Genocea Biosciences (GNCAQ) 10-K 17 Feb 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2015	Feb. 12, 2016	Jun. 30, 2015
Document and Entity Information
Entity Registrant Name	GENOCEA BIOSCIENCES, INC.
Entity Central Index Key	1,457,612
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		28,152,589
Entity Public Float			$ 224,213,867

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 17,259	$ 20,058
Investments, current portion	77,069	27,021
Prepaid expenses and other current assets	865	934
Total current assets	95,193	48,013
Property and equipment, net	4,083	1,956
Restricted cash	316	316
Investments, net of current portion	12,104	0
Other non-current assets	446	47
Total assets	112,142	50,332
Current liabilities:
Accounts payable	1,757	2,692
Accrued expenses and other current liabilities	3,975	2,593
Deferred revenue	235	555
Current portion of long-term debt	0	0
Other current liabilities	0	0
Total current liabilities	5,967	5,840
Non-current liabilities:
Long-term debt	16,477	11,389
Deferred revenue, net of current portion	0	350
Other non-current liabilities	37	246
Total liabilities	$ 22,481	$ 17,825
Commitments and contingencies (Note 8)
Stockholders’ equity:
Common stock - Authorized - 175,000 shares at December 31, 2015; Issued - 28,161 and 17,869 shares at December 31, 2015 and December 31, 2014, respectively; outstanding - 28,152 and 17,852 at December 31, 2015 and December 31, 2014, respectively	$ 28	$ 18
Additional paid-in-capital	247,550	147,923
Accumulated other comprehensive loss	(7)	(7)
Accumulated deficit	(157,910)	(115,427)
Total stockholders’ equity	89,661	32,507
Total liabilities and stockholders’ equity	$ 112,142	$ 50,332

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - shares	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Common stock, shares authorized	175,000,000
Common stock, shares issued	28,161,313	17,869,000
Common stock, shares outstanding	28,151,596	17,852,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Grant revenue	$ 670	$ 308	$ 731
Operating expenses:
Research and development	28,049	23,727	15,695
General and administrative	13,987	9,747	4,961
Total operating expenses	42,036	33,474	20,656
Loss from operations	(41,366)	(33,166)	(19,925)
Other expense:
Change in fair value of warrants	0	(725)	(222)
Loss on debt extinguishment	0	(435)	(200)
Interest expense, net	(1,117)	(970)	(459)
Other expense	(1,117)	(2,130)	(881)
Net loss	(42,483)	(35,296)	(20,806)
Reconciliation of net loss to net loss applicable to common stockholders
Net loss	(42,483)	(35,296)	(20,806)
Accretion of redeemable convertible preferred stock to redemption value	0	(180)	(1,605)
Net loss attributable to common stockholders	$ (42,483)	$ (35,476)	$ (22,411)
Net loss per share attributable to common stockholders-basic and diluted (in USD per share)	$ (1.74)	$ (2.27)	$ (75.46)
Weighted-average number of common shares used in net loss per share attributable to common stockholders - basic and diluted (in shares)	24,460	15,618	297

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net loss	$ (42,483)	$ (35,296)	$ (20,806)
Other comprehensive income (loss):
Unrealized loss on available-for-sale securities	(7)	(7)	0
Comprehensive loss	$ (42,490)	$ (35,303)	$ (20,806)

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Initial public offering	Secondary public offering	Employee stock purchase plan	Private placement	Common Stock	Common StockInitial public offering	Common StockSecondary public offering	Common StockEmployee stock purchase plan	Common StockPrivate placement	Additional Paid-In Capital	Additional Paid-In CapitalInitial public offering	Additional Paid-In CapitalSecondary public offering	Additional Paid-In CapitalEmployee stock purchase plan	Additional Paid-In CapitalPrivate placement	Other Comprehensive Income	Accumulated Deficit	Seed convertible preferred stock	Series A redeemable convertible preferred stock	Series B redeemable convertible preferred stock	Series C redeemable convertible preferred stock
Balance - Redeemable Convertible Preferred Stock at Dec. 31, 2012																		$ 3,000	$ 23,125	$ 23,332	$ 15,250
Balance - Redeemable Convertible Preferred Stock (in shares) at Dec. 31, 2012																		4,615	35,577	34,581	26,293
Balance - Stockholders' Equity (Deficit) at Dec. 31, 2012	$ (58,402)																$ (58,402)
Balance - Stockholders' Equity (Deficit) (in shares) at Dec. 31, 2012						295
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Issuance of Series C Preferred stock																					$ 15,250
Issuance of Series C Preferred stock (in shares)																					26,293
Accretion of dividends on redeemable convertible preferred stock	(1,605)										$ (682)						(923)			$ 1,605
Cashless exercise of warrants	0
Reclassification of warrants to additional paid-in capital	0
Exercise of stock options	9										9
Exercise of stock options (in shares)						7
Vesting of restricted stock	1										1
Vesting of restricted stock (in shares)						1
Stock-based compensation expense	672										672
Unrealized loss on investments	0
Net loss	(20,806)																(20,806)
Balance - Redeemable Convertible Preferred Stock at Dec. 31, 2013																		$ 3,000	$ 23,125	$ 24,937	$ 30,500
Balance - Redeemable Convertible Preferred Stock (in shares) at Dec. 31, 2013																		4,615	35,577	34,581	52,586
Balance - Stockholders' Equity (Deficit) at Dec. 31, 2013	(80,131)																(80,131)
Balance - Stockholders' Equity (Deficit) (in shares) at Dec. 31, 2013						303
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Accretion of dividends on redeemable convertible preferred stock	(180)										(180)									$ 180
Exercise of warrants for cash																			$ 33
Exercise of warrants for cash (in shares)																			51
Cashless exercise of warrants	98																		$ 98
Cashless exercise of warrants (in shares)						54													317
Conversion of redeemable convertible preferred stock into common stock	81,774					$ 11					81,763							$ (3,000)	$ (23,256)	$ (25,117)	$ (30,500)
Conversion of redeemable convertible preferred stock into common stock (in shares)						11,466												(4,615)	(35,945)	(34,581)	(52,586)
Reclassification of warrants to additional paid-in capital	1,381										1,381
Issuance of common stock		$ 58,977		$ 93	$ 1,964		$ 6					$ 58,971		$ 93	$ 1,964
Issuance of common stock (in shares)							5,500		16	223
Issuance of warrants, net of issuance costs of $6	334										334
Exercise of stock options	683					$ 1					682
Exercise of stock options (in shares)						282
Vesting of restricted stock	10										10
Vesting of restricted stock (in shares)						8
Stock-based compensation expense	2,905										2,905
Unrealized loss on investments	(7)															$ (7)
Net loss	(35,296)																(35,296)
Balance - Stockholders' Equity (Deficit) at Dec. 31, 2014	32,507					$ 18					147,923					(7)	(115,427)
Balance - Stockholders' Equity (Deficit) (in shares) at Dec. 31, 2014						17,852
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Cashless exercise of warrants	0
Reclassification of warrants to additional paid-in capital	0
Issuance of common stock			$ 95,183	$ 213				$ 10					$ 95,173	$ 213
Issuance of common stock (in shares)								10,123	41
Exercise of stock options	383										383
Exercise of stock options (in shares)						128
Vesting of restricted stock	10										10
Vesting of restricted stock (in shares)						8
Stock-based compensation expense	3,848										3,848
Unrealized loss on investments	(7)
Net loss	(42,483)																(42,483)
Balance - Stockholders' Equity (Deficit) at Dec. 31, 2015	$ 89,661					$ 28					$ 247,550					$ (7)	$ (157,910)
Balance - Stockholders' Equity (Deficit) (in shares) at Dec. 31, 2015						28,152

Consolidated Statements of Red7

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - Additional Paid-In Capital - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Issuance of warrants, issuance costs		$ 6
Initial public offering
Issuance of stock, issuance costs		2,403
Secondary public offering
Issuance of stock, issuance costs	$ 509
Private placement
Issuance of stock, issuance costs		$ 36

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net loss	$ (42,483)	$ (35,296)	$ (20,806)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	1,051	469	318
Stock-based compensation	3,848	2,905	672
Change in fair value of warrants liability	0	725	222
Non-cash interest expense	369	254	22
Loss on debt extinguishment	0	435	200
Changes in operating assets and liabilities:
Restricted cash	0	0	97
Prepaid expenses and other current assets	266	(442)	27
Other long-term assets	(399)	782	(1,539)
Accounts payable	(1,431)	524	724
Deferred revenue	(670)	893	12
Accrued expenses and other liabilities	1,093	1,147	178
Net cash used in operating activities	(38,356)	(27,604)	(19,873)
Investing activities
Purchases of property and equipment	(2,784)	(1,520)	(389)
Proceeds from maturities of investments	27,498	0	0
Purchase of investments	(89,651)	(27,053)	0
Net cash used in investing activities	(64,937)	(28,573)	(389)
Financing activities
Proceeds from IPO, net of issuance costs	0	59,974	0
Proceeds from underwritten public offering/sale of common stock, net of issuance costs	0	1,964	0
Proceeds from issuance of preferred stock, net	0	0	15,250
Proceeds from issuance of long-term debt, net of issuance costs	4,719	11,784	9,965
Repayment of long-term debt	0	(10,401)	(4,245)
Proceeds from issuance of common stock under ESPP	213	93	0
Proceeds from exercise of stock options	383	683	42
Proceeds from the exercise of warrants	0	33	0
Payments made under capital lease	(4)	0	0
Payments for debt issuance costs	0	(103)	(58)
Net cash provided by financing activities	100,494	64,027	20,954
Net increase in cash and cash equivalents	(2,799)	7,850	692
Cash and cash equivalents at beginning of period	20,058	12,208	11,516
Cash and cash equivalents at end of period	17,259	20,058	12,208
Supplemental cash flow information
Cash paid for interest	897	815	426
Supplemental disclosure of non-cash investing and financing activities
Conversion of preferred stock to common stock upon closing of IPO	0	81,774	0
Reclassification of prepaid IPO closing costs from non-current assets to additional paid-in capital	0	997	0
Reclassification of warrants to additional paid-in capital	0	1,381	0
Accretion of redeemable convertible preferred stock to redemption value	0	180	1,605
Vesting of restricted stock	10	10	1
Cashless exercise of warrants	0	98	0
Issuance of common stock warrant	0	340	0
Equipment purchased under capital lease	0	21	0
Property and equipment, net included in accounts payable and accrued expense	394	0	0
Underwritten public offering
Financing activities
Proceeds from underwritten public offering/sale of common stock, net of issuance costs	$ 95,183	$ 0	$ 0

Organization and operations

Organization and operations	12 Months Ended
	Dec. 31, 2015
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 vaccines and immunotherapies to address diseases with significant unmet needs through its AnTigen Lead Acquisition System ("ATLAS TM ") proprietary discovery platform. ATLAS is used to rapidly design vaccines and immunotherapies that act, in part, through T cell (or cellular) immune responses, in contrast to approved vaccines and immunotherapies, which are designed to act primarily through B cell (or antibody) immune responses. The Company believes that by harnessing T cells, first-in-class vaccines and immunotherapies can be developed to address diseases where T cells are central to the control of the disease. The Company has one product candidate in active Phase 2 clinical development, GEN-003, an immunotherapy for the treatment of genital herpes. The Company suspended development for another product candidate, GEN-004, a universal vaccine for the prevention of pneumococcal infections, pending further data analysis and consultation with the Company's advisers after statistically significant results were not achieved in a Phase 2a human challenge study. The Company also has active research and pre-clinical development programs for diseases including genital herpes, chlamydia and malaria and is investigating the application of ATLAS to immuno-oncology target discovery. 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 similar to those of other clinical stage companies, including dependence on key individuals, competition from other companies, the need and related uncertainty associated to the development of commercially viable products, and the need to obtain adequate additional financing to fund the development of its product candidates. The Company is also subject to a number of risks similar to other companies in the life sciences industry, including regulatory approval of products, uncertainty of market acceptance of products, competition from substitute products and larger companies, the need to obtain additional financing, compliance with government regulations, protection of proprietary technology, dependence on third parties, product liability, and dependence on key individuals. As of December 31, 2015, the Company had an accumulated deficit of approximately $ 157.9 million . The Company had cash, cash equivalents and investments of $106.4 million at December 31, 2015. The Company believes that its existing cash, cash equivalents and investments and available borrowings under the Company’s credit facility, will be sufficient to fund projected operating expenses and capital expenditure requirements into the second half of 2017. Underwritten public offerings On February 10, 2014, the Company completed its initial public offering (“IPO”) of its common stock pursuant to a registration statement on Form S-1, as amended. An aggregate of 5,500,000 shares of common stock registered under the registration statement were sold at a price of $12.00 per share. Net proceeds of the IPO were $61.4 million , excluding offering expenses of $2.4 million payable by the Company. In conjunction with this transaction, all shares of the Company’s redeemable convertible preferred stock were converted into 11,466,479 shares of common stock, and 96,988 employee and nonemployee performance-based options vested. On March 17, 2015, the Company completed an underwritten public offering of its common stock in which it sold 6,272,726 shares of common stock, including the exercise in full by the underwriters of their option to purchase an additional 818,181 shares of common stock, to the public at a price of $8.25 per share. The offering was completed under the shelf registration statement that was filed on Form S-3 and declared effective on March 10, 2015. Net proceeds of the underwritten public offering, after deducting the underwriting discounts and commissions, were $48.6 million , excluding offering expenses of $276 thousand incurred by the Company. On August 4 2015, the Company completed an underwritten public offering of its common stock in which it sold an aggregate of 3,850,000 shares of common stock to the public at a price of $13.00 per share. The offering was completed under the shelf registration statement that was filed on Form S-3 and declared effective May 14, 2015. Net proceeds of the underwritten public offering, after deducting the underwriting discounts and commissions, were $47 million , excluding offering expenses of $233 thousand incurred by the Company. At-the-market equity offering program On March 2, 2015, the Company entered into a Sales Agreement with Cowen and Company, LLC (the "Sales Agreement") to establish an at-the-market equity offering program (“ATM”) pursuant to which it was able to offer and sell up to $40 million of its Common Stock at prevailing market prices from time to time. On May 8, 2015, the Sales Agreement was amended to increase the offering amount under the ATM to $50 million of its Common Stock. As of December 31, 2015, the Company had not commenced sales under this program.

