Genocea Biosciences (GNCAQ) 10-Q 23 Jul 20 2020 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2020	Jul. 21, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
Document Transition Report	false
Entity File Number	001-36289
Entity Registrant Name	Genocea Biosciences, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	51-0596811
Entity Address, Address Line One	100 Acorn Park Drive
Entity Address, City or Town	Cambridge,
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02140
City Area Code	617
Local Phone Number	876-8191
Title of 12(b) Security	Common stock, $0.001 par value per share
Trading Symbol	GNCA
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		29,964,496
Entity Central Index Key	0001457612
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 22,108	$ 40,127
Prepaid expenses and other current assets	2,559	1,457
Total current assets	24,667	41,584
Property and equipment, net	2,519	2,617
Right of use assets	11,265	6,306
Restricted cash	631	631
Other non-current assets	1,434	1,473
Total assets	40,516	52,611
Current liabilities:
Accounts payable	678	553
Accrued expenses and other current liabilities	4,071	4,611
Deferred revenue	1,094	0
Lease liabilities	2,053	1,117
Current portion of long-term debt	13,627
Total current liabilities	21,523	6,281
Non-current liabilities:
Long-term debt, net of current portion	0	13,407
Warrant liability	1,483	2,486
Lease liabilities, net of current portion	9,473	5,395
Total liabilities	32,479	27,569
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock, $0.001 par value; (shares authorized of 25,000,000 at June 30, 2020 and December 31, 2019; 1,635 shares issued and outstanding at June 30, 2020 and December 31, 2019)	701	701
Common stock, $0.001 par value; (shares authorized of 170,000,000 at June 30, 2020 and 85,000,000 at December 31, 2019, 29,964,496 shares issued and outstanding at June 30, 2020 and 27,452,900 shares issued and outstanding at December 31, 2019)	30	27
Additional paid-in capital	362,434	355,268
Accumulated deficit	(355,128)	(330,954)
Total stockholders’ equity	8,037	25,042
Total liabilities and stockholders’ equity	$ 40,516	$ 52,611

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
License revenue	$ 906	$ 0	$ 906	$ 0
Operating expenses:
Research and development	8,587	6,849	18,574	13,309
General and administrative	3,480	3,217	6,868	6,234
Total operating expenses	12,067	10,066	25,442	19,543
Loss from operations	(11,161)	(10,066)	(24,536)	(19,543)
Other (expense) income:
Change in fair value of warrants	222	3,870	1,003	(1,917)
Interest expense, net	(365)	(299)	(624)	(601)
Other expense	(17)	0	(17)	(1)
Total other (expense) income	(160)	3,571	362	(2,519)
Net loss	(11,321)	(6,495)	(24,174)	(22,062)
Comprehensive loss	$ (11,321)	$ (6,495)	$ (24,174)	$ (22,062)
Net loss per share - basic and diluted	$ (0.39)	$ (0.42)	$ (0.84)	$ (1.57)
Weighted-average number of common shares used in computing net loss per share	29,142	15,344	28,642	14,035

Consolidated Consolidated State

Consolidated Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	ESPP	Common Stock	Common StockESPP	Preferred Shares	Additional Paid-In Capital	Additional Paid-In CapitalESPP	Accumulated Deficit
Balance - Stockholders' Equity (Deficit) (in shares) at Dec. 31, 2018			10,847		701
Balance - Stockholders' Equity (Deficit) at Dec. 31, 2018	$ 7,335		$ 11			$ 298,627		$ (292,004)
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Issuance of common stock (in shares)			3,200		0
Issuance of common stock	14,026		$ 3			14,023
Exercise of stock options (in shares)			3
Exercise of stock options	12					12
Stock-based compensation expense	429					429
Net loss	(15,567)							(15,567)
Balance - Stockholders' Equity (Deficit) (in shares) at Mar. 31, 2019			14,050		701
Balance - Stockholders' Equity (Deficit) at Mar. 31, 2019	6,235		$ 14			313,091		(307,571)
Balance - Stockholders' Equity (Deficit) (in shares) at Dec. 31, 2018			10,847		701
Balance - Stockholders' Equity (Deficit) at Dec. 31, 2018	7,335		$ 11			298,627		(292,004)
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Net loss	(22,062)
Balance - Stockholders' Equity (Deficit) (in shares) at Jun. 30, 2019			26,150		701
Balance - Stockholders' Equity (Deficit) at Jun. 30, 2019	38,438		$ 26			351,777		(314,066)
Balance - Stockholders' Equity (Deficit) (in shares) at Mar. 31, 2019			14,050		701
Balance - Stockholders' Equity (Deficit) at Mar. 31, 2019	6,235		$ 14			313,091		(307,571)
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Issuance of common stock (in shares)			12,074	24
Issuance of common stock	38,167	$ 48	$ 12			38,155	$ 48
Exercise of stock options (in shares)			2
Exercise of stock options	9					9
Stock-based compensation expense	474					474
Net loss	(6,495)							(6,495)
Balance - Stockholders' Equity (Deficit) (in shares) at Jun. 30, 2019			26,150		701
Balance - Stockholders' Equity (Deficit) at Jun. 30, 2019	38,438		$ 26			351,777		(314,066)
Balance - Stockholders' Equity (Deficit) (in shares) at Dec. 31, 2019			27,453		701
Balance - Stockholders' Equity (Deficit) at Dec. 31, 2019	25,042		$ 27			355,268		(330,954)
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Issuance of common stock (in shares)			187	4
Issuance of common stock	440		$ 1			439
Stock-based compensation expense	384					384
Net loss	(12,853)							(12,853)
Balance - Stockholders' Equity (Deficit) (in shares) at Mar. 31, 2020			27,644		701
Balance - Stockholders' Equity (Deficit) at Mar. 31, 2020	13,013		$ 28			356,091		(343,807)
Balance - Stockholders' Equity (Deficit) (in shares) at Dec. 31, 2019			27,453		701
Balance - Stockholders' Equity (Deficit) at Dec. 31, 2019	25,042		$ 27			355,268		(330,954)
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Net loss	(24,174)
Balance - Stockholders' Equity (Deficit) (in shares) at Jun. 30, 2020			29,964		701
Balance - Stockholders' Equity (Deficit) at Jun. 30, 2020	8,037		$ 30			362,434		(355,128)
Balance - Stockholders' Equity (Deficit) (in shares) at Mar. 31, 2020			27,644		701
Balance - Stockholders' Equity (Deficit) at Mar. 31, 2020	13,013		$ 28			356,091		(343,807)
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Issuance of common stock (in shares)			2,287	33
Issuance of common stock	5,799	$ 60	$ 2			5,797	$ 60
Stock-based compensation expense	486					486
Net loss	(11,321)							(11,321)
Balance - Stockholders' Equity (Deficit) (in shares) at Jun. 30, 2020			29,964		701
Balance - Stockholders' Equity (Deficit) at Jun. 30, 2020	$ 8,037		$ 30			$ 362,434		$ (355,128)

Condensed Consolidated Statemen

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Operating activities
Net loss	$ (24,174)	$ (22,062)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	556	550
Stock-based compensation	870	902
Change in fair value of warrant liability	(1,003)	1,917
Gain (loss) on sale of equipment	3	(19)
Non-cash interest expense	220	41
Asset impairment	97	0
Changes in operating assets and liabilities	(281)	729
Net cash used in operating activities	(23,712)	(17,942)
Investing activities
Purchases of property and equipment	(550)	(654)
Proceeds from sale of equipment	22	19
Net cash used in investing activities	(528)	(635)
Financing activities
Proceeds from issuance of common stock, net	6,239	52,194
Proceeds from the issuance of common stock under ESPP	60	48
Payments on finance lease	(78)	0
Proceeds from exercise of stock options	0	21
Repayment of long-term debt	0	(1,377)
Net cash provided by financing activities	6,221	50,886
Net (decrease) increase in cash, cash equivalents and restricted cash	(18,019)	32,309
Cash, cash equivalents and restricted cash at beginning of period	40,758	26,677
Cash, cash equivalents and restricted cash at end of period	22,739	58,986
Non-cash financing activities and supplemental cash flow information
Right-of-use asset obtained in exchange for lease liabilities	5,931	5,385
Cash paid in connection with operating lease liabilities	1,097	816
Cash paid for interest	523	577
Property and equipment included in accounts payable and accrued expenses	$ 0	$ 127

