Jounce Therapeutics (JNCE) 10-K 8 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Feb. 28, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	JOUNCE THERAPEUTICS, INC.
Entity Central Index Key	1,640,455
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Trading Symbol	JNCE
Entity Common Stock, Shares Outstanding		32,391,531
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 158,864,650

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 23,559	$ 44,848
Short-term investments	212,093	104,410
Prepaid expenses and other current assets	19,945	2,529
Total current assets	255,597	151,787
Property and equipment, net	16,151	7,241
Long-term investments	22,199	108,116
Other non-current assets	2,713	4,168
Total assets	296,660	271,312
Current liabilities:
Accounts payable	2,849	3,511
Accrued expenses	8,454	5,855
Deferred rent and lease incentive, current	61	720
Deferred revenue, current—related party	51,142	80,544
Other current liabilities	45	43
Total current liabilities	62,551	90,673
Deferred rent and lease incentive, net of current portion	1,955	1,452
Deferred revenue, net of current portion—related party	65,018	107,260
Other non-current liabilities	27	56
Total liabilities	129,551	199,441
Commitments and contingencies (Note 15)
Stockholders’ equity (deficit):
Preferred stock, $0.001 par value: 5,000 shares and no shares authorized at December 31, 2017 and 2016, respectively; no shares issued or outstanding at December 31, 2017 or 2016	0	0
Common stock, $0.001 par value: 160,000 shares and 29,810 shares authorized at December 31, 2017 and 2016, respectively; 32,265 and 2,518 shares issued at December 31, 2017 and 2016, respectively; 32,249 and 2,424 shares outstanding at December 31, 2017 and 2016, respectively	32	2
Additional paid-in capital	257,101	4,515
Accumulated other comprehensive loss	(409)	(433)
Accumulated deficit	(89,615)	(73,172)
Total stockholders’ equity (deficit)	167,109	(69,088)
Total liabilities, convertible preferred stock, contingently redeemable common stock and stockholders’ equity (deficit)	296,660	271,312
Series A Convertible Preferred Stock
Current liabilities:
Convertible preferred stock and contingently redeemable common stock	0	47,112
Series B Convertible Preferred Stock
Current liabilities:
Convertible preferred stock and contingently redeemable common stock	0	55,849
Series B-1 Convertible Preferred Stock
Current liabilities:
Convertible preferred stock and contingently redeemable common stock	0	36,077
Contingently Redeemable Common Stock
Current liabilities:
Convertible preferred stock and contingently redeemable common stock	$ 0	$ 1,921

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0
Preferred stock, shares authorized (in shares)	5,000,000	0
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	160,000,000	29,810,000
Common stock, shares issued (in shares)	32,265,000	2,518,000
Common stock, shares outstanding (in shares)	32,249,000	2,424,000
Series A Convertible Preferred Stock
Temporary equity, par value (in dollars per share)	$ 0.001	$ 0.001
Temporary equity, shares authorized (in shares)	0	47,000,000
Temporary equity, shares issued (in shares)	0	47,000,000
Temporary equity, shares outstanding (in shares)	0	47,000,000
Series B Convertible Preferred Stock
Temporary equity, par value (in dollars per share)	$ 0.001	$ 0.001
Temporary equity, shares authorized (in shares)	0	24,779,000
Temporary equity, shares issued (in shares)	0	24,779,000
Temporary equity, shares outstanding (in shares)	0	24,779,000
Series B-1 Convertible Preferred Stock
Temporary equity, par value (in dollars per share)	$ 0.001	$ 0.001
Temporary equity, shares authorized (in shares)	0	10,448,000
Temporary equity, shares issued (in shares)	0	10,448,000
Temporary equity, shares outstanding (in shares)	0	10,448,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Collaboration revenue—related party	$ 71,644	$ 37,197	$ 0
Operating expenses:
Research and development	67,798	34,904	22,130
General and administrative	23,061	16,759	8,266
Total operating expenses	90,859	51,663	30,396
Operating loss	(19,215)	(14,466)	(30,396)
Other income, net:
Other income, net	2,808	763	5
Other financing income, net	0	0	1,859
Total other income, net	2,808	763	1,864
Loss before provision for income taxes	(16,407)	(13,703)	(28,532)
Provision for income taxes	36	0	0
Net loss	(16,443)	(13,703)	(28,532)
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	(16,443)	(13,703)	(28,532)
Accretion of convertible preferred stock to redemption value	0	0	(1,011)
Loss on extinguishment of convertible preferred stock	0	0	(2,079)
Net loss attributable to common stockholders	$ (17,237)	$ (23,138)	$ (37,503)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.57)	$ (11)	$ (23.13)
Weighted-average common shares outstanding, basic and diluted (in shares)	30,055	2,103	1,621
Series A Convertible Preferred Stock
Reconciliation of net loss to net loss attributable to common stockholders:
Loss on extinguishment of convertible preferred stock			$ (2,100)
Accrued dividends on convertible preferred stock	$ (268)	$ (3,760)	(2,716)
Series B Convertible Preferred Stock
Reconciliation of net loss to net loss attributable to common stockholders:
Accrued dividends on convertible preferred stock	(318)	(4,460)	(3,165)
Series B-1 Convertible Preferred Stock
Reconciliation of net loss to net loss attributable to common stockholders:
Accrued dividends on convertible preferred stock	$ (208)	$ (1,215)	$ 0

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (16,443)	$ (13,703)	$ (28,532)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities	24	(433)	0
Comprehensive loss	$ (16,419)	$ (14,136)	$ (28,532)

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock, Contingently Redeemable Common Stock and Stockholders’ (Deficit) Equity - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock	Series B Convertible Preferred Stock	Series B-1 Convertible Preferred Stock	Contingently Redeemable Common Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2014		32,000,000	0	0
Beginning balance at Dec. 31, 2014		$ 27,313	$ 0	$ 0	$ 152
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of stock (in shares)		15,000,000	24,778,761
Issuance of stock		$ 14,984	$ 55,849
Reclassification of tranche rights upon issuance of preferred stock	$ 1,725	1,725
Stock-based compensation expense	849				503		$ 849
Accretion of preferred stock to redemption value		1,011
Extinguishment of Series A convertible preferred stock	(2,079)	$ 2,079							$ (2,079)
Ending balance (in shares) at Dec. 31, 2015		47,000,000	24,779,000	0
Ending balance at Dec. 31, 2015		$ 47,112	$ 55,849	$ 0	655
Beginning balance, common stock (in shares) at Dec. 31, 2014						1,414,000
Beginning balance at Dec. 31, 2014	(28,000)					$ 2	3	$ 0	(28,005)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)						6,000
Exercise of common stock options	3						3
Vesting of restricted common stock (in shares)						413,000
Vesting of restricted common stock	10						10
Stock-based compensation expense	849				503		849
Accretion of preferred stock to redemption value	(1,011)						(158)		(853)
Other comprehensive loss	0
Extinguishment of Series A convertible preferred stock	(2,079)	$ 2,079							(2,079)
Net loss	(28,532)
Ending balance, common stock (in shares) at Dec. 31, 2015						1,833,000
Ending balance at Dec. 31, 2015	(58,760)					$ 2	707	0	(59,469)
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of stock (in shares)				10,448,100
Issuance of stock				$ 36,077
Reclassification of tranche rights upon issuance of preferred stock	0
Stock-based compensation expense	3,723				1,266		3,723
Ending balance (in shares) at Dec. 31, 2016		47,000,000	24,779,000	10,448,000
Ending balance at Dec. 31, 2016		$ 47,112	$ 55,849	$ 36,077	1,921
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)						53,000
Exercise of common stock options	50						50
Vesting of restricted common stock (in shares)						538,000
Vesting of restricted common stock	35						35
Stock-based compensation expense	3,723				1,266		3,723
Other comprehensive loss	(433)							(433)
Net loss	$ (13,703)								(13,703)
Ending balance, common stock (in shares) at Dec. 31, 2016	2,424,000					2,424,000
Ending balance at Dec. 31, 2016	$ (69,088)					$ 2	4,515	(433)	(73,172)
Increase (Decrease) in Temporary Equity [Roll Forward]
Reclassification of tranche rights upon issuance of preferred stock	0
Conversion of convertible preferred stock into common stock upon closing of initial public offering (in shares)		(47,000,000)	(24,779,000)	(10,448,000)		22,284,000
Conversion of convertible preferred stock into common stock upon closing of initial public offering	139,038	$ (47,112)	$ (55,849)	$ (36,077)		$ 23	139,015
Reclassification of restricted stock awards upon termination of put option	2,191				(2,191)		2,191
Stock-based compensation expense	4,505				270		4,505
Ending balance (in shares) at Dec. 31, 2017		0	0	0
Ending balance at Dec. 31, 2017		$ 0	$ 0	$ 0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock (in shares)						7,320,000
Issuance of stock	106,388					$ 7	106,381
Conversion of convertible preferred stock into common stock upon closing of initial public offering (in shares)		(47,000,000)	(24,779,000)	(10,448,000)		22,284,000
Conversion of convertible preferred stock into common stock upon closing of initial public offering	139,038	$ (47,112)	$ (55,849)	$ (36,077)		$ 23	139,015
Reclassification of restricted stock awards upon termination of put option	$ 2,191				(2,191)		2,191
Exercise of common stock options (in shares)	144,000					144,000
Exercise of common stock options	$ 462						462
Vesting of restricted common stock (in shares)						77,000
Vesting of restricted common stock	32						32
Stock-based compensation expense	4,505				$ 270		4,505
Other comprehensive loss	24							24
Net loss	$ (16,443)								(16,443)
Ending balance, common stock (in shares) at Dec. 31, 2017	32,249,000					32,249,000
Ending balance at Dec. 31, 2017	$ 167,109					$ 32	$ 257,101	$ (409)	$ (89,615)

Consolidated Statements of Con7

Consolidated Statements of Convertible Preferred Stock, Contingently Redeemable Common Stock and Stockholders’ (Deficit) Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Common Stock
Issuance costs	$ 2,529
Series A Convertible Preferred Stock | Preferred Stock
Issuance costs			$ 16
Series B Convertible Preferred Stock | Preferred Stock
Issuance costs			$ 151
Series B-1 Convertible Preferred Stock | Preferred Stock
Issuance costs		$ 74

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net loss	$ (16,443)	$ (13,703)	$ (28,532)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Stock-based compensation expense	4,775	4,989	1,352
Depreciation expense	4,422	1,944	1,470
Change in other financing income, net	0	0	(1,859)
Net amortization of premiums and discounts on investments	1,172	327	0
Loss on disposal of property and equipment	75	0	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(17,416)	(1,979)	(23)
Other non-current assets	(16)	(527)	(99)
Accounts payable	373	(312)	673
Accrued expenses and other current liabilities	4,120	953	1,929
Deferred revenue—related party	(71,644)	187,804	0
Other non-current liabilities	0	0	(28)
Deferred rent	(156)	192	(622)
Net cash (used in) provided by operating activities	(90,738)	179,688	(25,739)
Investing activities:
Purchases of investments	(179,874)	(213,286)	0
Proceeds from maturities of investments	141,322	0	0
Proceeds from sales of investments	15,638	0	0
Purchases of property and equipment	(15,107)	(2,222)	(2,202)
Change in restricted cash	0	0	60
Net cash used in investing activities	(38,021)	(215,508)	(2,142)
Financing activities:
Proceeds from initial public offering of common stock, net of issuance costs	107,008	0	0
Proceeds from exercise of stock options and purchases of restricted stock	462	50	112
Cash paid for issuance costs	0	(620)	(241)
Net cash provided by financing activities	107,470	35,507	70,704
Net (decrease) increase in cash and cash equivalents	(21,289)	(313)	42,823
Cash and cash equivalents, beginning of period	44,848	45,161	2,338
Cash and cash equivalents, end of period	23,559	44,848	45,161
Non-cash investing and financing activities:
Accretion of convertible preferred stock to redemption value	0	0	1,011
Reclassification of tranche rights upon issuance of preferred stock	0	0	1,725
Purchases of property and equipment in accounts payable and accrued expenses	170	1,870	22
Issuance costs in accounts payable and accrued expenses	0	850	1,580
Supplemental cash flow information:
Cash paid for income taxes	16,750	0	0
Convertible preferred stock (Series A)
Financing activities:
Proceeds from the issuance of convertible preferred stock, net of issuance costs	0	0	14,984
Non-cash investing and financing activities:
Reclassification of tranche rights upon issuance of preferred stock			1,725
Series B Convertible Preferred Stock
Financing activities:
Proceeds from the issuance of convertible preferred stock, net of issuance costs	0	0	55,849
Cash paid for issuance costs			(200)
Series B-1 Convertible Preferred Stock
Financing activities:
Proceeds from the issuance of convertible preferred stock, net of issuance costs	$ 0	36,077	$ 0
Cash paid for issuance costs		$ (100)

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business	Nature of Business Jounce Therapeutics, Inc. (the “Company”) is a clinical stage immunotherapy company dedicated to transforming the treatment of cancer by developing therapies that enable the immune system to attack tumors and provide long-lasting benefits to patients. The Company is subject to a number of risks similar to those of other clinical stage immunotherapy companies, including dependence on key individuals; the need to develop commercially viable products; competition from other companies, many of which are larger and better capitalized; and the need to obtain adequate additional financing to fund the development of its products. The Company’s most advanced product candidate, JTX-2011, is a clinical-stage monoclonal antibody that binds to and activates the I nducible T cell CO-S timulator, or ICOS, a protein on the surface of certain T cells commonly found in many solid tumors. The Company submitted an Investigational New Drug Application for JTX-2011 to the Food and Drug Administration in July 2016 and began the Phase I portion of its JTX-2011 adaptive Phase I/II clinical trial in patients with solid tumors in August 2016. In June 2017, the Company presented preliminary safety, pharmacodynamic and pharmacokinetic data from the Phase I portion of this clinical trial as well as the recommended dose for the Phase II monotherapy cohorts at the 2017 American Society of Clinical Oncology Annual Meeting. In April 2017, the Company began the monotherapy cohorts of the Phase II portion of this clinical trial, which evaluate JTX-2011 as a monotherapy in at least three tumor-specific cohorts, including head and neck squamous cell cancer (“HNSCC”), non-small cell lung cancer (“NSCLC”), gastric cancer, non-indication specific solid tumors and additional tumor types identified through its Translational Science Platform. In July 2017, the Company began the combination cohorts of the Phase II portion of this clinical trial, which evaluate JTX-2011 in combination with nivolumab in at least six tumor types, including HNSCC, NSCLC, triple negative breast cancer, melanoma, gastric cancer and additional tumor types identified through its Translational Science Platform. The Company expects to provide preliminary efficacy data in the second quarter of 2018. On February 1, 2017, the Company closed its initial public offering (“IPO”) of 7,319,750 shares of the Company’s common stock at a public offering price of $16.00 per share, including 954,750 shares of common stock issued upon the full exercise by the underwriters of their option to purchase additional shares. The gross proceeds from the IPO were $117.1 million and net proceeds were $106.4 million , after deducting underwriting discounts and commissions and other offering expenses paid by the Company. Upon completion of the IPO, all outstanding preferred stock was automatically converted into an aggregate of 22,283,690 shares of common stock. In connection with the IPO, the board of directors and the stockholders of the Company approved a one-for-3.69 reverse stock split of the Company’s issued and outstanding common stock. The reverse stock split became effective on January 13, 2017. All share and per share amounts in the consolidated financial statements have been retroactively adjusted for all periods presented to give effect to the reverse stock split, including reclassifying an amount equal to the reduction in par value to additional paid-in capital. The Company has incurred losses in each annual period since its inception and had an accumulated deficit of $89.6 million as of December 31, 2017 . The Company expects to continue to incur significant losses for the foreseeable future. As of December 31, 2017 , the Company had cash, cash equivalents, and investments of $257.9 million . The Company expects that its existing cash, cash equivalents, and investments will enable it to fund its expected operating expenses and capital expenditure requirements for at least 24 months from March 8, 2018 , the filing date of this Annual Report on Form 10-K. The Company expects to finance its future cash needs through a combination of equity or debt financings and collaboration arrangements, including cash inflows from its Master Research and Collaboration Agreement (the “Celgene Collaboration Agreement”) with Celgene Corporation (“Celgene”).

