Jounce Therapeutics (JNCE) 10-Q 4 May 21 2021 Q1 Quarterly report Financial data

Cover

Cover - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-37998
Entity Registrant Name	JOUNCE THERAPEUTICS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	45-4870634
Entity Address, Address Line One	780 Memorial Drive
Entity Address, State or Province	MA
Entity Address, City or Town	Cambridge,
Entity Address, Postal Zip Code	02139
City Area Code	857
Local Phone Number	259‑3840
Title of 12(b) Security	Common Stock, $0.001 par value per share
Trading Symbol	JNCE
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		51,208,357
Entity Central Index Key	0001640455
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 196,273	$ 147,493
Short-term investments	61,205	58,985
Prepaid expenses and other current assets	9,535	4,913
Total current assets	267,013	211,391
Property and equipment, net	6,709	7,336
Long-term investments	13,808	6,710
Operating lease right-of-use asset	14,146	14,856
Other non-current assets	3,477	3,943
Total assets	305,153	244,236
Current liabilities:
Accounts payable	1,631	2,036
Accrued expenses	7,470	12,044
Deferred revenue, current - related party	392	1,931
Operating lease liability, current	3,378	3,271
Other current liabilities	54	42
Total current liabilities	12,925	19,324
Operating lease liability, net of current portion	12,774	13,618
Total liabilities	25,699	32,942
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.001 par value: 5,000 shares authorized at March 31, 2021 and December 31, 2020; no shares issued or outstanding at March 31, 2021 or December 31, 2020	0	0
Common stock, $0.001 par value: 160,000 shares authorized at March 31, 2021 and December 31, 2020; 51,200 and 41,729 shares issued and outstanding at March 31, 2021 and December 31, 2020, respectively	51	42
Additional paid-in capital	456,964	362,270
Accumulated other comprehensive income	(25)	(17)
Accumulated deficit	(177,536)	(151,001)
Total stockholders’ equity	279,454	211,294
Total liabilities and stockholders’ equity	$ 305,153	$ 244,236

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
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
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)	51,200,000	41,729,000
Common stock shares outstanding (in shares)	51,200,000	41,729,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue:
License and collaboration revenue—related party	$ 1,539	$ 0
Operating expenses:
Research and development	20,507	19,646
General and administrative	7,615	7,539
Total operating expenses	28,122	27,185
Operating loss	(26,583)	(27,185)
Other income, net	49	750
Loss before provision for income taxes	(26,534)	(26,435)
Provision for income taxes	1	8
Net loss	$ (26,535)	$ (26,443)
Net loss per share, basic and diluted (in dollars per share)	$ (0.58)	$ (0.78)
Weighted-average common shares outstanding, basic and diluted (in shares)	45,962	34,029
Comprehensive loss:
Net loss	$ (26,535)	$ (26,443)
Other comprehensive income:
Unrealized (loss) gain on available-for-sale securities	(8)	90
Comprehensive loss	$ (26,543)	$ (26,353)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Follow-on Public Offering	Common Stock	Common StockFollow-on Public Offering	Additional Paid-In Capital	Additional Paid-In CapitalFollow-on Public Offering	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit
Beginning balance, common stock (in shares) at Dec. 31, 2019			33,738
Beginning balance at Dec. 31, 2019	$ 174,593		$ 34		$ 281,664		$ 54	$ (107,159)
Issuance of common stock, net of issuance costs (in shares)			201
Issuance of common stock, net of issuance costs	1,648				1,648
Exercises of common stock options (in shares)			9
Exercises of common stock options	38				38
Vesting of restricted stock units (in shares)			101
Vesting of restricted stock units	0				0
Stock-based compensation expense	2,618				2,618
Other comprehensive income (loss)	90						90
Net loss	(26,443)							(26,443)
Ending balance (in shares) at Mar. 31, 2020			34,049
Ending balance at Mar. 31, 2020	$ 152,544		$ 34		285,968		144	(133,602)
Beginning balance, common stock (in shares) at Dec. 31, 2020	41,729		41,729
Beginning balance at Dec. 31, 2020	$ 211,294		$ 42		362,270		(17)	(151,001)
Issuance of common stock, net of issuance costs (in shares)			3,156	5,750
Issuance of common stock, net of issuance costs	$ 30,221	$ 60,638	$ 3	$ 6	30,218	$ 60,632
Exercises of common stock options (in shares)	342		342
Exercises of common stock options	$ 1,019				1,019
Vesting of restricted stock units (in shares)			223
Vesting of restricted stock units	0				0
Stock-based compensation expense	2,825				2,825
Other comprehensive income (loss)	(8)						(8)
Net loss	$ (26,535)							(26,535)
Ending balance (in shares) at Mar. 31, 2021	51,200		51,200
Ending balance at Mar. 31, 2021	$ 279,454		$ 51		$ 456,964		$ (25)	$ (177,536)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities:
Net loss	$ (26,535)	$ (26,443)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	2,825	2,618
Depreciation expense	785	938
Net amortization of premiums and discounts on investments	139	(84)
Other non-cash items	0	19
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(4,573)	(543)
Other non-current assets	466	18
Accounts payable	(518)	1,407
Accrued expenses and other current liabilities	(4,575)	(1,457)
Deferred revenue—related party	(1,539)	0
Other liabilities	(27)	(19)
Net cash used in operating activities	(33,552)	(23,546)
Investing activities:
Purchases of investments	(21,265)	(19,856)
Proceeds from maturities of investments	11,800	63,650
Purchases of property and equipment	(158)	(50)
Net cash (used in) provided by investing activities	(9,623)	43,744
Financing activities:
Proceeds from issuance of common stock, net of issuance costs	90,985	1,514
Proceeds from exercise of stock options	970	38
Net cash provided by financing activities	91,955	1,552
Net increase in cash, cash equivalents and restricted cash	48,780	21,750
Cash, cash equivalents and restricted cash, beginning of period	148,763	54,511
Cash, cash equivalents and restricted cash, end of period	197,543	76,261
Non-cash investing and financing activities:
Issuance costs in accounts payable and accrued expenses	163	0
Stock option exercise receivables in prepaid expenses and other current assets	49	0
Supplemental cash flow information:
Cash paid for lease liabilities	1,492	1,090
Cash paid for income taxes	$ 8	$ 0

Nature of Business

Nature of Business	3 Months Ended
	Mar. 31, 2021
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 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. As of March 31, 2021, the Company had cash, cash equivalents and investments of $271.3 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 May 4, 2021, the filing date of this Quarterly Report on Form 10-Q. The Company expects to finance its future cash needs through a combination of equity or debt financings, collaborations, licensing arrangements and strategic alliances.