Organization and operations

Organization and operations	6 Months Ended
	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and operations	Organization and operations The Company Genocea Biosciences, Inc. (the “Company”) is a biopharmaceutical company that was incorporated in Delaware on August 16, 2006 and has a principal place of business in Cambridge, Massachusetts. The Company seeks to discover and develop novel cancer immunotherapies using its ATLAS TM proprietary discovery platform. The ATLAS platform profiles each patient's CD4 + and CD8 + T cell immune responses to every potential target or “antigen” in that patient's tumor. The Company believes that this approach optimizes antigen selection for immunotherapies such as cancer vaccines and cellular therapies. Consequently, the Company believes that ATLAS could lead to more immunogenic and efficacious cancer immunotherapies. The Company’s most advanced program is GEN-009, a personalized neoantigen cancer vaccine, for which it is conducting a Phase 1/2a clinical trial. The GEN-009 program uses ATLAS to identify neoantigens, or immunogenic tumor mutations unique to each patient, for inclusion in each patient's GEN-009 vaccine. The Company is also advancing GEN-011, a neoantigen-specific adoptive T cell therapy program that also relies on ATLAS. In June 2020, the Company submitted an Investigational New Drug (“IND”) application to support the initiation of a Phase 1/2 clinical trial. The Company has received verbal notification from the U.S. Food and Drug Administration (“FDA”) that the agency has completed its review of the Company’s IND application for GEN-011. In this verbal feedback, the FDA informed the Company that it is placing the IND on clinical hold until it receives additional information pertaining to certain third-party reagents used in the GEN-011 manufacturing process. These reagents are not a component of the final cell therapy product. The Company expects to receive official written communication from the FDA regarding the hold and the FDA’s position in the near future and plans to work with the FDA to resolve their questions as quickly as possible. The Company is devoting substantially all of its efforts to product research and development, initial market development, and raising capital. The Company has not generated any product revenue related to its primary business purpose to date and is subject to a number of risks and uncertainties common to companies in the biotech and pharmaceutical industry, including, but not limited to, the risks associated with the uncertainty of success of its preclinical and clinical trials; the challenges associated with gaining regulatory approval of product candidates; the risks associated with commercializing pharmaceutical products, if approved for marketing and sale; the potential for development by third parties of new technological innovations that may compete with the Company’s products; the dependence on key personnel; the challenges of protecting proprietary technology; the need to comply with government regulations; the high cost of drug development; competition from other companies; the uncertainty of being able to secure additional capital when needed to fund operations; and the challenges and uncertainty associated with the recent outbreak of the coronavirus, or referred to as COVID-19, that have arisen in the global economy, that could adversely impact the Company's operations, supply chain, preclinical development work, clinical trials and ability to raise capital. Accounting Standards Codification (“ASC”) 205-40, Presentation of Financial Statements-Going Concern (“ASC 205-40”), requires the Company to evaluate whether conditions and/or events raise substantial doubt about its ability to meet its future financial obligations as they become due within one year after the financial statements are issued. As of June 30, 2020 , the Company had an accumulated deficit of $355.1 million and anticipates that it will continue to incur significant operating losses for the foreseeable future as it continues to develop its product candidates. Until such time, if ever, as the Company can generate substantial product revenue and achieve profitability, the Company expects to finance its cash needs through a combination of equity offerings, debt financing, strategic transactions, or other sources of funding. If the Company is unable to raise additional funds when needed, the Company may be required to implement further cost reduction strategies, including ceasing development of GEN-009, GEN-011, or other corporate programs and activities. As reflected in the consolidated financial statements, the Company had available cash and cash equivalents of $22.1 million at June 30, 2020 . In addition, the Company had cash used in operating activities of $23.7 million for the six months ended June 30, 2020 . In July 2020, the Company entered into a private placement financing transaction in which the Company will issue shares of its common stock, pre-funded warrants and warrants for gross cash proceeds of approximately $80.0 million , before deducting fees to the placement agent and other offering expenses payable by the Company. The closing of the private placement financing is expected to occur on or about July 24, 2020. The proceeds from this financing combined with the Company’s available cash and cash equivalents at June 30, 2020 are expected to fund operations to mid-2022.

Summary of significant accounti

Summary of significant accounting policies	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Summary of significant accounting policies	Summary of significant accounting policies The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the Company's audited consolidated financial statements and the accompanying notes included in the Company's Annual Report on Form 10-K for the year ended December 31, 2019 (“ 2019 Form 10-K”). The Company's accounting policies are described in the “Notes to Consolidated Financial Statements” in the Company's 2019 Form 10-K and updated, as necessary, in the Company's Quarterly Reports on Form 10-Q. The December 31, 2019 condensed consolidated balance sheet data presented for comparative purposes were derived from the Company's audited financial statements but do not include all disclosures required by U.S. GAAP. The results of operations for the three and six months ended June 30, 2020 are not necessarily indicative of the operating results for the full year or for any other subsequent interim period. Basis of presentation The accompanying unaudited condensed consolidated financial statements include those accounts of the Company and a wholly owned subsidiary after elimination of all intercompany accounts and transactions. The Company operates as one segment, which is discovering, researching, developing and commercializing novel cancer immunotherapies. Use of estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to clinical trial accruals, estimates related to prepaid and accrued research and development expenses, revenue recognition, and warrants to purchase redeemable securities. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions. Significant accounting policies There were no changes to significant accounting policies during the six months ended June 30, 2020 , as compared to the those disclosed in the 2019 Form 10-K, except as set forth below. Foreign Currency Translation Realized and unrealized gains and losses resulting from foreign currency transactions denominated in currencies other than the functional currency are reflected as other (expense) income, net in the consolidated statements of operations in accordance with ASC Topic 830, Foreign Currency Matters (“ASC 830”). Revenue Recognition In accordance with ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”) , revenue is recognized when a customer obtains control of promised goods or services. The amount of revenue recognized reflects the consideration to which the Company expects to be entitled in exchange for these goods and services. To achieve this core principle, the Company applies the following five steps: 1) identify the customer contract; 2) identify the contract’s performance obligations; 3) determine the transaction price; 4) allocate the transaction price to the performance obligations; and 5) recognize revenue when or as a performance obligation is satisfied. Licensing arrangements are analyzed to determine whether the promised goods or services, which include licenses and research and development materials and services, are distinct or whether they must be accounted for as part of a combined performance obligation. If the license is considered not to be distinct, the license would then be combined with other promised goods or services as a combined performance obligation. Certain contracts contain options to obtain future goods or services at a discount, which would not be provided without entering into the contract. These options are considered material rights, and therefore, are accounted for as separate performance obligations. The Company then determines the fair value to be allocated to this promised service. The transaction price is determined based on the consideration to which the Company will be entitled. The consideration promised may include fixed amounts, variable amounts, or both. For milestone payments, the Company estimates the amount of variable consideration by using the most likely amount method. In making this assessment, the Company evaluates factors such as the clinical, commercial and other risks that must be overcome to achieve the milestone. The Company re-evaluates the probability of achievement of such variable consideration and any related constraints at each reporting period. The Company includes variable consideration in the transaction price to the extent it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price among the performance obligations on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct good or service that forms part of a single performance obligation. The Company allocates the transaction price based on the estimated standalone selling price of the underlying performance obligations. The Company must develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the standalone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs to complete the respective performance obligation. Certain variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated to each performance obligation are consistent with the amount the Company would expect to receive for each performance obligation. The transaction price is generally allocated to each separate performance obligation on a relative standalone selling price basis. When a performance obligation is satisfied, revenue is recognized for the amount of the transaction price allocated to that performance obligation on a relative standalone selling price basis, which excludes estimates of variable consideration that are constrained. Significant management judgment is required in determining the level of effort required under an arrangement and the period over which the Company is expected to complete its performance obligations under an arrangement. For performance obligations consisting of licenses and other promises, the Company utilizes judgment to assess whether the combined performance obligation is satisfied over time or at a point in time and the recognition pattern of non-refundable, up-front fees. Contract liabilities The Company records a contract liability, classified in deferred revenue on the condensed consolidated balance sheet, when it has received payment but has not yet satisfied the related performance obligations. In the event of an early termination of a contract with customer, any contract liabilities would be recognized in the period in which all Company obligations under the agreement have been fulfilled. New Accounting Pronouncements The following new accounting pronouncements were adopted by the Company on January 1, 2020: In 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. The Company early adopted the standard on January 1, 2020. Based on the composition of the Company's investment portfolio, which includes only money market funds, and the insignificance of the Company's other financial assets, current market conditions, and historical credit loss activity, the adoption of this standard did not have a material impact on the Company's consolidated financial statements and related disclosures. In 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). The new standard requires public entities to disclose certain new information and modifies some disclosure requirements. The Company adopted the standard on the required effective date of January 1, 2020. This standard did not have a material impact on the Company's disclosures. In 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40) : Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). ASU 2018-15 requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance in Accounting Standards Codification 350-40 to determine which implementation costs to defer and recognize as an asset. The Company adopted the standard on the required effective date of January 1, 2020. This standard did not have a material impact on the Company's consolidated financial statements and related disclosures. The following new accounting pronouncements have been issued but are not yet effective: In 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

Fair value of financial instrum

Fair value of financial instruments	6 Months Ended
	Jun. 30, 2020
Cash and Cash Equivalents [Abstract]
Fair value of financial instruments	The Company has certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. • Level 1—Fair values are determined by utilizing quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access; • Level 2—Fair values are determined by utilizing quoted prices for similar assets and liabilities in active markets or other market observable inputs such as interest rates, yield curves and foreign currency spot rates; and • Level 3—Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable. The Company's financial assets consist of cash equivalents and the Company's financial liabilities consist of a warrant liability. The fair value of the Company’s cash equivalents is determined using quoted prices in active markets. The Company's cash equivalents consist of money market funds that are classified as Level 1. The fair value of the Company’s warrant liability is determined using a Monte Carlo simulation. See Note 9. Warrants for assumptions used and methodologies utilized in calculating the estimated fair value. The Company’s warrant liability is classified as Level 3. The following table sets forth the Company's assets and liabilities that are measured at fair value on a recurring basis as of June 30, 2020 and December 31, 2019 (in thousands): Quoted prices in active markets Significant other observable inputs Significant unobservable inputs Total (Level 1) (Level 2) (Level 3) June 30, 2020 Assets: Cash equivalents $ 21,927 $ 21,927 $ — $ — Total assets $ 21,927 $ 21,927 $ — $ — Liabilities: Warrant liability $ 1,483 $ — $ — $ 1,483 Total liabilities $ 1,483 $ — $ — $ 1,483 December 31, 2019 Assets: Cash equivalents $ 39,971 $ 39,971 $ — $ — Total assets $ 39,971 $ 39,971 $ — $ — Liabilities: Warrant liability $ 2,486 $ — $ — $ 2,486 Total liabilities $ 2,486 $ — $ — $ 2,486 The following table reflects the change in the Company’s Level 3 warrant liability (in thousands): Warrant Liability Balance at December 31, 2019 $ 2,486 Change in fair value (1,003 ) Balance at June 30, 2020 $ 1,483