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Consolidation The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”) and include the accounts of Jounce Therapeutics, Inc. and its wholly-owned subsidiary, Jounce Mass Securities, Inc., which was established in July 2016. All intercompany transactions and balances have been eliminated in consolidation. 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 in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s chief executive officer, views the Company’s operations and manages its business as a single operating segment. The Company operates only in the United States. Use of Estimates 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 the period of performance for units of accounting identified under the Celgene Collaboration Agreement, accrued research and development expenses, stock-based compensation and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. Actual results could differ from those estimates. Prior to the completion of the IPO, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company determined the estimated fair value of its common stock based on 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 its convertible preferred stock and the superior rights and preferences of the convertible preferred stock in relation to the Company’s common stock. The Company utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants (“AICPA”) Audit and Accounting Practice Aid Series: Valuation of Privately Held Company Equity Securities Issued as Compensation ( the “AICPA Practice Aid”) to estimate the fair value of its common stock. These methodologies included the option pricing method utilizing the backsolve method, which is a form of the market approach defined in the AICPA Practice Aid, and the probability-weighted expected return method based upon the probability of occurrence of certain future liquidity events such as an IPO or sale of the Company. Each valuation methodology included estimates and assumptions that required the Company’s judgment. Significant changes to the key assumptions used in the valuations could have resulted in different fair values of the Company’s common stock at each valuation date. Fair Value of Financial Instruments Accounting Standards Codification (“ASC”) 820, Fair Value Measurement , establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability 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 asset or liability, and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. • Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. To the extent that the 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. Cash Equivalents Cash equivalents are highly-liquid investments that are readily convertible into cash with original maturities of three months or less when purchased. These assets include investment in money market funds that invests in U.S. Treasury obligations. Investments Short-term investments consist of investments with maturities greater than ninety days and less than one year from the balance sheet date. Long-term investments consist of investments with maturities of greater than one year that are not expected to be used to fund current operations. The Company classifies all of its investments as available-for-sale securities. Accordingly, these investments are recorded at fair value. Realized gains and losses, amortization and accretion of discounts and premiums are included in other income, net. Unrealized gains and losses on available-for-sale securities are included in other comprehensive income (loss) as a component of stockholders’ equity (deficit) until realized. Restricted Cash Restricted cash as of December 31, 2017 and 2016 is comprised of amounts held as security deposits in the form of letters of credit for the Company’s leased facilities. If restrictions are expected to be lifted within the next twelve months, the restricted cash account is classified as current. Property and Equipment, Net Property and equipment is recorded at cost and consists of laboratory equipment, furniture and office equipment, computer equipment, leasehold improvements, and construction in progress. The Company capitalizes property and equipment that is acquired for research and development activities and that has alternate future use. Expenditures for maintenance and repairs are recorded to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. Leasehold improvements are depreciated over the lesser of their useful life or the term of the lease. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method. Impairment of Long-lived Assets The Company reviews its property and equipment whenever events or changes in circumstances indicate that the carrying value of certain assets might not be recoverable and recognizes an impairment loss when it is probable that an asset’s realizable value is less than the carrying value. Deferred Financing Costs The Company capitalizes deferred financing costs, which primarily consists of direct, incremental legal and accounting fees relating to the Company’s financing activities, within other non-current assets. Deferred financing costs are typically offset against financing proceeds received upon the consummation of an offering. As of the December 31, 2016, the Company had capitalized $1.5 million in deferred financing costs related to its IPO. These deferred financing costs were subsequently reclassified to stockholders’ equity (deficit) upon the completion of the IPO in February 2017. Revenue Recognition The Company recognizes revenue in accordance with ASC 605, Revenue Recognition . Accordingly, revenue is recognized when all of the following criteria are met: • persuasive evidence of an arrangement exists; • delivery has occurred or services have been rendered; • the seller’s price to the buyer is fixed or determinable; and • collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria are recognized as deferred revenue in the Company’s consolidated balance sheets. Amounts expected to be recognized as revenue within the twelve months following the balance sheet date are classified as deferred revenue, current. Amounts not expected to be recognized as revenue within the twelve months following the balance sheet date are classified as deferred revenue, net of current portion. Multiple-Element Arrangements Determination of Units of Accounting When evaluating multiple-element arrangements pursuant to ASC 605-25, Revenue Recognition—Multiple-Element Arrangements , the Company considers whether the deliverables under the arrangement represent separate units of accounting. This evaluation requires subjective determinations and requires management to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. In determining the units of accounting, management evaluates certain criteria, including whether the deliverables have standalone value, based on the consideration of the relevant facts and circumstances for each arrangement. The consideration received is allocated among the separate units of accounting using the relative selling price method, and the applicable revenue recognition criteria are applied to each of the separate units. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer on a standalone basis and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in the control of the Company. In assessing whether an item has standalone value, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can use the deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable is dependent on the undelivered item(s) and whether there are other vendors that can provide the undelivered element(s). Under multiple-element arrangements, options are considered substantive if, at the inception of the arrangement, the Company is at risk as to whether the collaboration partner will choose to exercise the option. Factors that the Company considers in evaluating whether an option is substantive include the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option, the likelihood the option will be exercised, and the cost to exercise the option. When an option is considered substantive, the Company does not consider the option or item underlying the option to be a deliverable at the inception of the arrangement and the associated option fees are not included in the allocable arrangement consideration, assuming the option is not priced at a significant and incremental discount. When an option is not considered substantive, the Company would consider the option, including other deliverables contingent upon the exercise of the option, to be a deliverable at the inception of the arrangement and a corresponding amount would be included in the allocable arrangement consideration. In addition, if the price of the option includes a significant incremental discount, the discount inherent in the option price would be included as a deliverable at the inception of the arrangement. Allocation of Arrangement Consideration Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. Then, the applicable revenue recognition criteria in ASC 605-25 are applied to each of the separate units of accounting in determining the appropriate period and pattern of recognition. The Company determines the selling price of a unit of accounting following the hierarchy of evidence prescribed by ASC 605-25. Accordingly, the Company determines the estimated selling price for units of accounting within each arrangement using vendor-specific objective evidence (“VSOE”) of selling price, if available, third-party evidence (“TPE”) of selling price if VSOE is not available, or best estimate of selling price (“BESP”) if neither VSOE nor TPE is available. The Company typically uses BESP to estimate the selling price, since it generally does not have VSOE or TPE of selling price for its units of accounting. Determining the BESP for a unit of accounting requires significant judgment. In developing the BESP for a unit of accounting, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP will have a significant effect on the allocation of arrangement consideration between multiple units of accounting. Patterns of Recognition The Company recognizes arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 are satisfied for that particular unit of accounting. The Company recognizes revenue associated with substantive options upon exercise of the option if the underlying license has standalone value from the other deliverables to be provided subsequent to delivery of the license. If the license does not have standalone value, the amounts allocated to the license option will be combined with the related undelivered items as a single unit of accounting. The Company recognizes the revenue amounts associated with research and development services and other service related deliverables ratably over the associated period of performance. If there is no discernible pattern of performance or objectively measurable performance measures do not exist, then the Company recognizes revenue under the arrangement on a straight-line basis over the period the Company is expected to complete its performance obligations. If the pattern of performance in which the service is provided to the customer can be determined and objectively measurable performance exists, then the Company recognizes revenue under the arrangement using the proportional performance method. Revenue recognized is limited to the lesser of the cumulative amount of payments received and the cumulative amount of revenue earned, as determined using the straight-line method or proportional performance, as applicable, as of each reporting period. Recognition of Milestones and Royalties At the inception of an arrangement that includes milestone payments, the Company evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluates factors such as clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. In accordance with ASC 605-28, Revenue Recognition—Milestone Method , clinical and regulatory milestones that are considered substantive, recognized as revenue in their entirety upon successful accomplishment of the milestone, assuming all other revenue recognition criteria are met. Milestones that are not considered substantive are recognized as revenue over the remaining period of performance, assuming all other revenue recognition criteria are met. Revenue from commercial milestones payments are recorded as revenue upon achievement of the milestone, assuming all other recognition criteria are met. Research and Development Expenses Expenditures relating to research and development are expensed as incurred. Research and development expenses include external expenses incurred under arrangements with third parties, academic and non-profit institutions and consultants; salaries and personnel-related costs, including non-cash stock-based compensation expense; license fees to acquire in-process technology and other expenses, which include direct and allocated expenses for laboratory, facilities and other costs. Intellectual Property Expenses The Company expenses costs associated with intellectual property-related matters as incurred and classifies such costs as general and administrative expenses within the consolidated statements of operations. Stock-based Compensation The Company accounts for share-based payments in accordance with ASC 718, Compensation—Stock Compensation. ASC 718 requires all share-based payments to employees, including grants of employee stock options and restricted stock awards, to be recognized as expense in the consolidated statements of operations based on their grant date fair values. For stock options granted to employees and to members of the Company’s Board of Directors for their services on the Board of Directors, the Company estimates the grant date fair value of each stock option using the Black-Scholes option-pricing model. For restricted stock awards granted to employees, the Company estimates the grant date fair value of each award using intrinsic value, which is based on the value of the underlying common stock less any purchase price. For share-based payments subject to service-based vesting conditions, the Company recognizes stock-based compensation expense equal to the grant date fair value of share-based payment on a straight-line basis over the requisite service period. In accordance with the provisions of ASC 505-50, Equity-Based Payments to Non-Employees , share-based payments issued to non-employees are initially recorded at their grant date fair values, remeasured at each reporting date as they vest and expensed over the related service period. The Black‑Scholes option pricing model requires the input of certain subjective assumptions, including (i) the calculation of expected term of the share-based payment, (ii) the risk‑free interest rate, (iii) the expected stock price volatility and (iv) the expected dividend yield. The Company uses the simplified method as proscribed by SEC Staff Accounting Bulletin No. 107 to calculate the expected term for stock options granted to employees as the Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The Company determines the risk‑free interest rate based on a treasury instrument whose term is consistent with the expected term of the stock options. Because there had been no public market for the Company’s common stock prior to the IPO, there is a lack of Company‑specific historical and implied volatility data. Accordingly, the Company bases its estimates of expected volatility on the historical volatility of a group of publicly-traded companies with similar characteristics to itself, including stage of product development and therapeutic focus within the life sciences industry. Historical volatility is calculated over a period of time commensurate with the expected term of the share-based payment. The Company uses an assumed dividend yield of zero as the Company has never paid dividends on its common stock, nor does it expect to pay dividends on its common stock in the foreseeable future. The Company utilizes similar Black-Scholes option-pricing model assumptions to value share-based payments issued to non-employees, except the contractual term of the share-based payment is utilized as the basis for the expected term assumption. For share-based payments subject to performance-based vesting conditions, the Company records stock-based compensation expense over the remaining service period when it determines that achievement of the performance condition is probable. The Company evaluates whether the achievement of a performance-based milestone is probable based on the expected satisfaction of the performance conditions as of the reporting date. Stock-based compensation expense for awards subject to performance-based vesting conditions is recognized using the accelerated attribution method. The Company accounts for forfeitures of all share-based payments when such forfeitures occur. Income Taxes Income taxes are recorded in accordance with ASC 740, Income Taxes , which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. A valuation allowance against deferred tax assets is recorded if, based on the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions using a more-likely-than-not threshold for recognizing and resolving uncertain tax positions. The evaluation of uncertain tax positions is based on factors, including, but not limited to, changes in the law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, new audit activity and changes in facts or circumstances related to a tax position. Comprehensive Loss Comprehensive loss is comprised of net loss and other comprehensive income (loss). Other comprehensive income (loss) for all periods presented consists solely of unrealized gain (loss) on available-for-sale securities. Net Loss per Share Basic net loss per share is calculated by dividing net loss attributable to common stockholders by the weighted average number of share common shares outstanding during the period. Diluted net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common equivalent shares outstanding for the period, including any dilutive effect from convertible preferred stock, outstanding stock options or unvested restricted common stock. The Company follows the two-class method when computing net loss per share for periods when issued shares that meet the definition of participating securities are outstanding. The two-class method calls for the calculation of net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders to be allocated between common and participating securities based upon their respective rights to received dividends as if all income for the period had been distributed. Net losses are not allocated to the Company’s preferred stockholders as they do not have an obligation to share in the Company’s net losses. Concentrations of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially expose the Company to concentrations of credit risk primarily consist of cash, cash equivalents and investments. The Company maintains its cash and cash equivalent balances with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. The Company’s cash equivalents and investments are comprised of money market funds that are invested in U.S. Treasury obligations, corporate debt securities, U.S. Treasury obligations and government agency securities. Credit risk in these securities is reduced as a result of the Company’s investment policy to limit the amount invested in any single issuer and to only invest in securities of a high credit quality. The Company has no significant off-balance sheet risk such as foreign exchange contracts, option contracts or other foreign hedging arrangements. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) , which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. This guidance was originally effective for interim and annual periods beginning after December 15, 2016 and allowed for adoption using a full retrospective method, or a modified retrospective method. Early adoption was originally not permitted. Subsequent to the issuance of ASU 2014-09, the FASB also issued the following updates related to ASC 606, Revenue from Contracts with Customers : • In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, whereby the effective date for the new revenue standard was deferred by one year. As a result of ASU 2015-14, the new revenue standard is now effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017, and early adoption is now permitted for annual periods beginning after December 15, 2016, including interim periods within that annual period. • In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net), to clarify the implementation guidance on principal versus agent considerations. • In April 2016, the FASB issued ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, to clarify the principle for determining whether a good or service is “separately identifiable” from other promises in the contract and to clarify the categorization of licenses of intellectual property. • In May 2016, the FASB issued ASU 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Technical Expedients, to clarify guidance on transition, determining collectability, non-cash consideration and the presentation of sales and other similar taxes. • In December 2016, the FASB issued ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, that allows entities not to make qualitative disclosures about remaining performance obligations in certain cases, adds disclosure requirements for entities that elect certain optional exemptions and adds twelve additional technical corrections and improvements to the new revenue standard. The Company will adopt ASC 606 effective January 1, 2018 under the modified retrospective method. The modified retrospective method requires that the cumulative effect of initially applying ASC 606 be recognized as an adjustment to the opening balance of retained earnings or accumulated deficit of the annual period that includes the date of initial application. Accordingly, during the first quarter of 2018, the Company currently expects to record an increase to the opening balance of accumulated deficit and a corresponding increase to deferred revenue. This cumulative adjustment is primarily attributable to the transition from recognizing revenue on a straight-line basis over the estimated performance period for each unit of accounting under ASC 605 to recognizing revenue on a proportional performance basis under ASC 606. As part of the adoption of ASC 606, the Company has implemented new processes to objectively measure the performance under the Celgene Collaboration Agreement. The Company will complete these processes in the first quarter of 2018, upon adoption of the new standard. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) , which requires a lessee to recognize assets and liabilities on the balance sheet for operating leases and changes many key definitions, including the definition of a lease. The new standard includes a short-term lease exception for leases with a term of 12 months or less, as part of which a lessee can make an accounting policy election not to recognize lease assets and lease liabilities. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases using classification criteria that are substantially similar to the previous guidance. The new standard will be effective beginning January 1, 2019, and early adoption is permitted for public entities. The Company is currently evaluating the potential impact that ASU 2016-02 may have on the consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . The new standard identifies areas for simplification involving several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, an option to recognize gross stock-based compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the consolidated statements of cash flows. The Company adopted ASU 2016-09 effective January 1, 2017, and the Company has elected to apply the simplification guidance related to the accounting for forfeitures. Accordingly, the Company will recognize gross stock-based compensation expense with actual forfeitures recognized as they occur. This simplification guidance related to the accounting for forfeitures is applied using a modified retrospective transition method. As forfeitures previously estimated by the Company through the year ended December 31, 2016 were not material, there was not a material cumulative-effect adjustment to accumulated deficit upon adoption of this guidance. The adoption of ASU 2016-09 also requires all excess tax benefits and tax deficiencies related to share-based payments to be recorded in the consolidated statements of operations. The adoption of ASU 2016-09 did not have a material impact on the Company’s consolidated financial statements as the increase in net deferred tax assets is offset by a corresponding increase in the deferred tax asset valuation allowance. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments , which is intended to reduce diversity in practice in how entities present certain types of cash transactions in the statement of cash flows. This guidance also clarifies how the predominance principle should be applied when classifying cash receipts and cash payments that have attributes of more than one class of cash flows. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and early adoption is permitted. An entity that elects early adoption must adopt all of the am

