0000950170-24-026866 | 10-K | XBRL Viewer

Print Document View Excel Document

Consolidated Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Total property and equipment	$ 9,078	$ 5,578
Accumulated depreciation and amortization	(4,382)	(3,457)
Property & equipment, net	4,696	2,121
Scientific Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	3,434	3,008
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	1,467	1,332
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	$ 4,177	$ 1,238

Consolidated Statements of Stockholders' Equity - USD ($)	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Retained Earnings (Accumulated deficit)
Beginning balance at Dec. 31, 2020	$ 323,197,000	$ 35,000	$ 396,443,000	$ 617,000	$ (73,898,000)
Beginning balance (in shares) at Dec. 31, 2020		35,044,758
Stock-based compensation	13,794,000		13,794,000
Common stock issued upon exercises of options	2,943,000		2,943,000
Common stock issued upon exercises of options (in shares)		421,243
Currency translation adjustment	(1,635,000)			(1,635,000)
Net Income (Loss)	214,521,000				214,521,000
Ending balance at Dec. 31, 2021	552,820,000	$ 35,000	413,180,000	(1,018,000)	140,623,000
Ending balance (in shares) at Dec. 31, 2021		35,466,001
Stock-based compensation	21,561,000		21,561,000
Common stock issued upon exercises of options	925,000	$ 1,000	924,000
Common stock issued upon exercises of options (in shares)		145,218
Currency translation adjustment	(8,478,000)			(8,478,000)
Unrealized loss on available-for-sale securities	(148,000)			(148,000)
Net Income (Loss)	96,652,000				96,652,000
Ending balance at Dec. 31, 2022	663,332,000	$ 36,000	435,665,000	(9,644,000)	237,275,000
Ending balance (in shares) at Dec. 31, 2022		35,611,219
Stock-based compensation	27,021,000		27,021,000
Common stock issued upon exercises of options, ESPP purchases, and restricted stock unit releases	$ 1,113,000		1,113,000
Common stock issued upon exercises of options, ESPP purchases, and restricted stock unit releases (in shares)		226,861
Common stock issued upon exercises of options (in shares)	184,937
Currency translation adjustment	$ (3,631,000)			(3,631,000)
Unrealized loss on available-for-sale securities	35,000			35,000
Net Income (Loss)	(112,642,000)				(112,642,000)
Ending balance at Dec. 31, 2023	$ 575,228,000	$ 36,000	$ 463,799,000	$ (13,240,000)	$ 124,633,000
Ending balance (in shares) at Dec. 31, 2023		35,838,080

Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs)

12 Months Ended

Dec. 31, 2023

Research and Development Arrangement with Federal Government [Abstract]

Government grant funding and potential repayment commitments under recoverable cash advance grants (RCAs)

Note 6. Government grant funding and potential repayment commitments under recoverable cash advance grants (RCAs)

The Company has been awarded grants from a federal region of Belgium (the Walloon Region), and the European Union (collectively, the granting agencies) to fund research and development activities. The grants reimburse a percentage (55-100%) of actual qualifying expenditures. The Company periodically submits proof of qualifying expenditures to the granting agencies for approval and reimbursement. To date, the Company received funding under several grants which included no obligation to repay and two grants that include potential obligations to repay (RCAs).

As the granting agencies do not meet the definition of a customer under Topic 606, qualifying grants receipts are recognized as grant income within other income, net in the consolidated statements of operations and comprehensive income (loss). Grant income recognized under all of the grants for research and development activities totaled $2.7 million, $2.1 million and $10.2 million for the years ended December 31, 2023, 2022 and 2021, respectively.

Grants which do not include an obligation to repay

As of December 31, 2023, the total amount that the granting agencies have agreed to fund in the future if the Company incurs qualifying research and development expenses under these grants is $7.6 million.

Grants which include a potential obligation to repay—RCAs

On July 20, 2017, the Company entered into an arrangement whereby the Walloon Region will provide the Company with up to $20.9 million for a research and development program to perform clinical validation of an A2A receptor antagonist drug candidate for immune-oncology (RCA-1). As of December 31, 2023, the Company has received $20.9 million under this grant.

On December 3, 2019, the Company entered into another recoverable cash advance grant with the Walloon Region (RCA-2) for up to $4.8 million to be received to fund a research and development program conducted to develop a TIGIT blocking antibody with anti-tumor properties. As of December 31, 2023, the Company has received $4.8 million under this grant.

Under the terms of both agreements, the Company must decide within 6 months after the end of the research period whether it will further pursue commercial development or out licensing of the drug candidate. The research period for RCA-1 ended in December 2021. The Company decided it would pursue commercialization or out licensing of RCA-1. The Company negotiated an extension on the research period for RCA-2 with the Walloon Region. The original research period for RCA-2 ended February 2021, and was extended to March 2022. The Company must repay 30% of the amount received under the grant by annual installments from 2023 to 2042 (the fixed annual repayments) unless the Company decides not to pursue commercial development or out licensing of the drug candidate, applies for a waiver from the Walloon Region justifying its decision based upon the failure of the program, and returns the intellectual property to the Walloon Region. Because of the requirement to repay 30% of the amounts received under the grant, the Company records the present value of such amounts as grants repayable on the consolidated balance sheets.

In addition, in the event that the Company receives revenue from products or services related to the results of the research, it has to pay to the Walloon Region a 0.33% royalty on revenue resulting from RCA-1 and a 0.15% royalty on revenue resulting from RCA-2 (increased from 0.12% effective December 2021). The maximum

amount payable to the Walloon Region under each grant, including the fixed annual repayments, the royalty on revenue, and the interest thereon, is twice the amount of funding received.

The Company assessed whether there is an obligation to make a royalty payment based on the probability of successful completion of the research and development and future sales and commercial success of the drug candidate. For the RCA-1, no grant repayable related to royalties was recorded as of December 31, 2023 or December 31, 2022. For the RCA-2, the Company recorded a royalty accrual of $0.8 million as of December 31, 2023, due to the upfront payment from the GSK Collaboration Agreement. The royalty accrual is included in the accrued expenses and other current liabilities in the consolidated balance sheet. The Company also recorded a royalty accrual of $0.8 million as of December 31, 2022.

The Company recorded grant income in the consolidated statement of operations and comprehensive income (loss) for the years ended December 31, 2023, 2022 and 2021 for amounts of grants received from the Walloon Region in the period during which the related qualifying expenses were incurred, net of any grants repayable recorded in the consolidated balance sheets.

The Company recorded receivables on the consolidated balance sheets related to amounts the Walloon Region owes the Company based on qualifying expenses incurred by the Company. The Company recorded deferred income in the consolidated balance sheets for amounts received from the Walloon Region in advance of incurring qualifying expenses.

The following table reflects activity for grant programs for the years ended December 31, 2023, 2022 and 2021 and end of year balances as of December 31, 2023, 2022 and 2021:


	RCA -1						RCA-2						Other Grants						Total
(In thousands)	2023		2022		2021		2023		2022		2021		2023		2022		2021		2023		2022		2021
Cash received	$	—	$	2,244	$	1,990	$	—	$	1,520		585	$	4,419	$	2,497	$	592	$	4,419	$	6,261	$	3,167
Grant income recognized		—		364		4,113		—		478		1,286		2,687		1,249		4,782		2,687		2,091	$	10,181
Grants receivable		—		5		1,832		—		—		1,097		—		996		1,093		—		1,001	$	4,022
Grants repayable		5,496		5,665		5,278		1,317		1,312		886		—		—		—		6,813		6,977	$	6,164

Of the total repayable balance, $0.2 million is the current portion and $6.6 million is the non-current portion. The current portion is recorded to accrued expenses and other liabilities.

Nature of Business and Basis of Presentation - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Net income (loss)	$ (112,642)	$ 96,652	$ 214,521
Retained earnings	$ 124,633	$ 237,275

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 28
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-28

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482765/220-10-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-8

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-9

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 13: http://www.xbrl.org/2003/role/exampleRef
-Topic 946
-SubTopic 830
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480167/946-830-55-10

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483581/946-220-45-7

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(18))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(9))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.6-09(1)(d))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-3

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 20: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(ii))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iv))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1A

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(i))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(A))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(B))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iv))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(5))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480097/470-10-S99-1B

Reference 29: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 30: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 31: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 60B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-60B

Reference 32: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 33: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 34: http://www.xbrl.org/2003/role/disclosureRef
-Topic 205
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483499/205-20-50-7

Reference 35: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-28

Reference 36: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1A

Reference 37: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482790/220-10-45-1B

Reference 38: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(20))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 39: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

+ Details

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

Commitments and Contingencies - Schedule Of Lease Terms And Discount Rate (Details)	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Weighted-average remaining lease term (years)	4 years 7 months 6 days
Weighted-average discount rate	4.75%

Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs) - Schedule of Activity for Grant Programs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Research And Development Arrangement Contract To Perform For Others [Line Items]
Cash received	$ 4,419	$ 6,261	$ 3,167
Grant income recognized	2,687	2,091	10,181
Grants receivable	0	1,001	4,022
Grant repayable	6,813	6,977	6,164
RCA- 1
Research And Development Arrangement Contract To Perform For Others [Line Items]
Cash received		2,244	1,990
Grant income recognized	0	364	4,113
Grants receivable		5	1,832
Grant repayable	5,496	5,665	5,278
RCA- 2
Research And Development Arrangement Contract To Perform For Others [Line Items]
Cash received		1,520	585
Grant income recognized		478	1,286
Grants receivable			1,097
Grant repayable	$ 1,317	1,312	886
Other Grants
Research And Development Arrangement Contract To Perform For Others [Line Items]
Cash received		2,497	592
Grant income recognized		1,249	4,782
Grants receivable		$ 996	$ 1,093

Stock-Based Compensation - Schedule of Company's restricted stock unit activity (Details) - Restricted Stock Units	12 Months Ended
	Dec. 31, 2023 $ / shares shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unvested as of December 31, 2022, Shares \| shares	10,000
Issued, Shares \| shares	512,000
Vested, Shares \| shares	(4,375)
Cancelled, Shares \| shares	0
Unvested as of December 31, 2023, Shares \| shares	517,625
Unvested as of December 31, 2022, Weighted average grant date fair value \| $ / shares	$ 35.86
Issued, Weighted average grant date fair value \| $ / shares	11.55
Vested, Weighted average grant date fair value \| $ / shares	35.86
Cancelled, Weighted average grant date fair value \| $ / shares	0
Unvested as of December 31, 2023, Weighted average grant date fair value \| $ / shares	$ 11.81

Income Taxes - Schedule of Significant Components of the Company Deferred Tax Assets and Lliabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets :
Net operating loss carryforward	$ 21,796	$ 13,359
Foreign research and development expenses	17,980	12,355
Section 174 capitalized research and development expenses	27,913	14,856
Stock-based compensation	5,002	3,860
Operating lease liabilities	1,539	1,201
Accrued vacation and bonus	846	552
Other	1,164	932
Total deferred tax assets	76,240	47,115
Valuation allowance	(74,398)	(45,421)
Deferred tax assets, net of valuation allowance	1,842	1,694
Deferred tax liabilities:
Operating lease right of use assets	(1,534)	(1,196)
Prepaid expenses	(243)	(394)
Depreciation and amortization	(65)	(104)
Total deferred tax liabilities	(1,842)	(1,694)
Deferred tax assets and liabilities, net of valuation allowance	$ 0	$ 0

Investment Securities and Fair Value Measurements - Summary of Amortized Cost, Fair Value, and Unrealized Losses by Type of Security (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 381,243	$ 446,735
Unrealized Gains	360	106
Unrealized Losses	(325)	(257)
Total available-for-sale securities, Estimated Fair Value	381,278	446,584
U.S. Government Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	193,231	254,881
Unrealized Gains	90	87
Unrealized Losses	(245)	(211)
Total available-for-sale securities, Estimated Fair Value	193,076	254,757
U.S. Treasury Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	103,476	186,496
Unrealized Gains	156	19
Unrealized Losses	(35)	(37)
Total available-for-sale securities, Estimated Fair Value	103,597	186,478
Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	84,536	5,358
Unrealized Gains	114	0
Unrealized Losses	(45)	(9)
Total available-for-sale securities, Estimated Fair Value	$ 84,605	$ 5,349

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Leases [Abstract]
2024	$ 1,500
2025	1,468
2026	1,435
2027	941
2028	764
Thereafter	590
Total lease payments	6,698
Less: Interest	(640)
Total lease liability	6,058
Lease liabilities - current	1,251	$ 836
Lease liabilities, net of current portion	$ 4,807	$ 3,837

Commitments and Contingencies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) m² ft²	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	May 31, 2023 m²	Nov. 30, 2021 USD ($)
Other Commitments [Line Items]
Land Subject to Ground Leases \| m²	1,577
Operating leases, rent expense	$ 1,200,000	$ 900,000	$ 700,000
Extension of office lease	In January 2021, the Company entered into an amendment to extend the lease, effective February 2021 with a termination date of January 2030, and increase the office and laboratory space
Gosselies, Belgium
Other Commitments [Line Items]
Operating lease, Hand serving to secure lease obligation	$ 131,000	99,000
Watertown Massachusetts [Member]
Other Commitments [Line Items]
Land Subject to Ground Leases \| ft²	9,068
Operating lease, Letter of credit to secure lease obligation					$ 142,000
Office and Laboratory Space \| Gosselies, Belgium
Other Commitments [Line Items]
Lease Commencement Date	May 31, 2016
Lease expiration date	Dec. 31, 2021
Office and Laboratory Space \| Amendment To Extend Lease [Member] \| Gosselies, Belgium
Other Commitments [Line Items]
Increase land subject to leases \| m²	201			453
Area of lease land \| m²				2,684
Office and Laboratory Space \| Agreement to Extend Lease [Member] \| Gosselies, Belgium
Other Commitments [Line Items]
Lease Commencement Date	Feb. 28, 2021
Increase land subject to leases \| m²	453
Lease expiration date	Jan. 31, 2030
Laboratory Space \| Gosselies, Belgium
Other Commitments [Line Items]
Land Subject to Ground Leases \| m²	859
Office Building \| Cambridge, Massachusetts
Other Commitments [Line Items]
Lease expiration date	Feb. 28, 2027
Office Building \| Watertown Massachusetts [Member]
Other Commitments [Line Items]
Lease Commencement Date	Nov. 30, 2021
Wu Xi Agreement
Other Commitments [Line Items]
Minimum commitments	$ 0	0
Payments for Royalties	0	0
Contract Termination
Other Commitments [Line Items]
Restructuring charges	$ 0	$ 0
Minimum
Other Commitments [Line Items]
Contractual Agreement Cancelation Notice period	30 days
Average car lease duration	48 days
Maximum
Other Commitments [Line Items]
Contractual Agreement Cancelation Notice period	60 days
Average car lease duration	60 months

Income Taxes - Schedule of Reconciliation of Income Tax Expense (Benefit) Computed at the Statutory Federal Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
U.S. statutory federal income tax rate	21.00%	21.00%	21.00%
State income taxes	4.90%	(2.20%)	(0.50%)
Foreign tax differential	1.20%	5.20%	4.70%
Non-deductible/non-taxable permanent differences	(0.10%)	0.10%	0.10%
Innovation income deduction tax exemption	0.00%	(33.40%)
Net GILTI Inclusion Income	(0.10%)	18.90%	15.20%
Unrecognized tax benefits	(1.60%)	14.90%
Other	(1.20%)	(3.00%)	(1.10%)
Change in valuation allowance	(25.60%)	13.50%	(1.40%)
Effective income tax rate	(3.30%)	35.00%	16.40%

Stockholders’ equity

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Stockholders' Equity

Note 7. Stockholders’ equity

The Company's restated Certificate of Incorporation authorizes the Company to issue up to 160,000,000 shares, of which (i) 150,000,000 shares are designated as common stock, par value $0.001 per share, and (ii) 10,000,000 shares are designated as undesignated preferred stock, par value $0.001 per share. Each share of common stock entitles the holders to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are not entitled to receive dividends, unless declared by the board of directors.