Revenue

Revenue	6 Months Ended
	Jun. 30, 2020
Revenue Recognition and Deferred Revenue [Abstract]
Revenue	Revenue In May 2020, the Company entered into a material transfer agreement (the “MTA”) with Shionogi & Co., Ltd. (“Shionogi”) pursuant to which the Company agreed to transfer certain HSV-2 antigens from its GEN-003 program to Shionogi to evaluate the potential development of a novel HSV-2 vaccine. In connection with the agreement, the Company provided Shionogi with an option to negotiate an exclusive development and commercialization license for the HSV-2 antigens. Under the terms of the MTA, Shionogi paid the Company a $2.0 million non-refundable, creditable (with respect to the up-front fee pursuant to a development and commercialization agreement) up-front fee and the Company could receive an additional payment if Shionogi elects to perform certain experiments. Prior to the expiration of the MTA, Shionogi has the option to negotiate a development and commercialization agreement. If executed, the terms of the development and commercialization agreement are expected to include an upfront payment, regulatory and sales milestones, and tiered royalties. Final terms of the development and commercialization agreement will be based on evaluation of the HSV-2 assets and overall diligence. If licensed, Shionogi will assume responsibility for global development and commercialization of an HSV-2 vaccine product. Management evaluated the promised goods and services within the MTA and determined those which represented separate performance obligations. As a result, management concluded there were two separate performance obligations at the inception of the MTA: (i) a combined performance obligation consisting of a limited use research license and the delivery of the initial antigen materials and (ii) the right to negotiate a license prior to expiration of the MTA, which was deemed to be a material right. The Company determined that the exclusive limited use research license and the delivery of the initial antigen materials should be combined as they are not capable of being distinct. A third party would not be able to provide the initial antigen materials as it contains the Company’s proprietary intellectual property and Shionogi could not benefit from the research license without the initial antigen materials. The Company determined that the option to negotiate the development and commercialization agreement prior to the expiration of the MTA is a material right. The $2.0 million upfront fee associated with the MTA is creditable against the upfront fee for the development and commercialization agreement and represents a discount that would otherwise not be available to the customer without entering into the MTA. The Company estimated the standalone selling price of the initial antigen materials based on the expected cost plus a margin approach. The Company developed its standalone selling price for the material right by applying a probability-weighted likelihood that Shionogi will exercise its option to license the HSV-2 assets. The transaction price was comprised of fixed consideration of $2.0 million . The fixed consideration was allocated to each of the performance obligations based on the relative standalone selling prices. The Company concluded the additional payment represents variable consideration and should be constrained, and therefore, did not allocate variable consideration to any of the performance obligations. The amount allocated to the limited use research license and the delivery of the initial antigen materials, or $0.9 million , was recognized upon delivery of the materials to Shionogi in the second quarter of 2020. The amount allocated to the material right will be recognized upon either (i) the execution of a development and commercialization agreement or (ii) the termination of the MTA and is recorded as deferred revenue on the Company's condensed consolidated balance sheet.

Accrued expenses and other curr

Accrued expenses and other current liabilities	6 Months Ended
	Jun. 30, 2020
Payables and Accruals [Abstract]
Accrued expenses and other current liabilities	Accrued expenses and other current liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): June 30, December 31, 2020 2019 Research and development costs $ 1,945 $ 1,607 Payroll and employee-related costs 1,351 2,245 Other current liabilities 775 759 Total $ 4,071 $ 4,611

Commitments and contingencies

Commitments and contingencies	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Operating leases As of June 30, 2020 , the Company has a lease for two floors of lab and office space in a multi-tenant building in Cambridge, Massachusetts. On January 1, 2019, the Company adopted ASU 2016-02, Leases (Topic 842) , (“ASC 842”), using the required retrospective approach and utilizing the effective date as the date of initial application. The Company's lease contains both an extension of an existing lease and an expansion for additional office and lab space. Both the extension and the expansion expire in February 2025. The Company's right to use and control the expansion space began in March 2020. As a result, the Company recognized an increase in the right of use (“ROU”) assets of $5.9 million and associated lease liabilities of $5.8 million in the first quarter of 2020. The Company has the option to extend the lease term for an additional five years , which is not included in the Company's ROU assets and associated lease liabilities as of June 30, 2020 . For the three months ended June 30, 2020 and 2019 lease expense, net of sublease income, was $0.8 million and $0.3 million , respectively. For the six months ended June 30, 2020 and 2019 lease expense, net of sublease income, was $1.3 million and $0.7 million , respectively. The weighted average remaining lease term and weighted average discount rate of the Company's operating leases are as follows: June 30, 2020 June 30, 2019 Weighted average remaining lease term in years 4.67 5.48 Weighted average discount rate 8.13 % 8.31 % Finance lease In December 2019, the Company entered into an agreement to lease lab equipment for a term of 15 months. The Company determined that the agreement qualifies as a finance lease based on the criteria that the Company holds the option to purchase the asset and is reasonably certain to exercise at the end of the lease term. The ROU asset and lease liability were calculated using an incremental borrowing rate of 7.95% . Lease payments on this lease began in January 2020. The following table summarizes the presentation in the Company's consolidated balance sheets: Leases (in thousands) Classification June 30, 2020 December 31, 2019 Assets Operating Lease ROU asset $ 11,175 $ 6,156 Finance Lease ROU asset 90 150 Total lease assets $ 11,265 $ 6,306 Liabilities Current Operating Lease liabilities $ 1,977 $ 990 Finance Lease liabilities 76 127 Non-current Operating Lease liabilities, net of current portion 9,473 5,373 Finance Lease liabilities, net of current portion — 22 Total lease liabilities $ 11,526 $ 6,512 The minimum lease payments related to the Company's operating and finance leases in accordance with ASC 842 as of June 30, 2020 were as follows (in thousands): Operating leases Finance lease Total 2020 $ 1,406 $ 56 $ 1,462 2021 2,871 23 2,894 2022 2,943 — 2,943 2023 3,017 — 3,017 2024 and thereafter 3,609 — 3,609 Total lease payments $ 13,846 $ 79 $ 13,925 Less imputed interest (2,396 ) (3 ) (2,399 ) Total $ 11,450 $ 76 $ 11,526 At June 30, 2020 and December 31, 2019 , the Company had an outstanding letter of credit of $0.6 million , with a financial institution related to a security deposit for the office and lab space lease, which is secured by cash on deposit and expires in February 2025. Contractual obligations The Company has entered into certain agreements with various contract research organizations (“CROs”) and contract manufacturing organizations (“CMOs”), which generally include cancellation clauses. Harvard University License Agreement The Company has an exclusive license agreement with Harvard University (“Harvard”), granting the Company an exclusive, worldwide, royalty-bearing, sublicensable license to three patent families, to develop, make, have made, use, market, offer for sale, sell, have sold and import licensed products and to perform licensed services related to the ATLAS discovery platform. The Company is also obligated to pay Harvard milestone payments up to $1.6 million in the aggregate upon the achievement of certain development and regulatory milestones. As of June 30, 2020 , the Company has paid $0.3 million in aggregate milestone payments. The Company is obligated under this license agreement to use commercially reasonable efforts to develop, market and sell licensed products in compliance with an agreed upon development plan. In addition, the Company is obligated to achieve specified development milestones and in the event the Company is unable to meet its development milestones for any type of product or service, absent any reasonable proposed extension or amendment thereof, Harvard has the right, depending on the type of product or service, to terminate this agreement with respect to such products or to convert the license to a non-exclusive, non-sublicensable license with respect to such products and services. Upon commercialization of our products covered by the licensed patent rights or discovered using the licensed methods, the Company is obligated to pay Harvard royalties on the net sales of such products and services sold by the Company, the Company's affiliates, and the Company's sublicensees. This royalty varies depending on the type of product or service but is in the low single digits. The sales-based royalty due by the Company’s sublicensees is the greater of the applicable royalty rate or a percentage in the high single digits or the low double digits of the royalties the Company receives from such sublicensee, depending on the type of product. Based on the type of commercialized product or service, royalties are payable until the expiration of the last-to-expire valid claim under the licensed patent rights or for a period of 10 years from first commercial sale of such product or service. The royalties payable to Harvard are subject to reduction, capped at a specified percentage, for any third-party payments required to be made. In addition to the royalty payments, if the Company receives any additional revenue (cash or non-cash) under any sublicense, the Company must pay Harvard a percentage of such revenue, excluding certain categories of payments, varying from the low single digits to up to the low double digits depending on the scope of the license that includes the sublicense. The license agreement with Harvard will expire on a product-by-product or service-by-service and country-by-country basis until the expiration of the last-to-expire valid claim under the licensed patent rights. The Company may terminate the agreement at any time by giving Harvard advance written notice. Harvard may also terminate the agreement in the event of a material breach by the Company that remains uncured; in the event of our insolvency, bankruptcy, or similar circumstances; or if the Company challenges the validity of any patents licensed to us. Oncovir License and Supply Agreement In January 2018, the Company entered into a License and Supply Agreement with Oncovir, Inc. (“Oncovir”). The agreement provides the terms and conditions under which Oncovir will manufacture and supply an immunomodulator and vaccine adjuvant, Hiltonol® (poly-ICLC) (“Hiltonol”), to the Company for use in connection with the research, development, use, sale, manufacture, commercialization and marketing of products combining Hiltonol with the Company's technology (the “Combination Product”). Hiltonol is the adjuvant component of GEN-009, which will consist of synthetic long peptides or neoantigens identified using the Company's proprietary ATLAS platform, formulated with Hiltonol. Oncovir granted the Company a non-exclusive, assignable, royalty-bearing worldwide license, with the right to grant sublicenses through one tier, to certain of Oncovir’s intellectual property in connection with the research, development, or commercialization of Combination Products, including the use of Hiltonol, but not the use of Hiltonol for manufacturing or the use or sale of Hiltonol alone. The license will become perpetual, fully paid-up, and royalty-free on the later of January 25, 2028 or the date on which the last valid claim of any patent licensed to the Company under the agreement expires. Under this agreement, the Company is obligated to pay Oncovir low to mid six figure milestone payments upon the achievement of certain clinical trial milestones for each Combination Product and the first marketing approval for each Combination Product in certain territories, as well as tiered royalties in the low-single digits on a product-by-product basis based on the net sales of Combination Products. The Company may terminate the agreement upon a decision to discontinue the development of the Combination Product or upon a determination by the Company or an applicable regulatory authority that Hiltonol or a Combination Product is not clinically safe or effective. The agreement may also be terminated by either party due to a material uncured breach by the other party, or due to the other party’s bankruptcy, insolvency, or dissolution.