Celgene Collaboration Agreement

Celgene Collaboration Agreement	12 Months Ended
	Dec. 31, 2017
Research and Development [Abstract]
Celgene Collaboration Agreement	Celgene Collaboration Agreement In July 2016, the Company entered into the Celgene Collaboration Agreement. The primary goal of the collaboration is to co-develop and co-commercialize innovative biologic immunotherapies that either activate or suppress the immune system by binding to targets identified by leveraging the Company’s Translational Science Platform. Under the Celgene Collaboration Agreement, the Company granted Celgene exclusive options to develop and commercialize the Company’s lead product candidate, JTX-2011, and up to four early-stage programs, consisting of targets to be selected from a pool of certain B cell, T regulatory cell and tumor-associated macrophage targets. Additionally, Celgene has an exclusive option to develop and commercialize the Company’s product candidate JTX-4014, which, upon exercise of such option, will be a shared program that may be used by both parties in and outside of the collaboration. Prior to Celgene exercising any of its options, the Company is responsible for all research and development activities under the Celgene Collaboration Agreement. The Company received a non-refundable upfront cash payment of $225.0 million upon the execution of the Celgene Collaboration Agreement. The Company also received $36.1 million from the sale of 10,448,100 shares of Series B-1 convertible preferred stock (“Series B-1 Preferred Stock”) upon the execution of a Series B-1 Preferred Stock Purchase Agreement with Celgene, which shares converted into 2,831,463 shares of common stock upon the completion of the IPO. If Celgene elects to exercise any of the program options, Celgene will pay the Company an option-exercise fee of $10.0 million to $60.0 million that varies by program, with an aggregate of $182.5 million if Celgene exercises all six program options. The initial research term of the collaboration is four years, which can be extended, at Celgene’s option, annually for up to three additional years for additional consideration that ranges from $30.0 million to $45.0 million per year, for an aggregate of $120.0 million if the term is extended for an additional three years. Worldwide Development Cost and U.S. Operating Profit and Loss Sharing Upon the exercise of each program option, the parties will enter into a co-development and co-commercialization agreement (“Co-Co Agreements”) or, in the case of JTX-4014, a license agreement (“JTX-4014 License Agreement”) that governs the development and commercialization of the applicable program. Although the agreements will not be executed unless and until Celgene exercises an option, the parties have agreed to the terms of the Co-Co Agreements and the JTX-4014 License Agreement as part of the Celgene Collaboration Agreement. Under the Co-Co Agreements and the JTX-4014 License Agreement, the Company will share with Celgene the U.S. profits or losses and development costs on such collaboration program as follows: • The Company will retain 60 percent of the U.S. operating profits or losses arising from commercialization of JTX-2011, with 40 percent allocated to Celgene. • The Company will retain 25 percent of the U.S. operating profits or losses arising from commercialization of the first program (the “Lead Program”), other than JTX-2011 or JTX-4014, for which an IND application is filed under the collaboration, with 75 percent allocated to Celgene. Celgene has a one-time right to substitute and swap the economics and governance of this program with that of another program for which it exercises an option (other than JTX-2011 and JTX-4014). • The Company and Celgene will equally share U.S. operating profits or losses arising from commercialization of up to three additional programs (other than JTX-2011, JTX-4014 or the Lead Program) (the “Other Programs”). • The Company and Celgene will share all development costs, other than for JTX-4014, in accordance with the applicable Co-Co Agreements, of which Celgene’s portion of the costs range from 67 percent to 85 percent. If Celgene exercises its option for a program other than JTX-4014, the Company will enter into a Co-Co Agreement, pursuant to which Celgene will have the exclusive right to develop and commercialize the products arising out of such collaboration program outside of the United States, and the Company will be eligible to receive tiered royalties ranging from a high single digit to mid-teen percentage rate on net product sales outside of the United States. Under each Co-Co Agreement, the Company will also have the right to opt out of profit sharing and instead receive milestones and royalties. Furthermore, if Celgene exercises its option for JTX-4014, the Company will enter into the JTX-4014 License Agreement, pursuant to which Celgene and the Company will each have equal rights to develop and commercialize JTX-4014 in combination with other proprietary molecules in their or the Company’s respective pipelines or in combination with products arising out of collaboration programs. Subject to terms specified in the license agreement for JTX-4014, the party owning the proprietary molecule that is combined with JTX-4014, if such molecule does not arise from a collaboration program with Celgene, will be solely responsible for all development and commercialization costs related to such combination. If JTX-4014 is combined with a product arising from a collaboration program, then the parties will share costs and, if co-packaged or co-formulated, profits or losses in accordance with the Co-Co Agreements for such other product. Milestones and Royalties Under the Co-Co Agreements and the JTX-4014 License Agreement, Celgene is required to pay the Company for specified development, regulatory and commercial milestones, if achieved, up to approximately $2.3 billion , across all collaboration programs. The development milestones are payable on initiation of certain clinical trials and range from $32.5 million to $105.0 million , per program, with an aggregate total of $290.0 million . The regulatory approval milestones are payable upon regulatory approval in the United States and outside the United States and range from $7.5 million to $50.0 million per milestone, with an aggregate total of $700.0 million . The commercial milestones are payable upon achievement of specified aggregate product sales outside the United States for each program and range from $40.0 million to $200.0 million per milestone, with an aggregate total of $1.270 billion . The Company is also eligible to receive royalties on product sales outside the United States ranging from high single digit to mid-teen royalties. Exercise of Options Celgene may exercise its option for a program at any time until the expiration of an option term for that program. For each program, the option term ends 45 to 60 days following Celgene’s receipt of a data package that includes certain information relating to the program’s research and development activities. The data package for a program may be delivered to Celgene after the applicable development milestone for such program has been achieved. Depending on the program, the applicable development milestone is (i) IND acceptance, (ii) availability of certain Phase 1a data, or (iii) availability of certain Phase I/II data. If Celgene fails to exercise its option during the option term for a program, the Company will continue to retain all rights to such program. If Celgene exercises its option for a program other than JTX-4014, then the Company will enter into a Co-Co Agreement with Celgene for such program in substantially the form attached to the agreement as an exhibit. Under the co-development and co-commercialization agreement for JTX-2011 and one additional program for which Celgene opts in that is not JTX-4014, the Company will be responsible for leading development and commercialization activities in the United States and Celgene will be responsible for development and commercialization activities outside the United States. For all other additional programs for which Celgene opts in, other than JTX-4014, Celgene will lead development and commercialization activities worldwide. If Celgene exercises its option for JTX-4014, the Company and Celgene will enter into a license agreement, in substantially the form attached to the agreement as an exhibit, pursuant to which the Company and Celgene will both be able to equally access JTX-4014 for combinations within each other’s portfolios and with other molecules that are subject to the agreement, subject to joint governance. Once Celgene opts in with respect to a given program, Celgene and the Company must each use commercially reasonable efforts to develop and commercialize the corresponding product in the United States. Termination At any point during the Celgene Collaboration Agreement, including during the research, development and clinical trial process, or during the term of the applicable co-development and co-commercialization or license agreement, respectively, Celgene can terminate the applicable agreement with the Company in its entirety, or with respect to any program under the Celgene Collaboration Agreement, upon 120 days’ notice and can terminate the entire agreement with the Company in connection with a material breach of the agreement by the Company that remains uncured for 90 days. Exclusivity During the Celgene Collaboration Agreement’s research term (i.e., for four years plus up to three one -year extensions that Celgene may elect), the Company may not alone, or with a third party, research, develop, manufacture or commercialize a biologic that binds to a defined pool of B cell, T regulatory cell or tumor-associated macrophage targets that meet certain criteria, termed an exclusive target, and inhibit, activate or otherwise modulate the activity of such exclusive target. In addition, if Celgene exercises its option for a program within the Celgene Collaboration Agreement, other than JTX-4014, then until termination or expiration of the applicable Co-Co Agreement for such program, the Company may not directly or indirectly research, develop, manufacture or commercialize, outside of the Celgene Collaboration Agreement, any biologic with specified activity against that program’s collaboration target. Accounting Analysis The Celgene Collaboration Agreement includes six deliverables: (i) research and development services for the product candidate, JTX-2011 (“JTX-2011 Research Services”) (ii) research and development services for the product candidate, JTX-4014 (“JTX-4014 Research Services”) (iii) research and development services associated with the Lead Program and Other Programs (“Lead and Other Programs Research Services”), (iv) research and development services associated with target screening (“Target Screening Services”), (v) non-transferable, sub-licensable and non-exclusive licenses to use the Company’s intellectual property and collaboration intellectual property to conduct research activities, on a program by program basis (“Research Licenses”), and (vi) participation in the joint steering committee (“JSC”). The six program options are considered substantive as the Company is at risk with regard to whether Celgene will exercise the options as a result of the significant uncertainties related to drug discovery, research and development as all options are for targets that have significant development risk. Additionally, there is also significant uncertainty regarding Celgene’s exercise of the option for JTX-4014 because, although not a novel immunotherapy agent, it has significant development risk associated with the Company’s ability to advance its development in a commercially viable manner in a short time frame. The research term extensions are also considered substantive options based upon the risk that Celgene will exercise the research term extension. In addition, there are substantial option exercise payments payable by Celgene upon exercise of each option that are not priced at a significant and incremental discount. Accordingly, the substantive options are not considered deliverables at the inception of the arrangement and the associated option exercise payments are not included in allocable arrangement consideration. The Company has also determined that any obligations which are contingent upon the exercise of a substantive option are not considered deliverables at the outset of the arrangement. The Target Screening Services and participation in the JSC deliverables each have standalone value from the other undelivered elements and therefore are separate units of accounting. The Company determined that the research licenses for the JTX-2011 and JTX-4014 programs do not have value to Celgene on a standalone basis primarily as a result of the fact that the research licenses allow Celgene to evaluate the results of the research and development services performed by the Company and the right to perform its duties under the agreement, but do not provide Celgene with any commercialization rights. Therefore, the research licenses do not have value to Celgene without the performance of the JTX-2011 Research Services and JTX-4014 Research Services and therefore are not separable from the JTX-2011 Research Services and JTX-4014 Research Services. The JTX-2011 Research Services are separate and distinct from the JTX-4014 Research Services, and therefore, the research license and the JTX-2011 Research Services are a separate combined unit of accounting and the research license and the JTX-4014 Research Services are a separate combined unit of accounting. The Lead and Other Programs Research Services deliverable does not include separate and distinct services and Celgene can use the Lead and Other Programs Research Services for its intended purpose without receipt of the research licenses that could be delivered for the Lead Program and Other Programs. The Lead and Other Programs Research Services therefore have been combined with the licenses that could be delivered for the Lead Program and Other Programs, which have an insignificant value, as a separate combined unit of accounting. The allocable arrangement consideration consists of the upfront fee of $225.0 million . As described above, Celgene also purchased 10,448,100 shares of Series B-1 convertible preferred stock for gross proceeds of $36.1 million , which shares converted into 2,831,463 shares of common stock upon the completion of the IPO. The Company determined the shares of Series B-1 convertible preferred stock were sold at fair value. Therefore, the proceeds from the issuance of Series B-1 convertible preferred stock did not impact the arrangement consideration to be allocated to the units of accounting. The Company has allocated the allocable arrangement consideration based on the relative selling price of each unit of accounting. For all units of accounting, the Company determined the selling price using the best estimate of selling price (“BESP”). The Company determined the BESP based on internal estimates of the costs to perform the services, including expected internal and external costs for services and supplies, adjusted to reflect a reasonable profit margin. The total cost of the research and development services reflects the nature of the services to be performed and the Company’s best estimate of the length of time required to perform the services. The Company determined that the BESP of the participation in the JSC was insignificant and therefore no consideration was allocated to this unit of accounting. Similarly, given the limited use of the research licenses, which is only required in the event Celgene performs research activities under the Celgene Collaboration Agreement which is not expected to be significant, the Company determined the estimated selling price for the research licenses were also insignificant. Therefore, the total allocable arrangement consideration has been allocated to the JTX-2011 Research Services, the JTX-4014 Research Services, the Lead and Other Programs Research Services and the Target Screening Services. The Company is recognizing the consideration allocated to each unit of accounting on a straight-line basis, as there is no discernible pattern or objective measure of performance of the services, over the estimated performance period. The estimated performance period reflects the Company’s estimate of the period over which it will perform the separate and distinct research and development services to deliver a pre-defined data package to Celgene for each program subject to an option. The performance periods for each unit of accounting range from twelve months to four years. The Company evaluated the milestones in the Celgene Collaboration Agreement, the Co-Co agreements, and the JTX-4014 License Agreement to determine if they are substantive. In evaluating if a milestone is substantive, the Company assesses whether: (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of the value of the delivered item(s) as a result of a specific outcome resulting from the Company performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. All development and regulatory milestones in the Celgene Collaboration Agreement, the Co-Co agreements, and the JTX-4014 License Agreement are considered substantive on the basis of the contingent nature of the milestone, specifically reviewing factors such as the scientific, clinical, regulatory, and other risks that must be overcome to achieve the milestone as well as the level of effort and investment required. Accordingly, such amounts will be recognized in the period in which the associated milestone is achieved, assuming all other revenue recognition criteria are met. All commercial milestones will be accounted for in the same manner as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met. During the years ended December 31, 2017 and 2016 , the Company recognized as revenue $71.6 million and $37.2 million , respectively, of the $225.0 million upfront payment received under the Celgene Collaboration Agreement. As of December 31, 2017 , the Company has $116.2 million of deferred revenue, which is classified as either current or net of current portion in the accompanying consolidated balance sheets based on the period over which the revenue is expected to be recognized.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company measures the fair value of money market funds, U.S. Treasuries and government agency securities based on quoted prices in active markets for identical securities. Investments also include corporate debt securities which are valued either based on recent trades of securities in inactive markets or based on quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data. The carrying amounts reflected in the consolidated balance sheets for cash, prepaid expenses and other current assets, accounts payable and accrued expenses approximate their fair values, due to their short-term nature. Assets measured at fair value on a recurring basis as of December 31, 2017 were as follows (in thousands): Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Money market funds, included in cash equivalents $ 21,059 $ 21,059 $ — $ — Investments: Corporate debt securities 65,173 — 65,173 — U.S. Treasuries 110,948 110,948 — — Government agency securities 58,171 58,171 — — Totals $ 255,351 $ 190,178 $ 65,173 $ — Assets measured at fair value on a recurring basis as of December 31, 2016 were as follows (in thousands): December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs Money market funds, included in cash equivalents $ 44,848 $ 44,848 $ — $ — Investments: Corporate debt securities 92,408 — 92,408 — U.S. Treasuries 120,118 120,118 — — Totals $ 257,374 $ 164,966 $ 92,408 $ — There were no changes in valuation techniques or transfers between the fair value measurement levels during the years ended December 31, 2017 or 2016 . There were no liabilities measured at fair value on a recurring basis as of December 31, 2017 or 2016 .

Investments

Investments	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Short-term investments consist of investments with maturities greater than ninety days and less than one year from the balance sheet date. Long-term investments consist of investments with maturities of greater than one year that are not expected to be used to fund current operations. The Company classifies all of its investments as available-for-sale securities. Accordingly, these investments are recorded at fair value. Realized gains and losses, amortization and accretion of discounts and premiums are included in other income, net. Unrealized gains and losses on available-for-sale securities are included in other comprehensive income (loss) as a component of stockholders’ equity (deficit) until realized. Cash equivalents, short-term investments and long-term investments as of December 31, 2017 were comprised as follows (in thousands): December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 21,059 $ — $ — $ 21,059 Corporate debt securities 58,136 — (64 ) 58,072 U.S. Treasuries 111,049 — (101 ) 110,948 Government agency securities 43,204 — (131 ) 43,073 Total cash equivalents and short-term investments 233,448 — (296 ) 233,152 Long-term investments: Corporate debt securities 7,117 — (16 ) 7,101 Government agency securities 15,195 — (97 ) 15,098 Total long-term investments 22,312 — (113 ) 22,199 Total cash equivalents and investments $ 255,760 $ — $ (409 ) $ 255,351 Cash equivalents, short-term investments and long-term investments as of December 31, 2016 were comprised as follows (in thousands): December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 44,848 $ — $ — $ 44,848 Corporate debt securities 92,549 — (141 ) 92,408 U.S. Treasuries 12,020 — (18 ) 12,002 Total cash equivalents and short-term investments 149,417 — (159 ) 149,258 Long-term investments: U.S. Treasuries 108,390 — (274 ) 108,116 Total long-term investments 108,390 — (274 ) 108,116 Total cash equivalents and investments $ 257,807 $ — $ (433 ) $ 257,374 As of December 31, 2017 and 2016 , the aggregate fair value of securities that were in an unrealized loss position for less than twelve months was $113.9 million and $192.3 million , respectively. As of December 31, 2017 , the aggregate fair value of securities that were in an unrealized loss position for more than twelve months was $107.9 million . The Company did not hold any securities in an unrealized loss position for more than twelve months as of December 31, 2016 . As of December 31, 2017 , the Company did not intend to sell, and would not be more likely than not required to sell, the securities in an unrealized loss position before recovery of their amortized cost bases. Furthermore, the Company determined that there was no material change in the credit risk of these securities. As a result, the Company determined it did not hold any securities with any other-than-temporary impairment as of December 31, 2017 . There were no realized gains or losses on available-for-sale securities during the years ended December 31, 2016 or 2015 . There were immaterial realized gains and losses on available-for-sale securities during the year ended December 31, 2017 .