In May 2023 the Company entered into a Sales Agreement with Cowen and Company LLC to offer and sell shares of its common stock having an aggregate offering price of up to $125,000,000, from time to time, through an at-the-market offering program. To date the Company has not made any sales pursuant to the at-the-market offering program.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-16

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs) - Additional Information (Details) - USD ($) $ in Thousands			12 Months Ended
	Dec. 03, 2019	Jul. 20, 2017	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant income recognized for research and development activities			$ 7,600
Grant repayable			6,813	$ 6,977	$ 6,164
RCA- 1
Research And Development Arrangement Contract To Perform For Others [Line Items]
Recoverable cash advance		$ 20,900
Grants received			$ 20,900
Percentage of royalty on revenue			0.33%
Grant repayable			$ 5,496	5,665	5,278
RCA- 2
Research And Development Arrangement Contract To Perform For Others [Line Items]
Royalty accruals			800	800
Recoverable cash advance	$ 4,800
Grants received			$ 4,800
Percentage of royalty on revenue			0.15%
Grant repayable			$ 1,317	1,312	886
RCA-1 and RCA-2
Research And Development Arrangement Contract To Perform For Others [Line Items]
Percentage of repayment amount received under grant			30.00%
Research And Development And Future Sales
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant repayable			$ 0	0
Research and Development Expenses
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant income recognized for research and development activities			2,700	$ 2,100	$ 10,200
Current Liability
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant repayable			200
Non-Current liability
Research And Development Arrangement Contract To Perform For Others [Line Items]
Grant repayable			$ 6,600
Minimum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Percentage of grant reimburse of actual qualifying expenditures			55.00%
Minimum \| RCA-1 and RCA-2
Research And Development Arrangement Contract To Perform For Others [Line Items]
Term of repayment amount received under grant			2023
Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Percentage of grant reimburse of actual qualifying expenditures			100.00%
Maximum \| RCA-1 and RCA-2
Research And Development Arrangement Contract To Perform For Others [Line Items]
Term of repayment amount received under grant			2042

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of presentation

The consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP).

Principles of consolidation

The consolidated financial statements include the Company’s accounts and those of its wholly owned subsidiaries. All intercompany accounts, transactions and balances have been eliminated.

Use of estimates

The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenue, and expenses, as well as the related disclosures of contingent assets and liabilities. The Company bases its estimates and assumptions on historical experiences, when available, and on various factors that it believes to be reasonable under the circumstances. The Company evaluates its estimates and assumptions on an ongoing basis. Actual results could differ materially from these estimates.

Cash, cash equivalents and restricted cash

Cash and cash equivalents consist of standard checking accounts, money market accounts, and a sweep account that consists of money market funds with highly liquid investments with maturities of three months or less. Restricted cash represents collateral provided for letters of credit issued as security deposits in connection with the Company’s leases of its corporate facilities.

Short-term and long-term investments

Short-term investments consist of fixed income securities with maturities more than three months but less than twelve months from the date of purchase. Long-term investments consist of fixed income securities with maturities greater than twelve months from the date of purchase. The Company intends to dispose of securities within its portfolio if the need for additional liquidity arises. As such, the Company classifies its securities as available-for-sale. The Company recognizes the impact of investment transactions as of a security's trade date. A payable is recorded to payable for investments in the consolidated balance sheets if an executed trade purchase has not settled prior to the period end date.

Foreign currency, currency translation and comprehensive Income

Foreign currency, currency translation and comprehensive income

The reporting currency of the consolidated financial statements is the U.S. dollar (USD). The functional currency for iTeos Belgium is the euro and the functional currency for iTeos Inc., iTeos SC, and iTeos LLC is the USD.

Income items and expenses are translated at the average exchange rate in effect during the period. Unrealized translation gains and losses are recorded as a cumulative translation adjustment, which is included in the Consolidated Statements of Stockholders’ Equity as a component of accumulated other comprehensive income. Adjustments that arise from exchange rate changes on transactions denominated in a currency other than the local currency are included in Other income, net in the Consolidated Statements of Operations and Comprehensive Income as settled.

Comprehensive income is defined as a change in equity of a business enterprise during a period, resulting from transactions from non-owner sources. The Company had unrealized gains from foreign currency translation of iTeos Belgium during the years ended December 31, 2023, 2022 and 2021, which meets the criteria as other comprehensive income and, therefore, the Company has reported comprehensive income and net income.

Fair Value Measurements

Fair value measurements

Fair value accounting is applied for all financial assets and liabilities. The carrying amount of the Company’s financial instruments, including grants receivable, R&D credits receivable—current, accounts payable, accrued expenses and other current liabilities approximate fair value due to the short-term duration of those instruments.

The carrying amounts of long-term R&D credits receivable and grants repayable approximate fair value due to low local market interest rates.

FASB ASC Topic 820, Fair Value Measurement and Disclosures (ASC 820), established a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are inputs that market participants would use in pricing the financial instrument based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the financial instrument and are developed based on the best information available in the circumstances.

The accounting standard describes a fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last unobservable, that may be used to measure fair value, which are the following:

•

Level 1—Quoted prices in active markets that are accessible at the market date for identical unrestricted assets or liabilities.

•

Level 2—Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs for which all significant inputs are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

•

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

To the extent that valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Financial instruments measured at fair value on a recurring basis include cash equivalents (money market funds) and fixed income securities. Fixed income securities include U.S. treasury securities, U.S. government agency backed securities, and investment grade corporate securities.

The fair value of cash equivalents and U.S. treasury securities was determined based on Level 1 inputs as described in Note 3. The fair value of U.S. government agency backed securities and corporate securities was determined based on Level 2 inputs as described in Note 3. An entity may elect to measure many financial instruments and certain other items at fair value at specified election dates. The Company did not elect to measure any additional financial instruments or other items at fair value.

There have been no changes to the valuation methods utilized by the Company during the years ended December 31, 2023, 2022 or 2021. The Company evaluates transfers between levels at the end of each reporting period. There were no transfers of financial instruments between levels during the years ended December 31, 2023, 2022 or 2021.

Concentration of credit risk

As of December 31, 2023 and 2022, the Company’s cash and cash equivalents consisted primarily of cash balances held in U.S. dollars in money market funds and money market accounts and euro in accounts with European banks in excess of publicly insured limits. The Company does not believe it is subject to unusual credit risk associated with commercial banking relationships.

As of December 31, 2023, the Company's fixed income securities consisted of investment grade U.S. treasury, U.S. government agency, and corporate securities. There are no securities in the Company's portfolio with a credit rating below "A-1". 69% of the Company's fixed income holdings as of December 31, 2023 consisted of U.S. treasury and U.S. government agency securities. The Company does not believe it is subject to unusual credit risk associated with its investment portfolio.

Research And Development Tax Credits

Research and development tax credits

iTeos Belgium is considered a biotech company in Belgium and therefore qualifies for a cash-based tax credit on research and development (R&D) expenses. The R&D tax credit is calculated based on a percentage of eligible R&D expenses defined by the Belgian government for each fiscal year (20.5% for 2023, 13.5% for 2022 and 2021) and then applying the effective tax rate to that result. Under current tax laws, the R&D tax credits are refundable if the Company is unable to use the credits to offset income taxes for the five subsequent tax years. The Company records a receivable and other income as the eligible R&D expenses are incurred, as it is reasonably assured that the R&D tax credit will be received, based upon its history of filing for the tax credits. R&D tax credits receivable where cash is expected to be received by the Company more than one year after the balance sheet date are classified as noncurrent in the consolidated balance sheets.

Property and equipment

Property and equipment, including leasehold improvements, are stated at cost and depreciated when placed into service using the straight-line method over the estimated useful lives as follows:


Asset		Estimated Useful Life
Computer equipment and software		3 years
Furniture, fixtures and other		5 years
Scientific equipment		5 – 6 years
Leasehold improvements		Shorter of useful life or term of lease

Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheets and the resulting gain or loss is reflected in the consolidated statements of operations and comprehensive income.

Impairment of long-lived assets

The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. An impairment charge would be recorded when estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, is assessed using discounted cash flows or other appropriate measures of fair value. As there were no indicators of impairment, the Company did not recognize any impairment charges for the years ended December 31, 2023, 2022 or 2021.

Revenue recognition

The Company analyzes its collaboration arrangements to assess whether they are within the scope of Accounting Standards Codification ASC Topic 808, Collaborative Arrangements (ASC 808). If the Company concludes that some or all aspects of the arrangement are within the scope of ASC 808 and do not represent a transaction with a customer, the Company recognizes its allocation of the shared costs incurred with respect to the jointly conducted activities pursuant to ASC 730, Research and Development. As such, the Company will expense costs as incurred, including any reimbursements made, and recognize reimbursements received as a reduction of research and development expense. If the Company concludes that some or all aspects of the arrangement represent a transaction with a customer, the Company accounts for those aspects of the arrangement within the scope of ASC 606, Revenue from Contracts with Customers (ASC 606).

At inception, the Company determines whether contracts are within the scope of ASC 606 or other topics. For contracts that are determined to be within the scope of ASC 606, revenue is recognized when a customer obtains control of promised goods or services. The amount of revenue recognized reflects the consideration to which the Company expects to be entitled to receive in exchange for these goods and services. To achieve this core principle, the Company applies the following five steps (i) identify the contract with the customer; (ii) identify the 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 performance obligation is satisfied. The Company only applies the five-step model to contracts when it determines that collection of substantially all consideration for goods and services that are transferred is probable based on the customer’s intent and ability to pay the promised consideration.

Performance obligations promised in a contract are identified based on the goods and services that will be transferred to the customer that are both capable of being distinct and are distinct in the context of the contract. To the extent a contract includes multiple promised goods and services, the Company applies judgment to determine whether promised goods and services are both capable of being distinct and distinct in the context of the contract. If these criteria are not met, the promised goods and services are accounted for as a combined performance obligation.

The transaction price is determined based on the consideration to which the Company will be entitled in exchange for transferring goods and services to the customer. To the extent the transaction price includes variable consideration, the Company estimates the amount of variable consideration that should be included in the transaction price utilizing either the expected value method or the most likely amount method, depending on the nature of the variable consideration. Variable consideration is included in the transaction price if, in management’s judgment, it is probable that a significant future reversal of cumulative revenue under the contract will not occur. Any estimates, including the effect of the constraint on variable consideration, are evaluated at each reporting period for any changes. Determining the transaction price requires significant judgment.

For arrangements that include sales-based royalties, including milestone payments based on levels of sales, if the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its agreements.

If the contract contains a single performance obligation, the entire transaction price is allocated to the single performance obligation. Contracts that contain multiple performance obligations require an allocation of the transaction price to each performance obligation on a relative standalone selling price basis unless the transaction price is variable and meets the criteria to be allocated entirely to a performance obligation or to a distinct service that forms part of a single performance obligation.

The Company satisfies performance obligations either over time or at a point in time. Revenue is recognized over time if either (i) the customer simultaneously receives and consumes the benefits provided by the entity’s performance, (ii) the entity’s performance creates or enhances an asset that the customer controls as the asset is created or enhanced, or (iii) the entity’s performance does not create an asset with an alternative use to the entity and the entity has an enforceable right to payment for performance completed to date. If the entity does not satisfy a performance obligation over time, the related performance obligation is satisfied at a point in time by transferring the control of a promised good or service to a customer.

For licenses of intellectual property (IP), if the license to the Company’s IP is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from consideration allocated to the license when the license is transferred to the customer and the customer can use and benefit from the licenses. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition.

At the inception of each arrangement that includes development or regulatory milestone payments, the Company evaluates the probability of reaching the milestones and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur in the future, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company’s control or the licensee’s, such as regulatory approvals, are not considered probable of being achieved until those approvals are received and therefore revenue is constrained as management is unable to assert that a reversal of revenue would not be possible. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. To date, the Company has not recognized any milestone revenue resulting from any of its agreements.

Deferred revenue arises from amounts received in advance of the transfer of control and is recognized as revenue in future periods as performance obligations are satisfied. Deferred revenue expected to be recognized within the next twelve months is classified as a current liability. Upfront payment contract liabilities resulting from the Company’s license agreements do not represent a financing component as the payment is not financing the

transfer of goods or services, and the technology underlying the licenses granted reflects research and development expenses already incurred by the Company.

Contract costs

The Company recognizes as an asset the incremental costs of obtaining a contract with a customer if the costs are expected to be recovered. The Company has elected the practical expedient in ASC 340, Other Assets and Deferred Costs, wherein it recognizes the incremental costs of obtaining a contract as an expense when incurred if, at inception, the expected amortization period of the asset that the Company otherwise would have recognized is one year or less.

Collaborative Arrangements

The Company analyzes its collaboration arrangements to assess whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards dependent on the commercial success of such activities and are, therefore within the scope of ASC Topic 808, Collaborative Arrangements. This assessment is performed throughout the life of the arrangement and takes into consideration changes in the responsibilities of all parties to the arrangement. Collaboration agreements may include reimbursements from and payments to parties due to the activities performed by either party. Any reimbursement from parties involved in a collaboration agreement are recorded as a reduction to research and development expense. Payments made to parties involved in a collaboration agreement are recorded as research and development expense.

Research and Development Expenses

Research and development expenses

Research and development costs are expensed as incurred. Research and development expenses consist of personnel costs for the Company’s research and product development employees, as well as non-personnel costs such as facilities and overhead costs attributable to research and development, and professional fees payable to third parties for preclinical and clinical studies and research services, clinical trial costs, laboratory supplies and equipment maintenance, and other consulting costs.

