ 178	$ 761

Equipment Loan Payable - Additional Information (Detail) - USD ($)	1 Months Ended
	Jul. 31, 2014	Dec. 31, 2017	Dec. 31, 2016
Class of Warrant or Right [Line Items]
Net exercise of warrants, exercise price per share		$ 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
Net exercise of warrants, shares	6,566
Net exercise of warrants, exercise price per share	$ 7.99
Borrowings outstanding under line of credit		$ 200,000	$ 800,000
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 - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended		12 Months Ended
	Jun. 16, 2016	Dec. 03, 2014	Oct. 31, 2014	Jul. 31, 2012	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					$ 1,400	$ 2,600
Intrinsic value of options exercised					$ 8	10
Weighted average grant date fair value of vested options					$ 3.92
Weighted average grant date fair value of options outstanding					$ 2.72
Stock-based compensation expense					$ 1,573	1,548
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense					1,162	1,057
Restricted stock-based compensation expense					$ 1	$ 2
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, recognition period					1 year 8 months 12 days	2 years 3 days
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to restricted stock awards						$ 1
Stock-based compensation expense					$ 1
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	300,000				982,841
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			51,832
Increase in authorized shares, percentage of common stock outstanding		1.00%

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, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Outstanding Beginning Balance	1,577,016
Number of Options, Granted	910,950
Number of Options, Exercised	(7,497)
Number of Options, Cancelled	(322,121)
Number of Options, Outstanding Ending Balance	2,158,348	1,577,016
Number of Options, Vested and expected to vest outstanding	1,968,878
Number of Options, Exercisable	958,201
Weighted Average Exercise Price, Outstanding Beginning Balance	$ 5.95
Weighted Average Exercise Price, Granted	1.74
Weighted Average Exercise Price, Exercised	0.76
Weighted Average Exercise Price, Cancelled	4.52
Weighted Average Exercise Price, Outstanding Ending Balance	4.40	$ 5.95
Weighted Average Exercise Price, Vested and expected to vest outstanding	4.54
Weighted Average Exercise Price, Exercisable	$ 5.78
Weighted Average Remaining Contractual Term, Outstanding	8 years 1 month 6 days	8 years 4 months 24 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 4 months 24 days
Aggregate Intrinsic Value, Outstanding	$ 436	$ 71
Aggregate Intrinsic Value, Vested and expected to vest outstanding	390
Aggregate Intrinsic Value, Exercisable	$ 153

Stock-Based Compensation - Additional Information about Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted-average grant date fair value per share of employee option grants within the year	$ 1.02	$ 1.26
Cash received upon exercise of options	$ 6	$ 3

Stock-Based Compensation - Schedule of Restricted Stock Awards Under the 2012 and 2013 Plans (Detail) - Restricted Stock [Member]	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, Unvested beginning balance	1,889
Vesting of restricted stock	(1,889)
Number of shares, Unvested ending balance	0
Weighted-average grant date fair value, Unvested beginning balance \| $ / shares	$ 0.83

Stock-Based Compensation - Summary of Stock-Based Compensation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,573	$ 1,548
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	411	491
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 1,162	$ 1,057

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, 2017	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]
Risk-free interest rate	2.03%	1.73%
Expected volatility	62.90%	72.50%
Expected term (in years)	6 years 29 days	6 years 29 days
Expected dividend yield	0.00%	0.00%

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, 2017	Dec. 31, 2016
Share Based Goods And Nonemployee Services Transaction [Abstract]
Risk-free interest rate	1.29%	1.57%
Expected volatility	62.30%	63.50%
Expected term (in years)	6 years 29 days	7 years
Expected dividend yield	0.00%	0.00%

Income Taxes - Components of Loss Before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
U.S.	$ (26,275)	$ (15,838)
Foreign	(140)	(369)
Total	$ (26,415)	$ (16,207)

Income Taxes - Schedule of Reconciliation of Income Tax Expense (Benefit) Computed at Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal income tax (benefit) at statutory rate	33.90%	34.00%
(Increase) decrease income tax benefit resulting from:
Permanent differences	(2.60%)	29.00%
Net Operating Loss Limitation	0.00%	(111.10%)
Federal Tax Rate change	(47.50%)	0.00%
R&D Credit Limitation	0.00%	(1.50%)
Change in valuation allowance	14.70%	48.70%
Other	1.50%	0.90%
Income tax expense (benefit)	0.00%	0.00%

Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 18,540	$ 16,146
Depreciation and amortization	4,121	6,229
Accrued expenses	2,304	2,082
Capitalized start-up costs	7,942	10,037
R&D credits	243	75
Other	(12)
Deferred tax assets before valuation allowance	33,138	34,569
Valuation allowance	$ (33,138)	$ (34,569)

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes Disclosure [Line Items]
Decrease in valuation allowance		$ (1,000,000)	$ (15,700,000)
Impact of a federal tax rate change		11,500,000
NOL carry forwards, net of limitations		$ 52,900,000
Federal corporate income tax rate		33.90%	34.00%
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	$ 562,000	$ 687,000
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 2016			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, 2017, include years 2013 through the present.
Maximum [Member]
Income Taxes Disclosure [Line Items]
Federal corporate income tax rate		34.00%
Scenario Plan [Member]
Income Taxes Disclosure [Line Items]
Federal corporate income tax rate	21.00%
U.S. Federal [Member]
Income Taxes Disclosure [Line Items]
NOL carryforwards		$ 43,900,000	24,500,000
NOL carryforwards, expiration date		Dec. 31, 2037
U.S. State [Member]
Income Taxes Disclosure [Line Items]
NOL carryforwards		$ 43,600,000	24,300,000
NOL carryforwards, expiration date		Dec. 31, 2037
Foreign [Member]
Income Taxes Disclosure [Line Items]
NOL carryforwards		$ 26.3	$ 26.1

Income Taxes - Summary of Changes In Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Unrecognized tax benefit, beginning of year	$ 562	$ 687
Increase (decrease) related to current year positions	(123)	(125)
Federal rate revision	(136)
Unrecognized tax benefit, end of year	$ 303	$ 562

Employee Benefits - Additional Information (Detail)	12 Months Ended
Employee Benefits - Additional Information (Detail)	Dec. 31, 2017 USD ($)
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 Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2012
Intrexon [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration Agreement cancellation notification	90 days
Collaboration Agreement cancellation with material breach that cannot be remedied	60 days
Accrued expenses due to related party	$ 3.0	$ 3.0
Intrexon [Member] \| Research and Development [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of reimbursement expenses	50.00%
Percentage of reimbursement expenses subject to acceptance	50.00%
Research and development expense from transaction with Intrexon	$ 0.0	3.0
Intrexon [Member] \| Commercialization Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Commercialization milestones obligation	12.0
Intrexon [Member] \| Sales Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales milestones	22.5
Purpose, Co. [Member]
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 Information (Detail) - USD ($) $ in Millions			12 Months Ended
	Jan. 25, 2018	Jan. 05, 2018	Dec. 31, 2016
Common Stock [Member]
Subsequent Event [Line Items]
Shares issued			2,596,059
Subsequent Event [Member] \| Common Stock [Member]
Subsequent Event [Line Items]
Shares issued	2,691,494
Net proceeds of offering after deducting underwriting discounts and commissions	$ 5.9
Subsequent Event [Member] \| Option To Purchase Additional Shares [Member] \| Common Stock [Member]
Subsequent Event [Line Items]
Shares issued	351,064
Subsequent Event [Member] \| MEDINET Co. [Member]
Subsequent Event [Line Items]
Upfront payment received under license agreement		$ 10.0
License agreement effective date		Dec. 21, 2017