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
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 condensed consolidated financial statements as of March 31, 2021 and December 31, 2020, and for the three months ended March 31, 2021 and 2020, 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”) for condensed consolidated financial information. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, these condensed consolidated financial statements reflect all normal recurring adjustments which are necessary for a fair presentation of the Company’s financial position and results of its operations, as of and for the periods presented. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 filed with the SEC on February 25, 2021 (the “Annual Report on Form 10-K”). The information presented in the condensed consolidated financial statements and related notes as of March 31, 2021, and for the three months ended March 31, 2021 and 2020, is unaudited. The December 31, 2020 condensed consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures, including notes, required by GAAP for complete financial statements. Interim results for the three months ended March 31, 2021 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2021, or any future period. The accompanying condensed consolidated financial statements include the accounts of Jounce Therapeutics, Inc. and its wholly-owned subsidiary, Jounce Mass Securities, Inc. All intercompany transactions and balances have been eliminated in consolidation. Summary of Significant Accounting Policies The significant accounting policies and estimates used in the preparation of the condensed consolidated financial statements are described in the Company’s audited financial statements as of and for the year ended December 31, 2020, and the notes thereto, which are included in the Annual Report on Form 10-K. There have been no material changes in the Company’s significant accounting policies during the three months ended March 31, 2021. 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, 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. Recent Accounting Pronouncements, Not Yet Adopted In June 2016, the FASB issued Accounting Standards Update (“ASU”) 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . This standard requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and it establishes additional disclosure requirements related to credit risks. For available-for-sale debt securities with expected credit losses, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. This guidance was originally effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption was permitted. In November 2019, the FASB subsequently issued ASU 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates , whereby the effective date of this standard for smaller reporting companies was deferred to annual reporting periods beginning after December 15, 2022, including interim periods within those annual reporting periods, and early adoption is still permitted. Accordingly, the Company will now adopt this standard effective January 1, 2023, and it is currently evaluating the potential impact that ASU 2016-13 may have on the consolidated financial statements.

