Jounce Therapeutics (JNCE) 10-K 6 Mar 19 2018 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2018	Mar. 01, 2019	Jun. 29, 2018
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	Accelerated Filer
Entity Small Business	true
Entity Ex Transition Period	true
Entity Emerging Growth Company	true
Entity Shell Company	false
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Trading Symbol	JNCE
Entity Common Stock, Shares Outstanding		32,972,345
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 120,393,951

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 47,906	$ 23,559
Short-term investments	141,968	212,093
Prepaid expenses and other current assets	2,335	19,945
Total current assets	192,209	255,597
Property and equipment, net	13,540	16,151
Long-term investments	5,990	22,199
Other non-current assets	2,713	2,713
Total assets	214,452	296,660
Current liabilities:
Accounts payable	3,272	2,849
Accrued expenses	6,952	8,454
Deferred rent and lease incentive, current	61	61
Deferred revenue, current—related party	55,157	51,142
Other current liabilities	104	45
Total current liabilities	65,546	62,551
Deferred rent and lease incentive, net of current portion	2,062	1,955
Deferred revenue, net of current portion—related party	42,715	65,018
Other non-current liabilities	0	27
Total liabilities	110,323	129,551
Commitments and contingencies (Note 15)
Stockholders’ equity:
Preferred stock, $0.001 par value: 5,000 shares authorized at December 31, 2018 and 2017; no shares issued or outstanding at December 31, 2018 or 2017	0	0
Common stock, $0.001 par value: 160,000 shares authorized at December 31, 2018 and 2017; 32,948 and 32,265 shares issued at December 31, 2018 and 2017, respectively; 32,941 and 32,249 shares outstanding at December 31, 2018 and 2017, respectively	33	32
Additional paid-in capital	268,081	257,101
Accumulated other comprehensive loss	(78)	(409)
Accumulated deficit	(163,907)	(89,615)
Total stockholders’ equity	104,129	167,109
Total liabilities and stockholders’ equity	$ 214,452	$ 296,660

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
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	160,000,000
Common stock, shares issued (in shares)	32,948,000	32,265,000
Common stock, shares outstanding (in shares)	32,941,000	32,249,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Collaboration revenue—related party	$ 65,201	$ 71,644
Operating expenses:
Research and development	70,052	67,798
General and administrative	26,443	23,061
Total operating expenses	96,495	90,859
Operating loss	(31,294)	(19,215)
Other income, net	3,961	2,808
Loss before provision for income taxes	(27,333)	(16,407)
Provision for income taxes	46	36
Net loss	(27,379)	(16,443)
Reconciliation of net loss to net loss attributable to common stockholders:
Net loss	(27,379)	(16,443)
Net loss attributable to common stockholders	$ (27,379)	$ (17,237)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.84)	$ (0.57)
Weighted-average common shares outstanding, basic and diluted (in shares)	32,567	30,055
Series A Convertible Preferred Stock
Reconciliation of net loss to net loss attributable to common stockholders:
Accrued dividends on convertible preferred stock	$ 0	$ (268)
Series B Convertible Preferred Stock
Reconciliation of net loss to net loss attributable to common stockholders:
Accrued dividends on convertible preferred stock	0	(318)
Series B-1 Convertible Preferred Stock
Reconciliation of net loss to net loss attributable to common stockholders:
Accrued dividends on convertible preferred stock	$ 0	$ (208)

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (27,379)	$ (16,443)
Other comprehensive income:
Unrealized gain on available-for-sale securities	331	24
Comprehensive loss	$ (27,048)	$ (16,419)

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock, Contingently Redeemable Common Stock and Stockholders’ (Deficit) Equity - USD ($) shares in Thousands, $ 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, 2016		47,000	24,779	10,448
Beginning balance at Dec. 31, 2016		$ 47,112	$ 55,849	$ 36,077	$ 1,921
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of convertible preferred stock into common stock upon closing of initial public offering (in shares)		(47,000)	(24,779)	(10,448)		22,284
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
Beginning balance, common stock (in shares) at Dec. 31, 2016						2,424
Beginning balance at Dec. 31, 2016	(69,088)					$ 2	4,515	$ (433)	$ (73,172)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock (in shares)						7,320
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)	(24,779)	(10,448)		22,284
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
Exercise of common stock options	462						462
Vesting of restricted stock awards (in shares)						77
Vesting of restricted stock awards	32						32
Stock-based compensation expense	4,505				270		4,505
Other comprehensive income	24							24
Net loss	$ (16,443)								(16,443)
Ending balance, common stock (in shares) at Dec. 31, 2017	32,249					32,249
Ending balance at Dec. 31, 2017	$ 167,109					$ 32	257,101	(409)	(89,615)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment upon adoption of ASC 606	(46,913)								(46,913)
Stock-based compensation expense	$ 9,407						9,407
Ending balance (in shares) at Dec. 31, 2018		0	0	0
Ending balance at Dec. 31, 2018		$ 0	$ 0	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	683
Exercise of common stock options	$ 1,546					$ 1	1,545
Vesting of restricted stock awards (in shares)						9
Vesting of restricted stock awards	28						28
Stock-based compensation expense	9,407						9,407
Other comprehensive income	331							331
Net loss	$ (27,379)								(27,379)
Ending balance, common stock (in shares) at Dec. 31, 2018	32,941					32,941
Ending balance at Dec. 31, 2018	$ 104,129					$ 33	$ 268,081	$ (78)	$ (163,907)

Consolidated Statements of Co_2

Consolidated Statements of Convertible Preferred Stock, Contingently Redeemable Common Stock and Stockholders’ (Deficit) Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Common Stock
Issuance costs	$ 2,529

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net loss	$ (27,379)	$ (16,443)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	9,407	4,775
Depreciation expense	3,831	4,422
Net amortization of premiums and discounts on investments	(1,107)	1,172
Loss on disposal of property and equipment	0	75
Changes in operating assets and liabilities:
Taxes receivable	16,737	0
Prepaid expenses and other current assets	873	(17,416)
Other non-current assets	0	(266)
Accounts payable	562	373
Accrued expenses and other current liabilities	(1,443)	4,120
Deferred revenue—related party	(65,201)	(71,644)
Deferred rent	107	(156)
Net cash used in operating activities	(63,613)	(90,988)
Investing activities:
Purchases of investments	(252,918)	(179,874)
Proceeds from maturities of investments	336,694	141,322
Proceeds from sales of investments	3,997	15,638
Purchases of property and equipment	(1,359)	(15,107)
Net cash provided by (used in) investing activities	86,414	(38,021)
Financing activities:
Proceeds from initial public offering of common stock, net of issuance costs	0	107,008
Proceeds from exercise of stock options	1,546	462
Net cash provided by financing activities	1,546	107,470
Net increase (decrease) in cash, cash equivalents and restricted cash	24,347	(21,539)
Cash, cash equivalents and restricted cash, beginning of period	24,829	46,368
Cash, cash equivalents and restricted cash, end of period	49,176	24,829
Non-cash investing and financing activities:
Purchases of property and equipment in accounts payable and accrued expenses	31	170
Supplemental cash flow information:
Cash paid for income taxes	$ 0	$ 16,750