The Company estimates preclinical and clinical study and research expenses based on the services performed, pursuant to contracts with research institutions that conduct and manage preclinical and clinical studies and research services on its behalf. The Company estimates these expenses based on discussions with internal management personnel and external service providers as to the progress or stage of completion of services and the contracted fees to be paid for such services. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. When third-party service providers’ billing terms do not coincide with the Company’s period-end, the Company is required to make estimates of its obligations to those third parties, including clinical trial and pharmaceutical development costs, contractual services costs and costs for supply of its drug candidates, incurred in a given accounting period and record accruals at the end of the period. The Company bases its estimates on its knowledge of the research and development programs, services performed for the period, history for related activities and the expected duration of the third-party service contract, where applicable. Payments associated with licensing agreements to acquire exclusive licenses to develop, use, manufacture and commercialize products that have not reached technological feasibility and do not have alternate commercial use are expensed as incurred. Payments made to third parties under these arrangements in advance of the performance of the related services by the third parties are recorded as prepaid expenses until the services are rendered.

Government grant funding and potential repayment commitments under recoverable cash advance grants (RCAs)

The Company has agreements with granting agencies whereby the Company receives funding under grants which partially or fully reimburse the Company for qualifying research and development expenditures. Certain grant agreements require the Company to repay the funding depending on whether the Company decides to pursue commercial development or out licensing of any drug candidate that is produced from the research program. The repayment provision includes a portion that is repayable in fixed annual installments (corresponding to 30% of the grant), which is effective unless the Company decides not to pursue commercial development or out licensing of the drug candidate. The repayment provision also includes a potential obligation to pay a royalty that is contingent upon achieving sales of a product developed through the program. The maximum amount repayable to the granting agency under each grant, including the fixed repayments, the royalty on revenue, and the interest thereon, is twice the amount of funding received.

Grant funding for research and development received under grant agreements where there is no obligation to repay is recognized as grant income in the period during which the related qualifying expenses are incurred, based on the applicable reimbursement percentage, provided that the grants are fully approved by the granting agencies and the conditions under which the grants were provided have been met.

Grant funding for research and development received under grant agreements where there is a repayment provision is recognized as grant income to the extent there is no potential obligation to repay this funding. The Company records the present value of the liability of the portion of funding relating to fixed repayment upon receipt in the consolidated balance sheets. The grant repayable is subsequently recorded at amortized cost.

The Company assesses whether there is an obligation to make a royalty payment based on the probability of successful completion of the research and development and future sales and commercial success of the drug candidate.

Grant funding that has been received by the Company in advance of incurring qualifying expenses is recorded as deferred income. Grant income recognized upon incurring qualifying expenses in advance of receipt of grant funding is recorded in the consolidated balance sheets as grants receivable.

Leases

At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present in the arrangement. Leases with a term greater than one year are recognized on the balance sheet as ROU assets and short-term and long-term lease liabilities, as applicable. The Company typically only includes an initial lease term deemed reasonable certain to occur. It also considers termination options and factors those into the determination of lease payments. Options to renew a lease are not included in the assessment unless there is reasonable certainty that the Company will renew.

Operating lease liabilities and their corresponding ROU assets are recorded based on the present value of lease payments over the expected remaining lease term. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rate, which reflects the fixed rate at which it could borrow on a collateralized basis the amount of the lease payments in the same currency, for a similar term, in a similar economic environment. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The Company is required to pay fees for operating expenses in addition to monthly base rent for certain operating leases (non-lease components). The Company will elect the practical expedient, which allows non-lease components to be combined with lease components on an asset-by-asset class basis. For real estate asset class, the Company has not elected the practical expedient. Variable non-lease components are not included within the lease right-of-use asset and lease liability on the consolidated balance sheet, and instead are reflected as expense in the period they are paid.

Stock-based compensation

The Company accounts for stock-based compensation arrangements with employees in accordance with ASC 718, Stock Compensation. Stock-based awards granted are in the form of stock options, Employee Stock Purchase Plan (ESPP) awards, and a limited amount of restricted stock units. ASC 718 requires the recognition of stock-based compensation expense, using a fair value-based method, for costs related to all stock awards granted. The Company’s determination of the fair value of stock options and ESPP awards with time-based vesting on the date of grant utilizes the Black-Scholes option-pricing model, and is impacted by the estimated fair value of its common stock as well as other variables including, but not limited to, the expected term that stock options will remain outstanding, the expected common stock price volatility over the term of the option, risk-free interest rates and expected dividends.

The fair value of stock options and ESPP awards is recognized over the period during which an optionee is required to provide services in exchange for the stock option award, known as the requisite service period (usually the vesting period) on a straight-line basis. Stock-based compensation expense is recognized based on the fair value determined on the date of grant and is reduced for forfeitures as they occur. For stock options granted to recipients in Belgium, option holders have a period of time (no longer than 30 days) to accept their awards. Accordingly, the grant date is determined based on the date of acceptance, as that is the point when a mutual understanding of the key terms of the awards are established.

The Black-Scholes option pricing model requires inputs based on certain subjective assumptions, including (i) the expected stock price volatility, (ii) the expected term of the award, (iii) the risk-free rate of interest, and (iv) expected dividends. Due to the lack of company-specific historical implied volatility data, the Company has based

its computations of expected volatility on the historical volatility of a representative group of public companies with similar characteristics of the Company, including stage of product development and life science industry focus. The historical volatility is calculated based on a period of time commensurate with the expected term assumption. The Company uses the simplified method as prescribed by the SEC Staff Accounting Bulletin No. 107, Share-Based Payment, to calculate the expected term for options granted to employees and non-employees, whereby, the expected term equals the arithmetic average of the vesting term and the original contractual term of the options due to its lack of sufficient historical data. The risk-free interest rate is based on U.S. Treasury securities with a maturity date commensurate with the expected term of the associated award. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on its common stock. The fair value of common stock is determined based on the quoted market price of the common stock.

The fair value of restricted stock units is also recognized over the requisite service period on a straight-line basis. The fair value of restricted stock units is based on the price of the Company's common stock on the grant date.

The Company classifies stock-based compensation expense in its statement of operations and comprehensive income in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.

Income Taxes

Income taxes

The Company provides for income taxes under the asset and liability method. Current income tax expense or benefit represents the amount of income taxes expected to be payable or refundable for the current year. Deferred income tax assets and liabilities are determined based on differences between the financial statement reporting and tax bases of assets and liabilities and net operating loss and credit carryforwards, and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. Deferred income tax assets are reduced, as necessary, by a valuation allowance when management determines it is more likely than not that some or all of the tax benefits will not be realized.

The global intangible low-taxed income (GILTI) provisions require the Company to include in its U.S. income tax return foreign subsidiary earnings in excess of an allowable return on the foreign subsidiary's tangible assets. The Company is electing to account for GILTI tax in the period in which it is incurred.

The Company accounts for uncertain tax positions in accordance with ASC 740-10, Accounting for Uncertainty in Income Taxes. The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. Assessing an uncertain tax position begins with the initial determination of the position’s sustainability and is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit might change as new information becomes available.

The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes.

Segment information

Operating segments are defined as components of an enterprise for which separate discrete financial information is available for evaluation by the chief operating decision maker (CODM) in deciding how to allocate resources and in assessing operating performance. The Company’s CODM is the Chief Executive Officer. The Company views its operations and manages its business in one operating segment, the business of developing cancer immunotherapies.

Net income per share attributable to common stockholders

Basic net income per share and diluted net income per share are computed using the weighted-average number of shares of common stock outstanding for the period. The effect of potentially dilutive shares is computed using the treasury stock method. Except where the result would be antidilutive to net income, diluted net income per share is computed assuming the exercise of common stock options.

Accounting standard updates

In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280) - Improvements to Reportable Segment Disclosures. This new standard will require the disclosure of significant segment expenses that are regularly provided to the CODM and included within each reported measure of segment profit or loss. Public entities will need to provide all annual disclosures currently required by Topic 280 in interim periods. Further, public entities will also be required to disclose the title and position of the CODM and an explanation of how the CODM uses the reported measure of segment profit or loss in assessing segment performance and deciding how to allocate resources. The Company adopted this standard on January 1, 2024. The adoption is not considered to have significantly impacted the Company's financial statements.

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740)—Improvements to Income Tax Disclosures, which establishes new income tax disclosure requirements. The new standard will require greater disaggregation of information within the effective tax rate reconciliation. Greater disaggregation of income taxes paid will also be required under adoption of this standard. This standard will become effective for the Company in the year ended December 31, 2025. While the Company is still evaluating the full impact that the adoption of this standard will have on its financial statements, the impact is not expected to be material as the resulting changes from this standard are expected to be disclosure-only.

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023
Trading Arrangements, by Individual
Material Terms of Trading Arrangement	During our fiscal quarter ended December 31, 2023, none of our directors or officers (as defined in Rule 16a-1(f) under the Exchange Act) entered into, modified (as to amount, price or timing of trades) or terminated (i) contracts, instructions or written plans for the purchase or sale of our securities that are intended to satisfy the conditions specified in Rule 10b5-1(c) under the Exchange Act for an affirmative defense against liability for trading in securities on the basis of material nonpublic information or (ii) non-Rule 10b5-1 trading arrangements (as defined in Item 408(c) of Regulation S-K).
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Rule 10b5-1 Arrangement Modified	false
Non-Rule 10b5-1 Arrangement Modified	false

Income Taxes - Schedule of Loss Before Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Domestic	$ (70,172)	$ (72,940)	$ (47,242)
Foreign	(38,858)	221,676	303,706
(Loss) income before income tax expense	$ (109,030)	$ 148,736	$ 256,464

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(11))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 235
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479557/942-235-S99-1

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 25
-Paragraph 1
-SubTopic 20
-Topic 940
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481913/940-20-25-1

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(15))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

+ Details

Summary of Significant Accounting Policies - Summary of Property and Equipment Estimated Useful Lives (Details)	Dec. 31, 2023
Computer equipment and software
Property Plant And Equipment [Line Items]
Useful life (in years)	3 years
Furniture, fixtures and other
Property Plant And Equipment [Line Items]
Useful life (in years)	5 years
Scientific equipment \| Minimum
Property Plant And Equipment [Line Items]
Useful life (in years)	5 years
Scientific equipment \| Maximum
Property Plant And Equipment [Line Items]
Useful life (in years)	6 years
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property, Plant, and Equipment, Useful Life, Term, Description [Extensible Enumeration]	us-gaap:UsefulLifeShorterOfTermOfLeaseOrAssetUtilityMember

Nature of Business and Basis of Presentation

12 Months Ended

Dec. 31, 2023

Disclosure Text Block [Abstract]

Nature of Business and Basis of Presentation

Note 1. Nature of Business and Basis of Presentation

Organization

iTeos Therapeutics, Inc. (iTeos Inc. or the Company), a Delaware corporation headquartered in Watertown, Massachusetts (incorporated on October 4, 2019), is the successor to iTeos Belgium SA (iTeos Belgium) a company organized under the laws of Belgium in 2011 and headquartered in Charleroi, Belgium. The Company is a clinical-stage biopharmaceutical company pioneering the discovery and development of a new generation of immuno-oncology therapeutics for people living with cancer. By leveraging its deep understanding of the tumor immunology and immunosuppressive pathways, we design novel product candidates with optimized pharmacologic properties to improve clinical outcomes by restoring the immune response against cancer. The Company is focused on advancing its innovative pipeline of monoclonal antibodies (mAbs) and small molecules for the treatment of cancer, especially solid tumors. Our three clinical-stage programs target novel, validated immuno-oncology pathways, including the TIGIT/CD226 pathway with TIGIT (T cell immunoreceptor with lg and ITIM domains) and the adenosine pathway with A2AR (adenosine 2A receptor) and ENT1 (equilibrative nucleoside transporter 1).

The Company’s lead antibody product candidate, belrestotug, also known as EOS-448/GSK4428859A, is an antagonist of TIGIT, an immune checkpoint with multiple mechanisms of action. Belrestotug was selected for its target affinity with TIGIT, potency and potential to engage the Fc gamma receptor (FcγR), a key regulator of immune response which triggers a multi-faceted mechanism of action that improves antitumor efficacy. This multi-faceted mechanism includes the activation of dendritic cells, natural killer cells, and macrophages, and the promotion of cytokine release and antibody-dependent cellular cytotoxicity (ADCC) activity. In 2020, the Company initiated an open-label Phase 1/2a clinical trial of belrestotug in adult cancer patients with advanced solid tumors. In April 2021, the Company reported preliminary safety, pharmacokinetic, engagement and pharmacodynamic data, indicating target engagement and early evidence of clinical activity as a single agent.

On June 11, 2021, the Company's wholly owned subsidiary, iTeos Belgium S.A., and GlaxoSmithKline Intellectual Property (No. 4) Limited, or GSK, executed a Collaboration and License Agreement, or the GSK Collaboration Agreement, which became effective on July 26, 2021. Pursuant to the GSK Collaboration Agreement, the Company granted GSK a license under certain of its intellectual property rights to develop, manufacture, and commercialize products comprised of or containing belrestotug, which license is exclusive in all countries outside of the United States and co-exclusive, with iTeos, in the United States. GSK and iTeos intend to develop belrestotug in combination, including with other oncology assets of GSK, and iTeos and GSK will jointly own the intellectual property created under the GSK Collaboration Agreement that covers such combinations. In partnership with GSK, the Company is enrolling patients in a Phase 2 platform trial assessing belrestotug and GSK's anti-PD-1 (Jemperli (dostarlimab-gxly)) in first-line non-small cell lung cancer, or NSCLC. In addition, the Company is enrolling patients in a Phase 2 platform study assessing the belrestotug and dostarlimab doublet and a triplet with GSK’s anti-CD96 antibody (GSK’608) with first-line, PD-L1 positive advanced or metastatic head and neck squamous cell carcinoma, or HNSCC, and a Phase 2 expansion trial assessing belrestotug and dostarlimab with first-line, PD-L1 positive advanced or metastatic HNSCC.The Company is also enrolling patients in a Phase 2 expansion trial assessing a belrestotug, dostarlimab and chemotherapy triplet in first-line advanced or metastatic NSCLC. The Company and GSK continue to explore two novel triplets in selected advanced solid tumors both in Phase 1b trials: belrestotug with dostarlimab and GSK’s investigational anti-CD96 antibody, and belrestotug with dostarlimab and GSK’s anti-PVRIG antibody (GSK’562).

The Company's next most advanced program is inupadenant, also known as EOS-850, a next-generation A2AR antagonist tailored to overcome the specific adenosine-mediated immunosuppression found in tumor microenvironment. The Company is investigating inupadenant in an open-label multi-arm Phase 1/2a clinical trial in adult cancer patients with advanced solid tumors. In April 2020, the Company reported preliminary safety data and early evidence of clinical activity as a single agent. The single-agent dose-escalation and expansion portions of the Company's Phase 1/2a clinical trial of inupadenant have demonstrated durable monotherapy antitumor activity in some patients with advanced solid tumors and safety consistent with previously reported results. The Company is also enrolling patients in the dose ranging part (Part 1) of an ongoing two-part Phase 2 trial in post-IO metastatic NSCLC to evaluate the combination of inupadenant with platinum-doublet chemotherapy compared to

standard platinum-doublet chemotherapy. The Company has also completed enrollment of the Phase 2 monotherapy high biomarker trial in advanced solid tumors.