Long-term debt

Long-term debt	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Long-term debt	ebt In April 2018, the Company entered into an amended and restated loan and security agreement with Hercules Capital, Inc (“Hercules”), which was subsequently amended in November 2019 (as amended, the “2018 Term Loan”). The 2018 Term Loan provides a $14.0 million term loan. The 2018 Term Loan matures on May 1, 2021 and accrues interest at a floating rate per annum equal to the greater of (i) 8.00% , or (ii) the sum of 3.00% plus the prime rate. The 2018 Loan Agreement provides for interest-only payments until January 1, 2021. Thereafter, payments will include equal installments of principal and interest through maturity. The 2018 Term Loan may be prepaid subject to a prepayment charge. The Company is obligated to pay an additional end of term charge of $1.0 million at maturity. The 2018 Term Loan is secured by a lien on substantially all assets of the Company, other than intellectual property. Hercules has a perfected first-priority security interest in certain cash, cash equivalents and investment accounts. The 2018 Term Loan contains non-financial covenants, representations and a Material Adverse Effect provision, as defined herein. There are no financial covenants. A “Material Adverse Effect” means a material adverse effect upon: (i) the business, operations, properties, assets or condition (financial or otherwise) of the Company; (ii) the ability of the Company to perform the secured obligations in accordance with the terms of the loan documents, or the ability of agent or lender to enforce any of its rights or remedies with respect to the secured obligations; or (iii) the collateral or agent’s liens on the collateral or the priority of such liens. Any event that has a Material Adverse Effect or would reasonably be expected to have a Material Adverse Effect is an event of default under the Loan Agreement and repayment of amounts due under the Loan Agreement may be accelerated by Hercules under the same terms as an event of default. As of June 30, 2020 , the Company was in compliance with all covenants of the 2018 Term Loan. The 2018 Term Loan is automatically redeemable upon a change in control. At June 30, 2020 , the entire debt balance is current based on the contractual payment terms. In connection with the 2018 Term Loan, the Company issued common stock warrants to Hercules (the “Hercules Warrant”). See Note 9. Warrants . As of June 30, 2020 and December 31, 2019 , the Company had outstanding borrowings of $13.6 million and $13.4 million , respectively. Interest expense was $0.4 million for the three months ended June 30, 2020 and 2019 , and $0.7 million and $0.9 million for the six months ended June 30, 2020 and 2019 , respectively. Future principal payments of $14.0 million

Stockholders' equity

Stockholders' equity	6 Months Ended
	Jun. 30, 2019
Equity [Abstract]
Stockholders' equity	Stockholders' equity Effective June 2, 2020, the Company increased the number of authorized shares of common stock from 85.0 million shares to 170.0 million shares. 2020 Private Placement In July 2020, the Company entered into a private placement financing transaction in which the Company will issue approximately 21.4 million shares of its common stock (the “Shares”), approximately 12.2 million pre-funded warrants to purchase additional shares of its common stock (the “2020 Pre-Funded Warrant”) and accompanying warrants (the “Closing Warrants” and together with the Shares and the 2020 Pre-Funded Warrants, the “Securities”) to purchase approximately 33.6 million shares of its common stock (the “2020 Warrant Shares”). The Securities will be sold at a purchase price of $2.38 per unit for aggregate gross proceeds of approximately $80.0 million , before deducting fees to the placement agent and other offering expenses payable by the Company. The warrants will be exercisable immediately upon issuance, in whole or in part, at an exercise price of $2.25 per share and will have a four years term. The closing of the private placement financing is expected to occur on or about July 24, 2020. Agreement with Lincoln Park Capital In October 2019 , the Company entered into a purchase agreement with Lincoln Park Capital (“LPC”) pursuant to which LPC purchased $2.5 million of shares of the Company's common stock at a purchase price of $2.587 per share. In addition, for a period of 30 months , the Company has the right, at its sole discretion, to sell up to an additional $27.5 million of the Company's common stock based on prevailing market prices of its common stock at the time of each sale. In consideration for entering into the purchase agreement, the Company issued approximately 0.3 million shares of its common stock to LPC as a commitment fee. The purchase agreement limits the Company's sales of shares of common stock to LPC to approximately 5.2 million shares of common stock, representing 19.99% of the shares of common stock outstanding on the date of the purchase agreement. The purchase agreement also prohibits the Company from directing LPC to purchase any shares of common stock if those shares, when aggregated with all other shares of the Company's common stock then beneficially owned by LPC and its affiliates, would result in LPC and its affiliates having beneficial ownership, at any single point in time, of more than 9.99% of the then total outstanding shares of the Company's common stock. In the six months ended June 30, 2020 , the Company sold approximately 1.5 million shares of common stock resulting in approximately $3.5 million of net proceeds. As of June 30, 2020 , the Company had approximately $24.0 million remaining under its agreement with LPC. At-the-market equity offering program In 2015, the Company entered into an agreement, as amended, with Cowen and Company, LLC to establish an at-the-market equity offering program (“ATM”) pursuant to which it was able to offer and sell up to $50.0 million of the Company's common stock at prevailing market prices. In the six months ended June 30, 2020 , the Company sold approximately 1.0 million shares under the ATM program and received net proceeds of $2.7 million , after deducting commissions. Through June 30, 2020 , the Company has sold an aggregate of approximately 1.5 million shares under the ATM and received approximately $6.7 million in net proceeds. As of June 30, 2020 , the Company had approximately $43.1 million in gross proceeds remaining under the ATM. 2019 Public Offering In June 2019, the Company entered into an underwriting agreement relating to the public offering of 10.5 million shares of the Company’s common stock, at a price of $3.50 per share, for gross proceeds of approximately $36.8 million (the “2019 Public Offering”). The Company also granted the underwriters an option to purchase up to approximately an additional 1.6 million shares of common stock (“Overallotment Option”). The underwriters exercised this option in full. The Company received approximately $5.5 million in gross proceeds from the underwriter’s exercise of the Overallotment Option. In connection with the 2019 Public Offering, inclusive of the Overallotment Option, the Company received net proceeds of $38.4 million . 2019 Private Placement In February 2019, the Company completed a private placement (the “2019 Private Placement”). The Company issued approximately 3.2 million shares of common stock, prefunded warrants (the “2019 Pre-Funded Warrants”) to purchase approximately 0.5 million shares of common stock (the “2019 Pre-Funded Warrant Shares”), and warrants (the “Private Placement Warrants”) to purchase up to approximately 0.9 million shares of common stock (the “2019 Warrant Shares”). The shares of common stock, 2019 Pre-Funded Warrants and Private Placement Warrants (collectively, the “Units”) were sold at a purchase price of $4.02 per Unit. The Company received net cash proceeds of approximately $13.8 million from the sale of the shares of common stock, 2019 Pre-Funded Warrants and Private Placement Warrants. See Note 9. Warrants . The Company had the option to issue additional shares of common stock in a second closing (the “Second Closing”) for gross proceeds of up to $24.2 million

