Genocea Biosciences (GNCAQ) 10-K 27 Feb 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 20, 2015	Jun. 30, 2014
Document and Entity Information
Entity Registrant Name	GENOCEA BIOSCIENCES, INC.
Entity Central Index Key	1457612
Document Type	10-K
Document Period End Date	31-Dec-14
Amendment Flag	FALSE
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Public Float			$67,992,844
Entity Common Stock, Shares Outstanding		17,858,705
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY

Balance_Sheets

Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$20,058,000	$12,208,000
Marketable securities	27,021,000
Restricted cash		157,000
Prepaid expenses and other current assets	963,000	510,000
Total current assets	48,042,000	12,875,000
Property and equipment, net	1,956,000	865,000
Restricted cash	316,000	158,000
Other assets	117,000	1,863,000
Total assets	50,431,000	15,761,000
Current liabilities:
Accounts payable	2,692,000	2,176,000
Accrued expenses and other current liabilities	2,486,000	1,418,000
Deferred revenue	555,000	12,000
Current portion of long-term debt		861,000
Current portion of deferred rent	107,000	26,000
Total current liabilities	5,840,000	4,493,000
Non-current liabilities:
Long-term debt, net of current portion	11,488,000	8,933,000
Accrued interest payable		11,000
Deferred rent, net of current portion	168,000	237,000
Warrants to purchase redeemable securities		656,000
Deferred revenue, net of current portion	350,000
Other non-current liabilities	78,000
Total liabilities	17,924,000	14,330,000
Commitments and contingencies (Note 9)
Stockholders' equity (deficit):
Common stock, $0.001 par value; Authorized - 175,000 shares, Issued - 17,869 and 327 shares at December 31, 2014 and December 31, 2013, respectively; outstanding - 17,852 and 303 at December 31, 2014 and December 31, 2013, respectively	18,000
Additional paid-in-capital	147,923,000
Accumulated other comprehensive loss	-7,000
Accumulated deficit	-115,427,000	-80,131,000
Total stockholders' equity (deficit)	32,507,000	-80,131,000
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	50,431,000	15,761,000
Seed convertible preferred stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock		3,000,000
Series A redeemable convertible preferred stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock		23,125,000
Series B redeemable convertible preferred stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock		24,937,000
Series C redeemable convertible preferred stock
Redeemable convertible preferred stock:
Redeemable convertible preferred stock		$30,500,000

Balance_Sheets_Parenthetical

Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Redeemable convertible preferred stock, shares authorized		321,340,959
Common stock, par value (in dollars per share)	$0.00	$0.00
Common stock, shares authorized	175,000,000
Common stock, shares issued	17,869,235	327,000
Common stock, shares outstanding	17,852,389	303,000
Seed convertible preferred stock
Redeemable convertible preferred stock, par value (in dollars per share)		$0.00
Redeemable convertible preferred stock, shares authorized	0	4,615,385
Redeemable convertible preferred stock, shares issued	0	4,615,000
Redeemable convertible preferred stock, shares outstanding	0	4,615,000
Redeemable convertible preferred stock, liquidation preference (in dollars)	$0	$3,000,000
Series A redeemable convertible preferred stock
Redeemable convertible preferred stock, par value (in dollars per share)		$0.00
Redeemable convertible preferred stock, shares authorized	0	36,661,538
Redeemable convertible preferred stock, shares issued	0	35,577,000
Redeemable convertible preferred stock, shares outstanding	0	35,577,000
Redeemable convertible preferred stock, liquidation preference (in dollars)	0	23,125,000
Series B redeemable convertible preferred stock
Redeemable convertible preferred stock, par value (in dollars per share)		$0.00
Redeemable convertible preferred stock, shares authorized	0	35,098,520
Redeemable convertible preferred stock, shares issued	0	34,581,000
Redeemable convertible preferred stock, shares outstanding	0	34,581,000
Redeemable convertible preferred stock, liquidation preference (in dollars)	0	24,937,000
Series C redeemable convertible preferred stock
Redeemable convertible preferred stock, par value (in dollars per share)		$0.00
Redeemable convertible preferred stock, shares authorized	0	53,275,861
Redeemable convertible preferred stock, shares issued	0	52,586,000
Redeemable convertible preferred stock, shares outstanding	0	52,586,000
Redeemable convertible preferred stock, liquidation preference (in dollars)	$0	$30,500,000

Statements_of_Operations

Statements of Operations (USD $)	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Statements of Operations and Comprehensive Loss
Grant revenue	$308	$731	$1,977
Operating expenses:
Research and development	23,727	15,695	11,240
General and administrative	9,747	4,961	3,690
Total operating expenses	33,474	20,656	14,930
Loss from operations	-33,166	-19,925	-12,953
Other expense:
Change in fair value of warrant	-725	-222	93
Loss on debt extinguishment	-435	-200
Interest expense, net	-970	-459	-507
Other expense	-2,130	-881	-414
Net loss	-35,296	-20,806	-13,367
Comprehensive loss	-35,303	-20,806	-13,367
Reconciliation of net loss to net loss attributable to common stockholders
Net loss	-35,296	-20,806	-13,367
Accretion of redeemable convertible preferred stock to redemption value	-180	-1,605	-1,781
Net loss attributable to common stockholders	($35,476)	($22,411)	($15,148)
Net loss per share attributable to common stockholders-basic and diluted (in dollars per share)	($2.27)	($75.46)	($51.35)
Weighted-average number of common shares used in net loss per share attributable to common stockholders - basic and diluted (in shares)	15,618	297	295

Statements_of_Comprehensive_Lo

Statements of Comprehensive Loss (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Statements of Comprehensive Loss
Net loss	($11,650)	($9,171)	($7,146)	($7,329)	($6,346)	($4,839)	($4,957)	($4,664)	($35,296)	($20,806)	($13,367)
Other comprehensive income (loss):
Unrealized loss on available-for-sale securities									-7
Comprehensive loss									($35,303)	($20,806)	($13,367)

Statements_of_Redeemable_Conve

Statements of Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity (USD $)	Seed convertible preferred stock	Series A redeemable convertible preferred stock	Series B redeemable convertible preferred stock	Series C redeemable convertible preferred stock	Common Stock	Common Stock	Common Stock	Common Stock	Additional Paid in Capital	Additional Paid in Capital	Additional Paid in Capital	Additional Paid in Capital	Other Comprehensive Income	Accumulated Deficit	Initial Public Offering	Employee stock purchase plan	Private Placement	Total
In Thousands, except Share data, unless otherwise specified					Initial Public Offering	Employee stock purchase plan	Private Placement		Initial Public Offering	Employee stock purchase plan	Private Placement
Balance - Stockholders' (Deficit) Equity at Dec. 31, 2011														($43,562)				($43,562)
Balance - Redeemable Convertible Preferred Stock at Dec. 31, 2011	3,000	23,125	21,723
Balance - Stockholders' (Deficit) Equity (in shares) at Dec. 31, 2011								295,000
Balance - Redeemable Convertible Preferred Stock (in shares) at Dec. 31, 2011	4,615,000	35,577,000	34,581,000
Increase (Decrease) in Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity
Issuance of Series C Preferred stock				15,250								-172						-172
Issuance of Series C Preferred stock (in shares)				26,293,000
Accretion of dividends on redeemable convertible preferred stock			1,609									-136		-1,473				-1,609
Exercise of stock options												1						1
Stock-based compensation expense												307						307
Net loss														-13,367				-13,367
Balance - Stockholders' (Deficit) Equity at Dec. 31, 2012	3,000	23,125	23,332	15,250										-58,402				-58,402
Balance - Stockholders' (Deficit) Equity (in shares) at Dec. 31, 2012	4,615,000	35,577,000	34,581,000	26,293,000
Balance - Redeemable Convertible Preferred Stock (in shares) at Dec. 31, 2012								295,000
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)				26,293,000
Accretion of dividends on redeemable convertible preferred stock			1,605									-682		-923				-1,605
Exercise of stock options								7				9						9
Vesting of restricted stock												1						1
Vesting of restricted stock (in shares)								1,000
Stock-based compensation expense												672						672
Net loss														-20,806				-20,806
Balance - Stockholders' (Deficit) Equity at Dec. 31, 2013														-80,131				-80,131
Balance - Redeemable Convertible Preferred Stock at Dec. 31, 2013	3,000	23,125	24,937	30,500
Balance - Stockholders' (Deficit) Equity (in shares) at Dec. 31, 2013								303,000
Balance - Redeemable Convertible Preferred Stock (in shares) at Dec. 31, 2013	4,615,000	35,577,000	34,581,000	52,586,000
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)		51,000
Cashless exercise of warrants		98																98
Cashless exercise of warrants (in shares)		317,000						54,000
Conversion of preferred stock to common stock upon closing of IPO	-3,000	-23,256	-25,117	-30,500				11				81,763						81,774
Conversion of preferred stock to common stock upon closing of IPO (in shares)	-4,615,000	-35,945,000	-34,581,000	-52,586,000				11,466,000
Reclassification of warrants to additional paid-in capital												1,381						1,381
Issuance of common stock					5,500	16	223		58,971	93	1,964				58,977	93	1,964
Issuance of common stock (in shares)					6,000
Issuance of warrants, net of issuance costs of $6												334						334
Exercise of stock options								1				682						683
Exercise of stock options (in shares)								282,000
Vesting of restricted stock												10						10
Vesting of restricted stock (in shares)								8,000
Stock-based compensation expense												2,905						2,905
Unrealized loss on marketable securities													-7					-7
Net loss														-35,296				-35,296
Balance - Stockholders' (Deficit) Equity at Dec. 31, 2014								$18				$147,923	($7)	($115,427)				$32,507
Balance - Stockholders' (Deficit) Equity (in shares) at Dec. 31, 2014								17,852,000

Statements_of_Redeemable_Conve1

Statements of Redeemable Convertible Preferred Stock and Stockholders' (Deficit) Equity (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2012
Issuance of warrants, issuance costs	$6
Series C redeemable convertible preferred stock
Issuance of stock, issuance costs		172
Initial Public Offering
Issuance of stock, issuance costs	2,403
Private Placement
Issuance of stock, issuance costs	$36

Statements_of_Cash_Flows

Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net loss	($35,296)	($20,806)	($13,367)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	469	318	300
Stock-based compensation	2,905	672	307
Amortization of premium on investments	26
Change in fair value of warrants liability	725	222	-93
Gain on sale of equipment	-18
Non-cash interest expense	254	22	46
Loss on debt extinguishment	435	200
Changes in operating assets and liabilities:
Restricted cash		97	-315
Prepaid expenses and other current assets	-442	27	-145
Other long-term assets	782	-1,539	-237
Accounts payable	516	724	515
Deferred revenue	893	12	-23
Accrued expenses and other liabilities	1,135	468	-191
Deferred rent	12	-155	376
Accrued interest payable		-135	146
Net cash used in operating activities	-27,604	-19,873	-12,681
Investing activities
Purchases of property and equipment	-1,520	-389	-460
Purchase of available-for-sale securities	-27,053
Net cash used in investing activities	-28,573	-389	-460
Financing activities
Proceeds from IPO, net of issuance costs	59,974
Proceeds from issuance of preferred stock, net		15,250	15,078
Proceeds from issuance of long-term debt, net of issuance costs	11,784	9,965	5,000
Repayment of long-term debt	-10,401	-4,245	-1,164
Proceeds from sale of common stock, net of issuance costs	1,964
Proceeds from issuance of common stock under ESPP	93
Proceeds from exercise of stock options	683	42	1
Proceeds form the exercise of warrants	33
Payments for debt issuance costs	-103	-58
Net cash provided by financing activities	64,027	20,954	18,915
Net increase in cash and cash equivalents	7,850	692	5,774
Cash and cash equivalents at beginning of period	12,208	11,516	5,742
Cash and cash equivalents at end of period	20,058	12,208	11,516
Supplemental cash flow information
Cash paid for interest	815	426	323
Supplemental disclosure of non-cash investing and financing activities
Conversion of preferred stock to common stock upon closing of IPO	81,774
Reclassification of prepaid IPO closing costs from non-current assets to additional paid-in capital	997
Reclassification of warrants to additional paid-in capital	1,381
Accretion of redeemable convertible preferred stock to redemption value	180	1,605	1,781
Vesting of restricted stock	10	1
Leasehold improvements financed by landlord			237
Cashless exercise of warrants	98
Issuance of common stock warrant	340
Equipment purchased under capital lease	$21