The Company began its research and development activities as a spin-off of Ludwig Cancer Research and have built significant expertise in designing novel cancer immunotherapies. The Company's internal research and development team has extensive expertise in tumor immunology, characterization of immunosuppressive mechanisms in the tumor microenvironment, pharmacology and translational medicine. The Company has also built discovery capabilities to develop both small molecules and antibodies with differentiated and optimized product profiles for targets validated by a strong scientific rationale. The Company continues to progress research programs focused on additional targets that complement its TIGIT and adenosine pathway programs or address additional immunosuppressive pathways. The most recent program to enter the clinic is EOS-984, a potentially first-in-class small molecule focused on a new mechanism in the adenosine pathway by targeting ENT1, a dominant transporter of adenosine on lymphocytes involved in T cell metabolism, expansion, effector function, and survival. The Company's expertise also allows it to integrate a biomarker-rich strategy into its clinical programs to measure the activity of a product candidate in patients, seek to optimize combination agents and identify patients it deems most likely to benefit from treatment.

On December 2, 2020, iTeos Securities Corporation (iTeos SC) was incorporated as a Massachusetts Security Corporation. It is a wholly-owned subsidiary of iTeos Inc. On July 27, 2021, iTeos BE, LLC (iTeos LLC) was incorporated as a Delaware Limited Liability Company. It is a wholly-owned subsidiary of iTeos Belgium.

Liquidity and capital resources

Since inception, the Company’s activities have consisted primarily of performing research and development to advance its product candidates. For the first time since inception, the Company earned income during the year ended December 31, 2021, which equaled net income of $214.5 million. For the year ended December 31, 2022, the Company had net income of $96.7 million and retained earnings of $237.3 million. For the year ended December 31, 2023, the Company had net loss of $112.6 million and retained earnings of $124.6 million. As of March 6, 2024, the issuance date of the consolidated financial statements for the year ended December 31, 2023, the Company expects that its cash and cash equivalents would be sufficient to fund its operating expenses, capital expenditure requirements and debt service payments through at least 12 months from the issuance date of the consolidated financial statements.

The Company may seek additional funding in order to reach its development and commercialization objectives. The Company may not be able to obtain funding on acceptable terms, or at all, and the Company may not be able to enter into collaborations or other arrangements. The terms of any funding may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects.

The Company’s future results of operations involve a number of risks and uncertainties. Factors that could affect the Company’s future operating results and cause actual results to vary materially from expectations include, but are not limited to, uncertainty regarding results of clinical trials and reaching milestones, uncertainty of regulatory approval of the Company’s current or future product candidates, uncertainty of market acceptance of the Company’s product candidates, if approved, competition from substitute products and larger companies, securing and protecting proprietary technology, strategic relationships and dependence on key individuals and sole source suppliers. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities and may not ultimately lead to a marketing approval and commercialization of a product.

The Company’s product candidates require approvals from the U.S. Food and Drug Administration (FDA) and comparable foreign regulatory agencies prior to commercial sales in their respective jurisdictions. There can be no assurance that any product candidates will receive the necessary approvals. If the Company was denied approval, approval was delayed or the Company was unable to maintain approval for any product candidate, it could have a materially adverse impact on the Company. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. The Company will need to generate significant revenue to achieve sustained profitability, and it may never do so.

Basis of presentation

The consolidated financial statements and accompanying notes have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP).

Investment Securities and Fair Value Measurements

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Investment Securities and Fair Value Measurements

Note 3. Investment securities and fair value measurements

Certain of the Company’s assets and liabilities are recorded at fair value, as described below.

The following tables set forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy:


	December 31, 2023
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents (money market funds)	$	228,406	$	—	$	—	$	228,406
U.S. government agency bonds		—		193,076		—	$	193,076
U.S. treasury bonds		103,597		—		—	$	103,597
Corporate debt securities		—		84,605		—	$	84,605
Totals	$	332,003	$	277,681	$	—	$	609,684


	December 31, 2022
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents (money market funds)	$	92,850	$	—	$	—	$	92,850
U.S. government agency bonds		—		267,748		—	$	267,748
U.S. treasury bonds		186,477		—		—	$	186,477
Corporate debt securities		—		5,349		—	$	5,349
Totals	$	279,327	$	273,097	$	—	$	552,424

Cash equivalents consist of money market funds, which are classified within Level 1 of the fair value hierarchy because they are valued using quoted market prices in an active market. U.S. treasury securities are also classified as Level 1 because they are valued using quoted prices. U.S. government agency and corporate securities are classified within Level 2 of the fair value hierarchy because they are valued using market-based models that consider inputs such as yield, prices of comparable securities, coupon rate, maturity, and credit quality.

During the periods presented, the Company has not changed the manner in which it values assets and liabilities that are measured at fair value. The Company recognizes transfers between levels of the fair value hierarchy as of the end of the reporting period. There were no transfers within the hierarchy during the years ended December 31, 2023 and 2022.

The Company's fixed income securities held as of December 31, 2023 and December 31, 2022 are classified as available-for-sale. The following table presents the amortized cost, fair value, and gross unrealized gains and losses by major security type, for the fixed income securities held by the Company:


	December 31, 2023
(in thousands)	Amortized cost		Gross unrealized gains in AOCI		Gross unrealized losses in AOCI			Fair value
U.S. government agency bonds	$	193,231	$	90	$	(245	)	$	193,076
U.S. treasury bonds		103,476		156		(35	)		103,597
Corporate debt securities		84,536		114		(45	)		84,605
Totals	$	381,243	$	360	$	(325	)	$	381,278


	December 31, 2022
(in thousands)	Amortized cost		Gross unrealized gains in AOCI		Gross unrealized losses in AOCI			Fair value
U.S. government agency bonds	$	254,881	$	87	$	(211	)	$	254,757
U.S. treasury bonds		186,496		19		(37	)		186,478
Corporate debt securities		5,358		—		(9	)		5,349
Totals	$	446,735	$	106	$	(257	)	$	446,584

The following table presents the amortized cost and fair value of the Company's fixed income securities by maturity grouping:


	December 31, 2023
(in thousands)	Amortized cost		Fair value
Due in one year or less	$	281,035	$	280,739
Due after one year through five years		100,208		100,539
Due after five years through ten years		—		—
Due after ten years		—		—
Total	$	381,243	$	381,278


	December 31, 2022
(in thousands)	Amortized cost		Fair value
Due in one year or less	$	328,405	$	328,359
Due after one year through five years		118,330		118,225
Due after five years through ten years		—		—
Due after ten years		—		—
Total	$	446,735	$	446,584

There were no securities which were determined to experience credit losses as of the years ended December 31, 2023 and December 31, 2022. There were no sales of securities which resulted in a realized loss during the year ended December 31, 2023 and December 31, 2022. The Company recognized $21.5 million of interest income earned from its available-for-sale debt securities and money market funds for the year ended December 31, 2023. The Company also recognized $10.2 million of accretion on its available-for-sale debt securities for the year ended December 31, 2023, which was recorded to interest income. The Company recognized $9.6 million of interest income earned from its available-for-sale debt securities and money market funds for the year ended December 31, 2022. The Company also recognized $1.8 million of accretion on its available-for-sale debt securities for the year ended December 31, 2022, which was recorded to interest income.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

License and Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 2023

License Agreements [Abstract]

Schedule Of Contract Assets And Liabilities

The following table presents changes in the Company’s GSK contract assets and liabilities during the year ended December 31, 2023:


Year Ended December 31, 2023
(in thousands)	Balance at Beginning of Year		Additions		Deductions			Balance at Year End
Contract liabilities
Deferred revenue	$	12,595	$	—	$	(12,595	)	$	—

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Product Information [Line Items]
Fair Value Assets Level1 To Level2 Transfers Amount1	$ 0	$ 0	$ 0
Research And Development Tax Credits Percentage	20.50%	13.50%	13.50%
Impairment charges	$ 0	$ 0	$ 0
Operating segment \| Segment	1
Revenue Benchmark \| Product Concentration Risk \| Investment Portfolio
Product Information [Line Items]
Concentration risk percentage	69.00%

License and Collaboration Agreements - Schedule Of Contract Assets And Liabilities (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2022 USD ($)
License Agreements [Abstract]
Deferred revenue, Deductions	$ (12,595)
Deferred revenue, Ending balance	$ 12,595

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

Note 9. Income taxes

For financial reporting purposes, income before income tax expense for the years ended December 31, 2023, 2022 and 2021 consisted of the following:


(in thousands)	2023			2022			2021
Domestic	$	(70,172	)	$	(72,940	)	$	(47,242	)
Foreign		(38,858	)		221,676			303,706
(Loss) income before income tax expense	$	(109,030	)	$	148,736		$	256,464

The Company’s worldwide effective tax rate for the years ended December 31, 2023, 2022 and 2021 was (3.3)%, 35.0% and 16.4%, respectively. The reconciliation of the statutory U.S. federal income tax rate (21%) to the effective income tax rate is as follows:


		2023			2022			2021
U.S. statutory federal income tax rate		21.0	%		21.0	%		21.0	%
State income taxes	4.9			(2.2)			(0.5)
Foreign tax differential	1.2			5.2			4.7
Non-deductible/non-taxable permanent differences	(0.1)			0.1			0.1
Innovation income deduction tax exemption	0			(33.4)				(28.2	)
Net GILTI Inclusion Income	(0.1)			18.9			15.2
Subpart F income	(1.8)			0			0
Unrecognized tax benefits	(1.6)			14.9				6.6
Other	(1.2)			(3.0)			(1.1)
Change in valuation allowance	(25.6)			13.5			(1.4)
Effective income tax rate	(3.3)%				35.0	%		16.4	%

The components of income tax expense for the years ended December 31, 2023, 2022 and 2021 consisted of the following:


(in thousands)	2023		2022		2021
Current
Domestic	$	3,612	$	50,750	$	41,535
Foreign		—		1,334		408
Deferred		—		—		—
Total income tax expense	$	3,612	$	52,084	$	41,943

Deferred income taxes reflected the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes and operating losses and tax credit carryforwards. The significant components of the Company’s deferred tax assets and liabilities are comprised of the following:


	December 31,
(in thousands)	2023			2022
Deferred tax assets :
Net operating loss carryforward	$	21,796		$	13,359
Foreign research and development expenses		17,980			12,355
Section 174 capitalized research and development expenses		27,913			14,856
Stock-based compensation		5,002			3,860
Operating lease liabilities		1,539			1,201
Accrued vacation and bonus		846			552
Other		1,164			932
Total deferred tax assets		76,240			47,115
Valuation allowance		(74,398	)		(45,421	)
Deferred tax assets, net of valuation allowance		1,842			1,694
Deferred tax liabilities:
Operating lease right of use assets		(1,534	)		(1,196	)
Prepaid expenses		(243	)		(394	)
Depreciation and amortization		(65	)		(104	)
Total deferred tax liabilities		(1,842	)		(1,694	)
Deferred tax assets and liabilities, net of valuation allowance	$	—		$	—

The Company has evaluated the positive and negative evidence bearing upon its ability to realize its deferred tax assets. Management has considered the Company’s history of losses in prior years, the nature of the Company’s deferred tax assets, and the timing, likelihood and amount, if any, of future taxable income during the periods in which those temporary differences and carryforwards become deductible and has concluded that it is more likely than not that the company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation will be maintained on the net deferred tax assets until there is sufficient evidence to support the reversal of some portion of these allowances. The valuation allowance increased $29.0 million during the year ended December 31, 2023 primarily due to net operating losses and an increase in cumulative temporary differences related to capitalized research and development under Section 174, stock-based compensation and foreign research and development expenses.

The Tax Cuts and Jobs Act, or TCJA, generally allows federal losses generated after 2017 to be carried over indefinitely, but will generally limit the net operating loss ("NOL") deduction to the lesser of the NOL carryover or 80% of a corporation’s taxable income (subject to Section 382 of the Internal Revenue Code of 1986, as amended). In addition, there is no carryback for losses generated after 2017.

As of December 31, 2023, the Company had Belgium NOL carryforwards for Belgian federal income tax purposes of $64.1 million, that can be carried forward indefinitely.

As of December 31, 2023, the Company had $8.5 million of U.S. federal NOL carryforwards, which may be available to offset future federal income tax liabilities. These carryforwards have no expiration. The Company also had $61.9 million of state NOL carryforwards, which may be available to offset future income tax liabilities in the state of Massachusetts. They expire at various dates through 2043.

Utilization of net operating loss and research and development credit carryforwards may be subject to limitation under Section 382 and Section 383 of the Internal Revenue Code of 1986, as amended, due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of NOL and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax, respectively. The latest Section 382 study was performed by the Company through January 3, 2022, through which it was noted that a historic ownership change has likely occurred. Nonetheless, the Company has determined that the utilization of all net operating loss and tax credit carryforwards on 2021 federal and state tax returns should not be limited due to ownership changes prior January 3, 2022. Although ownership changes after January 3, 2022 could impact the Company’s ability to utilize tax attributes generated after January 3, 2022, in the future. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development credit carryforwards before utilization, however, as the Company is maintaining a full valuation allowance against all NOL and credit carryforwards, the impact of any limitation under Section 382 and Section 383 after January 3, 2022 would be offset by an adjustment to the valuation allowance.

The Company files income tax returns in the U.S., New Hampshire, Massachusetts, Florida, Tennessee and Belgium. The Company is subject to U.S. federal, state and Belgium tax examinations by tax authorities for years 2019 through present. To the extent that the Company has tax attribute carryforwards, the tax years in which the attributes were generated may still be adjusted upon examination by the Internal Revenue Service, state or foreign tax authorities to the extent utilized in a future period.

Unrecognized tax benefits were $40.9 million and $39.2 million as of December 31, 2023 and 2022, respectively. During the years ended December 31, 2023 and 2022, the Company accrued interest relating to uncertain tax positions of $1.7 million and $2.2 million, respectively. As of December 31, 2023 and 2022, there was $3.9 million and $2.2 million, respectively, of accrued interest included in the consolidated balance sheets. There was no increase in the unrecognized tax benefits during the year ended December 31, 2023, except for additional accrued interest. The increase in the unrecognized tax benefits during the year ended December 31, 2022 was caused by the recognition of additional revenue, and the resulting income, during the year under the GSK Collaboration Agreement. As the uncertain tax position relates to the Company’s allocation of that revenue and resulting income between the U.S. and Belgium under the GSK Collaboration Agreement, the additional recognition of revenue under that agreement increased the liability for the uncertain tax position. All unrecognized tax benefits, if recognized, would affect our effective tax rate.