License and Collaboration Reven

License and Collaboration Revenue	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
License and Collaboration Revenue	License and Collaboration Revenue Gilead License Agreement On August 31, 2020, the Company and Gilead Sciences, Inc. (“Gilead”) entered into an exclusive license agreement (the “Gilead License Agreement”) to license the Company’s JTX-1811 program to Gilead. Concurrently with the license agreement, the Company and Gilead entered into a stock purchase agreement (the “Stock Purchase Agreement”) and a registration rights agreement (the “Registration Rights Agreement”, and together with the License Agreement and the Stock Purchase Agreement, the “Transaction Agreements”). Pursuant to the Gilead License Agreement, the Company granted to Gilead a worldwide and exclusive license to develop, manufacture and commercialize JTX-1811 and certain derivatives thereof (the “Licensed Products”). Gilead paid the Company a one-time, non-refundable upfront payment of $85.0 million pursuant to the Gilead License Agreement and the Company sold Gilead 5,539,727 shares of common stock pursuant to the Stock Purchase Agreement for proceeds of $35.0 million upon the closing in October 2020. The Company will continue to develop JTX-1811 during the initial development term, which includes conducting activities defined within the agreement to advance JTX-1811 through the clearance of an investigational new drug (“IND”) application or an earlier date specified by Gilead, at which time the program will be transitioned to Gilead. Milestone and Royalties The Company is entitled to receive payments from Gilead upon the achievement of specified clinical, regulatory and sales milestones, including potential clinical development and regulatory milestone payments up to an aggregate total of $510.0 million and potential sales milestone payments up to an aggregate total of $175.0 million. The Company is also eligible to receive tiered royalty payments based on a percentage of annual worldwide net sales ranging from the high-single digits to mid-teens, based on future annual net sales of the Licensed Products, on a Licensed Product-by-Licensed Product and country-by-country basis. Termination Gilead may terminate the License Agreement for convenience, at its sole discretion, in its entirety or on a Licensed Product-by-Licensed Product or region-by-region basis, at any time with prior written notice to the Company. Unless terminated earlier in accordance with its terms, the Gilead License Agreement provides that it will expire (i) on a Licensed Product-by-Licensed Product and country-by-country basis on the date of the expiration of the royalty term with respect to such Licensed Product in such country and (ii) in its entirety upon the expiration of all applicable royalty terms with respect to the Licensed Products in all countries, following which the applicable licenses under the License Agreement will become fully paid-up, perpetual, irrevocable and royalty-free. Accounting Analysis Identification of the Contract(s) The Company assessed the Gilead License Agreement and concluded that it represents a contract with a customer within the scope of ASC 606, Revenue from Contracts with Customers (“ASC 606”). In addition, the Company determined that the Gilead License Agreement and Stock Purchase Agreement should be evaluated as a combined contract in accordance with ASC 606 given that the agreements were executed contemporaneously, negotiated as a package and have the same commercial objective to provide funding to further the Company’s research and development activities. Identification of Promises and Performance Obligations The Company determined that the Gilead License Agreement contains the following promises: (i) delivery of a worldwide and exclusive license to develop, manufacture and commercialize JTX-1811 (the “JTX-1811 License”), (ii) provision of certain research transition activities, specifically outlined within the Gilead License Agreement, related to the advancement of JTX-1811 through the clearance of an IND application and transition of the JTX-1811 program to Gilead (the “Research and Transition Services”), (iii) appointment of an individual to act as an alliance manager and primary point of contact for Gilead, (iv) appointment of individuals to participate on the Joint Steering Committee (“JSC”), and (v) optional assistance by Jounce after completion of Research and Transition Services upon the request of Gilead. The Company assessed the above promises and concluded that each of the JTX-1811 License and Research and Transition Services is capable of being distinct and distinct within the context of the Gilead License Agreement. Based upon this evaluation, the Company concluded that its promise to deliver the JTX-1811 License and promise to perform Research and Transition Services represent separate performance obligations in the Gilead License Agreement. The Company determined that the appointment of an individual to act as an alliance manager and primary point of contact for Gilead, participation in alliance management meetings and the appointment of individuals to participate on the JSC do not constitute the transfer of a good or service to Gilead and as such, do not represent performance obligations under the contract. Finally, the Company assessed Gilead’s ability to request optional assistance by Jounce after completion of Research and Transition Services and determined that it was both quantitatively and qualitatively immaterial in the context of the Gilead License Agreement. Accordingly, the Company did not assess the optional assistance as a performance obligation. Determination of Transaction Price As noted above, the Company received a non-refundable upfront payment of $85.0 million upon the closing of the Gilead License Agreement. This upfront payment represents an element of fixed consideration under the Gilead License Agreement. The Company also evaluated as possible variable consideration the milestones and royalties discussed above. With respect to clinical development and regulatory milestones, based upon the high degree of uncertainty and risk associated with these potential payments, the Company concluded that all such amounts should be fully constrained and are not included in the initial transaction price. As part of the evaluation of the constraint the Company considered certain factors, including that receipt of such milestones is outside the control of the Company and the probability of success criteria is estimated. Each of these variable consideration items was evaluated under the most-likely amount method. As for royalties and sales milestones, the Company determined that the royalties and milestones relate solely to the JTX-1811 License, which is a license of intellectual property (“IP”). Accordingly, the Company did not include any potential royalty or sales milestone amounts in the initial transaction price, and the Company will not recognize revenue related to these royalties and sales milestones until the associated sales occur and relevant thresholds are met. The Company assessed proceeds of $35.0 million received under the Stock Purchase Agreement and determined that the fair value of the equity component was $55.7 million based on the closing price of $10.06 per share in October 2020. Pursuant to the agreement, the Company sold 5,539,727 shares of common stock for aggregate cash consideration of $35.0 million, or $6.32 per share, which is equal to the daily volume weighted average per share intraday price of the Common Stock on Nasdaq over the 30-trading day period ending on and including August 28, 2020 plus a 30% premium. As a result, the Company determined that the gross proceeds of $35.0 million received under the Stock Purchase Agreement included a discount to the fair value of the Company’s stock as of October 16, 2020 equal to $20.7 million. In accordance with ASC 606, the discount amount will be included in the transaction price for revenue recognition, resulting in an initial transaction price of $64.3 million. Allocation of Transaction Price to Performance Obligations The Company allocated the transaction price to each performance obligation on a relative estimated standalone selling price basis. The Company developed the estimated standalone selling price for the JTX-1811 License based on the present value of expected future cash flows associated with the license and related clinical development and regulatory milestones. In developing such estimate, the Company applied judgement in determining the timing needed to develop the Licensed Product, the probability of success, and the discount rate. The Company developed the estimated standalone selling price for the Research and Transition Services obligation based on the nature of the services to be performed and the Company’s best estimate of the length of time required to perform the services necessary to achieve clearance of an IND application for the JTX-1811 program. Based on the above considerations, $60.8 million of the initial transaction price was allocated to the JTX-1811 License performance obligation and $3.5 million was allocated to the Research and Transition Services performance obligation. Recognition of Revenue The Company determined that the JTX-1811 License is a functional license as the underlying IP has significant standalone functionality. In addition, the Company determined that the JTX-1811 License represents a right to use certain of the Company’s IP as it exists at a point in time. Finally, the Company determined that October 16, 2020 represents (i) the date at which the Company made available the IP to Gilead and (ii) the beginning of the period during which Gilead is able to use and benefit from its right to use the IP. Based upon these considerations, the Company recognized the entirety of the initial transaction price allocated to the JTX-1811 License performance obligation during the year ended December 31, 2020. Further, the Company determined the input method under ASC 606 is the most appropriate method of revenue recognition for the Research and Transition Services performance obligation. The method of measuring progress towards delivery of the services incorporated actual internal and external costs incurred, relative to total internal and external costs expected to be incurred to satisfy the performance obligation. The period over which total costs were estimated reflected the Company’s best estimate of the period over which it would perform the research and transition services to achieve clearance of an IND application of the JTX-1811 program and transition the program to Gilead. Based upon these considerations, the Company recognized $1.5 million in revenue related to the Research and Transition Services performance obligation during the three months ended March 31, 2021. The following table presents changes in the Company’s contract liabilities related to the Gilead License Agreement during the during the three months ended March 31, 2021 (in thousands): January 1, 2021 Additions Reductions March 31, 2021 Contract liabilities: Deferred revenue - related party 1,931 — (1,539) 392 Total $ 1,931 $ — $ (1,539) $ 392 The reductions to the deferred revenue contract liability during the three months ended March 31, 2021 was comprised of revenue recognized for Research and Transition services performed during the period. All revenue recognized during the three months ended March 31, 2021 related to the Gilead License Agreement was included within the beginning balance of the deferred revenue contract liability. As of March 31, 2021, the remaining amount of the transaction price allocated to the Research and Transition Services that was unsatisfied is expected to be recognized in 2021 as services are performed. The Company has not received any milestone or royalty payments under the Gilead License Agreement as of March 31, 2021