Warrants Warrants

Warrants Warrants	6 Months Ended
	Jun. 30, 2020
Warrants [Abstract]
Warrants	Warrants As of June 30, 2020 , the Company had the following potentially issuable shares of common stock related to unexercised warrants outstanding (shares in thousands): Shares Exercise price Expiration date Classification Hercules Warrant 41 $ 6.80 Q2 2023 Equity 2018 Public Offering Warrants 3,617 $ 9.60 Q1 2023 Liability Private Placement Warrants 933 $ 4.52 Q1 2024 Equity 2019 Pre-Funded Warrants 531 $ 0.08 Q1 2039 Equity 5,122 Hercules Warrant The exercise price and the number of shares are subject to adjustment upon a merger event, reclassification of the shares of common stock, subdivision or combination of the shares of common stock or certain dividends payments. The Company determined that the Hercules Warrant should be equity classified in accordance with ASC 480, Distinguishing Liabilities from Equity (“ASC 480”) for all periods presented. 2018 Public Offering Warrants In January 2018, the Company entered into two underwriting agreements, the first relating to the public offering of approximately 6.7 million shares of the Company’s common stock, par value $0.001 per share, and accompanying warrants to purchase up to approximately 3.3 million shares of common stock (“2018 Public Offering Warrants”). The exercise price and the number of shares are subject to adjustment upon a merger event, reclassification of the shares of common stock, subdivision or combination of the shares of common stock or certain dividends payments. In the event of an “Acquisition,” defined generally to include a merger or consolidation resulting in the sale of 50% or more of the voting securities of the Company, the sale of all, or substantially all, of the assets or voting securities of the Company, or other change of control transaction, as defined in the 2018 Public Offering Warrants, the Company will be obligated to use its best efforts to ensure that the holders of the 2018 Public Offering Warrants receive new warrants from the surviving or acquiring entity (the “Acquirer”). The new warrants to purchase shares in the Acquirer shall have the same expiration date as the 2018 Public Offering Warrants and a strike price that is based on the proportion of the value of the Acquirer’s stock to the Company’s common stock. If the Company is unable, despite its best efforts, to cause the Acquirer to issue new warrants in the Acquisition as described above, then, if the Company’s stockholders are to receive cash in the Acquisition, the Company will settle the 2018 Public Offering Warrants in cash and if the Company’s stockholders are to receive stock in the Acquisition, the Company will issue shares of its common stock to each Warrant holder. The Company determined that the 2018 Public Offering Warrants should be liability classified in accordance with ASC 480. As the 2018 Public Offering Warrants are liability-classified, the Company remeasures the fair value at each reporting date. The Company initially recorded the 2018 Public Offering Warrants at their estimated fair value of approximately $18.2 million . In connection with the Company's remeasurement of the 2018 Public Offering Warrants to fair value, the Company recorded income of $0.2 million and $3.9 million for the three months ended June 30, 2020 and 2019 , respectively, and income of $1.0 million and expense of $1.9 million for the six months ended June 30, 2020 and 2019 , respectively. The fair value of the warrant liability is approximately $1.5 million and $2.5 million as of June 30, 2020 and December 31, 2019 , respectively. The following table details the assumptions used in the Monte Carlo simulation models used to estimate the fair value of the Warrant Liability as of June 30, 2020 and December 31, 2019 , respectively: June 30, 2020 December 31, 2019 Stock price $ 2.30 $ 2.07 Volatility 50.0% - 88.3% 50.0% - 116.6% Remaining term (years) 2.5 3.1 Expected dividend yield — — Risk-free rate 0.2 % 1.6 % Annual acquisition event probability 30.0 % 20.0 % Private Placement and 2019 Pre-Funded Warrants The exercise price of the warrants is subject to appropriate adjustment in the event of stock dividends, subdivisions, stock splits, stock combinations, reclassifications, reorganizations or a change of control affecting our common stock. The Company determined that the Private Placement Warrants and the 2019 Pre-Funded Warrants should be equity classified in accordance with ASC 480 for all periods presented. The Company also determined that the 2019 Pre-Funded Warrants should be included in the determination of basic earnings per share in accordance with ASC 260, Earnings per Share .

Stock and employee benefit plan

Stock and employee benefit plans	6 Months Ended
	Jun. 30, 2020
Share-based Payment Arrangement [Abstract]
Stock and employee benefit plans	Stock and employee benefit plans In June 2020, the Company’s stockholders approved an increase of 2.8 million of shares to the Company's Amended and Restated 2014 Equity Incentive Plan. As of June 30, 2020, there were approximately 2.4 million shares remaining for future issuance. The Company issues stock options and restricted stock units (“RSUs”) to employees, which generally vest ratably over a four year service period. The Company measures the fair value of stock options on the date of grant using the Black-Scholes option pricing model. The Company measures the fair value of RSUs on the date of grant using the underlying common stock fair value. Stock-based compensation expense Total stock-based compensation expense recognized for stock options and RSUs is as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 218 $ 170 $ 378 $ 352 General and administrative 268 304 492 551 Total $ 486 $ 474 $ 870 $ 903 Stock options The following table summarizes stock option activity (in thousands): Shares Weighted-Average Weighted-Average Aggregate Outstanding at December 31, 2019 1,323 $ 11.65 $ — Granted 1,268 $ 2.06 Exercised — $ — Forfeited/cancelled (76 ) $ 3.80 Outstanding at June 30, 2020 2,515 $ 7.04 8.08 $ 456 Exercisable at June 30, 2020 685 $ 16.96 6.37 $ 18 RSUs The following table summarizes RSU activity (shares in thousands): Shares Weighted-Average Grant Date Fair Value Outstanding as of December 31, 2019 — $ — Granted 554 $ 2.05 Vested — $ — Forfeited/cancelled (21 ) $ 1.66 Outstanding as of June 30, 2020 533 $ 2.07 Employee stock purchase plan In February 2014, the Company’s board of directors adopted the 2014 Employee Stock Purchase Plan and subsequently amended the plan in June 2018 (the “ESPP”). The ESPP authorizes the issuance of up to approximately 0.3 million shares of common stock to participating eligible employees and provides for two six-month offering periods. As of June 30, 2020 , there were approximately 0.2 million

Net loss per share

Net loss per share	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Net loss per share	Net loss per share Basic and diluted net loss per share was calculated as follows for the three and six months ended June 30, 2020 and 2019 : Three months ended June 30, Six months ended June 30, 2020 2019 2020 2019 Basic net loss per share: Numerator: Net loss (in thousands) $ (11,321 ) $ (6,495 ) $ (24,174 ) $ (22,062 ) Denominator: Weighted average common stock outstanding - basic (in thousands) 29,142 15,344 28,642 14,035 Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units — — — — Weighted average common stock outstanding – diluted 29,142 15,344 28,642 14,035 Net loss per share - basic and diluted $ (0.39 ) $ (0.42 ) $ (0.84 ) $ (1.57 ) The following common stock equivalents outstanding as of June 30, 2020 and 2019 , presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect (in thousands): Six Months Ended June 30, 2020 2019 Warrants 4,591 4,600 Stock options 2,515 1,285 RSUs 533 — Total 7,639 5,885

Summary of significant accoun_2

Summary of significant accounting policies (Policies)	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Basis of presentation	Basis of presentation The accompanying unaudited condensed consolidated financial statements include those accounts of the Company and a wholly owned subsidiary after elimination of all intercompany accounts and transactions. The Company operates as one segment, which is discovering, researching, developing and commercializing novel cancer immunotherapies.
Use of estimates	Use of estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, the Company’s management evaluates its estimates, which include, but are not limited to, estimates related to clinical trial accruals, estimates related to prepaid and accrued research and development expenses, revenue recognition, and warrants to purchase redeemable securities. The Company bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results may differ from those estimates or assumptions.
Significant accounting policies	Significant accounting policies There were no changes to significant accounting policies during the six months ended June 30, 2020 , as compared to the those disclosed in the 2019 Form 10-K, except as set forth below. Foreign Currency Translation Realized and unrealized gains and losses resulting from foreign currency transactions denominated in currencies other than the functional currency are reflected as other (expense) income, net in the consolidated statements of operations in accordance with ASC Topic 830, Foreign Currency Matters (“ASC 830”). Revenue Recognition In accordance with ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”) , revenue is recognized when a customer obtains control of promised goods or services. The amount of revenue recognized reflects the consideration to which the Company expects to be entitled in exchange for these goods and services. To achieve this core principle, the Company applies the following five steps: 1) identify the customer contract; 2) identify the contract’s performance obligations; 3) determine the transaction price; 4) allocate the transaction price to the performance obligations; and 5) recognize revenue when or as a performance obligation is satisfied. Licensing arrangements are analyzed to determine whether the promised goods or services, which include licenses and research and development materials and services, are distinct or whether they must be accounted for as part of a combined performance obligation. If the license is considered not to be distinct, the license would then be combined with other promised goods or services as a combined performance obligation. Certain contracts contain options to obtain future goods or services at a discount, which would not be provided without entering into the contract. These options are considered material rights, and therefore, are accounted for as separate performance obligations. The Company then determines the fair value to be allocated to this promised service. The transaction price is determined based on the consideration to which the Company will be entitled. The consideration promised may include fixed amounts, variable amounts, or both. For milestone payments, the Company estimates the amount of variable consideration by using the most likely amount method. In making this assessment, the Company evaluates factors such as the clinical, commercial and other risks that must be overcome to achieve the milestone. The Company re-evaluates the probability of achievement of such variable consideration and any related constraints at each reporting period. The Company includes variable consideration in the transaction price to the extent it is probable that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price among the performance obligations on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct good or service that forms part of a single performance obligation. The Company allocates the transaction price based on the estimated standalone selling price of the underlying performance obligations. The Company must develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the standalone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs to complete the respective performance obligation. Certain variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated to each performance obligation are consistent with the amount the Company would expect to receive for each performance obligation. The transaction price is generally allocated to each separate performance obligation on a relative standalone selling price basis. When a performance obligation is satisfied, revenue is recognized for the amount of the transaction price allocated to that performance obligation on a relative standalone selling price basis, which excludes estimates of variable consideration that are constrained. Significant management judgment is required in determining the level of effort required under an arrangement and the period over which the Company is expected to complete its performance obligations under an arrangement. For performance obligations consisting of licenses and other promises, the Company utilizes judgment to assess whether the combined performance obligation is satisfied over time or at a point in time and the recognition pattern of non-refundable, up-front fees. Contract liabilities The Company records a contract liability, classified in deferred revenue on the condensed consolidated balance sheet, when it has received payment but has not yet satisfied the related performance obligations. In the event of an early termination of a contract with customer, any contract liabilities would be recognized in the period in which all Company obligations under the agreement have been fulfilled. New Accounting Pronouncements The following new accounting pronouncements were adopted by the Company on January 1, 2020: In 2016, the Financial Accounting Standards Board (“FASB”) issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), which amends the impairment model by requiring entities to use a forward-looking approach based on expected losses to estimate credit losses on certain types of financial instruments, including trade receivables and available-for-sale debt securities. The Company early adopted the standard on January 1, 2020. Based on the composition of the Company's investment portfolio, which includes only money market funds, and the insignificance of the Company's other financial assets, current market conditions, and historical credit loss activity, the adoption of this standard did not have a material impact on the Company's consolidated financial statements and related disclosures. In 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”). The new standard requires public entities to disclose certain new information and modifies some disclosure requirements. The Company adopted the standard on the required effective date of January 1, 2020. This standard did not have a material impact on the Company's disclosures. In 2018, the FASB issued ASU 2018-15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40) : Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract (“ASU 2018-15”). ASU 2018-15 requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance in Accounting Standards Codification 350-40 to determine which implementation costs to defer and recognize as an asset. The Company adopted the standard on the required effective date of January 1, 2020. This standard did not have a material impact on the Company's consolidated financial statements and related disclosures. The following new accounting pronouncements have been issued but are not yet effective: In 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes ("ASU 2019-12"). ASU 2019-12 simplifies the accounting for income taxes and will be effective beginning after December 15, 2020. The Company is currently evaluating the impact of ASU 2019-12 in the consolidated financial statements, including accounting policies, processes, and systems.
Fair value of financial instruments	The Company has certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements. • Level 1—Fair values are determined by utilizing quoted prices (unadjusted) in active markets for identical assets or liabilities that the Company has the ability to access; • Level 2—Fair values are determined by utilizing quoted prices for similar assets and liabilities in active markets or other market observable inputs such as interest rates, yield curves and foreign currency spot rates; and • Level 3—Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable. The Company's financial assets consist of cash equivalents and the Company's financial liabilities consist of a warrant liability.

