F-star Therapeutics (FSTX) 10-K 20 Feb 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 16, 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	2,017
Document Fiscal Period Focus	FY
Trading Symbol	sbph
Entity Registrant Name	Spring Bank Pharmaceuticals, Inc.
Entity Central Index Key	1,566,373
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 Public Float			$ 152.8
Entity Common Stock, Shares Outstanding		12,963,824

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 23,649	$ 10,684
Marketable securities	26,906	14,046
Prepaid expenses and other current assets	580	840
Total current assets	51,135	25,570
Marketable securities		752
Property and equipment, net	687	522
Restricted cash	484
Other assets	35	35
Total	52,341	26,879
Current liabilities:
Accounts payable	1,700	1,519
Accrued expenses and other current liabilities	2,734	1,982
Total current liabilities	4,434	3,501
Warrant liabilities	13,128	6,333
Other long-term liabilities	31	27
Total liabilities	17,593	9,861
Commitments (Note 9)
Stockholders’ equity:
Preferred stock, $0.0001 par value—authorized, 10,000,000 shares at December 31, 2017 and 2016; no shares issued or outstanding at December 31, 2017 and 2016
Common stock, $0.0001 par value—authorized, 200,000,000 shares at December 31, 2017 and 2016; 12,961,993 and 9,416,238 shares issued and outstanding outstanding at December 31, 2017 and 2016, respectively	1	1
Additional paid-in capital	113,984	68,559
Accumulated deficit	(79,214)	(51,535)
Other comprehensive loss	(23)	(7)
Total stockholders’ equity	34,748	17,018
Total	$ 52,341	$ 26,879

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	12,961,993	9,416,238
Common stock, shares outstanding	12,961,993	9,416,238

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Grant revenue		$ 352
Operating expenses:
Research and development	$ 13,075	14,017
General and administrative	8,178	5,739
Total operating expenses	21,253	19,756
Loss from operations	(21,253)	(19,404)
Interest income	369	96
Change in fair value of warrant liabilities	(6,795)	1,942
Net loss	(27,679)	(17,366)
Unrealized gain (loss) on marketable securities	(16)	11
Comprehensive loss	$ (27,695)	$ (17,355)
Net loss per common share – basic and diluted	$ (2.48)	$ (2.39)
Weighted-average number of shares outstanding – basic and diluted	11,153,269	7,256,671

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Sales Agreement [Member]	Public Offering [Member]	Initial Public Offering [Member]	Private Investment [Member]	License Agreement [Member]	Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member]Sales Agreement [Member]	Common Stock [Member]Public Offering [Member]	Common Stock [Member]Initial Public Offering [Member]	Common Stock [Member]Private Investment [Member]	Common Stock [Member]License Agreement [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Sales Agreement [Member]	Additional Paid-in Capital [Member]Public Offering [Member]	Additional Paid-in Capital [Member]Initial Public Offering [Member]	Additional Paid-in Capital [Member]Private Investment [Member]	Additional Paid-in Capital [Member]License Agreement [Member]	Accumulated Deficit [Member]	Other Comprehensive Income (Loss) [Member]
Balance at Dec. 31, 2015	$ 11,025							$ 1						$ 45,211						$ (34,169)	$ (18)
Balance, shares at Dec. 31, 2015							1,000,000	5,796,091
Stock-based compensation	1,410													1,410
Issuance of common stock for services rendered	28													28
Issuance of common stock for services rendered, shares								3,520
Exercise of warrants	5,342													5,342
Exercise of warrants, shares								641,743
Exercise of stock options	95													95
Exercise of stock options, shares								10,247
Issuance of common stock				$ 8,226	$ 5,467	$ 2,780											$ 8,226	$ 5,467	$ 2,780
Issuance of common stock, shares											944,900	1,644,737	125,000
Stock issued during period conversion of convertible securities, shares							(1,000,000)	250,000
Net unrealized gain (loss) on marketable securities	11																				11
Net loss	(17,366)																			(17,366)
Balance at Dec. 31, 2016	17,018							$ 1						68,559						(51,535)	(7)
Balance, shares at Dec. 31, 2016								9,416,238
Stock-based compensation	1,840													1,840
Issuance of common stock for services rendered	47													47
Issuance of common stock for services rendered, shares								3,133
Exercise of warrants	118													118
Exercise of warrants, shares								10,960
Exercise of stock options	92													92
Exercise of stock options, shares								10,000
Issuance of common stock		$ 3,653	$ 39,675												$ 3,653	$ 39,675
Issuance of common stock, shares									252,443	3,269,219
Net unrealized gain (loss) on marketable securities	(16)																				(16)
Net loss	(27,679)																			(27,679)
Balance at Dec. 31, 2017	$ 34,748							$ 1						$ 113,984						$ (79,214)	$ (23)
Balance, shares at Dec. 31, 2017								12,961,993

Consolidated Statements of Cha6

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Offering [Member]
Common stock issuance costs	$ 2,826
Initial Public Offering [Member]
Common stock issuance costs		$ 3,113
At-The-Market Offering [Member]
Common stock issuance costs	$ 273
Private Investment [Member]
Common stock issuance costs		$ 1,257

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (27,679)	$ (17,366)
Adjustments for:
Depreciation	158	118
Change in fair value of warrant liabilities	6,795	(1,942)
Non-cash investment income (expense)	(41)	30
Non-cash stock-based compensation	1,911	1,438
Non-cash issuance of common stock and warrants connected to license agreement		2,780
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	260	(527)
Other assets		(35)
Accounts payable	181	(812)
Accrued expenses and other liabilities	732	497
Net cash used in operating activities	(17,683)	(15,819)
Cash flows from investing activities:
Purchases of marketable securities	(34,397)	(14,978)
Proceeds from sale of marketable securities	22,314	8,684
Purchases of property and equipment	(323)	(213)
Net cash used in investing activities	(12,406)	(6,507)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs paid of $2,826	39,675
Proceeds from issuance of common stock in connection with at-the-market offering, net of issuance costs paid of $273	3,653
Proceeds from issuance of common stock and warrants in connection with private investment in a public entity, net of issuance costs paid of $966		14,034
Proceeds from issuance of common stock and warrants in connection with initial public offering, net of issuance costs paid of $2,147		9,192
Proceeds from exercise of warrants	118	5,342
Proceeds from exercise of stock options	92	95
Cash provided by financing activities	43,538	28,663
Net increase in cash, cash equivalents and restricted cash	13,449	6,337
Cash, cash equivalents and restricted cash, beginning of period	10,684	4,347
Cash, cash equivalents and restricted cash, end of period	24,133	10,684
Supplemental disclosures of cash flow information:
Cash paid for taxes	$ 1	1
Supplemental disclosures of noncash financing activities:
Fair value of warrant liabilities upon private investment in a public entity		8,275
Issuance of common stock warrants in connection with initial public offering		$ 218

Consolidated Statements of Cas8

Consolidated Statements of Cash Flows (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Proceeds from Issuance of common stock ,Issuance costs paid	$ 2,826
Private Investment [Member]
Proceeds from Issuance of common stock ,Issuance costs paid	966
At-The-Market Offering [Member]
Proceeds from Issuance of common stock ,Issuance costs paid	273
Initial Public Offering [Member]
Proceeds from Issuance of common stock ,Issuance costs paid	$ 2,147