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value MeasurementsFair value is an exit price, representing the amount that would be received from the sale of an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value is determined based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect certain market assumptions. As a basis for considering such assumptions, GAAP establishes a three-tier value hierarchy, which prioritizes the inputs used to develop the assumptions and for measuring fair value as follows: (Level 1) observable inputs such as quoted prices in active markets for identical assets; (Level 2) inputs other than the quoted prices in active markets that are observable either directly or indirectly; and (Level 3) unobservable inputs in which there is little or no market data, which requires the Company to develop its own assumptions. This hierarchy requires the Company to use observable market data, when available, and to minimize the use of unobservable inputs when determining fair value. 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 condensed 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 March 31, 2021 were as follows (in thousands): Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs Significant Unobservable Inputs Money market funds, included in cash equivalents $ 191,760 $ 191,760 $ — $ — Investments: Corporate debt securities 79,526 — 79,526 — Totals $ 271,286 $ 191,760 $ 79,526 $ — Assets measured at fair value on a recurring basis as of December 31, 2020 were as follows (in thousands): Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs Significant Unobservable Inputs Money market funds, included in cash equivalents $ 147,492 $ 147,492 $ — $ — Investments: Corporate debt securities 63,691 — 63,691 — Government agency securities 2,005 — 2,005 — Totals $ 213,188 $ 147,492 $ 65,696 $ — There were no changes in valuation techniques during the three months ended March 31, 2021 or during the year ended December 31, 2020. There were no liabilities measured at fair value on a recurring basis as of March 31, 2021 or December 31, 2020.

Investments

Investments	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Investments	InvestmentsShort-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 March 31, 2021 were comprised as follows (in thousands): March 31, 2021 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 191,760 $ — $ — $ 191,760 Corporate debt securities 65,728 1 (11) 65,718 Total cash equivalents and short-term investments 257,488 1 (11) 257,478 Long-term investments: Corporate debt securities 13,823 — (15) 13,808 Total long-term investments 13,823 — (15) 13,808 Total cash equivalents and investments $ 271,311 $ 1 $ (26) $ 271,286 Cash equivalents, short-term investments and long-term investments as of December 31, 2020 were comprised as follows (in thousands): December 31, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 147,492 $ — $ — $ 147,492 Corporate debt securities 56,985 9 (13) 56,981 Government agency securities 2,001 4 — 2,005 Total cash equivalents and short-term investments 206,478 13 (13) 206,478 Long-term investments: Corporate debt securities 6,727 — (17) 6,710 Total long-term investments 6,727 — (17) 6,710 Total cash equivalents and investments $ 213,205 $ 13 $ (30) $ 213,188 As of March 31, 2021 and December 31, 2020, the aggregate fair value of securities that were in an unrealized loss position for less than twelve months was $37.3 million and $28.3 million, respectively. As of both March 31, 2021 and December 31, 2020, there were no securities that were in an unrealized loss position for more than twelve months. As of March 31, 2021, 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 March 31, 2021. There were no realized gains or losses on available-for-sale securities during the three months ended March 31, 2021. There were immaterial realized gains and losses on available-for-sale securities during the three months ended March 31, 2020.

Restricted Cash

Restricted Cash	3 Months Ended
	Mar. 31, 2021
Cash and Cash Equivalents [Abstract]
Restricted Cash	Restricted CashAs of both March 31, 2021 and December 31, 2020, the Company maintained non-current restricted cash of $1.3 million. This amount is included within “Other non-current assets” in the accompanying condensed 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 condensed consolidated statements of cash flows (in thousands): Three Months Ended Three Months Ended Beginning of Period End of Period Beginning of Period End of Period Cash and cash equivalents $ 147,493 $ 196,273 $ 53,241 $ 74,991 Restricted cash 1,270 1,270 1,270 1,270 Cash, cash equivalents and restricted cash $ 148,763 $ 197,543 $ 54,511 $ 76,261

Accrued Expenses

Accrued Expenses	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Accrued Expenses	Accrued Expenses Accrued expenses as of March 31, 2021 and December 31, 2020 were comprised as follows (in thousands): March 31, December 31, 2021 2020 Employee compensation and benefits $ 2,955 $ 6,825 External research and professional services 4,219 4,855 Lab consumables and other 296 364 Total accrued expenses $ 7,470 $ 12,044

Common Stock and Preferred Stoc

Common Stock and Preferred Stock	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Common Stock and Preferred Stock	Common Stock and Preferred 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. On December 17, 2019, the Company entered into a Sales Agreement with Cowen and Company, LLC, or Cowen, pursuant to which the Company offered and sold shares of its common stock with an aggregate offering price of up to $50.0 million under an “at the market” offering program (the “ATM Offering”). The Sales Agreement provided that Cowen would be entitled to a sales commission equal to 3.0% of the gross sales price per share of all shares sold under the ATM Offering. During the three months ended March 31, 2021, the Company sold an aggregate of 3,156,200 shares of common stock at an average price of $9.87 per share under the ATM Offering for net proceeds of $30.2 million, which completed the sale of all available amounts under the ATM Offering. In addition, the Company completed a follow-on public offering of its common stock, selling an aggregate of 5,750,000 shares of common stock at a public offering price of $11.25 per share for net proceeds of $60.6 million, after deducting underwriting discounts and commissions and offering fees, during three months ended March 31, 2021. Preferred Stock The Company is authorized to issue 5,000,000 shares of undesignated preferred stock in one or more series. As of March 31, 2021, no shares of preferred stock were issued or outstanding. Shares Reserved for Future Issuance As of March 31, 2021 and December 31, 2020, the Company had reserved for future issuance the following number of shares of common stock (in thousands): March 31, December 31, 2021 2020 Shares reserved for vesting of restricted stock units 822 588 Shares reserved for exercises of outstanding stock options 7,174 6,586 Shares reserved for future issuance under the 2017 Stock Option and Incentive Plan 1,563 1,284 Total shares reserved for future issuance 9,559 8,458