Summary of significant accounti

Summary of significant accounting policies	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Summary of significant accounting policies	Summary of significant accounting policies Principles of Consolidation The consolidated financial statements include the accounts of Genocea Biosciences, Inc., and a wholly-owned subsidiary. All inter-company accounts and transactions have been eliminated Basis of presentation and use of estimates The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The preparation of financial statements in conformity with 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 prepaid and accrued research and development expenses, stock-based compensation expense, the valuation of common stock warrants and warrants to purchase redeemable securities, and reported amounts of revenues and expenses during the reported period. 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. For periods prior to the closing of the IPO, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company utilized various valuation methodologies in accordance with the framework of the 2004 and 2013 American Institute of Certified Public Accountants Technical Practice Aids, Valuation of Privately-Held Company Equity Securities Issued as Compensation , to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time and the likelihood of achieving a liquidity event, such as an IPO or a sale of the Company. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date and materially affect the financial statements. Following the closing of the IPO, the fair value of common stock is determined based on the quoted market price of the common stock. Segment information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company and the Company’s chief operating decision maker view the Company’s operations and manage its business in one operating segment, which is the business of developing and commercializing vaccines. The Company operates in only one geographic segment. Cash, cash equivalents and investments The Company determines the appropriate classification of its investments at the time of purchase. All liquid investments with original maturities of 90 days or less from the purchase date are considered to be cash equivalents. The Company’s current and non-current investments are comprised of certificates of deposit and government securities that are classified as available-for-sale in accordance with FASB ASC Topic 320, Investments—Debt and Equity Securities. The Company classifies investments available to fund current operations as current assets on its balance sheets. Investments are classified as non-current assets on the balance sheets if (i) the Company has the intent and ability to hold the investments for a period of at least one year and (ii) the contractual maturity date of the investments is greater than one year. Available-for-sale investments are recorded at fair value, with unrealized gains or losses included in Accumulated other comprehensive loss on the Company’s balance sheets. Realized gains and losses are determined using the specific identification method and are included as a component of Interest expense, net. There were no realized gains or losses recognized for the twelve months ended December 31, 2015 and 2014. The Company reviews investments for other-than-temporary impairment whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other-than-temporary, the Company considers its intent to sell, or whether it is more likely than not that the Company will be required to sell the investment before recovery of the investment’s amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, the severity and the duration of the impairment and changes in value subsequent to period end. As of December 31, 2015, there were no investments with a fair value that was significantly lower than the amortized cost basis or any investments that had been in an unrealized loss position for a significant period. Concentrations of credit risk and off-balance sheet risk Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash, cash equivalents and investments. The Company’s cash, cash equivalents and investments are held in accounts with financial institutions that management believes are creditworthy. The Company’s investment policy includes guidelines on the quality of the institutions and financial instruments and defines allowable investments that the Company believes minimizes the exposure to concentration of credit risk. These amounts at times may exceed federally insured limits. The Company has not experienced any credit losses in such accounts and does not believe it is exposed to any significant credit risk on these funds. The Company has no financial instruments with off-balance sheet risk of loss. Deferred financing costs Offering costs related to debt and equity financing primarily consist of direct and incremental external expenses. In accordance with ASU No. 2015-03 Interest—Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs (“ASU 2015-03”) the Company presents debt issuance costs related to a recognized debt liability in the balance sheet as a direct deduction of the carrying value of the debt liability, consistent with the accounting treatment of debt discounts. The adoption of ASU 2015-03 in the quarter ended June 30, 2015 resulted in the reclassification of approximately $ 99 thousand , as of December 31, 2014, of unamortized capitalized debt issuance costs previously included in both other current and other non-current assets to a direct deduction of the carrying value of the debt liability. The adoption of this standard did not have material impact on the Company’s financial conditions, results of operations, or cash flows. The amortization of deferred debt financing costs follows the effective interest rate method and was not impacted by the issuance or adoption of ASU 2015-03. Offering costs related to registration statements and the initiation of the ATM are recorded as an asset and are reclassified to equity on a pro-rata basis based upon the successful selling of common shares compared to the available limits in either equity program. The costs are reviewed for impairment and will be recorded to expense if and when the Company determines that future equity offerings are not probable of occurring. At December 31, 2015, the Company had $304 thousand of deferred offering costs recorded as an Other non-current asset. There were no deferred offering costs at December 31, 2014. Fair value of financial instruments The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. FASB ASC Topic 820, Fair Value Measurement and Disclosures , (“ASC 820”) established a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the financial instrument based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the financial instrument and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported or disclosed fair value of the financial instruments and is not a measure of the investment credit quality. Fair value measurements are classified and disclosed in one of the following three categories: • Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. • Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly. • Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Financial instruments measured at fair value on a recurring basis include cash equivalents and investments (Note 3) and warrants (Note 7). An entity may elect to measure many financial instruments and certain other items at fair value at specified election dates. Subsequent unrealized gains and losses on items for which the fair value option has been elected will be reported in net loss. The Company did not elect to measure any additional financial instruments or other items at fair value. The Company is also required to disclose the fair value of financial instruments not carried at fair value. The fair value of the Company’s long-term debt (Note 6) is determined using current applicable rates for similar instruments as of the balance sheet dates and assessment of the credit rating of the Company. The carrying value of the Company’s long-term debt approximates fair value because the Company’s interest rate yield is near current market rates. The Company’s long-term debt is considered a Level 3 liability within the fair value hierarchy. Except for the valuation methodology utilized to value the warrants to purchase redeemable securities (Note 7), there have been no changes to the valuation methods utilized by the Company during the three years ended December 31, 2015. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of financial instruments between levels during the years ended December 31, 2015, 2014 and 2013. Derivative Instruments The Company occasionally issues financial instruments in which a derivative instrument is “embedded”. Upon issuing the financial instrument, the Company assesses whether the economic characteristics of the embedded derivative are clearly and closely related to the economic characteristics of the remaining component of the financial instrument (i.e., the host contract) and whether a separate, non-embedded instrument with the same terms as the embedded instrument would meet the definition of a derivative instrument. When it is determined that (1) the embedded derivative possesses economic characteristics that are not clearly and closely related to the economic characteristics of the host contract and (2) a separate, stand-alone instrument with the same terms would qualify as a derivative instrument, the embedded derivative is separated from the host contract and carried at fair value with any changes in fair value recorded in current period earnings. In connection with the issuance of the 2014 Term Loan and the First Amendment (Note 6), the Company evaluated all features of the agreement noting none that required bifurcation under FASB ASC Topic 815, Derivatives and Hedging (“ASC 815”). Property and equipment Property and equipment is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred, while costs of major additions and betterments are capitalized. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the statements of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Asset Estimated useful life Laboratory equipment 5 Furniture and office equipment 5 Computer hardware and software 3-5 years Leasehold improvements Shorter of the useful life or remaining lease term Development of Software for Internal Use The Company accounts for the costs of software developed or obtained for internal use in accordance with ASC 350-40, Internal-Use Software . Costs of materials, consultants, payroll, and payroll-related costs for employees incurred in developing internal-use software are capitalized as incurred. These costs are included in Property and equipment, net. Costs incurred during the preliminary project and post-implementation stages are charged to expense. Impairment of long-lived assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value. The Company has not recognized any impairment losses in any reporting periods through December 31, 2015. Revenue recognition The Company has generated revenue solely through research and development grants with private not-for-profit organizations and federal agencies for the development and commercialization of product candidates. The Company recognizes revenue in accordance with FASB ASC Topic 605, Revenue Recognition (“ASC 605”). Accordingly, revenue is recognized for each unit of accounting when all of the following criteria are met: • persuasive evidence of an arrangement exist • delivery has occurred or services have been rendered • the fee is fixed or determinable • collectability is reasonably assured Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as a current liability. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as a non-current liability. Grant revenue Periodically, the Company receives grants from private not-for-profit organizations and federal agencies to conduct vaccine development research. Funds received in advance of services being performed are recorded as deferred revenue. Revenue under these grants is recognized as research services are performed. Multiple-element arrangements The Company analyzes multiple-element arrangements based on the guidance in FASB ASC Topic 605-25, Revenue Recognition—Multiple-Element Arrangements (“ASC 605-25”). The Company applies this guidance to new arrangements as well as existing arrangements that contain multiple deliverables. The Company determines the elements, or deliverables, included in the arrangement and allocates consideration under the arrangement to the various elements based on each element’s relative selling price. The identification of individual elements in a multiple-element arrangement and the estimation of the selling price of each element involves significant judgment, including consideration as to whether each delivered element has stand-alone value to the collaborator. The Company determines the estimated selling price for deliverables within the arrangement using vendor-specific objective evidence (“VSOE”) of selling price, if available, or third-party evidence of selling price if VSOE was not available or the Company’s best estimate of selling price, if neither VSOE nor third-party evidence was available. The Company uses its best estimate of a selling price to estimate the selling price for licenses for its technology, know-how, and trademarks since it does not have VSOE or third-party evidence of selling price for these deliverables. In order to determine the best estimate of selling price, the Company considers market conditions, as well as entity- specific factors, including those factors contemplated in negotiating the agreements, as well as internally developed estimates that include assumptions related to the market opportunity, estimated development costs, probability of success, and the time needed to commercialize assays. In validating its best estimate of selling price, the Company evaluates whether changes in the key assumptions used to determine best estimate of selling price would have a significant effect on the allocation of arrangement consideration between deliverables. The Company recognizes consideration allocated to an individual element when all other revenue recognition criteria are met for that element, which generally occurs upon delivery or over the period in which services are provided. Research and development expenses Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, facilities and overhead, clinical study and related clinical manufacturing costs, regulatory and other related costs. Nonrefundable advanced payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed. Stock-based compensation expense The Company accounts for its stock-based compensation awards to employees and directors in accordance with FASB ASC Topic 718, Compensation-Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees, including grants of employee stock options and restricted stock, to be recognized in the statements of operations and comprehensive loss based on their grant date fair values. Compensation expense related to awards to employees is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Share-based payments issued to non-employees are recorded at their fair values, and are periodically revalued as the equity instruments vest and are recognized as expense over the related service period in accordance with the provisions of ASC 718 and FASB ASC Topic 505, Equity, (“ASC 505”) and are expensed using an accelerated attribution model. The Company estimates the fair value of its stock options using the Black- Scholes option pricing model, which requires the input of subjective assumptions, including (a) the expected volatility of the Company’s stock price, (b) the expected term of the award, (c) the risk-free interest rate, (d) expected dividends and (e) the estimated fair value of the Company’s common stock on the measurement date. Due to the limited operating history of the Company as a public entity and a lack of company specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected term of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Due to the lack of Company specific historical option activity, the Company has estimated the expected term of its employee stock options using the “simplified” method, whereby, the expected term equals the arithmetic average of the vesting term and the original contractual term of the option. The expected term for non-employee awards is the remaining contractual term of the option. The risk-free interest rates are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid, and does not expect to pay dividends in the foreseeable future. Refer to Basis of presentation and use of estimates in Note 2 for a discussion of the Company’s estimated fair value of its common stock prior to the IPO. Following the closing of the Company’s IPO, the fair value of common stock is determined based on the quoted market price of the common stock. The Company is also required to estimate forfeitures at the time of grant, and revise those estimates in subsequent periods if actual forfeitures differ from its estimates. The Company uses historical data to estimate forfeitures and records stock-based compensation expense only for those awards that are expected to vest. To the extent that actual forfeitures differ from the Company’s estimates, the differences are recorded as a cumulative adjustment in the period the estimates were revised. Stock-based compensation expense recognized in the financial statements is based on awards that are ultimately expected to vest. Income taxes Income taxes are recorded in accordance with FASB ASC Topic 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial reporting and the tax reporting basis of assets and liabilities and are measured using the enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. The Company provides a valuation allowance against net deferred tax assets unless, based upon the available evidence, it is more likely than not that the deferred tax assets will be realized. The Company has evaluated available evidence and concluded that the Company may not realize the benefit of its deferred tax assets; therefore a valuation allowance has been established for the full amount of the deferred tax assets. The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2015 and 2014, the Company does not have any significant uncertain tax positions. The Company’s practice is to recognize interest and/or penalties related to income tax matters in income tax expense. Earnings per share Basic earnings per share attributable to common stockholders is calculated by dividing net loss attributable to common stockholders by the weighted average shares outstanding during the period, without consideration for common stock equivalents. Net loss attributable to common stockholders is calculated by adjusting the net loss of the Company for cumulative preferred stock dividends and accretion of preferred stock issuance costs. Diluted earnings per share attributable to common stockholders is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock and if-converted methods. For purposes of the diluted net loss per share attributable to common stockholders calculation, preferred stock, stock options, unvested restricted stock, and warrants are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share attributable to common stockholders, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented. Comprehensive loss Comprehensive loss consists of net loss and changes in equity during a period from transactions and other events and circumstances generated from non-owner sources. For all periods presented other comprehensive income (loss), if any, consists of unrealized gains and losses on the Company’s investments. Recent accounting pronouncements Standard Description Effect on the financial statements ASU 2014-09, Revenue from Contracts with Customers (Topic 606) The standard will replace existing revenue recognition standards and significantly expand the disclosure requirements for revenue arrangements. It may be adopted either retrospectively or on a modified retrospective basis to new contracts and existing contracts with remaining performance obligations as of the effective date. At this time, the Company has not decided on which method it will use to adopt the new standard, nor has it determined the effects of the new guidelines on its results of operations and financial position. For the foreseeable future, the Company’s revenues will be limited to grants received from government agencies or nonprofit organizations. The Company is currently evaluating the method of adoption and the impact of this standard on the financial statements. ASU No. 2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern (“ASU 2014-15”). The standard requires a company to evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the entity’s ability to continue as a going concern. Substantial doubt about an entity’s ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year after the date that the financial statements are issued. This ASU is effective for annual and interim periods ending after December 15, 2016 and earlier application is permitted. The Company is evaluating the effects of the new standard, but does not expect it will have a material impact on its financial conditions, results of operations, or cash flows.

Cash, cash equivalents and inve

Cash, cash equivalents and investments	12 Months Ended
	Dec. 31, 2015
Cash and Cash Equivalents [Abstract]
Cash, cash equivalents and investments	Cash, cash equivalents and investments As of December 31, 2015 and 2014, cash, cash equivalents and investments comprised funds in depository, money market accounts, U.S treasury securities, and FDIC-insured certificates of deposit. The following table presents the cash equivalents and investments carried at fair value in accordance with the hierarchy defined in Note 2 (in thousands): Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) December 31, 2015 Money Market funds, included in cash equivalents $ 14,207 $ 14,207 $ — $ — U.S treasuries, included in cash equivalents $ 2,203 2,203 — — Investments - U.S. treasuries $ 27,924 27,924 — — Investments - certificates of deposit 61,249 — 61,249 — Total $ 105,583 $ 44,334 $ 61,249 $ — 0 December 31, 2014 Money Market funds, included in cash equivalents $ 18,992 $ 18,992 $ — $ — Marketable securities - U.S. treasuries 27,021 27,021 — — Total $ 46,013 $ 46,013 $ — $ — Cash equivalents and marketable securities have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches and observable market inputs to determine value. The Company validates the prices provided by its third party pricing services by reviewing their pricing methods and obtaining market values from other pricing sources. After completing its validation procedures, the Company did not adjust any fair value measurements provided by the pricing services as of December 31, 2015 and 2014. Cash equivalents and investments at December 31, 2015 consist of the following (in thousands): Contracted Maturity Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and investments U.S. Treasuries 60-184 days $ 30,120 $ 7 $ — $ 30,127 Certificates of deposit 91-365 days 49,145 — — 49,145 Certificates of deposit greater than 365 days 12,104 — — 12,104 Total $ 91,369 $ 7 $ — $ 91,376 Interest income earned for the years ended December 31, 2015, 2014, and 2013, was $157 thousand , $32 thousand , and $6 thousand , respectively.

Property and equipment, net

Property and equipment, net	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property and equipment, net	Property and equipment, net Property and equipment, net consist of the following (in thousands): December 31, 2015 2014 Laboratory equipment $ 3,943 $ 2,510 Furniture office equipment 610 186 Computer hardware 259 257 Leasehold improvements 1,433 799 Computer software 338 — Total property and equipment 6,583 3,752 Accumulated depreciation (2,500 ) (1,796 ) Property and equipment, net $ 4,083 $ 1,956 Depreciation expense was $1.1 million , $0.5 million , and $0.3 million for the years ended December 31, 2015, 2014, 2013, respectively. The Company's internally developed computer software is not yet available to be placed into service and no amortization was recorded for the twelve months ended December 31, 2015.