Nature of Business

Nature of Business	12 Months Ended
	Dec. 31, 2018
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. 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. As of December 31, 2018 , the Company had cash, cash equivalents, and investments of $195.9 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 12 months from March 6, 2019 , 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 potential 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, 2018
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 accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and generally accepted accounting principles in the United States of America (“GAAP”) as found in the Accounting Standards Codification (“ASC”) of the Financial Accounting Standards Board (“FASB”). These consolidated financial statements 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 revenue recognized under the Celgene Collaboration Agreement (including estimates of internal and external costs expected to be incurred to satisfy performance obligations), accrued expenses, stock-based compensation expense 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. Fair Value of Financial Instruments 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 as a component of stockholders’ equity until realized. Property and Equipment 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. Revenue Recognition (Subsequent to Adoption of ASC 606) Effective January 1, 2018, the Company adopted ASC 606, Revenue from Contracts with Customers . Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. In applying ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the promises and performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies the performance obligations. The Company only applies the five-step model to contracts when it is probable that it will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract, determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. See Note 3, “Celgene Collaboration Agreement”, for further information on the application of ASC 606 to the Celgene Collaboration Agreement. Revenue Recognition (Prior to Adoption of ASC 606) Prior to January 1, 2018, the Company recognized revenue in accordance with ASC 605, Revenue Recognition . Revenue was recognized when all of the following criteria were 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 were 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 were classified as deferred revenue, current. Amounts not expected to be recognized as revenue within the twelve months following the balance sheet date were classified as deferred revenue, net of current portion. Multiple-Element Arrangements (Prior to Adoption of ASC 606) Determination of Units of Accounting When evaluating multiple-element arrangements pursuant to ASC 605-25, Revenue Recognition—Multiple-Element Arrangements , the Company considered whether the deliverables under the arrangement represented separate units of accounting. This evaluation required subjective determinations and required 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 evaluated certain criteria, including whether the deliverables had standalone value, based on the consideration of the relevant facts and circumstances for each arrangement. The consideration received was allocated among the separate units of accounting using the relative selling price method, and the applicable revenue recognition criteria were applied to each of the separate units. Deliverables were considered separate units of accounting provided that: (i) the delivered item(s) had value to the customer on a standalone basis and (ii) if the arrangement included a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) was considered probable and substantially in the control of the Company. In assessing whether an item had standalone value, the Company considered 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 considered whether the collaboration partner could use the deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable was dependent on the undelivered item(s) and whether there were other vendors that can provide the undelivered element(s). Under multiple-element arrangements, options were considered substantive if, at the inception of the arrangement, the Company was at risk as to whether the collaboration partner would choose to exercise the option. Factors that the Company considered in evaluating whether an option was substantive included the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option, the likelihood the option would be exercised, and the cost to exercise the option. When an option was considered substantive, the Company did not consider the option or item underlying the option to be a deliverable at the inception of the arrangement and the associated option fees were not included in the allocable arrangement consideration, assuming the option was not priced at a significant and incremental discount. When an option was 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 included 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 was allocated among the separate units of accounting using the relative selling price method. Then, the applicable revenue recognition criteria in ASC 605-25 were applied to each of the separate units of accounting in determining the appropriate period and pattern of recognition. The Company determined the selling price of a unit of accounting following the hierarchy of evidence prescribed by ASC 605-25. Accordingly, the Company determined 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 used BESP to estimate the selling price, since it generally did not have VSOE or TPE of selling price for its units of accounting. Determining the BESP for a unit of accounting required significant judgment. In developing the BESP for a unit of accounting, the Company considered 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 validated the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP would have a significant effect on the allocation of arrangement consideration between multiple units of accounting. Patterns of Recognition The Company recognized arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 were satisfied for that particular unit of accounting. The Company recognized revenue associated with substantive options upon exercise of the option if the underlying license had standalone value from the other deliverables to be provided subsequent to delivery of the license. If the license did not have standalone value, the amounts allocated to the license option would be combined with the related undelivered items as a single unit of accounting. The Company recognized the revenue amounts associated with research and development services and other service related deliverables ratably over the associated period of performance. If there was no discernible pattern of performance or objectively measurable performance measures did not exist, then the Company recognized revenue under the arrangement on a straight-line basis over the period the Company was expected to complete its performance obligations. If the pattern of performance in which the service is provided to the customer could be determined and objectively measurable performance existed, then the Company recognized revenue under the arrangement using the proportional performance method. Revenue recognized was 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 included milestone payments, the Company evaluated whether each milestone was substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation included an assessment of whether (i) the consideration was commensurate with either the Company’s performance to achieve the milestone or the enhancement of performance to achieve the milestone, (ii) the consideration related solely to past performance and (iii) the consideration was reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated 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 was considerable judgment involved in determining whether a milestone satisfied all of the criteria required to conclude that a milestone was substantive. In accordance with ASC 605-28, Revenue Recognition—Milestone Method , clinical and regulatory milestones that were considered substantive would be recognized as revenue in their entirety upon successful accomplishment of the milestone, assuming all other revenue recognition criteria were met. Milestones that were not considered substantive would be recognized as revenue over the remaining period of performance, assuming all other revenue recognition criteria were met. Revenue from commercial milestones payments would be recorded as revenue upon achievement of the milestone, assuming all other recognition criteria were 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, restricted stock awards (“RSAs”) and restricted stock units (“RSUs”), 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 RSUs and RSAs 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. 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 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. Other comprehensive income for all periods presented consists solely of unrealized gains 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, unvested RSAs or unvested RSUs. 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 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. Subsequent to the issuance of ASU 2014-09, the FASB also issued the following updates related to ASC 606: • 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 was 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 adopted 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 recorded an increase to the opening balance of accumulated deficit and a corresponding increase to deferred revenue of $46.9 million related to the Celgene Collaboration Agreement. Additionally, the following tables present a summary of the amount by which each financial statement line item was affected as of and during the year ended December 31, 2018 by the application of ASC 606 as compared to ASC 605, the revenue recognition guidance that was in effect before this change in accounting principle (in thousands, except per share amounts): December 31, 2018 ASC 606 ASC 605 Difference Deferred revenue, current—related party $ 55,157 $ 42,174 $ 12,983 Deferred revenue, net of current portion—related party $ 42,715 $ 22,844 $ 19,871 Total liabilities $ 110,323 $ 77,469 $ 32,854 Accumulated deficit $ (163,907 ) $ (131,053 ) $ (32,854 ) Total stockholders’ equity $ 104,129 $ 136,983 $ (32,854 ) Year Ended December 31, 2018 ASC 606 ASC 605 Difference Collaboration revenue—related party $ 65,201 $ 51,142 $ 14,059 Net loss $ (27,379 ) $ (41,438 ) $ 14,059 Net loss per share attributable to common stockholders, basic and diluted $ (0.84 ) $ (1.27 ) $ 0.43 The application of ASC 606 did not have an impact on the Company’s net cash used in operating activities for the year ended December 31, 2018 , but did result in offsetting adjustments to net loss and the change in deferred revenue presented within the consolidated statement of cash flows for that period. Both the cumulative adjustment of $46.9 million recorded upon the initial application of ASC 606 and the differences outlined above are primarily attributable to the transition from recognizing revenue on a straight-line basis over the estimated performance period for each unit of accounting, which was a permitted method of revenue recognition under ASC 605, to recognizing revenue based on the Company’s pattern of performance for each performance obligation under ASC 606. As part of the adoption of ASC 606, the Company implemented new processes to objectively measure the performance under the Celgene Collaboration Agreement. See Note 3, “Celgene Collaboration Agreement”, for further information on the application of ASC 606 to the Celgene Collaboration Agreement. 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. In July 2018, the FASB also issued ASU 2018-11, Leases (Topic 842): Targeted Improvements , which permits entities to continue applying legacy guidance in ASC 840, Leases , including its disclosure requirements, in the comparative periods presented in the year that the entity adopts the new leasing standard. The new standard will be effective for annual reporting periods beginning after December 15, 2018, including interim periods within those annual reporting periods, and early adoption is permitted for public entities. The Company will adopt this new standard on January 1, 2019 using the transition method permitted by ASU 2018-11. The Company has identified the population of leases subject to this new guidance, and it expects to utilize the package of practical expedients outlined within ASC 842-10-65-1(f), the hindsight practical expedient outlined within ASC 842-10-65-1(g) and the practical expedient related to not separating nonlease components permitted by ASC 842-10-15-37. The Company expects to record lease assets and lease liabilities upon adoption of this guidance, and it is in the process of completing its calculation of these amounts. 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 became effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods. Accordingly, the Company adopted ASU 2016-15 effective January 1, 2018, and there was not 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 requires 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 no longer separately present transfers between unrestricted cash and restricted cash. This guidance became effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods. Accordingly, the Company adopted ASU 2016-18 effective January 1, 2018 using a retrospective transition method, and there was not a material impact to the consolidated finan