Nature of Business, Basis of Pr

Nature of Business, Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Nature of Business Basis of presentation and Summary of Significant Accounting Policies	1. NATURE OF BUSINESS, BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Business Spring Bank Pharmaceuticals, Inc. (the “Company”) is a clinical-stage biopharmaceutical company engaged in the discovery and development of a novel class of therapeutics using a proprietary small molecule nucleic acid hybrid (“SMNH”) chemistry platform. The Company is developing its most advanced SMNH product candidate, inarigivir soproxil (“inarigivir”) (formerly known as SB 9200), for the treatment of chronic hepatitis B virus. Since inception in 2002 and prior to its initial public offering (“IPO”) in May 2016, the Company built its technology platform and product candidate pipeline using a semi-virtual business model, supported by grants and direct funding from the United States National Institutes of Health (“NIH”) as well as through private financings. In September 2015, the Company formed a wholly owned subsidiary, Sperovie Biosciences, Inc., and in December 2016, the Company formed a wholly owned subsidiary, SBP Securities Corporation. The Company’s success is dependent upon its ability to successfully complete clinical development and obtain regulatory approval of its product candidates, successfully commercialize approved products, generate revenue, and, ultimately, attain profitable operations. The Company’s operations to date have been primarily limited to financing and staffing the Company and the development of inarigivir, SB 11285, SB9225 and the Company’s other product candidates. Basis of Presentation and Liquidity The accompanying consolidated financial statements have been prepared in accordance with United States (“U.S.”) generally accepted accounting principles (“U.S. GAAP”). Prior to and in connection with the Company completing its IPO in May 2016, the Company effected a 1-for-4 reverse stock split of its common stock on March 8, 2016. All share and per share amounts and the number of shares of common stock set forth in the financial statements and notes thereto have been retroactively adjusted for all periods presented to give effect to the reverse stock split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in capital. As of December 31, 2017, the Company had an accumulated deficit of $79.2 million and $50.6 million in cash, cash equivalents and marketable securities. The Company expects to continue to incur significant and increasing losses for the foreseeable future. The Company anticipates that its expenses will increase significantly as it continues to develop inarigivir, SB 11285, SB 9225 and its other product candidates. The Company does not have any committed external source of funds. As a result, the Company will need additional financing to support its continuing operations. Adequate additional funds may not be available to the Company on acceptable terms, or at all. To the extent that the Company raises additional capital through the sale of equity or convertible debt securities, stockholders’ ownership interests will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect common stockholder rights. If the Company raises additional funds through collaborations, strategic alliances or licensing arrangements with third parties, the Company may have to relinquish valuable rights to its technologies, future revenue streams, research programs, or product candidates or grant licenses on terms that may not be favorable to the Company. Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Sperovie Biosciences, Inc. and SBP Securities Corporation. Sperovie Biosciences, Inc. had operations consisting mainly of legal fees associates with intellectual property activities as of December 31, 2017. SBP Securities Corporation had assets primarily related to investments in marketable securities and operations consisting primarily of interest income as of December 31, 2017. All intercompany balances and transactions have been eliminated in consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. Significant estimates relied upon in preparing the accompanying financial statements related to the fair value of common stock and warrant liabilities, accounting for stock-based compensation, income taxes, useful lives of long-lived assets, and accounting for certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis. The Company’s actual results may differ from these estimates. Cash, Cash Equivalents and Restricted Cash Cash equivalents are stated at fair value and include short-term, highly liquid investments with remaining maturities of 90 days or less at the date of purchase. Restricted cash consists of $484,000, of which $250,000 is held as collateral for the Company’s credit card program and $234,000 is held as a security deposit required in conjunction with the lease agreement entered into in October 2017. The Company had no restricted cash as of December 31, 2016. Included in cash and cash equivalents as of December 31, 2017 and 2016, are money market fund investments of $21.3 million and $9.5 million, respectively, which are reported at fair value (Note 5). Concentration of Credit Risk Financial instruments that subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, restricted cash and marketable securities. Substantially all of the Company’s cash is held at financial institutions that management believes to be of high-credit quality. Deposits with these financial institutions may exceed the amount of insurance provided on such deposits; however, these deposits may be redeemed upon demand and, therefore, bear minimal risk. The Company’s one source of revenue during the period ending December 31, 2016 was grants from the NIH, representing 100% of total grant revenue for such period. The Company did not have any sources of revenue for the period ended December 31, 2017. Investments in Marketable Securities The Company invests excess cash balances in short-term and long-term marketable securities. The Company classifies investments in marketable securities as either held-to-maturity or available-for-sale based on facts and circumstances present at the time of purchase. At each balance sheet date presented, all investments in securities are classified as available-for-sale. The Company reports available-for-sale investments at fair value at each balance sheet date and includes any unrealized holding gains and losses (the adjustment to fair value) in accumulated other comprehensive income (loss), a component of stockholders’ equity. 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 the value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other than temporary,” including the intention to sell and, if so, marks the investment to market through a charge to the Company’s consolidated statements of operations and comprehensive loss. Property and Equipment, Net Property and equipment are recorded at cost. Costs associated with maintenance and repairs are expensed as incurred. Depreciation and amortization are provided using the straight-line method over the estimated useful lives: Asset Category Useful Life Equipment 5-7 years Furniture and fixtures 5 years Leasehold improvements Lesser of 10 years or the remaining term of the respective lease Impairment of Long-Lived Assets Long-lived assets to be held and used are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. When such events occur, the Company compares the carrying amounts of the assets to their undiscounted expected future cash flows. If the undiscounted cash flows are insufficient to recover the carrying value, an impairment loss is recorded for the difference between the carrying value and fair value of the asset. Through December 31, 2017, no such impairment has occurred. Deferred Rent The Company’s operating leases include rent escalation payment terms and other incentives received from landlords. Deferred rent represents the difference between actual operating lease payments due and straight-line rent expense over the term of the lease, which is recorded in accrued expenses and other current liabilities. The Company had deferred aggregate rent for its research and development facility in Milford, Massachusetts and its headquarters in Hopkinton, Massachusetts of $35,000 as of December 31, 2017 and December 31, 2016. Revenue Recognition The Company recognizes revenue when all of the following criteria are met: there is persuasive evidence of an arrangement, the fee is fixed or determinable, delivery has occurred or services the Company recognized have been rendered and collection is reasonably assured. Generally, these criteria were met and revenue from grants from the NIH, which subsidized certain of the Company’s research projects, was recognized as efforts were expended and as eligible project costs were incurred. Research and Development Costs Research and development expenses consist primarily of costs incurred for the Company’s research activities, including discovery efforts, and the development of product candidates, which include: • expenses incurred under agreements with third parties, including contract research organizations, or CROs, that conduct research, preclinical activities and clinical trials on the Company’s behalf as well as contract manufacturing organizations, or CMOs, that manufacture drug products for use in the Company’s preclinical and clinical trials; • salaries, benefits and other related costs, including stock-based compensation expense, for personnel in the Company’s research and development functions; • costs of outside consultants, including their fees, stock-based compensation and related travel expenses; • the cost of laboratory supplies and acquiring, developing and manufacturing preclinical study and clinical trial materials; • costs related to compliance with regulatory requirements; and • facility-related expenses, which include direct depreciation costs and allocated expenses for rent and maintenance of facilities and other operating costs. The Company expenses research and development costs as incurred. The Company recognizes external development costs based on an evaluation of the progress to completion of specific tasks using information provided to the Company by its vendors and its clinical investigative sites. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and are reflected in the Company’s consolidated financial statements as prepaid or accrued research and development expenses. Warrants The Company reviews the terms of all warrants issued and classifies the warrants as a component of permanent equity if they are freestanding financial instruments that are legally detachable and separately exercisable, contingently exercisable, do not embody an obligation for the Company to repurchase its own shares, and permit the holders to receive a fixed number of shares of common stock upon exercise. In addition, the warrants must require physical settlement and may not provide any guarantee of value or return. Warrants that meet these criteria are initially recorded at their grant date fair value and are not subsequently remeasured. Warrants that do not meet this criteria are classified as liabilities and remeasured to their fair value at each reporting period. Stock-Based Compensation The Company accounts for all stock-based payment awards granted to employees and nonemployees using a fair value method. The Company’s stock-based payments include stock options and grants of common stock, including common stock subject to vesting. The measurement date for employee awards is the date of grant, and stock-based compensation costs are recognized as expense over the employees’ requisite service period, which is generally the vesting period, on a straight-line basis. The measurement date for nonemployee awards is the date the services are completed, resulting in periodic adjustments to stock-based compensation during the vesting period for changes in the fair value of the awards. Stock-based compensation costs for nonemployees are recognized as expense over the vesting period on a straight-line basis. Stock-based compensation expense is classified in the accompanying consolidated statements of operations and comprehensive loss based on the department to which the related services are provided. Financial Instruments The Company’s financial instruments consisted of cash equivalents, marketable securities, accounts payable and liability classified warrants. The carrying amounts of cash and cash equivalents and accounts payable approximate their fair value due to the short-term nature of those financial instruments. The fair value of the marketable securities and liability classified warrants are remeasured to fair value each reporting period as described in Note 5. Fair Value Measurements The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. Accounting Standards Codification 820, Fair Value Measurements and Disclosures Level 1 – Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 – Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly. Level 3 – Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The Company’s assets and liabilities measured at fair value on a recurring basis include cash equivalents, marketable securities and warrant liabilities. Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for the period, determined using the treasury-stock method and the as if-converted method, for convertible securities, if inclusion of these instruments is dilutive. As of December 31, 2017 and 2016, both methods are equivalent. Basic and diluted net loss per share is described further in Note 2. Income Taxes Deferred tax assets and liabilities are determined based upon the differences between the financial statement carrying amounts and the tax basis of existing assets and liabilities and for loss and credit carryforwards using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that some portion or all of the deferred tax asset will not be realized. The Company assesses its income tax positions and records tax benefits based upon management’s evaluation of the facts, circumstances, and information available at the reporting date. For those tax positions where it is more likely than not that a tax benefit will be sustained, the Company records the largest amount of tax benefit with a greater than 50% likelihood of being realized upon ultimate settlement with a taxing authority having full knowledge of all relevant information. For those income tax positions where it is not more likely than not that a tax benefit will be sustained, no tax benefit is recognized in the consolidated financial statements. The Company classifies interest and penalties associated with such uncertain tax positions as a component of interest expense. As of December 31, 2017 and 2016, the Company has not identified any material uncertain tax positions. Guarantees and Indemnifications As permitted under Delaware law, the Company indemnifies its officers and directors for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The Company leases office and laboratory space in Hopkinton, Massachusetts and research and development space in Milford, Massachusetts, under non-cancelable operating leases. The Company has standard indemnification arrangements under these leases that require it to indemnify the landlords against liability for injury, loss, accident, or damage from any claims, actions, proceedings, or costs resulting from certain acts, breaches, violations, or nonperformance under the Company’s lease. Through December 31, 2017, the Company had not experienced any losses related to these indemnification obligations and no material claims were outstanding. The Company does not expect significant claims related to these indemnification obligations, and consequently, concluded that the fair value of these obligations is negligible, and no related reserves were established. Segment Information Operating segments are identified as components of an enterprise about which separate and discrete financial information is available for evaluation by the chief operating decision maker, the Company’s Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment and does not track expenses on a program-by-program basis. Recently Issued Accounting Pronouncements In November 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash In March 2016, the FASB issued ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting The update requires the Company to recognize the income tax effect of awards in the income statement when the awards vest or are settled. It also allows the Company to repurchase more of an employee’s shares than it could prior to the update for tax withholding purposes without triggering a liability. The income tax related items had no effect on the current period presentation as the Company did not have any historical excess tax benefits. In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU 2014-09, Revenue from Contracts with Customers In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities Financial Instruments - Overall In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) In September 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments Statement of Cash Flows In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815): I. Accounting for Certain Financial Instruments with Down Round Features and II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception .

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Loss Per Share	2. NET LOSS PER SHARE The following table summarizes the computation of basic and diluted net loss per share of the Company for such periods (in thousands, except share and per share data): Year Ended December 31, 2017 2016 Net loss $ (27,679 ) $ (17,366 ) Weighted-average number of common shares-basic and diluted 11,153,269 7,256,671 Net loss per common share-basic and diluted $ (2.48 ) $ (2.39 ) Diluted net loss per common share is the same as basic net loss per common share for all periods presented. The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding, because such securities had an antidilutive impact due to the losses reported: Year 2017 2016 Common stock warrants 1,787,124 1,798,084 Stock options 988,565 704,315

Investments

Investments	12 Months Ended
	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Investments	3. INVESTMENTS Cash in excess of the Company’s immediate requirements is invested in accordance with the Company’s investments policy that primarily seeks to maintain adequate liquidity and preserve capital. The following table summarizes the Company’s investments, by category, as of December 31, 2017 and 2016 (in thousands): December 31, December 31, Investments - Current: 2017 2016 Marketable securities - available for sale $ 26,906 $ 14,046 Total $ 26,906 $ 14,046 Investments - Noncurrent: Marketable securities - available for sale $ — $ 752 Total $ — $ 752 A summary of the Company’s available-for-sale classified investments as of December 31, 2017 and 2016 consisted of the following (in thousands): At December 31, 2017 Cost Basis Unrealized Gains Unrealized Losses Fair Value Investments - Current: Commercial paper $ 9,584 $ — $ — $ 9,584 Corporate bonds 15,347 — (23 ) 15,324 United States treasury securities 1,998 — — 1,998 Total $ 26,929 $ — $ (23 ) $ 26,906 At December 31, 2016 Cost Basis Unrealized Gains Unrealized Losses Fair Value Investments - Current: Agency bonds $ 452 $ — $ — $ 452 Commercial paper 2,947 — — 2,947 Corporate bonds 8,499 — (7 ) 8,492 United States treasury securities 2,155 — — 2,155 Total $ 14,053 $ — $ (7 ) $ 14,046 Investments - Noncurrent: Corporate bonds 752 — — 752 Total $ 752 $ — $ — $ 752 The amortized cost and fair value of the Company’s available-for-sale investments, by contract maturity, as of December 31, 2017 consisted of the following (in thousands): Amortized Cost Fair Value Due in one year or less $ 26,929 $ 26,906 Due after one year through two years — — Total $ 26,929 $ 26,906