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets as of December 31, 2017 and 2016 were comprised as follows (in thousands): December 31, 2017 2016 Prepaid expenses $ 2,196 $ 1,310 Taxes receivable 16,737 — Interest receivable on investments 969 709 Other current assets 43 510 Total prepaid expenses and other current assets $ 19,945 $ 2,529 Taxes receivable as of December 31, 2017 were comprised of federal and state income tax payments for which the Company expects to be refunded during the year ended December 31, 2018.

Restricted Cash

Restricted Cash	12 Months Ended
	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Restricted Cash	Restricted Cash As of December 31, 2017 and 2016 , the Company maintained non-current restricted cash of $1.3 million and $1.5 million , respectively. Such amounts were comprised of letters of credit for the Company’s leased facilities.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net as of December 31, 2017 and 2016 was comprised as follows (in thousands): Estimated Useful Life (in Years) December 31, 2017 2016 Laboratory equipment 5 $ 9,409 $ 6,275 Furniture and office equipment 4 1,038 226 Computer equipment 3 1,380 492 Leasehold improvements Shorter of useful life or remaining lease term 8,498 3,997 Construction in progress — 1,048 Total property and equipment, gross 20,325 12,038 Less: accumulated depreciation (4,174 ) (4,797 ) Total property and equipment, net $ 16,151 $ 7,241 Depreciation expense for the years ended December 31, 2017 , 2016 and 2015 was $4.4 million , $1.9 million and $1.5 million , respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses as of December 31, 2017 and 2016 were comprised as follows (in thousands): December 31, 2017 2016 Employee compensation and benefits $ 3,683 $ 2,651 External research and professional services 4,647 1,923 Lab consumables and other 124 1,281 Total accrued expenses $ 8,454 $ 5,855

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Common Stock	Common Stock The Company is authorized to issue 160,000,000 shares of common stock. Holders of common stock are entitled to one vote per share. Holders of common stock are entitled to receive dividends, if and when declared by the Board of Directors. As of December 31, 2017 and 2016 , the Company had reserved for future issuance the following number of shares of common stock (in thousands): December 31, 2017 2016 Shares reserved for Series A convertible preferred stock outstanding — 12,737 Shares reserved for Series B convertible preferred stock outstanding — 6,715 Shares reserved for Series B-1 convertible preferred stock outstanding — 2,831 Shares reserved for vesting of restricted stock awards 16 94 Shares reserved for exercises of outstanding stock options 4,868 4,290 Shares reserved for future issuances under the 2017 Stock Incentive Plan 1,032 244 Total shares reserved for future issuance 5,916 26,911

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Preferred Stock	Preferred Stock Series A Preferred Stock At various closing dates during the years ended December 31, 2015, 2014 and 2013, the Company issued 47,000,000 shares of Series A convertible preferred stock (“Series A Preferred Stock”) for $1.00 per share. The shares were issued in exchange for cash proceeds of $44.6 million , net of issuance costs of $0.1 million , and the exchange of approximately $2.3 million in outstanding convertible promissory notes, including accrued interest. Tranche Rights Issued with Series A Preferred Stock Included in the terms of the Series A Preferred Stock Purchase Agreement were certain tranche rights (the “Tranche Rights”). The Tranche Rights obligated the investors in Series A Preferred Stock to purchase, and the Company to sell, an additional 10,000,000 shares of Series A Preferred Stock at $1.00 per share contingent upon the initiation of certain research and development programs and initiation of translational science (“Tranche Right I”). In addition, the investors were obligated to purchase, and the Company was obligated to sell, an additional 20,000,000 shares of Series A Preferred Stock upon developing product candidates and achieving certain clinical milestones (“Tranche Right II”). In addition, the Tranche Rights provided the investors with the ability to purchase these additional shares at their option at any time. The Tranche Rights were transferable by the investors, subject to approval by the Company’s Board of Directors. The Company concluded that the Tranche Rights met the definition of a freestanding financial instrument, as the Tranche Rights were legally detachable and separately exercisable from the Series A Preferred Stock. Therefore, the Company allocated the net proceeds between the Tranche Rights and the Series A Preferred Stock. Since the Series A Preferred Stock was contingently redeemable upon the occurrence of a deemed liquidation event, the Tranche Rights were classified as an asset or liability under ASC 480, Distinguishing Liabilities from Equity , and were initially recorded at fair value. The Tranche Rights were measured at fair value at each reporting period. Since the Tranche Rights were subject to fair value accounting, the Company allocated the proceeds to the Tranche Rights based on the fair value at the date of issuance with the remaining proceeds being allocated to the Series A Preferred Stock. The estimated fair value of the Tranche Rights was determined using a probability-weighted present value model that considered the probability of closing a tranche, the estimated future value of Series A Preferred Stock at each closing and the investment required at each closing. Future values were converted to present value using a discount rate appropriate for probability-adjusted cash flows. Tranche Right I was initially recorded as an asset of $1.2 million as the purchase price of the additional shares was greater than the estimated value of the Series A Preferred Stock at the expected settlement date. Conversely, Tranche Right II was initially recorded as a liability of $6.5 million as the purchase price of the additional shares was less than the estimated price of the Series A Preferred Stock at the expected settlement date. In February 2014, the Company amended the Tranche Rights, which changed the amount and timing of the subsequent closings related to Tranche Right I and Tranche Right II. The shares associated with Tranche Right I were increased by 5,000,000 to 15,000,000 , and the shares associated with Tranche Right II were decreased by 5,000,000 to 15,000,000 . The purchase price per share remained unchanged at $1.00 . Additionally, upon the achievement of the specified milestones, Tranche Right I and Tranche Right II would each be closed in two separate transactions whereby 50% of the commitment would be closed upon the achievement of the milestones and the remaining 50% commitment would be closed within six months of achieving the milestones. As a result of these modified Tranche Rights, the Company recognized income of $3.4 million related to the mark-to-market adjustment at the time of the amendment. The Company issued 15,000,000 additional shares under Tranche Right I in two separate closings during the year ended December 31, 2014 for total proceeds of $15.0 million , net of issuance costs. Prior to each closing, any changes in the value of Tranche Right I were recorded as other financing income, net. The fair value of the portion of the Tranche Right I settled at each closing was reclassified to Series A Preferred Stock. In January 2015 and April 2015, Tranche Right II was settled in two separate closings, prior to achieving the contingent milestones. The Company recognized income of $1.9 million related to the mark-to-market of Tranche Right II during the year ended December 31, 2015, which was recorded within other financing income, net. The fair value of the Tranche Right II settled at closing was reclassified to Series A Preferred Stock. The initial carrying amount of the Series A Preferred Stock issued upon the closing of Tranche Right II amounted to approximately $16.7 million , which exceeded the redemption value of $15.0 million . Therefore, the carrying value was not subsequently adjusted until such time as the redemption value exceeded the initial carrying amount. Series A Preferred Stock Extinguishment In April 2015, in connection with the issuance of shares of Series B convertible preferred stock (“Series B Preferred Stock”), the rights and preferences of the Series A Preferred Stock were modified and resulted in two primary changes. First, the right at the election of the holder to redeem the Series A Preferred Stock beginning in February 2020 was removed, and the right to participate in liquidating distributions with the common stock holders on a pro rata basis was also removed. The removal of these two features resulted in a fundamental change to the nature of the Series A Preferred Stock. As a result, the Company recognized a loss on extinguishment of the Series A Preferred Stock in the amount of $2.1 million during the year ended December 31, 2015, which caused the Series A Preferred Stock’s carrying value to equal its fair value of $47.1 million after the modification. As the amended Series A Preferred Stock was no longer redeemable at the option of the holder beginning in February 2020, and was only contingently redeemable upon the occurrence of a deemed liquidation event, the Company did not subsequently adjust the carrying value of the Series A Preferred Stock until such time that it was probable that the Series A preferred stock would be redeemed. Series B Preferred Stock During the year ended December 31, 2015, the Company issued 24,778,761 shares of Series B Preferred Stock for $2.26 per share. This issuance resulted in cash proceeds of $55.8 million , net of issuance costs of $0.2 million . Series B-1 Preferred Stock During the year ended December 31, 2016, the Company issued 10,448,100 shares of Series B-1 Preferred Stock to Celgene for $3.46 per share. This issuance resulted in cash proceeds of $36.1 million , net of issuance costs of $0.1 million . Conversion of Preferred Stock Upon IPO Prior to the Company’s IPO, the holders of the Company’s Series A Preferred Stock, Series B Preferred Stock and Series B-1 Preferred Stock had certain voting rights, dividend rights, liquidation preferences and conversion privileges. Upon completion of the Company’s IPO, all shares of outstanding convertible preferred stock were automatically converted into an aggregate of 22,283,690 shares of common stock. All rights, preferences and privileges associated with the outstanding convertible preferred stock were terminated upon this conversion. The Company is now authorized to issue 5,000,000 shares of undesignated preferred stock in one or more series. As of December 31, 2017 , no shares of preferred stock were issued or outstanding.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-based Compensation 2013 Stock Option and Grant Plan In February 2013, the Company’s Board of Directors adopted and the Company’s stockholders approved the 2013 Stock Option and Grant Plan (the “2013 Plan”), as amended and restated, under which it could grant incentive stock options (“ISOs”), non-qualified stock options and restricted stock awards to eligible employees, officers, directors, and consultants. The 2013 Plan was subsequently amended in January 2015, April 2015, July 2015, March 2016 and October 2016 to allow for the issuance of additional shares of common stock. 2017 Stock Option and Incentive Plan In January 2017, the Company’s Board of Directors adopted and the Company’s stockholders approved the 2017 Stock Option and Incentive Plan (the “2017 Plan”), which became effective immediately prior to the effectiveness of the Company’s IPO. Upon the adoption of the 2017 Plan, no further awards will be granted under the 2013 Plan. The 2017 Plan provides for the grant of ISOs, non-qualified stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards. The Company’s employees, officers, directors and consultants and advisors are eligible to receive awards under the 2017 Plan. The terms of stock options and restricted stock awards, including vesting requirements, are determined by the Board of Directors, subject to the provisions of the 2017 Plan. The Company registered on a Registration Statement on Form S-8 1,753,758 shares of common stock under the 2017 Plan, which is comprised of (i) 1,510,000 shares of common stock reserved for issuance under the 2017 Plan, plus (ii) 243,758 shares of common stock originally reserved for issuance under the 2013 Plan that became available for issuance under the 2017 Plan upon the completion of the Company’s IPO. The 2017 Plan also provides that an additional number of shares will automatically be added to the shares authorized for issuance under the 2017 Plan on January 1, 2018 and each January 1 thereafter. The number of shares added each year will be equal to the lesser of (i) 4% of the outstanding shares on the immediately preceding December 31 st or (ii) such amount as determined by the Compensation Committee of the Board of Directors. As of December 31, 2017 , there were 1,032,252 shares available for future issuance under the 2017 Plan. 2017 Employee Stock Purchase Plan In January 2017, the Board of Directors adopted and the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective upon the closing of the Company’s IPO. The Company reserved 302,000 shares of common stock for future issuance under the 2017 ESPP. No offering periods under the 2017 ESPP had been initiated as of December 31, 2017 . Founder Awards From December 2012 to February 2013, the Company issued 1,395,659 shares of restricted stock to non-employee founders (the “Founders”). Of the total restricted stock awarded to the Founders, 1,043,357 shares vested over one to four years, based on each Founder’s continued service relationship with the Company in varying capacities as advisors, as prescribed by the grantee’s individual restricted stock purchase agreements. The remaining 352,302 shares vested upon the determination by the Board of Directors of a Founder’s achievement of certain performance objectives, as set forth in the agreements. These performance criteria were linked to certain milestones specific to the Company’s research and development goals, including but not limited to preclinical and clinical development milestones related to the Company’s product candidates. As of December 31, 2017 , all restricted stock awards issued to Founders were vested. Restricted stock awards granted to two Founders originally contained options that enabled the Founders to sell their vested shares back to the Company at fair value upon both (i) the termination of the consulting agreement between the Founder and the Company for any reason and (ii) the determination by the Founder’s employer that the ownership of the restricted stock is in violation of the employer’s conflict of interest policy. The occurrence of these events was determined to be outside of the Founders’ and the Company’s control. As such, these restricted stock awards were previously recorded on the consolidated balance sheet as contingently redeemable common stock, residing in temporary equity, in accordance with the classification guidance of ASC 718, Compensation—Stock Compensation and ASC 480, Distinguishing Liabilities from Equity. In June 2017, the restricted stock purchase agreements related to the two Founders were amended such that these options expired on July 26, 2017. Accordingly, these restricted stock awards were reclassified from contingently redeemable common stock to additional paid-in capital as of that date. Stock-based Compensation Expense Total stock-based compensation expense recognized in the consolidated statements of operations for the years ended December 31, 2017 , 2016 and 2015 was as follows (in thousands): Year Ended December 31, 2017 2016 2015 Research and development $ 2,840 $ 4,161 $ 269 General and administrative 1,935 828 1,083 Total stock-based compensation expense $ 4,775 $ 4,989 $ 1,352 Restricted Stock Activity Pursuant to restricted stock agreements originally issued under the terms of the 2013 Plan, the Company, at its discretion, has the option to repurchase unvested shares of restricted stock at the initial purchase price if the employees or non-employees terminate their service relationship with the Company. The shares are recorded in stockholders’ equity (deficit) as they vest. No shares of restricted stock were issued during the years ended December 31, 2017 or 2016 . During the year ended December 31, 2015, the Company issued 27,099 shares of restricted stock to a member of the Board of Directors at an original purchase price of $4.02 per share. The following table summarizes changes in unvested restricted stock for the year ended December 31, 2017 (in thousands, except per share amounts): Shares Weighted-Average Grant Date Fair Value per Share Unvested restricted stock as of December 31, 2016 94 $ 0.07 Issued — $ — Vested (77 ) $ 0.08 Repurchased (1 ) $ 0.37 Unvested restricted stock as of December 31, 2017 16 $ — The aggregate fair value of restricted stock awards that vested during the years ended December 31, 2017 , 2016 and 2015 , based upon the fair values of the stock underlying the restricted stock awards on the day of vesting, was $1.3 million , $3.9 million and $1.1 million , respectively. Stock Option Activity The fair value of stock options granted to employees and directors during the years ended December 31, 2017 , 2016 and 2015 was calculated on the date of grant using the following weighted-average assumptions: Year Ended December 31, 2017 2016 2015 Risk-free interest rate 2.1 % 1.4 % 1.8 % Expected dividend yield — % — % — % Expected term (in years) 6.1 6.1 6.1 Expected volatility 70.1 % 71.9 % 67.0 % Using the Black-Scholes option pricing model, the weighted-average grant date fair value of stock options granted to employees and directors during the years ended December 31, 2017 , 2016 and 2015 was $10.96 , $5.10 and $1.70 per share, respectively. No stock options were granted to non-employees during the years ended December 31, 2017 or 2016 . During the year ended December 31, 2015, the Company granted 12,195 stock options to non-employees at a weighted-average grant date fair value of $0.85 per share. This weighted-average grant date fair value was calculated using the Black-Scholes option pricing model and a weighted-average risk-free interest rate of 2.0% , a weighted-average expected dividend yield of 0.0% , a weighted-average expected term of 9.8 years and a weighted-average expected volatility of 68.7% . The following table summarizes changes in stock option activity during the year ended December 31, 2017 (in thousands, except per share amounts): Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Outstanding at December 31, 2016 4,290 $ 3.95 8.7 $ 29,269 Granted 983 $ 17.19 Exercised (144 ) $ 3.20 Cancelled or forfeited (261 ) $ 10.71 Outstanding at December 31, 2017 4,868 $ 6.28 7.9 $ 35,178 Exercisable at December 31, 2017 2,217 $ 2.79 7.2 $ 22,170 The aggregate intrinsic value of stock options exercised during the years ended December 31, 2017 , 2016 and 2015 was $1.9 million , $0.3 million and less than $0.1 million , respectively. As of December 31, 2017 , there was unrecognized stock-based compensation expense related to unvested stock options of $13.8 million , which the Company expects to recognize over a weighted-average period of approximately 2.4 years .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for income taxes for the years ended December 31, 2017 , 2016 and 2015 was comprised as follows (in thousands): Year Ended December 31, 2017 2016 2015 Current taxes: Federal $ — $ — $ — State 36 — — Total current taxes 36 — — Deferred taxes: Federal — — — State — — — Total deferred taxes — — — Total provision for income taxes $ 36 $ — $ — The Tax Cuts and Jobs Act (the “Tax Act”) was enacted on December 22, 2017 and introduced significant changes to United States income tax law. Among these changes, the federal statutory tax rate was reduced to 21% and net operating loss (“NOL”) carrybacks are no longer permitted. In December 2017, the Securities and Exchange Commission staff issued Staff Accounting Bulletin No. 118 (“SAB 118”) to address the application of GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Act. Due to the timing of the enactment and the complexity involved in applying the provisions of the Tax Act, the Company has made reasonable estimates of the effects and recorded provisional amounts in its consolidated financial statements as of and for the year ended December 31, 2017. In accordance with SAB 118, the Company has determined that the revaluation of its deferred tax assets and associated valuation allowance reduction of $9.4 million are provisional amounts as of December 31, 2017. The ultimate impact may differ from these provisional amounts, possibly materially, due to, among other things, additional analysis, changes in interpretations and assumptions the Company has made, additional regulatory guidance that may be issued and actions the Company may take as a result of the Tax Act. The accounting for the tax effects of the Tax Act will be completed during the year ended December 31, 2018. A reconciliation of the federal statutory income tax rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2017 2016 2015 Income tax computed at federal statutory tax rate 34.0 % 34.0 % 34.0 % Deferred tax effects from the Tax Act (57.2 )% — % — % State taxes, net of federal benefit 4.7 % 3.1 % 5.3 % Tax credit carryforwards 26.8 % 11.7 % 4.5 % Non-deductible income (expense) (4.9 )% (11.1 )% 0.7 % Change in valuation allowance (1.8 )% (39.4 )% (44.5 )% Other (1.8 )% 1.7 % — % Effective tax rate (0.2 )% — % — % The principal components of the Company’s deferred tax assets and liabilities as of December 31, 2017 and 2016 were comprised as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 26,926 $ 24,435 Tax credit carryforwards 8,432 4,039 Deferred revenue 31,735 — Deferred lease incentive 120 553 Deferred rent 431 426 Intangibles 237 187 Accrued expenses and other 995 1,018 Unrealized loss on available-for-sale securities 112 169 Stock-based compensation 713 293 Total deferred tax assets 69,701 31,120 Less: valuation allowance (30,850 ) (30,548 ) Net deferred tax assets 38,851 572 Deferred tax liabilities: Section 481(a) method change (38,481 ) — Depreciation (370 ) (572 ) Total deferred tax liabilities (38,851 ) (572 ) Net deferred taxes $ — $ — The Company has incurred NOLs since inception. As of December 31, 2017 , the Company had federal and state NOL carryforwards of $98.5 million and $98.6 million , respectively, which expire at various dates from 2032 through 2037 . As of December 31, 2017 , the Company had federal research and development tax credit carryforwards of $6.0 million which expire at various dates from 2032 through 2037 . In addition, as of December 31, 2017 , the Company had state research and development and investment tax credit carryforwards of $2.6 million and $0.5 million , respectively. The state research and development tax credit carryforwards expire at various dates from 2027 through 2032 and the state investment tax credit carryforwards expire at various dates from 2019 through 2020 . Management has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are principally comprised of NOL carryforwards, tax credit carryforwards, deferred lease incentives and deferred rent. Management has determined that it is more likely than not that the Company will not realize the benefits of its deferred tax assets, and as a result, a valuation allowance of $30.9 million has been established at December 31, 2017 . The increase in the valuation allowance of $0.3 million during the year ended December 31, 2017 was primarily due to the additional operating loss generated by the Company. NOL and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service (“IRS”) and may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant shareholders over a three-year period in excess of 50% as defined under Sections 382 and 383 in the Internal Revenue Code (“IRC”). 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 Company’s value immediately prior to the ownership change. An IRC Section 382 study, completed in August 2016, identified three previous ownership changes for purposes of IRC Section 382. As a result of these ownership changes, the Company’s NOL and tax credit carryforwards allocable to the periods preceding each such ownership change are subject to limitations under IRC Section 382. Subsequent ownership changes may further affect the limitation in future years. The Company had no unrecognized tax benefits as of either December 31, 2017 or 2016 . During the year ended December 31, 2017, the Company completed a study of its research and development credit carryforwards generated during the years ended December 31, 2016 and 2015. The Company has not conducted a study of its research and development credit carryforwards generated during the year ended December 31, 2017 . 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. A full valuation allowance has been provided against the Company’s research and development credit carryforwards, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated statements of operations if an adjustment were required. Interest and penalty charges, if any, related to income taxes would be classified as a component of the provision for income taxes in the consolidated statements of operations. As of December 31, 2017 , the Company has no t incurred any interest or penalty charges. The Company files income tax returns in the United States federal tax jurisdiction and the Massachusetts state tax jurisdiction. Since the Company is in a loss carryforward position, it is generally subject to examination by federal and state tax authorities for all tax years in which a loss carryforward is available.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related-party Transactions	Related-party Transactions In July 2016, the Company entered into the Celgene Collaboration Agreement and a Series B-1 Preferred Stock Purchase Agreement with Celgene. Under the Celgene Collaboration Agreement, the Company received a non-refundable upfront payment of $225.0 million . Under the Series B-1 Preferred Stock Purchase Agreement, Celgene purchased 10,448,100 shares of Series B-1 preferred stock for $36.1 million . These shares of Series B-1 preferred stock converted into 2,831,463 shares of common stock upon the completion of the Company’s IPO. In addition, an affiliate of Celgene purchased 625,000 shares of the Company’s common stock in the January 2017 IPO at the public offering price of $16.00 per share for a total of $10.0 million .

