0001628280-23-038334 | 10-Q | XBRL Viewer

Print Document View Excel Document

License, Collaboration, and Funding Agreements	9 Months Ended
License, Collaboration, and Funding Agreements	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License, Collaboration, and Funding Agreements	LICENSE, COLLABORATION AND FUNDING AGREEMENTS Research and Development Incentive Program The Company participates in a research and development incentive program provided by the Austrian government whereby the Company is entitled to reimbursement by the Austrian government for a percentage of qualifying research and development expenses and capital expenditures incurred by the Company’s subsidiary in Austria. As of September 30, 2023, the amount due under the program is $0.4 million, which amount is included in research and development incentive receivable in the condensed consolidated balance sheet. During each of the nine months ended September 30, 2023 and 2022, the Company recorded $0.4 million of income related to the program within the condensed consolidated statements of operations as other income. License and Collaboration Agreements In July 2014, the Company entered into a license agreement with Genzyme (the “Genzyme Agreement”) pursuant to which the Company was granted an exclusive license to certain patents and intellectual property owned or controlled by Genzyme related to the CXCR4 receptor to develop and commercialize products containing licensed compounds (including but not limited to mavorixafor) for all therapeutic, prophylactic and diagnostic uses, with the exception of autologous and allogenic human stem cell therapy. Under the terms of the Genzyme Agreement, the Company is obligated to use commercially reasonable efforts to develop and commercialize licensed products for use in the field in the United States and at least one other major market country. The Company is obligated to pay Genzyme milestone payments in the aggregate amount of up to $25.0 million, contingent upon the achievement by the Company of certain clinical-stage regulatory and sales milestones with respect to licensed products. During the nine months ended September 30, 2023, the Company accrued $5.0 million related to a development milestone under the Genzyme Agreement as the Company believes that it is probable under ASC Topic 450, Contingencies, that the milestone will be achieved. The milestone was achieved on October 30, 2023. The $5.0 million accrued payment has been recorded within research and development expense on the condensed consolidated statements of operations. An additional $7.0 million of regulatory milestone payments are not yet probable but are reasonably possible of becoming payable with the next eight to nine month period under the Genzyme Agreement. The Company is also obligated to pay Genzyme tiered royalties based on net sales of licensed products that the Company commercializes under the agreement. Gain on Sale of Non-Financial Asset During the nine months ended September 30, 2022, a third party, who had previously acquired rights to certain intellectual property from the Company, terminated the arrangement and transferred these rights back to the Company. During the nine months ended September 30, 2022, the Company transferred these rights to another third party in return for $0.5 million. The Company has no continuing involvement in any ongoing research and development activities associated with the intellectual property. The Company concluded that these third parties are "non-customers" as the underlying intellectual property transferred to and from these third parties supports potential drug candidates that are not aligned with the Company's strategic focus and, therefore, are not an output of the Company's ordinary activities. Accordingly, the Company accounted for the sale of the intellectual property as the sale of a non-financial asset under ASC Topic 610-20, Gains and Losses from the Derecognition of Nonfinancial Assets ("ASC 610-20"), and included the gain in gain on sale of non-financial asset for the nine months ended September 30, 2022. There were no material modifications of the Company’s license or collaboration agreements during the nine months ended September 30, 2023.

Net Loss per Share - Summary of Basic and Diluted Net loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator:
Net loss	$ (2,305)	$ (55,712)	$ (24,020)	$ (21,586)	$ (21,212)	$ (21,965)	$ (82,037)	$ (64,763)
Dividends, Paid-in-kind	0			(287)			0	(2,546)
Net loss attributable to common stockholders	$ (2,305)			$ (21,873)			$ (82,037)	$ (67,309)
Denominator:
Weighted average shares of common stock outstanding—basic	196,988,000			83,211,000			170,751,000	50,976,000
Weighted average shares of common stock outstanding—diluted	196,988,000			83,211,000			170,751,000	50,976,000
Net loss per share attributable to common stockholders—basic	$ (0.01)			$ (0.26)			$ (0.48)	$ (1.32)
Net loss per share attributable to common stockholders—diluted	$ (0.01)			$ (0.26)			$ (0.48)	$ (1.32)

- 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

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, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

+ 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 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 3: 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 4: 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 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 6.B)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483621/220-10-S99-5

Reference 6: 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 7: 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 8: 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 9: 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 10: 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 11: 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 12: 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 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-11

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 260
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 60B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482689/260-10-45-60B

+ Details

Leases - Schedule of Components of Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Leases [Abstract]
Fixed operating lease cost	$ 518	$ 507	$ 1,561	$ 1,561
Total lease expense	518	507	1,561	1,561
Operating cash flows from operating leases	345	334	1,037	1,014
Sublease income	$ 49	$ 49	$ 97	$ 147
Weighted-average remaining lease term-operating leases (in years)	3 years 4 months 24 days		3 years 4 months 24 days
Weighted-average discount rate-operating leases	11.50%		11.50%

Fair Value of Financial Assets and Liabilities - Narrative (Details)	Sep. 30, 2023 USD ($)
Measurement Input, Discount Rate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	$ 0.14

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-6

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-6

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-6

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-6

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04(9)(e))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479617/946-210-S99-1

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5C
-Subparagraph (SX 210.12-13C(Column H)(Footnote 7))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-5C

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04(9)(b))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479617/946-210-S99-1

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04(9)(d))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479617/946-210-S99-1

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5
-Subparagraph (SX 210.12-13(Column G)(Footnote 8))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-5

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5C
-Subparagraph (SX 210.12-13C(Column H))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-5C

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5
-Subparagraph (SX 210.12-13(Column G))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-5

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5A
-Subparagraph (SX 210.12-13A(Column E))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-5A

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5B
-Subparagraph (SX 210.12-13B(Column E))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-5B

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5B
-Subparagraph (SX 210.12-13B(Column E)(Footnote 4))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-5B

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483466/210-20-50-3

Reference 22: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483444/210-20-55-22

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483444/210-20-55-10

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482907/825-10-50-10

+ Details

Property and Equipment, Net

9 Months Ended

Sep. 30, 2023

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

PROPERTY AND EQUIPMENT, NET

Property and equipment, net consisted of the following:


(in thousands)	September 30, 2023		December 31, 2022
Leasehold improvements	$	228	$	228
Furniture and fixtures	1,273		1,268
Computer equipment	181		173
Software	24		24
Lab equipment	651		639
	2,357		2,332
Less: Accumulated depreciation and amortization	(1,585)		(1,228)
	$	772	$	1,104

Depreciation and amortization expense related to property and equipment was $357 thousand and $389 thousand for the nine months ended September 30, 2023 and 2022, respectively.

Stock-Based Compensation Summary of Stock-Based Compensation Expense Classification (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 2,361	$ 1,111	$ 6,148	$ 4,092
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	1,259	576	3,210	1,990
Selling, general and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 1,102	$ 535	$ 2,938	$ 2,102

- 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

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Significant Accounting Policies—The Company’s significant accounting policies are disclosed in the audited consolidated financial statements and the notes thereto in the Company’s Annual Report on Form 10-K for the year ended December 31, 2022 filed with the SEC on March 21, 2023. Since the date of those consolidated financial statements, there have been no material changes to the Company’s significant accounting policies.

Cash and Cash Equivalents— The Company considers all highly liquid investments with maturities of 90 days or less at the date of purchase to be cash equivalents. Cash equivalents consisted of money market funds, treasury bills and federal government agency notes as of September 30, 2023 and December 31, 2022.

Marketable Securities— Marketable securities consist of short-term securities classified as available-for-sale having maturities greater than 90 days, but less than 365 days from the date of acquisition. The Company determines the appropriate classification of the securities at the time they are acquired and evaluate the appropriateness of such classifications at each balance sheet date. The Company’s marketable securities consist of available-for-sale securities that are classified as Level 2 because their value is based on valuations using significant inputs derived from, or corroborated by, observable market data. The cost of available-for-sale securities sold is based on the specific-identification method. Unrealized gain and losses on available-for-sale are included as a component of other comprehensive (loss) income on the condensed consolidated balance sheets and condensed consolidated statements of stockholders’ equity and as a component of total comprehensive (loss) income on the condensed consolidated statement of operations and comprehensive loss until realized. Realized gains and losses on the sale of marketable securities are determined using the specific-identification method and recorded in other (expense) income, net on the accompanying condensed consolidated statements of operations and comprehensive loss. The Company reviews marketable securities for impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable. Unrealized losses are evaluated for impairment under ASC 326, Financial Instruments - Credit Losses, to determine if the impairment is credit-related or noncredit-related. Credit-related impairment is recognized as an allowance on the condensed consolidated balance sheets with a

corresponding adjustment to earnings, and noncredit-related impairment is recognized in other comprehensive (loss) income, net of taxes. Evidence considered in this assessment includes reasons for the impairment, compliance with our investment policy, the severity of the impairment, collectability of the security, and any adverse conditions specifically related to the security, an industry, or geographic area.

Restricted Cash


(in thousands)	As of September 30, 2023		As of December 31, 2022

Letter of credit security: Waltham lease	$	250	$	250
Letter of credit security: Vienna Austria lease	202		205
Letter of credit security: Boston lease	571		855
Total restricted cash	$	1,023	$	1,310
Restricted cash included in prepaid expenses and other current assets	$	250	$	285
Restricted cash included in other assets	$	773	$	1,025

In connection with the Company’s lease agreements for its facilities in Massachusetts and Austria, the Company maintains letters of credit, which are secured by restricted cash, for the benefit of the respective landlord.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the condensed consolidated balance sheets to the sum of the total of amounts shown in the Company’s condensed consolidated statements of cash flows as of September 30, 2023 and December 31, 2022:


(in thousands)	September 30, 2023		December 31, 2022
Cash and cash equivalents	$	131,581	$	121,718
Restricted cash, current portion	250		285
Restricted cash, non-current	773		1,025
Total cash, cash equivalents and restricted cash	$	132,604	$	123,028

Goodwill— Goodwill is tested for impairment at the reporting unit level annually in the fourth quarter, or more frequently when events or changes in circumstances indicate that the asset might be impaired. Examples of such events or circumstances include, but are not limited to, a significant adverse change in legal or business climate, an adverse regulatory action or unanticipated competition. The Company has determined that it operates in a single operating segment and has a single reporting unit.