Organization_and_operations

Organization and operations	12 Months Ended
	Dec. 31, 2014
Organization and operations
Organization and operations
	1. Organization and operations
	The Company
	Genocea Biosciences, Inc. (the “Company”) is a clinical stage biopharmaceutical company that was incorporated in Delaware on August 16, 2006 and has a principal place of business in Cambridge, Massachusetts. The Company has two products in clinical development:
		·	GEN-003, which has completed a Phase 1/2a clinical trial and is currently in a Phase 2 dose optimization clinical trial, to treat patients with genital herpes, and
		·	GEN-004, which is being developed to prevent infections caused by pneumococcus. The Company has completed a Phase 1 clinical trial and is currently conducting a Phase 2a clinical trial.
	The Company also has other product candidates that are currently in preclinical development. The Company developed GEN-003, GEN-004 and its preclinical product candidates using its proprietary platform technology called the AnTigen Lead Acquisition System (“ATLAS™”). The ATLAS™ proprietary technology platform mimics the human immune response in the laboratory, potentially improving the effectiveness of vaccine discovery and reducing the time needed to create promising vaccines.
	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 for 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, 2014, the Company had an accumulated deficit of approximately $115.4 million.   The Company had cash, cash equivalents and marketable securities of $47.1 million as of December 31, 2014. The Company believes that its existing cash, cash equivalents and marketable securities and available future borrowings under the Company’s credit facility, will be sufficient to fund projected operating expenses and capital expenditure requirements into the first quarter of 2016.

Summary_of_significant_account

Summary of significant accounting policies	12 Months Ended
	Dec. 31, 2014
Summary of significant accounting policies
Summary of significant accounting policies
	2. Summary of significant accounting policies
	Initial Public Offering
	On February 10, 2014, the Company completed its initial public offering (“IPO”) of its common stock, $0.001 par value per share (“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.
	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 (“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 initial public offering 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 marketable securities
	The Company considers all highly liquid investments with maturities of 90 days or less from the purchase date to be cash equivalents. Cash and cash equivalents are held in depository and money market accounts and are reported at fair value.
	Marketable securities consist of U.S. treasury securities with maturities of more than 90 days. The Company has determined the appropriate balance sheet classification of the securities as current since they are available for use in current operating activities, regardless of actual maturity dates. Marketable securities are classified as available-for-sale pursuant to FASB ASC Topic 320, Investments — Debt and Equity Securities, (“ASC 320”) and are recorded on the balance sheet at fair value with unrealized gains and losses (excluding other-than-temporary impairments) reported as a separate component of accumulated other comprehensive income (loss). Realized gains and losses, as well as other-than-temporary impairments, are recognized in the statement of operations based on the specific identification method.
	The Company reviews its marketable securities for other-than-temporary impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable within a reasonable period of time. Other-than-temporary impairment of marketable securities are recognized in the statements of operations if the Company has experienced a credit loss, has the intent to sell the marketable securities, or if it is more likely than not that the Company will be required to sell the marketable securities before recovery of the amortized cost basis.
	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 marketable securities. The Company’s cash, cash equivalents and marketable securities are held in accounts with a financial institution that management believes is 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 initial public offering costs
	Deferred public offering costs, which primarily consist of direct, incremental legal and accounting fees related to the IPO, were capitalized within other assets as of December 31, 2013. The Company incurred $2.4 million in IPO costs and in February 2014, these public offering costs were offset against the proceeds upon completion of the IPO.
	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 marketable securities (Note 3) and warrants (Note 8).
	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 7) 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 8), there have been no changes to the valuation methods utilized by the Company during the years ended December 31, 2014, 2013, and 2012. 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, 2014, 2013 and 2012.
	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 (Note 7), 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 years
	Furniture and office equipment		5 years
	Computer equipment and software		3-5 years
	Leasehold improvements		Shorter of the useful life or remaining lease term
	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, 2014.
	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 our IPO. 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. Shares of Common Stock reserved for future issuance were presented on an as converted basis and the financial statements disclose the adjusted conversion ratios.
	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
	The Company has received grants from private not-for-profit organizations and federal agencies. Grant revenue consists of revenue earned from grants 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. The Company recognized a total of $308 thousand, $731 thousand, and $2.0 million in 2014, 2013, and 2012, respectively, related to these grants.
	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 of $308 thousand under the agreement in the fourth quarter of 2014.
	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.
	License agreement
	In 2012, the Company entered into a license agreement with a not-for-profit entity whereby the not-for-profit entity could utilize certain programs discovered or developed by the Company in certain developing countries. The Company did not receive any up-front consideration related to this agreement; however, the Company is entitled to receive reimbursement of a pro rata share of any payments, including milestone payments, that the Company is required to make under license agreements with third parties that comprise these programs. As of December 31, 2014, the licenses from third parties that comprise these programs have not been determined yet as these programs are either in the early stages of development or have not yet been identified. As a result, the Company is not currently eligible to receive any milestone payments under this arrangement.
	Concurrent with the execution of the license agreement, the not-for-profit entity also purchased 4,310,345 shares of the Company’s Series C Preferred Stock (Note 10).
	At the inception of the agreement, the Company evaluated whether each potential milestone payment that could be received from the not-for-profit entity for reimbursement of a portion of milestones owed to third parties from existing license agreements that could comprise these programs is substantive and at risk to both parties on the basis of the contingent nature of the milestone. The evaluation included an assessment of whether (a) the consideration is commensurate with either (i) the entity’s performance to achieve the milestone or (ii) the enhancement of the value of the delivered items as a result of a specific outcome resulting from the entity’s performance to achieve the milestone; (b) the consideration related solely to past performance; and (c) the consideration was reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated factors such as the scientific, regulatory, and other risks that must be overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone, and whether the milestone considerations are reasonable relative to all deliverables and payment terms in the arrangement in making this assessment. Substantive, at-risk milestones are recognized as revenue when the milestone is achieved.
	As there was no up-front consideration, there were no amounts to allocate to the various deliverables. The milestones under the arrangement related to reimbursement for milestone payments by the Company owed to third parties for existing license agreements that could comprise these programs are considered to be substantive and at risk and will be recognized when earned. Since the licenses from third parties that could comprise these programs have not been determined yet, the amount and timing of such milestones cannot be determined at this time.
	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 (“ACS 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, 2014 and 2013, 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.
Net loss per share attributable to common stockholders
Basic net loss 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. During periods of income, the Company allocates participating securities a proportional share of income determined by dividing total weighted average participating securities by the sum of the total weighted average common shares and participating securities (the “two-class method”). The Company’s redeemable convertible preferred stock and restricted stock participate in any dividends declared by the Company and are therefore considered to be participating securities. Participating securities have the effect of diluting both basic and diluted earnings per share during periods of income. During periods of loss, the Company allocates no loss to participating securities because they have no contractual obligation to share in the losses of the Company. Diluted net loss 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 income or 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		Date of adoption	Effect on the financial statements or other significant matters
Standards that are not yet adopted
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.		January 1, 2017	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, and the Company is evaluating the effects of the new standard on this type of revenue.
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.		January 1, 2017	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.
Standards that were adopted
ASU No. 2014-10, Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation (“ASU 2014-10”)		The standard eliminates the requirements for development stage entities to (1) present inception-to-date information in the statements of income, cash flows, and shareholder equity, (2) label the financial statements as those of a development stage entity, (3) disclose a description of the development stage activities in which the entity is engaged, and (4) disclose in the first year in which the entity is no longer a development stage entity that in prior years it had been in the development stage.		June 30, 2014	The Company adopted ASU 2014-10 on June 30, 2014, and the adoption did not have a material impact on its financial statements.
Subsequent events
The Company considers events or transactions that occur after the balance sheet date but prior to the date the financial statements are issued for potential recognition or disclosure in the financial statements.

Cash_cash_equivalents_and_mark

Cash, cash equivalents and marketable securities	12 Months Ended
	Dec. 31, 2014
Cash, cash equivalents and marketable securities
Cash, cash equivalents and marketable securities
	3. Cash, cash equivalents and marketable securities
	As of December 31, 2014 and 2013, cash, cash equivalents and, in the case of December 31, 2014, marketable securities comprised funds in depository, money market accounts and U.S. treasury securities.
	The following table presents the cash, cash equivalents and marketable securities carried at fair value in accordance with the hierarchy defined in Note 2 (in thousands):
					Quoted prices			Significant			Significant
					in active			other			unobservable
					markets			observable			inputs
								inputs
		Total			(Level 1)			(Level 2)			(Level 3)
	December 31, 2014
	Cash	$	1,066		$	1,066		$	—		$	—
	Money Market funds, included in cash equivalents	18,992			18,992			—			—
	Marketable securities - U.S. treasuries	27,021			27,021			—			—
	Total	$	47,079		$	47,079		$	—		$	—
	December 31, 2013
	Cash	$	249		$	249		$	—		$	—
	Money Market funds, included in cash equivalents	11,959			11,959			—			—
	Total	$	12,208		$	12,208		$	—		$	—
	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, 2014 and 2013.
	Marketable securities at December 31, 2014 consist of the following (in thousands):
		Contracted		Amortized			Unrealized			Unrealized			Fair Value
		Maturity		Cost			Gains			Losses
	Current
	U.S. Treasuries	166-365 days		$	27,028		$	—		$	(7	)	$	27,021
	Total			$	27,028		$	—		$	(7	)	$	27,021
	At December 31, 2014, the aggregate fair value of marketable securities in an unrealized loss position was $24.0 million with unrealized losses of $8 thousand. At December 31, 2014, the aggregate fair value of marketable securities in an unrealized gain position was $3.0 million with unrealized gains of $1 thousand. The Company evaluated its securities for other-than-temporary impairment and considered the decline in market value for the securities to be primarily attributable to current economic and market conditions. It is not more likely than not that the Company will be required to sell the securities, and the Company does not intend to do so prior to the recovery of the amortized cost basis. Based on this analysis, these marketable securities were not considered to be other-than-temporarily impaired as of December 31, 2014.
	The Company did not hold any marketable securities as of December 31, 2013.

Prepaid_expenses_and_other_cur

Prepaid expenses and other current assets	12 Months Ended
	Dec. 31, 2014
Prepaid expenses and other current assets
Prepaid expenses and other current assets
	4. Prepaid expenses and other current assets
	Prepaid expenses and other current assets consist of the following (in thousands):
		December 31,
		2014		2013
	Prepaid tenant improvement costs	$	—	$	237
	Prepaid insurance	90		7
	Prepaid research and development costs	664		190
	Interest receivable	21		—
	Other	188		76
	Total	$	963	$	510

Property_and_equipment_net

Property and equipment, net	12 Months Ended
	Dec. 31, 2014
Property and equipment, net
Property and equipment, net
	5. Property and equipment, net
	Property and equipment, net consist of the following (in thousands):
		December 31,
		2014			2013
	Laboratory equipment	$	2,510		$	1,694
	Furniture office equipment	186			14
	Computer equipment and software	257			142
	Leasehold improvements	799			344
	Total property and equipment	3,752			2,194
	Accumulated depreciation	(1,796		)	(1,329		)
	Property and equipment, net	$	1,956		$	865
	Depreciation expense was $469 thousand, $318 thousand and $300 thousand for the years ended December 31, 2014, 2013, 2012.
	During 2014, the Company sold fully depreciated fixed assets with an original cost basis of $12 thousand and a net book value of $10 thousand, recognizing a gain on sale of $18 thousand. The Company did not sell or dispose of any fixed assets during 2013.