Accrued expenses and other curr

Accrued expenses and other current liabilities	12 Months Ended
	Dec. 31, 2015
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): December 31, 2015 2014 Payroll and employee-related costs $ 1,736 $ 1,066 Research and development costs 1,359 1,117 Other current liabilities 880 410 Total $ 3,975 $ 2,593

Long-term debt

Long-term debt	12 Months Ended
	Dec. 31, 2015
Long-term Debt, Unclassified [Abstract]
Long-term debt	Long-term debt 2014 Term Loan, First Amendment On November 20, 2014 (the "Closing Date"), the Company entered into a loan and security agreement (the “Loan Agreement”) with Hercules Technology Growth Capital, Inc. (“Hercules”) which provided up to $27.0 million in debt financing in three separate tranches (the “2014 Term Loan”). The first tranche of $17.0 million was available through June 30, 2015, of which $12.0 million was drawn down at loan inception for which approximately $9.8 million of the proceeds were used to repay all outstanding indebtedness under the previously existing $10.0 million loan agreement (the "2013 Term Loan"). The Company recorded a $435 thousand loss on extinguishment of debt in other expense on the Statements of Operations related to deferred debt charges, the unamortized portion of the original issue discount related to the 2013 Term Loan and other fees associated with extinguishing the debt. The option to draw down the remaining $5.0 million under the first tranche expired unused on June 30, 2015. The second tranche of $5.0 million was subject to certain eligibility requirements which were achieved as of June 30, 2015 and the Company had the option to draw down the second tranche on or prior to December 15, 2015. The second tranche expired unused on December 15, 2015 The third tranche of $5.0 million was not eligible to draw as the Company did not achieve positive results from its Phase 2a human challenge study of GEN-004. In December 2015, the Company amended the Loan Agreement (the "First Amendment") with Hercules. The First Amendment required the Company to draw an additional $5.0 million and permits it to draw two additional $5.0 million tranches. One $5.0 million tranche is immediately available to draw through December 15, 2016 and a second $5.0 million tranche becomes available through December 15, 2016, subject to the Company demonstrating sufficient evidence of continued clinical progression of its GEN-003 product and making favorable progress in applying its proprietary technology platform toward the development of novel immunotherapies with application in oncology. At December 31, 2015, $17.0 million was outstanding under the amended 2014 Term Loan. During the amendment negotiations, but after the third quarter Form 10-Q was filed, the Company identified three separate covenant violations that resulted in an event of default as of September 30, 2015. The violated covenants related to certain investments the Company held as well as certain financial reporting obligations. Pursuant to the 2014 Term Loan, upon an event of default, Hercules can accelerate the repayment of all amounts due under the 2014 Term Loan at their discretion. Hercules did not make a repayment demand and the First Amendment included a permanent waiver of these covenant violations subject only to certain requirements that are within our control. The First Amendment also modified the Loan Agreement for the specific instances in which these violations arose, including redefining permitted investments to be in line with the Company's approved investment policies. 2014 Term Loan The 2014 Term Loan had an original maturity of July 1, 2018. The eligibility requirements for the second tranche also contained an election for the Company to extend the maturity date to January 1, 2019. During the second quarter of 2015, the Company elected to extend the maturity date of the 2014 Term Loan. The maturity date of January 1, 2019 remained unchanged by the First Amendment. Each advance accrues interest at a floating rate per annum equal to the greater of (i) 7.25% or (ii) the sum of 7.25% plus the prime rate minus 5.0% . The 2014 Term Loan provided for interest-only payments until December 31, 2015, which was extended by the Company for a six -month period as the eligibility requirements for the second tranche were met during the second quarter of 2015. The First Amendment subsequently extended the interest only period through June 30, 2017. Thereafter, beginning July 1, 2017, principal and interest payments will be made monthly for 18 months with a payoff schedule based upon a 30 -month amortization schedule, the original amortization term of the 2014 Term Loan. The remaining unpaid principal is due at January 1, 2019. The 2014 Term Loan may be prepaid in whole or in part upon seven business days’ prior written notice to Hercules. Prepayments will be subject to a charge of 3.0% if an advance is prepaid within 12 months following the Closing Date, 2.0% , if an advance is prepaid between 12 and 24 months following the Closing Date, and 1.0% thereafter. Amounts outstanding at the time of an event of default shall be payable on demand and shall accrue interest at an additional rate of 5.0% per annum on any outstanding amounts past due. The Company is also obligated to pay an end of term charge of 4.95% (the "End of Term Charge") of the balance drawn when the advances are repaid. The 2014 Term Loan is secured by a lien on substantially all of the assets of the Company, other than intellectual property, provided that such lien on substantially all assets includes any rights to payments and proceeds from the sale, licensing or disposition of intellectual property. The Loan Agreement contains non-financial covenants and representations, including a financial reporting covenant, and limitations on dividends, indebtedness, collateral, investments, distributions, transfers, mergers or acquisitions, taxes, corporate changes, deposit accounts, and subsidiaries. There are no financial covenants. Under the provisions of the 2014 Term Loan, the Company has also entered into account control agreements ("ACAs") with Hercules and certain of the Company's financial institutions in which cash, cash equivalents, and investments are held. These ACAs grant Hercules a perfected first priority security interest in the subject accounts. The ACAs do not restrict the Company's ability to utilize cash, cash equivalents, or investments to fund operations and capital expenditures unless there is an Event of Default and Hercules activates its rights under the ACAs. The Loan Agreement contains a Material Adverse Effect provision that requires all material adverse effects to be reported under the financial reporting covenant. Loan advances are subject to a representation that no event that has had or could reasonably be expected to have a Material Adverse Effect has occurred and is continuing. Under the Loan Agreement, a Material Adverse Effect means a material adverse effect upon: (i) the business, operations, properties, assets or condition (financial or otherwise) of the Company; or (ii) the ability of the Company to perform the secured obligations in accordance with the terms of the Loan Agreements, 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 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. Events of default under the Loan Agreement include failure to make any payments of principal or interest as due on any outstanding indebtedness, breach of any covenant, any false or misleading representations or warranties, insolvency or bankruptcy, any attachment or judgment on the Company’s assets of at least $100 thousand, or the occurrence of any material default of the Company involving indebtedness in excess of $100 thousand. If an event of default occurs, repayment of all amounts due under the Loan Agreement may be accelerated by Hercules, including the applicable Prepayment Charge. The 2014 Term Loan is automatically redeemable upon a change in control whereas the Company must prepay the outstanding principal and any accrued and unpaid interest through the prepayment date including any unpaid agent’s and lender’s fees and expenses accrued to the date of the repayment including the End of Term Charge and the applicable Prepayment Charge. If a change in control occurs, repayment of amounts due under the Loan Agreement may be accelerated by Hercules. In connection with the 2014 Term Loan, the Company issued a common stock warrant to Hercules on November 20, 2014. The warrant is exercisable for 73,725 shares of the Company’s common stock (equal to $607,500 divided by the exercise price of $8.24 ). 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 warrant is exercisable until November 20, 2019 and will be exercised automatically on a net issuance basis if not exercised prior to the expiration date and if the then-current fair market value of one share of common stock is greater than the exercise price then in effect. The warrant has been classified as equity for all periods it has been outstanding. Contemporaneously with the 2014 Term Loan, the Company also entered into an equity rights letter agreement on November 20, 2014 (the “Equity Rights Letter Agreement”). Pursuant to the Equity Rights Letter Agreement, the Company issued to Hercules 223,463 shares of the Company’s Common Stock for an aggregate purchase price of approximately $2.0 million at a price per share equal to the closing price of the Company’s Common Stock as reported on The NASDAQ Global Market on November 19, 2014. The shares will be subject to resale limitations and may be resold only pursuant to an effective registration statement or an exemption from registration. Additionally, under the Equity Rights Letter Agreement, Hercules has the right to participate in any one or more subsequent private placement equity financings of up to $2.0 million on the same terms and conditions as purchases by the other investors in each subsequent equity financing. The Equity Rights Letter Agreement, and all rights and obligations thereunder, will terminate upon the earlier of (1) such time when Hercules has purchased $2.0 million of subsequent equity financing securities in the aggregate and (2) the later of (a) the repayment of all indebtedness under the Loan Agreement and (b) the expiration or termination of the exercise period for the warrant issued in connection with the Loan Agreement. The Company allocated $36 thousand of financing costs to additional paid-in capital for issuance fees that were reimbursed to Hercules. The Company incurred $280 thousand in debt financing costs related to the First Amendment which was recorded as a debt discount and will be amortized over the remaining loan term. In connection with the issuance of the 2014 Term Loan, the Company incurred $103 thousand of financing costs and also reimbursed Hercules $210 thousand for debt financing costs which has been recorded as a debt discount and will be amortized over the remaining loan term. The End of Term Charge is amortized ratably over the term loan period based upon the outstanding debt and the increase in the amount of End of Term Charge due to the additional borrowing from the First Amendment is being amortized from the First Amendment date through maturity. The debt discount is being amortized to interest expense over the life of the 2014 Term Loan using the effective interest method. At December 31, 2015, the 2014 Term Loan bears an effective interest rate of 10.2% . As of December 31, 2015 and 2014, the Company had outstanding borrowings under the 2014 Term Loan of $17.0 million and $12.0 million , respectively. Interest expense related to the 2014 Term Loan was $1.3 million and $0.1 million for the years ended December 31, 2015 and 2014, respectively. Interest expense related to the 2013 Term Loan was $0.8 million and $0.1 million for the years ended December 31, 2014 and 2013, respectively. Future principal payments, including the End of Term Charge, on the 2014 Term Loan are as follows (in thousands): December 31, 2015 2016 $ — 2017 3,149 2018 6,659 2019 8,034 Total $ 17,842 2013 Term Loan On September 30, 2013, the Company entered into the 2013 Term Loan which provided up to $10.0 million . Upon the closing of the 2013 Term Loan, the Company drew down $3.5 million and paid off the remaining balance under the 2011 Term Loan (defined below). As part of the early repayment, the Company incurred a loss on debt extinguishment of $0.2 million . The 2013 Term Loan provided for a draw-down period on the remaining facility of $6.5 million , which the Company drew down on December 19, 2013. The Company was obligated to make interest-only payments for the first 9 months and 33 equal payments of principal, together with accrued interest thereafter for each advance. The 2013 Term Loan bore interest at a rate of 8% per annum. The Company was also obligated to pay 2% of the advance on the final repayment date of each draw. The final payment was accrued over the term of the debt and recorded in accrued interest payable on the balance sheet as at December 31, 2013. In connection with the 2013 Term Loan, the Company issued a warrant to purchase 689,655 shares of Series C Preferred Stock at $0.58 per share. Upon the completion of the Company's IPO, these Series C preferred stock warrants automatically converted into warrants exercisable for 57,954 shares of Common Stock at an exercise price of $6.90 per share (Note 7). 2011 Term Loan In October 2011, the Company entered into a loan and security agreement which provided for up to $5.0 million in debt financing (“2011 Term Loan”). In March 2012, the Company drew down the full $5.0 million available under the terms of this arrangement. In May 2012, the Company began making 36 equal monthly payments of principal and accrued interest thereafter. During the 36 -month period, the 2011 Term Loan bore interest at the greater of the financial institution’s prime rate plus 4.75% or 8.00% . The Company was also obligated to pay 6.50% of the advance on the final repayment date of the draw, which was April 1, 2015. This final payment was accrued over the term of the debt and was recorded in accrued interest payable.

Warrants

Warrants	12 Months Ended
	Dec. 31, 2015
Warrants and Rights Note Disclosure [Abstract]
Warrants	Warrants As of December 31, 2015 and December 31, 2014, the Company had warrants outstanding that represent the right to acquire 77,603 shares of common stock, of which 73,725 represented warrants issued to Hercules in relation to the 2014 Term Loan and 3,878 represented warrants to purchase common stock issued in periods prior to the Company's IPO. Hercules Warrants In accordance with ASC Topic No. 815, “ Derivatives and Hedging ” (Topic No. 815), the Company determined the common stock warrant issued to Hercules to be equity classified. The Company estimated the fair value of this warrant as of the issuance date using a Black-Scholes option pricing model (with a 10% discount for lack of marketability) with the following assumptions: November 20, Fair value of underlying instrument $ 9.05 Expected volatility 70.0 % Expected term (in years) 5 Risk-free interest rate 1.64 % Expected dividend yield 0.0 % The Company utilized this fair value in its allocation of debt proceeds between debt and the warrants which was performed on a relative fair value basis. Ultimately, the Company allocated $334 thousand to the Hercules warrants and recognized this amount in additional paid-in capital. As of December 31, 2015, the common stock warrants issued to Hercules had not been exercised and were still outstanding. Warrants to purchase redeemable securities As of December 31, 2013, the Company had outstanding warrants to purchase 2,291,512 shares of redeemable convertible preferred stock. On January 29, 2014, 21,695 warrants to purchase Series A preferred stock were exercised for cash. On February 4, 2014, an additional 28,926 warrants to purchase Series A preferred stock were exercised for cash. Prior to the completion of the Company's IPO on February 10, 2014, warrants to purchase 987,840 shares of Series A preferred stock were exercised in a cashless exercise for 316,932 shares of Series A preferred stock, which automatically converted into 26,633 shares of Common Stock upon the completion of the Company's IPO. Also upon the completion of the Company's IPO, warrants exercisable for 1,253,051 shares of redeemable convertible preferred stock were automatically converted into warrants exercisable for 105,297 shares of Common Stock. On February 12, 2014, 43,465 warrants were exercised in a cashless exercise for 16,593 shares of Common Stock. On April 23, 2014, 57,954 warrants were exercised in a cashless exercise for 37,250 shares of Common Stock. As of December 31, 2014, 3,878 of these warrants remained outstanding. In connection with the completion of the Company's IPO, all the warrants exercisable for redeemable convertible preferred stock were automatically converted into warrants exercisable for Common Stock, resulting in the reclassification of the related warrant to purchase redeemable securities liability to additional paid-in capital as the warrants to purchase shares of Common Stock are accounted for as equity instruments. The warrant to purchase redeemable securities liability was re-measured to fair value prior to reclassification to additional paid-in capital. As of December 31, 2015 and 2014, the Company had no outstanding warrants to purchase redeemable securities liability. These warrants are considered Level 3 liabilities because their fair value measurements are based, in part, on significant inputs not observed in the market and reflect the Company’s assumptions as to the expected volatility of the Company’s preferred stock. The Company determined the fair value of the warrants to purchase redeemable securities based on input from management and the board of directors, which utilized an independent valuation of the Company’s enterprise value, determined utilizing an analytical valuation model. Any reasonable changes in the assumptions used in the valuation could materially affect the financial results of the Company. The following table sets forth a summary of changes in the fair value of the Company’s warrants to purchase redeemable securities, which represents a recurring measurement that is classified within Level 3 of the fair value hierarchy wherein fair value is estimated using significant unobservable inputs (in thousands): Years ended December 31, 2015 2014 2013 Beginning balance $ — $ 656 $ 246 Warrants issued — — 188 Change in fair value — 725 222 Warrants exercised — (323 ) — Reclassification to accumulated paid-in capital — (1,058 ) — Ending balance $ — $ — $ 656 These warrants are considered Level 3 liabilities because their fair value measurements are based, in part, on significant inputs not observed in the market and reflect the Company’s assumptions as to the expected volatility of the Company’s preferred stock. At December 31, 2013, the Company determined the fair value of the warrants to purchase redeemable securities based on input from management and the board of directors, which utilized an independent valuation of the Company’s enterprise value, determined utilizing an analytical valuation model. Any reasonable changes in the assumptions used in the valuation could materially affect the financial results of the Company. At December 31, 2013, the analytical valuation model used to calculate the fair value of warrants to purchase redeemable securities was a hybrid approach based on an Option-Pricing Model (“OPM”) backsolve method and the Probability-Weighted Expected Return Model (“PWERM”). Thirty-five percent of the value was attributed to the OPM backsolve method and 65% was attributed to the PWERM. After the enterprise value was determined, the total enterprise value was then allocated to the various outstanding equity instruments, including the warrants to purchase redeemable securities, utilizing the OPM. The fair value of warrants to purchase 21,695 shares of Series A preferred stock prior to exercise on January 29, 2014 was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions: January 29, Fair value of underlying instrument $ 0.65 Expected Volatility 55.57 % Expected term (in years) 0.04 Risk-free interest rate 1.52 % Expected dividend yield 0.0 % These warrants were re-measured to a fair value of $8 thousand, which resulted in an increase in fair value of $2 thousand. The fair value of the warrants was reclassified to additional paid-in capital upon exercise on January 29, 2014. The fair value of warrants to purchase 28,926 shares of Series A preferred stock prior to exercise on February 4, 2014 was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions: February 4, Fair value of underlying instrument $ 0.65 Expected Volatility 55.03 % Expected term (in years) 0.02 Risk-free interest rate 1.46 % Expected dividend yield 0.0 % These warrants were re-measured to a fair value of $10 thousand, which resulted in an increase in fair value of $3 thousand. The fair value of the warrants was reclassified to additional paid-in capital upon exercise on February 4, 2014. The fair value of warrants to purchase 987,840 shares of Series A preferred stock prior to a cashless exercise for 316,932 shares of Series A preferred stock on February 10, 2014, which automatically converted into 26,633 shares of Common Stock upon the completion of the Company's IPO, was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions: February 10, Fair value of underlying instrument $ 7.74 Expected Volatility 50.81 % Expected term (in years) 1 Risk-free interest rate 1.48 % Expected dividend yield 0.0 % These warrants were re-measured to a fair value of $304 thousand, which resulted in an increase in fair value of $47 thousand. The fair value of the warrants was reclassified to additional paid-in capital upon exercise on February 10, 2014. The fair value of warrants exercisable for 1,253,051 shares of redeemable convertible preferred stock, which were automatically converted into warrants exercisable for 105,297 shares of Common Stock, was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions: February 10, Fair value of underlying instrument $ 6.96 Expected Volatility 92.9 % Expected term (in years) 8.66 Risk-free interest rate 2.43 % Expected dividend yield 0.0 % The fair value of the remaining 105,297 warrants to purchase Common Stock were re-measured to a fair value of $1,058 thousand, which resulted in an increase in fair value of $673 thousand. The fair value of the warrants was reclassified to additional paid-in capital upon conversion on February 10, 2014.