The Company assesses qualitative factors to determine whether the existence of events or circumstances would indicate that it is more likely than not that the fair value of the reporting unit is less than its carrying amount. If after assessing the totality of events or circumstances, the Company were to determine that it is more likely than not that the fair value of the reporting unit is less than its carrying amount, then the Company would perform an interim quantitative impairment test, whereby the Company compares the fair value of the reporting unit to its carrying value. If the fair value of the reporting unit exceeds the carrying value of its net assets, goodwill is not impaired, and no further testing is required. If the fair value of the reporting unit is less than its carrying value, the Company measures the amount of impairment loss, if any, as the excess of the carrying value over the fair value of the reporting unit. There were no triggering events during the three months ended September 30, 2023 that necessitated an interim impairment test of goodwill.

Recently Adopted Accounting Standards

In June 2016, the Financial Accounting Standards Board issued ASU 2016-13, Credit Losses (Topic 326) Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), as amended. ASU 2016-13 requires that financial assets measured at amortized cost, such as trade receivables, be presented net of expected credit losses, which may be estimated based on relevant information such as historical experience, current conditions, and future expectation for each pool of similar financial asset. The new guidance requires enhanced disclosures related to trade receivables and associated credit losses. The Company adopted ASU 2016-13 on January 1, 2023. As the Company did not have accounts receivable or marketable securities on its consolidated balance sheet as of the date of adoption, there was no impact to the adoption of ASU 2016-13.

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,357	$ 2,332
Less: Accumulated depreciation and amortization	(1,585)	(1,228)
Property and equipment, net	772	1,104
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	228	228
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,273	1,268
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	181	173
Software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	24	24
Lab equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 651	$ 639

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net loss	$ (82,037)	$ (64,763)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	6,148	4,092
Depreciation and amortization expense	357	389
Non-cash lease expense	1,173	1,104
Accretion of debt discount	681	653
Change in fair value of warrant liability	(743)	0
Other	(46)	255
Changes in operating assets and liabilities:
Prepaid expenses, other current assets and research and development incentive receivable	459	158
Accounts payable	426	(481)
Accrued expenses and other long-term liabilities	5,651	1,305
Lease liabilities	(834)	(721)
Net cash used in operating activities	(68,765)	(58,009)
Cash flows from investing activities:
Payments to Acquire Marketable Securities	(11,025)	0
Sales and maturities of marketable securities	1,000	0
Acquisition of property and equipment	(25)	(69)
Net cash used in investing activities	(10,050)	(69)
Cash flows from financing activities:
Proceeds from Issuance of Common Stock	8,615	70
Employee taxes paid related to net share settlement of vested restricted stock units	0	(12)
Fees paid to amendment loan and security agreement and issuance costs related to the sale of warrants	(631)	(3,300)
Repayments of Secured Debt	(2,064)	(795)
Proceeds from borrowings under loan and security agreement	22,500	0
Proceeds from sale of common stock, warrants and pre-funded warrants, net of issuance costs	59,999	60,623
Net cash provided by financing activities	88,419	56,586
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(28)	(468)
Net increase (decrease) in cash, cash equivalents and restricted cash	9,576	(1,960)
Cash, cash equivalents and restricted cash at beginning of period	123,028	83,108
Cash, cash equivalents and restricted cash at end of period	132,604	81,148
Supplemental Cash Flow Elements [Abstract]
Debt Issuance Costs Incurred During Noncash or Partial Noncash Transaction	$ 0	$ 22

Stock-Based Compensation - Restricted Stock Units (Details) - Restricted Stock Units (RSUs)	9 Months Ended
	Sep. 30, 2023 shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested beginning balance (in shares)	1,680,563
Granted (in shares)	5,064,691
Vested (in shares)	(926,572)
Forfeited (in shares)	(243,843)
Nonvested ending balance (in shares)	5,574,839

Fair Value of Financial Assets and Liabilities

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets and Liabilities

FAIR VALUE OF FINANCIAL ASSETS AND LIABILITIES

The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis and indicate the level of the fair value hierarchy used to determine such fair values:


	Fair Value Measurements as of September 30, 2023 Using:
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents—money market funds	$	98,119	$	—	$	—	$	98,119

Marketable securities— treasury bills, federal government agency notes	—		10,102		—		10,102
	$	98,119	$	10,102	$	—	$	108,221
Liabilities:
Embedded derivative liability	$	—	$	—	$	10	$	10
Class C warrant liability	—		—		22,014		22,014
	$	—	$	—	$	22,024	$	22,024


	Fair Value Measurements as of December 31, 2022 Using:
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents—money market funds	$	70,170	$	2,858	$	—	$	73,028
	$	70,170	$	2,858	$	—	$	73,028
Liabilities:
Embedded derivative liability	$	—	$	—	$	10	$	10
Class C warrant liability	—		—		23,131		23,131
	$	—	$	—	$	23,141	$	23,141

The Company’s cash equivalents consisted of money market funds invested primarily in short term commercial paper, asset- backed securities, certificate of deposits and repurchase agreements. The money market funds were valued based on reported market pricing for the identical assets, which represents a Level 1 measurement, or by using inputs observable in active markets for similar securities, which represents a Level 2 measurement. The Company has an investment portfolio of federal government agency notes and treasury bills. These investments are measured at fair value using Level 2 assumptions.

The following table provides a roll-forward of the aggregate fair values financial instruments for which fair values are determined using Level 3 inputs:


(in thousands)	Embedded Derivative Liability		Class C Warrant Liability		Total
Balance as of December 31, 2022	$	10	$	23,131	$	23,141

Change in fair value	—		(743)		(743)
Reclassification of warrant liability to permanent equity upon exercise	—		(374)		(374)
Balance as of September 30, 2023	$	10	$	22,014	$	22,024

Embedded Derivative Liability— The fair value of the embedded derivative liability recognized in connection with the Company’s loan agreement with Hercules (see Note 7), which is associated with additional fees due to Hercules upon events of default, was determined based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The fair value of this embedded derivative liability, which is reported within other non-current liabilities on the condensed consolidated balance sheets, is estimated by the Company at each reporting date based, in part, on the results of third party valuations, which are prepared based on a discounted cash flow model that considers the timing and

probability of occurrence of a redemption upon an event of default, the potential amount of prepayment fees or contingent interest upon an event of default and the Company’s risk-adjusted discount rate of 14%.

Class C Warrant Liability— In December 2022, the Company issued Class C Warrants for the purchase of shares of its common stock in a public offering of common stock. The Class C Warrants are accounted for as a liability on the condensed consolidated balance sheet and are adjusted to fair value at period end through “other income (expense), net” in the condensed, consolidated statements of operations and comprehensive loss.

The Company calculated the fair value of the Class C Warrants using the Black-Scholes option pricing model, which represents a Level 3 measurement within the fair value hierarchy, with the following inputs:


	September 30, 2023		December 31, 2022
Common stock price	$1.09		$0.99
Risk-free interest rate	4.6	%	4.0	%
Expected term (in years)	4.2		4.9
Expected volatility	91.3	%	101.7	%
Expected dividend yield	—	%	—	%

- 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

Accrued Expenses

9 Months Ended

Sep. 30, 2023

Payables and Accruals [Abstract]

Accrued Expenses

ACCRUED EXPENSESAccrued expenses consisted of the following:


(in thousands)	September 30, 2023		December 31, 2022
Accrued employee compensation and benefits	$	6,067	6,592
Accrued external research and development expenses	8,563		3,906
Accrued professional fees	976		571
Accrued deferred financing fees	—		591
Other	578		374
	$	16,184	$	12,034

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Common stock, par value (in usd per share)	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	164,705,712	121,667,250
Common stock, shares outstanding	164,705,712	121,667,250

Net Loss per Share (Tables)

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

Summary of Basic and Diluted Net Loss per Share Attributable to Common Stockholders

Basic and diluted net loss per share attributable to common stockholders was calculated as follow:


	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands, except per share data)	2023		2022		2023		2022
Numerator:
Net loss	$	(2,305)	$	(21,586)	$	(82,037)	$	(64,763)
Deemed dividend as a result of Class B warrant price reset	—		(287)		—		(2,546)
Net loss attributable to common stockholders	$	(2,305)	$	(21,873)	$	(82,037)	$	(67,309)
Denominator:
Weighted average shares of common stock outstanding—basic and diluted	196,988		83,211		170,751		50,976
Net loss per share attributable to common stockholders— basic and diluted	$	(0.01)	$	(0.26)	$	(0.48)	$	(1.32)

Schedule of Anti-dilutive Securities Excluded from Computation of Diluted Net Loss per Share Attributable to Common Stockholders

The Company excluded the following potential shares of common stock, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:


	Three Months Ended September 30,		Nine Months Ended September 30,
	2023	2022	2023	2022
Options to purchase shares of common stock	5,568,734	1,843,673	5,568,734	1,843,673
Unvested restricted stock units	5,574,839	1,397,789	5,574,839	1,397,789
Warrants to purchase shares of common stock (excluding prefunded warrants, which are included in basic shares outstanding)	80,244,959	60,374,393	80,244,959	60,374,393
	91,388,532	63,615,855	91,388,532	63,615,855

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Accounting Policies [Abstract]
Cash and cash equivalents	$ 131,581	$ 121,718
Restricted cash, current portion	250	285
Restricted cash, non-current	773	1,025
Total cash, cash equivalents and restricted cash	$ 132,604	$ 123,028	$ 81,148	$ 83,108

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK, REDEEMABLE COMMON STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (Parenthetical) $ in Thousands	3 Months Ended
	Jun. 30, 2023 USD ($)
Statement of Stockholders' Equity [Abstract]
Issuance costs
Stock Issued During Period, Value, New Issues	$ 60,443

- Definition

Equity impact of the value of new stock issued during the period. Includes shares issued in an initial public offering or a secondary public offering.

+ References + Details

Commitment and Contingencies	9 Months Ended
Commitment and Contingencies	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Commitment and Contingencies	COMMITMENTS AND CONTINGENCIES The Company has agreements with contract manufacturing organizations (“CMOs”) for the production of mavorixafor for use in clinical trials. The Company’s agreement with the CMO who produces batches of drug substance for use in the Company’s clinical drug supply contains cancellation provisions that would require the Company to pay up to the full contract value upon cancellation. As of September 30, 2023, the Company has approximately $1.8 million of such commitments in place subject to cancellation provisions. Indemnification Agreements— In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company to, among other things, indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnification obligations. The Company is not currently aware of any indemnification claims and has not accrued any liabilities related to such obligations in its condensed consolidated financial statements as of September 30, 2023 or December 31, 2022. Legal Proceedings— The Company is not a party to any litigation and does not have contingency reserves established for any litigation liabilities. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to any legal proceedings.