Accrued_expenses_and_other_cur

Accrued expenses and other current liabilities	12 Months Ended
	Dec. 31, 2014
Accrued expenses and other current liabilities.
Accrued expenses and Other current liabilities
	6. Accrued expenses and other current liabilities
	Accrued expenses and other current liabilities consisted of the following (in thousands):
		December 31,
		2014		2013
	Payroll and employee-related costs	$	1,066	$	738
	Research and development costs	1,117		323
	Accrued professional fees	270		303
	Other	33		54
	Total	$	2,486	$	1,418

Longterm_debt

Long-term debt	12 Months Ended
	Dec. 31, 2014
Long-Term Debt
Long-Term Debt
	7. Long-term debt
	In October 2011, the Company entered into a Loan and Security Agreement with a financial institution, which provided for up to $5.0 million in debt financing (“2011 Term Loan”). The 2011 Term Loan provided for a draw-down period on the facility through March 1, 2012. On March 1, 2012, the Company drew down the full $5.0 million available under the terms of this arrangement.
	From March 1, 2012 through May 1, 2012, the Company was obligated to make interest-only payments at the greater of the financial institution’s prime rate plus 5.00% or 8.00%. The Company began making 36 equal monthly payments of principal and accrued interest thereafter. During the 36-month period, the Term Loan bears 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.
	In connection with the 2011 Term Loan, the Company issued a fully-exercisable warrant to purchase 517,242 shares of Series B Preferred Stock. Upon completion of our IPO, these Series B preferred stock warrants automatically converted into warrants exercisable for 43,465 shares of Common Stock at an exercise price of $6.90 per share (Note 5). The 2011 Term Loan was collateralized by all the assets of the Company, except for those assets collateralized by an equipment term loan that was repaid as of December 31, 2013.
	On September 30, 2013, the Company entered into a new loan agreement which provided up to $10.0 million in debt financing (“2013 Term Loan”). 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. 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 is being 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 our 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 5).
	On November 20 2014, 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 (“2014 Term Loan”). The first tranche of $17.0 million is available through June 30, 2015. The second tranche of up to $5.0 million may be drawn, at the Company’s option, on or prior to December 15, 2015, subject to the Company receiving favorable data from its ongoing GEN-003 Phase 2 dose optimization trial and either (i) the commencement of the Company’s next clinical trial for GEN-003 or (ii) the receipt of at least $40.0 million in net proceeds from an equity financing and/or a strategic corporate partnership. The third tranche of up to $5.0 million may be drawn, at the Company’s option, on or prior to December 15, 2015, subject to the Company receiving favorable data from its ongoing Phase 2 human challenge study for GEN-004.
	The 2014 Term Loan matures on July 1, 2018. If the eligibility requirements for the second tranche are met, the maturity date may be extended to December 31, 2018 at the Company’s sole election.
	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 provides for interest-only payments until December 31, 2015, which may be extended at the Company’s sole election for a six month period if the eligibility requirements for the second tranche are met. Thereafter, payments will be made monthly in 30 equal installments of principal and interest (subject to recalculation upon a change in prime rates). 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 twelve months following the closing date, 2.0%, if an advance is prepaid between twelve months and twenty four months following the closing date, and 1.0% thereafter. Amounts outstanding during 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 must also pay an End of Term Charge of 4.95% 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.
	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 the lender 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 $100,000, or the occurrence of any material default of the Company involving indebtedness in excess of $100,000. If an event of default occurs, repayment of all amounts due under the Loan Agreement may be accelerated by the lender, 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 the lender.
	Upon closing the 2014 Term Loan, the Company drew down $12.0 million under the first tranche of the Loan Agreement using approximately $9.8 million of the proceeds to repay all outstanding indebtedness under the 2013 Term Loan. As a result, the Company recorded $435 thousand as a loss on extinguishment of debt which was recorded in other income / expense on the Statements of Operations. The loss on extinguishment consisted of 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.
	In connection with the 2014 Term Loan Agreement, 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 Loan Agreement, 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 “Initial Equity Investment”).  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.
	In connection with the issuance of the 2014 Term Loan, the Company incurred $103 thousand of financing costs which were recorded in other assets. The Company also reimbursed the lenders $210 thousand for debt financing costs which has been recorded as a debt discount. The 2014 Term Loan included various embedded features which were evaluated for separate accounting as derivatives under ASC Topic No. 815, “Derivatives and Hedging”. In accordance with Topic No. 815, it was determined that none of these embedded features required separate accounting from the debt host.  The debt discount is being amortized to interest expense over the life of the 2014 Term Loan using the effective interest method.
	As of December 31, 2014 and 2013, the Company had outstanding borrowings under the 2014 Term Loan of $12.0 million and none, respectively. Interest expense related to the 2014 Term Loan was $143 thousand and $0 for the years ended December 31, 2014 and 2013, respectively.
	As of December 31, 2014 and 2013, the Company had outstanding borrowings under the 2013 Term Loan of none and $10.0 million, respectively. Interest expense related to the 2013 Term Loan was $813 thousand and $124 thousand for the years ended December 31, 2014 and 2013, respectively.
	Future principal payments on the 2014 Term Loan are as follows (in thousands):
		December 31,
		2014
	2015	$	—
	2016	4,529
	2017	4,876
	2018	2,595
	Total	$	12,000

Warrants

Warrants	12 Months Ended
	Dec. 31, 2014
Warrants.
Warrants
	8. Warrants
	Warrants outstanding represent the right to acquire the following number of shares (in thousands):
		December 31,		December 31,
		2014		2013
	Warrants to purchase Series A Preferred Stock	—		1,085
	Warrants to purchase Series B Preferred Stock	—		517
	Warrants to purchase Series C Preferred Stock	—		690
	Warrants to purchase Common Stock	78		—
	Total	78		2,292
	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,
		2014
	Fair value of underlying instrument	$	9.05
	Expected volatility	70.0		%
	Expected term (in years)	5.00
	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, 2014, 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 our 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 our IPO. Also upon the completion of our 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 our 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, 2014, the Company had no outstanding warrants to purchase redeemable securities liability.
	The warrant to purchase redeemable securities liability measured at fair value as of December 31, 2013 is as follows (in thousands):
					Quoted		Significant			Significant
					prices in		other			unobservable
					active		observable			inputs
					markets		inputs
		Total			(Level 1)		(Level 2)			(Level 3)
	December 31, 2013
	Warrants to purchase redeemable securities	$	656		$	—	$	—		$	656
	Total	$	656		$	—	$	—		$	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. 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,
		2014			2013		2012
	Beginning balance	$	656		$	246	$	339
	Warrants issued				188		—
	Change in fair value	725			222		(93		)
	Warrants exercised	(323		)	—		—
	Reclassification to accumulated paid-in capital	(1,058		)	—		—
	Ending balance	$	—		$	656	$	246
	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 Probablity-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,
		2014
	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 $7,783, which resulted in an increase in fair value of $2,142. 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,
		2014
	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 $10,357, which resulted in an increase in fair value of $2,839. 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 our IPO, was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions:
		February 10,
	2014
Fair value of underlying instrument	$	7.74
Expected Volatility	50.81		%
Expected term (in years)	0.003
Risk-free interest rate	1.48		%
Expected dividend yield	0.0		%
These warrants were re-measured to a fair value of $304,423, which resulted in an increase in fair value of $46,581. 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,
	2014
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 $1,058,269, which resulted in an increase in fair value of $673,040. 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, 2014
Commitments and contingencies
Commitments and contingencies
	9. Commitments and contingencies
	Significant Contracts and Agreements
	In August 2006, the Company entered into an agreement to license certain intellectual property from The Regents of the University of California. The agreement calls for payments to be made by the Company upon the occurrence of a certain development milestone and a certain commercialization milestone for each distinct product covered by the licensed patents, in addition to certain royalties to be paid on marketed products or sublicense income. The Company did not incur any expenses under this agreement for the years ended December 31, 2014, 2013 and 2012.
	In November 2007, the Company entered into an agreement to license certain intellectual property from Harvard University. The agreement calls for payments to be made by the Company upon the occurrence of certain development and regulatory milestones, in addition to certain royalties on marketed products or sublicense income. In addition, the Company must make annual maintenance fee payments, which vary depending on the type of products under development. The Company incurred expenses of $157 thousand, $83 thousand and $83 thousand in annual maintenance fees and clinical milestones to Harvard University for the years ended December 31, 2014, 2013 and 2012, respectively. The Company notified the President and Fellows of Harvard College of its partial termination of the license agreement with regard to the intellectual property covering chlamydia antigens on December 8, 2014. Effective March 8, 2015, the license agreement with the President and Fellows of Harvard College with regard to the intellectual property covering chlamydia antigens will be terminated. The Company determined that the chlamydia antigens were not relevant to the continued development of GEN-001. The Company will continue to maintain exclusive rights to aspects of the ATLAS platform covered by Harvard University intellectual property.
	In August 2009, the Company entered into an agreement to license certain intellectual property from Isconova AB, now Novavax. The agreement calls for payments to be made by the Company upon the occurrence of certain development and commercial milestones, in addition to certain royalties to be paid on marketed products or sublicense income. The Company incurred expenses of $402 thousand, none and $290 thousand related to services provided by Novavax for the years ended December 31, 2014, 2013 and 2012, respectively.
	In January 2010, the Company entered into an agreement to license certain intellectual property from the University of Washington. The agreement also calls for payments to be made by the Company upon the occurrence of certain development and commercial milestones, in addition to certain royalties on marketed products or sublicense income. In addition, the Company must make annual maintenance fee payments, which vary depending on the number of years from the effective date. The Company incurred expenses of $24 thousand, $45 thousand and $15 thousand related to this agreement for the years ended December 31, 2014, 2013, 2012, respectively. Effective October 27, 2014, the agreement between the Company and the University of Washington was terminated. As of December 31, 2014 no further rights or obligations exist under the terminated agreement.
	In March 2014, the Company announced a joint research collaboration with Dana-Farber Cancer Institute and Harvard Medical School to characterize anti-tumor T cell responses in melanoma patients. This collaboration extends the use of our proprietary ATLAS platform for the rapid discovery of T cell antigens to cancer immunotherapy approaches.
	Supply agreement
	In August 2009, the Company entered into a supply agreement with a third party for the manufacture and supply of antigens used in the Company’s product candidates. The agreement calls for payments to be made by the Company upon the occurrence of certain manufacturing milestones, in addition to reimbursement of certain consumables. In June 2013, the Company entered into another supply agreement with the same vendor for the manufacture and supply of antigens to be used in the Company’s next clinical trials. The Company incurred expenses of $791 thousand, $1.5 million, $180 thousand related to these agreements for the years ended December 31, 2014, 2013, and 2012, respectively.
	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 of $3.5 million, none, and none, under this agreement for the years ended December 31, 2014, 2013 and 2012, respectively.
	In October 2014, the Company entered a product development and clinical supply agreement with Baxter Pharmaceutical Solutions LLC (“Baxter”). The product development and clinical supply agreement provides the terms and conditions under which Baxter will formulate, fill, inspect, package, label and test our lead product, GEN-003 for clinical supply. The Company is obligated to pay Baxter for each batch of GEN-003 manufactured. Additionally, certain set-up fees and equipment purchased for the purposes of batch production will be invoiced separately by Baxter. The Company is also responsible for the payment of a monthly service fee for project management services for the duration of the arrangement. The Company has not any incurred expenses under this agreement for the years ended December 31, 2014, 2013 and 2012.
	Lease commitments
	In July 2012, the Company leased office and laboratory space under an operating sublease (“2012 Facilities Sublease”) that expired in February 2014. The Company concurrently signed an operating lease for the same space with the master landlord (“2012 Master Facilities Lease”) that commenced in March 2014 and expires in February 2017.
	As of December 31, 2014, the minimum future lease payments under the 2012 Master Facilities Lease are as follows (in thousands):
		Operating
		lease
	2015	$	976
	2016	1,012
	2017	170
	Total minimum lease payments	$	2,158
	The Company recorded $803 thousand, $476 thousand, and $1.1 million in rent expense for the years ended December 31, 2014, 2013, and 2012, respectively.
	Restricted cash related to facilities leases
	Restricted cash related to facilities leases consisted of the following (in thousands):
		December 31,		December 31,
		2014		2013
	2012 Facilities Sublease	$	—	$	157
	2012 Master Facilities Lease	316		158
	Total	$	316	$	315
	At December 31, 2014, the Company has an outstanding letter of credit with a financial institution related to a security deposit for the 2012 Master Facilities Lease, which is secured by cash on deposit and expires on February 28, 2017. The letter of credit related to the 2012 Facilities Sublease expired on April 30, 2014.
	Litigation
	The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities.