Stock-based Compensation

Stock-based Compensation	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Stock-based Compensation	Stock-based Compensation 2013 Stock Option and Grant Plan In February 2013, the 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, restricted stock awards (“RSAs”) and restricted stock units (“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 board of directors adopted and the Company’s stockholders approved the 2017 Stock Option and Incentive Plan (the “2017 Plan”). 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 on Form S-8 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, 2020 and 2021, 1,349,526 and 1,669,162 additional shares, respectively, were automatically added to the shares authorized for issuance under the 2017 Plan. As of March 31, 2021, there were 1,563,376 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”). 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, 2020 and 2021, 337,381 and 417,291 additional shares, respectively, 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 March 31, 2021. Stock-based Compensation Expense Total stock-based compensation expense recognized in the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three Months Ended 2021 2020 Research and development $ 1,215 $ 1,181 General and administrative 1,610 1,437 Total stock-based compensation expense $ 2,825 $ 2,618 RSU Activity The Company has also granted RSUs to its employees under the 2017 Plan. The following table summarizes RSU activity for the three months ended March 31, 2021 (in thousands, except per share amounts): RSUs Weighted-Average Grant Date Fair Value per Share Unvested as of December 31, 2020 588 $ 5.82 Issued 472 $ 11.90 Vested (223) $ 5.64 Cancelled (15) $ 8.13 Unvested as of March 31, 2021 822 $ 9.32 The aggregate fair value of RSUs that vested during the three months ended March 31, 2021, based upon the fair values of the stock underlying the RSUs on the day of vesting, was $1.5 million. The aggregate fair value of RSUs that vested during the three months ended March 31, 2020, based upon the fair values of the stock underlying the RSUs on the day of vesting, was $0.8 million. As of March 31, 2021, there was unrecognized stock-based compensation expense related to unvested RSUs of $6.9 million, which the Company expects to recognize over a weighted-average period of approximately 2.2 years. Stock Option Activity The fair value of stock options granted during the three months ended March 31, 2021 and 2020 was calculated on the date of grant using the following weighted-average assumptions: Three Months Ended 2021 2020 Risk-free interest rate 0.6 % 1.4 % Expected dividend yield — % — % Expected term (in years) 6.1 6.1 Expected volatility 81.6 % 71.4 % Using the Black-Scholes option pricing model, the weighted-average grant date fair value of stock options granted during the three months ended March 31, 2021 and 2020 was $8.24 and $4.23 per share, respectively. The following table summarizes stock option activity during the three months ended March 31, 2021 (in thousands, except per share amounts): Options Weighted-Average Exercise Price Per Share Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Outstanding at December 31, 2020 6,586 $ 8.30 6.5 $ 13,110 Granted 1,027 $ 11.94 Exercised (342) $ 2.98 Cancelled (97) $ 11.61 Outstanding at March 31, 2021 7,174 $ 9.04 6.9 $ 25,472 Exercisable at March 31, 2021 4,474 $ 8.65 5.7 $ 18,973 The aggregate intrinsic value of stock options exercised during the three months ended March 31, 2021 and 2020 was $2.8 million and less than $0.1 million, respectively. As of March 31, 2021, there was unrecognized stock-based compensation expense related to unvested stock options of $15.4 million, which the Company expects to recognize over a weighted-average period of approximately 2.6 years.

Related-party Transactions

Related-party Transactions	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
Related-party Transactions	Related-party TransactionsIn August 2020, the Company entered into the Gilead License Agreement and Stock Purchase Agreement under which it received a non-refundable upfront payment of $85.0 million and cash consideration of $35.0 million for Gilead’s purchase of 5,539,727 shares of the Company’s common stock. As of March 31, 2021, the Company had no reimbursable expenses due from Gilead. As of December 31, 2020, the Company had recorded $0.1 million of reimbursement expenses due from Gilead within prepaid expenses and other current assets in the accompanying consolidated balance sheets.

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Loss per Share	Net Loss per Share For purposes of the diluted net loss per share calculation, outstanding stock options and unvested RSUs are considered to be potentially dilutive securities, however the following weighted-average amounts were excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive (in thousands): Three Months Ended 2021 2020 Outstanding stock options 6,953 6,339 Unvested RSUs 680 624 Total 7,633 6,963

Basis of Presentation and Sum_2

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements as of March 31, 2021 and December 31, 2020, and for the three months ended March 31, 2021 and 2020, 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”) for condensed consolidated financial information. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, these condensed consolidated financial statements reflect all normal recurring adjustments which are necessary for a fair presentation of the Company’s financial position and results of its operations, as of and for the periods presented. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 filed with the SEC on February 25, 2021 (the “Annual Report on Form 10-K”). The information presented in the condensed consolidated financial statements and related notes as of March 31, 2021, and for the three months ended March 31, 2021 and 2020, is unaudited. The December 31, 2020 condensed consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures, including notes, required by GAAP for complete financial statements.
Principles of Consolidation	The accompanying condensed consolidated financial statements include the accounts of Jounce Therapeutics, Inc. and its wholly-owned subsidiary, Jounce Mass Securities, Inc. All intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	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, 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.
Recent Accounting Pronouncements	Recent Accounting Pronouncements, Not Yet Adopted In June 2016, the FASB issued Accounting Standards Update (“ASU”) 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments . This standard requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and it establishes additional disclosure requirements related to credit risks. For available-for-sale debt securities with expected credit losses, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. This guidance was originally effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption was permitted. In November 2019, the FASB subsequently issued ASU 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates , whereby the effective date of this standard for smaller reporting companies was deferred to annual reporting periods beginning after December 15, 2022, including interim periods within those annual reporting periods, and early adoption is still permitted. Accordingly, the Company will now adopt this standard effective January 1, 2023, and it is currently evaluating the potential impact that ASU 2016-13 may have on the consolidated financial statements.
Fair Value Measurement Policy	.