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Lease commitments In February 2014, the Company signed an operating lease for office and laboratory space that commenced in March 2014 and expires in February 2017 (the "2014 Lease"). In June 2015, the Company signed a second operating lease for office space in the same building as the 2014 Lease, which also expires in February 2017 (the "2015 Lease"). The 2015 Lease has one three -year renewal period. Rent expense for the three years ended December 31, 2015, 2014, and 2013, was $1.2 million , $0.8 million , and $0.5 million , respectively. The minimum future lease payments under both the 2014 Lease and the 2015 Lease are as follows (in thousands): December 31, 2015 2016 $ 1,379 2017 231 Total $ 1,610 At December 31, 2015, the Company has an outstanding letter of credit of $316 thousand with a financial institution related to a security deposit for the 2014 Lease, which is secured by cash on deposit and expires on February 28, 2017. An additional unsecured deposit was required for the 2015 Lease. Significant Contracts and Agreements In addition to lease commitments, the Company enters into contractual arrangements that obligate it to make payments to the contractual counterparties upon the occurrence of future events. In the normal course of operations, the Company enters into license and other agreements and intends to continue to seek additional rights relating to compounds or technologies in connection with its discovery, manufacturing and development programs. These agreements may require payments to be made by the Company upon the occurrence of certain development milestones and certain commercialization milestones for each distinct product covered by the licensed patents (in addition to certain royalties to be paid on marketed products or sublicense income) contingent upon the occurrence of future events that cannot be reasonably estimated. In March 2014, the Company announced a joint research collaboration with Dana-Farber Cancer Institute to characterize anti-tumor T cell responses in melanoma patients. This collaboration extends the use of the Company's proprietary ATLAS platform for the rapid discovery of T cell antigens to cancer immunotherapy approaches. Under this agreement, the Company recognized revenue of $30 thousand and none for the years ended December 31, 2015 and 2014, respectively. In September 2014, the Company received $1.2 million in the form of a grant entered into with the Bill & Melinda Gates Foundation for the identification of protective T-cell antigens for malaria vaccines. The grant will allow for the continued expansion of the Company’s malaria antigen library and aid in the identification of novel protein antigens to facilitate the development of highly efficacious anti-infection malarial vaccines. The Company recognized revenue under the agreement of $640 thousand and $308 thousand for the years ended December 31, 2015 and 2014, respectively. The Company relies on research institutions, contract research organizations, clinical investigators as well as clinical and commercial material manufacturers for its product candidates. Under the terms of these agreements, the Company is obligated to make milestone payments upon the achievement of manufacturing or clinical milestones defined in the contracts. In some cases, monthly service fee for project management services are charged over the duration of the arrangement. In addition, clinical and manufacturing contracts generally require reimbursement to suppliers for certain set-up, production, travel, and other related costs as they are incurred. In some manufacturing contracts, the Company also may be responsible for the payment of a reservation fee, which will equal a percentage of the expected production fees, to reserve manufacturing slots in the production timeframe. Generally, the Company is liable for actual effort expended by these organizations at any point in time during the contract through the notice period. To the extent amounts paid to a supplier exceed the actual efforts expended, the Company records a prepaid asset, and to the extent actual efforts expended exceed amounts billed or billable under a contract, an accrual for the estimate of services rendered is recorded. In February 2014, the Company entered into a supply agreement with FUJIFILM Diosynth Biotechnologies U.S.A., Inc. (“Fujifilm”) for the manufacture and supply of antigens for future GEN-003 clinical trials. Under the agreement, the Company is obligated to pay Fujifilm manufacturing milestones, in addition to reimbursement of certain material production related costs. Additionally, the Company is responsible for the payment of a reservation fee, which will equal a percentage of the expected production fees, to reserve manufacturing slots in the production timeframe. The Company incurred expenses under this agreement of $4.2 million , $3.5 million , and none for the years ended December 31, 2015, 2014 and 2013, respectively. Litigation The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities.

Equity and net loss per share

Equity and net loss per share	12 Months Ended
	Dec. 31, 2015
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Equity and net loss per share	Equity and net loss per share At December 31, 2015, the Company authorized 175,000,000 shares of common stock at $0.001 par value per share, of which 28,161,313 shares of common stock were issued and 28,151,596 shares of common stock were outstanding. The Company computes basic and diluted earnings (loss) per share using a methodology that gives effect to the impact of outstanding participating securities (the “two-class method”). For the three years ended December 31, 2015, there is no income allocation required under the two-class method or dilution attributed to weighted average shares outstanding in the calculation of diluted loss per share. The following 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 (in thousands): Years ended December 31, 2015 2014 2013 Preferred stock — — 11,409 Warrants 78 78 193 Outstanding options 2,723 2,290 1,576 Total 2,801 2,368 13,178 Reverse stock split On January 20, 2014, the board of directors and stockholders approved a 1-for-11.9 reverse stock split of the Company’s common stock, which was effected on January 21, 2014. Stockholders entitled to fractional shares as a result of the reverse stock split received a cash payment in lieu of receiving fractional shares upon the completion of the Company's IPO on February 17, 2014. The Company’s historical share and per share information were retroactively adjusted to give effect to this reverse stock split. Shares of common stock underlying outstanding stock option were proportionately reduced and the respective exercise prices proportionately increased. Restricted stock During 2013, a Company director exercised stock options and received 31,092 shares of common stock that were subject to a Stock Restriction and Repurchase Agreement with the Company. Under the terms of the agreement, shares of common stock issued are subject to a vesting schedule and unvested shares are subject to repurchase by the Company. Vesting occurs periodically at specified time intervals and specified percentages. All shares of common stock become fully vested within four years of the date of grant. At both December 31, 2015 and December 31, 2014, the Company had issued 35,964 shares of restricted common stock. At December 31, 2015, 9,717 shares of nonvested restricted stock were subject to repurchase by the Company. At December 31, 2014, 16,840 shares of nonvested restricted stock were subject to repurchase by the Company

Stock and employee benefit plan

Stock and employee benefit plans	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock and employee benefit plans	Stock and employee benefit plans The Company’s board of directors adopted the 2014 Equity Incentive Plan (the “2014 Equity Plan”), which was approved by its stockholders and became effective prior to the commencement of the Company's IPO. The 2014 Equity Plan replaced the 2007 Equity Incentive Plan (the “2007 Equity Plan”). The 2014 Equity Plan provides for the grant of incentive stock options, non-qualified stock options, restricted stock and other awards to key employees and directors of, and consultants and advisors to, the Company. The maximum number of shares of common stock that may be delivered in satisfaction of awards under the 2014 Equity Plan is 903,494 shares, plus 219,765 shares that were available for grant under the 2007 Equity Plan on the date the 2014 Equity Plan was adopted. The 2014 Equity Plan provides that the number of shares available for issuance will automatically increase annually on each January 1, from January 1, 2015 through January 1, 2024, in amount equal to the lesser of 4.0% of the outstanding shares of the Company’s outstanding common stock as of the close of business on the immediately preceding December 31 or the number of shares determined the Company’s board of directors. On January 1, 2015 and 2016, the total number of shares available for issuance under the 2014 Equity Plan increased by 714,769 and 1,126,064 , respectively, for shares under this provision. Outstanding options awards granted from the 2007 Equity Plan, at the time of the adoption of the 2014 Equity Plan, remain outstanding and effective. The shares of common stock underlying awards that are cancelled, forfeited, repurchased, expire or are otherwise terminated under the 2007 Equity Plan are added to the shares of common stock available for issuance under the 2014 Equity Plan. As of December 31, 2015, the number of shares of common stock that may be issued is 3,246,017 and 522,706 . During the years ended 2015, 2014 and 2013, the Company granted a total of none , none , and 44,345 stock options, respectively, to consultants and members of its Scientific Advisory Board, which are included in the following stock option table. The options generally vest over a four -year period, and have a life of ten years . Certain senior advisors of the Company received options that vest upon the occurrence of certain milestones. Stock options issued to non-employees are accounted for using the fair value method of accounting, and are periodically revalued as the options vest, and are recognized as expense over the related service period. The total expense related to all nonemployee options for the years ended December 31, 2015, 2014 and 2013 was $263 thousand , $324 thousand , and $143 thousand , respectively. Stock Based Compensation Expense Total stock-based compensation expense is recognized for stock options granted to employees and non-employees and has been reported in the Company’s Statements of Operations as follows (in thousands): Years ended December 31, 2015 2014 2013 Research and development $ 1,690 $ 1,511 $ 322 General and administrative 2,158 1,394 350 Total $ 3,848 $ 2,905 $ 672 Stock Options The following table summarizes stock option activity for employees and nonemployees (shares in thousands): Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2014 2,290 $ 7.26 8.08 $ 5,332 Granted 715 $ 9.12 Exercised (128 ) $ 3.00 Canceled (154 ) $ 13.41 Outstanding at December 31, 2015 2,723 $ 7.60 7.61 $ 2,840 Exercisable at December 31, 2015 1,410 $ 5.71 6.66 $ 2,507 Vested or expected to vest at December 31, 2015 2,605 $ 7.54 7.58 $ 2,793 During the years ended December 31, 2015, 2014 and 2013, the Company granted stock options to purchase an aggregate of 715,262 , 1,064,640 , and 559,742 of its common stock, respectively, with a weighted-average grant date fair values of $9.12 , $10.11 , and $3.41 , respectively. The total intrinsic value of options exercised was $1.0 million , $3.1 million and was de minimis in the years ended December 31, 2015, 2014, and 2013, respectively. As of December 31, 2015, there was $8.0 million of total unrecognized compensation cost, net of related forfeiture estimates, related to employee nonvested stock options granted under the Company’s equity plans. The total unrecognized compensation costs, net of related forfeiture estimates, related to non-employees was $255 thousand , $55 thousand and was immaterial for the years ended December 31, 2015, 2014, and 2013, respectively. Total unrecognized compensation cost for employee and non-employee will be adjusted for future forfeitures. The Company expects to recognize that cost over a remaining weighted-average period of 2.73 years. The Company estimates the fair value of each employee stock award on the grant date using the Black-Scholes option-pricing model based on the following assumptions and the assumptions regarding the fair value of the underlying common stock on each measurement date: Years ended December 31, 2015 2014 2013 Expected Volatility 68.5% - 85.3% 86.2% - 103.6% 97.1% Risk-free interest rate 1.56% - 1.94% 1.75% - 2.00% 0.59% - 1.83% Expected term (in years) 5.50 - 6.08 6.25 6.25 Expected dividend yield 0% 0% 0% Performance-Based Stock Options The Company granted stock options to certain employees, executive officers and consultants, which contain performance-based vesting criteria. Milestone events are specific to the Company’s corporate goals, which include, but are not limited to, certain clinical development milestones, business development agreements and capital fundraising events. Stock-based compensation expense associated with these performance-based stock options is recognized if the performance conditions are considered probable of being achieved, using management’s best estimates. During the year ended December 31, 2014, the Company determined that 96,988 options related to performance-based milestones were probable of achievement and, accordingly, recorded $453 thousand in related stock-based compensation expense. As of December 31, 2014, there are 56,336 performance-based common stock options outstanding for which the probability of achievement was not deemed probable. During the year ended December 31, 2015, the Company recorded no stock based compensation expense related to the 56,336 performance-based common stock options that remain outstanding for which the probability of achievement was not deemed probable at December 31, 2015. Employee Stock Purchase Plan On February 10, 2014, the Company’s board of directors adopted the 2014 Employee Stock Purchase Plan (the “2014 ESPP”). The 2014 ESPP authorizes the initial issuance of up to a total of 200,776 shares of common stock to participating eligible employees. The 2014 ESPP provides for six -month option periods commencing on January 1 and ending June 30 and commencing July 1 and ending December 31 of each calendar year. The first offering under the 2014 ESPP began on July 1, 2014. For the year ended December 31, 2014, the Company incurred $43 thousand in stock-based compensation expense and 15,622 shares were issued. For the year ended December 31, 2015, the Company incurred $113 thousand in stock-based compensation expense and 40,912 shares were issued. Shares remaining for future issuance under the plan were 144,242 as of December 31, 2015. 401(k) Savings plan In 2007, the Company established a defined-contribution savings plan under Section 401(k) of the Internal Revenue Code (“401(k) Plan”). The 401(k) Plan covers all employees who meet defined minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pretax basis. Beginning January 1, 2015, the Company began making matching contributions to participants in this plan which totaled $174 thousand for the year ended December 31, 2015.