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Property and Equipment, Net	4. PROPERTY AND EQUIPMENT, NET Property and equipment as of December 31, 2017 and 2016 consisted of the following (in thousands): December 31, December 31, 2017 2016 Equipment $ 727 $ 576 Furniture and fixtures 292 140 Leasehold improvements 153 133 Total property and equipment 1,172 849 Less: accumulated depreciation and amortization (485 ) (327 ) Property and equipment, net $ 687 $ 522 Depreciation expense for the years ended December 31, 2017 and 2016 was $158,000 and $118,000, respectively.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	5 . FAIR VALUE MEASUREMENTS Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value are performed in a manner to maximize the use of observable inputs and minimize the use of unobservable inputs. The Company classified its money market funds within Level 1 because their fair values are based on their quoted market prices. The Company classified its commercial paper and fixed income securities within Level 2 because their fair values are determined using alternative pricing sources or models that utilized market observable inputs. A summary of the assets and liabilities that are measured at fair value as of December 31, 2017 and 2016 is as follows (in thousands): Fair Value Measurement at December 31, 2017 Carrying Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds (1) $ 21,265 $ 21,265 $ — $ — Fixed income securities 26,906 — 26,906 — Total $ 48,171 $ 21,265 $ 26,906 $ — Liabilities: Warrant liabilities $ 13,128 $ — $ — $ 13,128 Total $ 13,128 $ — $ — $ 13,128 Fair Value Measurement at December 31, 2016 Assets: Carrying Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Money market funds (1) $ 9,507 $ 9,507 $ — $ — Fixed income securities 14,798 — 14,798 — Total $ 24,305 $ 9,507 $ 14,798 $ — Liabilities: Warrant liabilities $ 6,333 $ — $ — $ 6,333 Total $ 6,333 $ — $ — $ 6,333 (1) Money market funds are included within cash and cash equivalents in the accompanying consolidated balance sheets are recognized at fair value. The following table reflects the change in the Company’s Level 3 liabilities, which consist of the warrants issued in a private placement in November 2016 (see Note 7), for the year ended December 31, 2017 (in thousands): November Private Placement Warrants Balance at December 31, 2015 $ — Issuance of warrants 8,275 Change in fair value (1,942 ) Balance at December 31, 2016 $ 6,333 Change in fair value 6,795 Balance at December 31, 2017 $ 13,128

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	6 . ACCRUED EXPENSES AND OTHER CURRENT LIABILITIES Accrued expenses as of December 31, 2017 and 2016 consisted of the following (in thousands): December 31, December 31, 2017 2016 Clinical $ 1,093 $ 738 Compensation and benefits 1,024 901 Accounting and legal 453 279 Other 164 64 Total accrued expenses $ 2,734 $ 1,982

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	7 . STOCKHOLDERS’ EQUITY Common Stock Effective February 1, 2016, the Company amended and restated its license agreement with BioHEP Technologies Ltd. (“BioHEP”). In connection with the amendment and restatement, the Company issued 125,000 shares of its common stock to BioHEP and granted to BioHEP a warrant to purchase an additional 125,000 shares of its common stock at an exercise price of $16.00 per share, which warrant will expire on August 1, 2018. The fair value of the common stock as of the date of issuance, $2.0 million, was expensed as research and development costs. In May 2016, the Company issued and sold in its IPO an aggregate of 944,000 shares of common stock at $12.00 per share, which included 24,900 shares that represented the exercise of an option to purchase additional shares granted to the underwriters in connection with the IPO. The offering resulted in $8.2 million of net proceeds to the Company, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. Upon the closing of the Company’s IPO, the Company filed an amended and restated certificate of incorporation, which authorized the Company to issue 200,000,000 shares of common stock and 10,000,000 shares of preferred stock. In connection with the closing of the IPO, the Company received approximately $5.3 million in proceeds upon the exercise of previously issued warrants to purchase 641,743 shares of common stock of the Company. Upon the closing of the Company’s IPO, all outstanding shares of the Company’s preferred stock automatically converted into 250,000 shares of the Company’s common stock. In November 2016, the Company entered into a definitive agreement with respect to the private placement of 1,644,737 shares of common stock and warrants to purchase 1,644,737 shares of common stock (the “November Private Placement Warrants”) to a group of accredited investors (the “November Private Placement”). These investors paid $9.12 for each share of common stock and warrant to purchase one share of common stock. The November Private Placement Warrants are exercisable at an exercise price of $10.79 per share and expire on November 23, 2021. The Company completed the November Private Placement on November 23, 2016, resulting in $13.7 million in net proceeds to the Company, after deducting placement agent fees and other offering expenses payable by the Company. In June 2017, the Company issued and sold in an underwritten public offering an aggregate of 3,269,219 shares of its common stock at $13.00 per share, which included 384,604 shares pursuant to the exercise of an option to purchase additional shares granted to the underwriters in connection with the offering. The offering resulted in $39.7 million of net proceeds to the Company, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. In August 2017, the Company entered into a Controlled Equity Offering SM aggregate Warrants In connection with the amendment and restatement of a license agreement with BioHEP, the Company issued a warrant to purchase 125,000 shares of the Company’s common stock to BioHEP (the “BioHEP Warrant”), effective February 1, 2016. The Company evaluated the terms of the warrant and concluded that it are equity-classified. The fair value of the warrant, $0.8 million, was estimated on the issuance date using a Black Scholes pricing model based on the following assumptions: an expected term of two and a half years, expected stock price volatility of 71%, a risk-free rate of 1.01%, and a dividend yield of 0%. The fair value was expensed as research and development costs. In connection with the Company’s IPO, the Company issued to the sole book-running manager for the IPO a warrant to purchase 27,600 shares of common stock in May 2016 and a warrant to purchase 747 shares of common stock in June 2016 (together, the “IPO Warrants”). The IPO Warrants are exercisable at an exercise price of $15.00 per share and expire on May 5, 2021. The Company evaluated the terms of the IPO Warrants and concluded that they should be equity-classified. The fair value of the May 2016 IPO Warrants was estimated on the applicable issuance dates using a Black Scholes pricing model based on the following assumptions: an expected term of 4.99 years; expected stock price volatility of 87%; a risk-free rate of 1.20%; and a dividend yield of 0%. The fair value of the June 2016 IPO Warrants was estimated on the applicable issuance dates using a Black Scholes pricing model based on the following assumptions: an expected term of 4.92 years; expected stock price volatility of 87%; a risk-free rate of 1.23%; and a dividend yield of 0%. The aggregate fair value of the IPO Warrants was $0.2 million. The Company received approximately $5.3 million in proceeds upon the exercise of warrants to purchase 641,743 shares of its common stock of the Company, which were exercised in connection with the closing of the IPO. Upon the closing of the Company’s IPO, all of the outstanding warrants that were not exercised, except the BioHEP warrant and the IPO Warrants, terminated in accordance with their original terms. In connection with the November Private Placement, the Company issued the November Private Placement Warrants to purchase 1,644,737 shares of common stock in November 2016 to a group of accredited investors. As of December 31, 2017, November Private Placement warrants to purchase 1,633,777 shares of common stock remained outstanding. The November Private Placement Warrants are exercisable at an exercise price of $10.79 per share and expire on November 23, 2021. The Company evaluated the terms of these warrants and concluded that they should be liability-classified. In November 2016, the Company recorded the fair value of these warrants of approximately $8.3 million using a Black Scholes pricing model. The Company must recognize any change in the value of the warrant liability each reporting period in the statement of operations. As of December 31, 2017 and 2016, the fair value of the November Private Placement Warrants was approximately $13.1 million and $6.3 million, respectively (see Note 5). . A summary of the Black Scholes pricing model assumptions used to record the fair value of the warrants is as follows: December 31, 2017 December 31, 2016 Risk-free interest rate 2.0 % 1.9 % Expected term (in years) 3.9 4.9 Expected volatility 73.1 % 65.5 % Expected dividend yield 0 % 0 % A summary of warrant activities during the years ended December 31, 2017 and 2016 is as follows: Warrants Outstanding at December 31, 2015 1,181,776 Grants 1,798,084 Exercises (641,743 ) Expirations/cancellations (540,033 ) Outstanding at December 31, 2016 1,798,084 Grants — Exercises (10,960 ) Expirations/cancellations — Outstanding at December 31, 2017 1,787,124 2014 Stock Incentive Plan In April 2014, the Company’s Board of Directors approved the 2014 Stock Incentive Plan (the “2014 Plan”) and authorized 750,000 shares of common stock to be issued under the 2014 Plan. The Company’s 2014 Plan provides for the issuance of common stock, stock options and other stock-based awards to employees, officers, directors, consultants, and advisors. The Company’s 2015 Stock Incentive Plan (the “2015 Plan”) became effective immediately prior to the closing of the Company’s IPO on May 11, 2016. Upon the effectiveness of the 2015 Plan, 116,863 shares of common stock that remained available for grant under the 2014 Plan became available for grant under the 2015 Plan, and no further awards were available to be issued under the 2014 Plan. 2015 Stock Incentive Plan The 2015 Plan provides for the issuance of common stock, stock options and other stock-based awards to employees, officers, directors, consultants and advisors of the Company. The number of shares reserved for issuance under the 2015 Plan is the sum of 750,000 shares of common stock, plus the number of shares equal to the sum of (i) 116,863 shares of common stock, which was the number of shares reserved for issuance under the 2014 Plan that remained available for grant under the 2014 Plan immediately prior to the closing of the Company’s IPO, and (ii) the number of shares of common stock subject to outstanding awards under the 2014 Plan that expire, terminate or are otherwise surrendered, cancelled or forfeited. The exercise price of stock options cannot be less than the fair value of the common stock on the date of grant. Stock options awarded under the 2015 Plan expire 10 years after the grant date, unless the Board sets a shorter term. As of December 31, 2017, the Company had 459,535 shares available for issuance under the 2015 Plan. The following table summarizes the option activity for the year ended December 31, 2017, under both the 2014 Plan and the 2015 Plan (collectively the “Plans”): Options Weighted-Average Exercise Price Per Share Aggregate Intrinsic Value Options outstanding at December 31, 2015 610,481 $ 11.99 — Granted 128,334 10.41 — Exercised (10,247 ) 9.28 29,550 Cancelled (24,253 ) 9.89 — Outstanding at December 31, 2016 704,315 $ 11.82 — Granted 297,500 8.45 — Exercised (10,000 ) 9.28 11,228 Cancelled (3,250 ) 12.44 — Options outstanding at December 31, 2017 988,565 $ 10.83 $ 2,617,859 Options exercisable at December 31, 2017 436,127 $ 11.74 $ 752,700 As of December 31, 2017, all options outstanding have a weighted-average remaining contractual life is 8.2 years. The weighted-average fair value of all stock options granted for the years ended December 31, 2017 and 2016 was $5.89 and $7.06, respectively. Intrinsic value at December 31, 2017 is based on the closing price of the Company’s common stock of $13.44 per share. Prior to the Company’s IPO on May 11, 2016, the Board determined the estimated fair value of the Company’s common stock on the date of grant based on a number of objective and subjective factors, including third party valuations. Since the IPO, the fair value of the Company’s common stock on the date of the grant is based on the closing price per share of the common stock on the Nasdaq Capital Market on the date of grant. The computation of expected volatility is based on the historical volatilities of peer companies. The peer companies include organizations that are in the same industry, with similar size and stage of growth. The Company estimates that the expected life of the options granted using the simplified method allowable under the Securities and Exchange Commission’s Staff Accounting Bulletin No. 107, Share Based Payments There were no stock options granted prior to 2015. The assumptions the Company used to determine the fair value of stock options granted to employees and directors in 2017 and 2016 are as follows, presented on a weighted-average basis: Year Ended December 31, 2017 2016 Risk-free interest rate 2.0 % 1.4 % Expected term (in years) 6.0 6.1 Expected volatility 80 % 78 % Expected dividend yield 0 % 0 % The following table summarizes the stock-based compensation expense for the years ended December 31, 2017 and 2016, under the Plans (in thousands): Year Ended December 31, Stock-based compensation: 2017 2016 Research and development $ 489 $ 390 General and administrative 1,422 1,048 Total Stock-based compensation $ 1,911 $ 1,438 The fair value of stock options vested during the year ended December 31, 2017 was $1.7 million. At December 31, 2017, there was $3.6 million of unrecognized stock-based compensation expense relating to stock options granted pursuant to the Plans, which will be recognized over the weighted-average remaining vesting period of 2.1 years. Reserved Shares As of December 31, 2017 and 2016, the Company has reserved the following shares of common stock for potential conversion of the Preferred Stock, exercise of warrants and outstanding options and issuance of shares available for grant under the 2015 Plan: December 31, 2017 2016 2016 BioHEP warrants 125,000 125,000 2016 IPO warrants 28,347 28,347 November Private Placement warrants 1,633,777 1,644,737 2014 and 2015 Stock incentive plans 1,448,100 1,461,233 Total 3,235,224 3,259,317