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Operating Leases In November 2016, the Company entered into an operating lease agreement to occupy 51,000 square feet of laboratory and office space in Cambridge, Massachusetts. This facility serves as the Company’s current corporate headquarters. The lease term began on November 1, 2016 and extends to March 31, 2025. The Company has the option to extend the lease term for one consecutive five -year period, at the market rate, by giving the landlord written notice of its election to exercise the extension at least twelve months prior to the original expiration of the lease term. The Company is recording rent expense on a straight-line basis through the end of the lease term and has recorded deferred rent on the consolidated balance sheets. The lease also provided the Company with a tenant improvement allowance of $0.5 million . The Company recorded the tenant improvement allowance as a deferred lease incentive and is amortizing the deferred lease incentive through a reduction of rent expense ratably over the lease term. Leasehold improvements related to this facility are being amortized over the shorter of their useful life or the lease term. The Company provided the landlord with a security deposit in the form of a letter of credit in the amount of $1.3 million , which is recorded as restricted cash in other non-current assets in the consolidated balance sheets. As of December 31, 2017 , the future minimum lease payments due under the operating lease for the Company’s corporate headquarters are as follows (in thousands): Years Ended December 31, Minimum Lease Payments 2018 $ 4,139 2019 4,263 2020 4,391 2021 4,523 2022 4,659 2023 and thereafter 10,996 Total future minimum lease payments $ 32,971 The Company leased its former corporate headquarters under an operating lease that was originally set to expire on October 15, 2018. The Company had the option to extend the term of the lease for an additional three -year period, at the market rate, by giving the landlord written notice of its election to exercise the extension at least nine months prior to the original expiration of the lease term. The Company recorded rent expense on a straight-line basis through the end of the lease term and recorded deferred rent on the consolidated balance sheets. The lease also provided the Company with a tenant improvement allowance of $2.8 million . The Company recorded the tenant improvement allowance as a deferred lease incentive and amortized the deferred lease incentive through a reduction of rent expense ratably over the lease term. In March 2015, the Company entered into a three -year sublease agreement to lease additional lab and office facilities at the same location as its former corporate headquarters. On May 19, 2017, the Company entered into a Lease Termination Agreement and a Sublease Termination Agreement (collectively, the “Lease Termination Agreements”) with its landlord related to the leases for its former corporate headquarters. As a result of the Lease Termination Agreements, rental payments for the Company’s former corporate headquarters ceased on May 31, 2017, with the exception of certain space that was utilized through August 31, 2017. The Lease Termination Agreements required the Company to pay an aggregate early termination fee of $0.7 million , which was paid in the second quarter of 2017. This early termination fee was recorded as a component of rent expense. During the years ended December 31, 2017 , 2016 and 2015 , the Company recorded total rent expense of $3.5 million , $1.8 million and $0.9 million , respectively. License and Collaboration Agreements The Company has entered into various license agreements for certain technology. The Company could be required to make aggregate technical, clinical development and regulatory milestone payments of up to $13.2 million and low single-digit royalty payments based on a percentage of net sales of licensed products. As of December 31, 2017 , the Company made $0.2 million in aggregate milestone payments under these license agreements. The Company may cancel these agreements at any time by providing 30 to 90 days notice to the licensors, and all payments not previously due would no longer be owed. The Company has also entered into collaboration agreements with various third parties for research services and access to proprietary technology platforms. Under certain of these collaboration agreements, the Company could be required to make aggregate technical, clinical development and regulatory milestones payments ranging from $12.5 million to $12.9 million per product candidate and low single-digit royalty payments based on a percentage of net sales on a product-by-product basis. As of December 31, 2017 , the Company made $0.3 million in aggregate milestone payments under these certain collaboration agreements. Under a certain other collaboration agreement, the Company could be required to make aggregate technical, clinical development and regulatory milestones payments of $0.7 million . As of December 31, 2017 , the Company made no milestone payments under this certain other collaboration agreement.

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2017
Retirement Benefits [Abstract]
401(k) Savings Plan	401(k) Savings Plan The Company has a defined-contribution savings plan under Section 401(k) of the IRC (the “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. As of December 31, 2017 , the Company was not required to make any contributions to the 401(k) Plan, nor did it make any contributions to the 401(k) Plan through December 31, 2017 .

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share For purposes of the diluted loss per share calculation, convertible preferred stock, outstanding stock options and unvested restricted common stock are considered to be potentially dilutive securities, however the following common stock equivalents have been excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive (in thousands): Year Ended December 31, 2017 2016 2015 Series A convertible preferred stock — 12,737 12,737 Series B convertible preferred stock — 6,715 6,715 Series B-1 convertible preferred stock — 2,831 — Outstanding stock options 4,868 4,290 2,960 Unvested restricted common stock 16 94 748 Total 4,884 26,667 23,160

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	Selected Quarterly Financial Data (Unaudited) The following tables contain selected quarterly financial information for the years ended December 31, 2017 and 2016 . The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. 2017 (in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue—related party $ 20,289 $ 20,289 $ 18,077 $ 12,989 Total operating expenses 20,536 23,317 22,465 24,541 Operating loss (247 ) (3,028 ) (4,388 ) (11,552 ) Total other income, net 632 752 721 703 Provision for (benefit from) income taxes — 1,104 417 (1,485 ) Net income (loss) $ 385 $ (3,380 ) $ (4,084 ) $ (9,364 ) Net loss attributable to common stockholders $ (409 ) $ (3,380 ) $ (4,084 ) $ (9,364 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.02 ) $ (0.11 ) $ (0.13 ) $ (0.29 ) 2016 (in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue—related party $ — $ — $ 16,908 $ 20,289 Total operating expenses 10,901 12,362 13,093 15,307 Operating (loss) income (10,901 ) (12,362 ) 3,815 4,982 Total other income, net 11 14 254 484 Net (loss) income $ (10,890 ) $ (12,348 ) $ 4,069 $ 5,466 Net (loss) income attributable to common stockholders $ (12,934 ) $ (14,392 ) $ 138 $ 258 Net (loss) income per share attributable to common stockholders, basic $ (6.81 ) $ (7.23 ) $ 0.06 $ 0.11 Net (loss) income per share attributable to common stockholders, diluted $ (6.81 ) $ (7.23 ) $ 0.03 $ 0.05