Income taxes

Income taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income taxes	Income taxes For the years ended December 31, 2015 and 2014, the Company did not record a current or deferred income tax expense or benefit. The Company’s losses before income taxes consist solely of domestic losses. The significant components of the Company’s deferred tax assets are comprised of the following: December 31, 2015 2014 Deferred tax assets: U.S and state net operating loss carryforwards $ 54,570 $ 39,721 Research and development credits 5,226 3,655 Stock based compensation 1,410 770 Purchased intangibles 220 245 Capitalized organizational and start up expenditures 133 153 Accruals and other temporary differences 1,119 659 Total deferred tax assets 62,678 45,203 Less valuation allowance (62,678 ) (45,203 ) Net deferred tax assets $ — $ — The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. Based on the Company’s history of operating losses, the Company has concluded that it is more likely than not that the benefit of its deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2015 and 2014. The valuation allowance increased approximately $17.5 million and $13.4 million during the years ended December 31, 2015 and 2014, respectively, due primarily to the generation of net operating losses during the period. A reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes as reflected in the financial statements is as follows: Years ended December 31, 2015 2014 2013 Federal income tax expense at statutory rate 34.0 % 34.0 % 34.0 % State income tax, net of federal benefit 6.1 % 4.6 % 5.1 % Permanent differences (1.6 )% (2.1 )% (0.9 )% Research and development credit 2.6 % 1.8 % 3.6 % Other 0.0 % 0.1 % 0.0 % Change in valuation allowance (41.1 )% (38.4 )% (41.8 )% Effective tax rate 0.0 % 0.0 % 0.0 % As of December 31, 2015, 2014, and 2013, the Company had U.S. federal net operating loss carryforwards of approximately $143.8 million , $105.0 million , and $71.4 million , respectively, which may be available to offset future income tax liabilities and expire at various dates through 2035. As of December 31, 2015, 2014, and 2013, the Company also had U.S. state net operating loss carryforwards of approximately $128.5 million , $90.5 million , and $64.5 million , respectively, which may be available to offset future income tax liabilities and expire at various dates through 2035. Included in the federal and state net operating loss carryforwards are approximately $2.8 million , $1.9 million , and $130 thousand , respectively, of deductions related to the exercise of stock options. These amounts represent an excess tax benefit which will be realized when it results in the reduction of cash income tax in accordance with ASC 718. As of December 31, 2015, 2014, and 2013, the Company had federal research and development tax credit carryforwards of approximately $3.7 million , $2.6 million , and $1.9 million , respectively, available to reduce future tax liabilities which expire at various dates through 2035. As of December 31, 2015, 2014, and 2013, the Company had state research and development tax credit carryforwards of approximately $2.4 million , $1.7 million , and $1.3 million , respectively, available to reduce future tax liabilities which expire at various dates through 2030. Under the provisions of the Internal Revenue Code of 1986, as amended (the "Code"), the net operating loss and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50% , as defined under Sections 382 and 383 of the Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception which may have resulted in a change in control as defined by Sections 382 and 383 of the Code, or could result in a change in control in the future. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2015 and 2014, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statements of operations and comprehensive loss. For all years through December 31, 2015, the Company generated research credits but has not conducted a study to document the qualified activities. This study may result in an adjustment to the Company’s research and development credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position for these two years . A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the deferred tax asset established for the research and development credit carryforwards and the valuation allowance. The Company files income tax returns in the United States and various state jurisdictions. The federal and state income tax returns are generally subject to tax examinations for the tax years ended December 31, 2012 through December 31, 2015. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service, state or foreign tax authorities to the extent utilized in a future period.

Quarterly financial information

Quarterly financial information (unaudited)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Quarterly financial information (unaudited)	Quarterly financial information (unaudited, in thousands, except share and per share data) Three Months Ended, March 31, 2015 June 30, 2015 September 30, 2015 December 31, 2015 Revenue $ 121 $ 115 $ 213 $ 221 Operating expenses 11,898 10,141 9,703 10,294 Net loss (12,084 ) (10,314 ) (9,771 ) (10,314 ) Net loss per share - basic and diluted $ (0.64 ) $ (0.43 ) $ (0.37 ) $ (0.37 ) Weighted-average number of common shares used in net loss per share - basic and diluted 18,834 24,154 26,610 28,118 Three Months Ended, March 31, 2014 June 30, 2014 September 30, 2014 December 31, 2014 Revenue $ — $ — $ — $ 308 Operating expenses 6,373 6,909 8,958 11,234 Net loss (7,329 ) (7,146 ) (9,171 ) (11,650 ) Net loss per attributable to common stockholders (7,509 ) (7,146 ) (9,171 ) (11,650 ) Net loss per share attributable to common stockholders - basic and diluted $ (0.76 ) $ (0.41 ) $ (0.53 ) $ (0.66 ) Weighted-average number of common shares used in net loss per share attributable to common stockholders - basic and diluted 9,859 17,346 17,465 17,696

Subsequent event

Subsequent event	12 Months Ended
	Dec. 31, 2015
Subsequent Events [Abstract]
Subsequent event	Subsequent event In August 2009, the Company entered into an exclusive license and collaboration agreement with Isconova AB, a Swedish company which subsequently was acquired by Novavax, Inc. ("Novavax"). Pursuant to the agreement, Novavax granted the Company a worldwide, sublicensable, exclusive license to two patent families, to import, make, have made, use, sell, offer for sale and otherwise exploit licensed vaccine products containing an adjuvant which incorporates or is developed from Matrix-A, Matrix-C and/or Matrix-M technology, in the fields of HSV and chlamydia. Matrix-M is the adjuvant used in GEN-003. The agreement also contained a research funding clause for which the Company made monthly payments to Novavax between August 2009 and March 2012 of approximately $1.6 million . All amounts of research funding provided were to be refunded by Novavax. After December 31, 2015, any amounts remaining due from Novavax, including accrued interest, could be received in cash upon 30 -day written notice provided by the Company. The Company provided this notice in January 2016 and received the $1.6 million refund in February 2016.

Summary of significant accoun22

Summary of significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of Genocea Biosciences, Inc., and a wholly-owned subsidiary. All inter-company accounts and transactions have been eliminated
Basis of presentation and use of estimates	Basis of presentation and use of estimates The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). The preparation of financial statements in conformity with 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 prepaid and accrued research and development expenses, stock-based compensation expense, the valuation of common stock warrants and warrants to purchase redeemable securities, and reported amounts of revenues and expenses during the reported period. 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. For periods prior to the closing of the IPO, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company utilized various valuation methodologies in accordance with the framework of the 2004 and 2013 American Institute of Certified Public Accountants Technical Practice Aids, Valuation of Privately-Held Company Equity Securities Issued as Compensation , to estimate the fair value of its common stock. Each valuation methodology includes estimates and assumptions that require the Company’s judgment. These estimates and assumptions include a number of objective and subjective factors, including external market conditions affecting the biotechnology industry sector, the prices at which the Company sold shares of preferred stock, the superior rights and preferences of securities senior to the Company’s common stock at the time and the likelihood of achieving a liquidity event, such as an IPO or a sale of the Company. Significant changes to the key assumptions used in the valuations could result in different fair values of common stock at each valuation date and materially affect the financial statements. Following the closing of the IPO, the fair value of common stock is determined based on the quoted market price of the common stock.
Segment information	Segment information Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company and the Company’s chief operating decision maker view the Company’s operations and manage its business in one operating segment, which is the business of developing and commercializing vaccines. The Company operates in only one geographic segment.
Cash and cash equivalents	Cash, cash equivalents and investments The Company determines the appropriate classification of its investments at the time of purchase. All liquid investments with original maturities of 90 days or less from the purchase date are considered to be cash equivalents.
Investments	The Company’s current and non-current investments are comprised of certificates of deposit and government securities that are classified as available-for-sale in accordance with FASB ASC Topic 320, Investments—Debt and Equity Securities. The Company classifies investments available to fund current operations as current assets on its balance sheets. Investments are classified as non-current assets on the balance sheets if (i) the Company has the intent and ability to hold the investments for a period of at least one year and (ii) the contractual maturity date of the investments is greater than one year. Available-for-sale investments are recorded at fair value, with unrealized gains or losses included in Accumulated other comprehensive loss on the Company’s balance sheets. Realized gains and losses are determined using the specific identification method and are included as a component of Interest expense, net. There were no realized gains or losses recognized for the twelve months ended December 31, 2015 and 2014. The Company reviews investments for other-than-temporary impairment whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other-than-temporary, the Company considers its intent to sell, or whether it is more likely than not that the Company will be required to sell the investment before recovery of the investment’s amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, the severity and the duration of the impairment and changes in value subsequent to period end.
Concentrations of credit risk and off-balance sheet risk	Concentrations of credit risk and off-balance sheet risk Financial instruments that potentially subject the Company to concentrations of credit risk are primarily cash, cash equivalents and investments. The Company’s cash, cash equivalents and investments are held in accounts with financial institutions that management believes are creditworthy. The Company’s investment policy includes guidelines on the quality of the institutions and financial instruments and defines allowable investments that the Company believes minimizes the exposure to concentration of credit risk.
Deferred financing costs	Deferred financing costs Offering costs related to debt and equity financing primarily consist of direct and incremental external expenses. In accordance with ASU No. 2015-03 Interest—Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs (“ASU 2015-03”) the Company presents debt issuance costs related to a recognized debt liability in the balance sheet as a direct deduction of the carrying value of the debt liability, consistent with the accounting treatment of debt discounts. The adoption of ASU 2015-03 in the quarter ended June 30, 2015 resulted in the reclassification of approximately $ 99 thousand , as of December 31, 2014, of unamortized capitalized debt issuance costs previously included in both other current and other non-current assets to a direct deduction of the carrying value of the debt liability. The adoption of this standard did not have material impact on the Company’s financial conditions, results of operations, or cash flows. The amortization of deferred debt financing costs follows the effective interest rate method and was not impacted by the issuance or adoption of ASU 2015-03. Offering costs related to registration statements and the initiation of the ATM are recorded as an asset and are reclassified to equity on a pro-rata basis based upon the successful selling of common shares compared to the available limits in either equity program. The costs are reviewed for impairment and will be recorded to expense if and when the Company determines that future equity offerings are not probable of occurring. At December 31, 2015, the Company had $304 thousand of deferred offering costs recorded as an Other non-current asset.
Fair value of financial instruments	Fair value of financial instruments The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. FASB ASC Topic 820, Fair Value Measurement and Disclosures , (“ASC 820”) established a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the financial instrument based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the financial instrument and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported or disclosed fair value of the financial instruments and is not a measure of the investment credit quality. Fair value measurements are classified and disclosed in one of the following three categories: • Level 1—Valuations based on unadjusted quoted prices in active markets for identical assets or liabilities that the Company has the ability to access at the measurement date. • Level 2—Valuations based on quoted prices for similar assets or liabilities in markets that are not active or for which all significant inputs are observable, either directly or indirectly. • Level 3—Valuations that require inputs that reflect the Company’s own assumptions that are both significant to the fair value measurement and unobservable. To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Financial instruments measured at fair value on a recurring basis include cash equivalents and investments (Note 3) and warrants (Note 7). An entity may elect to measure many financial instruments and certain other items at fair value at specified election dates. Subsequent unrealized gains and losses on items for which the fair value option has been elected will be reported in net loss. The Company did not elect to measure any additional financial instruments or other items at fair value. The Company is also required to disclose the fair value of financial instruments not carried at fair value. The fair value of the Company’s long-term debt (Note 6) is determined using current applicable rates for similar instruments as of the balance sheet dates and assessment of the credit rating of the Company. The carrying value of the Company’s long-term debt approximates fair value because the Company’s interest rate yield is near current market rates. The Company’s long-term debt is considered a Level 3 liability within the fair value hierarchy. Except for the valuation methodology utilized to value the warrants to purchase redeemable securities (Note 7), there have been no changes to the valuation methods utilized by the Company during the three years ended December 31, 2015. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of financial instruments between levels during the years ended December 31, 2015, 2014 and 2013.
Derivative Instruments	Derivative Instruments The Company occasionally issues financial instruments in which a derivative instrument is “embedded”. Upon issuing the financial instrument, the Company assesses whether the economic characteristics of the embedded derivative are clearly and closely related to the economic characteristics of the remaining component of the financial instrument (i.e., the host contract) and whether a separate, non-embedded instrument with the same terms as the embedded instrument would meet the definition of a derivative instrument. When it is determined that (1) the embedded derivative possesses economic characteristics that are not clearly and closely related to the economic characteristics of the host contract and (2) a separate, stand-alone instrument with the same terms would qualify as a derivative instrument, the embedded derivative is separated from the host contract and carried at fair value with any changes in fair value recorded in current period earnings.
Property and equipment	Property and equipment Property and equipment is stated at cost, less accumulated depreciation. Maintenance and repairs that do not improve or extend the lives of the respective assets are expensed to operations as incurred, while costs of major additions and betterments are capitalized. Upon disposal, the related cost and accumulated depreciation is removed from the accounts and any resulting gain or loss is included in the statements of operations. Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Asset Estimated useful life Laboratory equipment 5 Furniture and office equipment 5 Computer hardware and software 3-5 years Leasehold improvements Shorter of the useful life or remaining lease term
Development of Software for Internal Use	Development of Software for Internal Use The Company accounts for the costs of software developed or obtained for internal use in accordance with ASC 350-40, Internal-Use Software . Costs of materials, consultants, payroll, and payroll-related costs for employees incurred in developing internal-use software are capitalized as incurred. These costs are included in Property and equipment, net. Costs incurred during the preliminary project and post-implementation stages are charged to expense.
Impairment of long-lived assets	Impairment of long-lived assets The Company evaluates long-lived assets for potential impairment when events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Recoverability is measured by comparing the book values of the assets to the expected future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value. The Company has not recognized any impairment losses in any reporting periods through December 31, 2015.
Revenue recognition	Revenue recognition The Company has generated revenue solely through research and development grants with private not-for-profit organizations and federal agencies for the development and commercialization of product candidates. The Company recognizes revenue in accordance with FASB ASC Topic 605, Revenue Recognition (“ASC 605”). Accordingly, revenue is recognized for each unit of accounting when all of the following criteria are met: • persuasive evidence of an arrangement exist • delivery has occurred or services have been rendered • the fee is fixed or determinable • collectability is reasonably assured Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as a current liability. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as a non-current liability. Grant revenue Periodically, the Company receives grants from private not-for-profit organizations and federal agencies to conduct vaccine development research. Funds received in advance of services being performed are recorded as deferred revenue. Revenue under these grants is recognized as research services are performed. Multiple-element arrangements The Company analyzes multiple-element arrangements based on the guidance in FASB ASC Topic 605-25, Revenue Recognition—Multiple-Element Arrangements (“ASC 605-25”). The Company applies this guidance to new arrangements as well as existing arrangements that contain multiple deliverables. The Company determines the elements, or deliverables, included in the arrangement and allocates consideration under the arrangement to the various elements based on each element’s relative selling price. The identification of individual elements in a multiple-element arrangement and the estimation of the selling price of each element involves significant judgment, including consideration as to whether each delivered element has stand-alone value to the collaborator. The Company determines the estimated selling price for deliverables within the arrangement using vendor-specific objective evidence (“VSOE”) of selling price, if available, or third-party evidence of selling price if VSOE was not available or the Company’s best estimate of selling price, if neither VSOE nor third-party evidence was available. The Company uses its best estimate of a selling price to estimate the selling price for licenses for its technology, know-how, and trademarks since it does not have VSOE or third-party evidence of selling price for these deliverables. In order to determine the best estimate of selling price, the Company considers market conditions, as well as entity- specific factors, including those factors contemplated in negotiating the agreements, as well as internally developed estimates that include assumptions related to the market opportunity, estimated development costs, probability of success, and the time needed to commercialize assays. In validating its best estimate of selling price, the Company evaluates whether changes in the key assumptions used to determine best estimate of selling price would have a significant effect on the allocation of arrangement consideration between deliverables. The Company recognizes consideration allocated to an individual element when all other revenue recognition criteria are met for that element, which generally occurs upon delivery or over the period in which services are provided.
Research and development expenses	Research and development expenses Research and development costs are charged to expense as incurred in performing research and development activities. The costs include employee compensation costs, facilities and overhead, clinical study and related clinical manufacturing costs, regulatory and other related costs. Nonrefundable advanced payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are delivered or the services are performed.
Stock-based compensation expense	Stock-based compensation expense The Company accounts for its stock-based compensation awards to employees and directors in accordance with FASB ASC Topic 718, Compensation-Stock Compensation (“ASC 718”). ASC 718 requires all stock-based payments to employees, including grants of employee stock options and restricted stock, to be recognized in the statements of operations and comprehensive loss based on their grant date fair values. Compensation expense related to awards to employees is recognized on a straight-line basis based on the grant date fair value over the associated service period of the award, which is generally the vesting term. Share-based payments issued to non-employees are recorded at their fair values, and are periodically revalued as the equity instruments vest and are recognized as expense over the related service period in accordance with the provisions of ASC 718 and FASB ASC Topic 505, Equity, (“ASC 505”) and are expensed using an accelerated attribution model. The Company estimates the fair value of its stock options using the Black- Scholes option pricing model, which requires the input of subjective assumptions, including (a) the expected volatility of the Company’s stock price, (b) the expected term of the award, (c) the risk-free interest rate, (d) expected dividends and (e) the estimated fair value of the Company’s common stock on the measurement date. Due to the limited operating history of the Company as a public entity and a lack of company specific historical and implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies that are publicly traded. When selecting these public companies on which it has based its expected stock price volatility, the Company selected companies with comparable characteristics to it, including enterprise value, risk profiles, position within the industry, and with historical share price information sufficient to meet the expected term of the stock-based awards. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. Due to the lack of Company specific historical option activity, the Company has estimated the expected term of its employee stock options using the “simplified” method, whereby, the expected term equals the arithmetic average of the vesting term and the original contractual term of the option. The expected term for non-employee awards is the remaining contractual term of the option. The risk-free interest rates are based on the U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The Company has never paid, and does not expect to pay dividends in the foreseeable future. Refer to Basis of presentation and use of estimates in Note 2 for a discussion of the Company’s estimated fair value of its common stock prior to the IPO. Following the closing of the Company’s IPO, the fair value of common stock is determined based on the quoted market price of the common stock. The Company is also required to estimate forfeitures at the time of grant, and revise those estimates in subsequent periods if actual forfeitures differ from its estimates. The Company uses historical data to estimate forfeitures and records stock-based compensation expense only for those awards that are expected to vest. To the extent that actual forfeitures differ from the Company’s estimates, the differences are recorded as a cumulative adjustment in the period the estimates were revised. Stock-based compensation expense recognized in the financial statements is based on awards that are ultimately expected to vest.
Income taxes	Income taxes Income taxes are recorded in accordance with FASB ASC Topic 740, Income Taxes (“ASC 740”), which provides for deferred taxes using an asset and liability approach. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial reporting and the tax reporting basis of assets and liabilities and are measured using the enacted tax rates and laws that are expected to be in effect when the differences are expected to reverse. The Company provides a valuation allowance against net deferred tax assets unless, based upon the available evidence, it is more likely than not that the deferred tax assets will be realized. The Company has evaluated available evidence and concluded that the Company may not realize the benefit of its deferred tax assets; therefore a valuation allowance has been established for the full amount of the deferred tax assets. The Company accounts for uncertain tax positions in accordance with the provisions of ASC 740. When uncertain tax positions exist, the Company recognizes the tax benefit of tax positions to the extent that the benefit will more likely than not be realized. The determination as to whether the tax benefit will more likely than not be realized is based upon the technical merits of the tax position as well as consideration of the available facts and circumstances. As of December 31, 2015 and 2014, the Company does not have any significant uncertain tax positions. The Company’s practice is to recognize interest and/or penalties related to income tax matters in income tax expense.
Earnings per share	Earnings per share Basic earnings per share attributable to common stockholders is calculated by dividing net loss attributable to common stockholders by the weighted average shares outstanding during the period, without consideration for common stock equivalents. Net loss attributable to common stockholders is calculated by adjusting the net loss of the Company for cumulative preferred stock dividends and accretion of preferred stock issuance costs. Diluted earnings per share attributable to common stockholders is calculated by adjusting weighted average shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury-stock and if-converted methods. For purposes of the diluted net loss per share attributable to common stockholders calculation, preferred stock, stock options, unvested restricted stock, and warrants are considered to be common stock equivalents but have been excluded from the calculation of diluted net loss per share attributable to common stockholders, as their effect would be anti-dilutive for all periods presented. Therefore, basic and diluted net loss per share were the same for all periods presented.
Comprehensive loss	Comprehensive loss Comprehensive loss consists of net loss and changes in equity during a period from transactions and other events and circumstances generated from non-owner sources. For all periods presented other comprehensive income (loss), if any, consists of unrealized gains and losses on the Company’s investments.
Recent accounting pronouncements	Recent accounting pronouncements Standard Description Effect on the financial statements ASU 2014-09, Revenue from Contracts with Customers (Topic 606) The standard will replace existing revenue recognition standards and significantly expand the disclosure requirements for revenue arrangements. It may be adopted either retrospectively or on a modified retrospective basis to new contracts and existing contracts with remaining performance obligations as of the effective date. At this time, the Company has not decided on which method it will use to adopt the new standard, nor has it determined the effects of the new guidelines on its results of operations and financial position. For the foreseeable future, the Company’s revenues will be limited to grants received from government agencies or nonprofit organizations. The Company is currently evaluating the method of adoption and the impact of this standard on the financial statements. ASU No. 2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern (“ASU 2014-15”). The standard requires a company to evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the entity’s ability to continue as a going concern. Substantial doubt about an entity’s ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year after the date that the financial statements are issued. This ASU is effective for annual and interim periods ending after December 15, 2016 and earlier application is permitted. The Company is evaluating the effects of the new standard, but does not expect it will have a material impact on its financial conditions, results of operations, or cash flows.