Fair value of financial instr_2

Fair value of financial instruments (Tables)	6 Months Ended
	Jun. 30, 2020
Cash and Cash Equivalents [Abstract]
Schedule of Stockholders' Equity Note, Warrants or Rights	As of June 30, 2020 , the Company had the following potentially issuable shares of common stock related to unexercised warrants outstanding (shares in thousands): Shares Exercise price Expiration date Classification Hercules Warrant 41 $ 6.80 Q2 2023 Equity 2018 Public Offering Warrants 3,617 $ 9.60 Q1 2023 Liability Private Placement Warrants 933 $ 4.52 Q1 2024 Equity 2019 Pre-Funded Warrants 531 $ 0.08 Q1 2039 Equity 5,122
Schedule of financial instruments measured at fair value on recurring basis	Quoted prices in active markets Significant other observable inputs Significant unobservable inputs Total (Level 1) (Level 2) (Level 3) June 30, 2020 Assets: Cash equivalents $ 21,927 $ 21,927 $ — $ — Total assets $ 21,927 $ 21,927 $ — $ — Liabilities: Warrant liability $ 1,483 $ — $ — $ 1,483 Total liabilities $ 1,483 $ — $ — $ 1,483 December 31, 2019 Assets: Cash equivalents $ 39,971 $ 39,971 $ — $ — Total assets $ 39,971 $ 39,971 $ — $ — Liabilities: Warrant liability $ 2,486 $ — $ — $ 2,486 Total liabilities $ 2,486 $ — $ — $ 2,486
Fair Value Measurement Inputs and Valuation Techniques	The following table details the assumptions used in the Monte Carlo simulation models used to estimate the fair value of the Warrant Liability as of June 30, 2020 and December 31, 2019 , respectively: June 30, 2020 December 31, 2019 Stock price $ 2.30 $ 2.07 Volatility 50.0% - 88.3% 50.0% - 116.6% Remaining term (years) 2.5 3.1 Expected dividend yield — — Risk-free rate 0.2 % 1.6 % Annual acquisition event probability 30.0 % 20.0 %
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation	The following table reflects the change in the Company’s Level 3 warrant liability (in thousands): Warrant Liability Balance at December 31, 2019 $ 2,486 Change in fair value (1,003 ) Balance at June 30, 2020 $ 1,483

Accrued expenses and other cu_2

Accrued expenses and other current liabilities (Tables)	6 Months Ended
	Jun. 30, 2020
Payables and Accruals [Abstract]
Schedule of accrued expenses and other current liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): June 30, December 31, 2020 2019 Research and development costs $ 1,945 $ 1,607 Payroll and employee-related costs 1,351 2,245 Other current liabilities 775 759 Total $ 4,071 $ 4,611

Commitments and contingencies (

Commitments and contingencies (Tables)	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Lease, Cost	The weighted average remaining lease term and weighted average discount rate of the Company's operating leases are as follows: June 30, 2020 June 30, 2019 Weighted average remaining lease term in years 4.67 5.48 Weighted average discount rate 8.13 % 8.31 %
Assets And Liabilities, Lessee	The following table summarizes the presentation in the Company's consolidated balance sheets: Leases (in thousands) Classification June 30, 2020 December 31, 2019 Assets Operating Lease ROU asset $ 11,175 $ 6,156 Finance Lease ROU asset 90 150 Total lease assets $ 11,265 $ 6,306 Liabilities Current Operating Lease liabilities $ 1,977 $ 990 Finance Lease liabilities 76 127 Non-current Operating Lease liabilities, net of current portion 9,473 5,373 Finance Lease liabilities, net of current portion — 22 Total lease liabilities $ 11,526 $ 6,512
Lessee, Operating Lease, Liability, Maturity	The minimum lease payments related to the Company's operating and finance leases in accordance with ASC 842 as of June 30, 2020 were as follows (in thousands): Operating leases Finance lease Total 2020 $ 1,406 $ 56 $ 1,462 2021 2,871 23 2,894 2022 2,943 — 2,943 2023 3,017 — 3,017 2024 and thereafter 3,609 — 3,609 Total lease payments $ 13,846 $ 79 $ 13,925 Less imputed interest (2,396 ) (3 ) (2,399 ) Total $ 11,450 $ 76 $ 11,526
Finance Lease, Liability, Maturity	The minimum lease payments related to the Company's operating and finance leases in accordance with ASC 842 as of June 30, 2020 were as follows (in thousands): Operating leases Finance lease Total 2020 $ 1,406 $ 56 $ 1,462 2021 2,871 23 2,894 2022 2,943 — 2,943 2023 3,017 — 3,017 2024 and thereafter 3,609 — 3,609 Total lease payments $ 13,846 $ 79 $ 13,925 Less imputed interest (2,396 ) (3 ) (2,399 ) Total $ 11,450 $ 76 $ 11,526

Long-term debt (Tables)

Long-term debt (Tables)	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Schedule of future principal payments	Future principal payments of $14.0 million

Warrants (Tables)

Warrants (Tables)	6 Months Ended
	Jun. 30, 2020
Warrants [Abstract]
Schedule of Stockholders' Equity Note, Warrants or Rights	As of June 30, 2020 , the Company had the following potentially issuable shares of common stock related to unexercised warrants outstanding (shares in thousands): Shares Exercise price Expiration date Classification Hercules Warrant 41 $ 6.80 Q2 2023 Equity 2018 Public Offering Warrants 3,617 $ 9.60 Q1 2023 Liability Private Placement Warrants 933 $ 4.52 Q1 2024 Equity 2019 Pre-Funded Warrants 531 $ 0.08 Q1 2039 Equity 5,122
Fair Value Measurement Inputs and Valuation Techniques	The following table details the assumptions used in the Monte Carlo simulation models used to estimate the fair value of the Warrant Liability as of June 30, 2020 and December 31, 2019 , respectively: June 30, 2020 December 31, 2019 Stock price $ 2.30 $ 2.07 Volatility 50.0% - 88.3% 50.0% - 116.6% Remaining term (years) 2.5 3.1 Expected dividend yield — — Risk-free rate 0.2 % 1.6 % Annual acquisition event probability 30.0 % 20.0 %

Stock and employee benefit pl_2

Stock and employee benefit plans (Tables)	6 Months Ended
	Jun. 30, 2020
Share-based Payment Arrangement [Abstract]
Schedule of stock-based compensation expense for stock options granted to employees and non-employees	Total stock-based compensation expense recognized for stock options and RSUs is as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Research and development $ 218 $ 170 $ 378 $ 352 General and administrative 268 304 492 551 Total $ 486 $ 474 $ 870 $ 903
Schedule of stock option activity for employees and nonemployees	The following table summarizes stock option activity (in thousands): Shares Weighted-Average Weighted-Average Aggregate Outstanding at December 31, 2019 1,323 $ 11.65 $ — Granted 1,268 $ 2.06 Exercised — $ — Forfeited/cancelled (76 ) $ 3.80 Outstanding at June 30, 2020 2,515 $ 7.04 8.08 $ 456 Exercisable at June 30, 2020 685 $ 16.96 6.37 $ 18

Net loss per share (Tables)