Redeemable_convertible_preferr

Redeemable convertible preferred stock	12 Months Ended
	Dec. 31, 2014
Redeemable convertible preferred stock
Redeemable convertible preferred stock
	10. Redeemable convertible preferred stock
	Upon the completion of our IPO on February 10, 2014, all of the outstanding shares of the Company’s redeemable convertible preferred stock were converted into 11,466,479 shares of its Common Stock. As of December 31, 2014, the Company does not have any redeemable convertible preferred stock issued or outstanding.
	As of December 31, 2013, the total authorized capital stock of the Company was 321,340,959 shares, which included 4,615,385 shares of Seed Preferred Stock, $0.001 par value per share; 36,661,538 shares of Series A Preferred Stock $0.001 par value per share; 35,098,520 shares of Series B Preferred Stock, $0.001 par value per share; and 53,275,861 shares of Series C Preferred Stock, $0.001 par value per share. On February 10, 2014, the Company closed its IPO. 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.

Common_stock

Common stock	12 Months Ended
	Dec. 31, 2014
Common stock.
Common stock
	11. Common stock
	At December 31, 2014, the Company had authorized 175,000,000 shares of Common Stock, $0.001 par value per share, of which 17,869,235 shares were issued and 17,852,389 were outstanding.
	General
	Prior to the completion of our IPO on February 10, 2014, the voting, dividend and liquidation rights of the holders of shares of Common Stock were subject to and qualified by the rights, powers and preferences of the holders of shares of preferred stock. The Common Stock has the following characteristics:
	Voting
	The holders of shares of Common Stock are entitled to one vote for each share of Common Stock held at all meetings of stockholders and written actions in lieu of meetings. The Common Stockholders have the right to elect one of the eight Directors.
	Dividends
	The holders of shares of Common Stock are entitled to receive dividends, if and when declared by the board of directors. Cash dividends may not be declared or paid to holders of shares of Common Stock until paid on each series of outstanding preferred stock in accordance with their respective terms. As of December 31, 2014, no dividends have been declared or paid since the Company’s inception.
	Liquidation
	After payment to the holders of shares of preferred stock of their liquidation preferences, the holders of the Common Stock are entitled to share ratably in the Company’s assets available for distribution to stockholders, in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or upon the occurrence of a deemed liquidation event. As of December 31, 2014, the Company does not have any preferred stock issued or outstanding.
	Restricted stock
	During 2006 and 2007, the Company’s founders and certain employees were issued shares and entered into Stock Restriction and Repurchase Agreements with the Company. During 2013, a director of the Company early exercised stock options and received 31,092 shares of Common Stock which were subject to a Stock Restriction and Repurchase Agreement with the Company. Under the terms of the agreements, shares of Common Stock issued are subject to a vesting schedule. 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. As of December 31, 2013, the Company had 24,615 shares of nonvested restricted stock that were subject to repurchase by the Company. As of December 31, 2014, the Company has issued 35,964 shares of restricted common stock of which 19,124 shares have vested and 16,840 shares are subject to repurchase by the Company.
	Reserve for future issuance
	The Company has reserved for future issuances the following number of shares of Common Stock (in thousands):
		December 31,	December 31,
		2014	2013
	Conversion of Seed Preferred Stock	—	388
	Conversion of Series A Preferred Stock	—	2,990
	Conversion of Series B Preferred Stock	—	3,613
	Conversion of Series C Preferred Stock	—	4,419
	Options to purchase Common Stock	2,373	1,823
	Options to purchase Common Stock under ESPP	185	—
	Warrants to purchase Series A Preferred Stock	—	91
	Warrants to purchase Series B Preferred Stock	—	43
	Warrants to purchase Series C Preferred Stock	—	58
	Warrants to purchase Common Stock	78	—
		2,636	13,425

Stockbased_compensation

Stock-based compensation	12 Months Ended
	Dec. 31, 2014
Stock-based compensation
Stock-based compensation
	12. Stock-based compensation
	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 our IPO. The 2014 Equity Plan replaced the 2007 Equity Incentive Plan (the “2007 Equity Plan”).
	The 2014 Equity Plan provided for the grant of incentive stock options, non-qualified stock options and restricted stock 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.
	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, 2014, the number of common shares that may be issued under both equity plans is 2,373,348 and 83,015 remain available for future grants.
	During the years ended 2014, 2013 and 2012, the Company granted a total of none, 44,345 and 49,127 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, 2014, 2013 and 2012 was $324 thousand, $143 thousand and $18 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,
		2014			2013			2012
	Research and development	$	1,511		$	322		$	102
	General and administrative	1,394			350			205
	Total	$	2,905		$	672		$	307
	Stock Options
	The following table summarizes stock option activity for employees and nonemployees (shares in thousands):
							Weighted-
				Weighted-			Average
				Average			Remaining		Aggregate
				Exercise			Contractual		Intrinsic
		Shares		Price			Term (years)		Value
	Outstanding at December 31, 2013	1,576		$	2.66		7.64		$	6,682
	Granted	1,065		$	12.79
	Exercised	(282	)	$	2.42
	Canceled	(69	)	$	7.42
	Outstanding at December 31, 2014	2,290		$	7.26		8.08		$	5,332
	Exercisable at December 31, 2014	1,029		$	3.36		6.86		$	4,198
	Vested or expected to vest at December 31, 2014	2,078		$	6.98		7.99		$	5,123
	During the years ended December 31, 2014, 2013 and 2012, the Company granted stock options to purchase an aggregate of 1,064,640, 559,742 and 54,883 of its Common Stock, respectively, with a weighted-average grant date fair values of $10.11, $3.41 and $1.31, respectively.
	The total intrinsic value of options exercised in the year ended December 31, 2014 was $3.1 million and was de minimis in the years ended December 31, 2013 and 2012. As of December 31, 2014, there was $9.4 million of total unrecognized compensation cost related to employee nonvested stock options granted under the Company’s equity plans.
	The total unrecognized compensation costs related to non-employees in the year ended December 31, 2014, was $55 thousand and was immaterial in the years ended December 31, 2013 and 2012.
	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 3.23.
	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,
		2014		2013		2012
	Expected Volatility	86.2%-103.6%		97.10%		99.20%
	Risk-free interest rate	1.75%-2.00%		0.59%-1.83%		0.99%
	Expected term (in years)	6.25		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 during the year ended December 31, 2014. 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.
	Employee Stock Purchase Plan
	In connection with the completion of the Company’s IPO 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. During the year ended December 31, 2014, 15,622 shares were issued under the 2014 ESPP with 185,154 shares remaining for future issuance under the plan as of December 31, 2014. The Company incurred $43 thousand in stock-based compensation expense related to the 2014 ESPP for the year ended December 31, 2014.

401k_Savings_plan

401(k) Savings plan	12 Months Ended
	Dec. 31, 2014
401(k) Savings plan
401(k) Savings plan
	13. 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. The Company has not made any contributions to the 401(k) Plan to date.

Income_taxes

Income taxes	12 Months Ended
	Dec. 31, 2014
Income taxes
Income taxes
	14. Income taxes
	For the years ended December 31, 2014 and 2013, 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.
	Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statement and income tax purposes. The significant components of the Company’s deferred tax assets are comprised of the following (in thousands):
		December 31,
		2014			2013
	Deferred tax assets:
	U.S and state net operating loss carryforwards	$	39,721		$	27,616
	Research and development credits	3,655			2,749
	Stock based compensation	770			369
	Purchased intangibles	245			269
	Capitalized organizational and start up expenditures	153			173
	Accruals and other temporary differences	659			478
	Total deferred tax assets	45,203			31,654
	Less valuation allowance	(45,203		)	(31,654		)
	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, 2014 and 2013. The valuation allowance increased approximately $13.4 million and $8.7 million during the year ended December 31, 2014 and 2013, respectively, due primarily to the generation of net operating losses during each 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,
		2014		2013		2012
	Federal income tax expense at statutory rate	34.0	%	34.0	%	34.0	%
	State income tax, net of federal benefit	4.6	%	5.1	%	6.8	%
	Permanent differences	(2.1	)%	(0.9	)%	(0.2	)%
	Research and development credit	1.8	%	3.6	%	0.0	%
	Other	0.1	%	0.0	%	0.0	%
	Change in valuation allowance	(38.4	)%	(41.8	)%	(40.6	)%
	Effective tax rate	0.0	%	0.0	%	0.0	%
	As of December 31, 2014, 2013, and 2012, the Company had U.S. federal net operating loss carryforwards of approximately $105.0 million, $71.4 million, and $51.7 million, respectively, which may be available to offset future income tax liabilities and expire at various dates through 2034. As of December 31, 2014, 2013, and 2012, the Company also had U.S. state net operating loss carryforwards of approximately $90.5 million, $64.5 million, and $49.0 million, respectively, which may be available to offset future income tax liabilities and expire at various dates through 2034. Included in the federal and state net operating loss carryforwards are approximately $1.9 million, $130 thousand, and none, 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, 2014, 2013, and 2012, the Company had federal research and development tax credit carryforwards of approximately $2.6 million, $1.9 million, and $1.2 million, respectively, available to reduce future tax liabilities which expire at various dates through 2034. As of December 31, 2014, 2013 and 2012, the Company had state research and development tax credit carryforwards of approximately $1.7 million, $1.3 million, and $929 thousand, respectively, available to reduce future tax liabilities which expire at various dates through 2029.
	Under the provisions of the Internal Revenue 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 percent, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual 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 Internal Revenue Code, or could result in a change in control in the future.
	The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2014 and 2013, 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, 2014, 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, 2011 through December 31, 2014. 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.