Celgene Collaboration Agreement

Celgene Collaboration Agreement	12 Months Ended
	Dec. 31, 2018
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, vopratelimab (formerly 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, an anti-PD-1 antibody, 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 in July 2016 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 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. In January 2019, Celgene and Bristol-Myers Squibb Company (“BMS”) announced an agreement under which Celgene will be acquired by BMS, subject to shareholder and regulatory approvals. 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 vopratelimab, 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 vopratelimab or JTX-4014, for which an IND 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 vopratelimab 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 vopratelimab, 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 1/2 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-Co Agreement for vopratelimab and one additional program for which Celgene opts in, other than 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 ICOS or a defined pool of B cell, T regulatory cell or tumor-associated macrophage targets that meet certain criteria, each termed a “Collaboration Exclusive Target”, and inhibit, activate or otherwise modulate the activity of such Collaboration 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 Exclusive Target. Accounting Analysis under ASC 606 Identification of the Contract(s) The Company assessed the Celgene Collaboration Agreement and concluded that it represents a contract with a customer within the scope of ASC 606. The Company also concluded that each of the Co-Co Agreements and the JTX-4014 License Agreement, if executed in the future, would represent separate contracts apart from the Celgene Collaboration Agreement. Identification of Promises and Performance Obligations The Company determined that the Celgene Collaboration Agreement contains the following promises: (i) research and development services for the product candidate, vopratelimab (“Vopratelimab 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 services associated with target screening (“Target Screening Services”), (v) non-transferable, limited sub-licensable and non-exclusive licenses to use the Company’s intellectual property and the Company’s rights in the collaboration intellectual property to conduct certain activities, on a program-by-program basis (the “Research Licenses”), (vi) various record-keeping and reporting requirements on a program-by-program basis, (vii) exclusivity provisions with respect to each Collaboration Exclusive Target and biologics binding to such Collaboration Exclusive Targets and (viii) establishment of and participation in a joint steering committee (the “JSC”) and a joint patent committee (the “JPC”). The Company also evaluated the six program options as well as the research term extension options and concluded that none convey a material right to Celgene. Accordingly, neither the program options nor the research term extension options are considered to be promises within the Celgene Collaboration Agreement. The Company assessed the above promises and concluded that each of the Vopratelimab Research Services, JTX-4014 Research Services, Lead and Other Programs Research Services and Target Screening Services are both capable of being distinct and distinct within the context of the Celgene Collaboration Agreement. Therefore, the Company has concluded that each of the Vopratelimab Research Services, JTX-4014 Research Services, Lead and Other Programs Research Services and Target Screening Services represent separate performance obligations. The Company determined that the Research Licenses are not distinct within the context of the Celgene Collaboration Agreement as 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 Celgene Collaboration Agreement, but do not provide Celgene with any commercialization rights. Celgene can only benefit from the Research Licenses in conjunction with the related research and development services. Accordingly, the Research Licenses related to vopratelimab, JTX-4014 and the Lead and Other Programs have been combined with their respective research and development services performance obligations. Similarly, the Company also determined that the various record-keeping and reporting requirements related to each program and the exclusivity provisions with respect to each Collaboration Exclusive Target and biologics binding to such Collaboration Exclusive Targets are not distinct within the context of the Celgene Collaboration Agreement. Accordingly, the various record-keeping and reporting requirements on a program-by-program basis and the exclusivity provisions with respect to each Collaboration Exclusive Target and biologics binding to such Collaboration Exclusive Targets have been combined with their respective research and development services performance obligations. Finally, the Company assessed its participation in the JSC and the JPC and concluded that, while it does meet the definition of a performance obligation, it is both quantitatively and qualitatively immaterial in the context of the Celgene Collaboration Agreement. Accordingly, the Company has disregarded its participation in the JSC and the JPC as a performance obligation. Determination of Transaction Price As noted above, the Company received a non-refundable upfront cash payment of $225.0 million upon the execution of the Celgene Collaboration Agreement. This upfront payment represents an element of fixed consideration under the Celgene Collaboration Agreement. Celgene also purchased 10,448,100 shares of Series B-1 convertible preferred stock (“Series B-1 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 Preferred Stock were sold at fair value. Therefore, the proceeds from the issuance of Series B-1 Preferred Stock did not impact the transaction price to be allocated to the performance obligations. The Company evaluated as possible variable consideration the milestones, royalties, development cost sharing and profit sharing provisions discussed above. The Company concluded that none of these items represent variable consideration under the Celgene Collaboration Agreement as all such amounts are dependent upon the execution of a related Co-Co Agreement or the JTX-4014 License Agreement. The Co-Co Agreements and the JTX-4014 License Agreement, if executed in the future, would represent separate contracts apart from the Celgene Collaboration Agreement. The Company also considered the existence of any significant financing component within the Celgene Collaboration Agreement given its upfront payment structure. Based upon this assessment, the Company concluded that any difference between the promised consideration and the cash selling price of the services under the Celgene Collaboration Agreement arises for reasons other than the provision of financing, and the difference between those amounts is proportional to the reason for the difference. Accordingly, the Company has concluded that the upfront payment structure of the Celgene Collaboration Agreement does not result in the existence of a significant financing component. Based upon the above considerations, the Company has concluded that the transaction price associated with the Celgene Collaboration Agreement consists solely of the upfront payment of $225.0 million . Allocation of Transaction Price to Performance Obligations The Company has allocated the transaction price to each performance obligation on a relative standalone selling price basis. For all performance obligations, the Company determined the standalone selling price using estimates of the costs to perform the research and development services, including expected internal and external costs for services and supplies, adjusted to reflect a reasonable profit margin. The total estimated 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. Recognition of Revenue The Company recognizes revenue related to the Celgene Collaboration Agreement over time as the services related to each performance obligation are rendered. The Company has concluded that an input method under ASC 606 is a representative depiction of the transfer of services under the Celgene Collaboration Agreement. The method of measuring progress towards delivery of the services incorporates actual internal and external costs incurred, relative to total internal and external costs expected to be incurred to satisfy the performance obligations. The period over which total costs are estimated reflects the Company’s estimate of the period over which it will perform the research and development services to deliver a pre-defined data package to Celgene for each program subject to an option. The Company recognizes revenue for each performance obligation over periods ranging from twelve months to four years. Changes in estimates of total internal and external costs expected to be incurred are recognized in the period of change as a cumulative catch-up adjustment. For the year ended December 31, 2018 , the Company recognized collaboration revenue of $65.2 million under the Celgene Collaboration Agreement related to the $225.0 million upfront payment received in 2016. As of December 31, 2018 , the Company has $97.9 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. This deferred revenue balance represents the aggregate amount of the transaction price allocated to the performance obligations that are partially unsatisfied as of December 31, 2018 . The Company expects to recognize revenue related to these performance obligations through July 2020. The following table presents changes in the Company’s contract liabilities during the year ended December 31, 2018 (in thousands): Balance as of Balance as of January 1, 2018 Additions Reductions December 31, 2018 Contract liabilities: Deferred revenue $ 163,073 $ — $ (65,201 ) $ 97,872 Totals $ 163,073 $ — $ (65,201 ) $ 97,872 The reductions to the deferred revenue contract liability during the year ended December 31, 2018 were comprised of revenue recognized for research and development services performed, as well as a cumulative catch-up adjustment of $7.1 million arising from changes in costs estimated to be incurred under the Celgene Collaboration Agreement. All revenue recognized during the year ended December 31, 2018 was included within the beginning balance of the deferred revenue contract liability. As of December 31, 2018 , the Company had not received any option exercise, research term extension, milestone or royalty payments under the Celgene Collaboration Agreement. Accounting Analysis under ASC 605 Prior to January 1, 2018, the Company recognized revenue related the Celgene Collaboration Agreement in accordance with ASC 605. Under ASC 605, the Company determined that the Celgene Collaboration Agreement included six deliverables: (i) the Vopratelimab Research Services, (ii) the JTX-4014 Research Services, (iii) the Lead and Other Programs Research Services, (iv) the Target Screening Services, (v) the Research Licenses and (vi) participation in the JSC. The six program options were considered substantive as the Company was at risk with regard to whether Celgene would exercise the options as a result of the significant uncertainties related to drug discovery, research and development given the significant development risk of the targets subject to the options. Additionally, there was also significant uncertainty regarding Celgene’s exercise of the option for JTX-4014 because, although not a novel immunotherapy agent, the Company identified a significant development risk associated with its ability to advance the development of JTX-4014 in a commercially viable manner in a short time frame. The research term extensions were also considered substantive options based upon the risk that Celgene would exercise the research term extension. In addition, the substantial option exercise payments payable by Celgene upon exercise of each option were not priced at a significant and incremental discount. Accordingly, the substantive options were not considered deliverables at the inception of the arrangement and the associated option exercise payments were not included in allocable arrangement consideration. The Company also determined that any obligations contingent upon the exercise of a substantive option were not considered deliverables at the outset of the arrangement. The Target Screening Services and participation in the JSC deliverables each had standalone value from the other undelivered elements and therefore were separate units of accounting. The Company determined that the research licenses for the vopratelimab and JTX-4014 programs did 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 Company determined that the research licenses did not have value to Celgene without the performance of the Vopratelimab Research Services and JTX-4014 Research Services and therefore were not separable from the Vopratelimab Research Services and JTX-4014 Research Services. The Vopratelimab Research Services were separate and distinct from the JTX-4014 Research Services, and therefore, the research license and the Vopratelimab Research Services were a separate combined unit of accounting and the research license and the JTX-4014 Research Services were a separate combined unit of accounting. The Lead and Other Programs Research Services deliverable did not include separate and distinct services and Celgene could 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 were combined with the licenses that could be delivered for the Lead Program and Other Programs, which had an insignificant value, as a separate combined unit of accounting. The allocable arrangement consideration consisted of the upfront fee of $225.0 million . As described above, Celgene also purchased 10,448,100 shares of Series B-1 Preferred Stock for gross proceeds of $36.1 million . The Company determined the shares of Series B-1 Preferred Stock were sold at fair value. Therefore, the proceeds from the issuance of Series B-1 convertible preferred stock did not have an impact on the arrangement consideration that was allocated to the units of accounting. The Company 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 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 reflected 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. Therefore, the total allocable arrangement consideration was allocated to the Vopratelimab Research Services, the JTX-4014 Research Services, the Lead and Other Programs Research Services and the Target Screening Services. The Company recognized the consideration allocated to each unit of accounting on a straight-line basis, as there was no discernible pattern or objective measure of performance of the services, over the estimated performance period. The estimated performance period reflected the Company’s estimate of the period over which it would 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 ranged 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 were substantive. In evaluating if a milestone was substantive, the Company assessed whether: (i) the consideration was 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’s performance to achieve the milestone, (ii) the consideration related solely to past performance and (iii) the consideration was 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 were 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, the Company concluded that such amounts would be recognized in the period in which the associated milestone was achieved, assuming all other revenue recognition criteria were met. All commercial milestones would be accounted for in the same manner as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria were met. Under ASC 605, the Company recognized collaboration revenue of $71.6 million for year ended December 31, 2017 . As of December 31, 2017 , the Company had $116.2 million of deferred revenue, which was classified as either “current” or “net of current portion” in the accompanying consolidated balance sheets based on the period over which the revenue was expected to be recognized.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
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, 2018 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 $ 41,434 $ 41,434 $ — $ — Investments: Corporate debt securities 67,843 — 67,843 — U.S. Treasuries 53,758 53,758 — — Government agency securities 32,829 32,829 — — Totals $ 195,864 $ 128,021 $ 67,843 $ — 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 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 $ — There were no changes in valuation techniques or transfers between the fair value measurement levels during the years ended December 31, 2018 or 2017 . There were no liabilities measured at fair value on a recurring basis as of December 31, 2018 or 2017 .

Investments

Investments	12 Months Ended
	Dec. 31, 2018
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 as a component of stockholders’ equity until realized. Cash equivalents, short-term investments and long-term investments as of December 31, 2018 were comprised as follows (in thousands): December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 41,434 $ — $ — $ 41,434 Corporate debt securities 65,887 2 (39 ) 65,850 U.S. Treasuries 53,765 1 (8 ) 53,758 Government agency securities 28,866 — (34 ) 28,832 Total cash equivalents and short-term investments 189,952 3 (81 ) 189,874 Long-term investments: Corporate debt securities 2,001 — (8 ) 1,993 Government agency securities 3,989 8 — 3,997 Total long-term investments 5,990 8 (8 ) 5,990 Total cash equivalents and investments $ 195,942 $ 11 $ (89 ) $ 195,864 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 As of December 31, 2018 and 2017 , the aggregate fair value of securities that were in an unrealized loss position for less than twelve months was $81.4 million and $113.9 million , respectively. As of December 31, 2018 and 2017 , the aggregate fair value of securities that were in an unrealized loss position for more than twelve months was $22.3 million and $107.9 million , respectively. As of December 31, 2018 , 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, 2018 . There were immaterial realized gains and losses on available-for-sale securities during the years ended December 31, 2018 and 2017 .

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 were comprised as follows (in thousands): December 31, 2018 2017 Prepaid expenses $ 1,921 $ 2,196 Taxes receivable — 16,737 Interest receivable on investments 414 969 Other current assets — 43 Total prepaid expenses and other current assets $ 2,335 $ 19,945 Taxes receivable decreased from December 31, 2017 to December 31, 2018 due to the Company’s receipt of $16.8 million in federal and state income tax refunds during the year ended December 31, 2018 .