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Business Acquisition [Line Items]
Cash, Cash Equivalents, and Short-Term Investments	$ 141,700	$ 141,700
Accumulated deficit	(458,775)	(458,775)		$ (376,738)
Net cash used in operating activities	$ (68,800)	$ (68,765)	$ (58,009)

- Definition

Amount of accumulated undistributed earnings (deficit).

+ References + Details

License, Collaboration, and Funding Agreements - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Collaboration License And Funding Arrangements [Line Items]
Other income (expense), net	$ 17,000	$ (441,000)	$ 342,000	$ (440,000)
Gain (Loss) on Disposition of Other Assets	500,000
Research and Development Incentive
Collaboration License And Funding Arrangements [Line Items]
Grant receivable	400,000		400,000
Other income (expense), net	$ 400,000		$ 400,000

Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2023	Nov. 07, 2023
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	001-38295
Entity Registrant Name	X4 PHARMACEUTICALS, INC
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-3181608
Entity Address, Address Line One	61 North Beacon Street
Entity Address, Address Line Two	4th Floor
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02134
City Area Code	857
Local Phone Number	529-8300
Title of 12(b) Security	Common Stock
Trading Symbol	XFOR
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		167,291,209
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001501697
Current Fiscal Year End Date	--12-31

Fair Value of Financial Assets and Liabilities (Tables)

3 Months Ended

9 Months Ended

Sep. 30, 2023

Fair Value Disclosures [Abstract]

Schedule of Assets and Liabilities Measured at Fair Value


	Fair Value Measurements as of September 30, 2023 Using:
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents—money market funds	$	98,119	$	—	$	—	$	98,119

Marketable securities— treasury bills, federal government agency notes	—		10,102		—		10,102
	$	98,119	$	10,102	$	—	$	108,221
Liabilities:
Embedded derivative liability	$	—	$	—	$	10	$	10
Class C warrant liability	—		—		22,014		22,014
	$	—	$	—	$	22,024	$	22,024


	Fair Value Measurements as of December 31, 2022 Using:
(in thousands)	Level 1		Level 2		Level 3		Total
Assets:
Cash equivalents—money market funds	$	70,170	$	2,858	$	—	$	73,028
	$	70,170	$	2,858	$	—	$	73,028
Liabilities:
Embedded derivative liability	$	—	$	—	$	10	$	10
Class C warrant liability	—		—		23,131		23,131
	$	—	$	—	$	23,141	$	23,141

Summary of Aggregate Fair Values of Warrant Liability and Derivative Liability

The following table provides a roll-forward of the aggregate fair values financial instruments for which fair values are determined using Level 3 inputs:


(in thousands)	Embedded Derivative Liability		Class C Warrant Liability		Total
Balance as of December 31, 2022	$	10	$	23,131	$	23,141

Change in fair value	—		(743)		(743)
Reclassification of warrant liability to permanent equity upon exercise	—		(374)		(374)
Balance as of September 30, 2023	$	10	$	22,014	$	22,024

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions


	September 30, 2023		December 31, 2022
Common stock price	$1.09		$0.99
Risk-free interest rate	4.6	%	4.0	%
Expected term (in years)	4.2		4.9
Expected volatility	91.3	%	101.7	%
Expected dividend yield	—	%	—	%

Fair Value of Financial Assets and Liabilities - Fair Value Assumptions (Details) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended		9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (in percentage)			4.20%	3.30%	4.00%	2.40%
Expected term (in years)			6 years 1 month 6 days	6 years 1 month 6 days	6 years	6 years 1 month 6 days
Expected volatility (in percentage)			94.70%	95.70%	93.50%	94.80%
Expected dividend yield (in percentage)			0.00%	0.00%	0.00%	0.00%
Fair value of warrant liability	$ 22,024	$ 23,141	$ 22,024		$ 22,024
Class C Warrant Liability
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Price (in dollars per share)	$ 1.09	$ 0.99	$ 1.09		$ 1.09
Risk-free interest rate (in percentage)	4.60%	4.00%	4.60%
Expected term (in years)	4 years 2 months 12 days	4 years 10 months 24 days	5 years 1 month 9 days
Expected volatility (in percentage)	91.30%	101.70%	97.40%
Expected dividend yield (in percentage)	0.00%	0.00%	0.00%

- 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

+ Details

Common Stock Warrants

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Common Stock Warrants

COMMON STOCK AND COMMON STOCK WARRANTS

As of September 30, 2023, the Company’s Restated Certificate of Incorporation authorized the Company to issue 500 million shares of common stock, par value $0.001 per share. The voting, dividend and liquidation rights of the holders of the Company’s common stock are subject to and qualified by the rights, powers and preferences of the holders of any preferred stock that may be issued. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the board of directors, if any. No cash dividends have been declared or paid to date.

Q2 2023 Private Placement

On May 15, 2023, the Company entered into a securities purchase agreement pursuant to which it agreed to issue and sell to several institutional and accredited investors (the “Investors”), in a private placement (the “Q2 2023 Private Placement”),

34,521,046 shares of common stock at a price of $1.52 per share and pre-funded warrants to purchase 8,263,157 shares of common stock at a purchase price of $1.519 per pre-funded warrant (representing the price of $1.52 per share minus the $0.01 per share exercise price of each such prefunded warrant). The pre-funded warrants are exercisable, subject to certain beneficial ownership restrictions, at any time after their original issuance and will not expire. The Q2 2023 Private Placement closed on May 18, 2023. The Company received gross proceeds of $65.0 million, before deducting offering expenses paid by the Company.

Also on May 15, 2023, the Company entered into a registration rights agreement (the “Registration Rights Agreement”) with the Investors, pursuant to which the Company agreed to register for resale the common shares issued in the Q2 2023 Private Placement and the issuance of the shares of common stock underlying the pre-funded warrants held by the Investors (the “Registrable Securities”). Under the Registration Rights Agreement, the Company agreed to file a registration

statement covering the resale of the Registrable Securities by no later than June 14, 2023. Such registration statement was filed on June 9, 2023 and was declared effective by the SEC on June 20, 2023. The Company has agreed to use commercially reasonable efforts to keep such registration statement effective until the date the shares of common stock sold in the Q2 2023 Private Placement and the shares of common stock underlying the pre-funded warrants covered by such registration statement have been sold or may be resold pursuant to Rule 144 without restriction.

Warrants and Pre-Funded Warrants

In connection with public and private sales of shares of its common stock, the Company has issued warrants and pre-funded warrants, which are exercisable for the purchase shares of the Company’s common stock. All outstanding warrants and pre-funded warrants are currently exercisable and do not have price reset provisions. Upon the closing of these public and private offerings, the Company received approximately 99% of the exercise price for the pre-funded warrants, for which the remaining exercise price is equal to or less than $0.01 per share.

Warrant Exercises

During the nine months ended September 30, 2023, 7,475,814 warrants were exercised and the Company received $8.4 million in proceeds.

As of September 30, 2023, the Company’s outstanding warrants and pre-funded warrants to purchase shares of common stock consisted of the following:


Issuance Date	Number of Shares of Common Stock Issuable	Exercise Price			Expiration Date
October 25, 2016	5,155	$	19.78		October 24, 2026
December 28, 2017	115,916	$	19.78		December 28, 2027
September 12, 2018	20,220	$	19.78		September 12, 2028
October 19, 2018	20,016	$	19.78		October 19, 2028
March 13, 2019	5,000	$	19.78		March 12, 2029
April 16, 2019	3,866,154	$	13.20		April 15, 2024

November 29, 2019	1,250,000	$	12.00	(a)	n/a
March 23, 2021	50,000	$	8.70	(b)	n/a
November 9, 2021	2,008,032	$	4.98	(c)	n/a
March 3, 2022	766,666	$	1.80	(d)	n/a
July 6, 2022	13,276,279	$	1.095	(e)	n/a
July 6, 2022	44,075,050	$	1.095		July 6, 2027
December 9, 2022	32,137,448	$	1.50		December 9, 2027
December 9, 2022	6,800,000	$	1.10	(f)	n/a
May 19, 2023	8,263,157	$	1.52	(g)	n/a
	112,659,093

(a) In November 2019, the Company received $11.999 per pre-funded warrant, or $21.0 million in aggregate proceeds. Each pre-funded

warrant may be exercised for an additional $0.001 per pre-funded warrant. (b) In March 2021, the Company received $8.69 per pre-funded warrant, or $435 thousand in aggregate proceeds. Each pre-funded warrant may be exercised for an additional $0.01 per pre-funded warrant. (c) In November 2021, the Company received $4.97 per pre-funded warrant, or $10.0 million in aggregate proceeds. Each

pre-funded warrant may be exercised for an additional $0.01 per pre-funded warrant. (d) In March 2022, the Company received $1.79 per pre-funded warrant, or $1.4 million in aggregate proceeds. Each pre-funded warrant may be exercised for an additional $0.01 per pre-funded warrant. (e) In July 2022, the Company received $1.094 per pre-funded warrant, or $14.5 million in aggregate proceeds. Each pre-funded warrant may be exercised for an additional $0.001 per pre-funded warrant. (f) In December 2022, the Company received $1.099 per pre-funded warrant, or $7.5 million in aggregate proceeds. (g) In May 2023, the Company received $1.519 per pre-funded warrant, or $12.6 million in aggregate proceeds. Each pre-funded warrant may be exercised for an additional $0.001 per pre-funded warrant.

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXESThe Company did not record a U.S. federal or state income tax benefit for its losses for the nine months ended September 30, 2023 and 2022, due to the conclusion that a full valuation allowance is required against the Company’s U.S. federal and state deferred tax assets. For the nine months ended September 30, 2023 and 2022, the Company recorded an immaterial income tax provision related to its Austrian subsidiary.