License and Collaboration Rev_2

License and Collaboration Revenue (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Contract with Customer, Asset and Liability	The following table presents changes in the Company’s contract liabilities related to the Gilead License Agreement during the during the three months ended March 31, 2021 (in thousands): January 1, 2021 Additions Reductions March 31, 2021 Contract liabilities: Deferred revenue - related party 1,931 — (1,539) 392 Total $ 1,931 $ — $ (1,539) $ 392

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Assets Measured at Fair Value	Assets measured at fair value on a recurring basis as of March 31, 2021 were as follows (in thousands): Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs Significant Unobservable Inputs Money market funds, included in cash equivalents $ 191,760 $ 191,760 $ — $ — Investments: Corporate debt securities 79,526 — 79,526 — Totals $ 271,286 $ 191,760 $ 79,526 $ — Assets measured at fair value on a recurring basis as of December 31, 2020 were as follows (in thousands): Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs Significant Unobservable Inputs Money market funds, included in cash equivalents $ 147,492 $ 147,492 $ — $ — Investments: Corporate debt securities 63,691 — 63,691 — Government agency securities 2,005 — 2,005 — Totals $ 213,188 $ 147,492 $ 65,696 $ —

Investments (Tables)

Investments (Tables)	3 Months Ended
	Mar. 31, 2021
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 March 31, 2021 were comprised as follows (in thousands): March 31, 2021 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 191,760 $ — $ — $ 191,760 Corporate debt securities 65,728 1 (11) 65,718 Total cash equivalents and short-term investments 257,488 1 (11) 257,478 Long-term investments: Corporate debt securities 13,823 — (15) 13,808 Total long-term investments 13,823 — (15) 13,808 Total cash equivalents and investments $ 271,311 $ 1 $ (26) $ 271,286 Cash equivalents, short-term investments and long-term investments as of December 31, 2020 were comprised as follows (in thousands): December 31, 2020 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents and short-term investments: Money market funds, included in cash equivalents $ 147,492 $ — $ — $ 147,492 Corporate debt securities 56,985 9 (13) 56,981 Government agency securities 2,001 4 — 2,005 Total cash equivalents and short-term investments 206,478 13 (13) 206,478 Long-term investments: Corporate debt securities 6,727 — (17) 6,710 Total long-term investments 6,727 — (17) 6,710 Total cash equivalents and investments $ 213,205 $ 13 $ (30) $ 213,188

Restricted Cash (Tables)

Restricted Cash (Tables)	3 Months Ended
	Mar. 31, 2021
Cash and Cash Equivalents [Abstract]
Schedule of Restricted Cash	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 condensed consolidated statements of cash flows (in thousands): Three Months Ended Three Months Ended Beginning of Period End of Period Beginning of Period End of Period Cash and cash equivalents $ 147,493 $ 196,273 $ 53,241 $ 74,991 Restricted cash 1,270 1,270 1,270 1,270 Cash, cash equivalents and restricted cash $ 148,763 $ 197,543 $ 54,511 $ 76,261
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 condensed consolidated statements of cash flows (in thousands): Three Months Ended Three Months Ended Beginning of Period End of Period Beginning of Period End of Period Cash and cash equivalents $ 147,493 $ 196,273 $ 53,241 $ 74,991 Restricted cash 1,270 1,270 1,270 1,270 Cash, cash equivalents and restricted cash $ 148,763 $ 197,543 $ 54,511 $ 76,261

Accrued Expenses (Tables)

Accrued Expenses (Tables)	3 Months Ended
	Mar. 31, 2021
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses as of March 31, 2021 and December 31, 2020 were comprised as follows (in thousands): March 31, December 31, 2021 2020 Employee compensation and benefits $ 2,955 $ 6,825 External research and professional services 4,219 4,855 Lab consumables and other 296 364 Total accrued expenses $ 7,470 $ 12,044

Common Stock and Preferred St_2

Common Stock and Preferred Stock (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Schedule of Stock by Class	As of March 31, 2021 and December 31, 2020, the Company had reserved for future issuance the following number of shares of common stock (in thousands): March 31, December 31, 2021 2020 Shares reserved for vesting of restricted stock units 822 588 Shares reserved for exercises of outstanding stock options 7,174 6,586 Shares reserved for future issuance under the 2017 Stock Option and Incentive Plan 1,563 1,284 Total shares reserved for future issuance 9,559 8,458

Stock-based Compensation (Table

Stock-based Compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Schedule of Stock-Based Compensation Expense	Total stock-based compensation expense recognized in the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2021 and 2020 was as follows (in thousands): Three Months Ended 2021 2020 Research and development $ 1,215 $ 1,181 General and administrative 1,610 1,437 Total stock-based compensation expense $ 2,825 $ 2,618
Schedule of Restricted Stock Activity	The Company has also granted RSUs to its employees under the 2017 Plan. The following table summarizes RSU activity for the three months ended March 31, 2021 (in thousands, except per share amounts): RSUs Weighted-Average Grant Date Fair Value per Share Unvested as of December 31, 2020 588 $ 5.82 Issued 472 $ 11.90 Vested (223) $ 5.64 Cancelled (15) $ 8.13 Unvested as of March 31, 2021 822 $ 9.32
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The fair value of stock options granted during the three months ended March 31, 2021 and 2020 was calculated on the date of grant using the following weighted-average assumptions: Three Months Ended 2021 2020 Risk-free interest rate 0.6 % 1.4 % Expected dividend yield — % — % Expected term (in years) 6.1 6.1 Expected volatility 81.6 % 71.4 %
Schedule of Stock Options, Activity	The following table summarizes stock option activity during the three months ended March 31, 2021 (in thousands, except per share amounts): Options Weighted-Average Exercise Price Per Share Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value Outstanding at December 31, 2020 6,586 $ 8.30 6.5 $ 13,110 Granted 1,027 $ 11.94 Exercised (342) $ 2.98 Cancelled (97) $ 11.61 Outstanding at March 31, 2021 7,174 $ 9.04 6.9 $ 25,472 Exercisable at March 31, 2021 4,474 $ 8.65 5.7 $ 18,973