Summary of significant accoun23

Summary of significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Schedule of estimated useful lives of assets	Depreciation is recorded using the straight-line method over the estimated useful lives of the respective assets, which are as follows: Asset Estimated useful life Laboratory equipment 5 Furniture and office equipment 5 Computer hardware and software 3-5 years Leasehold improvements Shorter of the useful life or remaining lease term
Schedule of recent accounting pronouncements	Standard Description Effect on the financial statements ASU 2014-09, Revenue from Contracts with Customers (Topic 606) The standard will replace existing revenue recognition standards and significantly expand the disclosure requirements for revenue arrangements. It may be adopted either retrospectively or on a modified retrospective basis to new contracts and existing contracts with remaining performance obligations as of the effective date. At this time, the Company has not decided on which method it will use to adopt the new standard, nor has it determined the effects of the new guidelines on its results of operations and financial position. For the foreseeable future, the Company’s revenues will be limited to grants received from government agencies or nonprofit organizations. The Company is currently evaluating the method of adoption and the impact of this standard on the financial statements. ASU No. 2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern (“ASU 2014-15”). The standard requires a company to evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the entity’s ability to continue as a going concern. Substantial doubt about an entity’s ability to continue as a going concern exists when relevant conditions and events, considered in the aggregate, indicate that it is probable that the entity will be unable to meet its obligations as they become due within one year after the date that the financial statements are issued. This ASU is effective for annual and interim periods ending after December 15, 2016 and earlier application is permitted. The Company is evaluating the effects of the new standard, but does not expect it will have a material impact on its financial conditions, results of operations, or cash flows.

Cash, cash equivalents and in24

Cash, cash equivalents and investments (Tables)	12 Months Ended
	Dec. 31, 2015
Cash and Cash Equivalents [Abstract]
Schedule of cash, cash equivalents and investments carried at fair value	The following table presents the cash equivalents and investments carried at fair value in accordance with the hierarchy defined in Note 2 (in thousands): Total Quoted prices in active markets (Level 1) Significant other observable inputs (Level 2) Significant unobservable inputs (Level 3) December 31, 2015 Money Market funds, included in cash equivalents $ 14,207 $ 14,207 $ — $ — U.S treasuries, included in cash equivalents $ 2,203 2,203 — — Investments - U.S. treasuries $ 27,924 27,924 — — Investments - certificates of deposit 61,249 — 61,249 — Total $ 105,583 $ 44,334 $ 61,249 $ — 0 December 31, 2014 Money Market funds, included in cash equivalents $ 18,992 $ 18,992 $ — $ — Marketable securities - U.S. treasuries 27,021 27,021 — — Total $ 46,013 $ 46,013 $ — $ —
Schedule of investments	Cash equivalents and investments at December 31, 2015 consist of the following (in thousands): Contracted Maturity Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and investments U.S. Treasuries 60-184 days $ 30,120 $ 7 $ — $ 30,127 Certificates of deposit 91-365 days 49,145 — — 49,145 Certificates of deposit greater than 365 days 12,104 — — 12,104 Total $ 91,369 $ 7 $ — $ 91,376

Property and equipment, net (Ta

Property and equipment, net (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Schedule of property and equipment, net	Property and equipment, net consist of the following (in thousands): December 31, 2015 2014 Laboratory equipment $ 3,943 $ 2,510 Furniture office equipment 610 186 Computer hardware 259 257 Leasehold improvements 1,433 799 Computer software 338 — Total property and equipment 6,583 3,752 Accumulated depreciation (2,500 ) (1,796 ) Property and equipment, net $ 4,083 $ 1,956

Accrued expenses and other cu26

Accrued expenses and other current liabilities (Tables)	12 Months Ended
	Dec. 31, 2015
Payables and Accruals [Abstract]
Schedule of accrued expenses and other current liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): December 31, 2015 2014 Payroll and employee-related costs $ 1,736 $ 1,066 Research and development costs 1,359 1,117 Other current liabilities 880 410 Total $ 3,975 $ 2,593

Long-term debt (Tables)

Long-term debt (Tables)	12 Months Ended
	Dec. 31, 2015
Long-term Debt, Unclassified [Abstract]
Schedule of future principal payments on the 2014 Term Loan	Future principal payments, including the End of Term Charge, on the 2014 Term Loan are as follows (in thousands): December 31, 2015 2016 $ — 2017 3,149 2018 6,659 2019 8,034 Total $ 17,842

Warrants (Tables)

Warrants (Tables)	12 Months Ended
	Dec. 31, 2015
Warrants
Schedule of changes in fair value of warrants to purchase redeemable securities measured on recurring basis	The following table sets forth a summary of changes in the fair value of the Company’s warrants to purchase redeemable securities, which represents a recurring measurement that is classified within Level 3 of the fair value hierarchy wherein fair value is estimated using significant unobservable inputs (in thousands): Years ended December 31, 2015 2014 2013 Beginning balance $ — $ 656 $ 246 Warrants issued — — 188 Change in fair value — 725 222 Warrants exercised — (323 ) — Reclassification to accumulated paid-in capital — (1,058 ) — Ending balance $ — $ — $ 656
Common stock
Warrants
Schedule of weighted average assumptions used to calculate the fair value of warrants	The Company estimated the fair value of this warrant as of the issuance date using a Black-Scholes option pricing model (with a 10% discount for lack of marketability) with the following assumptions: November 20, Fair value of underlying instrument $ 9.05 Expected volatility 70.0 % Expected term (in years) 5 Risk-free interest rate 1.64 % Expected dividend yield 0.0 %
Warrants to purchase shares of series A preferred stock exercised, one
Warrants
Schedule of weighted average assumptions used to calculate the fair value of warrants	The fair value of warrants to purchase 21,695 shares of Series A preferred stock prior to exercise on January 29, 2014 was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions: January 29, Fair value of underlying instrument $ 0.65 Expected Volatility 55.57 % Expected term (in years) 0.04 Risk-free interest rate 1.52 % Expected dividend yield 0.0 %
Warrants to purchase shares of series A preferred stock exercised, two
Warrants
Schedule of weighted average assumptions used to calculate the fair value of warrants	The fair value of warrants to purchase 28,926 shares of Series A preferred stock prior to exercise on February 4, 2014 was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions: February 4, Fair value of underlying instrument $ 0.65 Expected Volatility 55.03 % Expected term (in years) 0.02 Risk-free interest rate 1.46 % Expected dividend yield 0.0 %
Warrants to purchase shares of series A preferred stock in cashless exercise
Warrants
Schedule of weighted average assumptions used to calculate the fair value of warrants	The fair value of warrants to purchase 987,840 shares of Series A preferred stock prior to a cashless exercise for 316,932 shares of Series A preferred stock on February 10, 2014, which automatically converted into 26,633 shares of Common Stock upon the completion of the Company's IPO, was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions: February 10, Fair value of underlying instrument $ 7.74 Expected Volatility 50.81 % Expected term (in years) 1 Risk-free interest rate 1.48 % Expected dividend yield 0.0 %
Warrants to purchase redeemable convertible preferred stock automatically converted to warrants to purchase common stock
Warrants
Schedule of weighted average assumptions used to calculate the fair value of warrants	The fair value of warrants exercisable for 1,253,051 shares of redeemable convertible preferred stock, which were automatically converted into warrants exercisable for 105,297 shares of Common Stock, was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions: February 10, Fair value of underlying instrument $ 6.96 Expected Volatility 92.9 % Expected term (in years) 8.66 Risk-free interest rate 2.43 % Expected dividend yield 0.0 %

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Schedule of minimum future lease payments under the operating leases	The minimum future lease payments under both the 2014 Lease and the 2015 Lease are as follows (in thousands): December 31, 2015 2016 $ 1,379 2017 231 Total $ 1,610

Equity and net loss per share (

Equity and net loss per share (Tables)	12 Months Ended
	Dec. 31, 2015
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Schedule of common stock equivalents	The following 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 (in thousands): Years ended December 31, 2015 2014 2013 Preferred stock — — 11,409 Warrants 78 78 193 Outstanding options 2,723 2,290 1,576 Total 2,801 2,368 13,178

Stock and employee benefit pl31

Stock and employee benefit plans (Tables)	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of stock-based compensation expense for stock options granted to employees and non-employees	Total stock-based compensation expense is recognized for stock options granted to employees and non-employees and has been reported in the Company’s Statements of Operations as follows (in thousands): Years ended December 31, 2015 2014 2013 Research and development $ 1,690 $ 1,511 $ 322 General and administrative 2,158 1,394 350 Total $ 3,848 $ 2,905 $ 672
Schedule of stock option activity for employees and nonemployees	The following table summarizes stock option activity for employees and nonemployees (shares in thousands): Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Term (years) Aggregate Intrinsic Value Outstanding at December 31, 2014 2,290 $ 7.26 8.08 $ 5,332 Granted 715 $ 9.12 Exercised (128 ) $ 3.00 Canceled (154 ) $ 13.41 Outstanding at December 31, 2015 2,723 $ 7.60 7.61 $ 2,840 Exercisable at December 31, 2015 1,410 $ 5.71 6.66 $ 2,507 Vested or expected to vest at December 31, 2015 2,605 $ 7.54 7.58 $ 2,793
Schedule of assumptions underlying common stock on each measurement date	The Company estimates the fair value of each employee stock award on the grant date using the Black-Scholes option-pricing model based on the following assumptions and the assumptions regarding the fair value of the underlying common stock on each measurement date: Years ended December 31, 2015 2014 2013 Expected Volatility 68.5% - 85.3% 86.2% - 103.6% 97.1% Risk-free interest rate 1.56% - 1.94% 1.75% - 2.00% 0.59% - 1.83% Expected term (in years) 5.50 - 6.08 6.25 6.25 Expected dividend yield 0% 0% 0%

Income taxes (Tables)