- 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

Summary of Significant Accounting Policies - Schedule of Compensating Balance Arrangements (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Cash and Cash Equivalents [Line Items]
Total restricted cash	$ 773	$ 1,025
Restricted Cash	1,023	1,310
Restricted cash, current portion	250	285
Letter of Credit \| Waltham Lease
Cash and Cash Equivalents [Line Items]
Restricted Cash	250	250
Letter of Credit \| Vienna Austria Lease
Cash and Cash Equivalents [Line Items]
Restricted Cash	202	205
Letter of Credit \| Allston Lease Agreement
Cash and Cash Equivalents [Line Items]
Restricted Cash	$ 571	$ 855

Accrued Expenses (Tables)

9 Months Ended

Sep. 30, 2023

Payables and Accruals [Abstract]

Schedule of Accrued Expenses

Accrued expenses consisted of the following:


(in thousands)	September 30, 2023		December 31, 2022
Accrued employee compensation and benefits	$	6,067	6,592
Accrued external research and development expenses	8,563		3,906
Accrued professional fees	976		571
Accrued deferred financing fees	—		591
Other	578		374
	$	16,184	$	12,034

Long-Term Debt (Tables)

9 Months Ended

Sep. 30, 2023

Debt Disclosure [Abstract]

Summary of Long Term Debt

Long-term debt consisted of the following:


(in thousands)	September 30, 2023		December 31, 2022
Principal amount of long-term debt	$	55,000	$	32,500
Debt discount, net of accretion	(1,007)		(196)
Cumulative accretion of end of term payments	329		1,315
Long-term debt	$	54,322	$	33,619
Less: current portion	$	—	$	(1,315)
Long-term debt, net of current portion	$	54,322	$	32,304

Interest Income and Interest Expense Disclosure

The Company recognized interest expense under the Hercules Loan Agreement as follows:


(in thousands)	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Total interest expense	$	1,397	$	1,018	$	3,210	$	2,845
Non-cash interest expense	$	237	$	256	$	681	$	653

Schedule of Future Principal Payments and the Final Payments Due

As of September 30, 2023, future principal and accrued end-of-term payments due under the Hercules Loan Agreement were as follows (in thousands):


Year Ending December 31,	Total
2023	$	—
2024	—
2025	24,720
2026	30,609
Long-term debt	$	55,329

Leases

9 Months Ended

Sep. 30, 2023

Leases [Abstract]

Leases

LEASES

The Company has lease agreements for its facilities in Boston, Massachusetts, which is the Company’s principal executive office; Vienna, Austria, which is the Company’s research and development center; and Waltham, Massachusetts, which the Company has sublet to a third party. There are no restrictions or financial covenants associated with any of the lease agreements.

•Vienna Austria Leases— The Company has an operating lease for approximately 1,200 square meters of laboratory and office space in Vienna, Austria (“Vienna Lease”), which commenced in February 2021 for a term of 7 years. The annual base rent for the Vienna Lease is approximately $285 thousand.

•Boston Lease— The Company leases approximately 28,000 square feet of office space in Boston, Massachusetts (“Boston Lease”), which serves as the Company’s headquarters. Base rental payments are approximately $1.1 million annually, plus certain operating expenses. The term of the Boston Lease will continue until November 2026, unless earlier terminated. The Company has the right to sublease the premises, subject to landlord consent and also has the right to renew the Boston Lease for an additional five years at the then prevailing effective market rental rate. The Company is required to maintain a security deposit in the form of a letter of credit for $0.6 million for the benefit of the landlord.

•Waltham Lease— The Company leases approximately 6,000 square feet of office space in Waltham, Massachusetts (“Waltham Lease”). The Waltham Lease, as amended, commenced on January 1, 2019, and expires on December 31, 2023. The base rent is approximately $0.3 million annually. In addition to the base rent, the Company is also responsible for its share of operating expenses, electricity and real estate taxes, which costs are not included in the determination of the leases’ right-of-use assets or lease liabilities. The Company is subleasing the space to a third party for the duration of the lease. The right-of-use asset is being amortized to rent expense over the five-year term of the lease.

As the Company’s leases do not provide an implicit rate, the Company estimated the incremental borrowing rate in calculating the present value of the lease payments. The Company utilizes its incremental borrowing rates, which are the rates incurred to borrow on a collateralized basis over a similar term and amount equal to the lease payments in a similar economic environment.

The components of lease expense for the three and nine months ended September 30, 2023 and 2022 were as follows:


(dollars in thousands)	Three Months Ended September 30,					Nine Months Ended September 30,
Lease Cost	2023			2022		2023		2022
Fixed operating lease cost	$	518		$	507	$	1,561	$	1,561

Total lease expense	$	518		$	507	$	1,561	$	1,561
Other information

Operating cash flows from operating leases	$	345		$	334	$	1,037	$	1,014
Sublease income	$	49		$	49	$	97	$	147
Weighted-average remaining lease term—operating leases	3.4 years
Weighted-average discount rate—operating leases	11.5		%

Maturities of lease liabilities due under lease agreements that have commenced as of September 30, 2023 are as follows (in thousands)


Maturity of lease liabilities	Operating Leases
2023 (remainder of the year)	$	403
2024	1,370
2025	1,398
2026	1,329
2027	276
Thereafter	46
Total lease payments	4,822
Less: interest	(858)
Total operating lease liabilities as of September 30, 2023	$	3,964

Nature of the Business and Basis of Presentation	9 Months Ended
Nature of the Business and Basis of Presentation	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	NATURE OF THE BUSINESS AND BASIS OF PRESENTATION X4 Pharmaceuticals, Inc. (together with its subsidiaries, the “Company”) is a late-stage clinical biopharmaceutical company discovering and developing novel therapeutics for the treatment of rare diseases and those with limited treatment options, with a focus on conditions resulting from dysfunction of the immune system. The Company’s lead clinical candidate is mavorixafor, a small-molecule antagonist of the chemokine receptor CXCR4 that is being developed as an oral, once-daily therapy. Due to its ability to increase the mobilization of mature, functional white blood cells from the bone marrow into the bloodstream, the Company believes that mavorixafor has the potential to provide therapeutic benefit across a variety of chronic neutropenic disorders and WHIM (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis) syndrome (“WHIM”), a rare, primary immunodeficiency. Following announcement of positive top-line data from the Company’s pivotal, global, Phase 3 clinical trial in November 2022, the Company submitted a New Drug Application (“NDA”) to the U.S. Food and Drug Administration (“FDA”) in August 2023, seeking approval of oral, once-daily mavorixafor in the treatment of people aged 12 years and older with WHIM syndrome. The FDA accepted the NDA on October 30, 2023 for Priority Review, establishing a PDUFA/action date of April 30, 2024. As the Company prepares for a potential launch of mavorixafor for WHIM in the U.S. in the second quarter of 2024, the Company is also enrolling participants in a Phase 2 clinical trial evaluating the safety and efficacy of mavorixafor in people with certain chronic neutropenic disorders. X4 also expects to initiate a pivotal, global, Phase 3 clinical trial in the first half of 2024 in certain chronic neutropenic disorders. The Company is headquartered in Boston, Massachusetts and has a research facility in Vienna, Austria. Going Concern Assessment—In accordance with Accounting Standards Update (“ASU”) No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40) (“ASU 2014-15”), the Company has evaluated whether there are certain conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after November 9, 2023, which is the date that the condensed consolidated financial statements were issued. Since inception, the Company has incurred significant operating losses and negative cash flows from operations. As of September 30, 2023, the Company had $141.7 million of cash, cash equivalents and short-term marketable securities, and an accumulated deficit of $458.8 million. Net cash used in operating activities was $68.8 million for the nine months ended September 30, 2023. On August 2, 2023, the Company entered into an amendment (the “Amendment”) to its Second Amended and Restated Loan and Security Agreement (as amended by the Amendment, the “Hercules Loan Agreement”) with Hercules Capital Inc. (“Hercules”). The Amendment extended the interest-only period from September 2024 to March 2025, provided an additional $22.5 million in borrowings at closing and increased the available borrowing capacity to $115.0 million. The Hercules Loan Agreement requires that the Company maintain a minimum level of cash of $20 million through January 2025 and thereafter subject to reductions upon the Company’s achievement of operational milestones. Management has assessed the Company’s ability to continue as a going concern in accordance with the requirements of Accounting Standards Codification (“ASC”) 205-40. The Company has adequate financial resources to fund its forecasted operating costs for at least one year after the date that these condensed consolidated financial statements were issued on November 9, 2023. Accordingly, the condensed consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern, which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. Based on its current cash flow projections and considering the terms of the Hercules Loan Agreement and with no additional funding, the Company believes it has sufficient cash, cash equivalents and marketable securities to fund operations into 2025. However, to finance its operations in 2025 and beyond, the Company will need to raise additional capital, which cannot be assured. Unless and until the Company reaches profitability in the future, it will require additional capital to fund our operations, which could be raised through a combination of equity offerings, debt financings, other third-party funding, marketing and distribution arrangements and other collaborations and strategic alliances. If the Company is unable to obtain funding, it could be forced to delay, reduce or eliminate some or all of its research and development programs, product portfolio expansion or commercialization efforts, which would adversely affect its business prospects, or it may be unable to continue operations. Principles of Consolidation—The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, including X4 Pharmaceuticals (Austria) GmbH, which is incorporated in Vienna, Austria (“X4 Austria”), and X4 Therapeutics, Inc. All significant intercompany accounts and transactions have been eliminated. Unaudited Interim Condensed Consolidated Financial Statements— The condensed consolidated balance sheet at December 31, 2022 that is presented in these interim condensed consolidated financial statements was derived from audited financial statements but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). The accompanying condensed consolidated financial statements are unaudited. The accompanying unaudited interim condensed consolidated financial statements have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These unaudited interim condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto for the year ended December 31, 2022 included in the 2022 Annual Report filed with the SEC on March 21, 2023. In the opinion of management, all adjustments, consisting only of normal recurring adjustments as necessary, for the fair statement of the Company’s condensed financial position, condensed results of its operations and cash flows have been made. The results of operations for the three and nine months ended September 30, 2023 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2023. Use of Estimates— The preparation of the Company’s condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the impairment or lack of impairment of long-lived assets including operating lease right-of-use assets and goodwill, and assumptions underlying the fair value of warrant liabilities. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates when there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. As of the date of issuance of these condensed consolidated financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the carrying value of its assets or liabilities. Actual results could differ from those estimates, and any such differences may be material to the Company’s consolidated financial statements.