Basis of Presentation and Sum27

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”)
Principles of Consolidation	include the accounts of Jounce Therapeutics, Inc. and its wholly-owned subsidiary, Jounce Mass Securities, Inc., which was established in July 2016. All intercompany transactions and balances have been eliminated in consolidation.
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 in deciding how to allocate resources and assess performance. The Company and the Company’s chief operating decision maker, the Company’s chief executive officer, views the Company’s operations and manages its business as a single operating segment. The Company operates only in the United States.
Use of Estimates	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 the period of performance for units of accounting identified under the Celgene Collaboration Agreement, accrued research and development expenses, stock-based compensation and income taxes. The Company bases its estimates on historical experience and other market specific or other relevant assumptions it believes to be reasonable under the circumstances. Actual results could differ from those estimates. Prior to the completion of the IPO, the Company utilized significant estimates and assumptions in determining the fair value of its common stock. The Company determined the estimated fair value of its common stock based on 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 its convertible preferred stock and the superior rights and preferences of the convertible preferred stock in relation to the Company’s common stock. The Company utilized various valuation methodologies in accordance with the framework of the American Institute of Certified Public Accountants (“AICPA”) Audit and Accounting Practice Aid Series: Valuation of Privately Held Company Equity Securities Issued as Compensation ( the “AICPA Practice Aid”) to estimate the fair value of its common stock. These methodologies included the option pricing method utilizing the backsolve method, which is a form of the market approach defined in the AICPA Practice Aid, and the probability-weighted expected return method based upon the probability of occurrence of certain future liquidity events such as an IPO or sale of the Company. Each valuation methodology included estimates and assumptions that required the Company’s judgment. Significant changes to the key assumptions used in the valuations could have resulted in different fair values of the Company’s common stock at each valuation date.
Fair Value of Financial Instruments	Accounting Standards Codification (“ASC”) 820, Fair Value Measurement , establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability 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 asset or liability, and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following: • Level 1 inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities. • Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. • Level 3 inputs are unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. Financial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. To the extent that the 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.
Cash Equivalents	Cash equivalents are highly-liquid investments that are readily convertible into cash with original maturities of three months or less when purchased. These assets include investment in money market funds that invests in U.S. Treasury obligations.
Investments	Short-term investments consist of investments with maturities greater than ninety days and less than one year from the balance sheet date. Long-term investments consist of investments with maturities of greater than one year that are not expected to be used to fund current operations. The Company classifies all of its investments as available-for-sale securities. Accordingly, these investments are recorded at fair value. Realized gains and losses, amortization and accretion of discounts and premiums are included in other income, net. Unrealized gains and losses on available-for-sale securities are included in other comprehensive income (loss) as a component of stockholders’ equity (deficit) until realized.
Restricted Cash	Restricted cash as of December 31, 2017 and 2016 is comprised of amounts held as security deposits in the form of letters of credit for the Company’s leased facilities. If restrictions are expected to be lifted within the next twelve months, the restricted cash account is classified as current.
Property and Equipment, Net	Property and equipment is recorded at cost and consists of laboratory equipment, furniture and office equipment, computer equipment, leasehold improvements, and construction in progress. The Company capitalizes property and equipment that is acquired for research and development activities and that has alternate future use. Expenditures for maintenance and repairs are recorded to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. Leasehold improvements are depreciated over the lesser of their useful life or the term of the lease. Depreciation is calculated over the estimated useful lives of the assets using the straight-line method.
Impairment of Long-lived Assets	The Company reviews its property and equipment whenever events or changes in circumstances indicate that the carrying value of certain assets might not be recoverable and recognizes an impairment loss when it is probable that an asset’s realizable value is less than the carrying value.
Deferred Financing Costs	The Company capitalizes deferred financing costs, which primarily consists of direct, incremental legal and accounting fees relating to the Company’s financing activities, within other non-current assets. Deferred financing costs are typically offset against financing proceeds received upon the consummation of an offering.
Revenue Recognition	The Company recognizes revenue in accordance with ASC 605, Revenue Recognition . Accordingly, revenue is recognized when all of the following criteria are met: • persuasive evidence of an arrangement exists; • delivery has occurred or services have been rendered; • the seller’s price to the buyer is fixed or determinable; and • collectability is reasonably assured. Amounts received prior to satisfying the revenue recognition criteria are recognized as deferred revenue in the Company’s consolidated balance sheets. Amounts expected to be recognized as revenue within the twelve months following the balance sheet date are classified as deferred revenue, current. Amounts not expected to be recognized as revenue within the twelve months following the balance sheet date are classified as deferred revenue, net of current portion.
Multiple-Element Arrangements	Determination of Units of Accounting When evaluating multiple-element arrangements pursuant to ASC 605-25, Revenue Recognition—Multiple-Element Arrangements , the Company considers whether the deliverables under the arrangement represent separate units of accounting. This evaluation requires subjective determinations and requires management to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. In determining the units of accounting, management evaluates certain criteria, including whether the deliverables have standalone value, based on the consideration of the relevant facts and circumstances for each arrangement. The consideration received is allocated among the separate units of accounting using the relative selling price method, and the applicable revenue recognition criteria are applied to each of the separate units. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer on a standalone basis and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in the control of the Company. In assessing whether an item has standalone value, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can use the deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable is dependent on the undelivered item(s) and whether there are other vendors that can provide the undelivered element(s). Under multiple-element arrangements, options are considered substantive if, at the inception of the arrangement, the Company is at risk as to whether the collaboration partner will choose to exercise the option. Factors that the Company considers in evaluating whether an option is substantive include the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option, the likelihood the option will be exercised, and the cost to exercise the option. When an option is considered substantive, the Company does not consider the option or item underlying the option to be a deliverable at the inception of the arrangement and the associated option fees are not included in the allocable arrangement consideration, assuming the option is not priced at a significant and incremental discount. When an option is not considered substantive, the Company would consider the option, including other deliverables contingent upon the exercise of the option, to be a deliverable at the inception of the arrangement and a corresponding amount would be included in the allocable arrangement consideration. In addition, if the price of the option includes a significant incremental discount, the discount inherent in the option price would be included as a deliverable at the inception of the arrangement. Allocation of Arrangement Consideration Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. Then, the applicable revenue recognition criteria in ASC 605-25 are applied to each of the separate units of accounting in determining the appropriate period and pattern of recognition. The Company determines the selling price of a unit of accounting following the hierarchy of evidence prescribed by ASC 605-25. Accordingly, the Company determines the estimated selling price for units of accounting within each arrangement using vendor-specific objective evidence (“VSOE”) of selling price, if available, third-party evidence (“TPE”) of selling price if VSOE is not available, or best estimate of selling price (“BESP”) if neither VSOE nor TPE is available. The Company typically uses BESP to estimate the selling price, since it generally does not have VSOE or TPE of selling price for its units of accounting. Determining the BESP for a unit of accounting requires significant judgment. In developing the BESP for a unit of accounting, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the customer and estimated costs. The Company validates the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP will have a significant effect on the allocation of arrangement consideration between multiple units of accounting. Patterns of Recognition The Company recognizes arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 are satisfied for that particular unit of accounting. The Company recognizes revenue associated with substantive options upon exercise of the option if the underlying license has standalone value from the other deliverables to be provided subsequent to delivery of the license. If the license does not have standalone value, the amounts allocated to the license option will be combined with the related undelivered items as a single unit of accounting. The Company recognizes the revenue amounts associated with research and development services and other service related deliverables ratably over the associated period of performance. If there is no discernible pattern of performance or objectively measurable performance measures do not exist, then the Company recognizes revenue under the arrangement on a straight-line basis over the period the Company is expected to complete its performance obligations. If the pattern of performance in which the service is provided to the customer can be determined and objectively measurable performance exists, then the Company recognizes revenue under the arrangement using the proportional performance method. Revenue recognized is limited to the lesser of the cumulative amount of payments received and the cumulative amount of revenue earned, as determined using the straight-line method or proportional performance, as applicable, as of each reporting period. Recognition of Milestones and Royalties At the inception of an arrangement that includes milestone payments, the Company evaluates whether each milestone is substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation includes an assessment of whether (i) the consideration is commensurate with either the Company’s performance to achieve the milestone or the enhancement of performance to achieve the milestone, (ii) the consideration relates solely to past performance and (iii) the consideration is reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluates factors such as clinical, regulatory, commercial and other risks that must be overcome to achieve the respective milestone and the level of effort and investment required to achieve the respective milestone in making this assessment. There is considerable judgment involved in determining whether a milestone satisfies all of the criteria required to conclude that a milestone is substantive. In accordance with ASC 605-28, Revenue Recognition—Milestone Method , clinical and regulatory milestones that are considered substantive, recognized as revenue in their entirety upon successful accomplishment of the milestone, assuming all other revenue recognition criteria are met. Milestones that are not considered substantive are recognized as revenue over the remaining period of performance, assuming all other revenue recognition criteria are met. Revenue from commercial milestones payments are recorded as revenue upon achievement of the milestone, assuming all other recognition criteria are met.
Research and Development Expenses	Expenditures relating to research and development are expensed as incurred. Research and development expenses include external expenses incurred under arrangements with third parties, academic and non-profit institutions and consultants; salaries and personnel-related costs, including non-cash stock-based compensation expense; license fees to acquire in-process technology and other expenses, which include direct and allocated expenses for laboratory, facilities and other costs.
Intellectual Property Expenses	The Company expenses costs associated with intellectual property-related matters as incurred and classifies such costs as general and administrative expenses within the consolidated statements of operations.
Stock-based Compensation	The Company accounts for share-based payments in accordance with ASC 718, Compensation—Stock Compensation. ASC 718 requires all share-based payments to employees, including grants of employee stock options and restricted stock awards, to be recognized as expense in the consolidated statements of operations based on their grant date fair values. For stock options granted to employees and to members of the Company’s Board of Directors for their services on the Board of Directors, the Company estimates the grant date fair value of each stock option using the Black-Scholes option-pricing model. For restricted stock awards granted to employees, the Company estimates the grant date fair value of each award using intrinsic value, which is based on the value of the underlying common stock less any purchase price. For share-based payments subject to service-based vesting conditions, the Company recognizes stock-based compensation expense equal to the grant date fair value of share-based payment on a straight-line basis over the requisite service period. In accordance with the provisions of ASC 505-50, Equity-Based Payments to Non-Employees , share-based payments issued to non-employees are initially recorded at their grant date fair values, remeasured at each reporting date as they vest and expensed over the related service period. The Black‑Scholes option pricing model requires the input of certain subjective assumptions, including (i) the calculation of expected term of the share-based payment, (ii) the risk‑free interest rate, (iii) the expected stock price volatility and (iv) the expected dividend yield. The Company uses the simplified method as proscribed by SEC Staff Accounting Bulletin No. 107 to calculate the expected term for stock options granted to employees as the Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term. The Company determines the risk‑free interest rate based on a treasury instrument whose term is consistent with the expected term of the stock options. Because there had been no public market for the Company’s common stock prior to the IPO, there is a lack of Company‑specific historical and implied volatility data. Accordingly, the Company bases its estimates of expected volatility on the historical volatility of a group of publicly-traded companies with similar characteristics to itself, including stage of product development and therapeutic focus within the life sciences industry. Historical volatility is calculated over a period of time commensurate with the expected term of the share-based payment. The Company uses an assumed dividend yield of zero as the Company has never paid dividends on its common stock, nor does it expect to pay dividends on its common stock in the foreseeable future. The Company utilizes similar Black-Scholes option-pricing model assumptions to value share-based payments issued to non-employees, except the contractual term of the share-based payment is utilized as the basis for the expected term assumption. For share-based payments subject to performance-based vesting conditions, the Company records stock-based compensation expense over the remaining service period when it determines that achievement of the performance condition is probable. The Company evaluates whether the achievement of a performance-based milestone is probable based on the expected satisfaction of the performance conditions as of the reporting date. Stock-based compensation expense for awards subject to performance-based vesting conditions is recognized using the accelerated attribution method. The Company accounts for forfeitures of all share-based payments when such forfeitures occur.
Income Taxes	Income taxes are recorded in accordance with ASC 740, Income Taxes , which provides for deferred taxes using an asset and liability approach. The Company recognizes deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the consolidated financial statements or tax returns. Deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. A valuation allowance against deferred tax assets is recorded if, based on the weight of the available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. The Company accounts for uncertain tax positions using a more-likely-than-not threshold for recognizing and resolving uncertain tax positions. The evaluation of uncertain tax positions is based on factors, including, but not limited to, changes in the law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, new audit activity and changes in facts or circumstances related to a tax position.
Comprehensive Loss	Comprehensive loss is comprised of net loss and other comprehensive income (loss). Other comprehensive income (loss) for all periods presented consists solely of unrealized gain (loss) on available-for-sale securities.
Net Loss per Share	Basic net loss per share is calculated by dividing net loss attributable to common stockholders by the weighted average number of share common shares outstanding during the period. Diluted net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common equivalent shares outstanding for the period, including any dilutive effect from convertible preferred stock, outstanding stock options or unvested restricted common stock. The Company follows the two-class method when computing net loss per share for periods when issued shares that meet the definition of participating securities are outstanding. The two-class method calls for the calculation of net loss per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders to be allocated between common and participating securities based upon their respective rights to received dividends as if all income for the period had been distributed. Net losses are not allocated to the Company’s preferred stockholders as they do not have an obligation to share in the Company’s net losses.
Concentrations of Credit Risk	Financial instruments that potentially expose the Company to concentrations of credit risk primarily consist of cash, cash equivalents and investments. The Company maintains its cash and cash equivalent balances with high-quality financial institutions and, consequently, the Company believes that such funds are subject to minimal credit risk. The Company’s cash equivalents and investments are comprised of money market funds that are invested in U.S. Treasury obligations, corporate debt securities, U.S. Treasury obligations and government agency securities. Credit risk in these securities is reduced as a result of the Company’s investment policy to limit the amount invested in any single issuer and to only invest in securities of a high credit quality.
Off-Balance Sheet Risk	The Company has no significant off-balance sheet risk such as foreign exchange contracts, option contracts or other foreign hedging arrangements.
Recent Accounting Pronouncements	In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) , which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. This guidance was originally effective for interim and annual periods beginning after December 15, 2016 and allowed for adoption using a full retrospective method, or a modified retrospective method. Early adoption was originally not permitted. Subsequent to the issuance of ASU 2014-09, the FASB also issued the following updates related to ASC 606, Revenue from Contracts with Customers : • In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, whereby the effective date for the new revenue standard was deferred by one year. As a result of ASU 2015-14, the new revenue standard is now effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017, and early adoption is now permitted for annual periods beginning after December 15, 2016, including interim periods within that annual period. • In March 2016, the FASB issued ASU 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (Reporting Revenue Gross versus Net), to clarify the implementation guidance on principal versus agent considerations. • In April 2016, the FASB issued ASU 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing, to clarify the principle for determining whether a good or service is “separately identifiable” from other promises in the contract and to clarify the categorization of licenses of intellectual property. • In May 2016, the FASB issued ASU 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Technical Expedients, to clarify guidance on transition, determining collectability, non-cash consideration and the presentation of sales and other similar taxes. • In December 2016, the FASB issued ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, that allows entities not to make qualitative disclosures about remaining performance obligations in certain cases, adds disclosure requirements for entities that elect certain optional exemptions and adds twelve additional technical corrections and improvements to the new revenue standard. The Company will adopt ASC 606 effective January 1, 2018 under the modified retrospective method. The modified retrospective method requires that the cumulative effect of initially applying ASC 606 be recognized as an adjustment to the opening balance of retained earnings or accumulated deficit of the annual period that includes the date of initial application. Accordingly, during the first quarter of 2018, the Company currently expects to record an increase to the opening balance of accumulated deficit and a corresponding increase to deferred revenue. This cumulative adjustment is primarily attributable to the transition from recognizing revenue on a straight-line basis over the estimated performance period for each unit of accounting under ASC 605 to recognizing revenue on a proportional performance basis under ASC 606. As part of the adoption of ASC 606, the Company has implemented new processes to objectively measure the performance under the Celgene Collaboration Agreement. The Company will complete these processes in the first quarter of 2018, upon adoption of the new standard. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) , which requires a lessee to recognize assets and liabilities on the balance sheet for operating leases and changes many key definitions, including the definition of a lease. The new standard includes a short-term lease exception for leases with a term of 12 months or less, as part of which a lessee can make an accounting policy election not to recognize lease assets and lease liabilities. Lessees will continue to differentiate between finance leases (previously referred to as capital leases) and operating leases using classification criteria that are substantially similar to the previous guidance. The new standard will be effective beginning January 1, 2019, and early adoption is permitted for public entities. The Company is currently evaluating the potential impact that ASU 2016-02 may have on the consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . The new standard identifies areas for simplification involving several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, an option to recognize gross stock-based compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the consolidated statements of cash flows. The Company adopted ASU 2016-09 effective January 1, 2017, and the Company has elected to apply the simplification guidance related to the accounting for forfeitures. Accordingly, the Company will recognize gross stock-based compensation expense with actual forfeitures recognized as they occur. This simplification guidance related to the accounting for forfeitures is applied using a modified retrospective transition method. As forfeitures previously estimated by the Company through the year ended December 31, 2016 were not material, there was not a material cumulative-effect adjustment to accumulated deficit upon adoption of this guidance. The adoption of ASU 2016-09 also requires all excess tax benefits and tax deficiencies related to share-based payments to be recorded in the consolidated statements of operations. The adoption of ASU 2016-09 did not have a material impact on the Company’s consolidated financial statements as the increase in net deferred tax assets is offset by a corresponding increase in the deferred tax asset valuation allowance. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments , which is intended to reduce diversity in practice in how entities present certain types of cash transactions in the statement of cash flows. This guidance also clarifies how the predominance principle should be applied when classifying cash receipts and cash payments that have attributes of more than one class of cash flows. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and early adoption is permitted. An entity that elects early adoption must adopt all of the amendments in the same period. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash , which will require entities to show the change in the total of cash, cash equivalents, restricted cash and restricted cash equivalents within the statement of cash flows. As a result, entities will no longer separately present transfers between unrestricted cash and restricted cash. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and early adoption is permitted. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance. In May 2017, the FASB issued ASU 2017-09, Compensation—Stock Compensation (Topic 718): Scope of Modification Accounting . This guidance is intended to provide clarity and reduce diversity in practice as to when changes to the terms or conditions of share-based payments are accounted for as modifications. Under this new guidance, entities will apply modification accounting if the fair value, vesting conditions or classification of the award changes. This guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and early adoption is permitted. The guidance per ASU 2017-09 is to be adopted prospectively to an award modified on or after the adoption date. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Assets Measured at Fair Value	Assets measured at fair value on a recurring basis as of December 31, 2017 were as follows (in thousands): Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Money market funds, included in cash equivalents $ 21,059 $ 21,059 $ — $ — Investments: Corporate debt securities 65,173 — 65,173 — U.S. Treasuries 110,948 110,948 — — Government agency securities 58,171 58,171 — — Totals $ 255,351 $ 190,178 $ 65,173 $ — Assets measured at fair value on a recurring basis as of December 31, 2016 were as follows (in thousands): December 31, 2016 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs Money market funds, included in cash equivalents $ 44,848 $ 44,848 $ — $ — Investments: Corporate debt securities 92,408 — 92,408 — U.S. Treasuries 120,118 120,118 — — Totals $ 257,374 $ 164,966 $ 92,408 $ —

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Schedule of Available-for-sale Securities by Security Type	Cash equivalents, short-term investments and long-term investments as of December 31, 2017 were comprised as follows (in thousands): December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 21,059 $ — $ — $ 21,059 Corporate debt securities 58,136 — (64 ) 58,072 U.S. Treasuries 111,049 — (101 ) 110,948 Government agency securities 43,204 — (131 ) 43,073 Total cash equivalents and short-term investments 233,448 — (296 ) 233,152 Long-term investments: Corporate debt securities 7,117 — (16 ) 7,101 Government agency securities 15,195 — (97 ) 15,098 Total long-term investments 22,312 — (113 ) 22,199 Total cash equivalents and investments $ 255,760 $ — $ (409 ) $ 255,351 Cash equivalents, short-term investments and long-term investments as of December 31, 2016 were comprised as follows (in thousands): December 31, 2016 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 44,848 $ — $ — $ 44,848 Corporate debt securities 92,549 — (141 ) 92,408 U.S. Treasuries 12,020 — (18 ) 12,002 Total cash equivalents and short-term investments 149,417 — (159 ) 149,258 Long-term investments: U.S. Treasuries 108,390 — (274 ) 108,116 Total long-term investments 108,390 — (274 ) 108,116 Total cash equivalents and investments $ 257,807 $ — $ (433 ) $ 257,374

Prepaid Expenses and Other Cu30

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Schedule of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets as of December 31, 2017 and 2016 were comprised as follows (in thousands): December 31, 2017 2016 Prepaid expenses $ 2,196 $ 1,310 Taxes receivable 16,737 — Interest receivable on investments 969 709 Other current assets 43 510 Total prepaid expenses and other current assets $ 19,945 $ 2,529

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property and equipment, net as of December 31, 2017 and 2016 was comprised as follows (in thousands): Estimated Useful Life (in Years) December 31, 2017 2016 Laboratory equipment 5 $ 9,409 $ 6,275 Furniture and office equipment 4 1,038 226 Computer equipment 3 1,380 492 Leasehold improvements Shorter of useful life or remaining lease term 8,498 3,997 Construction in progress — 1,048 Total property and equipment, gross 20,325 12,038 Less: accumulated depreciation (4,174 ) (4,797 ) Total property and equipment, net $ 16,151 $ 7,241