The changes to the unrecognized tax benefits during the year ended December 31, 2023 were as follows:


(in thousands)
Balance at December 31, 2022	$	39,200
Increase related to current year tax positions		1,730
Balance at December 31, 2023	$	40,930

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

License and Collaboration Agreements - Additional Information (Details) - USD ($)		12 Months Ended
	Jun. 11, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront payment received		$ 625,000,000
License and collaboration revenue		12,595,000	$ 267,630,000	$ 344,775,000
Accrued expenses and other current liabilities		7,058,000	14,092,000
Deferred revenue		0	$ 12,595,000
Adimab L L C
Research And Development Arrangement Contract To Perform For Others [Line Items]
Maximum additional receivable based on achievement of research milestones		14,500,000
Adimab L L C \| License revenue
Research And Development Arrangement Contract To Perform For Others [Line Items]
Option Fees		1,000,000
Additional milestone payment accrued		2,000,000
License and collaboration revenue		5,400,000
Adimab L L C \| Development Regulatory and Sales Milestone
Research And Development Arrangement Contract To Perform For Others [Line Items]
Maximum option fees receivable based on achievement of research milestones		45,800,000
GSK
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront payment received	$ 625,000,000
Milestone payments	$ 1,450,000,000
Eligible royalty payments percentage	20.00%
Accrued expenses and other current liabilities		400,000
Deferred revenue		0
Costs related to the cost-sharing provisions		39,600,000
Capitalized contract cost, net		$ 6,800,000
Costs related to global development plan		60.00%
GSK \| Related Party
Research And Development Arrangement Contract To Perform For Others [Line Items]
Operating Costs and Expenses		$ 900,000,000
GSK \| License revenue
Research And Development Arrangement Contract To Perform For Others [Line Items]
License and collaboration revenue		$ 12,600,000

Commitments and Contingencies - Schedule Of Cash Flow And Other Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Operating lease liabilities arising from obtaining right-of-use assets (non-cash)	$ 2,155	$ 350	$ 5,877
Operating cash flows used in operating leases	$ 1,201

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 251,177	$ 284,803
Short-term investments (amortized cost of $281,035)	280,739	328,359
Grants receivable	0	1,001
Research and development tax credits receivable	135	0
Refundable income taxes	6,365	1,434
Prepaid expenses and other current assets	12,236	12,701
Total current assets	550,652	628,298
Property and equipment, net	4,696	2,121
Long-term investments (amortized cost of $100,208)	100,539	118,225
Research and development tax credits receivable, net of current portion	4,508	1,128
Restricted cash	274	235
Right of use assets	6,036	4,652
Other assets	883	332
Total assets	667,588	754,991
Current liabilities:
Accounts payable	11,293	7,662
Accrued expenses and other current liabilities	7,058	14,092
Accrued personnel expenses	8,562	5,635
Payable for investments	9,787	0
Deferred income	2,063	1,180
Deferred revenue	0	12,595
Lease liabilities	1,251	836
Total current liabilities	40,014	42,000
Grants repayable	6,609	6,622
Lease liabilities, net of current portion	4,807	3,837
Unrecognized tax benefits	40,930	39,200
Total liabilities	92,360	91,659
Commitments and contingencies (Note 10)
Stockholders’ equity (deficit):
Common stock, $0.001 par value, 150,000,000 shares authorized at December 31, 2023 and 2022, respectively; 35,838,080 and 35,611,219 shares issued and outstanding at December 31, 2023 and 2022, respectively	36	36
Additional paid-in capital	463,799	435,665
Accumulated other comprehensive (loss)	(13,240)	(9,644)
Retained earnings	124,633	237,275
Total stockholders' equity	575,228	663,332
Total liabilities and stockholders' equity	$ 667,588	$ 754,991

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 10. Commitments and contingencies

Purchase commitments

The Company has contractual arrangements with research and development organizations and suppliers; however, these contracts are generally cancelable on 30-60 days’ notice and the obligations under these contracts are largely based on services performed. The Company may also enter into contracts in the normal course of business with clinical research organizations for clinical trials, with contract manufacturing organizations for clinical supplies and with other vendors for preclinical studies, supplies and other services and products for

operating purposes. These contracts generally provide for termination on notice. As of December 31, 2023 and 2022, there were no amounts accrued related to termination charges.

The Company has entered into a Biologics Master Services Agreement with WuXi Biologics (Hong Kong) Limited (WuXi) herein referred to as the WuXi Agreement. The WuXi Agreement includes the terms and conditions under which WuXi will coordinate the Company’s biologics development and manufacturing services. Pursuant to the WuXi Agreement, the Company may be required to pay WuXi a royalty percentage or a one-time milestone payment on global net sales of third-party manufactured products at the Company’s election. The royalty or one-time milestone payment is only payable if the Company does not use WuXi as the manufacturer in part, or in totality. As of December 31, 2023 and 2022, there are no minimum commitments under the WuXi Agreement. Additionally, as of December 31, 2023 and 2022, there are no royalties or milestones payable.

Leases

The Company’s operating leases are as follows:

•

An April 2016 lease for 1,577 square meters of office and laboratory space in Gosselies, Belgium, which commenced in May 2016 and terminated in December 2021. In January 2021, the Company entered into an amendment to extend the lease, effective February 2021 with a termination date of January 2030, and increase the office and laboratory space by 201 square meters. In October 2021, the Company entered into an amendment to increase the office and laboratory space by 453 square meters. In May 2023, the Company entered into another amendment to again increase the office and laboratory space by an additional 453 square meters for a total of 2,684 square meters.

•

A November 2021 lease for 9,068 square feet of office space in Watertown, Massachusetts, which commenced in November 2021 and terminates in February 2027. The lease is subject to fixed-rate rent escalations.

•

In July 2023, the Company entered into an agreement to access 859 square meters of laboratory space in Gosselies, Belgium for the purpose of building out future laboratory space. The space had not yet been occupied by the Company as of December 31, 2023. This lease will not contain any variable lease payments. There will be no option to terminate nor to extend the lease prior to the termination date. The lease will terminate five years from the commencement of the occupancy agreement, once effective.

•

Various car leases that the Company enters into from time to time. The life of each car lease ranges from 48 to 60 months.

The Company identified and assessed the following estimates in recognizing the operating lease right of use assets and corresponding liabilities.

Expected lease term: The expected lease term includes non-cancelable lease periods and, when applicable, periods covered by an option to extend the lease if the Company is reasonably certain to exercise that option, as well as periods covered by an option to terminate the lease if the Company is reasonably certain not to exercise that option.

Incremental borrowing rate: As the discount rates in the Company’s lease are not implicit, management estimated the incremental borrowing rate based on the rate of interest the Company would have to pay to borrow a similar amount on a collateralized basis over a similar term.

Lease and non-lease components: The Company is required to pay fees for operating expenses in addition to monthly base rent for certain operating leases (non-lease components). The Company has not elected the practical expedient which allows non-lease components to be combined with lease components for all asset classes. Variable non-lease components are not included within the lease right-of-use asset and lease liability on the consolidated balance sheet, and instead are reflected as expense in the period they are paid.

Rent expense was $1.2 million, $0.9 million and $0.7 million for the year ended December 31, 2023, 2022 and 2021, respectively.

The following table summarizes lease terms and discount rate:


	December 31,
	2023
Weighted-average remaining lease term (years)		4.6
Weighted-average discount rate		4.75	%

The following table summarizes the cash flow and other information:


	Year ended December 31,
(in thousands)	2023
Operating lease liabilities arising from obtaining right-of-use assets (non-cash)	$	2,155
Operating cash flows used in operating leases	$	1,201

As of December 31, 2023, the Company had the following future minimum lease payments under non-cancelable operating leases for the future years thereafter (in thousands):


Year ending December 31:
2024	$	1,500
2025		1,468
2026		1,435
2027		941
2028		764
Thereafter		590
Total Lease Payments		6,698
Less: Interest		(640	)
Total Lease Liability	$	6,058
Lease liabilities - current	$	1,251
Lease liabilities, net of current portion	$	4,807

In November 2021, the Company provided a letter of credit for $142 thousand to secure its obligation under its lease in Watertown, Massachusetts. The Company maintains that amount of cash on hand (restricted) to fund any necessary draws on the letter of credit. In addition, as of December 31, 2023 and 2022, the Company had $131 thousand and $99 thousand on hand serving as a guarantee for its lease obligation in Belgium. These amounts have been classified as restricted cash in the consolidated balance sheets as of December 31, 2023 and 2022.

Consolidated Balance Sheet Components (Tables)

12 Months Ended

Dec. 31, 2023

Supplemental Balance Sheet Information [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net consisted of the following:


	December 31,
(in thousands)	2023			2022
Scientific equipment	$	3,434		$	3,008
Furniture & office equipment		1,467			1,332
Leasehold improvements		4,177			1,238
Total		9,078			5,578
Accumulated depreciation and amortization		(4,382	)		(3,457	)
Property & equipment, net	$	4,696		$	2,121

Schedule of Accrued Expenses

Accrued liabilities consisted of the following:


	December 31,
(in thousands)	2023		2022
Accrued clinical trial costs	$	6,956	$	13,496
Accrued professional fees and other		102		596
Total accrued expenses and other current liabilities	$	7,058	$	14,092

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities
Net (loss) income	$ (112,642)	$ 96,652	$ 214,521
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
Depreciation and amortization	898	803	603
Stock-based compensation	27,021	21,561	13,794
Net accretion of available-for-sale debt securities	(10,234)	(1,728)	0
Change in operating lease right-of-use assets	0	10	12
Changes in operating assets and liabilities:
Grants receivable	1,015	2,751	(4,071)
Research and development tax credits receivable	(3,400)	1,237	727
Refundable income taxes	(4,934)	6,107	(7,544)
Prepaid expenses and other current assets	184	590	(11,789)
Accounts payable	3,036	2,761	2,280
Accrued expenses and other liabilities	5,342	3,096	9,959
Deferred income	823	397	(3,480)
Deferred revenue	(12,595)	(267,630)	281,128
Unrecognized tax benefits	1,730	22,200	17,000
Net cash (used in) provided by operating activities	(103,756)	(111,193)	513,140
Cash flows from investing activities
Purchases of investments	(290,541)	(445,004)	0
Proceeds from maturities of investments	366,264	0	0
Purchase of property and equipment	(2,966)	(938)	(1,181)
Purchase of other assets	(99)	(120)	(61)
Net cash provided by (used in) investing activities	72,658	(446,062)	(1,242)
Cash flows from financing activities
Proceeds from issuance of common stock upon exercise of options and ESPP purchase	1,113	925	2,943
Proceeds from grants repayable	0	1,059	716
Net cash provided by financing activities	1,113	1,984	3,659
Effects of exchange rate changes on cash, cash equivalents and restricted cash	(3,602)	(8,526)	(3,176)
Net (decrease) increase in cash, cash equivalents and restricted cash	(33,587)	(563,797)	512,381
Cash, cash equivalents and restricted cash at beginning of year	285,038	848,835	336,454
Cash, cash equivalents and restricted cash at end of year	251,451	285,038	848,835
Non-cash investing and financing activities
Capital expenditure included in accounts payable	354	94	175
Operating lease liabilities arising from obtaining right-of-use assets (non-cash)	2,155	350	5,877
Unrealized loss on available-for-sale securities	35	148	0
Supplemental disclosure of cash flows
Cash paid for taxes	$ 6,816	$ 22,816	$ 32,019

Condensed Consolidated Statements of Operations and Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenue:
License and collaboration revenue	$ 12,595	$ 267,630	$ 344,775
Total revenue	12,595	267,630	344,775
Operating expenses:
Research and development expenses	113,300	97,359	59,369
General and administrative expenses	50,396	43,947	40,505
Total operating expenses	163,696	141,306	99,874
(Loss) income from operations	(151,101)	126,324	244,901
Other income:
Grant income	2,687	2,091	10,181
Research and development tax credits	3,527	1,172	0
Interest income	31,774	11,361	78
Other income, net	4,083	7,788	1,304
(Loss) income before income tax expense	(109,030)	148,736	256,464
Income tax expense	3,612	52,084	41,943
Net (loss) income	(112,642)	96,652	214,521
Net (loss) income attributable to common stockholders	$ (112,642)	$ 96,652	$ 214,521
Basic net (loss) income per common share	$ (3.15)	$ 2.72	$ 6.1
Diluted net (loss) income per common share	$ (3.15)	$ 2.56	$ 5.68
Weighted-average common shares outstanding - basic	35,763,520	35,552,025	35,181,383
Weighted-average common shares outstanding - diluted	35,763,520	37,766,507	37,774,790
Net Income (Loss)	$ (112,642)	$ 96,652	$ 214,521
Foreign currency translation adjustments	(3,631)	(8,478)	(1,635)
Unrealized gain (loss) related to available-for-sale debt securities	35	(148)	0
Comprehensive (loss) income	$ (116,238)	$ 88,026	$ 212,886

Investment Securities and Fair Value Measurements - Summary of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - Fair Value Measurements Recurring - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	$ 609,684	$ 552,424
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents (money market funds)	228,406	92,850
U.S. Government Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	193,076	267,748
U.S. Treasury Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	103,597	186,477
Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	84,605	5,349
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	332,003	279,327
Level 1 \| Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents (money market funds)	228,406	92,850
Level 1 \| U.S. Treasury Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	103,597	186,477
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	277,681	273,097
Level 2 \| U.S. Government Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	193,076	267,748
Level 2 \| Corporate Debt Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	$ 84,605	$ 5,349

Net income (loss) per share attributable to common stockholders

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Net Loss Per Share Attributable to Common Stock

Note 13. Net (loss) income per share attributable to common stockholders

The Company granted certain stock options under the 2019 Plan, and currently grants certain stock options under the 2020 Plan, which are considered common stock equivalents. For the year ended December 31, 2023, the common stock equivalents were excluded from the weighted-average diluted shares calculation as they were anti-dilutive. For the years ended December 31, 2022 and 2021, the common stock equivalents were included to calculate weighted-average diluted shares outstanding. The Company used the treasury stock method.

The following table summarizes the impact of the treasury stock method:


Net (loss) income per share		December 31,
(in thousands, except per share amounts)		2023				2022			2021
Numerator
Net (loss) income attributable to common stockholders	$		(112,642	)	$		96,652	$		214,521
Denominator
Weighted-average shares used to compute net (loss) income per share, basic			35,763,520				35,552,025			35,181,383
Effect of dilutive securities (a)			—				2,214,482			2,593,407
Weighted-average shares used to compute net (loss) income per share, diluted			35,763,520				37,766,507			37,774,790
Net (loss) income per share:
Basic	$		(3.15	)	$		2.72	$		6.10
Diluted	$		(3.15	)	$		2.56	$		5.68

(a) The common stock equivalents, which equaled 1,692,558 stock awards outstanding as of December 31, 2023, were excluded for the year ending December 31, 2023, due to their anti-dilutive effect.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of significant accounting policies

Note 2. Summary of significant accounting policies

Principles of consolidation

The consolidated financial statements include the Company’s accounts and those of its wholly owned subsidiaries. All intercompany accounts, transactions and balances have been eliminated.

Use of estimates

Cash, cash equivalents and restricted cash

Short-term and long-term investments

Foreign currency, currency translation and comprehensive income

Fair value measurements

The carrying amounts of long-term R&D credits receivable and grants repayable approximate fair value due to low local market interest rates.

•

Level 1—Quoted prices in active markets that are accessible at the market date for identical unrestricted assets or liabilities.