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	8 . INCOME TAXES A reconciliation of the statutory U.S. Federal Tax Rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2017 2016 U.S. statutory federal income tax rate (34.0 )% (34.0 )% State income taxes, net of federal income tax benefit (3.8 )% (5.7 )% Permanent items 0.8 % 0.9 % Warrant adjustment 8.3 % (3.8 )% R&D credit (0.3 )% (0.4 )% Change in valuation allowance — 43.0 % Change in federal rate impact 29.2 % — Other (0.2 )% — Effective income tax rate 0.0 % 0.0 % The significant components of the Company’s deferred tax assets as of December 31, 2017 and 2016 are as follows (in thousands): December 31, 2017 2016 Net operating loss carryforwards $ 16,781 $ 16,634 Research and development credits 520 385 Accrued expenses 265 322 Property and equipment (11 ) (1 ) License payments 663 1,025 Stock based compensation 831 682 Other – net 22 17 Deferred tax assets 19,071 19,064 Valuation allowance (19,071 ) (19,064 ) Net deferred tax asset and liability $ — $ — Because of the Company’s recurring losses since inception, management has concluded that it is more likely than not that the benefits of losses to date which result in deferred tax assets will not be realized and, accordingly, the Company provided a full valuation allowance against the net deferred tax assets. The valuation allowance increased by approximately $8,000 in 2017 due to the increase in the deferred tax assets (primarily due to the net operating loss carryforwards) largely offset by a decrease from the deferred tax assets previously being valued at 34% and now being valued at 21%. The change in the tax rate is due to tax reform enacted during 2017, see further discussion below. The valuation allowance increased by approximately $7,464,000 in 2016 due to the increase in the deferred tax assets (primarily due to the net operating loss carryforwards). At December 31, 2017, the Company had federal and state net operating loss carryforwards of approximately $61,552,000 and $60,997,000, respectively available to reduce future taxable income, if any. The federal and state net operating loss carryforwards expire beginning in 2029 and ending in 2037, respectively. At December 31, 2017, the Company had available federal and state income tax credits of approximately $294,000 and $287,000, respectively, which are available to reduce future income taxes, if any, through 2037. Realization of the future tax benefits is dependent on many factors, including the Company’s ability to generate taxable income within the net operating loss carryforward period. Under the provisions of the Internal Revenue Code, the net operating loss and tax credit carry-forwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss and tax credit carry-forwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitations is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception, which may have resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code, or could result in a change in control in the future but has not completed an analysis of whether a limitation noted above exists. The Company has not performed a Section 382 study yet but it will complete an appropriate analysis before its tax attributes are utilized. The Company has generated research and development tax credits but has not conducted a study to document its activities that qualify for research and development tax credits. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, since the Company has not conducted a study any adjustment is unknown, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s research and development tax credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development tax credit carry-forwards and the valuation allowance. The Company files income tax returns in the U.S. federal and Massachusetts jurisdictions. The statute of limitations for assessment by the Internal Revenue Service, or IRS, and state tax authorities is closed for tax years prior to 2014, although carryforward attributes that were generated prior to tax year 2014 may still be adjusted upon examination by the IRS or state tax authorities if they either have been or will be used in a future period. The Company is currently not under examination by the Internal Revenue Service or any other jurisdictions for any tax years. The Company’s policy is to record interest and penalties on any unrecognized tax benefits as part of tax expense. The Company has not recorded any interest or penalties on any unrecognized tax benefits since its inception. The Company does not believe material uncertain tax positions have arisen to date. During the first quarter of 2016, the FASB issued ASU 2016-09 that amends its guidance on certain aspects of accounting for share-based payments to employees. Companies will no longer record excess tax benefits and tax deficiencies related to stock compensation in addition paid-in capital (APIC). Excess tax benefits occur when the amount deductible for an award of equity instruments on the employer’s tax return is more than the cumulative compensation cost recognized for financial reporting purposes. Tax deficiencies occur when the amount deductible for an award of equity instruments on the employer’s tax return is less than the cumulative compensation cost recognized for financial reporting purposes. Under ASU 2016-09, all excess tax benefits and tax deficiencies are recorded as income tax expense or benefit in the income statement in the interim period in which they occur. The Company adopted ASU 2016-09 in the first quarter of 2017 and there was no impact to the income tax provision or footnote as a result of the adoption because the Company did not have any historical excess tax benefits. On December 22, 2017 the President signed the Tax Cuts and Jobs Act (“TCJA”) which reduced the US corporate income tax rate to 21% effective January 1, 2018 as well as a variety of other changes including the limitation of the tax deductibility of interest expense, acceleration of expensing of certain business assets and reductions in the amount of executive pay that could qualify as a tax deduction. ASC 740 requires us to recognize the effect of the tax law changes in the period of enactment. The Company recalculated its deferred tax balances at the new 21% corporate tax rate and recorded an offset for the net amount as a component of income tax expense. This change was offset by a corresponding change in the valuation allowance because the Company maintains a full valuation allowance as of December 31, 2017. The Securities and Exchange Commission staff issued Staff Accounting Bulletin 118 which allowed the Company to record provisional amounts for the impact of the TCJA during a measurement period which is similar to the measurement period used when accounting for business combinations. At December 31, 2017, the Company made a reasonable estimate of the effects of the TCJA on its existing deferred tax balances. The final impact of the TCJA may differ from this estimate, possibly materially, due to, among other things, changes in interpretations and assumptions the Company has made and guidance that may be issued. In addition to the reduced corporate rate, TCJA creates a territorial tax system which allows companies to repatriate future foreign source income without incurring taxes and provides a 100% exemption for the foreign source portion of dividends. It also imposes a one-time transiting tax on unearned foreign earnings of foreign subsidiaries of US companies taxes at a 15.55% rate. The bill also imposes a base erosion anti-abuse tax, a tax for any costs paid by a US company to a foreign affiliate that would be capitalized to inventory. Given the Company does not have foreign operations, it determined these changes do not currently affect its income tax provision or footnote.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	9 . COMMITMENTS AND CONTINGENCIES Leases In April 2015, the Company entered into an amendment to the lease for its research and development facility in Milford, Massachusetts to extend the term of the lease through March 31, 2018 and expand the leased laboratory space. In March 2016, the Company entered into an operating lease for its headquarters in Hopkinton, Massachusetts with a lease term through May 31, 2021. The total payments due during the term of the lease are approximately $771,000. In October 2017, the Company entered into a lease agreement in Hopkinton, Massachusetts. The premises covered by the lease will serve as the Company’s new principal office and laboratory space. The initial term of the lease is 125 months beginning on the date on which the landlord substantially completes certain renovations to the premises covered by the lease. The Company has the option to extend the lease one time for an additional 5-year period. Following an eleven-month rent abatement period, the Company will be obligated to make monthly rent payments in the amount of $34,533, which is subject to increase by approximately 3% annually for the first five years of the lease and by approximately 2.5% annually thereafter. The total lease payments due during the term of the lease are approximately $4.4 million. In addition, the Company is responsible under the lease for specified costs and charges, including certain operating expenses, utilities, taxes and insurance. Rent paid under both leases for the years ended December 31, 2017 and 2016 was $233,000 and $166,000, respectively. Future minimum commitments due under all leases at December 31, 2017 are as follows (in thousands): Year 2018 $ 174 2019 468 2020 587 2021 506 Thereafter 3,265 Total minimum lease payments $ 5,000 The commitments under the lease agreement entered into in October 2017 are included in the table above. BioHEP Technologies Ltd. License Agreement In January 2016, the Company entered into an amended and restated license agreement with BioHEP, which became effective on February 1, 2016. Under the amended and restated license agreement, the Company agreed to pay BioHEP up to $3.5 million in development and regulatory milestone payments for disease(s) caused by each distinct virus for which the Company develops licensed product(s). BioHEP is also eligible to receive tiered royalties in the low-to-mid single-digits on net product sales of licensed products by the Company and its affiliates and sub licensees, and a specified share of non-royalty sublicensing revenues the Company and its affiliates receive from sub licensees, which share of sublicensing revenues is capped at a maximum aggregate of $2.0 million under all such sublicenses. Milestone and royalty payments associated with the Company’s amended and restated license agreement with BioHEP have not been included in the above table of contractual obligations as the Company cannot reasonably estimate if or when they will occur. As of December 31, 2017, there have been no milestone or royalty payments made to BioHEP. Contingencies The Company accrues for contingent liabilities to the extent that the liability is probable and estimable. There are no accruals for contingent liabilities in these consolidated financial statements. During May 2015, the Company entered into a transition agreement with the Company’s former President and Chief Executive Officer. Under the transition agreement, he continued to serve as the Company’s president and chief executive officer for a transition period that ended on August 17, 2015. Following the transition period, the Company made 18 monthly payments totaling $464,000 and also provided benefits consistent with the coverage that was provided prior to the execution of the transition agreement. There was no remaining unpaid balance relating to his obligation at December 31, 2017.

