X4 Pharmaceuticals (XFOR) 10-Q13 Nov 242024 Q3 Quarterly reportFinancial data

Company Profile

Cover Page

Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2024	Nov. 11, 2024
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2024
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, par value $0.001 per share
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		170,546,469
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001501697
Current Fiscal Year End Date	--12-31

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 97,412	$ 99,216
Marketable securities	37,565	15,000
Research and development incentive receivable	1,073	562
Inventory	2,445	0
Prepaid expenses and other current assets	4,477	7,298
Total current assets	142,972	122,076
Property and equipment, net	820	745
Goodwill	17,351	17,351
Finite-Lived Intangible Assets, Net	10,188	0
Right-of-use assets	4,471	5,650
Other assets	2,363	1,436
Total assets	178,165	147,258
Current liabilities:
Accounts payable	8,577	8,947
Accrued expenses (Note 9)	19,459	12,816
Current portion of lease liability	1,222	1,099
Total current liabilities	29,258	22,862
Long-term debt, including accretion, net of discount	75,224	54,570
Lease liabilities	1,757	2,612
Warrant liability (Note 5)	11,087	15,683
Other liabilities	1,218	432
Total liabilities	118,544	96,159
Commitments and contingencies (Note 12)
Stockholders’ equity:
Common stock, $0.001 par value, 500,000,000 shares authorized as of September 30, 2024 and December 31, 2023, respectively; 168,511,264 and 167,434,595 shares issued and outstanding as of September 30, 2024 and December 31, 2023, respectively	168	167
Additional paid-in capital	535,101	528,956
Accumulated other comprehensive loss	(114)	(119)
Accumulated deficit	(475,534)	(477,905)
Total stockholders’ equity	59,621	51,099
Total liabilities and stockholders’ equity	$ 178,165	$ 147,258

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2024	Dec. 31, 2023
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	168,511,264	167,434,595
Common stock, shares outstanding	168,511,264	167,434,595

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Statement [Abstract]
Product revenue, net	$ 560	$ 0	$ 1,123	$ 0
Costs and operating expenses:
Cost of revenue	227	0	495	0
Research and development	19,173	19,081	59,941	56,745
Selling, general and administrative	15,660	8,133	46,373	25,578
Gain on sale of non-financial asset (Note 17)	0	0	(105,000)	0
Total operating expense	35,060	27,214	1,809	82,323
Loss from operations	(34,500)	(27,214)	(686)	(82,323)
Other (expense) income, net:
Interest income	1,871	1,388	4,502	3,137
Interest expense	(2,414)	(1,634)	(6,464)	(3,891)
Change in fair value of warrant liability	(1,864)	25,164	4,596	743
Other income, net	226	17	475	342
Total other (expense) income, net	(2,181)	24,935	3,109	331
(Loss) income before provision for income taxes	(36,681)	(2,279)	2,423	(81,992)
Provision for income taxes	15	26	52	45
Net (loss) income	$ (36,696)	$ (2,305)	$ 2,371	$ (82,037)
Net loss per share attributable to common stockholders—basic	$ (0.18)	$ (0.01)	$ 0.01	$ (0.48)
Net loss per share attributable to common stockholders—diluted	$ (0.18)	$ (0.01)	$ 0.01	$ (0.48)
Weighted average shares of common stock outstanding—basic	200,865,276	196,987,827	200,434,027	170,751,244
Weighted average shares of common stock outstanding—diluted	200,865,276	196,987,827	200,611,232	170,751,244
Supplemental Income Statement Elements [Abstract]
Change in net unrealized gains on marketable debt securities	$ 45	$ 0	$ 5	$ 0
Comprehensive (loss) income	$ (36,651)	$ (2,305)	$ 2,376	$ (82,037)