Common Stock Warrants - Summary of Outstanding Warrants to Purchase Shares of Common Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2023	Dec. 09, 2022	Jul. 06, 2022	Mar. 03, 2022	Nov. 09, 2021	Mar. 23, 2021	Nov. 02, 2020	Nov. 29, 2019
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	112,659,093
Class Of Warrant Or Right. Aggregate Proceeds From Warrants Issued		$ 7,500	$ 14,500	$ 1,400	$ 10,000	$ 435		$ 21,000
Class of Warrant or Right, Additional Exercise Price of Warrants or Rights			$ 0.001	$ 0.01			$ 0.01	$ 0.001
Funded
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)			$ 1.094	$ 1.79	$ 4.97	$ 8.69		$ 11.999
Issuance On October 25, 2016
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On October 25, 2016 \| Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	5,155
Issuance On December 28, 2017 One
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On December 28, 2017 One \| Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	115,916
Issuance On September 12, 2018 One
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On September 12, 2018 One \| Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	20,220
Issuance On October 19, 2018
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On October 19, 2018 \| Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	20,016
Issuance On March 13, 2019
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 19.78
Issuance On March 13, 2019 \| Legacy Warrants
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	5,000
Issuance On April 16, 2019
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 13.20
Issuance On April 16, 2019 \| Class A Warrant
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	3,866,154
Issuance On November 29, 2019 One
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 12.00
Issuance On November 29, 2019 One \| Pre Funded Warrant
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	1,250,000
Issuance On March 23, 2021
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 8.70
Issuance On March 23, 2021 \| Pre Funded Warrant
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	50,000
Issuance on November Nine Two Thousand Twenty One
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	2,008,032
Exercise Price (usd per share)	$ 4.98
Issuance on March 3 2022
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	766,666
Exercise Price (usd per share)	$ 1.80
Issuance on July 2022 1
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	13,276,279
Exercise Price (usd per share)	$ 1.095
Issuance on July 6 2022 Two
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	44,075,050
Exercise Price (usd per share)	$ 1.095
Issuance on December 9 2022
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	32,137,448
Exercise Price (usd per share)	$ 1.50
Issuance on December 9 2022 2
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	6,800,000
Exercise Price (usd per share)	$ 1.10
Issuance On May 19, 2023
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 1.52
Issuance On May 19, 2023 \| Pre Funded Warrant
Class of Warrant or Right [Line Items]
Number of Shares of Common Stock Issuable (in shares)	8,263,157

Long Term Debt - Hercules Loan Agreement - Additional Information (Detail) - USD ($)		3 Months Ended	9 Months Ended	30 Months Ended
	Jul. 01, 2024	Sep. 30, 2023	Sep. 30, 2023	Mar. 31, 2021
Debt Instrument [Line Items]
Principal payments		$ 2,100,000
Hercules Loan Agreement
Debt Instrument [Line Items]
Proceeds from lines of credit				$ 55,000,000
Debt instrument variable percentage		10.15%
Interest rate increase percentage		4.00%
Effective interest rate of loan		13.60%	13.60%
Principal payments			$ 0
Hercules Loan Agreement \| Forecast [Member]
Debt Instrument [Line Items]
Line of credit facility periodic payment	$ 2,100,000
Hercules Loan Agreement \| Prime Rate
Debt Instrument [Line Items]
Debt instrument variable percentage			3.15%
Hercules Second Amended Loan Agreement \| Min Cash Test Date 1
Debt Instrument [Line Items]
Line of Credit, Covenant, Minimum Cash		$ 20,000,000	$ 20,000,000

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 357	$ 389

Leases - Schedule of Maturities of Lease Liabilities (Detail) $ in Thousands	Sep. 30, 2023 USD ($)
Leases [Abstract]
2020	$ 403
2021	1,370
2022	1,398
2023	1,329
2024	276
2025	46
Total lease payments	4,822
Less: interest	(858)
Operating lease, liability	$ 3,964

Commitment and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Indemnification Agreements
Contingencies And Commitments [Line Items]
Accrued liabilities	$ 0.0	$ 0.0

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 131,581	$ 121,718
Marketable securities	10,102	0
Research and development incentive receivable	393	1,152
Prepaid expenses and other current assets	5,796	5,807
Total current assets	147,872	128,677
Property and equipment, net	772	1,104
Goodwill	17,351	17,351
Right-of-use assets	6,054	7,229
Other assets	1,244	1,225
Total assets	173,293	155,586
Current liabilities:
Accounts payable	8,132	7,777
Accrued expenses	16,184	12,034
Current portion of lease liability	1,116	1,198
Current portion of long-term debt	0	1,315
Total current liabilities	25,432	22,324
Long-term debt, net of discount and current portion	54,322	32,304
Lease liabilities	2,848	3,603
Warrant liability (Note 4)	22,014	23,131
Other liabilities	1,083	173
Total liabilities	105,699	81,535
Commitments and contingencies (Note 9)
Stockholders’ equity:
Common stock, $0.001 par value, 500,000,000 shares authorized as of September 30, 2023 and December 31, 2022, respectively; 164,705,712 and 121,667,250 shares issued and outstanding as of September 30, 2023 and December 31, 2022, respectively	165	122
Additional paid-in capital	526,323	450,786
Accumulated other comprehensive loss	(119)	(119)
Accumulated deficit	(458,775)	(376,738)
Total stockholders’ equity	67,594	74,051
Total liabilities and stockholders’ equity	$ 173,293	$ 155,586

Long-Term Debt - Summary of Long Term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Principal amount of long-term debt	$ 55,000	$ 32,500
Debt discount, net of accretion	(1,007)	(196)
Cumulative accretion of end of term payments	329	1,315
Long-term debt	54,322	33,619
Current portion of long-term debt	0	(1,315)
Long-term debt, net of current portion	$ 54,322	$ 32,304

- Definition

Amount, after deduction of unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

+ References + Details

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2023
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation—The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, including X4 Pharmaceuticals (Austria) GmbH, which is incorporated in Vienna, Austria (“X4 Austria”), and X4 Therapeutics, Inc. All significant intercompany accounts and transactions have been eliminated.
Use of Estimates	Use of Estimates— The preparation of the Company’s condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the impairment or lack of impairment of long-lived assets including operating lease right-of-use assets and goodwill, and assumptions underlying the fair value of warrant liabilities. The Company bases its estimates on historical experience, known trends and other market-specific or other relevant factors that it believes to be reasonable under the circumstances. On an ongoing basis, management evaluates its estimates when there are changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. As of the date of issuance of these condensed consolidated financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, assumptions and judgments or revise the carrying value of its assets or liabilities. Actual results could differ from those estimates, and any such differences may be material to the Company’s consolidated financial statements.
Cash and Cash Equivalents	Cash and Cash Equivalents— The Company considers all highly liquid investments with maturities of 90 days or less at the date of purchase to be cash equivalents. Cash equivalents consisted of money market funds, treasury bills and federal government agency notes as of September 30, 2023 and December 31, 2022. Marketable Securities— Marketable securities consist of short-term securities classified as available-for-sale having maturities greater than 90 days, but less than 365 days from the date of acquisition. The Company determines the appropriate classification of the securities at the time they are acquired and evaluate the appropriateness of such classifications at each balance sheet date. The Company’s marketable securities consist of available-for-sale securities that are classified as Level 2 because their value is based on valuations using significant inputs derived from, or corroborated by, observable market data. The cost of available-for-sale securities sold is based on the specific-identification method. Unrealized gain and losses on available-for-sale are included as a component of other comprehensive (loss) income on the condensed consolidated balance sheets and condensed consolidated statements of stockholders’ equity and as a component of total comprehensive (loss) income on the condensed consolidated statement of operations and comprehensive loss until realized. Realized gains and losses on the sale of marketable securities are determined using the specific-identification method and recorded in other (expense) income, net on the accompanying condensed consolidated statements of operations and comprehensive loss. The Company reviews marketable securities for impairment whenever the fair value of a marketable security is less than the amortized cost and evidence indicates that a marketable security’s carrying amount is not recoverable. Unrealized losses are evaluated for impairment under ASC 326, Financial Instruments - Credit Losses, to determine if the impairment is credit-related or noncredit-related. Credit-related impairment is recognized as an allowance on the condensed consolidated balance sheets with a corresponding adjustment to earnings, and noncredit-related impairment is recognized in other comprehensive (loss) income, net of taxes. Evidence considered in this assessment includes reasons for the impairment, compliance with our investment policy, the severity of the impairment, collectability of the security, and any adverse conditions specifically related to the security, an industry, or geographic area.
Goodwill	Goodwill— Goodwill is tested for impairment at the reporting unit level annually in the fourth quarter, or more frequently when events or changes in circumstances indicate that the asset might be impaired. Examples of such events or circumstances include, but are not limited to, a significant adverse change in legal or business climate, an adverse regulatory action or unanticipated competition. The Company has determined that it operates in a single operating segment and has a single reporting unit. The Company assesses qualitative factors to determine whether the existence of events or circumstances would indicate that it is more likely than not that the fair value of the reporting unit is less than its carrying amount. If after assessing the totality of events or circumstances, the Company were to determine that it is more likely than not that the fair value of the reporting unit is less than its carrying amount, then the Company would perform an interim quantitative impairment test, whereby the Company compares the fair value of the reporting unit to its carrying value. If the fair value of the reporting unit exceeds the carrying value of its net assets, goodwill is not impaired, and no further testing is required. If the fair value of the reporting unit is less than its carrying value, the Company measures the amount of impairment loss, if any, as the excess of the carrying value over the fair value of the reporting unit. There were no triggering events during the three months ended September 30, 2023 that necessitated an interim impairment test of goodwill.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting StandardsIn June 2016, the Financial Accounting Standards Board issued ASU 2016-13, Credit Losses (Topic 326) Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”), as amended. ASU 2016-13 requires that financial assets measured at amortized cost, such as trade receivables, be presented net of expected credit losses, which may be estimated based on relevant information such as historical experience, current conditions, and future expectation for each pool of similar financial asset. The new guidance requires enhanced disclosures related to trade receivables and associated credit losses. The Company adopted ASU 2016-13 on January 1, 2023. As the Company did not have accounts receivable or marketable securities on its consolidated balance sheet as of the date of adoption, there was no impact to the adoption of ASU 2016-13.
Research and Development Expense, Policy