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
401(k) Plan	10. 401(k) PLAN The Company has a 401(k)-defined contribution plan (the “401(k) Plan”) for substantially all of its employees. Eligible employees may make pretax contributions to the 401(k) Plan up to statutory limits. At the election of its Board, the Company may elect to match employee contributions. For the years ended December 31, 2017 and 2016, the Company paid a match of up to 4%, which amounted to $124,000 and $89,000, respectively.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions	11. RELATED PARTY TRANSACTIONS During the year ended December 31, 2016, the Company reimbursed BioHEP, a greater than five percent stockholder, $14,000 for legal expenses that BioHEP incurred in connection with entering into the Amended License Agreement. The Company incurred no such payments during the year ended December 31, 2017.

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	12. SUBSEQUENT EVENTS The Company has evaluated subsequent events through the date on which the consolidated financial statements were issued, to ensure that this submission includes appropriate disclosure of events both recognized in the consolidated financial statements and events which occurred subsequently but were not recognized in the consolidated financial statements.

Nature of Business, Basis of 21

Nature of Business, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation and Liquidity	Basis of Presentation and Liquidity The accompanying consolidated financial statements have been prepared in accordance with United States (“U.S.”) generally accepted accounting principles (“U.S. GAAP”). Prior to and in connection with the Company completing its IPO in May 2016, the Company effected a 1-for-4 reverse stock split of its common stock on March 8, 2016. All share and per share amounts and the number of shares of common stock set forth in the financial statements and notes thereto have been retroactively adjusted for all periods presented to give effect to the reverse stock split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in capital. As of December 31, 2017, the Company had an accumulated deficit of $79.2 million and $50.6 million in cash, cash equivalents and marketable securities. The Company expects to continue to incur significant and increasing losses for the foreseeable future. The Company anticipates that its expenses will increase significantly as it continues to develop inarigivir, SB 11285, SB 9225 and its other product candidates. The Company does not have any committed external source of funds. As a result, the Company will need additional financing to support its continuing operations. Adequate additional funds may not be available to the Company on acceptable terms, or at all. To the extent that the Company raises additional capital through the sale of equity or convertible debt securities, stockholders’ ownership interests will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect common stockholder rights. If the Company raises additional funds through collaborations, strategic alliances or licensing arrangements with third parties, the Company may have to relinquish valuable rights to its technologies, future revenue streams, research programs, or product candidates or grant licenses on terms that may not be favorable to the Company.
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Sperovie Biosciences, Inc. and SBP Securities Corporation. Sperovie Biosciences, Inc. had operations consisting mainly of legal fees associates with intellectual property activities as of December 31, 2017. SBP Securities Corporation had assets primarily related to investments in marketable securities and operations consisting primarily of interest income as of December 31, 2017. All intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The Company bases estimates and assumptions on historical experience when available and on various factors that it believes to be reasonable under the circumstances. Significant estimates relied upon in preparing the accompanying financial statements related to the fair value of common stock and warrant liabilities, accounting for stock-based compensation, income taxes, useful lives of long-lived assets, and accounting for certain accruals. The Company evaluates its estimates and assumptions on an ongoing basis. The Company’s actual results may differ from these estimates.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash Cash equivalents are stated at fair value and include short-term, highly liquid investments with remaining maturities of 90 days or less at the date of purchase. Restricted cash consists of $484,000, of which $250,000 is held as collateral for the Company’s credit card program and $234,000 is held as a security deposit required in conjunction with the lease agreement entered into in October 2017. The Company had no restricted cash as of December 31, 2016. Included in cash and cash equivalents as of December 31, 2017 and 2016, are money market fund investments of $21.3 million and $9.5 million, respectively, which are reported at fair value (Note 5).
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that subject the Company to significant concentrations of credit risk consist primarily of cash, cash equivalents, restricted cash and marketable securities. Substantially all of the Company’s cash is held at financial institutions that management believes to be of high-credit quality. Deposits with these financial institutions may exceed the amount of insurance provided on such deposits; however, these deposits may be redeemed upon demand and, therefore, bear minimal risk. The Company’s one source of revenue during the period ending December 31, 2016 was grants from the NIH, representing 100% of total grant revenue for such period. The Company did not have any sources of revenue for the period ended December 31, 2017.
Investments in Marketable Securities	Investments in Marketable Securities The Company invests excess cash balances in short-term and long-term marketable securities. The Company classifies investments in marketable securities as either held-to-maturity or available-for-sale based on facts and circumstances present at the time of purchase. At each balance sheet date presented, all investments in securities are classified as available-for-sale. The Company reports available-for-sale investments at fair value at each balance sheet date and includes any unrealized holding gains and losses (the adjustment to fair value) in accumulated other comprehensive income (loss), a component of stockholders’ equity. 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 the value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other than temporary,” including the intention to sell and, if so, marks the investment to market through a charge to the Company’s consolidated statements of operations and comprehensive loss.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are recorded at cost. Costs associated with maintenance and repairs are expensed as incurred. Depreciation and amortization are provided using the straight-line method over the estimated useful lives: Asset Category Useful Life Equipment 5-7 years Furniture and fixtures 5 years Leasehold improvements Lesser of 10 years or the remaining term of the respective lease
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets to be held and used are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. When such events occur, the Company compares the carrying amounts of the assets to their undiscounted expected future cash flows. If the undiscounted cash flows are insufficient to recover the carrying value, an impairment loss is recorded for the difference between the carrying value and fair value of the asset. Through December 31, 2017, no such impairment has occurred.
Deferred Rent	Deferred Rent The Company’s operating leases include rent escalation payment terms and other incentives received from landlords. Deferred rent represents the difference between actual operating lease payments due and straight-line rent expense over the term of the lease, which is recorded in accrued expenses and other current liabilities. The Company had deferred aggregate rent for its research and development facility in Milford, Massachusetts and its headquarters in Hopkinton, Massachusetts of $35,000 as of December 31, 2017 and December 31, 2016.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when all of the following criteria are met: there is persuasive evidence of an arrangement, the fee is fixed or determinable, delivery has occurred or services the Company recognized have been rendered and collection is reasonably assured. Generally, these criteria were met and revenue from grants from the NIH, which subsidized certain of the Company’s research projects, was recognized as efforts were expended and as eligible project costs were incurred.
Research and Development Costs	Research and Development Costs Research and development expenses consist primarily of costs incurred for the Company’s research activities, including discovery efforts, and the development of product candidates, which include: • expenses incurred under agreements with third parties, including contract research organizations, or CROs, that conduct research, preclinical activities and clinical trials on the Company’s behalf as well as contract manufacturing organizations, or CMOs, that manufacture drug products for use in the Company’s preclinical and clinical trials; • salaries, benefits and other related costs, including stock-based compensation expense, for personnel in the Company’s research and development functions; • costs of outside consultants, including their fees, stock-based compensation and related travel expenses; • the cost of laboratory supplies and acquiring, developing and manufacturing preclinical study and clinical trial materials; • costs related to compliance with regulatory requirements; and • facility-related expenses, which include direct depreciation costs and allocated expenses for rent and maintenance of facilities and other operating costs. The Company expenses research and development costs as incurred. The Company recognizes external development costs based on an evaluation of the progress to completion of specific tasks using information provided to the Company by its vendors and its clinical investigative sites. Payments for these activities are based on the terms of the individual agreements, which may differ from the pattern of costs incurred, and are reflected in the Company’s consolidated financial statements as prepaid or accrued research and development expenses.
Warrants	Warrants The Company reviews the terms of all warrants issued and classifies the warrants as a component of permanent equity if they are freestanding financial instruments that are legally detachable and separately exercisable, contingently exercisable, do not embody an obligation for the Company to repurchase its own shares, and permit the holders to receive a fixed number of shares of common stock upon exercise. In addition, the warrants must require physical settlement and may not provide any guarantee of value or return. Warrants that meet these criteria are initially recorded at their grant date fair value and are not subsequently remeasured. Warrants that do not meet this criteria are classified as liabilities and remeasured to their fair value at each reporting period.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for all stock-based payment awards granted to employees and nonemployees using a fair value method. The Company’s stock-based payments include stock options and grants of common stock, including common stock subject to vesting. The measurement date for employee awards is the date of grant, and stock-based compensation costs are recognized as expense over the employees’ requisite service period, which is generally the vesting period, on a straight-line basis. The measurement date for nonemployee awards is the date the services are completed, resulting in periodic adjustments to stock-based compensation during the vesting period for changes in the fair value of the awards. Stock-based compensation costs for nonemployees are recognized as expense over the vesting period on a straight-line basis. Stock-based compensation expense is classified in the accompanying consolidated statements of operations and comprehensive loss based on the department to which the related services are provided.
Financial Instruments	Financial Instruments The Company’s financial instruments consisted of cash equivalents, marketable securities, accounts payable and liability classified warrants. The carrying amounts of cash and cash equivalents and accounts payable approximate their fair value due to the short-term nature of those financial instruments. The fair value of the marketable securities and liability classified warrants are remeasured to fair value each reporting period as described in Note 5.
Fair Value Measurements	Fair Value Measurements The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. Accounting Standards Codification 820, Fair Value Measurements and Disclosures Level 1 – Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. Level 2 – Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly. Level 3 – Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The Company’s assets and liabilities measured at fair value on a recurring basis include cash equivalents, marketable securities and warrant liabilities.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock outstanding for the period. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock and dilutive common stock equivalents outstanding for the period, determined using the treasury-stock method and the as if-converted method, for convertible securities, if inclusion of these instruments is dilutive. As of December 31, 2017 and 2016, both methods are equivalent. Basic and diluted net loss per share is described further in Note 2.
Income Taxes	Income Taxes Deferred tax assets and liabilities are determined based upon the differences between the financial statement carrying amounts and the tax basis of existing assets and liabilities and for loss and credit carryforwards using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. Deferred tax assets are reduced by a valuation allowance if it is more likely than not that some portion or all of the deferred tax asset will not be realized. The Company assesses its income tax positions and records tax benefits based upon management’s evaluation of the facts, circumstances, and information available at the reporting date. For those tax positions where it is more likely than not that a tax benefit will be sustained, the Company records the largest amount of tax benefit with a greater than 50% likelihood of being realized upon ultimate settlement with a taxing authority having full knowledge of all relevant information. For those income tax positions where it is not more likely than not that a tax benefit will be sustained, no tax benefit is recognized in the consolidated financial statements. The Company classifies interest and penalties associated with such uncertain tax positions as a component of interest expense. As of December 31, 2017 and 2016, the Company has not identified any material uncertain tax positions.
Guarantees and Indemnifications	Guarantees and Indemnifications As permitted under Delaware law, the Company indemnifies its officers and directors for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The Company leases office and laboratory space in Hopkinton, Massachusetts and research and development space in Milford, Massachusetts, under non-cancelable operating leases. The Company has standard indemnification arrangements under these leases that require it to indemnify the landlords against liability for injury, loss, accident, or damage from any claims, actions, proceedings, or costs resulting from certain acts, breaches, violations, or nonperformance under the Company’s lease. Through December 31, 2017, the Company had not experienced any losses related to these indemnification obligations and no material claims were outstanding. The Company does not expect significant claims related to these indemnification obligations, and consequently, concluded that the fair value of these obligations is negligible, and no related reserves were established.
Segment Information	Segment Information Operating segments are identified as components of an enterprise about which separate and discrete financial information is available for evaluation by the chief operating decision maker, the Company’s Chief Executive Officer, in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment and does not track expenses on a program-by-program basis.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In November 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash In March 2016, the FASB issued ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting The update requires the Company to recognize the income tax effect of awards in the income statement when the awards vest or are settled. It also allows the Company to repurchase more of an employee’s shares than it could prior to the update for tax withholding purposes without triggering a liability. The income tax related items had no effect on the current period presentation as the Company did not have any historical excess tax benefits. In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU 2014-09, Revenue from Contracts with Customers In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities Financial Instruments - Overall In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) In September 2016, the FASB issued ASU 2016-15, Classification of Certain Cash Receipts and Cash Payments Statement of Cash Flows In July 2017, the FASB issued ASU 2017-11, Earnings Per Share (Topic 260), Distinguishing Liabilities from Equity (Topic 480), Derivatives and Hedging (Topic 815): I. Accounting for Certain Financial Instruments with Down Round Features and II. Replacement of the Indefinite Deferral for Mandatorily Redeemable Financial Instruments of Certain Nonpublic Entities and Certain Mandatorily Redeemable Noncontrolling Interests with a Scope Exception .