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2017
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses as of December 31, 2017 and 2016 were comprised as follows (in thousands): December 31, 2017 2016 Employee compensation and benefits $ 3,683 $ 2,651 External research and professional services 4,647 1,923 Lab consumables and other 124 1,281 Total accrued expenses $ 8,454 $ 5,855

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of Stock by Class	As of December 31, 2017 and 2016 , the Company had reserved for future issuance the following number of shares of common stock (in thousands): December 31, 2017 2016 Shares reserved for Series A convertible preferred stock outstanding — 12,737 Shares reserved for Series B convertible preferred stock outstanding — 6,715 Shares reserved for Series B-1 convertible preferred stock outstanding — 2,831 Shares reserved for vesting of restricted stock awards 16 94 Shares reserved for exercises of outstanding stock options 4,868 4,290 Shares reserved for future issuances under the 2017 Stock Incentive Plan 1,032 244 Total shares reserved for future issuance 5,916 26,911

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Stock-Based Compensation Expense	Total stock-based compensation expense recognized in the consolidated statements of operations for the years ended December 31, 2017 , 2016 and 2015 was as follows (in thousands): Year Ended December 31, 2017 2016 2015 Research and development $ 2,840 $ 4,161 $ 269 General and administrative 1,935 828 1,083 Total stock-based compensation expense $ 4,775 $ 4,989 $ 1,352
Schedule of Restricted Stock Activity	The following table summarizes changes in unvested restricted stock for the year ended December 31, 2017 (in thousands, except per share amounts): Shares Weighted-Average Grant Date Fair Value per Share Unvested restricted stock as of December 31, 2016 94 $ 0.07 Issued — $ — Vested (77 ) $ 0.08 Repurchased (1 ) $ 0.37 Unvested restricted stock as of December 31, 2017 16 $ —
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The fair value of stock options granted to employees and directors during the years ended December 31, 2017 , 2016 and 2015 was calculated on the date of grant using the following weighted-average assumptions: Year Ended December 31, 2017 2016 2015 Risk-free interest rate 2.1 % 1.4 % 1.8 % Expected dividend yield — % — % — % Expected term (in years) 6.1 6.1 6.1 Expected volatility 70.1 % 71.9 % 67.0 %
Schedule of Stock Options, Activity	The following table summarizes changes in stock option activity during the year ended December 31, 2017 (in thousands, except per share amounts): Options Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Outstanding at December 31, 2016 4,290 $ 3.95 8.7 $ 29,269 Granted 983 $ 17.19 Exercised (144 ) $ 3.20 Cancelled or forfeited (261 ) $ 10.71 Outstanding at December 31, 2017 4,868 $ 6.28 7.9 $ 35,178 Exercisable at December 31, 2017 2,217 $ 2.79 7.2 $ 22,170

Income Taxes Income Taxes (Tabl

Income Taxes Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Summary of Components of the Provision for Income Taxes	The provision for income taxes for the years ended December 31, 2017 , 2016 and 2015 was comprised as follows (in thousands): Year Ended December 31, 2017 2016 2015 Current taxes: Federal $ — $ — $ — State 36 — — Total current taxes 36 — — Deferred taxes: Federal — — — State — — — Total deferred taxes — — — Total provision for income taxes $ 36 $ — $ —
Reconciliation of the Federal Statutory Income Tax Rate to the Effective Tax Rate	A reconciliation of the federal statutory income tax rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2017 2016 2015 Income tax computed at federal statutory tax rate 34.0 % 34.0 % 34.0 % Deferred tax effects from the Tax Act (57.2 )% — % — % State taxes, net of federal benefit 4.7 % 3.1 % 5.3 % Tax credit carryforwards 26.8 % 11.7 % 4.5 % Non-deductible income (expense) (4.9 )% (11.1 )% 0.7 % Change in valuation allowance (1.8 )% (39.4 )% (44.5 )% Other (1.8 )% 1.7 % — % Effective tax rate (0.2 )% — % — %
Schedule of Components of Deferred Tax Assets and Liabilities	The principal components of the Company’s deferred tax assets and liabilities as of December 31, 2017 and 2016 were comprised as follows (in thousands): December 31, 2017 2016 Deferred tax assets: Net operating loss carryforwards $ 26,926 $ 24,435 Tax credit carryforwards 8,432 4,039 Deferred revenue 31,735 — Deferred lease incentive 120 553 Deferred rent 431 426 Intangibles 237 187 Accrued expenses and other 995 1,018 Unrealized loss on available-for-sale securities 112 169 Stock-based compensation 713 293 Total deferred tax assets 69,701 31,120 Less: valuation allowance (30,850 ) (30,548 ) Net deferred tax assets 38,851 572 Deferred tax liabilities: Section 481(a) method change (38,481 ) — Depreciation (370 ) (572 ) Total deferred tax liabilities (38,851 ) (572 ) Net deferred taxes $ — $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	As of December 31, 2017 , the future minimum lease payments due under the operating lease for the Company’s corporate headquarters are as follows (in thousands): Years Ended December 31, Minimum Lease Payments 2018 $ 4,139 2019 4,263 2020 4,391 2021 4,523 2022 4,659 2023 and thereafter 10,996 Total future minimum lease payments $ 32,971

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Net Loss per Share	For purposes of the diluted loss per share calculation, convertible preferred stock, outstanding stock options and unvested restricted common stock are considered to be potentially dilutive securities, however the following common stock equivalents have been excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive (in thousands): Year Ended December 31, 2017 2016 2015 Series A convertible preferred stock — 12,737 12,737 Series B convertible preferred stock — 6,715 6,715 Series B-1 convertible preferred stock — 2,831 — Outstanding stock options 4,868 4,290 2,960 Unvested restricted common stock 16 94 748 Total 4,884 26,667 23,160

Selected Quarterly Financial 38

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information	The following tables contain selected quarterly financial information for the years ended December 31, 2017 and 2016 . The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. 2017 (in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue—related party $ 20,289 $ 20,289 $ 18,077 $ 12,989 Total operating expenses 20,536 23,317 22,465 24,541 Operating loss (247 ) (3,028 ) (4,388 ) (11,552 ) Total other income, net 632 752 721 703 Provision for (benefit from) income taxes — 1,104 417 (1,485 ) Net income (loss) $ 385 $ (3,380 ) $ (4,084 ) $ (9,364 ) Net loss attributable to common stockholders $ (409 ) $ (3,380 ) $ (4,084 ) $ (9,364 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.02 ) $ (0.11 ) $ (0.13 ) $ (0.29 ) 2016 (in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Collaboration revenue—related party $ — $ — $ 16,908 $ 20,289 Total operating expenses 10,901 12,362 13,093 15,307 Operating (loss) income (10,901 ) (12,362 ) 3,815 4,982 Total other income, net 11 14 254 484 Net (loss) income $ (10,890 ) $ (12,348 ) $ 4,069 $ 5,466 Net (loss) income attributable to common stockholders $ (12,934 ) $ (14,392 ) $ 138 $ 258 Net (loss) income per share attributable to common stockholders, basic $ (6.81 ) $ (7.23 ) $ 0.06 $ 0.11 Net (loss) income per share attributable to common stockholders, diluted $ (6.81 ) $ (7.23 ) $ 0.03 $ 0.05

Nature of Business (Details)

Nature of Business (Details) $ / shares in Units, $ in Thousands	Mar. 08, 2018	Feb. 01, 2017USD ($)$ / sharesshares	Jan. 13, 2017	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from initial public offering of common stock, net of issuance costs				$ 107,008	$ 0	$ 0
Reverse stock split			0.2710
Accumulated deficit				(89,615)	$ (73,172)
Cash, cash equivalents, and marketable securities				$ 257,900
IPO
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of common stock (in shares) | shares		7,319,750
Public offering share price (in dollars per share) | $ / shares		$ 16
Proceeds from initial public offering of common stock, net of issuance costs		$ 117,100
Proceeds from IPO, net of discounts, commissions, and other offering expenses		$ 106,400
Stock converted upon completion of IPO (in shares) | shares		22,283,690
Over-Allotment Option
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Issuance of common stock (in shares) | shares		954,750
Scenario, Forecast
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Duration of funding requirement	24 months

Basis of Presentation and Sum40

Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) $ in Millions	Dec. 31, 2016USD ($)
Accounting Policies [Abstract]
Deferred financing costs	$ 1.5

Celgene Collaboration Agreeme41

Celgene Collaboration Agreement (Details) $ in Thousands	Feb. 01, 2017shares	Jul. 31, 2016USD ($)extensiondeliverablecustomer_programshares	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)shares
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue—related party			$ 71,600	$ 37,200
Deferred revenue			$ 116,200
Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of early-stage programs | customer_program		4
Non-refundable upfront payment received for research agreement		$ 225,000
Aggregate option-exercise fees from program options		$ 182,500
Number of program options | deliverable		6
Initial research term		4 years
Potential addition to research term		3 years
Aggregate consideration for additional years of research		$ 120,000
Potential milestone revenue		2,300,000
Aggregate development milestone revenue		290,000
Aggregate regulatory approval milestone revenue		700,000
Aggregate commercial milestone revenue		$ 1,270,000
Number of program extensions | extension		3
Program extension research term		1 year
Series B-1 Convertible Preferred Stock
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Issuances of convertible preferred stock				$ 36,077
Issuances of convertible preferred stock (in shares) | shares				10,448,100
Series B-1 Convertible Preferred Stock | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Issuances of convertible preferred stock		$ 36,100
Issuances of convertible preferred stock (in shares) | shares		10,448,100
Minimum | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Option-exercise fee for program option		$ 10,000
Consideration for additional year of research		30,000
Development milestone revenue, per program		32,500
Regulatory approval milestone revenue, per program		7,500
Commercial milestone revenue, per program		$ 40,000
Program option term		45 days
Performance period for unit of accounting		12 months
Maximum | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Option-exercise fee for program option		$ 60,000
Consideration for additional year of research		45,000
Development milestone revenue, per program		105,000
Regulatory approval milestone revenue, per program		50,000
Commercial milestone revenue, per program		$ 200,000
Program option term		60 days
Performance period for unit of accounting		4 years
JTX-2011 | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percent of operating profit or loss retained		60.00%
JTX-2011 | Celgene Corporation | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percent of operating profit or loss retained		40.00%
Lead Program | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percent of operating profit or loss retained		25.00%
Lead Program | Celgene Corporation | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percent of operating profit or loss retained		75.00%
Other Programs | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percent of operating profit or loss retained		50.00%
Other Programs | Celgene Corporation | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percent of operating profit or loss retained		50.00%
All Programs, Excluding JTX-4014 | Celgene Corporation | Minimum | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percent of development costs		67.00%
All Programs, Excluding JTX-4014 | Celgene Corporation | Maximum | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Percent of development costs		85.00%
IPO
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Stock converted upon completion of IPO (in shares) | shares	22,283,690
Celgene Corporation | Celgene Collaboration Agreement | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Non-refundable upfront payment received for research agreement		$ 225,000
Celgene Corporation | Celgene Collaboration Agreement | Series B-1 Convertible Preferred Stock | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Issuances of convertible preferred stock		$ 36,100
Issuances of convertible preferred stock (in shares) | shares		10,448,100
Celgene Corporation | Celgene Collaboration Agreement | IPO | Common Stock
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Stock converted upon completion of IPO (in shares) | shares	2,831,463

Fair Value Measurements - Asset

Fair Value Measurements - Assets Measured at Fair Value (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Measurements, Recurring
Investments:
Totals	$ 255,351,000	$ 257,374,000
Liabilities measured at fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Investments:
Totals	190,178,000	164,966,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Investments:
Totals	65,173,000	92,408,000
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Investments:
Totals	0	0
Money market funds, included in cash equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	21,059,000	44,848,000
Money market funds, included in cash equivalents | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	21,059,000	44,848,000
Money market funds, included in cash equivalents | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	21,059,000	44,848,000
Money market funds, included in cash equivalents | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	0	0
Money market funds, included in cash equivalents | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds, included in cash equivalents	0	0
Corporate debt securities | Fair Value, Measurements, Recurring
Investments:
Available-for-sale debt securities, fair value	65,173,000	92,408,000
Corporate debt securities | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Investments:
Available-for-sale debt securities, fair value	0	0
Corporate debt securities | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Investments:
Available-for-sale debt securities, fair value	65,173,000	92,408,000
Corporate debt securities | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Investments:
Available-for-sale debt securities, fair value	0	0
U.S. Treasuries | Fair Value, Measurements, Recurring
Investments:
Available-for-sale debt securities, fair value	110,948,000	120,118,000
U.S. Treasuries | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Investments:
Available-for-sale debt securities, fair value	110,948,000	120,118,000
U.S. Treasuries | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Investments:
Available-for-sale debt securities, fair value	0	0
U.S. Treasuries | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Investments:
Available-for-sale debt securities, fair value	0	$ 0
Government agency securities | Fair Value, Measurements, Recurring
Investments:
Available-for-sale debt securities, fair value	58,171,000
Government agency securities | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Investments:
Available-for-sale debt securities, fair value	58,171,000
Government agency securities | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Investments:
Available-for-sale debt securities, fair value	0
Government agency securities | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Investments:
Available-for-sale debt securities, fair value	$ 0

Investments - Available-for-sal

Investments - Available-for-sale Securities by Security Type (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Unrealized Gains	$ 0	$ 0
Unrealized Losses	(409)	(433)
Cash equivalents, short-term and long-term investments, carrying value	255,760	257,807
Cash equivalents, short-term and long-term investments, fair vale disclosure	255,351	257,374
Money market funds, included in cash equivalents
Schedule of Available-for-sale Securities [Line Items]
Cash equivalents at carrying value	21,059	44,848
Cash equivalents at fair value	21,059	44,848
Short-term Investments
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Unrealized Gains	0	0
Unrealized Losses	(296)	(159)
Total cash equivalents and short-term investments, carrying value	233,448	149,417
Total cash equivalents and short-term investments, fair value	233,152	149,258
Short-term Investments | Corporate debt securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	58,136	92,549
Unrealized Gains	0	0
Unrealized Losses	(64)	(141)
Available-for-sale debt securities, fair value	58,072	92,408
Short-term Investments | U.S. Treasuries
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	111,049	12,020
Unrealized Gains	0	0
Unrealized Losses	(101)	(18)
Available-for-sale debt securities, fair value	110,948	12,002
Short-term Investments | Government agency securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	43,204
Unrealized Gains	0
Unrealized Losses	(131)
Available-for-sale debt securities, fair value	43,073
Long-term Investments
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	22,312	108,390
Unrealized Gains	0	0
Unrealized Losses	(113)	(274)
Available-for-sale debt securities, fair value	22,199	108,116
Long-term Investments | Corporate debt securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	7,117
Unrealized Gains	0
Unrealized Losses	(16)
Available-for-sale debt securities, fair value	7,101
Long-term Investments | U.S. Treasuries
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis		108,390
Unrealized Gains		0
Unrealized Losses		(274)
Available-for-sale debt securities, fair value		$ 108,116
Long-term Investments | Government agency securities
Available-for-sale Securities, Fair Value to Amortized Cost Basis [Abstract]
Available-for-sale debt securities, amortized cost basis	15,195
Unrealized Gains	0
Unrealized Losses	(97)
Available-for-sale debt securities, fair value	$ 15,098

Investments - Narrative (Detail

Investments - Narrative (Details)	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)investment	Dec. 31, 2015USD ($)
Investments, Debt and Equity Securities [Abstract]
Available-for-sale securities in an unrealized loss position for less than twelve months	$ 113,900,000	$ 192,300,000
Aggregate fair value of the securities in an unrealized loss position for more than twelve months	107,900,000
Number of securities in unrealized loss position, greater than 12 months | investment		0
Realized gains or losses on available-for-sale securities	$ 0	$ 0	$ 0

Prepaid Expenses and Other Cu45

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 2,196	$ 1,310
Taxes receivable	16,737	0
Interest receivable on investments	969	709
Other current assets	43	510
Total prepaid expenses and other current assets	$ 19,945	$ 2,529

Restricted Cash (Details)

Restricted Cash (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Non-current restricted cash	$ 1.3	$ 1.5

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 20,325	$ 12,038
Less: accumulated depreciation	(4,174)	(4,797)
Total property and equipment, net	$ 16,151	7,241
Laboratory equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	5 years
Property and equipment, gross	$ 9,409	6,275
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	4 years
Property and equipment, gross	$ 1,038	226
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	3 years
Property and equipment, gross	$ 1,380	492
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	8,498	3,997
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 0	$ 1,048

Property and Equipment, Net - N

Property and Equipment, Net - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 4,422	$ 1,944	$ 1,470