Net_loss_per_share_attributabl

Net loss per share attributable to common stockholders	12 Months Ended
	Dec. 31, 2014
Net loss per share attributable to common stockholders
Net loss per share attributable to common stockholders
	15. Net loss per share attributable to common stockholders
	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”). As the years ended December 31, 2014, 2013 and 2012 resulted in net losses, 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,
		2014	2013	2012
	Preferred stock	—	11,409	8,493
	Warrants	78	193	135
	Outstanding options	2,290	1,576	1,054
	Total	2,368	13,178	9,682

Quarterly_financial_informatio

Quarterly financial information	12 Months Ended
	Dec. 31, 2014
Quarterly financial information
Quarterly financial information
	16. Quarterly financial information (unaudited, in thousands, except share and per share data)
		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
		Three Months Ended,
		March 31, 2013			June 30, 2013			September 30, 2013			December 31, 2013
	Revenue	$	259		$	228		$	224		$	20
	Operating expenses	4,790			4,977			4,699			6,190
	Net loss	(4,664		)	(4,957		)	(4,839		)	(6,346		)
	Net loss per attributable to common stockholders	(5,059		)	(5,357		)	(5,244		)	(6,751		)
	Net loss per share attributable to common stockholders - basic and diluted	$	(17.09	)	$	(18.10	)	$	(17.72	)	$	(22.50	)
	Weighted-average number of common shares used in net loss per share attributable to common stockholders - basic and diluted	296			296			296			300

Subsequent_events

Subsequent events	12 Months Ended
	Dec. 31, 2014
Subsequent events
Subsequent events
	17. Subsequent events
	The Company has completed an evaluation of all subsequent events after the audited balance sheet date of December 31, 2014 through February 27, 2015, the date the financial statements were issued, to ensure that this filing includes appropriate disclosure of events both recognized in the financial statements as of December 31, 2014 and events which occurred subsequently but were not recognized in the financial statements. The Company has no subsequent events to disclose.

Summary_of_significant_account1

Summary of significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2014
Summary of significant accounting policies
Initial Public Offering
	Initial Public Offering
	On February 10, 2014, the Company completed its initial public offering (“IPO”) of its common stock, $0.001 par value per share (“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.
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 (“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 initial public offering 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 marketable securities
	The Company considers all highly liquid investments with maturities of 90 days or less from the purchase date to be cash equivalents. Cash and cash equivalents are held in depository and money market accounts and are reported at fair value.
Marketable securities
	Marketable securities consist of U.S. treasury securities with maturities of more than 90 days. The Company has determined the appropriate balance sheet classification of the securities as current since they are available for use in current operating activities, regardless of actual maturity dates. Marketable securities are classified as available-for-sale pursuant to FASB ASC Topic 320, Investments — Debt and Equity Securities, (“ASC 320”) and are recorded on the balance sheet at fair value with unrealized gains and losses (excluding other-than-temporary impairments) reported as a separate component of accumulated other comprehensive income (loss). Realized gains and losses, as well as other-than-temporary impairments, are recognized in the statement of operations based on the specific identification method.
	The Company reviews its marketable securities for other-than-temporary impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable within a reasonable period of time. Other-than-temporary impairment of marketable securities are recognized in the statements of operations if the Company has experienced a credit loss, has the intent to sell the marketable securities, or if it is more likely than not that the Company will be required to sell the marketable securities before recovery of the amortized cost basis.
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 marketable securities. The Company’s cash, cash equivalents and marketable securities are held in accounts with a financial institution that management believes is 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 initial public offering costs
	Deferred initial public offering costs
	Deferred public offering costs, which primarily consist of direct, incremental legal and accounting fees related to the IPO, were capitalized within other assets as of December 31, 2013. The Company incurred $2.4 million in IPO costs and in February 2014, these public offering costs were offset against the proceeds upon completion of the IPO.
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 marketable securities (Note 3) and warrants (Note 8).
	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 7) 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 8), there have been no changes to the valuation methods utilized by the Company during the years ended December 31, 2014, 2013, and 2012. 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, 2014, 2013 and 2012.
Derivative Instrument
	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 (Note 7), 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
	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 years
	Furniture and office equipment		5 years
	Computer equipment and software		3-5 years
	Leasehold improvements		Shorter of the useful life or remaining lease term
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, 2014.
Reverse stock split
	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 our IPO. 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. Shares of Common Stock reserved for future issuance were presented on an as converted basis and the financial statements disclose the adjusted conversion ratios.
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
	The Company has received grants from private not-for-profit organizations and federal agencies. Grant revenue consists of revenue earned from grants 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. The Company recognized a total of $308 thousand, $731 thousand, and $2.0 million in 2014, 2013, and 2012, respectively, related to these grants.
	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 of $308 thousand under the agreement in the fourth quarter of 2014.
	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.
	License agreement
	In 2012, the Company entered into a license agreement with a not-for-profit entity whereby the not-for-profit entity could utilize certain programs discovered or developed by the Company in certain developing countries. The Company did not receive any up-front consideration related to this agreement; however, the Company is entitled to receive reimbursement of a pro rata share of any payments, including milestone payments, that the Company is required to make under license agreements with third parties that comprise these programs. As of December 31, 2014, the licenses from third parties that comprise these programs have not been determined yet as these programs are either in the early stages of development or have not yet been identified. As a result, the Company is not currently eligible to receive any milestone payments under this arrangement.
	Concurrent with the execution of the license agreement, the not-for-profit entity also purchased 4,310,345 shares of the Company’s Series C Preferred Stock (Note 10).
	At the inception of the agreement, the Company evaluated whether each potential milestone payment that could be received from the not-for-profit entity for reimbursement of a portion of milestones owed to third parties from existing license agreements that could comprise these programs is substantive and at risk to both parties on the basis of the contingent nature of the milestone. The evaluation included an assessment of whether (a) the consideration is commensurate with either (i) the entity’s performance to achieve the milestone or (ii) the enhancement of the value of the delivered items as a result of a specific outcome resulting from the entity’s performance to achieve the milestone; (b) the consideration related solely to past performance; and (c) the consideration was reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated factors such as the scientific, regulatory, and other risks that must be overcome to achieve the respective milestone, the level of effort and investment required to achieve the respective milestone, and whether the milestone considerations are reasonable relative to all deliverables and payment terms in the arrangement in making this assessment. Substantive, at-risk milestones are recognized as revenue when the milestone is achieved.
	As there was no up-front consideration, there were no amounts to allocate to the various deliverables. The milestones under the arrangement related to reimbursement for milestone payments by the Company owed to third parties for existing license agreements that could comprise these programs are considered to be substantive and at risk and will be recognized when earned. Since the licenses from third parties that could comprise these programs have not been determined yet, the amount and timing of such milestones cannot be determined at this time.
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 (“ACS 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, 2014 and 2013, 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.
Net loss per share attributable to common stockholders
	Net loss per share attributable to common stockholders
	Basic net loss 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. During periods of income, the Company allocates participating securities a proportional share of income determined by dividing total weighted average participating securities by the sum of the total weighted average common shares and participating securities (the “two-class method”). The Company’s redeemable convertible preferred stock and restricted stock participate in any dividends declared by the Company and are therefore considered to be participating securities. Participating securities have the effect of diluting both basic and diluted earnings per share during periods of income. During periods of loss, the Company allocates no loss to participating securities because they have no contractual obligation to share in the losses of the Company. Diluted net loss 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 income or 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		Date of adoption	Effect on the financial statements or other significant matters
	Standards that are not yet adopted
	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.		January 1, 2017	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, and the Company is evaluating the effects of the new standard on this type of revenue.
	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.		January 1, 2017	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.
	Standards that were adopted
	ASU No. 2014-10, Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation (“ASU 2014-10”)		The standard eliminates the requirements for development stage entities to (1) present inception-to-date information in the statements of income, cash flows, and shareholder equity, (2) label the financial statements as those of a development stage entity, (3) disclose a description of the development stage activities in which the entity is engaged, and (4) disclose in the first year in which the entity is no longer a development stage entity that in prior years it had been in the development stage.		June 30, 2014	The Company adopted ASU 2014-10 on June 30, 2014, and the adoption did not have a material impact on its financial statements.
Subsequent events
	Subsequent events
	The Company considers events or transactions that occur after the balance sheet date but prior to the date the financial statements are issued for potential recognition or disclosure in the financial statements.

Summary_of_significant_account2

Summary of significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2014
Summary of significant accounting policies
Schedule of estimated useful lives of assets
	Asset	Estimated useful life
	Laboratory equipment	5 years
	Furniture and office equipment	5 years
	Computer equipment and software	3-5 years
	Leasehold improvements	Shorter of the useful life or remaining lease term
Schedule of recent accounting pronouncements
	Standard	Description	Date of adoption	Effect on the financial statements or other significant matters
	Standards that are not yet adopted
	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.	January 1, 2017	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, and the Company is evaluating the effects of the new standard on this type of revenue.
	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.	January 1, 2017	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.
	Standards that were adopted
	ASU No. 2014-10, Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation (“ASU 2014-10”)	The standard eliminates the requirements for development stage entities to (1) present inception-to-date information in the statements of income, cash flows, and shareholder equity, (2) label the financial statements as those of a development stage entity, (3) disclose a description of the development stage activities in which the entity is engaged, and (4) disclose in the first year in which the entity is no longer a development stage entity that in prior years it had been in the development stage.	June 30, 2014	The Company adopted ASU 2014-10 on June 30, 2014, and the adoption did not have a material impact on its financial statements.

Cash_and_cash_equivalents_and_

Cash and cash equivalents and marketable securities (Tables)	12 Months Ended
	Dec. 31, 2014
Schedule of marketable securities
	Marketable securities at December 31, 2014 consist of the following (in thousands):
		Contracted		Amortized			Unrealized			Unrealized			Fair Value
		Maturity		Cost			Gains			Losses
	Current
	U.S. Treasuries	166-365 days		$	27,028		$	—		$	(7	)	$	27,021
	Total			$	27,028		$	—		$	(7	)	$	27,021
Cash, cash equivalents and marketable securities
Schedule of cash, cash equivalents and marketable securities carried at fair value	The following table presents the cash, cash equivalents and marketable securities carried at fair value in accordance with the hierarchy defined in Note 2 (in thousands):
					Quoted prices			Significant			Significant
					in active			other			unobservable
					markets			observable			inputs
								inputs
		Total			(Level 1)			(Level 2)			(Level 3)
	December 31, 2014
	Cash	$	1,066		$	1,066		$	—		$	—
	Money Market funds, included in cash equivalents	18,992			18,992			—			—
	Marketable securities - U.S. treasuries	27,021			27,021			—			—
	Total	$	47,079		$	47,079		$	—		$	—
	December 31, 2013
	Cash	$	249		$	249		$	—		$	—
	Money Market funds, included in cash equivalents	11,959			11,959			—			—
	Total	$	12,208		$	12,208		$	—		$	—

Prepaid_expenses_and_other_cur1

Prepaid expenses and other current assets (Tables)	12 Months Ended
	Dec. 31, 2014
Prepaid expenses and other current assets
Schedule of prepaid expenses and other current assets
	Prepaid expenses and other current assets consist of the following (in thousands):
		December 31,
		2014		2013
	Prepaid tenant improvement costs	$	—	$	237
	Prepaid insurance	90		7
	Prepaid research and development costs	664		190
	Interest receivable	21		—
	Other	188		76
	Total	$	963	$	510

Property_and_equipment_net_Tab

Property and equipment, net (Tables)	12 Months Ended
	Dec. 31, 2014
Property and equipment, net
Schedule of property and equipment, net
	Property and equipment, net consist of the following (in thousands):
		December 31,
		2014			2013
	Laboratory equipment	$	2,510		$	1,694
	Furniture office equipment	186			14
	Computer equipment and software	257			142
	Leasehold improvements	799			344
	Total property and equipment	3,752			2,194
	Accumulated depreciation	(1,796		)	(1,329		)
	Property and equipment, net	$	1,956		$	865

Accrued_expenses_and_other_cur1

Accrued expenses and other current liabilities (Tables)	12 Months Ended
	Dec. 31, 2014
Accrued expenses and other current liabilities.
Schedule of accrued expenses and other current liabilities
	Accrued expenses and other current liabilities consisted of the following (in thousands):
		December 31,
		2014		2013
	Payroll and employee-related costs	$	1,066	$	738
	Research and development costs	1,117		323
	Accrued professional fees	270		303
	Other	33		54
	Total	$	2,486	$	1,418