Nature of Business, Basis of 22

Nature of Business, Basis of Presentation and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Estimated Useful Lives of Property and Equipment	Depreciation and amortization are provided using the straight-line method over the estimated useful lives: Asset Category Useful Life Equipment 5-7 years Furniture and fixtures 5 years Leasehold improvements Lesser of 10 years or the remaining term of the respective lease

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Summary of Computation of Basic and Diluted Net Loss Per Share	The following table summarizes the computation of basic and diluted net loss per share of the Company for such periods (in thousands, except share and per share data): Year Ended December 31, 2017 2016 Net loss $ (27,679 ) $ (17,366 ) Weighted-average number of common shares-basic and diluted 11,153,269 7,256,671 Net loss per common share-basic and diluted $ (2.48 ) $ (2.39 )
Summary of Potentially Dilutive Securities Outstanding Excluded from Computation of Diluted Weighted-Average Shares Outstanding	The following potentially dilutive securities outstanding, prior to the use of the treasury stock method or if-converted method, have been excluded from the computation of diluted weighted-average shares outstanding, because such securities had an antidilutive impact due to the losses reported: Year 2017 2016 Common stock warrants 1,787,124 1,798,084 Stock options 988,565 704,315

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Summary of Investments by Category	The following table summarizes the Company’s investments, by category, as of December 31, 2017 and 2016 (in thousands): December 31, December 31, Investments - Current: 2017 2016 Marketable securities - available for sale $ 26,906 $ 14,046 Total $ 26,906 $ 14,046 Investments - Noncurrent: Marketable securities - available for sale $ — $ 752 Total $ — $ 752
Summary of Available-for-Sale Classified Investments	A summary of the Company’s available-for-sale classified investments as of December 31, 2017 and 2016 consisted of the following (in thousands): At December 31, 2017 Cost Basis Unrealized Gains Unrealized Losses Fair Value Investments - Current: Commercial paper $ 9,584 $ — $ — $ 9,584 Corporate bonds 15,347 — (23 ) 15,324 United States treasury securities 1,998 — — 1,998 Total $ 26,929 $ — $ (23 ) $ 26,906 At December 31, 2016 Cost Basis Unrealized Gains Unrealized Losses Fair Value Investments - Current: Agency bonds $ 452 $ — $ — $ 452 Commercial paper 2,947 — — 2,947 Corporate bonds 8,499 — (7 ) 8,492 United States treasury securities 2,155 — — 2,155 Total $ 14,053 $ — $ (7 ) $ 14,046 Investments - Noncurrent: Corporate bonds 752 — — 752 Total $ 752 $ — $ — $ 752
Schedule of Amortized Cost and Fair Value of Available-for-Sale Investments, by Contract Maturity	The amortized cost and fair value of the Company’s available-for-sale investments, by contract maturity, as of December 31, 2017 consisted of the following (in thousands): Amortized Cost Fair Value Due in one year or less $ 26,929 $ 26,906 Due after one year through two years — — Total $ 26,929 $ 26,906

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2017
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment as of December 31, 2017 and 2016 consisted of the following (in thousands): December 31, December 31, 2017 2016 Equipment $ 727 $ 576 Furniture and fixtures 292 140 Leasehold improvements 153 133 Total property and equipment 1,172 849 Less: accumulated depreciation and amortization (485 ) (327 ) Property and equipment, net $ 687 $ 522

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Summary of Assets and Liabilities Measured at Fair Value	A summary of the assets and liabilities that are measured at fair value as of December 31, 2017 and 2016 is as follows (in thousands): Fair Value Measurement at December 31, 2017 Carrying Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds (1) $ 21,265 $ 21,265 $ — $ — Fixed income securities 26,906 — 26,906 — Total $ 48,171 $ 21,265 $ 26,906 $ — Liabilities: Warrant liabilities $ 13,128 $ — $ — $ 13,128 Total $ 13,128 $ — $ — $ 13,128 Fair Value Measurement at December 31, 2016 Assets: Carrying Value Quoted Prices in Active Markets for Identical Assets (Level 1) Significant other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Money market funds (1) $ 9,507 $ 9,507 $ — $ — Fixed income securities 14,798 — 14,798 — Total $ 24,305 $ 9,507 $ 14,798 $ — Liabilities: Warrant liabilities $ 6,333 $ — $ — $ 6,333 Total $ 6,333 $ — $ — $ 6,333 (1) Money market funds are included within cash and cash equivalents in the accompanying consolidated balance sheets are recognized at fair value.
Summary of Change in Company's Level 3 Liabilities, Warrants Issued in a Private Placement	The following table reflects the change in the Company’s Level 3 liabilities, which consist of the warrants issued in a private placement in November 2016 (see Note 7), for the year ended December 31, 2017 (in thousands): November Private Placement Warrants Balance at December 31, 2015 $ — Issuance of warrants 8,275 Change in fair value (1,942 ) Balance at December 31, 2016 $ 6,333 Change in fair value 6,795 Balance at December 31, 2017 $ 13,128

Accrued Expenses and Other Cu27

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2017
Payables And Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses as of December 31, 2017 and 2016 consisted of the following (in thousands): December 31, December 31, 2017 2016 Clinical $ 1,093 $ 738 Compensation and benefits 1,024 901 Accounting and legal 453 279 Other 164 64 Total accrued expenses $ 2,734 $ 1,982

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Summary of Assumptions Used to Record Fair Value of Warrants	A summary of the Black Scholes pricing model assumptions used to record the fair value of the warrants is as follows: December 31, 2017 December 31, 2016 Risk-free interest rate 2.0 % 1.9 % Expected term (in years) 3.9 4.9 Expected volatility 73.1 % 65.5 % Expected dividend yield 0 % 0 %
Summary of Warrant Activities	A summary of warrant activities during the years ended December 31, 2017 and 2016 is as follows: Warrants Outstanding at December 31, 2015 1,181,776 Grants 1,798,084 Exercises (641,743 ) Expirations/cancellations (540,033 ) Outstanding at December 31, 2016 1,798,084 Grants — Exercises (10,960 ) Expirations/cancellations — Outstanding at December 31, 2017 1,787,124
Summary of Option Activity	The following table summarizes the option activity for the year ended December 31, 2017, under both the 2014 Plan and the 2015 Plan (collectively the “Plans”): Options Weighted-Average Exercise Price Per Share Aggregate Intrinsic Value Options outstanding at December 31, 2015 610,481 $ 11.99 — Granted 128,334 10.41 — Exercised (10,247 ) 9.28 29,550 Cancelled (24,253 ) 9.89 — Outstanding at December 31, 2016 704,315 $ 11.82 — Granted 297,500 8.45 — Exercised (10,000 ) 9.28 11,228 Cancelled (3,250 ) 12.44 — Options outstanding at December 31, 2017 988,565 $ 10.83 $ 2,617,859 Options exercisable at December 31, 2017 436,127 $ 11.74 $ 752,700
Summary of Assumptions to Determine Fair Value of Stock Options Granted to Employees and Directors	There were no stock options granted prior to 2015. The assumptions the Company used to determine the fair value of stock options granted to employees and directors in 2017 and 2016 are as follows, presented on a weighted-average basis Year Ended December 31, 2017 2016 Risk-free interest rate 2.0 % 1.4 % Expected term (in years) 6.0 6.1 Expected volatility 80 % 78 % Expected dividend yield 0 % 0 %
Summary of Stock-Based Compensation Expense	The following table summarizes the stock-based compensation expense for the years ended December 31, 2017 and 2016, under the Plans (in thousands): Year Ended December 31, Stock-based compensation: 2017 2016 Research and development $ 489 $ 390 General and administrative 1,422 1,048 Total Stock-based compensation $ 1,911 $ 1,438
Summary of Shares of Common Stock Reserved	As of December 31, 2017 and 2016, the Company has reserved the following shares of common stock for potential conversion of the Preferred Stock, exercise of warrants and outstanding options and issuance of shares available for grant under the 2015 Plan: December 31, 2017 2016 2016 BioHEP warrants 125,000 125,000 2016 IPO warrants 28,347 28,347 November Private Placement warrants 1,633,777 1,644,737 2014 and 2015 Stock incentive plans 1,448,100 1,461,233 Total 3,235,224 3,259,317