Restricted Cash

Restricted Cash	12 Months Ended
	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Restricted Cash	Restricted Cash As of both December 31, 2018 and 2017 , the Company maintained non-current restricted cash of $1.3 million . This amount is included within “Other non-current assets” in the accompanying consolidated balance sheets and is comprised solely of a letter of credit required pursuant to the lease for the Company’s corporate headquarters. The following table provides a reconciliation of cash, cash equivalents and restricted cash that sums to the total of the same such amounts shown in the consolidated statements of cash flows (in thousands): Year Ended Year Ended Beginning of Period End of Period Beginning of Period End of Period Cash and cash equivalents $ 23,559 $ 47,906 $ 44,848 $ 23,559 Restricted cash 1,270 1,270 1,520 1,270 Cash, cash equivalents and restricted cash $ 24,829 $ 49,176 $ 46,368 $ 24,829

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net as of December 31, 2018 and 2017 was comprised as follows (in thousands): Estimated Useful Life (in Years) December 31, 2018 2017 Laboratory equipment 5 $ 10,435 $ 9,409 Furniture and office equipment 4 1,071 1,038 Computer equipment 3 1,505 1,380 Leasehold improvements Shorter of useful life or remaining lease term 8,534 8,498 Total property and equipment, gross 21,545 20,325 Less: accumulated depreciation (8,005 ) (4,174 ) Total property and equipment, net $ 13,540 $ 16,151 Depreciation expense for the years ended December 31, 2018 and 2017 was $3.8 million and $4.4 million , respectively.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses as of December 31, 2018 and 2017 were comprised as follows (in thousands): December 31, 2018 2017 Employee compensation and benefits $ 4,063 $ 3,683 External research and professional services 2,796 4,647 Lab consumables and other 93 124 Total accrued expenses $ 6,952 $ 8,454

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 , the Company had reserved for future issuance the following number of shares of common stock (in thousands): December 31, 2018 2017 Shares reserved for vesting of restricted stock awards 7 16 Shares reserved for vesting of restricted stock units 371 — Shares reserved for exercises of outstanding stock options 5,023 4,868 Shares reserved for future issuances under the 2017 Stock Option and Incentive Plan 1,114 1,032 Total shares reserved for future issuance 6,515 5,916

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2018
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. Series B Preferred Stock During the year ended December 31, 2015, the Company issued 24,778,761 shares of Series B convertible preferred stock (“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, 2018 , no shares of preferred stock were issued or outstanding.

Stock-based Compensation

Stock-based Compensation	12 Months Ended
	Dec. 31, 2018
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, RSAs and RSUs 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, RSAs, RSUs, 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 awards, including vesting requirements, are determined by the Board of Directors, subject to the provisions of the 2017 Plan. The Company initially registered 1,753,758 shares of common stock under the 2017 Plan, which was 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 st 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. Effective January 1, 2018, 1,290,609 additional shares were automatically added to the shares authorized for issuance under the 2017 Plan. As of December 31, 2018 , there were 1,113,539 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 initially reserved 302,000 shares of common stock for future issuance under the 2017 ESPP. The 2017 ESPP also provides that an additional number of shares will automatically be added to the shares authorized for issuance under the 2017 ESPP on January 1, 2018 and each January 1 st thereafter through January 1, 2027. The number of shares added each year will be equal to the lesser of (i) 1% of the outstanding shares on the immediately preceding December 31 st , (ii) 603,000 shares or (iii) such amount as determined by the Compensation Committee of the Board of Directors. Effective January 1, 2018, 322,652 additional shares were automatically added to the shares authorized for issuance under the 2017 ESPP. No offering periods under the 2017 ESPP had been initiated as of December 31, 2018 . Stock-based Compensation Expense Total stock-based compensation expense recognized in the consolidated statements of operations for the years ended December 31, 2018 and 2017 was as follows (in thousands): Year Ended December 31, 2018 2017 Research and development $ 4,540 $ 2,840 General and administrative 4,867 1,935 Total stock-based compensation expense $ 9,407 $ 4,775 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, 2018 , 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. RSA Activity Pursuant to RSA agreements originally issued under the terms of the 2013 Plan, the Company, at its discretion, has the option to repurchase unvested shares underlying RSAs at the initial purchase price if the employees or non-employees terminate their service relationships with the Company. The shares underlying RSAs are recorded in stockholders’ equity as they vest. The following table summarizes RSA activity for the year ended December 31, 2018 (in thousands, except per share amounts): RSAs Weighted-Average Grant Date Fair Value per Share Unvested as of December 31, 2017 16 $ — Issued — $ — Vested (9 ) $ — Repurchased — $ — Unvested as of December 31, 2018 7 $ — The aggregate fair value of RSAs that vested during the years ended December 31, 2018 and 2017 , based upon the fair values of the stock underlying the RSAs on the day of vesting, was less than $0.1 million and $1.3 million , respectively. RSU Activity The Company has also granted RSUs to its employees under the 2017 Plan. The following table summarizes RSU activity for the year ended December 31, 2018 (in thousands, except per share amounts): RSUs Weighted-Average Grant Date Fair Value per Share Unvested as of December 31, 2017 — $ — Issued 388 $ 8.02 Vested — $ — Cancelled (17 ) $ 8.02 Unvested as of December 31, 2018 371 $ 8.02 No RSUs vested during the years ended December 31, 2018 or 2017 . As of December 31, 2018 , there was unrecognized stock-based compensation expense related to unvested RSUs of $2.4 million , which the Company expects to recognize over a weighted-average period of approximately 1.6 years . Stock Option Activity The fair value of stock options granted to employees and directors during the years ended December 31, 2018 and 2017 was calculated on the date of grant using the following weighted-average assumptions: Year Ended December 31, 2018 2017 Risk-free interest rate 2.7 % 2.1 % Expected dividend yield — % — % Expected term (in years) 6.0 6.1 Expected volatility 65.2 % 70.1 % 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, 2018 and 2017 was $12.88 and $10.96 per share, respectively. The following table summarizes changes in stock option activity during the year ended December 31, 2018 (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, 2017 4,868 $ 6.28 7.9 $ 35,178 Granted 1,581 $ 21.15 Exercised (683 ) $ 2.26 Cancelled (743 ) $ 14.95 Outstanding at December 31, 2018 5,023 $ 10.23 7.6 $ 3,133 Exercisable at December 31, 2018 2,733 $ 5.91 6.8 $ 3,014 The aggregate intrinsic value of stock options exercised during the years ended December 31, 2018 and 2017 was $5.7 million and $1.9 million , respectively. As of December 31, 2018 , there was unrecognized stock-based compensation expense related to unvested stock options of $19.7 million , which the Company expects to recognize over a weighted-average period of approximately 2.3 years .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for income taxes for the years ended December 31, 2018 and 2017 was comprised as follows (in thousands): Year Ended December 31, 2018 2017 Current taxes: Federal $ — $ — State 46 36 Total current taxes 46 36 Deferred taxes: Federal — — State — — Total deferred taxes — — Total provision for income taxes $ 46 $ 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%, net operating loss (“NOL”) carrybacks are no longer permitted and NOLs generated in years beginning after December 31, 2017 may be carried forward indefinitely, subject to a limitation of 80% of taxable income. In December 2017, the SEC 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 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 determined that the revaluation of its deferred tax assets and associated valuation allowance reduction of $9.4 million were provisional amounts as of December 31, 2017. The accounting for the tax effects of the Tax Act was completed during the year ended December 31, 2018, and no adjustments were made to these provisional amounts. A reconciliation of the federal statutory income tax rate to the Company’s effective tax rate is as follows: Year Ended December 31, 2018 2017 Income tax computed at federal statutory tax rate 21.0 % 34.0 % Deferred tax effects from the Tax Act — % (57.2 )% State taxes, net of federal benefit 10.3 % 4.7 % Tax credit carryforwards 12.2 % 26.8 % Non-deductible income (expense) — % (4.9 )% Change in valuation allowance (42.7 )% (1.8 )% Other (1.0 )% (1.8 )% Effective tax rate (0.2 )% (0.2 )% The principal components of the Company’s deferred tax assets and liabilities as of December 31, 2018 and 2017 were comprised as follows (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 37,417 $ 26,926 Tax credit carryforwards 12,751 8,432 Deferred revenue 26,739 31,735 Deferred lease incentive 103 120 Deferred rent 476 431 Intangibles 552 237 Accrued expenses and other 1,091 995 Unrealized loss on available-for-sale securities 39 112 Stock-based compensation 2,119 713 Total deferred tax assets 81,287 69,701 Less: valuation allowance (55,348 ) (30,850 ) Net deferred tax assets 25,939 38,851 Deferred tax liabilities: Section 481(a) method change (25,653 ) (38,481 ) Depreciation (286 ) (370 ) Total deferred tax liabilities (25,939 ) (38,851 ) Net deferred taxes $ — $ — The Company has incurred NOLs since inception. As of December 31, 2018 , the Company had federal and state NOL carryforwards of $136.4 million and $138.7 million , respectively. Federal NOLs generated through the year ended December 31, 2017 expire at various dates from 2032 through 2037 , and federal NOLs generated during the year ended December 31, 2018 may be carried forward indefinitely. State NOLs expire at various dates from 2032 through 2038 . As of December 31, 2018 , the Company had federal research and development tax credit carryforwards of $9.3 million which expire at various dates from 2032 through 2038 . In addition, as of December 31, 2018 , the Company had state research and development and investment tax credit carryforwards of $3.8 million and $0.6 million , respectively. The state research and development tax credit carryforwards expire at various dates from 2029 through 2033 and the state investment tax credit carryforwards expire at various dates from 2019 through 2021 . 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 revenue and stock-based compensation. 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 $55.3 million has been established at December 31, 2018 . The increase in the valuation allowance of $24.5 million during the year ended December 31, 2018 was primarily due to the increase in the deferred tax asset related to deferred revenue upon the adoption of ASC 606 as well as 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, 2018 or 2017 . 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, 2018 . 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, 2018 , 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, 2018
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, 2018
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, 2018 , 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 2019 $ 4,260 2020 4,380 2021 4,505 2022 4,633 2023 4,764 2024 and thereafter 6,142 Total future minimum lease payments $ 28,684 The Company leased its former corporate headquarters under an operating lease that was originally set to expire on October 15, 2018. Under this lease, the Company was recording rent expense on a straight-line basis through the end of the lease term and was recording deferred rent on the consolidated balance sheets. The lease also provided the Company with a tenant improvement allowance of $2.8 million . The Company was recording the tenant improvement allowance as a deferred lease incentive and was amortizing 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. In addition, the remaining deferred rent and deferred lease incentive balances related to the Company’s former corporate headquarters were recognized in full as reductions of rent expense. During the years ended December 31, 2018 and 2017 , the Company recorded total rent expense of $4.0 million and $3.5 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 $13.4 million and low single-digit royalty payments based on a percentage of net sales of licensed products. As of December 31, 2018 , the Company had 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 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, 2018 , the Company had made $0.5 million in aggregate milestone payments under these collaboration agreements.