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Payables and Accruals [Abstract]
Employee compensation and benefits	$ 3,683	$ 2,651
External research and professional services	4,647	1,923
Lab consumables and other	124	1,281
Total accrued expenses	$ 8,454	$ 5,855

Common Stock - Narrative (Detai

Common Stock - Narrative (Details)	Dec. 31, 2017voteshares	Dec. 31, 2016shares
Equity [Abstract]
Common stock, shares authorized (in shares) | shares	160,000,000	29,810,000
Common stock, votes per share | vote	1

Common Stock - Shares Reserved

Common Stock - Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2017	Jan. 31, 2017	Dec. 31, 2016
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	5,916,000	1,753,758	26,911,000
Series A Convertible Preferred Stock
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	0		12,737,000
Series B Convertible Preferred Stock
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	0		6,715,000
Series B-1 Convertible Preferred Stock
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	0		2,831,000
Restricted Stock
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	16,000		94,000
Outstanding Employee Stock Options
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	4,868,000		4,290,000
Future Issuances from Employee Stock Options
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	1,032,000		244,000

Preferred Stock (Details)

Preferred Stock (Details) $ / shares in Units, $ in Thousands	Feb. 01, 2017shares	Feb. 28, 2014USD ($)transaction$ / sharesshares	Apr. 30, 2015transaction	Dec. 31, 2017USD ($)shares	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares	Dec. 31, 2014USD ($)transactionshares	Dec. 31, 2015USD ($)$ / sharesshares	Dec. 31, 2013USD ($)$ / sharesshares
Class of Stock [Line Items]
Issuance costs				$ 0	$ 620	$ 241
Loss on extinguishment of convertible preferred stock				$ 0	$ 0	$ 2,079
Preferred stock, shares authorized (in shares) | shares				5,000,000	0
Preferred stock, shares issued (in shares) | shares				0	0
Preferred stock, shares outstanding (in shares) | shares				0	0
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Issuances of convertible preferred stock (in shares) | shares						15,000,000		47,000,000
Temporary Equity, Par or Stated Value Per Share | $ / shares						$ 1		$ 1
Proceeds from the issuance of convertible preferred stock, net of issuance costs				$ 0	$ 0	$ 14,984		$ 44,600
Issuance costs								100
Exercise price of tranche rights (in dollars per share) | $ / shares		$ 1
Number of separate closing transactions | transaction		2
Portion of commitment to be closed upon achievement of milestones		50.00%
Portion of commitment to be closed subsequent to achieving milestones		50.00%
Duration of commitment closed		6 months
Fair value adjustment of rights		$ 3,400
Convertible preferred stock and contingently redeemable common stock				0	47,112	47,112	$ 27,313	$ 47,112
Loss on extinguishment of convertible preferred stock						$ 2,100
Series B Convertible Preferred Stock
Class of Stock [Line Items]
Issuances of convertible preferred stock (in shares) | shares						24,778,761
Temporary Equity, Par or Stated Value Per Share | $ / shares						$ 2.26		$ 2.26
Proceeds from the issuance of convertible preferred stock, net of issuance costs				0	0	$ 55,849
Issuance costs						200
Convertible preferred stock and contingently redeemable common stock				0	$ 55,849	55,849	0	$ 55,849
Series B-1 Convertible Preferred Stock
Class of Stock [Line Items]
Issuances of convertible preferred stock (in shares) | shares					10,448,100
Temporary Equity, Par or Stated Value Per Share | $ / shares					$ 3.46
Proceeds from the issuance of convertible preferred stock, net of issuance costs				0	$ 36,077	0
Issuance costs					100
Convertible preferred stock and contingently redeemable common stock				$ 0	$ 36,077	0	$ 0	0
IPO
Class of Stock [Line Items]
Stock converted upon completion of IPO (in shares) | shares	22,283,690
Convertible Promissory Note Receivable | Series A Convertible Preferred Stock
Class of Stock [Line Items]
Outstanding convertible promissory notes						2,300		2,300
Tranche Right I | Series A Convertible Preferred Stock
Class of Stock [Line Items]
Issuances of convertible preferred stock (in shares) | shares							15,000,000
Proceeds from the issuance of convertible preferred stock, net of issuance costs							$ 15,000
Number of shares called by tranche rights (in shares) | shares		15,000,000							10,000,000
Exercise price of tranche rights (in dollars per share) | $ / shares									$ 1
Fair value asset (liability) of right									$ 1,200
Increase (decrease) in number of securities called by tranche rights (in shares) | shares		5,000,000
Number of separate closing transactions | transaction							2
Tranche Right II | Series A Convertible Preferred Stock
Class of Stock [Line Items]
Number of shares called by tranche rights (in shares) | shares		15,000,000							20,000,000
Fair value asset (liability) of right									$ (6,500)
Increase (decrease) in number of securities called by tranche rights (in shares) | shares		(5,000,000)
Number of separate closing transactions | transaction			2
Fair value adjustment of rights						1,900
Convertible preferred stock and contingently redeemable common stock						16,700		16,700
Aggregate amount of redemption requirement						$ 15,000		$ 15,000

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended			61 Months Ended
	Feb. 28, 2013shares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)non-employee$ / sharesshares	Dec. 31, 2015USD ($)$ / sharesshares	Dec. 31, 2017USD ($)shares	Jun. 30, 2017non-employee	Jan. 31, 2017shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock eligible to be purchased (in shares)		5,916,000	26,911,000		5,916,000		1,753,758
Weighted average fair value of options granted (in dollars per share) | $ / shares		$ 10.96	$ 5.10	$ 1.70
Stock options issued (in shares)		983,000
Intrinsic value of stock options exercised | $		$ 1.9	$ 0.3	$ 0.1
Unrecognized stock-based compensation expense, options | $		$ 13.8			$ 13.8
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock eligible to be purchased (in shares)		16,000	94,000		16,000
Issued (in shares)		0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period		77,000
Aggregate fair value of awards vested in period | $		$ 1.3	$ 3.9	$ 1.1
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate		2.10%	1.40%	1.80%
Expected dividend yield		0.00%	0.00%	0.00%
Expected term (in years)		6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility		70.10%	71.90%	67.00%
Remaining weighted average vesting period		2 years 5 months 5 days
2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance (in shares)							0
Shares of common stock eligible to be purchased (in shares)							243,758
2013 Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issued (in shares)		0	0	27,099
Purchase price (in dollars per share) | $ / shares				$ 4.02
2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance (in shares)		1,032,252			1,032,252
Shares of common stock eligible to be purchased (in shares)							1,510,000
Percent of outstanding shares able to be added each year							4.00%
2017 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock eligible to be purchased (in shares)							302,000
Founder Agreements | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issued (in shares)	1,395,659
Number of non-employee founders | non-employee			2			2
Founder Agreements | Restricted Stock | Share-Based Compensation Award, Founder Awards, Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					1,043,357
Founder Agreements | Restricted Stock | Share-Based Compensation Award, Founder Awards, Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period					352,302
Founder Agreements | Restricted Stock | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	1 year
Founder Agreements | Restricted Stock | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
2013 Stock Option and Grant Plan, Non-Employees | Non-Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average fair value of options granted (in dollars per share) | $ / shares				$ 0.85
Stock options issued (in shares)		0	0	12,195
Risk-free interest rate				2.00%
Expected dividend yield				0.00%
Expected term (in years)				9 years 9 months 18 days
Expected volatility				68.70%

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4,775	$ 4,989	$ 1,352
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	2,840	4,161	269
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,935	$ 828	$ 1,083

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Activity (Details) - Restricted Stock shares in Thousands	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning unvested balance (in shares) | shares	94
Issued (in shares) | shares	0
Vested (in shares) | shares	(77)
Repurchased (in shares) | shares	(1)
Ending unvested balance (in shares) | shares	16
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning unvested balance (in dollars per share) | $ / shares	$ 0.07
Issued (in dollars per share) | $ / shares	0
Vested (in dollars per share) | $ / shares	0.08
Repurchased (in dollars per share) | $ / shares	0.37
Ending unvested balance (in dollars per share) | $ / shares	$ 0

Stock-Based Compensation - Weig

Stock-Based Compensation - Weighted Average Assumptions (Details) - Employee Stock Option	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.10%	1.40%	1.80%
Expected dividend yield	0.00%	0.00%	0.00%
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility	70.10%	71.90%	67.00%

Stock-Based Compensation - St57

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning outstanding balance (in shares)	4,290
Granted (in shares)	983
Exercised (in shares)	(144)
Cancelled or forfeited (in shares)	(261)
Ending oustanding balance (in shares)	4,868	4,290
Exercisable (in shares)	2,217
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning outstanding balance (in dollars per share)	$ 3.95
Granted (in dollars per share)	17.19
Exercised (in dollars per share)	3.20
Cancelled or forfeited (in dollars per share)	10.71
Ending outstanding balance (in dollars per share)	6.28	$ 3.95
Exercisable (in dollars per share)	$ 2.79
Remaining contractual life, outstanding	7 years 10 months 28 days	8 years 8 months 12 days
Remaining contractual life, exercisable	7 years 2 months 12 days
Aggregate intrinsic value, outstanding	$ 35,178	$ 29,269
Aggregate intrinsic value, exercisable	$ 22,170

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income Tax Provision (Details) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current taxes:
Federal					$ 0	$ 0	$ 0
State					36	0	0
Total current taxes					36	0	0
Deferred taxes:
Federal					0	0	0
State					0	0	0
Total deferred taxes					0	0	0
Total provision for income taxes	$ (1,485)	$ 417	$ 1,104	$ 0	$ 36	$ 0	$ 0

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details)	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Aug. 31, 2016change
Operating Loss Carryforwards [Line Items]
Tax reform, revaluation of deferred tax assets	$ 9,400,000
Tax reform, valuation allowance reduction	9,400,000
Cash paid for income taxes	16,750,000	$ 0	$ 0
Less: valuation allowance	(30,850,000)	(30,548,000)
Decrease in deferred tax asset valuation allowance	(300,000)
Number of previous ownership changes | change				3
Unrecognized tax benefits	0	$ 0
Interest and penalty charges incurred	0
Federal Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	98,500,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	98,600,000
Research and Development Tax Credit Carryforwards | Federal Tax Authority
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	6,000,000
Research and Development Tax Credit Carryforwards | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	2,600,000
Investment Tax Credit Carryforwards | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 500,000

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory tax rate	34.00%	34.00%	34.00%
Deferred tax effects from the Tax Act	(57.20%)	0.00%	0.00%
State taxes, net of federal benefit	4.70%	3.10%	5.30%
Tax credit carryforwards	26.80%	11.70%	4.50%
Non-deductible income (expense)	(4.90%)	(11.10%)	0.70%
Change in valuation allowance	(1.80%)	(39.40%)	(44.50%)
Other	(1.80%)	1.70%	0.00%
Effective tax rate	(0.20%)	0.00%	0.00%

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 26,926	$ 24,435
Tax credit carryforwards	8,432	4,039
Deferred revenue	31,735	0
Deferred lease incentive	120	553
Deferred rent	431	426
Intangibles	237	187
Accrued expenses and other	995	1,018
Unrealized loss on available-for-sale securities	112	169
Stock-based compensation	713	293
Total deferred tax assets	69,701	31,120
Less: valuation allowance	(30,850)	(30,548)
Net deferred tax assets	38,851	572
Deferred tax liabilities:
Section 481(a) method change	(38,481)	0
Depreciation	(370)	(572)
Total deferred tax liabilities	(38,851)	(572)
Net deferred taxes	$ 0	$ 0

Related-Party Transactions (Det

Related-Party Transactions (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 01, 2017	Jul. 31, 2016	Dec. 31, 2016
Celegene Collaborative Arrangement
Related Party Transaction [Line Items]
Non-refundable upfront payment received for research agreement		$ 225,000
Series B-1 Convertible Preferred Stock
Related Party Transaction [Line Items]
Issuances of convertible preferred stock (in shares)			10,448,100
Issuances of convertible preferred stock			$ 36,077
Series B-1 Convertible Preferred Stock | Celegene Collaborative Arrangement
Related Party Transaction [Line Items]
Issuances of convertible preferred stock (in shares)		10,448,100
Issuances of convertible preferred stock		$ 36,100
IPO
Related Party Transaction [Line Items]
Stock converted upon completion of IPO (in shares)	22,283,690
Proceeds from IPO, net of discounts, commissions, and other offering expenses	$ 106,400
Celgene Corporation | Celgene Collaboration Agreement | Celegene Collaborative Arrangement
Related Party Transaction [Line Items]
Non-refundable upfront payment received for research agreement		$ 225,000
Celgene Corporation | Celgene Collaboration Agreement | Series B-1 Convertible Preferred Stock | Celegene Collaborative Arrangement
Related Party Transaction [Line Items]
Issuances of convertible preferred stock (in shares)		10,448,100
Issuances of convertible preferred stock		$ 36,100
Celgene Corporation | IPO | Celgene Collaboration Agreement | Common Stock
Related Party Transaction [Line Items]
Stock converted upon completion of IPO (in shares)	2,831,463
Affiliated Entity | Celgene Corporation | IPO | Celgene Collaboration Agreement | Common Stock
Related Party Transaction [Line Items]
Sale of stock, number of shares issued (in shares)	625,000
Sale of stock, price per share (USD per share)	$ 16
Proceeds from IPO, net of discounts, commissions, and other offering expenses	$ 10,000

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) ft² in Thousands	1 Months Ended	3 Months Ended	5 Months Ended	12 Months Ended
	Nov. 30, 2016USD ($)ft²consecutive_extension_period	Jun. 30, 2017USD ($)	May 31, 2017USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Loss Contingencies [Line Items]
Lease space occupied (in square feet) | ft²	51
Number of consecutive extension periods | consecutive_extension_period	1
Renewal term	5 years		3 months
Renewal notice period	12 months		9 months
Tenant improvement allowance	$ 500,000		$ 2,800,000
Security deposit, in form of letter of credit	$ 1,300,000
Sublease term			3 years
Early termination fee		$ 700,000
Rent expense				$ 3,500,000	$ 1,800,000	$ 900,000
Costs incurred, third party agreements				300,000
Potential costs, other agreements				700,000
Costs incurred, other agreements				$ 0
Minimum
Loss Contingencies [Line Items]
Cancellation notice period, technology agreements				30 days
Potential costs, third party agreements				$ 12,500,000
Maximum
Loss Contingencies [Line Items]
Cancellation notice period, technology agreements				90 days
Potential costs, third party agreements				$ 12,900,000
License And Collaboration Agreements | Maximum
Loss Contingencies [Line Items]
Potential costs, technology agreements				13,200,000
Costs incurred, technology agreements				$ 200,000

Commitments and Contingencies64

Commitments and Contingencies - Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 4,139
2,019	4,263
2,020	4,391
2,021	4,523
2,022	4,659
2023 and thereafter	10,996
Total future minimum lease payments	$ 32,971

Net Loss per Share (Details)

Net Loss per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	4,884	26,667	23,160
Outstanding stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	4,868	4,290	2,960
Unvested restricted common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	16	94	748
Series A Convertible Preferred Stock | Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	0	12,737	12,737
Series B convertible preferred stock | Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	0	6,715	6,715
Series B-1 convertible preferred stock | Convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	0	2,831	0

Selected Quarterly Financial 66

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Collaboration revenue—related party	$ 12,989	$ 18,077	$ 20,289	$ 20,289	$ 20,289	$ 16,908	$ 0	$ 0	$ 71,644	$ 37,197	$ 0
Total operating expenses	24,541	22,465	23,317	20,536	15,307	13,093	12,362	10,901	90,859	51,663	30,396
Operating loss	(11,552)	(4,388)	(3,028)	(247)	4,982	3,815	(12,362)	(10,901)	(19,215)	(14,466)	(30,396)
Total other income, net	703	721	752	632	484	254	14	11	2,808	763	1,864
Provision for income taxes	(1,485)	417	1,104	0					36	0	0
Net loss	(9,364)	(4,084)	(3,380)	385	5,466	4,069	(12,348)	(10,890)	(16,443)	(13,703)	(28,532)
Net loss attributable to common stockholders	$ (9,364)	$ (4,084)	$ (3,380)	$ (409)	$ 258	$ 138	$ (14,392)	$ (12,934)	$ (17,237)	$ (23,138)	$ (37,503)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.29)	$ (0.13)	$ (0.11)	$ (0.02)					$ (0.57)	$ (11)	$ (23.13)
Net (loss) income per share attributable to common stockholders, basic (in dollars per share)					$ 0.11	$ 0.06	$ (7.23)	$ (6.81)
Net (loss) income per share attributable to common stockholders, diluted (in dollars per share)					$ 0.05	$ 0.03	$ (7.23)	$ (6.81)