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Antidilutive Securities Excluded from Computation of Net Loss per Share	For purposes of the diluted net loss per share calculation, outstanding stock options and unvested RSUs are considered to be potentially dilutive securities, however the following weighted-average amounts were excluded from the calculation of diluted net loss per share because their effect would be anti-dilutive (in thousands): Three Months Ended 2021 2020 Outstanding stock options 6,953 6,339 Unvested RSUs 680 624 Total 7,633 6,963

Nature of Business (Details)

Nature of Business (Details) - USD ($) $ in Millions	May 06, 2021	Mar. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cash, cash equivalents, and marketable securities		$ 271.3
Scenario, Forecast
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Duration of funding requirement	12 months

License and Collaboration Rev_3

License and Collaboration Revenue - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 16, 2020	Aug. 31, 2020	Oct. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Research and Development Arrangement, Contract to Perform for Others [Line Items]
License and collaboration revenue—related party				$ 1,539	$ 0
Gilead Transaction Agreements
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Non-refundable upfront payment received for research agreement			$ 85,000
Aggregate revenue for clinical and regulatory milestones		$ 510,000
Aggregate revenue for sales milestones		$ 175,000
Transaction price	$ 64,300
Gilead Transaction Agreements | JTX-1811 License
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Transaction price	60,800
Gilead Transaction Agreements | Research and Transition Services
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Transaction price	3,500
License and collaboration revenue—related party				$ 1,500
Gilead Stock Purchase Agreement
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Proceeds from stock offering, net			$ 35,000
Aggregate fair value of shares issued on transaction	$ 55,700
Closing price per share (in USD per share)	$ 10.06
Sale of stock, number of shares issued (in shares)	5,539,727
Sale of stock, price per share (USD per share)	$ 6.32
Consecutive trading days to determine weighted average share price	30 days
Sale amount over weighted average share price, percent	30.00%
Discount on shares issued on transaction	$ 20,700

License and Collaboration Rev_4

License and Collaboration Revenue - Schedule of Contract Liabilities (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Revenue, Performance Obligation, Contract Liability [Roll Forward]
Beginning balance	$ 1,931
Additions	0
Reductions	(1,539)
Ending balance	392
Gilead Transaction Agreements | Gilead Sciences, Inc.
Revenue, Performance Obligation, Contract Liability [Roll Forward]
Beginning balance	1,931
Additions	0
Reductions	(1,539)
Ending balance	$ 392

Fair Value Measurements - Asset

Fair Value Measurements - Assets Measured at Fair Value (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Measurements, Recurring
Investments:
Totals	$ 271,286,000	$ 213,188,000
Liabilities measured at fair value	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Investments:
Totals	191,760,000	147,492,000
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Investments:
Totals	79,526,000	65,696,000
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Investments:
Totals	0	0
Corporate debt securities | Fair Value, Measurements, Recurring
Investments:
Available-for-sale debt securities, fair value	79,526,000	63,691,000
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	79,526,000	63,691,000
Corporate debt securities | 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		2,005,000
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		0
Government agency securities | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Investments:
Available-for-sale debt securities, fair value		2,005,000
Government agency securities | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Investments:
Available-for-sale debt securities, fair value		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	191,760,000	147,492,000
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	191,760,000	147,492,000
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	191,760,000	147,492,000
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

Investments - Available-for-sal

Investments - Available-for-sale Securities by Security Type (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Unrealized Gains	$ 1	$ 13
Unrealized Losses	(26)	(30)
Cash equivalents, short-term and long-term investments, carrying value	271,311	213,205
Cash equivalents, short-term and long-term investments, fair vale disclosure	271,286	213,188
Short-term Investments
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Unrealized Gains	1	13
Unrealized Losses	(11)	(13)
Total cash equivalents and short-term investments, carrying value	257,488	206,478
Total cash equivalents and short-term investments, fair value	257,478	206,478
Short-term Investments | Corporate debt securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Available-for-sale debt securities, amortized cost basis	65,728	56,985
Unrealized Gains	1	9
Unrealized Losses	(11)	(13)
Available-for-sale debt securities, fair value	65,718	56,981
Short-term Investments | Government agency securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Available-for-sale debt securities, amortized cost basis		2,001
Unrealized Gains		4
Unrealized Losses		0
Available-for-sale debt securities, fair value		2,005
Long-term Investments
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Available-for-sale debt securities, amortized cost basis	13,823	6,727
Unrealized Gains	0	0
Unrealized Losses	(15)	(17)
Available-for-sale debt securities, fair value	13,808	6,710
Long-term Investments | Corporate debt securities
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Available-for-sale debt securities, amortized cost basis	13,823	6,727
Unrealized Gains	0	0
Unrealized Losses	(15)	(17)
Available-for-sale debt securities, fair value	13,808	6,710
Money market funds, included in cash equivalents
Debt Securities, Available-for-sale [Line Items]
Cash equivalents at carrying value	191,760	147,492
Cash equivalents at fair value	191,760	147,492
Debt Securities, Available-for-sale, Fair Value to Amortized Cost [Abstract]
Unrealized Gains	0	0
Unrealized Losses	$ 0	$ 0

Investments - Narrative (Detail

Investments - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
aggregate fair value of securities in an unrealized loss position for less than twelve months	$ 37,300,000		$ 28,300,000
Realized gains or losses on available-for-sale securities	$ 0	$ 0