•

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

Concentration of credit risk

Research and development tax credits

Property and equipment

Property and equipment, including leasehold improvements, are stated at cost and depreciated when placed into service using the straight-line method over the estimated useful lives as follows:


Asset		Estimated Useful Life
Computer equipment and software		3 years
Furniture, fixtures and other		5 years
Scientific equipment		5 – 6 years
Leasehold improvements		Shorter of useful life or term of lease

Impairment of long-lived assets

Revenue recognition

transfer of goods or services, and the technology underlying the licenses granted reflects research and development expenses already incurred by the Company.

Contract costs

Collaborative Arrangements

Research and development expenses

Government grant funding and potential repayment commitments under recoverable cash advance grants (RCAs)

Leases

Stock-based compensation

Income taxes

The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes.

Segment information

Net income per share attributable to common stockholders

Accounting standard updates

Net income (loss) per share attributable to common stockholders - Schedule of Net Income (loss) Per Shares By Treasury Stock Method (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Numerator
Net (loss) income attributable to common stockholders	$ (112,642)	$ 96,652	$ 214,521
Denominator
Weighted-average shares used to compute net (loss) income per share, basic	35,763,520	35,552,025	35,181,383
Effect of dilutive securities	0	2,214,482	2,593,407
Weighted-average shares used to compute net (loss) income per share, diluted	35,763,520	37,766,507	37,774,790
Basic net (loss) income per common share	$ (3.15)	$ 2.72	$ 6.1
Diluted net (loss) income per common share	$ (3.15)	$ 2.56	$ 5.68

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482635/260-10-55-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (e)(4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-7

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 60B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-60B

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482662/260-10-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-10

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(25))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(27))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(23))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 16: http://www.xbrl.org/2003/role/exampleRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 52
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482635/260-10-55-52

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-7

+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-3

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482635/260-10-55-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (e)(4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 65
-Paragraph 1
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480175/815-40-65-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-11

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-7

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 60B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-60B

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 250
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483443/250-10-50-4

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482662/260-10-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(25))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-2

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(27))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483589/942-220-S99-1

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(23))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1

Reference 15: http://www.xbrl.org/2003/role/exampleRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 52
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482635/260-10-55-52

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-7

+ Details

- Definition

Amount after tax of income (loss) from continuing operations attributable to the parent.

+ References

+ Details

Employee benefit plan

12 Months Ended

Dec. 31, 2023

Retirement Benefits [Abstract]

Employee benefit plan

Note 11. Employee benefit plan

iTeos Belgium sponsors a defined contribution insurance plan (the Plan) for its employees. In the first quarter of each year, iTeos Belgium pays an annual premium to the insurance company which corresponds to 5% of employees’ gross salaries. Interest accrues each year into a pool for each employee and when they retire, they collect the total in their accounts. The Company contributed $675 thousand, $398 thousand and $254 thousand to the Plan for the years ended December 31, 2023, 2022 and 2021, respectively.

iTeos Inc. has a 401(k) defined contribution plan (the 401(k) Plan) for its U.S. employees. The 401(k) plan provides for voluntary tax-deferred salary deductions for all employees of up to 100% of their annual compensation, as limited by an annual maximum amount as determined by the Internal Revenue Service. The Company may match employee contributions in amounts to be determined at the Company’s sole discretion. The Company contributed $312 thousand, $278 thousand and $82 thousand to the 401(k) Plan for the years ended December 31, 2023, 2022 and 2021, respectively.

- Definition

The entire disclosure for retirement benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480794/715-70-50-1

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (q)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//715/tableOfContent

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (o)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (p)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (r)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480126/715-20-S99-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 60
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480266/715-60-50-3

+ Details

Investment Securities and Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Summary of Financial Instruments Measured at Fair Value on a Recurring Basis

The following tables set forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy:


	December 31, 2023
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents (money market funds)	$	228,406	$	—	$	—	$	228,406
U.S. government agency bonds		—		193,076		—	$	193,076
U.S. treasury bonds		103,597		—		—	$	103,597
Corporate debt securities		—		84,605		—	$	84,605
Totals	$	332,003	$	277,681	$	—	$	609,684


	December 31, 2022
(in thousands)	Level 1		Level 2		Level 3		Total
Cash equivalents (money market funds)	$	92,850	$	—	$	—	$	92,850
U.S. government agency bonds		—		267,748		—	$	267,748
U.S. treasury bonds		186,477		—		—	$	186,477
Corporate debt securities		—		5,349		—	$	5,349
Totals	$	279,327	$	273,097	$	—	$	552,424

Summary of Amortized Cost, Fair Value, and Unrealized Losses by Type of Security


	December 31, 2023
(in thousands)	Amortized cost		Gross unrealized gains in AOCI		Gross unrealized losses in AOCI			Fair value
U.S. government agency bonds	$	193,231	$	90	$	(245	)	$	193,076
U.S. treasury bonds		103,476		156		(35	)		103,597
Corporate debt securities		84,536		114		(45	)		84,605
Totals	$	381,243	$	360	$	(325	)	$	381,278


	December 31, 2022
(in thousands)	Amortized cost		Gross unrealized gains in AOCI		Gross unrealized losses in AOCI			Fair value
U.S. government agency bonds	$	254,881	$	87	$	(211	)	$	254,757
U.S. treasury bonds		186,496		19		(37	)		186,478
Corporate debt securities		5,358		—		(9	)		5,349
Totals	$	446,735	$	106	$	(257	)	$	446,584

Schedule of Investments Classified by Contractual Maturity Date

The following table presents the amortized cost and fair value of the Company's fixed income securities by maturity grouping:


	December 31, 2023
(in thousands)	Amortized cost		Fair value
Due in one year or less	$	281,035	$	280,739
Due after one year through five years		100,208		100,539
Due after five years through ten years		—		—
Due after ten years		—		—
Total	$	381,243	$	381,278


	December 31, 2022
(in thousands)	Amortized cost		Fair value
Due in one year or less	$	328,405	$	328,359
Due after one year through five years		118,330		118,225
Due after five years through ten years		—		—
Due after ten years		—		—
Total	$	446,735	$	446,584

- Definition

Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-9

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (aaa)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-3

+ Details

Stockholders' Equity - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	May 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Class Of Stock [Line Items]
Common stock, shares authorized		150,000,000	150,000,000
Common stock, par value		$ 0.001	$ 0.001
Common stock, voting rights		Each share of common stock entitles the holders to one vote on all matters submitted to a vote of the Company’s stockholders.
IPO
Class Of Stock [Line Items]
Capital units, authorized		160,000,000
Common stock, shares authorized		150,000,000
Common stock, par value		$ 0.001
Preferred Stock Shares Authorized		10,000,000
Preferred Stock, par value		$ 0.001
Sales Agreement with Cowen and Company LLC \| At-the-market offering program
Class Of Stock [Line Items]
Aggregate offering price	$ 125,000,000

Employee benefit plan - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, employer contribution, percent	5.00%
Defined contribution plan,contributions by employer	$ 675	$ 398	$ 254
401(k) defined contribution plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan,contributions by employer	$ 312	$ 278	$ 82
Defined contribution plan, maximum annual contributions per employee, percent	100.00%

Stock-based compensation

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-based compensation

Note 8. Stock-based compensation

General

The Board of Directors, at its sole discretion, shall determine the exercise price. Stock options expire 7 to 10 years from the date of grant. The stock options generally vest 25% upon the one-year anniversary of the service inception date and then ratably each month over the remaining 36 months. Upon termination of service, any unvested stock options are automatically returned to Company. Vested stock options that are not exercised within the specified period, according to the terms and conditions of the option plan, following the termination as an

employee, consultant, or service provider to the Company are surrendered back to the Company. Those stock options are added back to the pool and made available for future grants.

2019 Stock Option and Grant Plan

The Company’s 2019 Stock Option and Grant Plan (the 2019 Plan) provided for the Company to grant stock options and other stock-based awards to employees and non-employees to purchase the Company’s common stock. Total authorized options under the 2019 Stock Option and Grant Plan is 3,464,316. Upon the effectiveness of the 2020 Plan (as defined below), no further issuances will be made under the 2019 Plan.

On July 15, 2020, the Company’s Board of Directors approved an amendment to stock options outstanding under the 2019 Stock Option and Grant Plan to provide for immediate 100% vesting for all outstanding options under the plan upon the consummation of a Sale Event, as defined by the amendment.

2020 Stock Option and Incentive Plan

The 2020 Stock Option and Incentive Plan (the 2020 Plan) was approved by the Company’s board of directors on July 15, 2020, and the Company’s stockholders on July 20, 2020 and became effective on July 22, 2020, the date immediately prior to the date on which the registration statement for the Company’s IPO became effective. The 2020 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights to the Company’s officers, employees, directors and consultants. The number of shares of common stock reserved for issuance as of December 31, 2023 under the 2020 Plan was 9,115,915 and will be increased each January 1 by 5% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares as determined by the Company’s compensation committee of the board of directors. Accordingly, on January 1, 2024, the number of shares of common stock reserved and available for issuance under the 2020 Plan increased by 1,791,904. The 2020 Plan replaced the 2019 Plan, as the Company’s board of directors is not expected to make additional awards under the 2019 Plan following the completion of the IPO. However, the 2019 Plan will continue to govern outstanding equity awards granted thereunder.

Employee Stock Purchase Plan

The 2020 Employee Stock Purchase Plan (the 2020 ESPP) was approved by the Company’s board of directors on July 15, 2020, and the Company’s stockholders on July 20, 2020, and became effective on July 22, 2020, the date immediately prior to the date on which the registration statement for the Company’s IPO was declared effective. The number of shares of common stock reserved for issuance as of December 31, 2023 under the 2020 ESPP was 612,642. The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1 thereafter by the lesser of 634,969 shares of common stock, 1% of the outstanding number of shares of common stock on the immediately preceding December 31, or such lesser number of shares as determined by the Company’s compensation committee. There was no increase to the number of shares of common stock reserved and available for issuance under the 2020 ESPP on January 1, 2024. During the year ended December 31, 2023, 37,549 shares were issued at a weighted-average price of $10.91 under the 2020 ESPP. The purchase price of the stock is equal to 85% of the lesser of the market value of such shares at either first date of the offering period or the last date of the offering period. The estimated weighted-average fair value of the issued shares was $7.19 per share. The assumptions utilized to estimate the fair value are include in the assumption table below.

Stock-Based Compensation Expense

The following table summarizes stock option activity for the year ended December 31, 2023:


	Stock Options
	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (In thousands)
Outstanding as of December 31, 2022		6,401,987		$	18.50		7.1
Granted		2,324,597			15.25
Exercised		(184,937	)		3.92
Forfeited		(271,427	)		24.14
Outstanding as of December 31, 2023		8,270,220		$	17.73		6.5	$	16,299
Vested and expected to vest as of December 31, 2023		8,270,220		$	17.73		6.5	$	16,299
Exercisable at December 31, 2023		4,746,431		$	16.01		5.3	$	14,859

The following table summarizes stock-based compensation expense, and also the allocation within the consolidated statements of operations and comprehensive income (loss):


	Year Ended December 31,
(in thousands)	2023		2022		2021
Research and development	$	6,619	$	4,152	$	1,906
General and administrative		20,402		17,409		11,888
Total stock-based compensation expense	$	27,021	$	21,561	$	13,794

Of the $27.0 million of stock-based compensation expense recognized during the year ended December 31, 2023, $25.8 million related to stock options, $1.0 million related to restricted stock units, and $0.2 million related to ESPP awards.The weighted-average grant-date fair value of options awarded during the years ended December 31, 2023, 2022 and 2021 was $11.60 per share, $23.94 per share and $27.46 per share, respectively. The aggregate intrinsic value of stock options exercised during the years ended December 31, 2023, 2022 and 2021 was $2.2 million, $3.2 million and $11.0 million, respectively. The aggregate grant date fair value of stock options vested during the years ended December 31, 2023, 2022 and 2021 was $28.1 million, $20.4 million and $10.7 million, respectively. As of December 31, 2023, there was a total of $46.7 million of unrecognized employee compensation costs related to non-vested stock option awards expected to be recognized over a weighted average period of 2.7 years.

The Company estimates the fair value of stock-based compensation utilizing the Black-Scholes option pricing model, which is dependent upon several variables, such as expected term, volatility, risk-free interest rate, and expected dividends. Each of these inputs is subjective and generally requires significant judgment to determine.

The following table summarizes the range of key assumptions used to determine the fair value of stock options and ESPP awards granted during:


	Year Ended December 31,
	2023			2022			2021
Stock Options:
Risk-free interest rate	3.46% - 4.73%			1.37% - 4.23%			0.42% - 1.27%
Expected term (in years)	5.5 - 6			5.5 - 6				6
Expected volatility	82% - 96%			86% - 94%			92% - 100%
Expected dividend yield	0				0	%	0%
Estimated fair value of common stock	$9.76 - $21.15			$17.50 - $46.56			$20.54 - $46.68
ESPP Awards:
Risk-free interest rate	1.63% - 5.44%				1.63	%		-
Expected term (in years)	0.5				0.5			-
Expected volatility	77% - 95%				81	%		-
Expected dividend yield		0	%		0	%		-
Estimated fair value of common stock	$15.85 - $20.92			$17.30				-

Restricted Stock Units

The Company issued restricted stock units in 2023, which vest over a two-year period, and in 2022, which vest over a four-year period. The following table summarizes the Company's restricted stock unit activity:


	Shares			Weighted average grant date fair value
Unvested as of December 31, 2022		10,000		$	35.86
Issued		512,000			11.55
Vested		(4,375	)		35.86
Cancelled		—			—
Unvested as of December 31, 2023		517,625		$	11.81

The restricted stock units granted in 2023 cliff vest 100% on the second anniversary of the grant date. The restricted stock units granted in 2022 cliff vested 25% on the anniversary of the grant date. The remainder of these units will vest in quarterly increments over the remaining three years of the vesting period. 4,375 restricted stock units had vested as of December 31, 2023. As of December 31, 2023, there was $5.2 million of unrecognized stock-based compensation expense related to restricted stock units that are expected to vest. These costs are expected to be recognized over a weighted-average period of 1.6 years.