Net loss per share (Tables)	6 Months Ended
	Jun. 30, 2020
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	Basic and diluted net loss per share was calculated as follows for the three and six months ended June 30, 2020 and 2019 : Three months ended June 30, Six months ended June 30, 2020 2019 2020 2019 Basic net loss per share: Numerator: Net loss (in thousands) $ (11,321 ) $ (6,495 ) $ (24,174 ) $ (22,062 ) Denominator: Weighted average common stock outstanding - basic (in thousands) 29,142 15,344 28,642 14,035 Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units — — — — Weighted average common stock outstanding – diluted 29,142 15,344 28,642 14,035 Net loss per share - basic and diluted $ (0.39 ) $ (0.42 ) $ (0.84 ) $ (1.57 )
Schedule of common stock equivalents, presented on converted basis, were excluded from calculation of net loss per share due to anti-dilutive effect	The following common stock equivalents outstanding as of June 30, 2020 and 2019 , presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect (in thousands): Six Months Ended June 30, 2020 2019 Warrants 4,591 4,600 Stock options 2,515 1,285 RSUs 533 — Total 7,639 5,885

Organization and operations (De

Organization and operations (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Subsequent Event [Line Items]
Document Period End Date	Jun. 30, 2020
Accumulated deficit	$ (355,128)		$ (330,954)
Cash and cash equivalents	22,108		$ 40,127
Net Cash Provided by (Used in) Operating Activities	23,712	$ 17,942
Proceeds from issuance of common stock	$ 6,239	$ 52,194

Summary of significant accoun_3

Summary of significant accounting policies - Narrative (Details)	6 Months Ended
	Jun. 30, 2020Segment
Accounting Policies [Abstract]
Number of operating segments	1

Revenue (Details)

Revenue (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue		$ 906	$ 0	$ 906	$ 0
Material Transfer Agreement | Shionogi & Co., Ltd.
Disaggregation of Revenue [Line Items]
Revenue	$ 2,000
Proceeds recognized allocated to MTA		$ 900

Fair value of financial instr_3

Fair value of financial instruments - Schedule of cash equivalents and investments carried at fair value (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jan. 01, 2018
Fair Value, Measurements, Recurring
Assets:
Total assets	$ 21,927	$ 39,971
Liabilities:
Total liabilities	1,483	2,486
Fair Value, Measurements, Recurring | (Level 1)
Assets:
Total assets	21,927	39,971
Liabilities:
Warrant liability	0	0
Total liabilities	0	0
Fair Value, Measurements, Recurring | (Level 2)
Assets:
Total assets	0	0
Liabilities:
Warrant liability	0	0
Total liabilities	0	0
Fair Value, Measurements, Recurring | (Level 3)
Assets:
Total assets	0	0
Liabilities:
Warrant liability	1,483	2,486
Total liabilities	1,483	2,486
Money market funds | Fair Value, Measurements, Recurring
Assets:
Included in cash equivalents	21,927	39,971
Money market funds | Fair Value, Measurements, Recurring | (Level 1)
Assets:
Included in cash equivalents	21,927	39,971
Money market funds | Fair Value, Measurements, Recurring | (Level 2)
Assets:
Included in cash equivalents	0	0
Money market funds | Fair Value, Measurements, Recurring | (Level 3)
Assets:
Included in cash equivalents	0	0
Warrants | (Level 3)
Liabilities:
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	$ 1,483	$ 2,486	$ 18,200

Fair value of financial instr_4

Fair value of financial instruments - Assumptions used in the Monte Carlo simulation models (Details)	Jun. 30, 2020$ / shares	Dec. 31, 2019$ / shares	Jan. 01, 2018
Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input			0.024
Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input			0.025
Stock price | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	2.30	2.07
Volatility | Minimum | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.500	0.500
Volatility | Maximum | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	1.245	1.166
Remaining term (years) | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and rights outstanding, term	2 years 6 months	3 years 1 month 6 days
Expected dividend yield | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0	0
Risk-free rate | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.002	0.016
Risk-free rate | Minimum | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input		0.024
Risk-free rate | Maximum | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input		0.025
Annual acquisition event probability | Warrants
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.300	0.200
Annual acquisition event probability | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.150		0
Annual acquisition event probability | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Measurement Input	0.300		0.300

Fair value of financial instr_5

Fair value of financial instruments - Change in the Company’s Level 3 Warrant liabilities (Details) - Warrants - (Level 3) $ in Thousands	6 Months Ended
	Jun. 30, 2020USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Issuance of Warrants	$ 2,486
Change in fair value	(1,003)
Balance at June 30, 2020	$ 1,483

Accrued expenses and other cu_3

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Payables and Accruals [Abstract]
Research and development costs	$ 1,945	$ 1,607
Payroll and employee-related	1,351	2,245
Other current liabilities	775	759
Total	$ 4,071	$ 4,611

Commitments and contingencies -

Commitments and contingencies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Jul. 31, 2019
Operating Leased Assets [Line Items]
Operating lease, right-of-use asset	$ 11,175		$ 11,175		$ 6,156
Operating lease liability	11,450		11,450
Rent expense	800	$ 300	1,300	$ 700
Incremental borrowing rate, percent					7.95%
Licensing agreement, amount	$ 1,600		1,600
Licensing agreement, milestone payment, amount			$ 300
Lease Extension for office and lab space
Operating Leased Assets [Line Items]
Operating lease, right-of-use asset						$ 5,900
Operating lease liability						$ 5,800
Operating lease, renewal term	5 years		5 years
Master Facilities Operating Lease Due February 28, 2025
Operating Leased Assets [Line Items]
Restricted cash and cash equivalents					$ 600

Commitments and contingencies_2

Commitments and contingencies - Operating Lease Term and Discount Rate (Details)	Jun. 30, 2020	Jun. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Weighted average remaining lease term in years	4 years 8 months 1 day	5 years 5 months 23 days
Weighted average discount rate	8.13%	8.31%

Commitments and contingencies_3

Commitments and contingencies - Supplemental Balance Sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Lease Assets [Abstract]
Operating lease, right-of-use asset	$ 11,175	$ 6,156
Finance Lease, Right-of-Use Asset	90	150
Finance and Operating Lease, Right-of-Use Asset	11,265	6,306
Lease Liabilities, Current [Abstract]
Operating Lease, Liability, Current	1,977	990
Finance Lease, Liability, Current	76	127
Lease Liabilities, Noncurrent [Abstract]
Operating Lease, Liability, Noncurrent	9,473	5,373
Finance Lease, Liability, Noncurrent	0	22
Total	$ 11,526	$ 6,512

Commitments and contingencies_4

Commitments and contingencies - Future minimum lease payments (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Lessee, Operating Lease, Liability, Payment, Due [Abstract]
2020	$ 1,406
2021	2,871
2022	2,943
2023	3,017
2024	3,609
Total lease payments	13,846
Less imputed interest	(2,396)
Total	11,450
Finance Lease, Liability, Payment, Due [Abstract]
2020	56
2021	23
2022	0
2023	0
2024 and thereafter	0
Total lease payments	79
Less imputed interest	(3)
Total	76
Finance and Operating Lease, Liability, Payment, Due [Abstract]
2020	1,462
2021	2,894
2022	2,943
2023	3,017
2024 and thereafter	3,609
Total lease payments	13,925
Less imputed interest	(2,399)
Total	$ 11,526	$ 6,512

Long-term debt - Narrative (Det

Long-term debt - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Apr. 24, 2018
Long-Term Debt
Future principal payments due in 2021		$ 14
2018 Term Loan | Line of Credit
Long-Term Debt
Debt financing					$ 14
Interest rate (as a percent)					8.00%
End of term charge					$ 1
2018 Term Loan | Line of Credit | Prime rate
Long-Term Debt
Variable rate (as a percent)					3.00%
2014 Term Loan, First Tranche | Line of Credit
Long-Term Debt
Outstanding borrowings		13.6		$ 13.4
2014 Term Loan | Line of Credit
Long-Term Debt
Interest expense	$ 0.4	$ 0.7	$ 0.9

Stockholders' equity - Narrativ

Stockholders' equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands

Jun. 21, 2019

Jul. 31, 2020

Oct. 31, 2019

Feb. 28, 2019

Jun. 30, 2020

Mar. 31, 2020

Jun. 30, 2019

Mar. 31, 2019

Jun. 30, 2020

Jun. 30, 2019

Dec. 31, 2015

Jun. 30, 2020

Jul. 22, 2020

Jun. 02, 2020

Jun. 01, 2020

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shares authorized

170,000,000

85,000,000

Proceeds from issuance of common stock

$ 6,239

$ 52,194

Issuance of common stock

$ 5,799

$ 440

$ 38,167

$ 14,026

Pre-Funded Warrants

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Exercise price (in dollars per share)

$ 0.08

$ 0.08

$ 0.08

Warrants to purchase common stock (in shares)

531,000

531,000

531,000

Private Placement Warrants

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Exercise price (in dollars per share)

$ 4.52

$ 4.52

$ 4.52

Warrants to purchase common stock (in shares)

933,000

933,000

933,000

Common Stock

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Issuance of common stock (in shares)

2,287,000

187,000

12,074,000

3,200,000

Issuance of common stock

$ 2

$ 1

$ 12

$ 3

Common Stock | At-the-market equity offering program

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Issuance of common stock (in shares)

1,500,000

Proceeds from issuance of common stock

$ 6,700

Shares authorized for issuance, remaining amount

43,100

$ 43,100

43,100

2019 Public Offering | Common Stock | Concurrent Offerings

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Issuance of common stock (in shares)

10,500,000

2019 Public Offering | Common Stock | Over-Allotment Option

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Proceeds from issuance of common stock