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Reconciliation of Statutory U.S. Federal Tax Rate with Effective Tax Rate	A reconciliation of the statutory U.S. Federal Tax Rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2017 2016 U.S. statutory federal income tax rate (34.0 )% (34.0 )% State income taxes, net of federal income tax benefit (3.8 )% (5.7 )% Permanent items 0.8 % 0.9 % Warrant adjustment 8.3 % (3.8 )% R&D credit (0.3 )% (0.4 )% Change in valuation allowance — 43.0 % Change in federal rate impact 29.2 % — Other (0.2 )% — Effective income tax rate 0.0 % 0.0 %
Components of Deferred Tax Assets	The significant components of the Company’s deferred tax assets as of December 31, 2017 and 2016 are as follows (in thousands): December 31, 2017 2016 Net operating loss carryforwards $ 16,781 $ 16,634 Research and development credits 520 385 Accrued expenses 265 322 Property and equipment (11 ) (1 ) License payments 663 1,025 Stock based compensation 831 682 Other – net 22 17 Deferred tax assets 19,071 19,064 Valuation allowance (19,071 ) (19,064 ) Net deferred tax asset and liability $ — $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Summary of Future Minimum Lease Payments for Operating Leases	Future minimum commitments due under all leases at December 31, 2017 are as follows (in thousands): Year 2018 $ 174 2019 468 2020 587 2021 506 Thereafter 3,265 Total minimum lease payments $ 5,000

Nature of Business, Basis of 31

Nature of Business, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Detail)	Mar. 08, 2016	Dec. 31, 2017USD ($)Segment	Dec. 31, 2016USD ($)
Nature Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Accumulated deficit		$ (79,214,000)	$ (51,535,000)
Cash, cash equivalents, restricted cash and marketable securities		50,600,000
Restricted cash		484,000	0
Impairment of long-lived assets		0
Deferred aggregate rent		35,000	35,000
Income tax benefit		0	0
Uncertain tax positions		0	$ 0
Indemnification obligations loss		0
Outstanding material claims		0
Indemnification obligation reserve		$ 0
Number of operating segment | Segment		1
Prior to Adoption of ASU 2016-09 [Member]
Nature Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Forfeiture rate to share-based compensation		0.00%
ASU 2016-09 [Member]
Nature Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment to the opening period		$ 0
Revenue from Rights Concentration Risk [Member] | Revenue, Rights Granted [Member]
Nature Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Concentration risk percentage		0.00%	100.00%
Money Market Funds [Member]
Nature Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents fair value		$ 21,300,000	$ 9,500,000
Lease Agreement [Member]
Nature Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Restricted cash		234,000
Collateral for Credit Card Program [Member]
Nature Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Restricted cash		$ 250,000
IPO [Member]
Nature Of Business Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Reverse stock split description		1-for-4 reverse stock split
Reverse stock split ratio	0.25

Nature of Business, Basis of 32

Nature of Business, Basis of Presentation and Summary of Significant Accounting Policies - Summary of Estimated Useful Lives of Property and Equipment (Detail)	12 Months Ended
	Dec. 31, 2017
Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	Lesser of 10 years or the remaining term of the respective lease

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Computation of Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share Basic And Diluted [Abstract]
Net loss	$ (27,679)	$ (17,366)
Weighted-average number of common shares-basic and diluted	11,153,269	7,256,671
Net loss per common share-basic and diluted	$ (2.48)	$ (2.39)

Net Loss Per Share - Summary 34

Net Loss Per Share - Summary of Potentially Dilutive Securities Outstanding Excluded from Computation of Diluted Weighted-Average Shares Outstanding (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding excluded from the computation of diluted weighted-average shares outstanding	1,787,124	1,798,084
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities outstanding excluded from the computation of diluted weighted-average shares outstanding	988,565	704,315

Investments - Summary of Invest

Investments - Summary of Investments by Category (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments - Current:
Marketable securities - available for sale	$ 26,906	$ 14,046
Total	$ 26,906	14,046
Investments - Noncurrent:
Marketable securities - available for sale		752
Total		$ 752

Investments - Summary of Availa

Investments - Summary of Available-for-Sale Classified Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments - Current [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	$ 26,929	$ 14,053
Unrealized Losses	(23)	(7)
Fair Value	26,906	14,046
Investments - Current [Member] | Agency Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost Basis		452
Fair Value		452
Investments - Current [Member] | Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	15,347	8,499
Unrealized Losses	(23)	(7)
Fair Value	15,324	8,492
Investments - Current [Member] | Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	9,584	2,947
Fair Value	9,584	2,947
Investments - Current [Member] | United States Treasury Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost Basis	1,998	2,155
Fair Value	$ 1,998	2,155
Investments - Noncurrent [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost Basis		752
Fair Value		752
Investments - Noncurrent [Member] | Corporate Bonds [Member]
Schedule Of Available For Sale Securities [Line Items]
Cost Basis		752
Fair Value		$ 752

Investments - Schedule of Amort

Investments - Schedule of Amortized Cost and Fair Value of Available-for-Sale Investments, by Contract Maturity (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Investments Debt And Equity Securities [Abstract]
Due in one year or less, Amortized Cost	$ 26,929
Total, Amortized Cost	26,929
Due in one year or less, Fair Value	26,906
Total, Fair Value	$ 26,906

Property and Equipment, Net - S

Property and Equipment, Net - 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	$ 1,172	$ 849
Less: accumulated depreciation and amortization	(485)	(327)
Property and equipment, net	687	522
Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	727	576
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	292	140
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 153	$ 133

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 158	$ 118

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Assets and Liabilities Measured at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 21,300	$ 9,500
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Total	48,171	24,305
Liabilities, Total	13,128	6,333
Carrying Value [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	21,265	9,507
Carrying Value [Member] | Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed income securities	26,906	14,798
Carrying Value [Member] | Warrant Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liabilities	13,128	6,333
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Total	21,265	9,507
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	21,265	9,507
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Total	26,906	14,798
Significant Other Observable Inputs (Level 2) [Member] | Fixed Income Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed income securities	26,906	14,798
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, Total	13,128	6,333
Significant Unobservable Inputs (Level 3) [Member] | Warrant Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant liabilities	$ 13,128	$ 6,333

Fair Value Measurements - Sum41

Fair Value Measurements - Summary of Change in Company's Level 3 Liabilities, Warrants Issued in a Private Placement (Detail) - Private Placement [Member] - Warrants [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance	$ 6,333	$ 0
Issuance of warrants		8,275
Change in fair value	6,795	(1,942)
Ending balance	$ 13,128	$ 6,333

Accrued Expenses and Other Cu42

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities And Other Liabilities [Abstract]
Clinical	$ 1,093	$ 738
Compensation and benefits	1,024	901
Accounting and legal	453	279
Other	164	64
Total accrued expenses	$ 2,734	$ 1,982

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)

Nov. 23, 2016

May 11, 2016

Feb. 01, 2016

Jun. 30, 2017

Nov. 30, 2016

Jun. 30, 2016

May 31, 2016

Dec. 31, 2017

Dec. 31, 2017

Dec. 31, 2016

Dec. 31, 2015

Aug. 31, 2017

Apr. 30, 2014

Class of Stock [Line Items]

Warrants issued to purchase shares of common stock

1,644,737

Purchase and exercise price of common stock upon warrant exercise

$ 10.79

Warrant expiration date

Nov. 23, 2021

Net proceeds from initial public offering of common stock

$ 9,192,000

Common stock, shares authorized

200,000,000

200,000,000

200,000,000

Convertible preferred stock, shares authorized

10,000,000

10,000,000

10,000,000

Proceed from exercise of warrants

$ 5,300,000

$ 5,300,000

$ 118,000

$ 5,342,000

Warrants exercised, common stock shares

641,743

641,743

Net proceeds from issuance of common stock

$ 39,675,000

Dividend yield

0.00%

0.00%

Expected life (in years)

6 years

6 years 1 month 6 days

Warrants to purchase shares of common stock remained outstanding

1,633,777

Number of shares remain available for grant

0

Stock options granted

0

2014 Stock Incentive Plan [Member]

Class of Stock [Line Items]

Number of authorized shares of common stock to be issued

750,000

Weighted-average remaining contractual life

8 years 2 months 12 days

Weighted-average fair value of all stock options granted

$ 5.89

$ 7.06

2015 Stock Incentive Plan [Member]

Class of Stock [Line Items]

Number of shares remain available for grant

116,863

459,535

459,535

Number of shares of common stock reserved for future issuance

750,000

Expiry date of stock options awarded

10 years

2014 and 2015 Stock Incentive Plans [Member]

Class of Stock [Line Items]

Exercise of an option to purchase additional shares granted to underwriters in connection with offering

10,000

10,247

Stock options granted

297,500

128,334

Fair value of stock options vested

$ 1,700,000

Unrecognized stock-based compensation expense

$ 3,600,000

$ 3,600,000

Weighted-average remaining vesting period

2 years 1 month 6 days

May 2016 IPO warrants [Member]

Class of Stock [Line Items]

Expected volatility of common stock Minimum

87.00%

Risk free rate

1.20%

Dividend yield

0.00%

Expected life (in years)

4 years 11 months 26 days

June 2016 IPO warrants [Member]

Class of Stock [Line Items]

Expected volatility of common stock Minimum

87.00%

Risk free rate

1.23%

Dividend yield

0.00%

Expected life (in years)

4 years 11 months 1 day

Maximum [Member] | 2015 Stock Incentive Plan [Member]

Class of Stock [Line Items]

Number of shares remain available for grant

116,863

Sales Agreement [Member] | Cantor Fitzgerald & Co. [Member]

Class of Stock [Line Items]