CONDENSED CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK, REDEEMABLE COMMON STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]
Beginning balance, shares at Dec. 31, 2021		28,127,657
Beginning balance at Dec. 31, 2021	$ 64,412	$ 28	$ 347,374	$ (119)	$ (282,871)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues		2,512,902
Stock Issued During Period, Value, New Issues	5,820	$ 3	5,817
Restricted Stock, Shares Issued Net of Shares for Tax Withholdings		168,817
Restricted Stock, Value, Shares Issued Net of Tax Withholdings	(12)		(12)
Stock Issued During Period Shares Warrants Exercised		100
APIC, Share-Based Payment Arrangement, Increase for Cost Recognition	1,459		1,459
Net loss	(21,965)				(21,965)
Ending balance, shares at Mar. 31, 2022		30,809,476
Ending balance at Mar. 31, 2022	49,714	$ 31	354,638	(119)	(304,836)
Beginning balance, shares at Dec. 31, 2021		28,127,657
Beginning balance at Dec. 31, 2021	64,412	$ 28	347,374	(119)	(282,871)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(64,763)
Ending balance, shares at Sep. 30, 2022		68,734,553
Ending balance at Sep. 30, 2022	61,849	$ 69	409,533	(119)	(347,634)
Beginning balance, shares at Mar. 31, 2022		30,809,476
Beginning balance at Mar. 31, 2022	49,714	$ 31	354,638	(119)	(304,836)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues		108,995
Stock Issued During Period, Value, Employee Stock Ownership Plan	49		49
Stock Issued During Period, Shares, Employee Stock Ownership Plan		72,727
APIC, Share-Based Payment Arrangement, Increase for Cost Recognition	1,522		1,522
Net loss	(21,212)				(21,212)
Ending balance, shares at Jun. 30, 2022		30,991,198
Ending balance at Jun. 30, 2022	30,073	$ 31	356,209	(119)	(326,048)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, New Issues		37,649,086
Reclassifications of Temporary to Permanent Equity	38,754		38,754
Stock Issued During Period, Value, New Issues	13,497	$ 38	13,459
Restricted Stock, Shares Issued Net of Shares for Tax Withholdings		94,269
APIC, Share-Based Payment Arrangement, Increase for Cost Recognition	1,111		1,111
Net loss	(21,586)				(21,586)
Ending balance, shares at Sep. 30, 2022		68,734,553
Ending balance at Sep. 30, 2022	61,849	$ 69	409,533	(119)	(347,634)
Beginning balance, shares at Dec. 31, 2022		121,667,250
Beginning balance at Dec. 31, 2022	74,051	$ 122	450,786	(119)	(376,738)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		540,238
APIC, Share-Based Payment Arrangement, Increase for Cost Recognition	1,645		1,645
Net loss	(24,020)				(24,020)
Ending balance, shares at Mar. 31, 2023		122,207,488
Ending balance at Mar. 31, 2023	51,676	$ 122	452,431	(119)	(400,758)
Beginning balance, shares at Dec. 31, 2022		121,667,250
Beginning balance at Dec. 31, 2022	$ 74,051	$ 122	450,786	(119)	(376,738)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercised (in shares)	2,031
Net loss	$ (82,037)
Ending balance, shares at Sep. 30, 2023		164,705,712
Ending balance at Sep. 30, 2023	67,594	$ 165	526,323	(119)	(458,775)
Beginning balance, shares at Mar. 31, 2023		122,207,488
Beginning balance at Mar. 31, 2023	51,676	$ 122	452,431	(119)	(400,758)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		98,555
Stock Issued During Period, Shares, New Issues		34,521,046
Stock Issued During Period, Value, New Issues	60,443	$ 35	60,408
Stock Issued During Period, Value, Employee Stock Ownership Plan	175		175
Stock Issued During Period, Shares, Employee Stock Ownership Plan		114,577
Exercised (in shares)		7,476,345
Stock Issued During Period, Value, Stock Options Exercised	8,811	$ 7	8,804
APIC, Share-Based Payment Arrangement, Increase for Cost Recognition	2,142		2,142
Net loss	(55,712)				(55,712)
Ending balance, shares at Jun. 30, 2023		164,418,011
Ending balance at Jun. 30, 2023	67,535	$ 164	523,960	(119)	(456,470)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Vesting of restricted stock units (in shares)		286,201
Vesting of restricted stock units	1	$ 1
Exercised (in shares)		1,500
Stock Issued During Period, Value, Stock Options Exercised	2		2
APIC, Share-Based Payment Arrangement, Increase for Cost Recognition	2,361		2,361
Net loss	(2,305)				(2,305)
Ending balance, shares at Sep. 30, 2023		164,705,712
Ending balance at Sep. 30, 2023	$ 67,594	$ 165	$ 526,323	$ (119)	$ (458,775)

Net Loss per Share

9 Months Ended

Sep. 30, 2023

Earnings Per Share [Abstract]

Net Loss per Share

NET LOSS PER SHARE

Basic and diluted net loss per share attributable to common stockholders was calculated as follow:


	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands, except per share data)	2023		2022		2023		2022
Numerator:
Net loss	$	(2,305)	$	(21,586)	$	(82,037)	$	(64,763)
Deemed dividend as a result of Class B warrant price reset	—		(287)		—		(2,546)
Net loss attributable to common stockholders	$	(2,305)	$	(21,873)	$	(82,037)	$	(67,309)
Denominator:
Weighted average shares of common stock outstanding—basic and diluted	196,988		83,211		170,751		50,976
Net loss per share attributable to common stockholders— basic and diluted	$	(0.01)	$	(0.26)	$	(0.48)	$	(1.32)

Basic and diluted weighted average shares of common stock outstanding for the three and nine months ended September 30, 2023 and September 30, 2022 include the weighted average effect of outstanding pre-funded warrants for the purchase of shares of common stock for which the remaining unfunded exercise price is $0.01 or less per share. During the nine months ended September 30, 2022, in accordance with the Company’s Class B Warrant agreement, the exercise price of each outstanding Class B Warrant was adjusted to the price of shares of the Company’s common stock sold in public or private offerings to the extent such price is lower than the previous Class B warrant price. These price adjustments were accounted for as a deemed dividend that adjusts net loss available to common shareholders for purposes of basic earnings per share. The deemed dividend was calculated using the Black-Scholes pricing model, taking into account historical volatility of the Company’s common stock and the estimated remaining life of the outstanding Class B Warrants. The Class B Warrants expired in December 2022.

The Company’s potentially dilutive securities include outstanding stock options, unvested restricted stock units and warrants to purchase shares of common stock for the three and nine months ended September 30, 2023 and 2022. All potentially dilutive securities have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share, and thus they are considered “anti-dilutive.” Therefore, the weighted average number of shares of common stock outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The Company excluded the following potential shares of common stock, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:


	Three Months Ended September 30,		Nine Months Ended September 30,
	2023	2022	2023	2022
Options to purchase shares of common stock	5,568,734	1,843,673	5,568,734	1,843,673
Unvested restricted stock units	5,574,839	1,397,789	5,574,839	1,397,789
Warrants to purchase shares of common stock (excluding prefunded warrants, which are included in basic shares outstanding)	80,244,959	60,374,393	80,244,959	60,374,393
	91,388,532	63,615,855	91,388,532	63,615,855

Common Stock Warrants - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Jul. 06, 2022	Mar. 03, 2022	Mar. 23, 2021	Nov. 02, 2020	Nov. 29, 2019
Class of Warrant or Right [Line Items]
Common stock, shares authorized	500,000,000	500,000,000
Common stock, par value (in usd per share)	$ 0.001	$ 0.001
Dividends on common stock declared or paid	$ 0
Class of Warrant or Right, Additional Exercise Price of Warrants or Rights			$ 0.001	$ 0.01		$ 0.01	$ 0.001
Q1 2022 Private Placement
Class of Warrant or Right [Line Items]
Class of Warrant or Right, Additional Exercise Price of Warrants or Rights					$ 0.01

Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2023

Accounting Policies [Abstract]

Schedule of Restricted Cash

Restricted Cash


(in thousands)	As of September 30, 2023		As of December 31, 2022

Letter of credit security: Waltham lease	$	250	$	250
Letter of credit security: Vienna Austria lease	202		205
Letter of credit security: Boston lease	571		855
Total restricted cash	$	1,023	$	1,310
Restricted cash included in prepaid expenses and other current assets	$	250	$	285
Restricted cash included in other assets	$	773	$	1,025

Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash


(in thousands)	September 30, 2023		December 31, 2022
Cash and cash equivalents	$	131,581	$	121,718
Restricted cash, current portion	250		285
Restricted cash, non-current	773		1,025
Total cash, cash equivalents and restricted cash	$	132,604	$	123,028

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Stock Option Valuation

The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted to employees, directors and non-employees.


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Risk-free interest rate	4.2	%	3.3	%	4.0	%	2.4	%
Expected term (in years)	6.1		6.1		6.0		6.1
Expected volatility	94.7	%	95.7	%	93.5	%	94.8	%
Expected dividend yield	0	%	0	%	0	%	0	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2023:


	Number of Shares	Weighted Average Exercise Price		Weighted Average Contractual Term (Years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2022	2,021,480	$	6.99	6.5	$	1
Granted	3,648,650	1.31
Exercised	(2,031)	1.50
Forfeited and Expired	(99,365)	9.91
Outstanding as of September 30, 2023	5,568,734	$	3.22	8.7	$	164
Exercisable as of September 30, 2023	1,217,001	$	9.26	5.8	$	2
Vested and expected to vest as of September 30, 2023	4,102,969	$	3.86	8.4	$	108

Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity

Restricted Stock Units— The following table summarizes the Company's restricted stock unit activity for the nine months ended September 30, 2023:


			Number of Shares
Unvested as of December 31, 2022			1,680,563
Granted			5,064,691
Vested			(926,572)
Forfeited			(243,843)
Unvested as of September 30, 2023			5,574,839

Summary of Stock-Based Compensation Expense Classification

Stock-based compensation expense was classified in the condensed consolidated statements of operations as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2023		2022		2023		2022
Research and development expense	$	1,259	$	576	$	3,210	$	1,990
Selling, general and administrative expense	1,102		535		2,938		2,102
Total stock-based compensation	$	2,361	$	1,111	6,148		4,092

Share-Based Payment Arrangement, Option and Stock Appreciation Rights, Activity

The calculation of the fair value of the outstanding SARs as of September 30, 2023 includes the closing price of the Company’s common stock of $1.09 and the following assumptions on a weighted average basis:


	September 30, 2023
Risk free rate	4.6	%
Expected term (years)	5.11
Expected volatility	97.4	%
Expected dividend yield	—	%
Expected forfeiture rate	19	%

Net Loss per Share - Additional Information (Detail)	Sep. 30, 2023 $ / shares
Pre Funded Warrant \| Maximum
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Exercise Price (usd per share)	$ 0.01

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Income Tax Disclosure [Abstract]
Federal income tax benefit			$ 0	$ 0
State income tax benefit			0	0
Provision for income taxes	$ 26	$ (13)	$ 45	$ 14

- Definition

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

+ References + Details

Stock-Based Compensation

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

STOCK-BASED COMPENSATION

Summary of Plans— The Company has the following equity incentive plans:

•The X4 Pharmaceuticals Inc. 2015 Employee, Director and Consultant Equity Incentive Plan, as amended (the “2015 Plan”);

•The X4 Pharmaceuticals Inc. 2017 Equity Incentive Plan (the “2017 Plan”); and

•The X4 Pharmaceuticals Inc. Amended and Restated 2019 Inducement Equity Incentive Plan (the “2019 Plan”)

The Company also has the following employee stock purchase plan:

•The X4 Pharmaceutical Inc. Amended and Restated 2017 Employee Stock Purchase Plan (the “2017 ESPP”)

These plans are administered by the Board of Directors or by a committee of the Board of Directors. The exercise prices, vesting and other restrictions are determined at the discretion of the Board of Directors, or its committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of the stock option may not be greater than ten years. Incentive stock options granted to employees and restricted stock awards granted to employees, officers, members of the board of directors, advisors, and consultants of the Company typically vest over four years. Non-statutory options granted to employees, officers, members of the board of directors, advisors, and consultants of the Company typically vest over three or four years. Shares that are expired, terminated, surrendered or canceled under the Plans without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards.