Income Taxes - Schedule of Changes to the Unrecognized Tax Benefits (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Beginning Balance	$ 39,200
Increase related to current year tax positions	1,730
Unrecognized Tax Benefits, Ending Balance	$ 40,930

Investment Securities and Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Class Of Warrant Or Right [Line Items]
Transfers within hierarchy	$ 0	$ 0
Accretion on its available-for-sale debt securities	10,200,000	1,800,000
Interest Income \| Money Market Funds
Class Of Warrant Or Right [Line Items]
Total available-for-sale securities, Estimated Fair Value	$ 21,500,000	$ 9,600,000

Income Taxes - Schedule of Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Domestic	$ 3,612	$ 50,750	$ 41,535
Foreign	0	1,334	408
Deferred	0	0	0
Total income tax expense	$ 3,612	$ 52,084	$ 41,943

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Public Utility Property, Plant, and Equipment [Table Text Block]

Property and equipment, including leasehold improvements, are stated at cost and depreciated when placed into service using the straight-line method over the estimated useful lives as follows:


Asset		Estimated Useful Life
Computer equipment and software		3 years
Furniture, fixtures and other		5 years
Scientific equipment		5 – 6 years
Leasehold improvements		Shorter of useful life or term of lease

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Amortized cost of short-term investments	$ 281,035	$ 281,035
Amortized cost of long-term investments	$ 100,208	$ 100,208
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	35,838,080	35,611,219
Common stock, shares outstanding	35,838,080	35,611,219

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2023	Mar. 01, 2024
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Document Annual Report	true
Document Transition Report	false
Trading Symbol	ITOS
Entity Registrant Name	iTeos Therapeutics, Inc.
Entity Central Index Key	0001808865
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Incorporation, State or Country Code	DE
Entity Shell Company	false
Entity File Number	001-39401
Entity Tax Identification Number	84-3365066
Entity Address Address Line1	321 Arsenal St
Entity Address City Or Town	Watertown
Entity Address State Or Province	MA
Entity Address Postal Zip Code	02472
City Area Code	339
Local Phone Number	217 0162
Entity Common Stock Shares Outstanding		35,843,131
Entity Public Float		$ 380.4
Security12b Title	Common stock, $0.001 par value per share
Security Exchange Name	NASDAQ
ICFR Auditor Attestation Flag	false
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement for its 2023 Annual Meeting of Stockholders to be filed pursuant to Regulation 14A within 120 days of the end of the registrant’s fiscal year ended December 31, 2023 are incorporated by reference into Part III of this Annual Report on Form 10-K to the extent stated herein.
Auditor Name	Deloitte Bedrijfsrevisoren/Réviseurs d’Entreprises BV/SRL
Auditor Location	Zaventem, Belgium
Auditor Firm ID	1133
Document Financial Statement Error Correction [Flag]	false

Investment Securities and Fair Value Measurements - Schedule of Investments Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Due in one year or less, Amortized Cost	$ 281,035	$ 328,405
Due after one year through five years, Amortized Cost	100,208	118,330
In one year or less, Estimated Fair Value	280,739	328,359
Due after one year through five years, fair value	100,539	118,225
Amortized Cost	381,243	446,735
Total available-for-sale securities, Estimated Fair Value	$ 381,278	$ 446,584

License and Collaboration Agreements

12 Months Ended

Dec. 31, 2023

License Agreements [Abstract]

License and collaboration agreements

Note 5. License and collaboration agreements

Adimab

In January 2017, the Company entered into a collaboration agreement (as amended, the Adimab Agreement) with Adimab, LLC (Adimab). Adimab has developed an antibody discovery and optimization technology platform. This collaboration enables the Company’s research and development efforts on discovery and optimization of new antibodies against immuno-oncology targets the Company may identify.

Under the terms of the Adimab Agreement, Adimab has granted the Company a worldwide, non-exclusive research license for a one-year research term period and evaluation period for up to 18 months per research program. The Company is required to use commercially reasonable efforts to perform its research activities under the Adimab Agreement and, if the Company exercises its right to obtain a development and commercialization license, the Company is required to use commercially reasonable efforts to pursue development and commercialization of a product directed to the applicable target. Under the terms of the Adimab Agreement, the Company granted Adimab a worldwide, non-exclusive license under all of its patents and know-how that are reasonably necessary or useful for Adimab to perform its research activities under the Adimab Agreement.

In February 2021, the Company entered into an amendment to the Adimab Agreement (the Amended Adimab Agreement). The Amended Adimab Agreement specifies different milestone payments for new products that are derived from research programs beginning after February 22, 2021 (the New Products). For New Products, on a per target basis, the Company may be required to pay development, regulatory and commercial milestone payments totaling up to an aggregate of $45.8 million for the first three products and additional milestone payments up to $14.5 million for each additional product.

The Company will pay Adimab low to mid single-digit percentage royalties on a country-by-country and product-by-product basis, on worldwide net product sales of licensed products. Royalties are payable on a licensed product-by-licensed product and country-by-country basis until the later of (i) expiration of the last valid claim of a licensed patent right that covers such licensed product in such country, and (ii) ten years following the first commercial sale of such licensed product in such country.

Through December 31, 2023, the Company has paid a total of $5.4 million to Adimab under the Adimab Agreement. In 2022, the Company made a payment of $2.0 million due to reaching an additional milestone (dosing of first patient for Phase 2 clinical trial). In the fourth quarter of 2023, the Company obtained an exclusive

licensing option from Adimab and incurred a $1.0 million option fee. The accrual for this fee payment was recorded to accrued expenses and other current liabilities as of December 31, 2023.

Adimab controls the filing, prosecution, maintenance and enforcement of the intellectual property that it licenses to the Company under the Adimab Agreement. The Company has the right to enforce such licensed intellectual property against infringement if the infringement is competitive with the Company’s licensed products and Adimab does not pursue enforcement. The Company controls the filing, prosecution, maintenance and enforcement of the intellectual property the Company licenses to Adimab under the Adimab Agreement and all program antibody patents.

The term of the Adimab Agreement will continue until the last to expire royalty term on a product-by-product and country-by-country basis if the Company exercises its option, or in the event no option is exercised, the conclusion of the last-to-expire evaluation term, unless terminated earlier by either party. Each party has the right to terminate the Adimab Agreement due to the other party’s uncured material breach or the Company’s abandonment of the product.

GlaxoSmithKline (GSK)

Summary of Agreement

On June 11, 2021, the Company’s wholly owned subsidiary, iTeos Belgium S.A., and GSK executed a Collaboration and License Agreement, or the GSK Collaboration Agreement, pursuant to which the Company agreed to grant GSK a license under certain of the Company’s intellectual property rights to develop, manufacture, and commercialize products comprised of or containing the Company’s antibody product, belrestotug. Under the GSK Collaboration Agreement, GSK agreed to make an upfront nonrefundable payment of $625.0 million to the Company within 10 business days of the date on which the GSK Collaboration Agreement became effective, which occurred on July 26, 2021. Additionally, the Company is eligible to receive up to $1.45 billion in milestone payments, contingent upon the belrestotug program achieving certain development and commercial milestones. Within the collaboration, GSK and the Company agree to share responsibility and costs for the global development of belrestotug beyond the Phase 1 study (the "Global Development Plan") and will jointly commercialize and equally split profits in the United States. Outside of the United States, GSK will receive an exclusive license for commercialization, and the Company is eligible to receive tiered double digit royalty payments up to 20% during a customary royalty term.

Collaboration

The Company concluded that the GSK Collaboration Agreement is under the scope of ASC 808 as both parties will actively participate in a joint operating activity and are exposed to significant risks and rewards that depend on the activity’s commercial success. ASC 808 provides that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer in the context of a unit of account. In those situations, all of the guidance in ASC 606 should be applied, including recognition, measurement, presentation, and disclosure requirements related to such unit of account. The unit-of-account guidance in ASC 808, which aligns with the guidance in ASC 606 (that is, a distinct good or service) is used when an entity is assessing whether the collaborative arrangement or a part of the arrangement is within the scope of ASC 606.

The Company determined that the co-development in Phases 2 and 3 and the co-commercialization efforts of the GSK Collaboration Agreement represent joint operating activities in which both parties are active participants and of which both parties are exposed to significant risks and rewards that are dependent on the success of the activities. Accordingly, the Company is accounting for these activities in accordance with ASC No. 808, Collaborative Arrangements (ASC 808). Additionally, the Company has determined that in the context of these activities, GSK does not represent a customer as contemplated by ASC 606-10-15, Revenue from Contracts with Customers – Scope and Scope Exceptions. As a result, these activities are accounted for as a component of the related expense in the period incurred in accordance with ASC 730, Research and Development. Additionally, reimbursements received from GSK in connection with the joint operating activities are recognized as a reduction to research and development expense.

GSK is responsible for 60% of the costs related to the Global Development Plan. During the year ended December 31, 2023, the Company recorded to research and development expense $39.6 million related to the cost-sharing provisions of the GSK Collaboration Agreement. $0.4 million of these costs are payable to GSK, and were recorded in accrued expenses and other current liabilities in the condensed consolidated balance sheet as of December 31, 2023. The Company and GSK have collectively agreed to spend an aggregate of $900.0 million on the Global Development Plan.

Revenue Recognition

The Company also evaluated the elements of the GSK Collaboration Agreement in accordance with the provisions of ASC 606 and concluded that the contract counterparty, GSK, is a customer. The Company’s

arrangement with GSK contains the following material promises under the contract at inception: (i) transfer of the license under certain of the Company’s intellectual property related to belrestotug, (ii) completion of the Phase 1 clinical study related to belrestotug, (iii) transfer of “Know How” under the belrestotug intellectual property, and (iv) manufacturing until the “Know How” transfer is complete. The Company evaluated the above material promises under ASC 606 and determined that it has one combined performance obligation. These promises are considered to be outputs of the Company's ordinary activities and ongoing major operations. As GSK provided the Company consideration in exchange for these promises, GSK meets the definition of a customer under ASC 606-10-20 in the context of the combined performance obligation. These promises are distinct from the co-development and co-commercialization activities in which the Company and GSK jointly participate. Accordingly, the context in which GSK is a customer is limited to the material promises described above.

The transaction price totaling $625.0 million was comprised of the upfront license payment. As of December 31, 2023, no development or regulatory milestones have been assessed as probable of being reached and thus have been fully constrained. As part of its evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensee’s efforts. Any consideration related to sales-based milestones will be recognized when the related sales occur as they were determined to relate predominantly to the license granted to GSK and therefore have also been excluded from the transaction price. The Company is applying the royalty exception for sales-based royalties and will not recognize revenue until the subsequent sale of product occurs.

The transaction price is being recognized as revenue over time as the costs to complete the Phase 1 study, perform interim clinical supply manufacturing, and perform the know-how transfer are incurred. The combined performance obligation was fully completed in early 2023. Revenue was recognized using a percent complete method based on costs incurred compared with the total expected costs to be incurred (cost to cost measure of progress). As a result, an input method was appropriate. A cost to cost measure of progress provides a faithful depiction of the transfer of services to the customer since the predominant inputs to the performance obligation are labor costs, research and development supplies and manufacturing supplies related to the Phase 1 Study, clinical manufacturing and know-how transfer.

During the year ended December 31, 2023, the Company recognized revenue totaling $12.6 million with respect to the GSK Collaboration Agreement. The revenue is classified as license and collaboration revenue in the accompanying consolidated statements of operations. As of December 31, 2023, there was no deferred revenue related to the GSK Collaboration Agreement recorded in the balance sheet as all revenue had been recognized in 2023.

Contract Costs

The Company incurred $6.8 million of capitalizable costs to obtain the contract. The Company utilized the practical expedient in ASC 340 and recognized such costs immediately in 2021 as the Company expected to complete its performance obligations under the GSK Collaboration Agreement in less than 12 months.

Contract Assets and Liabilities

The following table presents changes in the Company’s GSK contract assets and liabilities during the year ended December 31, 2023:


Year Ended December 31, 2023
(in thousands)	Balance at Beginning of Year		Additions		Deductions			Balance at Year End
Contract liabilities
Deferred revenue	$	12,595	$	—	$	(12,595	)	$	—

MSD International GmbH

On December 10, 2019, the Company entered into a Clinical Trial Collaboration and Supply Agreement (the MSD Agreement) with MSD International GmbH (MSD), a subsidiary of Merck & Co., Inc. Under the MSD Agreement, the Company will sponsor a clinical trial in which both the Company’s compound and MSD’s compound will be dosed in combination. The Company will conduct the research at its own cost and MSD will contribute its compound towards the study at no cost to the Company. The parties will equally own the clinical data and inventions from the study, with the exception of inventions relating solely to each party’s compound class. The MSD Agreement will expire upon the delivery of a written report on the results of the study, unless earlier terminated or agreed by the parties.

The Company began receiving compounds from MSD on April 1, 2020 and the Company began the research study in the third quarter of 2020. The terms of the MSD Agreement meet the criteria under ASC 808, as both parties are active participants in the activity and are exposed to the risks and rewards dependent on the commercial success of the activity. ASC 808 does not provide guidance on how to account for the activities under the collaboration, and the Company determined that neither party met the definition of a customer under ASC 606, Revenue from Contracts with Customers. Accordingly, the Company considered other guidance to determine the accounting for the respective elements of the arrangement. The Company accounted for the collaboration activities by analogy to ASC Topic 845, Nonmonetary Transactions, and recognized nonmonetary income with an offsetting entry to expense for amounts received from MSD within research and development expense in the consolidated statement of operations and comprehensive income.

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Contingency [Line Items]
Effective income tax rate reconciliation, percent	(3.30%)	35.00%	16.40%
Effective income tax rate reconciliation, at federal statutory income tax rate, percent	21.00%	21.00%	21.00%
Increase in valuation allowance	$ 29,000
Deferred tax assets valuation allowance	74,398	$ 45,421
Net operating loss Carry forwards deductible at maximum rate of corporations taxable income				80.00%
Foreign	(38,858)	221,676	$ 303,706
U.S. Federal NOL carryforwards	8,500
Unrecognized tax benefits	40,930	39,200
Income tax expense benefit	3,612	52,084	$ 41,943
Unrecognized tax benefits income tax interest accrued	$ 1,700	$ 2,200
Federal
Income Tax Contingency [Line Items]
Operating loss carryforwards expiration year	2043
State
Income Tax Contingency [Line Items]
Operating loss carryforwards expiration year	2043
Gosselies, Belgium
Income Tax Contingency [Line Items]
Foreign	$ 64,100

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Stock Options Activity

The following table summarizes stock option activity for the year ended December 31, 2023:


	Stock Options
	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (in years)		Aggregate Intrinsic Value (In thousands)
Outstanding as of December 31, 2022		6,401,987		$	18.50		7.1
Granted		2,324,597			15.25
Exercised		(184,937	)		3.92
Forfeited		(271,427	)		24.14
Outstanding as of December 31, 2023		8,270,220		$	17.73		6.5	$	16,299
Vested and expected to vest as of December 31, 2023		8,270,220		$	17.73		6.5	$	16,299
Exercisable at December 31, 2023		4,746,431		$	16.01		5.3	$	14,859

Summary of Stock-Based Compensation Expense

The following table summarizes stock-based compensation expense, and also the allocation within the consolidated statements of operations and comprehensive income (loss):


	Year Ended December 31,
(in thousands)	2023		2022		2021
Research and development	$	6,619	$	4,152	$	1,906
General and administrative		20,402		17,409		11,888
Total stock-based compensation expense	$	27,021	$	21,561	$	13,794

Schedule of Fair Value Assumptions for Stock Options Granted

The following table summarizes the range of key assumptions used to determine the fair value of stock options and ESPP awards granted during:


	Year Ended December 31,
	2023			2022			2021
Stock Options:
Risk-free interest rate	3.46% - 4.73%			1.37% - 4.23%			0.42% - 1.27%
Expected term (in years)	5.5 - 6			5.5 - 6				6
Expected volatility	82% - 96%			86% - 94%			92% - 100%
Expected dividend yield	0				0	%	0%
Estimated fair value of common stock	$9.76 - $21.15			$17.50 - $46.56			$20.54 - $46.68
ESPP Awards:
Risk-free interest rate	1.63% - 5.44%				1.63	%		-
Expected term (in years)	0.5				0.5			-
Expected volatility	77% - 95%				81	%		-
Expected dividend yield		0	%		0	%		-
Estimated fair value of common stock	$15.85 - $20.92			$17.30				-

Schedule of Restricted Stock Unit Activity

The following table summarizes the Company's restricted stock unit activity:


	Shares			Weighted average grant date fair value
Unvested as of December 31, 2022		10,000		$	35.86
Issued		512,000			11.55
Vested		(4,375	)		35.86
Cancelled		—			—
Unvested as of December 31, 2023		517,625		$	11.81

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pay vs Performance Disclosure
Net Income (Loss)	$ (112,642)	$ 96,652	$ 214,521

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Consolidated Balance Sheet Components

12 Months Ended

Dec. 31, 2023

Supplemental Balance Sheet Information [Abstract]

Consolidated Balance Sheet Components

Note 4. Consolidated balance sheet components

Property and equipment

Property and equipment, net consisted of the following:


	December 31,
(in thousands)	2023			2022
Scientific equipment	$	3,434		$	3,008
Furniture & office equipment		1,467			1,332
Leasehold improvements		4,177			1,238
Total		9,078			5,578
Accumulated depreciation and amortization		(4,382	)		(3,457	)
Property & equipment, net	$	4,696		$	2,121

Depreciation and amortization expense was $0.9 million, $0.8 million and $0.6 million for the years ended December 31, 2023, 2022 and 2021, respectively.