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Schedule of the significant components of the deferred tax assets	The significant components of the Company’s deferred tax assets are comprised of the following: December 31, 2015 2014 Deferred tax assets: U.S and state net operating loss carryforwards $ 54,570 $ 39,721 Research and development credits 5,226 3,655 Stock based compensation 1,410 770 Purchased intangibles 220 245 Capitalized organizational and start up expenditures 133 153 Accruals and other temporary differences 1,119 659 Total deferred tax assets 62,678 45,203 Less valuation allowance (62,678 ) (45,203 ) Net deferred tax assets $ — $ —
Schedule of a reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes	A reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes as reflected in the financial statements is as follows: Years ended December 31, 2015 2014 2013 Federal income tax expense at statutory rate 34.0 % 34.0 % 34.0 % State income tax, net of federal benefit 6.1 % 4.6 % 5.1 % Permanent differences (1.6 )% (2.1 )% (0.9 )% Research and development credit 2.6 % 1.8 % 3.6 % Other 0.0 % 0.1 % 0.0 % Change in valuation allowance (41.1 )% (38.4 )% (41.8 )% Effective tax rate 0.0 % 0.0 % 0.0 %

Quarterly financial informati33

Quarterly financial information (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Schedule of quarterly financial information	Three Months Ended, March 31, 2015 June 30, 2015 September 30, 2015 December 31, 2015 Revenue $ 121 $ 115 $ 213 $ 221 Operating expenses 11,898 10,141 9,703 10,294 Net loss (12,084 ) (10,314 ) (9,771 ) (10,314 ) Net loss per share - basic and diluted $ (0.64 ) $ (0.43 ) $ (0.37 ) $ (0.37 ) Weighted-average number of common shares used in net loss per share - basic and diluted 18,834 24,154 26,610 28,118 Three Months Ended, March 31, 2014 June 30, 2014 September 30, 2014 December 31, 2014 Revenue $ — $ — $ — $ 308 Operating expenses 6,373 6,909 8,958 11,234 Net loss (7,329 ) (7,146 ) (9,171 ) (11,650 ) Net loss per attributable to common stockholders (7,509 ) (7,146 ) (9,171 ) (11,650 ) Net loss per share attributable to common stockholders - basic and diluted $ (0.76 ) $ (0.41 ) $ (0.53 ) $ (0.66 ) Weighted-average number of common shares used in net loss per share attributable to common stockholders - basic and diluted 9,859 17,346 17,465 17,696

Organization and operations - T

Organization and operations - The Company (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)product	Dec. 31, 2014USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of products in clinical development | product	1
Accumulated deficit	$ 157,910	$ 115,427
Cash, cash equivalents and investments	$ 106,400

Organization and operations Org

Organization and operations Organization and operations - Underwritten public offerings and At-the-market equity offering program (Details) - USD ($)	Aug. 04, 2015	Mar. 17, 2015	Feb. 10, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	May. 08, 2015	Mar. 02, 2015
Subsidiary, Sale of Stock [Line Items]
Common stock, par value (in dollars per share)				$ 0.001
Net proceeds of the underwritten public offering, net of discounts and commissions				$ 0	$ 1,964,000	$ 0
At-the-market equity offering program, maximum value of common stock to offer and sale							$ 50,000,000	$ 40,000,000
Common stock
Subsidiary, Sale of Stock [Line Items]
Conversion of preferred stock to common stock upon closing of IPO (in shares)					11,466,000
Initial public offering
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares)			5,500,000
Initial public offering price (in dollars per share)			$ 12
Net proceeds of the underwritten public offering, net of discounts and commissions			$ 61,400,000
Offering expenses			$ 2,400,000
Employee and nonemployee performance based options vested (in shares)			96,988
Initial public offering | Common stock
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares)					5,500,000
Conversion of preferred stock to common stock upon closing of IPO (in shares)			11,466,479
Underwritten public offering
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares)	3,850,000	6,272,726
Initial public offering price (in dollars per share)	$ 13	$ 8.25
Net proceeds of the underwritten public offering, net of discounts and commissions	$ 47,000,000	$ 48,600,000		$ 95,183,000	$ 0	$ 0
Offering expenses	$ 233,000	$ 276,000
Over-allotment option
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock (in shares)		818,181

Summary of significant accoun36

Summary of significant accounting policies - Additional information (Details)	12 Months Ended
	Dec. 31, 2015USD ($)instrumentsegment	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Segment information
Number of operating segments | segment	1
Number of geographical segments | segment	1
Cash, cash equivalents and investments
Maximum maturity period for a highly liquid investment to be considered cash and cash equivalents	90 days
Minimum maturity period for marketable securities	1 year
Realized gains (losses) recognized for available-for-sale investments	$ 0	$ 0
Number of investments in an unrealized loss position | instrument	0
Concentrations of credit risk and off-balance sheet risk
Number of financial instruments with off-balance sheet risk of loss | instrument	0
Deferred financing costs
Deferred offering costs	$ 304,000	0
Fair value of financial instruments
Transfers of financial assets between levels	0	0	$ 0
Transfers of financial liabilities between levels	$ 0	0	$ 0
Adjustments for new accounting pronouncement
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of unamortized capitalized debt issuance costs from current assets to direct deduction of the debt liability		$ 99,000

Summary of significant accoun37

Summary of significant accounting policies - Property and equipment (Details)	12 Months Ended
	Dec. 31, 2015
Laboratory equipment
Property and equipment
Estimated useful life	5 years
Furniture and office equipment
Property and equipment
Estimated useful life	5 years
Computer hardware and software | Minimum
Property and equipment
Estimated useful life	3 years
Computer hardware and software | Maximum
Property and equipment
Estimated useful life	5 years

Cash, cash equivalents and in38

Cash, cash equivalents and investments - Schedule of cash, cash equivalents and investments (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Cash equivalents and investments
Marketable securities	$ 91,376
Recurring
Cash equivalents and investments
Money Market funds, included in cash equivalents	14,207	$ 18,992
U.S treasuries, included in cash equivalents	2,203
Total	105,583	46,013
Recurring | Quoted prices in active markets (Level 1)
Cash equivalents and investments
Money Market funds, included in cash equivalents	14,207	18,992
U.S treasuries, included in cash equivalents	2,203
Total	44,334	46,013
Recurring | Significant other observable inputs (Level 2)
Cash equivalents and investments
Money Market funds, included in cash equivalents	0	0
U.S treasuries, included in cash equivalents	0
Total	61,249	0
Recurring | Significant unobservable inputs (Level 3)
Cash equivalents and investments
Money Market funds, included in cash equivalents	0	0
U.S treasuries, included in cash equivalents	0
Total	0	0
U.S. Treasuries | Recurring
Cash equivalents and investments
Marketable securities	27,924	27,021
U.S. Treasuries | Recurring | Quoted prices in active markets (Level 1)
Cash equivalents and investments
Marketable securities	27,924	27,021
U.S. Treasuries | Recurring | Significant other observable inputs (Level 2)
Cash equivalents and investments
Marketable securities	0	0
U.S. Treasuries | Recurring | Significant unobservable inputs (Level 3)
Cash equivalents and investments
Marketable securities	0	$ 0
Certificates of deposit | Recurring
Cash equivalents and investments
Marketable securities	61,249
Certificates of deposit | Recurring | Quoted prices in active markets (Level 1)
Cash equivalents and investments
Marketable securities	0
Certificates of deposit | Recurring | Significant other observable inputs (Level 2)
Cash equivalents and investments
Marketable securities	61,249
Certificates of deposit | Recurring | Significant unobservable inputs (Level 3)
Cash equivalents and investments
Marketable securities	$ 0

Cash, cash equivalents and in39

Cash, cash equivalents and investments - Schedule of investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash and Cash Equivalents [Abstract]
Interest income earned	$ 157	$ 32	$ 6
Schedule of Investments [Line Items]
Contracted maturity	1 year
Amortized Cost	$ 91,369
Unrealized Gains	7
Unrealized Losses	0
Fair Value	91,376
U.S. Treasuries | Current assets
Schedule of Investments [Line Items]
Amortized Cost	30,120
Unrealized Gains	7
Unrealized Losses	0
Fair Value	$ 30,127
U.S. Treasuries | Current assets | Minimum
Schedule of Investments [Line Items]
Contracted maturity	60 days
U.S. Treasuries | Current assets | Maximum
Schedule of Investments [Line Items]
Contracted maturity	184 days
Certificates of deposit | Current assets
Schedule of Investments [Line Items]
Amortized Cost	$ 49,145
Unrealized Gains	0
Unrealized Losses	0
Fair Value	$ 49,145
Certificates of deposit | Current assets | Minimum
Schedule of Investments [Line Items]
Contracted maturity	91 days
Certificates of deposit | Current assets | Maximum
Schedule of Investments [Line Items]
Contracted maturity	365 days
Certificates of deposit | Noncurrent assets
Schedule of Investments [Line Items]
Amortized Cost	$ 12,104
Unrealized Gains	0
Unrealized Losses	0
Fair Value	$ 12,104
Certificates of deposit | Noncurrent assets | Minimum
Schedule of Investments [Line Items]
Contracted maturity	365 days

Property and equipment, net (De

Property and equipment, net (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property and equipment, net
Total property and equipment	$ 6,583,000	$ 3,752,000
Accumulated depreciation	(2,500,000)	(1,796,000)
Property and equipment, net	4,083,000	1,956,000
Depreciation expense	1,100,000	500,000	$ 300,000
Laboratory equipment
Property and equipment, net
Total property and equipment	3,943,000	2,510,000
Furniture and office equipment
Property and equipment, net
Total property and equipment	610,000	186,000
Computer hardware
Property and equipment, net
Total property and equipment	259,000	257,000
Leasehold improvements
Property and equipment, net
Total property and equipment	1,433,000	799,000
Computer software
Property and equipment, net
Total property and equipment	338,000	$ 0
Depreciation expense	$ 0

Accrued expenses and other cu41

Accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Payroll and employee-related costs	$ 1,736	$ 1,066
Research and development costs	1,359	1,117
Other current liabilities	880	410
Total	$ 3,975	$ 2,593

Long-term debt (Details)

Long-term debt (Details)	Nov. 20, 2014USD ($)trancheinstallment$ / sharesshares	Sep. 30, 2013USD ($)installment$ / sharesshares	May. 31, 2012installment	Dec. 31, 2015USD ($)Violationtrancheshares	Dec. 31, 2014USD ($)shares	Dec. 31, 2013USD ($)	Jun. 30, 2015USD ($)	Feb. 10, 2014$ / sharesshares	Dec. 19, 2013USD ($)	Mar. 31, 2012USD ($)	Oct. 31, 2011USD ($)
Long-Term Debt
Repay indebtedness				$ 0	$ 10,401,000	$ 4,245,000
Loss on debt extinguishment				$ 0	435,000	200,000
Private placement
Long-Term Debt
Issuance of common stock					$ 1,964,000
Private placement | Common stock
Long-Term Debt
Issuance of common stock (in shares) | shares					223,000
Warrants to purchase Common Stock
Long-Term Debt
Exercisable amount (in shares) | shares				77,603	77,603			105,297
Hercules Technology Growth Capital, Inc. | Private placement
Long-Term Debt
Issuance of common stock	$ 2,000,000
Subsequent private placement equity financings, amount	2,000,000
Financing costs allocated to additional paid-in capital	$ 36,000
Hercules Technology Growth Capital, Inc. | Private placement | Common stock
Long-Term Debt
Issuance of common stock (in shares) | shares	223,463
Issuance of common stock	$ 2,000,000
Hercules Technology Growth Capital, Inc. | Warrants to purchase Common Stock
Long-Term Debt
Exercisable amount (in shares) | shares	73,725			73,725	73,725
Warrant, exercisable, value	$ 607,500
Exercise price of warrant (in dollars per share) | $ / shares	$ 8.24
Line of credit
Long-Term Debt
Number of tranches | tranche	3
Line of credit | 2014 Term Loan
Long-Term Debt
Debt financing	$ 27,000,000
Extended term	6 months
Period of monthly payments of principal and accrued interest	18 months
Number of monthly payments of principal and accrued interest | installment	30
Prepayment, written notice period	7 days
Prepayment charge, first twelve months (as a percent)	3.00%
Prepayment charge, between twelve months and twenty four months (as a percent)	2.00%
Prepayment charge, after twenty four months (as a percent)	1.00%
Additional interest rate (as a percent)	5.00%
End of term charge (as a percent)	4.95%
Attachment or judgment on the Company's assets causing an event of default, minimum	$ 100,000
Default of the Company's involving indebtedness causing an event of default, minimum	100,000
Financing costs	103,000			$ 280,000
Debt discount	210,000
Effective interest rate (as a percent)				10.20%
Outstanding borrowings				$ 17,000,000	$ 12,000,000
Interest expense				1,300,000	100,000
Line of credit | 2014 Term Loan, first tranche
Long-Term Debt
Debt financing	17,000,000
Draw downs	12,000,000			17,000,000
Expired amount of borrowing capacity							$ 5,000,000
Line of credit | 2014 Term Loan, second tranche
Long-Term Debt
Debt financing	$ 5,000,000
Interest rate (as a percent)	7.25%
Line of credit | 2014 Term Loan, second tranche | Prime rate
Long-Term Debt
Variable rate basis (as a percent)	7.25%
Spread on variable rate basis (as a percent)	5.00%
Line of credit | 2014 Term Loan, third tranche
Long-Term Debt
Debt financing	$ 5,000,000
Line of credit | Term Loan 2014, First Amendment
Long-Term Debt
Debt financing				$ 5,000,000
Number of tranches | tranche				2
Number of covenant violations that resulted in an event of default | Violation				3
Line of credit | Term Loan 2014, First Amendment, tranche 1
Long-Term Debt
Debt financing				$ 5,000,000
Line of credit | Term Loan 2014, First Amendment, tranche 2
Long-Term Debt
Debt financing				$ 5,000,000
Line of credit | 2013 Term Loan
Long-Term Debt
Debt financing		$ 10,000,000
Draw downs		3,500,000							$ 6,500,000
Repay indebtedness	9,800,000
Loss on debt extinguishment		$ 200,000
Interest rate (as a percent)		8.00%
Interest expense					$ 800,000	$ 100,000
Period of monthly payments of accrued interest		9 months
Number of payments of principal | installment		33
Percentage of advance payment on final repayment date		2.00%
Line of credit | 2013 Term Loan | Warrants to purchase shares of series C preferred stock
Long-Term Debt
Exercise price of warrant (in dollars per share) | $ / shares		$ 0.58						$ 6.90
Number of shares that may be purchased by warrant | shares		689,655						57,954
Line of credit | 2013 Term Loan | Other income / expense
Long-Term Debt
Loss on debt extinguishment	$ 435,000
Line of credit | 2011 Term Loan
Long-Term Debt
Debt financing											$ 5,000,000
Draw downs										$ 5,000,000
Interest rate (as a percent)			8.00%
Period of monthly payments of principal and accrued interest			36 months
Number of monthly payments of principal and accrued interest | installment			36
Percentage of advance payment on final repayment date			6.50%
Line of credit | 2011 Term Loan | Prime rate
Long-Term Debt
Spread on variable rate basis (as a percent)			(4.75%)

Long-term debt - Schedule of fu

Long-term debt - Schedule of future principal payments (Details) - Line of credit - 2014 Term Loan $ in Thousands	Dec. 31, 2015USD ($)
Future principal payments
2,016	$ 0
2,017	3,149
2,018	6,659
2,019	8,034
Total	$ 17,842

Warrants (Details)