Issuance of common stock

252,443

Shares issued price per share

$ 15.55

$ 15.55

Sales Commission Percentage On Common Stock

3.00%

Gross proceeds from issuance of controlled equity offering

$ 3,900,000

Net proceeds from issuance of controlled equity offering

3,700,000

Sales Agreement [Member] | Cantor Fitzgerald & Co. [Member] | Maximum [Member]

Class of Stock [Line Items]

Aggregate offering price

$ 50,000,000

IPO [Member]

Class of Stock [Line Items]

Warrants issued to purchase shares of common stock

747

27,600

Purchase and exercise price of common stock upon warrant exercise

$ 15

Warrant expiration date

May 5, 2021

Fair value of equity

$ 200,000

$ 200,000

Convertible preferred stock converted into common stock

250,000

250,000

Private Placement [Member]

Class of Stock [Line Items]

Issuance of common stock

1,644,737

Warrants issued to purchase shares of common stock

1,644,737

Purchase and exercise price of common stock upon warrant exercise

$ 10.79

Warrant expiration date

Nov. 23, 2021

Shares issued price per share

$ 9.12

Net proceeds from issuance of common stock

$ 13,700,000

Common Stock [Member]

Class of Stock [Line Items]

Exercise of an option to purchase additional shares granted to underwriters in connection with offering

10,000

10,247

Warrants exercised, common stock shares

10,960

641,743

Common Stock [Member] | 2014 Stock Incentive Plan [Member]

Class of Stock [Line Items]

Shares issued price per share

$ 13.44

$ 13.44

Common Stock [Member] | Sales Agreement [Member]

Class of Stock [Line Items]

Issuance of common stock

252,443

Common Stock [Member] | IPO [Member]

Class of Stock [Line Items]

Issuance of common stock

944,000

944,900

Shares issued price per share

$ 12

Exercise of an option to purchase additional shares granted to underwriters in connection with offering

24,900

Net proceeds from initial public offering of common stock

$ 8,200,000

Common stock, shares authorized

200,000,000

Common Stock [Member] | Private Placement [Member]

Class of Stock [Line Items]

Issuance of common stock

1,644,737

Common Stock [Member] | Public Offering [Member]

Class of Stock [Line Items]

Issuance of common stock

3,269,219

3,269,219

Shares issued price per share

$ 13

Exercise of an option to purchase additional shares granted to underwriters in connection with offering

384,604

Net proceeds from issuance of common stock

$ 39,700,000

Preferred Stock [Member] | IPO [Member]

Class of Stock [Line Items]

Convertible preferred stock, shares authorized

10,000,000

Common Stock Warrants [Member]

Class of Stock [Line Items]

Fair value of equity

$ 8,300,000

$ 800,000

$ 800,000

Expected volatility of common stock Minimum

71.00%

Risk free rate

1.01%

Dividend yield

0.00%

Expected life (in years)

2 years 6 months

Common Stock Warrants [Member] | Private Placement [Member]

Class of Stock [Line Items]

Fair value of equity

$ 13,100,000

$ 13,100,000

$ 6,300,000

License Agreement [Member] | Common Stock [Member]

Class of Stock [Line Items]

Issuance of common stock

125,000

License Agreement [Member] | BioHEP Technologies Ltd. [Member]

Class of Stock [Line Items]

Issuance of common stock

125,000

Warrants issued to purchase shares of common stock

125,000

Purchase and exercise price of common stock upon warrant exercise

$ 16

Warrant expiration date

Aug. 1, 2018

License Agreement [Member] | BioHEP Technologies Ltd. [Member] | Common Stock [Member]

Class of Stock [Line Items]

Fair value of equity

$ 2,000,000

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Assumptions Used to Record Fair Value of Warrants (Detail) - Warrants [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.00%	1.90%
Expected term (in years)	3 years 10 months 24 days	4 years 10 months 24 days
Expected volatility	73.10%	65.50%
Expected dividend yield	0.00%	0.00%

Stockholders' Equity - Summar45

Stockholders' Equity - Summary of Warrant Activities (Detail) - Common Stock Warrants [Member] - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Class of Warrant or Right [Line Items]
Outstanding, Beginning Balance	1,798,084	1,181,776
Grants	0	1,798,084
Exercises	(10,960)	(641,743)
Expirations/cancellations	0	(540,033)
Outstanding, Ending balance	1,787,124	1,798,084

Stockholders' Equity - Summar46

Stockholders' Equity - Summary of Option Activity (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Granted			0
2014 and 2015 Stock Incentive Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding, Beginning Balance	704,315	610,481
Options Granted	297,500	128,334
Options Exercised	(10,000)	(10,247)
Options Cancelled	(3,250)	(24,253)
Options outstanding, Ending balance	988,565	704,315	610,481
Options exercisable	436,127
Weighted-Average Exercise Price Per Share, Options outstanding, Beginning Balance	$ 11.82	$ 11.99
Weighted-Average Exercise Price Per Share, Granted	8.45	10.41
Weighted-Average Exercise Price Per Share, Exercised	9.28	9.28
Weighted-Average Exercise Price Per Share, Cancelled	12.44	9.89
Weighted-Average Exercise Price Per Share, Options outstanding, Ending Balance	10.83	$ 11.82	$ 11.99
Weighted-Average Exercise Price Per Share, Options exercisable	$ 11.74
Aggregate Intrinsic Value, Exercised	$ 11,228	$ 29,550
Aggregate Intrinsic Value, Options outstanding, Ending Balance	2,617,859
Aggregate Intrinsic Value, Option exercisable	$ 752,700

Stockholders' Equity - Summar47

Stockholders' Equity - Summary of Assumptions to Determine Fair Value of Stock Options Granted to Employees and Directors (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	2.00%	1.40%
Expected term (in years)	6 years	6 years 1 month 6 days
Expected volatility	80.00%	78.00%
Expected dividend yield	0.00%	0.00%

Stockholders' Equity - Summar48

Stockholders' Equity - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,911	$ 1,438
2014 and 2015 Stock Incentive Plans [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,911	1,438
2014 and 2015 Stock Incentive Plans [Member] | Stock Options [Member] | Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	489	390
2014 and 2015 Stock Incentive Plans [Member] | Stock Options [Member] | General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,422	$ 1,048

Stockholders' Equity - Summar49

Stockholders' Equity - Summary of Shares of Common Stock Reserved (Detail) - shares	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved	3,235,224	3,259,317
2014 and 2015 Stock Incentive Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved	1,448,100	1,461,233
Private Placement Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved	1,633,777	1,644,737
2016 BioHEP warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved	125,000	125,000
2016 IPO warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved	28,347	28,347

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of The Statutory Federal Tax Rate to The Company's Effective Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Effective Income Tax Rate Continuing Operations Tax Rate Reconciliation [Abstract]
U.S. statutory federal income tax rate	(34.00%)	(34.00%)
State income taxes, net of federal income tax benefit	(3.80%)	(5.70%)
Permanent items	0.80%	0.90%
Warrant adjustment	8.30%	(3.80%)
R&D credit	(0.30%)	(0.40%)
Change in valuation allowance		43.00%
Change in federal rate impact	29.20%
Other	(0.20%)
Effective income tax rate	(0.00%)	(0.00%)

Income Taxes - Schedule of Sign

Income Taxes - Schedule of Significant Components of the Company's Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Components Of Deferred Tax Assets And Liabilities [Abstract]
Net operating loss carryforwards	$ 16,781	$ 16,634
Research and development credits	520	385
Accrued expenses	265	322
Property and equipment	(11)	(1)
License payments	663	1,025
Stock based compensation	831	682
Other – net	22	17
Deferred tax assets	19,071	19,064
Valuation allowance	$ (19,071)	$ (19,064)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Line Items]
Increase in valuation allowance due to increase in deferred tax assets		$ 8,000	$ 7,464,000
U.S. statutory federal income tax rate		34.00%	34.00%
Period for cumulative change in ownership		3 years
Cumulative change in ownership interest percentage		50.00%
Uncertain tax position		$ 0	$ 0
Scenario, Forecast [Member]
Income Taxes [Line Items]
U.S. statutory federal income tax rate	21.00%
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 61,552,000
Operating loss carryforwards expiration beginning year		2,029
Operating loss carryforwards expiration ending year		2,037
Income tax credits		$ 294,000
Income tax credit carryforward expiration year		Dec. 31, 2037
State [Member]
Income Taxes [Line Items]
Net operating loss carryforwards		$ 60,997,000
Operating loss carryforwards expiration beginning year		2,029
Operating loss carryforwards expiration ending year		2,037
Income tax credits		$ 287,000
Income tax credit carryforward expiration year		Dec. 31, 2037

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Oct. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Commitments And Contingencies [Line Items]
Total lease commitment		$ 5,000,000
Rent paid		233,000	$ 166,000
Accruals for contingent liabilities		0
License Agreement [Member] | BioHEP Technologies Ltd. [Member]
Commitments And Contingencies [Line Items]
Maximum estimated development and regulatory milestone payments		3,500,000
Maximum aggregate sublicensing revenues		2,000,000
Milestone and royalty payments		0
Transition Agreement [Member] | President And Chief Executive Officer [Member]
Commitments And Contingencies [Line Items]
Accruals for contingent liabilities		0
Payments for transition services		$ 464,000
Transition services monthly payments		18 months
Milford, Massachusetts [Member]
Commitments And Contingencies [Line Items]
Lease extended term date		Mar. 31, 2018
Hopkinton, Massachusetts [Member]
Commitments And Contingencies [Line Items]
Lease term expiration date		May 31, 2021
Total lease commitment	$ 4,400,000			$ 771,000
Initial term of new lease	125 months
One time option to extend new lease term	5 years
Rent abatement period	11 months
Monthly rent payments	$ 34,533
Percentage of annual rent increase for first five years	3.00%
Percentage of annual rent increase after five years	2.50%

Commitments and Contingencies54

Commitments and Contingencies - Summary of Future Minimum Lease Payments for Operating Leases (Detail) $ in Thousands	Dec. 31, 2017USD ($)
Leases, Operating [Abstract]
2,018	$ 174
2,019	468
2,020	587
2,021	506
Thereafter	3,265
Total minimum lease payments	$ 5,000

401(k) Plan - Additional Inform

401(k) Plan - Additional Information (Detail) - 401(k) Plan [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Contribution by company	$ 124,000	$ 89,000
Maximum [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan, employer matching contribution, percent of match	4.00%	4.00%

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - BioHEP Technologies Ltd. [Member] - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Related Party Transaction [Line Items]
Legal expenses related party	$ 0	$ 14,000
Minimum [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		5.00%