Accrued expenses and other current liabilities

Accrued liabilities consisted of the following:


	December 31,
(in thousands)	2023		2022
Accrued clinical trial costs	$	6,956	$	13,496
Accrued professional fees and other		102		596
Total accrued expenses and other current liabilities	$	7,058	$	14,092

Government Grant Funding and Potential Repayment Commitments Under Recoverable Cash Advance Grants (RCAs) (Tables)

12 Months Ended

Dec. 31, 2023

Research and Development Arrangement with Federal Government [Abstract]

Schedule of Activity for Grant Programs

The following table reflects activity for grant programs for the years ended December 31, 2023, 2022 and 2021 and end of year balances as of December 31, 2023, 2022 and 2021:


	RCA -1						RCA-2						Other Grants						Total
(In thousands)	2023		2022		2021		2023		2022		2021		2023		2022		2021		2023		2022		2021
Cash received	$	—	$	2,244	$	1,990	$	—	$	1,520		585	$	4,419	$	2,497	$	592	$	4,419	$	6,261	$	3,167
Grant income recognized		—		364		4,113		—		478		1,286		2,687		1,249		4,782		2,687		2,091	$	10,181
Grants receivable		—		5		1,832		—		—		1,097		—		996		1,093		—		1,001	$	4,022
Grants repayable		5,496		5,665		5,278		1,317		1,312		886		—		—		—		6,813		6,977	$	6,164

Related Party Transactions - Additional Information (Details)		12 Months Ended
	Jun. 11, 2018 Investor	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Related Party Transaction [Line Items]
Net product sales		$ 12,595,000	$ 267,630,000	$ 344,775,000
Royalty Transfer Agreement
Related Party Transaction [Line Items]
Royalty owed to charitable foundation		$ 0	0	0
Royalty Transfer Agreement \| MPM Oncology Charitable Foundation, Inc. and UBS Optimus Foundation
Related Party Transaction [Line Items]
Number of investors \| Investor	2
Obligation to pay royalties		royalty equal to 1% of its net product sales on any product developed or owned by iTeos Therapeutics, Inc. or iTeos Belgium S.A., each year within 120 days following each year end.
Percentage of royalty required to pay	1.00%
Royalty Transfer Agreement \| Product
Related Party Transaction [Line Items]
Net product sales		$ 0	$ 0	$ 0

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

+ Details

Stock-Based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Jul. 15, 2020	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2024
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage upon sale		25.00%
Stock options vesting period		36 months
Stock-based compensation expense		$ 27,021	$ 21,561	$ 13,794
Weighted-average estimated fair value of options awarded (in dollars per share)		$ 11.6	$ 23.94	$ 27.46
Aggregate intrinsic value of options exercise		$ 2,200	$ 3,200	$ 11,000
Aggregate grant date fair value of stock options vested		$ 28,100	$ 20,400	$ 10,700
2020 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		612,642			0
Percentage of outstanding shares increase in shares reserved for issuance	1.00%
Maximum increase in common stock shares reserved for issuance	634,969
Stock Issued under Employee Stock Purchase Plans		37,549
Percentage of purchase price to fair market value		85.00%
Estimated weighted-average fair value of issued shares		$ 7.19
Share based compensation, weighted-average price per share		$ 10.91
Non Vested Stock Awards
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized compensation costs for non-vested stock awards		$ 46,700
Recognition period for compensation cost not yet recognized (in years, months, and days)		2 years 8 months 12 days
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 1,000
Unrecognized compensation costs for non-vested stock awards		$ 5,200
Recognition period for compensation cost not yet recognized (in years, months, and days)		1 year 7 months 6 days
Restricted stock units vested		100.00%	25.00%
Retricted stock units		4,375
Unvested units, remaining contractual term		3 years
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 25,800
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term				6 years
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense		$ 200
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term		6 months	6 months
2019 Stock Option And Grant Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of options authorized		3,464,316
Stock options issued during period		0
Amendment to 2019 Stock Option and Grant Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage upon sale	100.00%
2020 Stock Option and Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for future issuance		9,115,915
Cumulative increase in common stock reserve for issuance, percentage	5.00%
Cumulative increase in common stock reserve for issuance					1,791,904
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation, stock options expiry period		7 years
Minimum \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term		5 years 6 months	5 years 6 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation, stock options expiry period		10 years
Maximum \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-Based Compensation Arrangement by Share-Based Payment Award, Fair Value Assumptions, Expected Term		6 years	6 years

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule of Income Before Income Tax Expense

For financial reporting purposes, income before income tax expense for the years ended December 31, 2023, 2022 and 2021 consisted of the following:


(in thousands)	2023			2022			2021
Domestic	$	(70,172	)	$	(72,940	)	$	(47,242	)
Foreign		(38,858	)		221,676			303,706
(Loss) income before income tax expense	$	(109,030	)	$	148,736		$	256,464

Schedule of Reconciliation of Income Tax Expense (Benefit) Computed at the Statutory Federal Income Tax Rate

The reconciliation of the statutory U.S. federal income tax rate (21%) to the effective income tax rate is as follows:


		2023			2022			2021
U.S. statutory federal income tax rate		21.0	%		21.0	%		21.0	%
State income taxes	4.9			(2.2)			(0.5)
Foreign tax differential	1.2			5.2			4.7
Non-deductible/non-taxable permanent differences	(0.1)			0.1			0.1
Innovation income deduction tax exemption	0			(33.4)				(28.2	)
Net GILTI Inclusion Income	(0.1)			18.9			15.2
Subpart F income	(1.8)			0			0
Unrecognized tax benefits	(1.6)			14.9				6.6
Other	(1.2)			(3.0)			(1.1)
Change in valuation allowance	(25.6)			13.5			(1.4)
Effective income tax rate	(3.3)%				35.0	%		16.4	%

Schedule of Components of Income Tax Expense

The components of income tax expense for the years ended December 31, 2023, 2022 and 2021 consisted of the following:


(in thousands)	2023		2022		2021
Current
Domestic	$	3,612	$	50,750	$	41,535
Foreign		—		1,334		408
Deferred		—		—		—
Total income tax expense	$	3,612	$	52,084	$	41,943

Schedule of Significant Components of the Company Deferred Tax Assets and Lliabilities

The significant components of the Company’s deferred tax assets and liabilities are comprised of the following:


	December 31,
(in thousands)	2023			2022
Deferred tax assets :
Net operating loss carryforward	$	21,796		$	13,359
Foreign research and development expenses		17,980			12,355
Section 174 capitalized research and development expenses		27,913			14,856
Stock-based compensation		5,002			3,860
Operating lease liabilities		1,539			1,201
Accrued vacation and bonus		846			552
Other		1,164			932
Total deferred tax assets		76,240			47,115
Valuation allowance		(74,398	)		(45,421	)
Deferred tax assets, net of valuation allowance		1,842			1,694
Deferred tax liabilities:
Operating lease right of use assets		(1,534	)		(1,196	)
Prepaid expenses		(243	)		(394	)
Depreciation and amortization		(65	)		(104	)
Total deferred tax liabilities		(1,842	)		(1,694	)
Deferred tax assets and liabilities, net of valuation allowance	$	—		$	—

Schedule of Changes to the Unrecognized Tax Benefits

The changes to the unrecognized tax benefits during the year ended December 31, 2023 were as follows:


(in thousands)
Balance at December 31, 2022	$	39,200
Increase related to current year tax positions		1,730
Balance at December 31, 2023	$	40,930

Related party transactions	12 Months Ended
Related party transactions	Dec. 31, 2023
Related Party Transactions [Abstract]
Related Party Transactions	Note 12. Related party transactions On June 11, 2018, the Company entered into a Royalty Transfer Agreement with the charitable foundations of two of its investors (MPM Oncology Charitable Foundation, Inc. and UBS Optimus Foundation), which requires it to pay a royalty equal to 1% of its net product sales on any product developed or owned by iTeos Therapeutics, Inc. or iTeos Belgium S.A., each year within 120 days following each year end. Such agreement was entered into as a result of the capital contributions received from the investors. As the Company had no product sales in 2023, 2022 or 2021, no royalties were owed to these charitable foundations as of December 31, 2023, 2022 or 2021.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Stock-Based Compensation - Summary of Stock Options Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Shares
Outstanding as of December 31, 2022	6,401,987
Granted	2,324,597
Exercised	(184,937)
Forfeited	(271,427)
Outstanding as of December 31, 2023	8,270,220	6,401,987
Vested and expected to vest as of December 31, 2023	8,270,220
Exercisable at December 31, 2023	4,746,431
Weighted-Average Exercise Price Per Share
Outstanding as of December 31, 2022	$ 18.5
Granted	15.25
Exercised	3.92
Forfeited	24.14
Outstanding as of December 31, 2023	17.73	$ 18.5
Vested and expected to vest as of December 31, 2023	17.73
Exercisable at December 31, 2023	$ 16.01
Weighted-Average Remaining Contractual Term
Options outstanding	6 years 6 months	7 years 1 month 6 days
Vested and expected to vest as of December 31, 2023	6 years 6 months
Exercisable at December 31, 2023	5 years 3 months 18 days
Aggregate Intrinsic Value
Outstanding as of December 31, 2023	$ 16,299
Vested and expected to vest as of December 31, 2023	16,299
Exercisable at December 31, 2023	$ 14,859

Stock-Based Compensation - Schedule of Fair Value Assumptions for Stock Options Granted (Details) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	3.46%	1.37%	0.42%
Risk-free interest rate, maximum	4.73%	4.23%	1.27%
Expected term (in years)			6 years
Expected Volatility, minimum	82.00%	86.00%	92.00%
Expected Volatility, maximum	96.00%	94.00%	100.00%
Expected dividend yield	0.00%	0.00%	0.00%
ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate		1.63%	0.00%
Risk-free interest rate, minimum	1.63%
Risk-free interest rate, maximum	5.44%
Expected term (in years)	6 months	6 months
Expected volatility		81.00%	0.00%
Expected Volatility, minimum	77.00%
Expected Volatility, maximum	95.00%
Expected dividend yield	0.00%	0.00%	0.00%
Estimated fair value of common stock		$ 17.3	$ 0
Minimum \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months
Estimated fair value of common stock	$ 9.76	$ 17.5	20.54
Minimum \| ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated fair value of common stock	$ 15.85
Maximum \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years	6 years
Estimated fair value of common stock	$ 21.15	$ 46.56	$ 46.68
Maximum \| ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Estimated fair value of common stock	$ 20.92

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Schedule Of Lease Terms And Discount Rate

The following table summarizes lease terms and discount rate:


	December 31,
	2023
Weighted-average remaining lease term (years)		4.6
Weighted-average discount rate		4.75	%

Schedule Of Cash Flow And Other Information

The following table summarizes the cash flow and other information:


	Year ended December 31,
(in thousands)	2023
Operating lease liabilities arising from obtaining right-of-use assets (non-cash)	$	2,155
Operating cash flows used in operating leases	$	1,201

Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases

As of December 31, 2023, the Company had the following future minimum lease payments under non-cancelable operating leases for the future years thereafter (in thousands):


Year ending December 31:
2024	$	1,500
2025		1,468
2026		1,435
2027		941
2028		764
Thereafter		590
Total Lease Payments		6,698
Less: Interest		(640	)
Total Lease Liability	$	6,058
Lease liabilities - current	$	1,251
Lease liabilities, net of current portion	$	4,807

Consolidated Balance Components - Schedule of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued clinical trial costs	$ 6,956	$ 13,496
Accrued professional fees and other	102	596
Total accrued expenses and other current liabilities	$ 7,058	$ 14,092

Net income (loss) per share attributable to common stockholders (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Schedule of Net Income Per Shares By Treasury Stock Method

The following table summarizes the impact of the treasury stock method:


Net (loss) income per share		December 31,
(in thousands, except per share amounts)		2023				2022			2021
Numerator
Net (loss) income attributable to common stockholders	$		(112,642	)	$		96,652	$		214,521
Denominator
Weighted-average shares used to compute net (loss) income per share, basic			35,763,520				35,552,025			35,181,383
Effect of dilutive securities (a)			—				2,214,482			2,593,407
Weighted-average shares used to compute net (loss) income per share, diluted			35,763,520				37,766,507			37,774,790
Net (loss) income per share:
Basic	$		(3.15	)	$		2.72	$		6.10
Diluted	$		(3.15	)	$		2.56	$		5.68

(a) The common stock equivalents, which equaled 1,692,558 stock awards outstanding as of December 31, 2023, were excluded for the year ending December 31, 2023, due to their anti-dilutive effect.

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 27,021	$ 21,561	$ 13,794
Research and Development Expenses
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	6,619	4,152	1,906
General And Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 20,402	$ 17,409	$ 11,888

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-1D

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-3

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(01)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(02)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(02)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(03)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (e)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 26: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 27: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(iv)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 28: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (f)(2)(v)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Consolidated Balance Sheet Components - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Supplemental Balance Sheet Information [Abstract]
Depreciation and amortization	$ 898	$ 803	$ 603

Net income (loss) per share attributable to common stockholders - Additional Informatiion (Details)	Dec. 31, 2023 shares
stock awards outstanding	1,692,558