Warrants (Details) - USD ($) $ in Thousands	Nov. 20, 2014	Apr. 23, 2014	Feb. 12, 2014	Feb. 10, 2014	Feb. 04, 2014	Jan. 29, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Warrants
Amount recognized in additional paid-in capital								$ 334
Percentage of fair value of warrants to purchase redeemable securities attributable to OPM Backsolve method									35.00%
Percentage of fair value of warrants to purchase redeemable securities attributable to PWERM									65.00%
Warrants							$ 0	0	$ 656	$ 246
Change in fair value							$ 0	$ 725	$ 222
Warrants to purchase Common Stock
Warrants
Warrants outstanding (in shares)				105,297			77,603	77,603
Change in fair value				$ 673
Warrants to purchase Common Stock | Fair value
Warrants
Warrants				$ 1,058
Warrants to purchase Common Stock | Hercules Technology Growth Capital, Inc.
Warrants
Warrants outstanding (in shares)	73,725						73,725	73,725
Discount for lack of marketability (as a percent)	10.00%
Amount recognized in additional paid-in capital	$ 334
Warrants to purchase redeemable securities
Warrants
Warrants outstanding (in shares)							0	0
Warrants to purchase redeemable convertible preferred stock
Warrants
Warrants outstanding (in shares)									2,291,512
Warrants to purchase shares of series A preferred stock exercised, one
Warrants
Warrants outstanding (in shares)						21,695
Change in fair value						$ 2
Warrants to purchase shares of series A preferred stock exercised, one | Fair value
Warrants
Warrants						$ 8
Warrants to purchase shares of series A preferred stock exercised, two
Warrants
Warrants outstanding (in shares)					28,926
Change in fair value					$ 3
Warrants to purchase shares of series A preferred stock exercised, two | Fair value
Warrants
Warrants					$ 10
Warrants to purchase shares of series A preferred stock in cashless exercise
Warrants
Warrants outstanding (in shares)				987,840				3,878
Series A Preferred stock resulting from the cashless exercise of warrants (in shares)		57,954	43,465	316,932
Common stock resulting from the automatic conversion of Series A Preferred stock (in shares)		37,250	16,593	26,633
Change in fair value				$ 47
Warrants to purchase shares of series A preferred stock in cashless exercise | Fair value
Warrants
Warrants				$ 304
Warrants to purchase redeemable convertible preferred stock automatically converted to warrants to purchase common stock
Warrants
Warrants outstanding (in shares)				1,253,051			3,878

Warrants - Weighted average ass

Warrants - Weighted average assumptions used to calculate the fair value of warrants (Details) - $ / shares	Nov. 20, 2014	Feb. 10, 2014	Feb. 04, 2014	Jan. 29, 2014
Common stock | Hercules Technology Growth Capital, Inc.
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)	$ 9.05
Expected Volatility	70.00%
Expected term	5 years
Risk-free interest rate	1.64%
Expected dividend yield	0.00%
Warrants to purchase shares of series A preferred stock exercised, one
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)				$ 0.65
Expected Volatility				55.57%
Expected term				15 days
Risk-free interest rate				1.52%
Expected dividend yield				0.00%
Warrants to purchase shares of series A preferred stock exercised, two
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)			$ 0.65
Expected Volatility			55.03%
Expected term			7 days
Risk-free interest rate			1.46%
Expected dividend yield			0.00%
Warrants to purchase shares of series A preferred stock in cashless exercise
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)		$ 7.74
Expected Volatility		50.81%
Expected term		1 year
Risk-free interest rate		1.48%
Expected dividend yield		0.00%
Warrants to purchase redeemable convertible preferred stock automatically converted to warrants to purchase common stock
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)		$ 6.96
Expected Volatility		92.90%
Expected term		8 years 7 months 28 days
Risk-free interest rate		2.43%
Expected dividend yield		0.00%

Warrants - Changes in the fair

Warrants - Changes in the fair value of warrants to purchase redeemable securities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in the fair value of warrants to purchase redeemable securities, which represents a recurring measurement
Beginning balance	$ 0	$ 656	$ 246
Warrants issued	0	0	188
Change in fair value	0	725	222
Warrants exercised	0	(323)	0
Reclassification to accumulated paid-in capital	0	(1,058)	0
Ending balance	$ 0	$ 0	$ 656

Commitments and contingencies -

Commitments and contingencies - Lease commitments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)Renewal	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Operating Leased Assets [Line Items]
Rent expense	$ 1,200	$ 800	$ 500
Minimum future lease payments under operating leases
2,016	1,379
2,017	231
Total minimum future lease payments	$ 1,610
2015 Lease
Operating Leased Assets [Line Items]
Number of renewal periods | Renewal	1
Renewal term	3 years
2014 Lease
Operating Leased Assets [Line Items]
Security deposit	$ 316

Commitments and contingencies48

Commitments and contingencies - Significant contracts and agreements (Details) - USD ($)	1 Months Ended	3 Months Ended								12 Months Ended
	Sep. 30, 2014	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments and contingencies
Revenue from grants		$ 221,000	$ 213,000	$ 115,000	$ 121,000	$ 308,000	$ 0	$ 0	$ 0	$ 670,000	$ 308,000	$ 731,000
Amount expensed related to agreements										28,049,000	23,727,000	15,695,000
Bill And Melinda Gates Foundation
Commitments and contingencies
Revenue from grants										640,000	308,000
Grant received	$ 1,200,000
Joint research collaboration agreement | Dana-Farber Cancer Institute
Commitments and contingencies
Revenue from grants										30,000	0
Supply agreement | FUJIFILM Diosynth Biotechnologies U.S.A. Inc.
Commitments and contingencies
Amount expensed related to agreements										$ 4,200,000	$ 3,500,000	$ 0

Equity and net loss per share49

Equity and net loss per share (Details)	Jan. 20, 2014	Sep. 30, 2015	Dec. 31, 2015$ / sharesshares	Dec. 31, 2014shares	Dec. 31, 2013shares
Common Stock, Number of Shares, Par Value and Other Disclosures [Abstract]
Common stock, shares authorized			175,000,000
Common stock, par value (in dollars per share) | $ / shares			$ 0.001
Common stock, shares issued			28,161,313	17,869,000
Common stock, shares outstanding			28,151,596	17,852,000
Anti-dilutive effect on common stock equivalents
Total of common stock equivalents excluded due to anti-dilutive effect			2,801,000	2,368,000	13,178,000
Reverse stock split
Reverse stock split of the Common Stock	0.0840
Employee And Nonemployee Stock Option [Member]
Restricted stock
Options exercised (in shares)			128,000
Restricted stock
Restricted stock
Vesting period		4 years
Number of shares issued			35,964	35,964
Number of shares subject to repurchase by entity			9,717	16,840
Director | Employee And Nonemployee Stock Option [Member]
Restricted stock
Options exercised (in shares)					31,092
Preferred stock
Anti-dilutive effect on common stock equivalents
Total of common stock equivalents excluded due to anti-dilutive effect			0	0	11,409,000
Warrants
Anti-dilutive effect on common stock equivalents
Total of common stock equivalents excluded due to anti-dilutive effect			78,000	78,000	193,000
Employee And Nonemployee Stock Option [Member]
Anti-dilutive effect on common stock equivalents
Total of common stock equivalents excluded due to anti-dilutive effect			2,723,000	2,290,000	1,576,000

Stock and employee benefit pl50

Stock and employee benefit plans (Details) - USD ($) $ in Thousands	Jan. 01, 2016	Jan. 01, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock-based compensation
Stock-based compensation expense			$ 3,848	$ 2,905	$ 672
Outstanding options
Stock-based compensation
Stock options granted (in shares)			715,262	1,064,640	559,742
Outstanding options | Consultants and members of its Scientific Advisory Board
Stock-based compensation
Stock options granted (in shares)			0	0	44,345
Vesting period			4 years
Term of exercising options from the date of grant			10 years
Nonemployee options | Consultants and members of its Scientific Advisory Board
Stock-based compensation
Stock-based compensation expense			$ 263	$ 324	$ 143
2014 Equity Plan
Stock-based compensation
Number of shares authorized (in shares)			903,494
Percentage applied on total number of shares of common stock outstanding on previous calendar year for automatic inclusion in the plan (lessor of)			4.00%
Increase in the number of the shares available for issuance (in shares)		714,769
2014 Equity Plan | Subsequent event
Stock-based compensation
Increase in the number of the shares available for issuance (in shares)	1,126,064
2007 Equity Plan
Stock-based compensation
Number of shares available for grant (in shares)			219,765
2007 Equity Plan and 2014 Equity Plan | Outstanding options
Stock-based compensation
Number of shares available for grant (in shares)			522,706
Common shares that may be issued (in shares)			3,246,017

Stock and employee benefit pl51

Stock and employee benefit plans - Stock based compensation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock Based Compensation Expense
Total stock-based compensation expense	$ 3,848	$ 2,905	$ 672
Research and development
Stock Based Compensation Expense
Total stock-based compensation expense	1,690	1,511	322
General and administrative
Stock Based Compensation Expense
Total stock-based compensation expense	$ 2,158	$ 1,394	$ 350

Stock and employee benefit pl52

Stock and employee benefit plans - Stock options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair value of each employee stock award on the grant date and the assumptions regarding the fair value of the underlying common stock
Expected volatility (as a percent)			97.10%
Expected term		6 years 3 months	6 years 3 months
Expected dividend yield	0.00%	0.00%	0.00%
Minimum
Fair value of each employee stock award on the grant date and the assumptions regarding the fair value of the underlying common stock
Expected volatility (as a percent)	68.50%	86.20%
Risk-free interest rate	1.56%	1.75%	0.59%
Expected term	5 years 6 months
Maximum
Fair value of each employee stock award on the grant date and the assumptions regarding the fair value of the underlying common stock
Expected volatility (as a percent)	85.30%	103.60%
Risk-free interest rate	1.94%	2.00%	1.83%
Expected term	6 years 29 days
Outstanding options
Shares
Outstanding at the beginning of the period (in shares)	2,290,000
Granted (in shares)	715,262	1,064,640	559,742
Exercised (in shares)	(128,000)
Canceled (in shares)	(154,000)
Outstanding at the end of the period (in shares)	2,723,000	2,290,000
Exercisable at the end of the period (in shares)	1,410,000
Vested or expected to vest at the end of the period (in shares)	2,605,000
Weighted - Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 7.26
Granted (in dollars per share)	9.12	$ 10.11	$ 3.41
Exercised (in dollars per share)	3
Canceled (in dollars per share)	13.41
Outstanding at the end of the period (in dollars per share)	7.60	$ 7.26
Exercisable at the end of the period (in dollars per share)	5.71
Vested or expected to vest at the end of the period (in dollars per share)	$ 7.54
Weighted- Average Remaining Contractual Term
Outstanding at the end of the period	7 years 7 months 10 days	8 years 29 days
Exercisable at the end of the period	6 years 7 months 28 days
Vested or expected to vest at the end of the period	7 years 6 months 29 days
Aggregate Intrinsic Value
Outstanding at the beginning of the period (in dollars)	$ 5,332
Outstanding at the end of the period (in dollars)	2,840	$ 5,332
Exercisable at the end of the period (in dollars)	2,507
Vested or expected to vest at the end of the period (in dollars)	2,793
Exercised (in dollars)	$ 1,000	3,100
Expected term for recognition of unrecognized compensation cost (in years)	2 years 8 months 23 days
Employee stock options
Aggregate Intrinsic Value
Total unrecognized compensation cost, net of related forfeiture estimates	$ 8,000
Nonemployee options
Aggregate Intrinsic Value
Total unrecognized compensation cost, net of related forfeiture estimates	$ 255	$ 55

Stock and employee benefit pl53

Stock and employee benefit plans - Performance Based Stock Options, Employee Stock Purchase Plan and 401(k) Savings plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 10, 2014
Additional disclosures
Stock-based compensation expense	$ 3,848,000	$ 2,905,000	$ 672,000
401(k) Savings plan
Additional disclosures
Contributions made by employer to the plan	174,000
Performance-based stock options
Additional disclosures
Number of options probable to achieve performance-based milestones		96,988
Stock-based compensation expense	$ 0	$ 453,000
Options outstanding (in shares)	56,336	56,336
Employee stock purchase plan | 2014 ESPP
Additional disclosures
Stock-based compensation expense	$ 113,000	$ 43,000
Number of shares of common stock authorized under the plan				200,776
Option period	6 months
Number of shares issued	40,912	15,622
Shares remaining for future issuance (in shares)	144,242

Income taxes (Details)

Income taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred tax assets:
U.S and state net operating loss carryforwards	$ 54,570	$ 39,721
Research and development credits	5,226	3,655
Stock based compensation	1,410	770
Purchased intangibles	220	245
Capitalized organizational and start up expenditures	133	153
Accruals and other temporary differences	1,119	659
Total deferred tax assets	62,678	45,203
Less valuation allowance	(62,678)	(45,203)
Net deferred tax assets	0	0
Increase in valuation allowance	$ 17,500	$ 13,400
Reconciliation of income tax expense
Federal income tax expense at statutory rate	34.00%	34.00%	34.00%
State income tax, net of federal benefit	6.10%	4.60%	5.10%
Permanent differences	(1.60%)	(2.10%)	(0.90%)
Research and development credit	2.60%	1.80%	3.60%
Other	0.00%	0.10%	0.00%
Change in valuation allowance	(41.10%)	(38.40%)	(41.80%)
Effective tax rate	0.00%	0.00%	0.00%

Income taxes - Additional infor

Income taxes - Additional information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income taxes
Deductions related to stock options	$ 2,800,000	$ 1,900,000	$ 130,000
Unrecognized accrued interest or penalties related to uncertain tax positions	0	0
Uncertain tax position	$ 0	0
Number of years for which amount of tax benefit will not be recognized as an uncertain tax position	2 years
U.S. federal
Income taxes
Net operating loss carryforwards	$ 143,800,000	105,000,000	71,400,000
U.S. federal | Research and development
Income taxes
Tax credit carryforwards	3,700,000	2,600,000	1,900,000
U.S. state
Income taxes
Net operating loss carryforwards	128,500,000	90,500,000	64,500,000
U.S. state | Research and development
Income taxes
Tax credit carryforwards	$ 2,400,000	$ 1,700,000	$ 1,300,000

Quarterly financial informati56

Quarterly financial information (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Grant revenue	$ 221	$ 213	$ 115	$ 121	$ 308	$ 0	$ 0	$ 0	$ 670	$ 308	$ 731
Operating expenses	10,294	9,703	10,141	11,898	11,234	8,958	6,909	6,373	42,036	33,474	20,656
Net loss	$ (10,314)	$ (9,771)	$ (10,314)	$ (12,084)	(11,650)	(9,171)	(7,146)	(7,329)	(42,483)	(35,296)	(20,806)
Net loss per attributable to common stockholders					$ (11,650)	$ (9,171)	$ (7,146)	$ (7,509)	$ (42,483)	$ (35,476)	$ (22,411)
Net loss per share - basic and diluted (in USD per share)	$ (0.37)	$ (0.37)	$ (0.43)	$ (0.64)	$ (0.66)	$ (0.53)	$ (0.41)	$ (0.76)	$ (1.74)	$ (2.27)	$ (75.46)
Weighted-average number of common shares used in net loss per share - basic and diluted (in shares)	28,118	26,610	24,154	18,834	17,696	17,465	17,346	9,859	24,460	15,618	297

Subsequent event Subsequent eve

Subsequent event Subsequent event (Details) $ in Millions	12 Months Ended	32 Months Ended
	Dec. 31, 2015	Mar. 31, 2012USD ($)	Feb. 12, 2016USD ($)	Aug. 31, 2009license
Subsequent Event [Line Items]
Number of exclusive license rights provided in agreement | license				2
Research expense, period to provide written notice	30 days
Novavax
Subsequent Event [Line Items]
Total of monthly payments by Company for which a refund to due		$ 1.6
Novavax | Subsequent event
Subsequent Event [Line Items]
Contingent gain recorded in other income			$ 1.6