401(k) Savings Plan

401(k) Savings Plan	12 Months Ended
	Dec. 31, 2018
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. Beginning on January 1, 2018, the Company matches 50% of an employee’s 401(k) contributions up to a maximum of 6% of the participant’s salary, subject to employer match limitations under the IRC. As such, the Company made $0.5 million in contributions to the 401(k) Plan for the year ended December 31, 2018 . The Company did not make any contributions to the 401(k) Plan for the year ended December 31, 2017 .

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2018
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share For purposes of the diluted loss per share calculation, outstanding stock options, unvested RSAs and unvested RSUs are considered to be potentially dilutive securities, however the following amounts were excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive (in thousands): Year Ended December 31, 2018 2017 Outstanding stock options 5,023 4,868 Unvested RSAs 7 16 Unvested RSUs 371 — Total 5,401 4,884

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	The accompanying consolidated financial statements have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and generally accepted accounting principles in the United States of America (“GAAP”) as found in the Accounting Standards Codification (“ASC”) of the Financial Accounting Standards Board (“FASB”).
Principles of Consolidation	These consolidated financial statements 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 revenue recognized under the Celgene Collaboration Agreement (including estimates of internal and external costs expected to be incurred to satisfy performance obligations), accrued expenses, stock-based compensation expense 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.
Fair Value of Financial Instruments	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 as a component of stockholders’ equity until realized
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.
Revenue Recognition	Effective January 1, 2018, the Company adopted ASC 606, Revenue from Contracts with Customers . Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. In applying ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the promises and performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies the performance obligations. The Company only applies the five-step model to contracts when it is probable that it will collect the consideration to which it is entitled in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract, determines those that are performance obligations and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. See Note 3, “Celgene Collaboration Agreement”, for further information on the application of ASC 606 to the Celgene Collaboration Agreement. Revenue Recognition (Prior to Adoption of ASC 606) Prior to January 1, 2018, the Company recognized revenue in accordance with ASC 605, Revenue Recognition . Revenue was recognized when all of the following criteria were 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 were 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 were classified as deferred revenue, current. Amounts not expected to be recognized as revenue within the twelve months following the balance sheet date were classified as deferred revenue, net of current portion. Multiple-Element Arrangements (Prior to Adoption of ASC 606) Determination of Units of Accounting When evaluating multiple-element arrangements pursuant to ASC 605-25, Revenue Recognition—Multiple-Element Arrangements , the Company considered whether the deliverables under the arrangement represented separate units of accounting. This evaluation required subjective determinations and required 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 evaluated certain criteria, including whether the deliverables had standalone value, based on the consideration of the relevant facts and circumstances for each arrangement. The consideration received was allocated among the separate units of accounting using the relative selling price method, and the applicable revenue recognition criteria were applied to each of the separate units. Deliverables were considered separate units of accounting provided that: (i) the delivered item(s) had value to the customer on a standalone basis and (ii) if the arrangement included a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) was considered probable and substantially in the control of the Company. In assessing whether an item had standalone value, the Company considered 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 considered whether the collaboration partner could use the deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable was dependent on the undelivered item(s) and whether there were other vendors that can provide the undelivered element(s). Under multiple-element arrangements, options were considered substantive if, at the inception of the arrangement, the Company was at risk as to whether the collaboration partner would choose to exercise the option. Factors that the Company considered in evaluating whether an option was substantive included the overall objective of the arrangement, the benefit the collaborator might obtain from the arrangement without exercising the option, the likelihood the option would be exercised, and the cost to exercise the option. When an option was considered substantive, the Company did not consider the option or item underlying the option to be a deliverable at the inception of the arrangement and the associated option fees were not included in the allocable arrangement consideration, assuming the option was not priced at a significant and incremental discount. When an option was 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 included 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 was allocated among the separate units of accounting using the relative selling price method. Then, the applicable revenue recognition criteria in ASC 605-25 were applied to each of the separate units of accounting in determining the appropriate period and pattern of recognition. The Company determined the selling price of a unit of accounting following the hierarchy of evidence prescribed by ASC 605-25. Accordingly, the Company determined 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 used BESP to estimate the selling price, since it generally did not have VSOE or TPE of selling price for its units of accounting. Determining the BESP for a unit of accounting required significant judgment. In developing the BESP for a unit of accounting, the Company considered 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 validated the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP would have a significant effect on the allocation of arrangement consideration between multiple units of accounting. Patterns of Recognition The Company recognized arrangement consideration allocated to each unit of accounting when all of the revenue recognition criteria in ASC 605 were satisfied for that particular unit of accounting. The Company recognized revenue associated with substantive options upon exercise of the option if the underlying license had standalone value from the other deliverables to be provided subsequent to delivery of the license. If the license did not have standalone value, the amounts allocated to the license option would be combined with the related undelivered items as a single unit of accounting. The Company recognized the revenue amounts associated with research and development services and other service related deliverables ratably over the associated period of performance. If there was no discernible pattern of performance or objectively measurable performance measures did not exist, then the Company recognized revenue under the arrangement on a straight-line basis over the period the Company was expected to complete its performance obligations. If the pattern of performance in which the service is provided to the customer could be determined and objectively measurable performance existed, then the Company recognized revenue under the arrangement using the proportional performance method. Revenue recognized was 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 included milestone payments, the Company evaluated whether each milestone was substantive and at risk to both parties on the basis of the contingent nature of the milestone. This evaluation included an assessment of whether (i) the consideration was commensurate with either the Company’s performance to achieve the milestone or the enhancement of performance to achieve the milestone, (ii) the consideration related solely to past performance and (iii) the consideration was reasonable relative to all of the deliverables and payment terms within the arrangement. The Company evaluated 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 was considerable judgment involved in determining whether a milestone satisfied all of the criteria required to conclude that a milestone was substantive. In accordance with ASC 605-28, Revenue Recognition—Milestone Method , clinical and regulatory milestones that were considered substantive would be recognized as revenue in their entirety upon successful accomplishment of the milestone, assuming all other revenue recognition criteria were met. Milestones that were not considered substantive would be recognized as revenue over the remaining period of performance, assuming all other revenue recognition criteria were met. Revenue from commercial milestones payments would be recorded as revenue upon achievement of the milestone, assuming all other recognition criteria were 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, restricted stock awards (“RSAs”) and restricted stock units (“RSUs”), 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 RSUs and RSAs 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. 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 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. Other comprehensive income for all periods presented consists solely of unrealized gains 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, unvested RSAs or unvested RSUs. 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 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. Subsequent to the issuance of ASU 2014-09, the FASB also issued the following updates related to ASC 606: • 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 was 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 adopted 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 recorded an increase to the opening balance of accumulated deficit and a corresponding increase to deferred revenue of $46.9 million related to the Celgene Collaboration Agreement. Additionally, the following tables present a summary of the amount by which each financial statement line item was affected as of and during the year ended December 31, 2018 by the application of ASC 606 as compared to ASC 605, the revenue recognition guidance that was in effect before this change in accounting principle (in thousands, except per share amounts): December 31, 2018 ASC 606 ASC 605 Difference Deferred revenue, current—related party $ 55,157 $ 42,174 $ 12,983 Deferred revenue, net of current portion—related party $ 42,715 $ 22,844 $ 19,871 Total liabilities $ 110,323 $ 77,469 $ 32,854 Accumulated deficit $ (163,907 ) $ (131,053 ) $ (32,854 ) Total stockholders’ equity $ 104,129 $ 136,983 $ (32,854 ) Year Ended December 31, 2018 ASC 606 ASC 605 Difference Collaboration revenue—related party $ 65,201 $ 51,142 $ 14,059 Net loss $ (27,379 ) $ (41,438 ) $ 14,059 Net loss per share attributable to common stockholders, basic and diluted $ (0.84 ) $ (1.27 ) $ 0.43 The application of ASC 606 did not have an impact on the Company’s net cash used in operating activities for the year ended December 31, 2018 , but did result in offsetting adjustments to net loss and the change in deferred revenue presented within the consolidated statement of cash flows for that period. Both the cumulative adjustment of $46.9 million recorded upon the initial application of ASC 606 and the differences outlined above are primarily attributable to the transition from recognizing revenue on a straight-line basis over the estimated performance period for each unit of accounting, which was a permitted method of revenue recognition under ASC 605, to recognizing revenue based on the Company’s pattern of performance for each performance obligation under ASC 606. As part of the adoption of ASC 606, the Company implemented new processes to objectively measure the performance under the Celgene Collaboration Agreement. See Note 3, “Celgene Collaboration Agreement”, for further information on the application of ASC 606 to the Celgene Collaboration Agreement. 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. In July 2018, the FASB also issued ASU 2018-11, Leases (Topic 842): Targeted Improvements , which permits entities to continue applying legacy guidance in ASC 840, Leases , including its disclosure requirements, in the comparative periods presented in the year that the entity adopts the new leasing standard. The new standard will be effective for annual reporting periods beginning after December 15, 2018, including interim periods within those annual reporting periods, and early adoption is permitted for public entities. The Company will adopt this new standard on January 1, 2019 using the transition method permitted by ASU 2018-11. The Company has identified the population of leases subject to this new guidance, and it expects to utilize the package of practical expedients outlined within ASC 842-10-65-1(f), the hindsight practical expedient outlined within ASC 842-10-65-1(g) and the practical expedient related to not separating nonlease components permitted by ASC 842-10-15-37. The Company expects to record lease assets and lease liabilities upon adoption of this guidance, and it is in the process of completing its calculation of these amounts. 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 became effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods. Accordingly, the Company adopted ASU 2016-15 effective January 1, 2018, and there was not 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 requires 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 no longer separately present transfers between unrestricted cash and restricted cash. This guidance became effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods. Accordingly, the Company adopted ASU 2016-18 effective January 1, 2018 using a retrospective transition method, and there was not a material impact to the consolidated financial statements as a result of the adoption of this guidance. See Note 7, “Restricted Cash”, for incremental disclosures associated with the adoption of ASU 2016-18. 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 are required to apply modification accounting if the fair value, vesting conditions or classification of the award changes. This guidance became effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods, and early adoption was permitted. The guidance per ASU 2017-09 is to be adopted prospectively to an award modified on or after the adoption date. The Company adopted ASU 2017-09 effective January 1, 2018, and there was no impact to the consolidated financial statements as a result of the adoption of this guidance. In June 2018, the FASB issued ASU 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting . This guidance is intended to simplify the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees, with certain exceptions. This guidance will be effective for annual reporting periods beginning after December 15, 2018, 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 August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates, adds and modifies certain disclosure requirements for fair value measurements. This guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption is permitted. More specifically, an entity is permitted to early adopt any removed or modified disclosure requirements immediately and delay adoption of additional disclosure requirements until the effective date of this guidance. The Company does not anticipate a material impact to the consolidated financial statements as a result of the adoption of this guidance. In November 2018, the FASB issued ASU 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction between Topic 808 and Topic 606 , which clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606 when the counterparty is a customer. In addition, ASU 2018-18 adds unit-of-account guidance to ASC Topic 808, Collaborative Arrangements , in order to align this guidance with ASC 606 and also precludes an entity from presenting consideration from a transaction in a collaborative arrangement as revenue from contracts with customers if the counterparty is not a customer for that transaction. This guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption is permitted. The Company is currently evaluating the potential impact that ASU 2018-18 may have on the consolidated financial statements.