CONDENSED CONSOLIDATED STATEM_2

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, 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
Vesting of restricted stock units	0
Stock-based compensation expense	1,645		1,645
Net income	(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]
Net income	(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]
Issuance of common stock and prefunded warrants in private placement equity transaction, net of issuance costs (in shares)		34,521,046
Issuance of common stock and prefunded warrants in private placement equity transaction, net of issuance costs	60,443	$ 35	60,408
Issuance of shares of common stock under employee stock purchase plan (in shares)		114,577
Issuance of shares of common stock under employee stock purchase plan	175		175
Exercise of stock and warrants (in shares)		7,476,345
Exercise of stock and warrants	8,811	$ 7	8,804
Vesting of restricted stock units (in shares)		98,555
Vesting of restricted stock units	0
Stock-based compensation expense	2,142		2,142
Net income	(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]
Exercise of stock and warrants (in shares)		1,500
Vesting of restricted stock units (in shares)		286,201
Vesting of restricted stock units	1
Reclassifications of Temporary to Permanent Equity	2		2
Stock-based compensation expense	2,361		2,361
Net income	(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)
Beginning balance, shares at Dec. 31, 2023		167,434,595
Beginning balance at Dec. 31, 2023	51,099	$ 167	528,956	(119)	(477,905)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock and warrants	0		(1)
Vesting of restricted stock units (in shares)		503,186
Vesting of restricted stock units		$ 1
Stock-based compensation expense	1,739		1,739
Unrealized loss on marketable securities	(36)			(36)
Net income	(51,766)				(51,766)
Ending balance, shares at Mar. 31, 2024		167,937,781
Ending balance at Mar. 31, 2024	1,036	$ 168	530,694	(155)	(529,671)
Beginning balance, shares at Dec. 31, 2023		167,434,595
Beginning balance at Dec. 31, 2023	51,099	$ 167	528,956	(119)	(477,905)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,371
Ending balance, shares at Sep. 30, 2024		168,511,264
Ending balance at Sep. 30, 2024	59,621	$ 168	535,101	(114)	(475,534)
Beginning balance, shares at Mar. 31, 2024		167,937,781
Beginning balance at Mar. 31, 2024	1,036	$ 168	530,694	(155)	(529,671)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of shares of common stock under employee stock purchase plan (in shares)		235,068
Issuance of shares of common stock under employee stock purchase plan	158		158
Exercise of stock and warrants	0
Vesting of restricted stock units (in shares)		23,331
Stock-based compensation expense	2,428		2,428
Unrealized loss on marketable securities	(4)			(4)
Net income	90,833				90,833
Ending balance, shares at Jun. 30, 2024		168,196,180
Ending balance at Jun. 30, 2024	94,451	$ 168	533,280	(159)	(438,838)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock and warrants			1
Vesting of restricted stock units (in shares)		315,084
Vesting of restricted stock units	1
Stock-based compensation expense	1,820		1,820
Unrealized loss on marketable securities	45			45
Net income	(36,696)				(36,696)
Ending balance, shares at Sep. 30, 2024		168,511,264
Ending balance at Sep. 30, 2024	$ 59,621	$ 168	$ 535,101	$ (114)	$ (475,534)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Cash flows from operating activities:
Net income	$ 2,371	$ (82,037)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Stock-based compensation expense	5,987	6,148
Depreciation and amortization expense	523	357
Gain on sale of non-financial asset (Note 17)	(105,000)	0
Non-cash lease expense	1,179	1,173
Accretion of debt discount	655	681
Change in fair value of warrant liability	(4,596)	(743)
Other	(504)	(46)
Changes in operating assets and liabilities:
Inventory, Net	(2,445)	0
Prepaid expenses, other current and non-current assets and research and development incentive receivable	1,197	459
Accounts payable	(364)	426
Accrued expenses and other long-term liabilities	3,832	5,651
Lease liabilities	(741)	(834)
Net cash used in operating activities	(97,906)	(68,765)
Cash flows from investing activities:
Acquisition of intangible asset	(7,000)	0
Proceeds from sale of non-financial asset	105,000	0
Purchase of marketable securities	(34,354)	(11,025)
Sales and maturities of marketable securities	12,250	1,000
Acquisition of property and equipment	(285)	(25)
Net cash provided by (used in) investing activities	75,611	(10,050)
Cash flows from financing activities:
Proceeds from Issuance of Common Stock	159	8,615
Fees paid to amendment loan agreement and issuance costs related to the sale of warrants	0	(631)
Repayments of borrowings and accrued end-of-term fees under loan and security agreement	0	(2,064)
Proceeds from borrowings under loan and security agreement	20,000	22,500
Proceeds from sale of common stock, warrants and pre-funded warrants, net of issuance costs	0	59,999
Net cash provided by financing activities	20,159	88,419
Effect of exchange rate changes on cash, cash equivalents and restricted cash	88	(28)
Net increase in cash, cash equivalents and restricted cash	(2,048)	9,576
Cash, cash equivalents and restricted cash at beginning of period	100,248	123,028
Cash, cash equivalents and restricted cash at end of period	98,200	132,604
Supplemental Cash Flow Information [Abstract]
Acquisition of intangible assets included in accrued expenses	$ 3,500	$ 0