Longterm_debt_Tables

Long-term debt (Tables)	12 Months Ended
	Dec. 31, 2014
Long-Term Debt
Schedule of future principal payments on the new term loan
	Future principal payments on the 2014 Term Loan are as follows (in thousands):
		December 31,
		2014
	2015	$	—
	2016	4,529
	2017	4,876
	2018	2,595
	Total	$	12,000

Warrants_Tables

Warrants (Tables)	12 Months Ended
	Dec. 31, 2014
Warrants
Schedule of warrants outstanding
	Warrants outstanding represent the right to acquire the following number of shares (in thousands):
		December 31,		December 31,
		2014		2013
	Warrants to purchase Series A Preferred Stock	—		1,085
	Warrants to purchase Series B Preferred Stock	—		517
	Warrants to purchase Series C Preferred Stock	—		690
	Warrants to purchase Common Stock	78		—
	Total	78		2,292
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,
		2014			2013		2012
	Beginning balance	$	656		$	246	$	339
	Warrants issued				188		—
	Change in fair value	725			222		(93		)
	Warrants exercised	(323		)	—		—
	Reclassification to accumulated paid-in capital	(1,058		)	—		—
	Ending balance	$	—		$	656	$	246
Common stock
Warrants
Schedule of weighted average assumptions used to calculate the fair value of warrants
		November 20,
		2014
	Fair value of underlying instrument	$	9.05
	Expected volatility	70.0		%
	Expected term (in years)	5.00
	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
		January 29,
		2014
	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
		February 4,
		2014
	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
		February 10,
		2014
	Fair value of underlying instrument	$	7.74
	Expected Volatility	50.81		%
	Expected term (in years)	0.003
	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
		February 10,
		2014
	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		%
Warrants to purchase redeemable securities
Warrants
Schedule of warrant to purchase redeemable securities liability measured at fair value
	The warrant to purchase redeemable securities liability measured at fair value as of December 31, 2013 is as follows (in thousands):
					Quoted		Significant			Significant
					prices in		other			unobservable
					active		observable			inputs
					markets		inputs
		Total			(Level 1)		(Level 2)			(Level 3)
	December 31, 2013
	Warrants to purchase redeemable securities	$	656		$	—	$	—		$	656
	Total	$	656		$	—	$	—		$	656

Commitments_and_contingencies_

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and contingencies
Schedule of minimum future lease payments under the operating leases
	As of December 31, 2014, the minimum future lease payments under the 2012 Master Facilities Lease are as follows (in thousands):
		Operating
		lease
	2015	$	976
	2016	1,012
	2017	170
	Total minimum lease payments	$	2,158
Schedule of restricted cash related to facilities leases
	Restricted cash related to facilities leases consisted of the following (in thousands):
		December 31,		December 31,
		2014		2013
	2012 Facilities Sublease	$	—	$	157
	2012 Master Facilities Lease	316		158
	Total	$	316	$	315

Common_stock_Tables

Common stock (Tables)	12 Months Ended
	Dec. 31, 2014
Common stock.
Schedule of shares of common stock reserved for future issuance
	The Company has reserved for future issuances the following number of shares of Common Stock (in thousands):
		December 31,	December 31,
		2014	2013
	Conversion of Seed Preferred Stock	—	388
	Conversion of Series A Preferred Stock	—	2,990
	Conversion of Series B Preferred Stock	—	3,613
	Conversion of Series C Preferred Stock	—	4,419
	Options to purchase Common Stock	2,373	1,823
	Options to purchase Common Stock under ESPP	185	—
	Warrants to purchase Series A Preferred Stock	—	91
	Warrants to purchase Series B Preferred Stock	—	43
	Warrants to purchase Series C Preferred Stock	—	58
	Warrants to purchase Common Stock	78	—
		2,636	13,425

Stockbased_compensation_Tables

Stock-based compensation (Tables)	12 Months Ended
	Dec. 31, 2014
Stock-based compensation
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,
		2014			2013			2012
	Research and development	$	1,511		$	322		$	102
	General and administrative	1,394			350			205
	Total	$	2,905		$	672		$	307
Schedule of stock option activity for employees and nonemployees
	The following table summarizes stock option activity for employees and nonemployees (shares in thousands):
							Weighted-
				Weighted-			Average
				Average			Remaining		Aggregate
				Exercise			Contractual		Intrinsic
		Shares		Price			Term (years)		Value
	Outstanding at December 31, 2013	1,576		$	2.66		7.64		$	6,682
	Granted	1,065		$	12.79
	Exercised	(282	)	$	2.42
	Canceled	(69	)	$	7.42
	Outstanding at December 31, 2014	2,290		$	7.26		8.08		$	5,332
	Exercisable at December 31, 2014	1,029		$	3.36		6.86		$	4,198
	Vested or expected to vest at December 31, 2014	2,078		$	6.98		7.99		$	5,123
Schedule of assumptions underlying common stock on each measurement date
		Years ended December 31,
		2014		2013		2012
	Expected Volatility	86.2%-103.6%		97.10%		99.20%
	Risk-free interest rate	1.75%-2.00%		0.59%-1.83%		0.99%
	Expected term (in years)	6.25		6.25		6.25
	Expected dividend yield	0%		0%		0%

Income_taxes_Tables

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income taxes
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 (in thousands):
		December 31,
		2014			2013
	Deferred tax assets:
	U.S and state net operating loss carryforwards	$	39,721		$	27,616
	Research and development credits	3,655			2,749
	Stock based compensation	770			369
	Purchased intangibles	245			269
	Capitalized organizational and start up expenditures	153			173
	Accruals and other temporary differences	659			478
	Total deferred tax assets	45,203			31,654
	Less valuation allowance	(45,203		)	(31,654		)
	Net deferred tax assets	$	—		$	—
Schedule of a reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes
		Years ended December 31,
		2014		2013		2012
	Federal income tax expense at statutory rate	34.0	%	34.0	%	34.0	%
	State income tax, net of federal benefit	4.6	%	5.1	%	6.8	%
	Permanent differences	(2.1	)%	(0.9	)%	(0.2	)%
	Research and development credit	1.8	%	3.6	%	0.0	%
	Other	0.1	%	0.0	%	0.0	%
	Change in valuation allowance	(38.4	)%	(41.8	)%	(40.6	)%
	Effective tax rate	0.0	%	0.0	%	0.0	%

Net_loss_per_share_attributabl1

Net loss per share attributable to common stockholders (Tables)	12 Months Ended
	Dec. 31, 2014
Net loss per share attributable to common stockholders
Schedule of common stock equivalents, presented on converted basis, were excluded from calculation of net loss per share due to anti-dilutive effect
	The following common stock equivalents, 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,
		2014	2013	2012
	Preferred stock	—	11,409	8,493
	Warrants	78	193	135
	Outstanding options	2,290	1,576	1,054
	Total	2,368	13,178	9,682

Quarterly_financial_informatio1

Quarterly financial information (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly financial information
Schedule of quarterly financial information
		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
		Three Months Ended,
		March 31, 2013			June 30, 2013			September 30, 2013			December 31, 2013
	Revenue	$	259		$	228		$	224		$	20
	Operating expenses	4,790			4,977			4,699			6,190
	Net loss	(4,664		)	(4,957		)	(4,839		)	(6,346		)
	Net loss per attributable to common stockholders	(5,059		)	(5,357		)	(5,244		)	(6,751		)
	Net loss per share attributable to common stockholders - basic and diluted	$	(17.09	)	$	(18.10	)	$	(17.72	)	$	(22.50	)
	Weighted-average number of common shares used in net loss per share attributable to common stockholders - basic and diluted	296			296			296			300

Organization_and_operations_De

Organization and operations (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
	product
Organization and operations
Number of products in clinical development	2
Accumulated deficit	$115,427,000	$80,131,000
Cash, cash equivalents and marketable securities	$47,100,000

Summary_of_significant_account3

Summary of significant accounting policies (Details) (USD $)	12 Months Ended	0 Months Ended
	Dec. 31, 2014	Feb. 10, 2014	Dec. 31, 2013
Initial Public Offering
Common stock, par value (in dollars per share)	$0.00		$0.00
Net proceeds of IPO excluding offering expenses payable	$59,974,000
Initial Public Offering
Initial Public Offering
Common stock, par value (in dollars per share)		$0.00
Issuance of common stock (in shares)		5,500,000
Initial public offering price (in dollars per share)		$12
Net proceeds of IPO excluding offering expenses payable		61,400,000
Offering expenses payable		$2,400,000
Number of shares of common stock after conversion of redeemable convertible preferred stock to common stock		11,466,479
Employee and nonemployee performance based options vested (in shares)		96,988

Summary_of_significant_account4

Summary of significant accounting policies (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	instrument
	segment
Segment information
Number of operating segments	1
Number of geographical segments	1
Cash, cash equivalents and investments in debt securities
Maximum maturity period for a highly liquid investment to be considered cash and cash equivalents	90 days
Minimum maturity period for marketable securities	90 days
Concentrations of credit risk and off-balance sheet risk
Number of financial instruments with off-balance sheet risk of loss	0
Deferred initial public offering costs
Public offering costs incurred in IPO		$2,400,000
Fair value of financial instruments
Transfers of financial assets between levels	0	0	0
Transfers of financial liabilities between levels	$0	$0	$0

Summary_of_significant_account5

Summary of significant accounting policies (Details 3)	12 Months Ended
	Dec. 31, 2014
Laboratory equipment
Property and equipment
Estimated useful life	5 years
Furniture and office equipment
Property and equipment
Estimated useful life	5 years
Computer equipment and software | Minimum
Property and equipment
Estimated useful life	3 years
Computer equipment and software | Maximum
Property and equipment
Estimated useful life	5 years

Summary_of_significant_account6

Summary of significant accounting policies (Details 4) (USD $)	0 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Jan. 20, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reverse stock split
Reverse stock split ratio	0.084034
Grant revenue
Revenue from grants recognized as research services performed		$308	$731	$1,977

Summary_of_significant_account7

Summary of significant accounting policies (Details 5) (USD $)	12 Months Ended			1 Months Ended	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Dec. 31, 2014
Grant revenue
Grant revenue	$308,000	$731,000	$1,977,000
Bill and Melinda Gates Foundation
Grant revenue
Grant received				1,200,000
Grant revenue					$308,000

Summary_of_significant_account8

Summary of significant accounting policies (Details 6) (License agreement, USD $)	12 Months Ended
	Dec. 31, 2014
License agreement
Amount of up-front consideration	$0
Amount allocated to various deliverables	$0
Series C Preferred Stock
License agreement
Preferred stock issued (in shares)	4,310,345

Summary_of_significant_account9

Summary of significant accounting policies (Details 7) (USD $)	12 Months Ended
	Dec. 31, 2014
Net loss per share attributable to common stockholders
Amount of allocation of loss to participating securities	$0

Cash_and_cash_equivalents_and_1

Cash and cash equivalents and marketable securities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Cash, cash equivalents and marketable securities
Total	$47,100
Recurring | Quoted prices in active markets (Level 1)
Cash, cash equivalents and marketable securities
Cash	1,066	249
Money Market funds, included in cash equivalents	18,992	11,959
Marketable securities - U.S. treasuries	27,021
Total	47,079	12,208
Recurring | Total
Cash, cash equivalents and marketable securities
Cash	1,066	249
Money Market funds, included in cash equivalents	18,992	11,959
Marketable securities - U.S. treasuries	27,021
Total	$47,079	$12,208