Basis of Presentation and Sum_3

Basis of Presentation and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	Additionally, the following tables present a summary of the amount by which each financial statement line item was affected as of and during the year ended December 31, 2018 by the application of ASC 606 as compared to ASC 605, the revenue recognition guidance that was in effect before this change in accounting principle (in thousands, except per share amounts): December 31, 2018 ASC 606 ASC 605 Difference Deferred revenue, current—related party $ 55,157 $ 42,174 $ 12,983 Deferred revenue, net of current portion—related party $ 42,715 $ 22,844 $ 19,871 Total liabilities $ 110,323 $ 77,469 $ 32,854 Accumulated deficit $ (163,907 ) $ (131,053 ) $ (32,854 ) Total stockholders’ equity $ 104,129 $ 136,983 $ (32,854 ) Year Ended December 31, 2018 ASC 606 ASC 605 Difference Collaboration revenue—related party $ 65,201 $ 51,142 $ 14,059 Net loss $ (27,379 ) $ (41,438 ) $ 14,059 Net loss per share attributable to common stockholders, basic and diluted $ (0.84 ) $ (1.27 ) $ 0.43

Celgene Collaboration Agreeme_2

Celgene Collaboration Agreement (Tables)	12 Months Ended
	Dec. 31, 2018
Research and Development [Abstract]
Contract with Customer, Asset and Liability	The following table presents changes in the Company’s contract liabilities during the year ended December 31, 2018 (in thousands): Balance as of Balance as of January 1, 2018 Additions Reductions December 31, 2018 Contract liabilities: Deferred revenue $ 163,073 $ — $ (65,201 ) $ 97,872 Totals $ 163,073 $ — $ (65,201 ) $ 97,872

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Assets Measured at Fair Value	Assets measured at fair value on a recurring basis as of December 31, 2018 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 $ 41,434 $ 41,434 $ — $ — Investments: Corporate debt securities 67,843 — 67,843 — U.S. Treasuries 53,758 53,758 — — Government agency securities 32,829 32,829 — — Totals $ 195,864 $ 128,021 $ 67,843 $ — 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 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 $ —

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 were comprised as follows (in thousands): December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 41,434 $ — $ — $ 41,434 Corporate debt securities 65,887 2 (39 ) 65,850 U.S. Treasuries 53,765 1 (8 ) 53,758 Government agency securities 28,866 — (34 ) 28,832 Total cash equivalents and short-term investments 189,952 3 (81 ) 189,874 Long-term investments: Corporate debt securities 2,001 — (8 ) 1,993 Government agency securities 3,989 8 — 3,997 Total long-term investments 5,990 8 (8 ) 5,990 Total cash equivalents and investments $ 195,942 $ 11 $ (89 ) $ 195,864 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

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 were comprised as follows (in thousands): December 31, 2018 2017 Prepaid expenses $ 1,921 $ 2,196 Taxes receivable — 16,737 Interest receivable on investments 414 969 Other current assets — 43 Total prepaid expenses and other current assets $ 2,335 $ 19,945

Restricted Cash (Tables)

Restricted Cash (Tables)	12 Months Ended
	Dec. 31, 2018
Cash and Cash Equivalents [Abstract]
Schedule of Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents and restricted cash that sums to the total of the same such amounts shown in the consolidated statements of cash flows (in thousands): Year Ended Year Ended Beginning of Period End of Period Beginning of Period End of Period Cash and cash equivalents $ 23,559 $ 47,906 $ 44,848 $ 23,559 Restricted cash 1,270 1,270 1,520 1,270 Cash, cash equivalents and restricted cash $ 24,829 $ 49,176 $ 46,368 $ 24,829
Restrictions on Cash and Cash Equivalents	The following table provides a reconciliation of cash, cash equivalents and restricted cash that sums to the total of the same such amounts shown in the consolidated statements of cash flows (in thousands): Year Ended Year Ended Beginning of Period End of Period Beginning of Period End of Period Cash and cash equivalents $ 23,559 $ 47,906 $ 44,848 $ 23,559 Restricted cash 1,270 1,270 1,520 1,270 Cash, cash equivalents and restricted cash $ 24,829 $ 49,176 $ 46,368 $ 24,829

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property and equipment, net as of December 31, 2018 and 2017 was comprised as follows (in thousands): Estimated Useful Life (in Years) December 31, 2018 2017 Laboratory equipment 5 $ 10,435 $ 9,409 Furniture and office equipment 4 1,071 1,038 Computer equipment 3 1,505 1,380 Leasehold improvements Shorter of useful life or remaining lease term 8,534 8,498 Total property and equipment, gross 21,545 20,325 Less: accumulated depreciation (8,005 ) (4,174 ) Total property and equipment, net $ 13,540 $ 16,151

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses as of December 31, 2018 and 2017 were comprised as follows (in thousands): December 31, 2018 2017 Employee compensation and benefits $ 4,063 $ 3,683 External research and professional services 2,796 4,647 Lab consumables and other 93 124 Total accrued expenses $ 6,952 $ 8,454

Common Stock (Tables)

Common Stock (Tables)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Schedule of Stock by Class	As of December 31, 2018 and 2017 , the Company had reserved for future issuance the following number of shares of common stock (in thousands): December 31, 2018 2017 Shares reserved for vesting of restricted stock awards 7 16 Shares reserved for vesting of restricted stock units 371 — Shares reserved for exercises of outstanding stock options 5,023 4,868 Shares reserved for future issuances under the 2017 Stock Option and Incentive Plan 1,114 1,032 Total shares reserved for future issuance 6,515 5,916

Stock-based Compensation (Table

Stock-based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017 was as follows (in thousands): Year Ended December 31, 2018 2017 Research and development $ 4,540 $ 2,840 General and administrative 4,867 1,935 Total stock-based compensation expense $ 9,407 $ 4,775
Schedule of Restricted Stock and Restricted Stock Units Activity	The following table summarizes RSA activity for the year ended December 31, 2018 (in thousands, except per share amounts): RSAs Weighted-Average Grant Date Fair Value per Share Unvested as of December 31, 2017 16 $ — Issued — $ — Vested (9 ) $ — Repurchased — $ — Unvested as of December 31, 2018 7 $ — The Company has also granted RSUs to its employees under the 2017 Plan. The following table summarizes RSU activity for the year ended December 31, 2018 (in thousands, except per share amounts): RSUs Weighted-Average Grant Date Fair Value per Share Unvested as of December 31, 2017 — $ — Issued 388 $ 8.02 Vested — $ — Cancelled (17 ) $ 8.02 Unvested as of December 31, 2018 371 $ 8.02
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, 2018 and 2017 was calculated on the date of grant using the following weighted-average assumptions: Year Ended December 31, 2018 2017 Risk-free interest rate 2.7 % 2.1 % Expected dividend yield — % — % Expected term (in years) 6.0 6.1 Expected volatility 65.2 % 70.1 %
Schedule of Stock Options, Activity	The following table summarizes changes in stock option activity during the year ended December 31, 2018 (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, 2017 4,868 $ 6.28 7.9 $ 35,178 Granted 1,581 $ 21.15 Exercised (683 ) $ 2.26 Cancelled (743 ) $ 14.95 Outstanding at December 31, 2018 5,023 $ 10.23 7.6 $ 3,133 Exercisable at December 31, 2018 2,733 $ 5.91 6.8 $ 3,014