Restricted Cash - Narrative (De

Restricted Cash - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
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	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 196,273	$ 147,493	$ 74,991	$ 53,241
Restricted cash	1,270	1,270	1,270	1,270
Cash, cash equivalents and restricted cash	$ 197,543	$ 148,763	$ 76,261	$ 54,511

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Employee compensation and benefits	$ 2,955	$ 6,825
External research and professional services	4,219	4,855
Lab consumables and other	296	364
Total accrued expenses	$ 7,470	$ 12,044

Common Stock and Preferred St_3

Common Stock and Preferred Stock - Narrative (Details) $ / shares in Units, $ in Millions	Dec. 17, 2019USD ($)	Mar. 31, 2021USD ($)vote$ / sharesshares	Dec. 31, 2020shares
Subsidiary, Sale of Stock [Line Items]
Common stock shares authorized (in shares)		160,000,000	160,000,000
Common stock, votes per share | vote		1
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
ATM Offering
Subsidiary, Sale of Stock [Line Items]
Aggregate offering price shares | $	$ 50
Sales commission percentage	3.00%
Sale of stock, number of shares issued (in shares)		3,156,200
Sale of stock, price per share (USD per share) | $ / shares		$ 9.87
Proceeds from stock offering, net | $		$ 30.2
Follow-on Public Offering
Subsidiary, Sale of Stock [Line Items]
Sale of stock, number of shares issued (in shares)		5,750,000
Sale of stock, price per share (USD per share) | $ / shares		$ 11.25
Proceeds from stock offering, net | $		$ 60.6

Common Stock and Preferred St_4

Common Stock and Preferred Stock - Shares Reserved for Future Issuance (Details) - shares	Mar. 31, 2021	Dec. 31, 2020	Jan. 31, 2017
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	9,559,000	8,458,000	1,753,758
Restricted Stock Units (RSUs)
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	822,000	588,000
Outstanding Stock Options
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	7,174,000	6,586,000
Future Issuances Under 2017 Stock Option and Incentive Plan
Conversion of Stock [Line Items]
Common stock reserved for potential conversion (in shares)	1,563,000	1,284,000

Stock-based Compensation - Narr

Stock-based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 01, 2021	Jan. 01, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Jan. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock eligible to be purchased (in shares)			9,559,000		8,458,000	1,753,758
Weighted average fair value of options granted (in dollars per share)			$ 8.24	$ 4.23
Intrinsic value of stock options exercised			$ 2.8	$ 0.1
Unrecognized stock-based compensation expense, options			$ 15.4
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)			822,000		588,000
Aggregate fair value of awards vested in period			$ 1.5	$ 0.8
Vested (in shares)			223,000
Unrecognized stock-based compensation expense, RSUs			$ 6.9
Remaining weighted average vesting period			2 years 2 months 12 days
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted average vesting period			2 years 7 months 6 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)			1,563,376
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)	1,669,162	1,349,526
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
Percent of outstanding shares able to be added each year						1.00%
Number of additional shares authorized (in shares)	417,291	337,381
Shares of common stock to determine number of additional shares (in shares)						603,000

Stock-based Compensation - Stoc

Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,825	$ 2,618
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,215	1,181
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,610	$ 1,437

Stock-based Compensation - RSU

Stock-based Compensation - RSU Activity (Details) - Restricted Stock Units (RSUs) shares in Thousands	3 Months Ended
	Mar. 31, 2021$ / sharesshares
RSUs
Beginning unvested balance (in shares) | shares	588
Issued (in shares) | shares	472
Vested (in shares) | shares	(223)
Cancelled (in shares) | shares	(15)
Ending unvested balance (in shares) | shares	822
Weighted-Average Grant Date Fair Value per Share
Beginning unvested balance (in dollars per share) | $ / shares	$ 5.82
Issued (in dollars per share) | $ / shares	11.90
Vested (in dollars per share) | $ / shares	5.64
Cancelled (in dollars per share) | $ / shares	8.13
Ending unvested balance (in dollars per share) | $ / shares	$ 9.32

Stock-based Compensation - Weig

Stock-based Compensation - Weighted Average Assumptions (Details) - Employee Stock Option	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	0.60%	1.40%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days
Expected volatility	81.60%	71.40%

Stock-based Compensation - St_2

Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Options
Beginning outstanding balance (in shares)	6,586
Granted (in shares)	1,027
Exercised (in shares)	(342)
Cancelled (in shares)	(97)
Ending outstanding balance (in shares)	7,174	6,586
Exercisable (in shares)	4,474
Weighted-Average Exercise Price Per Share
Beginning outstanding balance (in dollars per share)	$ 8.30
Granted (in dollars per share)	11.94
Exercised (in dollars per share)	2.98
Cancelled or forfeited (in dollars per share)	11.61
Ending outstanding balance (in dollars per share)	9.04	$ 8.30
Exercisable (in dollars per share)	$ 8.65
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Remaining contractual life, outstanding	6 years 10 months 24 days	6 years 6 months
Remaining contractual life, exercisable	5 years 8 months 12 days
Aggregate intrinsic value, outstanding	$ 25,472	$ 13,110
Aggregate intrinsic value, exercisable	$ 18,973

Related-party Transactions (Det

Related-party Transactions (Details) - Gilead Transaction Agreements - USD ($) $ in Millions	1 Months Ended
	Oct. 31, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Non-refundable upfront payment received for research agreement	$ 85
Gilead Transaction Agreements | Gilead Sciences, Inc.
Related Party Transaction [Line Items]
Reimbursable expenses due from Celgene		$ 0.1

Net Loss per Share Schedule of

Net Loss per Share Schedule of Antidilutive Securities Excluded from Computation of Net Loss per Share (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of net loss per share (in shares)	7,633	6,963
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)	6,953	6,339
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)	680	624