Cash_and_cash_equivalents_and_2

Cash and cash equivalents and marketable securities (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014
Marketable securities
Fair Value, Total	$27,021,000
U.S. Treasuries
Marketable securities
U.S. Treasuries (due 166-365 days) Amortized Cost	27,028,000
U.S. Treasuries (due 166-365 days) Unrealized Losses	-7,000
U.S. Treasuries (due 166-365 days) Fair Value	27,021,000
Amortized Cost, Total	27,028,000
Unrealized Losses, Total	-7,000
Fair Value, Total	27,021,000
Aggregate fair value of marketable securities in an unrealized loss position	24,000,000
Unrealized losses on marketable securities	8,000
Aggregate fair value of marketable securities in an unrealized gain position	3,000,000
Unrealized gains on marketable securities	$1,000
U.S. Treasuries | Minimum
Marketable securities
Contracted Maturity - U.S. Treasuries (due 166-365 days)	166 days
U.S. Treasuries | Maximum
Marketable securities
Contracted Maturity - U.S. Treasuries (due 166-365 days)	365 days

Prepaid_expenses_and_other_cur2

Prepaid expenses and other current assets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Prepaid expenses and other current assets
Prepaid tenant improvement costs		$237
Prepaid insurance	90	7
Prepaid research and development costs	664	190
Interest receivable	21
Other	188	76
Total	$963	$510

Property_and_equipment_net_Det

Property and equipment, net (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property and equipment, net
Total property and equipment	$3,752	$2,194
Accumulated depreciation	-1,796	-1,329
Property, Plant and Equipment, Net, Total	1,956	865
Depreciation expense	469	318	300
Cost basis of fixed assets sold	12
Net book value of fixed assets sold	10
Gain on sale of fixed assets	18
Laboratory equipment
Property and equipment, net
Total property and equipment	2,510	1,694
Furniture and office equipment
Property and equipment, net
Total property and equipment	186	14
Computer equipment and software
Property and equipment, net
Total property and equipment	257	142
Leasehold improvements
Property and equipment, net
Total property and equipment	$799	$344

Accrued_expenses_and_other_cur2

Accrued expenses and other current liabilities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Accrued expenses and other current liabilities.
Payroll and employee-related costs	$1,066	$738
Research and development costs	1,117	323
Accrued professional fees	270	303
Other	33	54
Total	$2,486	$1,418

Longterm_debt_Details

Long-term debt (Details) (USD $)	12 Months Ended			32 Months Ended	2 Months Ended	0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	1-May-12	Nov. 20, 2014	Sep. 30, 2013	Feb. 10, 2014	Mar. 01, 2012	Oct. 31, 2011	Dec. 19, 2013
				payment			payment
Long-Term Debt
Exercisable amount (in shares)	78,000	2,292,000		78,000
Repay indebtedness	$10,401,000	$4,245,000	$1,164,000
Loss on debt extinguishment	435,000	200,000
Warrants to purchase shares of series B preferred stock
Long-Term Debt
Exercisable amount (in shares)		517,000
Warrants to purchase shares of series C preferred stock
Long-Term Debt
Exercisable amount (in shares)		690,000
Common stock
Long-Term Debt
Exercisable amount (in shares)	78,000			78,000				105,297
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%
Number of monthly payments of principal and accrued interest				36
Period of monthly payments of principal and accrued interest				36 months
Percentage of advance payment on final repayment date				6.50%
Line of Credit | 2011 Term Loan | Warrants to purchase shares of series B preferred stock
Long-Term Debt
Exercisable amount (in shares)										517,242
Line of Credit | 2011 Term Loan | Common stock
Long-Term Debt
Number of shares that may be purchased by warrant	43,465			43,465
Exercise price of warrant (in dollars per share)	$6.90			6.9
Line of Credit | 2011 Term Loan | Prime rate
Long-Term Debt
Interest rate (as a percent)	8.00%			8.00%
Spread on variable rate basis (as a percent)				4.75%	5.00%
Line of Credit | 2013 Term Loan
Long-Term Debt
Debt financing							10,000,000
Draw downs							3,500,000
Remaining borrowing capacity											6,500,000
Interest rate (as a percent)							8.00%
Percentage of advance payment on final repayment date							2.00%
Number of shares that may be purchased by warrant	57,954			57,954
Repay indebtedness						9,800,000
Loss on debt extinguishment							200,000
Period of monthly payments of accrued interest							9 months
Number of payments of principal							33
Outstanding borrowings	0	10,000,000		0
Interest expense	813,000	124,000
Line of Credit | 2013 Term Loan | Other income / expense
Long-Term Debt
Loss on debt extinguishment						435,000
Line of Credit | 2013 Term Loan | Warrants to purchase shares of series C preferred stock
Long-Term Debt
Number of shares that may be purchased by warrant							689,655
Exercise price of warrant (in dollars per share)							$0.58
Line of Credit | 2013 Term Loan | Common stock
Long-Term Debt
Exercise price of warrant (in dollars per share)	$6.90			6.9
Line of Credit | 2014 Term Loan
Long-Term Debt
Debt financing						27,000,000
Extended term						6 months
Number of monthly payments of principal and accrued interest						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						100,000,000
Default of the Company's involving indebtedness causing an event of default, minimum						100,000,000
Debt discount						210,000
Outstanding borrowings	12,000,000			12,000,000
Interest expense	143,000,000	0
Line of Credit | 2014 Term Loan | Other current assets
Long-Term Debt
Financing costs						103,000
Line of Credit | 2014 Term Loan, First Tranche
Long-Term Debt
Debt financing						17,000,000
Draw downs						12,000,000
Line of Credit | 2014 Term Loan, Second Tranche
Long-Term Debt
Debt financing						5,000,000
Net proceeds from an equity financing and/or strategic corporate partnership, minimum						40,000,000
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
Hercules Technology Growth Capital, Inc. | Common stock
Long-Term Debt
Exercisable amount (in shares)						73,725
Warrant, exercisable, value						607,500
Exercise price of warrant (in dollars per share)						$8.24
Expected term						5 years
Private Placement
Long-Term Debt
Issuance of common stock	1,964,000
Private Placement | Common Stock
Long-Term Debt
Issuance of common stock	223,000
Private Placement | Hercules Technology Growth Capital, Inc.
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						$36,000,000
Private Placement | Hercules Technology Growth Capital, Inc. | Common Stock
Long-Term Debt
Issuance of common stock (in shares)						223,463

Longterm_debt_Details_2

Long-term debt (Details 2) (2014 Term Loan, Line of Credit, USD $)	Dec. 31, 2014
2014 Term Loan | Line of Credit
Future principal payments
2016	$4,529,000
2017	4,876,000
2018	2,595,000
Total	$12,000,000

Warrants_Details

Warrants (Details) (USD $)	0 Months Ended
	Apr. 23, 2014	Feb. 12, 2014	Feb. 10, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 29, 2014	Feb. 04, 2014
Warrants
Warrants (in shares)				78,000	2,292,000
Warrants					$656,000	$246,000	$339,000
Recurring | Significant unobservable inputs (Level 3)
Warrants
Warrants					656,000
Warrants to purchase redeemable convertible preferred stock
Warrants
Warrants (in shares)					2,291,512
Warrants to purchase redeemable convertible preferred stock | Recurring | Total
Warrants
Warrants					656,000
Warrants to purchase redeemable convertible preferred stock | Recurring | Total | Significant unobservable inputs (Level 3)
Warrants
Warrants					656,000
Warrants to purchase shares of series A preferred stock
Warrants
Warrants (in shares)					1,085,000
Warrants to purchase shares of series A preferred stock exercised, one
Warrants
Warrants (in shares)								21,695
Warrants to purchase shares of series A preferred stock exercised, one | Total
Warrants
Warrants								7,783
Warrants to purchase shares of series A preferred stock exercised, two
Warrants
Warrants (in shares)									28,926
Warrants to purchase shares of series A preferred stock exercised, two | Total
Warrants
Warrants									10,357
Warrants to purchase shares of series A preferred stock in cashless exercise
Warrants
Warrants (in shares)			987,840
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
Warrants to purchase shares of series A preferred stock in cashless exercise | Total
Warrants
Warrants			304,423
Warrants to purchase shares of series B preferred stock
Warrants
Warrants (in shares)					517,000
Warrants to purchase shares of series C preferred stock
Warrants
Warrants (in shares)					690,000
Warrants to purchase redeemable convertible preferred stock automatically converted to warrants to purchase common stock
Warrants
Warrants (in shares)			1,253,051	3,878
Common stock
Warrants
Warrants (in shares)			105,297	78,000
Common stock | Total
Warrants
Warrants			1,058,269

Warrants_Details_2

Warrants (Details 2) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Changes in the fair value of warrants to purchase redeemable securities, which represents a recurring measurement
Beginning balance	$656	$246	$339
Class of Warrant or Right, Warrants Issued, Amount		188
Change in fair value	725	222	-93
Warrants exercised	-323
Reclassification to accumulated paid-in capital	-1,058
Ending balance		$656	$246
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_Details_3

Warrants (Details 3) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 29, 2014	Feb. 04, 2014	Apr. 23, 2014	Feb. 12, 2014	Feb. 10, 2014	Nov. 20, 2014	Dec. 31, 2011
Warrants
Amount recognized in additional paid-in capital	$334,000
Warrants (in shares)	78,000	2,292,000
Warrants		656,000	246,000							339,000
Weighted average assumptions used to calculate the fair value of warrants
Change in fair value	725,000	222,000	-93,000
Warrants to purchase shares of series A preferred stock exercised, one
Warrants
Warrants (in shares)				21,695
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)				$0.65
Expected Volatility (as a percent)				55.57%
Expected term				15 days
Risk-free interest rate (as a percent)				1.52%
Expected dividend yield (as a percent)				0.00%
Change in fair value				2,142
Warrants to purchase shares of series A preferred stock exercised, one | Total
Warrants
Warrants				7,783
Warrants to purchase shares of series A preferred stock exercised, two
Warrants
Warrants (in shares)					28,926
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)					$0.65
Expected Volatility (as a percent)					55.03%
Expected term					7 days
Risk-free interest rate (as a percent)					1.46%
Expected dividend yield (as a percent)					0.00%
Change in fair value					2,839
Warrants to purchase shares of series A preferred stock exercised, two | Total
Warrants
Warrants					10,357
Warrants to purchase shares of series A preferred stock in cashless exercise
Warrants
Warrants (in shares)								987,840
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
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)								$7.74
Expected Volatility (as a percent)								50.81%
Expected term								1 day
Risk-free interest rate (as a percent)								1.48%
Expected dividend yield (as a percent)								0.00%
Change in fair value								46,581
Warrants to purchase shares of series A preferred stock in cashless exercise | Total
Warrants
Warrants								304,423
Common stock
Warrants
Warrants (in shares)	78,000							105,297
Weighted average assumptions used to calculate the fair value of warrants
Change in fair value								673,040
Common stock | Total
Warrants
Warrants								1,058,269
Common stock | Hercules Technology Growth Capital, Inc.
Warrants
Amount recognized in additional paid-in capital									334,000
Warrants (in shares)									73,725
Warrant, exercisable, value									$607,500
Exercise price of warrant (in dollars per share)									$8.24
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)									$9.05
Expected Volatility (as a percent)									70.00%
Expected term									5 years
Risk-free interest rate (as a percent)									1.64%
Expected dividend yield (as a percent)									0.00%
Warrants to purchase redeemable convertible preferred stock automatically converted to warrants to purchase common stock
Warrants
Warrants (in shares)	3,878							1,253,051
Weighted average assumptions used to calculate the fair value of warrants
Fair value of underlying instrument (in dollars per share)								$6.96
Expected Volatility (as a percent)								92.90%
Expected term								8 years 7 months 28 days
Risk-free interest rate (as a percent)								2.43%
Expected dividend yield (as a percent)								0.00%

Commitments_and_contingencies_1

Commitments and contingencies (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments and contingencies
Amount expensed related to supply agreements	$23,727	$15,695	$11,240
Agreement to license certain intellectual property | Harvard University
Commitments and contingencies
Annual maintenance fees and clinical milestones incurred	157	83	83
Agreement to license certain intellectual property | Novavax
Commitments and contingencies
Amount expensed related to supply agreements	402	0	290
Agreement to license certain intellectual property | University of Washington
Commitments and contingencies
Amount expensed related to supply agreements	$24	$45	$15