Income Taxes Income Taxes (Tabl

Income Taxes Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Summary of Components of the Provision for Income Taxes	The provision for income taxes for the years ended December 31, 2018 and 2017 was comprised as follows (in thousands): Year Ended December 31, 2018 2017 Current taxes: Federal $ — $ — State 46 36 Total current taxes 46 36 Deferred taxes: Federal — — State — — Total deferred taxes — — Total provision for income taxes $ 46 $ 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, 2018 2017 Income tax computed at federal statutory tax rate 21.0 % 34.0 % Deferred tax effects from the Tax Act — % (57.2 )% State taxes, net of federal benefit 10.3 % 4.7 % Tax credit carryforwards 12.2 % 26.8 % Non-deductible income (expense) — % (4.9 )% Change in valuation allowance (42.7 )% (1.8 )% Other (1.0 )% (1.8 )% Effective tax rate (0.2 )% (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, 2018 and 2017 were comprised as follows (in thousands): December 31, 2018 2017 Deferred tax assets: Net operating loss carryforwards $ 37,417 $ 26,926 Tax credit carryforwards 12,751 8,432 Deferred revenue 26,739 31,735 Deferred lease incentive 103 120 Deferred rent 476 431 Intangibles 552 237 Accrued expenses and other 1,091 995 Unrealized loss on available-for-sale securities 39 112 Stock-based compensation 2,119 713 Total deferred tax assets 81,287 69,701 Less: valuation allowance (55,348 ) (30,850 ) Net deferred tax assets 25,939 38,851 Deferred tax liabilities: Section 481(a) method change (25,653 ) (38,481 ) Depreciation (286 ) (370 ) Total deferred tax liabilities (25,939 ) (38,851 ) Net deferred taxes $ — $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	As of December 31, 2018 , 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 2019 $ 4,260 2020 4,380 2021 4,505 2022 4,633 2023 4,764 2024 and thereafter 6,142 Total future minimum lease payments $ 28,684

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2018
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, outstanding stock options, unvested RSAs and unvested RSUs are considered to be potentially dilutive securities, however the following amounts were excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive (in thousands): Year Ended December 31, 2018 2017 Outstanding stock options 5,023 4,868 Unvested RSAs 7 16 Unvested RSUs 371 — Total 5,401 4,884

Nature of Business (Details)

Nature of Business (Details) $ / shares in Units, $ in Thousands	Mar. 06, 2019	Feb. 01, 2017USD ($)$ / sharesshares	Jan. 13, 2017	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from initial public offering of common stock, net of issuance costs				$ 0	$ 107,008
Reverse stock split			0.27100271
Cash, cash equivalents, and marketable securities				$ 195,900
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	12 months

Basis of Presentation and Sum_4

Basis of Presentation and Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (163,907)	$ (89,615)
Deferred revenue	97,872	163,073
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (32,854)	(46,900)
Deferred revenue		$ 46,900

Basis of Presentation and Sum_5

Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Revenue Recognition (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current—related party	$ 55,157	$ 51,142
Deferred revenue, net of current portion—related party	42,715	65,018
Total liabilities	110,323	129,551
Accumulated deficit	(163,907)	(89,615)
Total stockholders’ equity	104,129	167,109	$ (69,088)
Collaboration revenue—related party	65,201	71,644
Net loss	$ (27,379)	$ (16,443)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.84)	$ (0.57)
Calculated under Revenue Guidance in Effect before Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current—related party	$ 42,174
Deferred revenue, net of current portion—related party	22,844
Total liabilities	77,469
Accumulated deficit	(131,053)
Total stockholders’ equity	136,983
Collaboration revenue—related party	51,142	$ 71,600
Net loss	$ (41,438)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (1.27)
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue, current—related party	$ 12,983
Deferred revenue, net of current portion—related party	19,871
Total liabilities	32,854
Accumulated deficit	(32,854)	$ (46,900)
Total stockholders’ equity	(32,854)
Collaboration revenue—related party	14,059
Net loss	$ 14,059
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ 0.43

Celgene Collaboration Agreeme_3

Celgene Collaboration Agreement - Narrative (Details) $ in Thousands	Feb. 01, 2017shares	Jul. 31, 2016USD ($)extensiondeliverablecustomer_programshares	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)shares
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue—related party			$ 65,201	$ 71,644
Deferred revenue			97,872	$ 163,073
Cumulative catch-up adjustment from changes in costs estimated to be incurred			7,100
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 (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
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
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%
Other Programs | Celgene Corporation | Maximum | Celegene Collaborative Arrangement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Number of program options | deliverable		3
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
Accounting Standards Update 2014-09 | Calculated under Revenue Guidance in Effect before Topic 606
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Collaboration revenue—related party			$ 51,142	$ 71,600
Deferred revenue				$ 116,200

Celgene Collaboration Agreeme_4

Celgene Collaboration Agreement - Performance Obligations (Details) - Celegene Collaborative Arrangement - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01	Dec. 31, 2018
Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance period for unit of accounting	12 months
Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance period for unit of accounting	4 years

Celgene Collaboration Agreeme_5

Celgene Collaboration Agreement - Schedule of Contract Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018USD ($)
Revenue, Performance Obligation, Contract Liability [Roll Forward]
Beginning balance	$ 163,073
Additions	0
Reductions	(65,201)
Ending balance	$ 97,872

Fair Value Measurements - Asset

Fair Value Measurements - Assets Measured at Fair Value (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Measurements, Recurring
Investments:
Totals	$ 195,864,000	$ 255,351,000
Liabilities measured at fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Investments:
Totals	128,021,000	190,178,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Investments:
Totals	67,843,000	65,173,000
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	41,434,000	21,059,000
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	41,434,000	21,059,000
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	41,434,000	21,059,000
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	67,843,000	65,173,000
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	67,843,000	65,173,000
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	53,758,000	110,948,000
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	53,758,000	110,948,000
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	32,829,000	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	32,829,000	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	0
Government agency securities | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Investments:
Available-for-sale debt securities, fair value	$ 0	$ 0

Investments - Schedule of Inves

Investments - Schedule of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, unrealized gains	$ 11	$ 0
Available-for-sale debt securities, unrealized losses	(89)	(409)
Cash equivalents, short-term and long-term investments, carrying value	195,942	255,760
Cash equivalents, short-term and long-term investments, fair vale disclosure	195,864	255,351
Money market funds, included in cash equivalents
Debt Securities, Available-for-sale [Line Items]
Cash equivalents at carrying value	41,434	21,059
Money market funds, included in cash equivalents	41,434	21,059
Short-term Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, unrealized gains	3	0
Available-for-sale debt securities, unrealized losses	(81)	(296)
Total cash equivalents and short-term investments, carrying value	189,952	233,448
Total cash equivalents and short-term investments, fair value	189,874	233,152
Short-term Investments | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	65,887	58,136
Available-for-sale debt securities, unrealized gains	2	0
Available-for-sale debt securities, unrealized losses	(39)	(64)
Available-for-sale debt securities, fair value	65,850	58,072
Short-term Investments | U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	53,765	111,049
Available-for-sale debt securities, unrealized gains	1	0
Available-for-sale debt securities, unrealized losses	(8)	(101)
Available-for-sale debt securities, fair value	53,758	110,948
Short-term Investments | Government agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	28,866	43,204
Available-for-sale debt securities, unrealized gains	0	0
Available-for-sale debt securities, unrealized losses	(34)	(131)
Available-for-sale debt securities, fair value	28,832	43,073
Long-term Investments
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	5,990	22,312
Available-for-sale debt securities, unrealized gains	8	0
Available-for-sale debt securities, unrealized losses	(8)	(113)
Available-for-sale debt securities, fair value	5,990	22,199
Long-term Investments | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	2,001	7,117
Available-for-sale debt securities, unrealized gains	0	0
Available-for-sale debt securities, unrealized losses	(8)	(16)
Available-for-sale debt securities, fair value	1,993	7,101
Long-term Investments | U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Available-for-sale debt securities, amortized cost basis	3,989	15,195
Available-for-sale debt securities, unrealized gains	8	0
Available-for-sale debt securities, unrealized losses	0	(97)
Available-for-sale debt securities, fair value	$ 3,997	$ 15,098

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Aggregate fair value of securities in an unrealized loss position for less than twelve months	$ 81.4	$ 113.9
Aggregate fair value of securities in an unrealized position for more than twelve months	22.3	107.9
Realized gains or losses on available-for-sale securities	$ 0	$ 0

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Prepaid expenses	$ 1,921	$ 2,196
Taxes receivable	0	16,737
Interest receivable on investments	414	969
Other current assets	0	43
Total prepaid expenses and other current assets	$ 2,335	$ 19,945

Prepaid Expenses and Other Cu_4

Prepaid Expenses and Other Current Assets - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018USD ($)
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Receipt of federal and state income tax refunds	$ 16.8

Restricted Cash - Narrative (De

Restricted Cash - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Abstract]
Non-current restricted cash	$ 1.3	$ 1.3

Restricted Cash - Schedule of C

Restricted Cash - Schedule of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 47,906	$ 23,559	$ 44,848
Restricted cash	1,270	1,270	1,520
Cash, cash equivalents and restricted cash	$ 49,176	$ 24,829	$ 46,368

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 21,545	$ 20,325
Less: accumulated depreciation	(8,005)	(4,174)
Total property and equipment, net	$ 13,540	16,151
Laboratory equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	5 years
Property and equipment, gross	$ 10,435	9,409
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	4 years
Property and equipment, gross	$ 1,071	1,038
Computer equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	3 years
Property and equipment, gross	$ 1,505	1,380
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 8,534	$ 8,498

Property and Equipment, Net - N

Property and Equipment, Net - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 3,831	$ 4,422

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Employee compensation and benefits	$ 4,063	$ 3,683
External research and professional services	2,796	4,647
Lab consumables and other	93	124
Total accrued expenses	$ 6,952	$ 8,454

Common Stock - Narrative (Detai

Common Stock - Narrative (Details)	Dec. 31, 2018voteshares	Dec. 31, 2017shares
Equity [Abstract]
Common stock, shares authorized (in shares) | shares	160,000,000	160,000,000
Common stock, votes per share | vote	1