As of September 30, 2023, there are an aggregate of approximately 2.0 million shares of common stock available for issuance under the Company’s equity incentive plans. Approximately 5.0 million shares of common stock remain available for issuance under the 2017 ESPP.

Stock Option Valuation— The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted to employees, directors and non-employees.


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Risk-free interest rate	4.2	%	3.3	%	4.0	%	2.4	%
Expected term (in years)	6.1		6.1		6.0		6.1
Expected volatility	94.7	%	95.7	%	93.5	%	94.8	%
Expected dividend yield	0	%	0	%	0	%	0	%

Stock Options

The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2023:


	Number of Shares	Weighted Average Exercise Price		Weighted Average Contractual Term (Years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2022	2,021,480	$	6.99	6.5	$	1
Granted	3,648,650	1.31
Exercised	(2,031)	1.50
Forfeited and Expired	(99,365)	9.91
Outstanding as of September 30, 2023	5,568,734	$	3.22	8.7	$	164
Exercisable as of September 30, 2023	1,217,001	$	9.26	5.8	$	2
Vested and expected to vest as of September 30, 2023	4,102,969	$	3.86	8.4	$	108

The weighted average grant-date fair value per share of stock options granted during the nine months ended September 30, 2023 and 2022 was $1.02 and $1.24, respectively.

Restricted Stock Units— The following table summarizes the Company's restricted stock unit activity for the nine months ended September 30, 2023:


			Number of Shares
Unvested as of December 31, 2022			1,680,563
Granted			5,064,691
Vested			(926,572)
Forfeited			(243,843)
Unvested as of September 30, 2023			5,574,839

During the nine months ended September 30, 2023, the Company granted performance-based restricted stock units (“PRSUs”) to its employees. The PRSUs vest 50% based on the Company’s achievement of each of two operational milestones conditioned on the grantee’s continued employment with the Company. As of September 30, 2023, neither of the two performance criteria had been met. The Company believes that the achievement of these operational milestones is probable and, accordingly, stock-based compensation expense has been recognized for the awards using the accelerated attribution model based on the fair value of the awards as of the date of grant and management’s best estimate of the date each operational milestone will be achieved. The Company updates its estimates related to the probability and timing of achievement of the operational milestones each period until the award either vests or is forfeited.

Stock-Based Compensation— As of September 30, 2023, total unrecognized compensation expense related to unvested stock options and restricted stock units was $5.4 million, which is expected to be recognized over a weighted average period of 2.2 years.

Stock-based compensation expense was classified in the condensed consolidated statements of operations as follows:


	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2023		2022		2023		2022
Research and development expense	$	1,259	$	576	$	3,210	$	1,990
Selling, general and administrative expense	1,102		535		2,938		2,102
Total stock-based compensation	$	2,361	$	1,111	6,148		4,092

Leases (Tables)

9 Months Ended

Sep. 30, 2023

Leases [Abstract]

Schedule of Components of Lease Expense

The components of lease expense for the three and nine months ended September 30, 2023 and 2022 were as follows:


(dollars in thousands)	Three Months Ended September 30,					Nine Months Ended September 30,
Lease Cost	2023			2022		2023		2022
Fixed operating lease cost	$	518		$	507	$	1,561	$	1,561

Total lease expense	$	518		$	507	$	1,561	$	1,561
Other information

Operating cash flows from operating leases	$	345		$	334	$	1,037	$	1,014
Sublease income	$	49		$	49	$	97	$	147
Weighted-average remaining lease term—operating leases	3.4 years
Weighted-average discount rate—operating leases	11.5		%

Schedule of Maturities of Lease Liabilities

Maturities of lease liabilities due under lease agreements that have commenced as of September 30, 2023 are as follows (in thousands)


Maturity of lease liabilities	Operating Leases
2023 (remainder of the year)	$	403
2024	1,370
2025	1,398
2026	1,329
2027	276
Thereafter	46
Total lease payments	4,822
Less: interest	(858)
Total operating lease liabilities as of September 30, 2023	$	3,964

Long-Term Debt - Schedule of Future Principal Payments and the Final Payments Due (Detail) $ in Thousands	Aug. 02, 2023 USD ($)
Debt Disclosure [Abstract]
2023	$ 0
2024	0
2025	24,720
2026	30,609
Principal amount of long-term debt	$ 55,329

Common Stock Warrants (Tables)

9 Months Ended

Sep. 30, 2023

Equity [Abstract]

Schedule of Warrants

As of September 30, 2023, the Company’s outstanding warrants and pre-funded warrants to purchase shares of common stock consisted of the following:


Issuance Date	Number of Shares of Common Stock Issuable	Exercise Price			Expiration Date
October 25, 2016	5,155	$	19.78		October 24, 2026
December 28, 2017	115,916	$	19.78		December 28, 2027
September 12, 2018	20,220	$	19.78		September 12, 2028
October 19, 2018	20,016	$	19.78		October 19, 2028
March 13, 2019	5,000	$	19.78		March 12, 2029
April 16, 2019	3,866,154	$	13.20		April 15, 2024

November 29, 2019	1,250,000	$	12.00	(a)	n/a
March 23, 2021	50,000	$	8.70	(b)	n/a
November 9, 2021	2,008,032	$	4.98	(c)	n/a
March 3, 2022	766,666	$	1.80	(d)	n/a
July 6, 2022	13,276,279	$	1.095	(e)	n/a
July 6, 2022	44,075,050	$	1.095		July 6, 2027
December 9, 2022	32,137,448	$	1.50		December 9, 2027
December 9, 2022	6,800,000	$	1.10	(f)	n/a
May 19, 2023	8,263,157	$	1.52	(g)	n/a
	112,659,093

(a) In November 2019, the Company received $11.999 per pre-funded warrant, or $21.0 million in aggregate proceeds. Each pre-funded

Stock-Based Compensation - Schedule of Assumptions Used in Black-Scholes Option-Pricing Model to Determine Grant-date Fair Value of Stock Options Granted (Detail)			3 Months Ended		9 Months Ended
	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (in percentage)			4.20%	3.30%	4.00%	2.40%
Expected term (in years)			6 years 1 month 6 days	6 years 1 month 6 days	6 years	6 years 1 month 6 days
Expected volatility (in percentage)			94.70%	95.70%	93.50%	94.80%
Expected dividend yield (in percentage)			0.00%	0.00%	0.00%	0.00%
Class C Warrant Liability
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (in percentage)	4.60%	4.00%	4.60%
Expected term (in years)	4 years 2 months 12 days	4 years 10 months 24 days	5 years 1 month 9 days
Expected volatility (in percentage)	91.30%	101.70%	97.40%
Expected dividend yield (in percentage)	0.00%	0.00%	0.00%
Expected forfeiture rate (in percentage)			19.00%

- 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

+ Details

Fair Value of Financial Assets and Liabilities - Aggregate Fair Values Financial Instruments (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2023 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 23,141
Change in fair value	(743)
Reclassification of warrant liability to permanent equity upon exercise	(374)
Ending balance	22,024
Embedded Derivative Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	10
Change in fair value	0
Reclassification of warrant liability to permanent equity upon exercise	0
Ending balance	10
Class C Warrant Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	23,131
Change in fair value	(743)
Reclassification of warrant liability to permanent equity upon exercise	(374)
Ending balance	$ 22,014

Net Loss per Share - Schedule of Anti-dilutive Securities Excluded from Computation of Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share (in shares)	91,388,532	63,615,855	91,388,532	63,615,855
Employee Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share (in shares)	5,568,734	1,843,673	5,568,734	1,843,673
Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share (in shares)	5,574,839	1,397,789	5,574,839	1,397,789
Class C Warrant Liability
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share (in shares)	80,244,959	60,374,393	80,244,959	60,374,393

Stock-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($) $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares
Number of Shares
Beginning balance (in shares) \| shares	2,021,480
Granted (in shares) \| shares	3,648,650
Exercised (in shares) \| shares	(2,031)
Forfeited (in shares) \| shares	(99,365)
Ending balance (in shares) \| shares	5,568,734	2,021,480
Number of shares Options, Exercisable (in shares) \| shares	1,217,001
Number of shares Options, Vested and expected to vest (in shares) \| shares	4,102,969
Weighted Average Exercise Price
Beginning balance (in usd per share) \| $ / shares	$ 6.99
Granted (in usd per share) \| $ / shares	1.31
Exercised (in usd per share) \| $ / shares	1.50
Forfeited (in usd per share) \| $ / shares	9.91
Ending balance (in usd per share) \| $ / shares	3.22	$ 6.99
Weighted average exercise price, Exercisable (in usd per share) \| $ / shares	9.26
Weighted average exercise price, Vested and expected to vest (in usd per share) \| $ / shares	$ 3.86
Weighted average contractual term outstanding (in years)	8 years 8 months 12 days	6 years 6 months
Weighted average contractual term outstanding, Exercisable (in years)	5 years 9 months 18 days
Weighted average contractual term outstanding, Vested and expected to vest (in years)	8 years 4 months 24 days
Aggregate intrinsic value, Beginning balance \| $	$ 1
Aggregate intrinsic value, Ending balance \| $	164	$ 1
Aggregate intrinsic value, exercisable \| $	2
Aggregate intrinsic value, vested and expected to vest \| $	$ 108

Long-Term Debt - Summary of Interest Expense (Details) - Hercules Loan Agreement - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Debt Instrument [Line Items]
Interest expense, debt	$ 1,397	$ 1,018	$ 3,210	$ 2,845
Amortization of debt discount	$ 237	$ 256	$ 681	$ 653

- 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 835
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482900/835-30-50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04(a))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-3

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69B

Reference 6: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69C
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69C