$ 38,400

Sale of stock, consideration received on transaction

$ 5,500

Warrants to purchase common stock (in shares)

1,600,000

2019 Public Offering | Common Class A

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Share price (in dollars per share)

$ 3.50

Sale of stock, consideration received on transaction

$ 36,800

Private placement

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Sale of stock, price per share (in dollars per share)

$ 4.02

Sale of stock, consideration received on transaction

$ 13,800

Private placement | Common Stock | At-the-market equity offering program

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Shares authorized for issuance, value

$ 50,000

Number of shares issued in transaction (in shares)

1,000,000

Sale of stock, consideration received on transaction

$ 2,700

Private placement | Common Stock

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Number of shares issued in transaction (in shares)

3,200,000

Private Placement - Second Closing

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Sale of stock, consideration received on transaction

$ 24,200

Subsequent Event | 2020 Private Placement

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Proceeds from issuance of common stock

$ 80,000

Subsequent Event | 2020 Private Placement | Concurrent Offerings

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Exercise price (in dollars per share)

$ 2.25

Warrants and rights outstanding, term

4 years

Subsequent Event | 2020 Private Placement | Pre-Funded Warrants

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Issuance of common stock (in shares)

12,200,000

Subsequent Event | 2020 Private Placement | Private Placement Warrants

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Issuance of common stock (in shares)

33,600,000

Sale of stock, price per share (in dollars per share)

$ 2.38

Subsequent Event | 2020 Private Placement | Common Stock

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Issuance of common stock (in shares)

21,400,000

Lincoln Park Capital | Common Stock

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Issuance of common stock (in shares)

1,500,000

Issuance of common stock

$ 2,500

$ 3,500

Share price (in dollars per share)

$ 2.587

Purchase agreement period (in months)

30 months

Shares authorized for issuance, value

$ 27,500

Shares issued as commitment fee

300,000

Shares authorized for issuance, remaining amount

$ 24,000

$ 24,000

$ 24,000

Lincoln Park Capital | Common Stock | Maximum

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Issuance of common stock (in shares)

5,200,000

Shares outstanding, agreement threshold, percent

19.99%

Shares outstanding of affiliate beneficial ownership, agreement threshold, percent

9.99%

Warrants - Issuable Shares of C

Warrants - Issuable Shares of Common Stock Related to Unexercised Warrants Outstanding (Details) shares in Thousands	Jun. 30, 2020$ / sharesshares
Total
Class of Stock [Line Items]
Shares	5,122
Hercules Warrant
Class of Stock [Line Items]
Shares	41
Exercise price (in dollars per share) | $ / shares	$ 6.80
2018 Public Offering Warrants
Class of Stock [Line Items]
Shares	3,617
Exercise price (in dollars per share) | $ / shares	$ 9.60
Private Placement Warrants
Class of Stock [Line Items]
Shares	933
Exercise price (in dollars per share) | $ / shares	$ 4.52
Pre-Funded Warrants
Class of Stock [Line Items]
Shares	531
Exercise price (in dollars per share) | $ / shares	$ 0.08

Warrants - Narrative (Details)

Warrants - Narrative (Details) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2018Underwriter_Agreement$ / sharesshares	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2019USD ($)	Jan. 01, 2018USD ($)
Class of Stock [Line Items]
Change in fair value of warrants		$ 222	$ 3,870	$ 1,003	$ (1,917)
Warrant liability		1,483		1,483		$ 2,486
(Level 3) | Warrants
Class of Stock [Line Items]
Issuance of Warrants		1,483		1,483		2,486	$ 18,200
Change in fair value of warrants		200	$ 3,900	1,000	$ (1,900)
Warrant liability		$ 1,500		$ 1,500		$ 2,500
2018 Public Offering | Common Stock
Class of Stock [Line Items]
Number of underwriting agreements | Underwriter_Agreement	2
Number of shares issued in transaction (in shares) | shares	6.7
Par value (in dollars per share) | $ / shares	$ 0.001
Total | 2018 Public Offering
Class of Stock [Line Items]
Number of shares issued in transaction (in shares) | shares	3.3

Warrants - Fair Value Warrant L

Warrants - Fair Value Warrant Liability Assumptions (Details)	Jun. 30, 2020$ / shares	Dec. 31, 2019$ / shares	Jan. 01, 2018
Minimum
Class of Stock [Line Items]
Measurement Input			0.024
Maximum
Class of Stock [Line Items]
Measurement Input			0.025
Annual acquisition event probability | Minimum
Class of Stock [Line Items]
Measurement Input	0.150		0
Annual acquisition event probability | Maximum
Class of Stock [Line Items]
Measurement Input	0.300		0.300
Warrants | Stock price
Class of Stock [Line Items]
Measurement Input	2.30	2.07
Warrants | Volatility | Minimum
Class of Stock [Line Items]
Measurement Input	0.500	0.500
Warrants | Volatility | Maximum
Class of Stock [Line Items]
Measurement Input	1.245	1.166
Warrants | Remaining term (years)
Class of Stock [Line Items]
Warrants and rights outstanding, term	2 years 6 months	3 years 1 month 6 days
Warrants | Expected dividend yield
Class of Stock [Line Items]
Measurement Input	0	0
Warrants | Risk-free rate
Class of Stock [Line Items]
Measurement Input	0.002	0.016
Warrants | Risk-free rate | Minimum
Class of Stock [Line Items]
Measurement Input		0.024
Warrants | Risk-free rate | Maximum
Class of Stock [Line Items]
Measurement Input		0.025
Warrants | Annual acquisition event probability
Class of Stock [Line Items]
Measurement Input	0.300	0.200

Stock and employee benefit pl_3

Stock and employee benefit plans - Schedule of stock-based compensation expense for stock options granted to employees and non-employees (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock Based Compensation Expense
Total	$ 486	$ 474	$ 870	$ 903
Research and development
Stock Based Compensation Expense
Total	218	170	378	352
General and administrative
Stock Based Compensation Expense
Total	$ 268	$ 304	$ 492	$ 551

Stock and employee benefit pl_4

Stock and employee benefit plans - Schedule of stock option activity for employees and nonemployees (Details) - Stock options - USD ($) $ / shares in Units, shares in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Shares
Outstanding at the beginning of the period (in shares)	1,323
Granted (in shares)	1,268
Exercised (in shares)	0
Canceled (in shares)	(76)
Outstanding at the end of the period (in shares)	2,515	1,323
Exercisable at the end of the period (in shares)	685
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 11.65
Granted (in dollars per share)	2.06
Exercised (in dollars per share)	0
Canceled (in dollars per share)	3.80
Outstanding at the end of the period (in dollars per share)	7.04	$ 11.65
Exercisable at the end of the period (in dollars per share)	$ 16.96
Weighted-Average Remaining Contractual Term (years)
Outstanding at the beginning/end of the period	8 years 29 days
Exercisable at the end of the period	6 years 4 months 13 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 456,000	$ 0
Exercisable at the end of the period (in dollars)	$ 18,000

Stock and employee benefit pl_5

Stock and employee benefit plans - Schedule of RSU Activity (Details) - Restricted Stock Units (RSUs) shares in Thousands	6 Months Ended
	Jun. 30, 2020$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Beginning Balance, Shares | shares	0
Granted (in shares) | shares	554
Vested, Shares | shares	0
Forfeited/cancelled, Shares | shares	(21)
Ending Balance, Shares | shares	533
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning Balance, Weighted-Average Grant Date Fair Value | $ / shares	$ 0
Granted, Weighted-Average Grant Date Fair Value | $ / shares	2.05
Vested, Weighted-Average Grant Date Fair Value | $ / shares	0
Forfeited/cancelled, Weighted-Average Grant Date Fair Value | $ / shares	1.66
Ending Balance, Weighted-Average Grant Date Fair Value | $ / shares	$ 2.07

Stock and employee benefit pl_6

Stock and employee benefit plans - Narrative (Details) - ESPP - shares	Jun. 30, 2020	Feb. 10, 2014
Stock option activity for employees and nonemployees
Shares reserved for future issuance	200,000
Amended and Restated 2014 Equity Incentive Plan
Stock option activity for employees and nonemployees
Number of shares of common stock authorized under the plan	2,800,000
Shares reserved for future issuance	2,400,000
ESPP
Stock option activity for employees and nonemployees
Number of shares of common stock authorized under the plan		300,000

Net loss per share - Schedule o

Net loss per share - Schedule of earnings per share, basic and diluted (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net loss (in thousands)	$ (11,321)	$ (12,853)	$ (6,495)	$ (15,567)	$ (24,174)	$ (22,062)
Weighted average common stock outstanding - basic (in thousands)	29,142		15,344		28,642	14,035
Dilutive effect of shares of common stock equivalents resulting from common stock options and restricted stock units	0		0		0	0
Weighted average common stock outstanding – diluted	29,142		15,344		28,642	14,035
Net loss per share - basic and diluted	$ (0.39)		$ (0.42)		$ (0.84)	$ (1.57)

- Attributable to common stockh

- Attributable to common stockholders (Details) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Common stock equivalents, presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect
Common stock equivalents (in shares)	7,639	5,885
Stock options
Common stock equivalents, presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect
Common stock equivalents (in shares)	2,515	1,285
Warrants
Common stock equivalents, presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect
Common stock equivalents (in shares)	4,591	4,600
Restricted Stock Units (RSUs)
Common stock equivalents, presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect
Common stock equivalents (in shares)	533	0