Common Stock - Shares Reserved

Common Stock - Shares Reserved for Future Issuance (Details) - shares	Dec. 31, 2018	Dec. 31, 2017	Jan. 31, 2017
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	6,515,000	5,916,000	1,753,758
Restricted Stock
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	7,000	16,000
Restricted Stock Units (RSUs)
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	371,000	0
Outstanding Employee Stock Options
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	5,023,000	4,868,000
Future Issuances from Employee Stock Options
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	1,114,000	1,032,000

Preferred Stock (Details)

Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	Feb. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		5,000,000			5,000,000
Preferred stock, shares issued (in shares)		0			0
Preferred stock, shares outstanding (in shares)		0			0
Series A Convertible Preferred Stock
Class of Stock [Line Items]
Issuances of convertible preferred stock (in shares)				47,000,000
Convertible preferred stock, par or stated value (in dollars per share)			$ 1
Proceeds from the issuance of convertible preferred stock, net of issuance costs				$ 44.6
Issuance costs				$ 0.1
Series B Convertible Preferred Stock
Class of Stock [Line Items]
Issuances of convertible preferred stock (in shares)			24,778,761
Convertible preferred stock, par or stated value (in dollars per share)			$ 2.26
Proceeds from the issuance of convertible preferred stock, net of issuance costs			$ 55.8
Issuance costs			0.2
Series B-1 Convertible Preferred Stock
Class of Stock [Line Items]
Issuances of convertible preferred stock (in shares)		10,448,100
Convertible preferred stock, par or stated value (in dollars per share)		$ 3.46
Proceeds from the issuance of convertible preferred stock, net of issuance costs		$ 36.1
Issuance costs		$ 0.1
IPO
Class of Stock [Line Items]
Stock converted upon completion of IPO (in shares)	22,283,690
Convertible Promissory Note Receivable | Series A Convertible Preferred Stock
Class of Stock [Line Items]
Outstanding convertible promissory notes			$ 2.3

Stock-based Compensation - Narr

Stock-based Compensation - Narrative (Details) $ / shares in Units, $ in Millions	Jan. 01, 2018shares	Feb. 28, 2013shares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)non-employee$ / sharesshares	Dec. 31, 2017non-employeeshares	Jan. 31, 2017shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock eligible to be purchased (in shares)			6,515,000	5,916,000	5,916,000	1,753,758
Weighted average fair value of options granted (in dollars per share) | $ / shares			$ 12.88	$ 10.96
Intrinsic value of stock options exercised | $			$ 5.7	$ 1.9
Unrecognized stock-based compensation expense, options | $			$ 19.7
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock eligible to be purchased (in shares)			7,000	16,000	16,000
Issued (in shares)			0
Vested (in shares)			9,000
Aggregate fair value of awards vested in period | $			$ 0.1	$ 1.3
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock eligible to be purchased (in shares)			371,000	0	0
Issued (in shares)			388,000
Vested (in shares)			0	0
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options | $			$ 2.4
Remaining weighted average vesting period			1 year 7 months 13 days
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate			2.70%	2.10%
Expected dividend yield			0.00%	0.00%
Expected term (in years)			6 years 7 days	6 years 1 month 6 days
Expected volatility			65.20%	70.10%
Remaining weighted average vesting period			2 years 3 months 18 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
2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance (in shares)			1,113,539
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%
Number of additional shares authorized (in shares)	1,290,609
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
Number of additional shares authorized (in shares)	322,652
Percent of outstanding shares						1.00%
Maximum annual amount, shares authorized (in shares)						603,000
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]
Vested (in shares)					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]
Vested (in shares)					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

Stock-based Compensation - Stoc

Stock-based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 9,407	$ 4,775
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	4,540	2,840
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4,867	$ 1,935

Stock-based Compensation - Rest

Stock-based Compensation - Restricted Stock Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Restricted Stock
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)	16,000
Issued (in shares)	0
Vested (in shares)	(9,000)
Repurchased (in shares)	0
Ending unvested balance (in shares)	7,000	16,000
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)	$ 0
Issued (in dollars per share)	0
Vested (in dollars per share)	0
Repurchased (in dollars per share)	0
Ending unvested balance (in dollars per share)	$ 0	$ 0
Restricted Stock Units (RSUs)
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)	0
Issued (in shares)	388,000
Vested (in shares)	0	0
Cancelled (in shares)	(17,000)
Ending unvested balance (in shares)	371,000	0
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)	$ 0
Issued (in dollars per share)	8.02
Vested (in dollars per share)	0
Cancelled (in dollars per share)	8.02
Ending unvested balance (in dollars per share)	$ 8.02	$ 0

Stock-based Compensation - Weig

Stock-based Compensation - Weighted Average Assumptions (Details) - Employee Stock Option	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.70%	2.10%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	6 years 7 days	6 years 1 month 6 days
Expected volatility	65.20%	70.10%

Stock-based Compensation - St_2

Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning outstanding balance (in shares)	4,868
Granted (in shares)	1,581
Exercised (in shares)	(683)
Cancelled or forfeited (in shares)	(743)
Ending outstanding balance (in shares)	5,023	4,868
Exercisable (in shares)	2,733
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)	$ 6.28
Granted (in dollars per share)	21.15
Exercised (in dollars per share)	2.26
Cancelled or forfeited (in dollars per share)	14.95
Ending outstanding balance (in dollars per share)	10.23	$ 6.28
Exercisable (in dollars per share)	$ 5.91
Remaining contractual life, outstanding	7 years 6 months 26 days	7 years 10 months 24 days
Remaining contractual life, exercisable	6 years 9 months 22 days
Aggregate intrinsic value, outstanding	$ 3,133	$ 35,178
Aggregate intrinsic value, exercisable	$ 3,014

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income Tax Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Current taxes:
Federal	$ 0	$ 0
State	46	36
Total current taxes	46	36
Deferred taxes:
Federal	0	0
State	0	0
Total deferred taxes	0	0
Total provision for income taxes	$ 46	$ 36

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details)	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	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	$ 0	16,750,000
Valuation allowance	55,348,000	30,850,000
Increase in deferred tax asset valuation allowance	24,500,000
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	136,400,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	138,700,000
Research and Development Tax Credit Carryforwards | Federal Tax Authority
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	9,300,000
Research and Development Tax Credit Carryforwards | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	3,800,000
Investment Tax Credit Carryforwards | State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Tax credit carryforwards	$ 600,000

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory tax rate	21.00%	34.00%
Deferred tax effects from the Tax Act	0.00%	(57.20%)
State taxes, net of federal benefit	10.30%	4.70%
Tax credit carryforwards	12.20%	26.80%
Non-deductible income (expense)	0.00%	(4.90%)
Change in valuation allowance	(42.70%)	(1.80%)
Other	(1.00%)	(1.80%)
Effective tax rate	(0.20%)	(0.20%)

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 37,417	$ 26,926
Tax credit carryforwards	12,751	8,432
Deferred revenue	26,739	31,735
Deferred lease incentive	103	120
Deferred rent	476	431
Intangibles	552	237
Accrued expenses and other	1,091	995
Unrealized loss on available-for-sale securities	39	112
Stock-based compensation	2,119	713
Total deferred tax assets	81,287	69,701
Less: valuation allowance	(55,348)	(30,850)
Net deferred tax assets	25,939	38,851
Deferred tax liabilities:
Section 481(a) method change	(25,653)	(38,481)
Depreciation	(286)	(370)
Total deferred tax liabilities	(25,939)	(38,851)
Net deferred taxes	$ 0	$ 0

Related-party Transactions (Det

Related-party Transactions (Details) - USD ($) $ / shares in Units, $ in Millions	Feb. 01, 2017	Jul. 31, 2016	Dec. 31, 2017
Celegene Collaborative Arrangement
Related Party Transaction [Line Items]
Non-refundable upfront payment received for research agreement		$ 225
Series B-1 Convertible Preferred Stock
Related Party Transaction [Line Items]
Issuances of convertible preferred stock (in shares)			10,448,100
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		$ 36.1
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	$ 106.4
Celgene Corporation | Celgene Collaboration Agreement | Celegene Collaborative Arrangement
Related Party Transaction [Line Items]
Non-refundable upfront payment received for research agreement		$ 225
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		$ 36.1
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

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) $ in Millions	1 Months Ended	3 Months Ended	5 Months Ended	12 Months Ended
	Nov. 30, 2016USD ($)ft²consecutive_extension_period	Jun. 30, 2018USD ($)	May 31, 2017USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Loss Contingencies [Line Items]
Lease space occupied (in square feet) | ft²	51,000
Number of consecutive extension periods | consecutive_extension_period	1
Renewal term	5 years
Renewal notice period	12 months
Tenant improvement allowance	$ 0.5		$ 2.8
Security deposit, in form of letter of credit	$ 1.3
Sublease term			3 years
Early termination fee		$ 0.7
Rent expense				$ 4	$ 3.5
Costs incurred, third party agreements				$ 0.5
Minimum
Loss Contingencies [Line Items]
Cancellation notice period, technology agreements				30 days
Potential costs, third party agreements				$ 12.5
Maximum
Loss Contingencies [Line Items]
Cancellation notice period, technology agreements				90 days
Potential costs, third party agreements				$ 12.9
License And Collaboration Agreements | Maximum
Loss Contingencies [Line Items]
Potential costs, technology agreements				13.4
Costs incurred, technology agreements				$ 0.2

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,019	$ 4,260
2,020	4,380
2,021	4,505
2,022	4,633
2,023	4,764
2024 and thereafter	6,142
Total future minimum lease payments	$ 28,684

401(k) Savings Plan - Narrative

401(k) Savings Plan - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Contribution Plan Disclosure [Line Items]
Percent match	50.00%
Contributions to plan	$ 500,000	$ 0
Maximum
Defined Contribution Plan Disclosure [Line Items]
Maximum percent for match	6.00%

Net Loss per Share (Details)

Net Loss per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	5,401	4,884
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)	5,023	4,868
Unvested RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	7	16
Unvested RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	371	0