Reference 7: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69E
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69E

Reference 8: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 69F
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481568/470-20-55-69F

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 11: http://www.xbrl.org/2003/role/exampleRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1B

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1D

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1D

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1D
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1D

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1E
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1E

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 24: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1F
-Subparagraph (b)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1F

Reference 25: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1I
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481139/470-20-50-1I

+ Details

Property and Equipment, Net (Tables)

9 Months Ended

Sep. 30, 2023

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment, net consisted of the following:


(in thousands)	September 30, 2023		December 31, 2022
Leasehold improvements	$	228	$	228
Furniture and fixtures	1,273		1,268
Computer equipment	181		173
Software	24		24
Lab equipment	651		639
	2,357		2,332
Less: Accumulated depreciation and amortization	(1,585)		(1,228)
	$	772	$	1,104

Leases - Additional Information (Detail) $ in Thousands		9 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Nov. 11, 2019 USD ($)	Sep. 30, 2023 USD ($) m² ft²	Dec. 31, 2022 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease, liability		$ 3,964
Right-of-use assets		$ 6,054	$ 7,229
Waltham Lease
Lessee, Lease, Description [Line Items]
Current office space under lease agreement \| ft²		6,000
Current base rent		$ 300
Lease, term of contract (years)		5 years
Vienna Lease
Lessee, Lease, Description [Line Items]
Office space \| m²		1,200
Lease not yet commenced, term of contract		7 years
Annual base rent		$ 285
Allston Lease
Lessee, Lease, Description [Line Items]
Lease not yet commenced	$ 1,100

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating expenses:
Research and development	$ 19,081	$ 14,110	$ 56,745	$ 42,044
Selling, general and administrative	8,133	6,044	25,578	20,457
Gain (Loss) on Disposition of Assets	0	0	0	(509)
Total operating expenses	27,214	20,154	82,323	61,992
Loss from operations	(27,214)	(20,154)	(82,323)	(61,992)
Other income (expense), net:
Interest income	1,388	14	3,137	21
Interest expense	(1,634)	(1,018)	(3,891)	(2,849)
Other income (expense), net	17	(441)	342	(440)
Total other income (expense), net	24,935	(1,445)	331	(2,757)
Loss before provision for income taxes	(2,279)	(21,599)	(81,992)	(64,749)
Provision for income taxes	26	(13)	45	14
Net loss and comprehensive loss	(2,305)	(21,586)	(82,037)	(64,763)
Deemed dividend on Class B Warrant price reset	0	(287)	0	(2,546)
Net loss attributable to common stockholders	$ (2,305)	$ (21,873)	$ (82,037)	$ (67,309)
Net loss per share attributable to common stockholders—basic	$ (0.01)	$ (0.26)	$ (0.48)	$ (1.32)
Net loss per share attributable to common stockholders—diluted	$ (0.01)	$ (0.26)	$ (0.48)	$ (1.32)
Weighted average shares of common stock outstanding—diluted	196,988,000	83,211,000	170,751,000	50,976,000
Weighted average shares of common stock outstanding—basic	196,988,000	83,211,000	170,751,000	50,976,000
Embedded derivative liability
Other income (expense), net:
Derivative, gain (loss) on derivative, net	$ 0	$ 0	$ 0	$ 511
Warrant Liability
Other income (expense), net:
Derivative, gain (loss) on derivative, net	$ 25,164	$ 0	$ 743	$ 0

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
Accrued employee compensation and benefits	$ 6,067	$ 6,592
Accrued external research and development expenses	8,563	3,906
Accrued professional fees	976	571
Accrued deferred financing fees	0	591
Other	578	374
Total accrued expenses	$ 16,184	$ 12,034

Long-Term Debt

9 Months Ended

Sep. 30, 2023

Debt Disclosure [Abstract]

Long-Term Debt

Long-term debt consisted of the following:


(in thousands)	September 30, 2023		December 31, 2022
Principal amount of long-term debt	$	55,000	$	32,500
Debt discount, net of accretion	(1,007)		(196)
Cumulative accretion of end of term payments	329		1,315
Long-term debt	$	54,322	$	33,619
Less: current portion	$	—	$	(1,315)
Long-term debt, net of current portion	$	54,322	$	32,304

Hercules Loan Agreement

In October 2018, the Company entered into the Hercules Loan Agreement, as amended most recently in August 2023, with Hercules. The Hercules Loan Agreement provides for a term loan facility of up to $115.0 million, including: (i) $32.5 million outstanding (the “Conversion Balance”) prior to effectiveness of the most recent amendment in August 2023 (the “Amendment”), (ii) a $22.5 million term loan tranche drawn upon the closing of the Amendment, (iii) an additional tranche of up to $20.0 million, which will be available in either one or two drawings following potential U.S. approval of mavorixafor in individuals with WHIM syndrome (“Approval”) until the earlier of (A) 45 days following Approval and (B) September 30, 2024 in the case of the first drawing, and until December 15, 2024 in the case of a second drawing, (iv) an additional tranche of $7.5 million, which will be available following achievement of a certain clinical development-related milestone through the earlier of (A) 45 days following achievement of such milestone and (B) December 15, 2024 and (v) an additional tranche of up to $32.5 million, which will be available subject to approval by Hercules in its sole discretion. under which the Company has borrowed an aggregate of $55.0 million of term loans to date representing the maximum borrowings.

Borrowings under the Hercules Loan Agreement accrue interest at a variable rate equal to the greater of (i) 10.15% or (ii) The Wall Street Journal prime rate plus 3.15%. In an event of default and until such event is no longer continuing, the interest rate applicable to borrowings would be increased by 4.0%. Borrowings are repayable in monthly interest-only payments through March 1, 2025, and in equal monthly payments of principal and accrued interest from April 1, 2025 (the “Amortization Date”) until the maturity date of the loans. The Amortization Date may be extended (i) to October 1, 2026, if Approval occurs on or prior to September 30, 2026, and (ii) to the maturity date if an extension pursuant to the foregoing clause (i) has occurred and no event of default occurs. The loans mature on October 1, 2026; provided, however, such maturity date will be extended to July 1, 2027 if the Amortization Date is extended pursuant to clause (i) of the foregoing sentence. At the Company’s option, the Company may prepay all, but not less than all, of the outstanding borrowings, subject to a prepayment premium of 3% during the first 12 months following January 6, 2023 (the “Original Closing Date”), 2% during the following 12 months and 1% thereafter. In addition, the Hercules Loan Agreement provides for payment of end-of-term fees of $2.1 million plus 3.5% of the aggregate principal amount of loans drawn, if any, subsequent to the Amendment, payable upon the earlier of maturity or the repayment in full of all obligations under the Hercules Loan Agreement. Borrowings under the Hercules Loan Agreement are

collateralized by substantially all of the Company’s personal property and other assets except for its intellectual property (but including rights to payment and proceeds from the sale, licensing or disposition of the intellectual property).

Under the Hercules Loan Agreement, the Company has agreed to affirmative and negative covenants. Prior to January 31, 2025, the Company must maintain cash in an account or accounts in which Hercules has a first priority security interest (“Qualified Cash”) in an aggregate amount equal to at least $20.0 million.

•On and after January 31, 2025, such amount must equal at least 20% of the aggregate principal amount of loans outstanding under the Hercules Loan Agreement.

•From and after January 31, 2025, the Company must maintain trailing six month net product revenue of at least 55% of its forecast as approved by the Company’s Board of Directors (the “Performance Covenant”). However, the Performance Covenant will be waived during any period in which

◦(i) the Company maintains Qualified Cash in an aggregate amount equal to at least 75% of loans outstanding under the Amended Loan Agreement or

◦(ii) both (x) the Company maintains a Market Capitalization (as defined in the Hercules Loan Agreement) of at least $450.0 million and (y) the Company maintains Qualified Cash in an aggregate amount equal to at least 45% of loans outstanding.

The Hercules Loan Agreement also restricts the Company’s ability to incur additional indebtedness, pay dividends, encumber its intellectual property, or engage in certain fundamental business transactions, such as mergers or acquisitions of other businesses, with certain exceptions.

The Company recognized interest expense under the Hercules Loan Agreement as follows:


(in thousands)	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Total interest expense	$	1,397	$	1,018	$	3,210	$	2,845
Non-cash interest expense	$	237	$	256	$	681	$	653

The annual effective interest rate of the Hercules Loan Agreement as of September 30, 2023 is 13.6%. There were no principal payments due or paid under the Hercules Loan Agreement during the nine months ended September 30, 2023. End-of-term payments of $2.1 million were paid during the nine months ended September 30, 2023.

The Company concluded that the amendments to the Hercules Loan Agreement in January 2023 and August 2023 represented modifications to the debt. Accordingly, fees paid to third parties directly related to the amendments were expensed as incurred and fees paid to Hercules in conjunction with the amendments have been deferred and are being amortized to interest expense over the life of the debt arrangement using the effective interest method.

As of September 30, 2023, future principal and accrued end-of-term payments due under the Hercules Loan Agreement were as follows (in thousands):


Year Ending December 31,	Total
2023	$	—
2024	—
2025	24,720
2026	30,609
Long-term debt	$	55,329

Fair Value of Financial Assets and Liabilities - Schedule of Assets and Liabilities Measured at Fair Value (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	$ 108,221	$ 73,028
Fair value of derivative liability	22,024	23,141
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	98,119
US Treasury Bill Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	10,102
Embedded derivative liability
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	10	10
Class C Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	22,014	23,131
Level 1
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	98,119	70,170
Fair value of derivative liability	0	0
Level 1 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	98,119
Level 1 \| US Treasury Bill Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	0
Level 1 \| Embedded derivative liability
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	0	0
Level 1 \| Class C Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	0	0
Level 2
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	10,102	2,858
Fair value of derivative liability	0	0
Level 2 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	0
Level 2 \| US Treasury Bill Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	10,102
Level 2 \| Embedded derivative liability
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	0	0
Level 2 \| Class C Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	0	0
Level 3
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	0	0
Fair value of derivative liability	22,024	23,141
Level 3 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	0
Level 3 \| US Treasury Bill Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	0
Level 3 \| Embedded derivative liability
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	10	10
Level 3 \| Class C Warrant Liability
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	$ 22,014	$ 23,131

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, weighted average grant date fair value (in usd per share)	$ 1.02	$ 1.24
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost of stock based awards	$ 5,400
Unrecognized compensation cost of stock based awards, recognition period	2 years 2 months 12 days
2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance	2,000,000
Two Thousand Seventeen Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance	5,000,000

- 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

+ Details