Commitments_and_contingencies_2

Commitments and contingencies (Details 2) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commitments and contingencies
Amount expensed related to supply agreements	$23,727	$15,695	$11,240
Supply agreement | Third party vendor
Commitments and contingencies
Amount expensed related to supply agreements	791	1,500	180,000
Supply agreement | Fujifilm
Commitments and contingencies
Amount expensed related to supply agreements	$3,500	$0	$0

Commitments_and_contingencies_3

Commitments and contingencies (Details 3) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Minimum future lease payments under operating leases
2015	$976
2016	1,012
2017	170
Total minimum lease payments	2,158
Rent expense	$803	$476	$1,100

Commitments_and_contingencies_4

Commitments and contingencies (Details 4) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Restricted cash related to facilities leases
Restricted cash	$316	$315
2012 Facilities Sublease
Restricted cash related to facilities leases
Restricted cash		157
2012 Master Facilities Lease
Restricted cash related to facilities leases
Restricted cash	$316	$158

Redeemable_convertible_preferr1

Redeemable convertible preferred stock (Details) (USD $)	0 Months Ended
	Feb. 10, 2014	Dec. 31, 2013	Dec. 31, 2014
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized		321,340,959
Initial Public Offering
Class of Stock [Line Items]
Number of shares of common stock after conversion of redeemable convertible preferred stock to common stock	11,466,479
Seed convertible preferred stock
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized		4,615,385	0
Redeemable convertible preferred stock, par value (in dollars per share)		0.001
Series A redeemable convertible preferred stock
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized		36,661,538	0
Redeemable convertible preferred stock, par value (in dollars per share)		0.001
Series B redeemable convertible preferred stock
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized		35,098,520	0
Redeemable convertible preferred stock, par value (in dollars per share)		0.001
Series C redeemable convertible preferred stock
Class of Stock [Line Items]
Redeemable convertible preferred stock, shares authorized		53,275,861	0
Redeemable convertible preferred stock, par value (in dollars per share)		0.001

Common_stock_Details

Common stock (Details) (USD $)	12 Months Ended	101 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
	director
	Vote
Common stock
Common stock, shares authorized	175,000,000	175,000,000
Common stock, par value (in dollars per share)	$0.00	$0.00	0.001
Common stock, shares issued	17,869,235	17,869,235	327,000
Common stock, shares outstanding	17,852,389	17,852,389	303,000
Number of vote for each share	1
Number of directors that can be elected by the common stockholders	1
Number of directors	8
Dividend declared	$0	$0
Dividend paid		$0
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance	2,636,000	2,636,000	13,425,000
Warrants to purchase shares of series A preferred stock
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance			91,000
Warrants to purchase shares of series B preferred stock
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance			43,000
Warrants to purchase shares of series C preferred stock
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance			58,000
Common stock
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance	78,000	78,000
Seed convertible preferred stock
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance			388,000
Series A redeemable convertible preferred stock
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance			2,990,000
Series B redeemable convertible preferred stock
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance			3,613,000
Series C redeemable convertible preferred stock
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance			4,419,000
Outstanding options
Common stock
Options exercised (in shares)	282,000
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance	2,373,000	2,373,000	1,823,000
Employee stock purchase plan
Shares of common stock reserved for future issuance
Total common shares reserved for future issuance	185,000	185,000
Restricted common stock
Common stock
Vesting period			4 years
Number of shares issued	35,964
Number of shares vested	19,124
Number of shares subject to repurchase by entity	16,840		24,615
Director | Outstanding options
Common stock
Options exercised (in shares)			31,092

Stockbased_compensation_Detail

Stock-based compensation (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 10, 2014
Stock-based compensation
Common shares that may be issued	2,636,000	13,425,000
Stock-based compensation expense	$2,905	$672	$307
Performance-based stock options
Stock-based compensation
Number of options probable to achieve performance-based milestones	96,988
Stock-based compensation expense	453
Options outstanding (in shares)	56,336
Employee stock purchase plan
Stock-based compensation
Common shares that may be issued	185,000
Outstanding options
Stock-based compensation
Common shares that may be issued	2,373,000	1,823,000
Options outstanding (in shares)	2,290,000	1,576,000
Stock options granted (in shares)	1,064,640	559,742	54,883
2014 Equity Plan
Stock-based compensation
Number of shares authorized	903,494
2014 Equity Plan | Maximum
Stock-based compensation
Percentage applied on total number of shares of common stock outstanding on previous calendar year for automatic inclusion in the plan	4.00%
2007 Equity Plan
Stock-based compensation
Number of shares available for grant				219,765
2007 Equity Plan | Outstanding options | Consultants and members of its Scientific Advisory Board
Stock-based compensation
Stock-based compensation expense	324	143	18
Vesting period	4 years
Term of exercising options from the date of grant	10 years
Stock options granted (in shares)		44,345	49,127
2007 Equity Plan and 2014 Equity Plan | Outstanding options
Stock-based compensation
Common shares that may be issued	2,373,348
Number of shares available for grant	0
2014 ESPP | Employee stock purchase plan
Stock-based compensation
Number of shares authorized				200,776
Stock-based compensation expense	$43
Option period	6 months

Stockbased_compensation_Detail1

Stock-based compensation (Details 2) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Based Compensation Expense
Stock-based compensation expense	$2,905	$672	$307
Research and development
Stock Based Compensation Expense
Stock-based compensation expense	1,511	322	102
General and administrative
Stock Based Compensation Expense
Stock-based compensation expense	$1,394	$350	$205

Stockbased_compensation_Detail2

Stock-based compensation (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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%	99.20%
Risk-free interest rate (as a percent)			0.99%
Expected term	6 years 3 months	6 years 3 months	6 years 3 months
Expected dividend yield (as a percent)	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)	86.20%
Risk-free interest rate (as a percent)	1.75%	0.59%
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)	103.60%
Risk-free interest rate (as a percent)	0.59%	1.83%
Outstanding options
Shares
Outstanding at the beginning of the period (in shares)	1,576,000
Granted (in shares)	1,064,640	559,742	54,883
Exercised (in shares)	-282,000
Canceled (in shares)	-69,000
Outstanding at the end of the period (in shares)	2,290,000	1,576,000
Exercisable at the end of the period (in shares)	1,029,000
Vested or expected to vest at the end of the period (in shares)	2,078,000
Weighted - Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	2.66
Granted (in dollars per share)	10.11	3.41	1.31
Exercised (in dollars per share)	2.4
Canceled (in dollars per share)	7.4
Outstanding at the end of the period (in dollars per share)	7.26	2.66
Exercisable at the end of the period (in dollars per share)	3.36
Vested or expected to vest at the end of the period (in dollars per share)	6.98
Weighted- Average Remaining Contractual Term
Outstanding at the end of the period	8 years 29 days	7 years 7 months 21 days
Exercisable at the end of the period	6 years 10 months 10 days
Vested or expected to vest at the end of the period	7 years 11 months 27 days
Aggregate Intrinsic Value
Outstanding at the beginning of the period (in dollars )	6,682,000
Exercised (in dollars)	3,100,000
Outstanding at the end of the period (in dollars )	5,332,000	6,682,000
Exercisable at the end of the period (in dollars )	4,198,000
Vested or expected to vest at the end of the period (in dollars )	5,123,000
Number of shares expected to vest upon the occurrence of the IPO	2,078,000
Expected term for recognition of unrecognized compensation cost	3 years 2 months 23 days
Employee stock options
Aggregate Intrinsic Value
Total unrecognized compensation cost	9,400,000
Non-employee Stock Option
Aggregate Intrinsic Value
Total unrecognized compensation cost	55,000

Stockbased_compensation_Detail3

Stock-based compensation (Details 4) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 10, 2014
Additional disclosures
Stock-based compensation expense	$2,905	$672	$307
Performance-based stock options
Additional disclosures
Number of options probable to achieve performance-based milestones	96,988
Stock-based compensation expense	453
Options outstanding (in shares)	56,336
Employee stock purchase plan | 2014 ESPP
Additional disclosures
Number of shares of common stock authorized under the plan				200,776
Option period	6 months
Shares remaining for future issuance (in shares)	185,154
Number of shares issued	15,622
Stock-based compensation expense	$43

401k_Savings_plan_Details

401(k) Savings plan (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2007
401(k) Savings plan
Contributions made by employer to the plan	$0	$0

Income_taxes_Details

Income taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets:
U.S and state net operating loss carryforwards	$39,721,000	$27,616,000
Research and development credits	3,655,000	2,749,000
Stock based compensation	770,000	369,000
Purchased intangibles	245,000	269,000
Capitalized organizational and start up expenditures	153,000	173,000
Accruals and other temporary differences	659,000	478,000
Total deferred tax assets	45,203,000	31,654,000
Less valuation allowance	-45,203,000	-31,654,000
Increase in valuation allowance	$13,400,000	$8,700,000
Reconciliation of income tax expense
Federal income tax expense at statutory rate (as a percent)	34.00%	34.00%	34.00%
State income tax, net of federal benefit (as a percent)	4.60%	5.10%	6.80%
Permanent differences (as a percent)	-2.10%	-0.90%	-0.20%
Research and development credit (as a percent)	1.80%	3.60%	0.00%
Other (as a percent)	0.10%	0.00%	0.00%
Change in valuation allowance (as a percent)	-38.40%	-41.80%	-40.60%
Effective tax rate (as a percent)	0.00%	0.00%	0.00%

Income_taxes_Details_2

Income taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2012
Income taxes
Unrecognized accrued interest or penalties related to uncertain tax positions	$0	$0	$0
Uncertain tax position	0	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	71,400,000	105,000,000	51,700,000
Deductions related to stock options		1,900,000
U.S. state
Income taxes
Net operating loss carryforwards	64,500,000	90,500,000	49,000,000
Deductions related to stock options		130,000
Research and development | U.S. federal
Income taxes
Tax credit carryforwards	1,900,000	2,600,000	1,200,000
Research and development | U.S. state
Income taxes
Tax credit carryforwards	$1,300,000	$1,700,000	$929,000

Net_loss_per_share_attributabl2

Net loss per share attributable to common stockholders (Details)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common stock equivalents, presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect
Common stock equivalents (in shares)	2,368	13,178	9,682
Preferred stock
Common stock equivalents, presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect
Common stock equivalents (in shares)		11,409	8,493
Warrants
Common stock equivalents, presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect
Common stock equivalents (in shares)	78	193	135
Outstanding options
Common stock equivalents, presented on an as converted basis, were excluded from the calculation of net loss per share for the periods presented, due to their anti-dilutive effect
Common stock equivalents (in shares)	2,290	1,576	1,054

Quarterly_financial_informatio2

Quarterly financial information (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly financial information
Revenue	$308				$20	$224	$228	$259
Operating expenses	11,234	8,958	6,909	6,373	6,190	4,699	4,977	4,790	33,474	20,656	14,930
Net loss	-11,650	-9,171	-7,146	-7,329	-6,346	-4,839	-4,957	-4,664	-35,296	-20,806	-13,367
Net loss attributable to common stockholders	($11,650)	($9,171)	($7,146)	($7,509)	($6,751)	($5,244)	($5,357)	($5,059)	($35,476)	($22,411)	($15,148)
Net loss per share attributable to common stockholders-basic and diluted (in dollars per share)	($0.66)	($0.53)	($0.41)	($0.76)	($22.50)	($17.72)	($18.10)	($17.09)	($2.27)	($75.46)	($51.35)
Weighted-average number of common shares used in net loss per share attributable to common stockholders - basic and diluted	17,696	17,465	17,346	9,859	300	296	296	296	15,618	297	295