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
Nature of the Business and Basis of Presentation	Sep. 30, 2024
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 biopharmaceutical company discovering, developing, and commercializing 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. On April 29, 2024, the Company announced that the FDA approved the Company’s New Drug Application (“NDA”) for mavorixafor, which is being marketed in the U.S. under the trade name XOLREMDI, for use as an oral, once-daily therapy in patients 12 years of age and older with WHIM syndrome (warts, hypogammaglobulinemia, infections, and myelokathexis), to increase the number of circulating mature neutrophils and lymphocytes. WHIM syndrome is a rare combined primary immunodeficiency and chronic neutropenic disorder. The Company is currently engaged in its U.S. launch of XOLREMDI in WHIM syndrome while also planning to seek regulatory approvals to commercialize mavorixafor outside of the U.S. The U.S. approval of XOLREMDI in the WHIM syndrome indication is the first for mavorixafor, which is an orally bioavailable selective antagonist of chemokine receptor CXCR4, a key regulator of the movement of immune cells throughout the body. Due to its ability to increase the mobilization of 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 immune system disorders in addition to WHIM syndrome. As a result, the Company has completed a Phase 2 study evaluating the safety and efficacy of mavorixafor as a monotherapy and in combination with human granulocyte colony-stimulating factor (“G-CSF”) in people with certain chronic neutropenic disorders. Results from this six-month Phase 2 study showed mavorixafor was generally well tolerated and able to durably increase study participants’ mean absolute neutrophil count (“ANC”) both as a monotherapy and in combination with G-CSF. The Company has initiated a global, pivotal Phase 3 clinical trial of mavorixafor (the 4WARD study) that aims to evaluate the efficacy, safety, and tolerability of oral once-daily mavorixafor with or without G-CSF in people with congenital or acquired primary autoimmune and idiopathic chronic neutropenia who are experiencing recurrent and/or serious infections. The Company is headquartered in Boston, Massachusetts and has a research facility in Vienna, Austria. Going Concern Assessment— In accordance with the requirements of Accounting Standards Codification (“ASC”) 205-40, 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 the date that the condensed consolidated financial statements are issued. Although the Company has an approved drug product, sales of the Company’s drug product over the next 12 months will not be sufficient to fund the Company’s operating expenses. Since inception, the Company has incurred significant operating losses and negative cash flows from operations and the Company expects to continue to generate operating losses and negative cash flows from operations for the foreseeable future. As of September 30, 2024, the Company had $135.0 million of cash, cash equivalents and short-term marketable securities, and an accumulated deficit of $475.5 million. Net cash used in operating activities was $97.9 million for the nine months ended September 30, 2024. The Company has a covenant (the “Minimum Cash Covenant”) under its Second Amended and Restated Loan and Security Agreement, as amended, (the “Hercules Loan Agreement”) with Hercules Capital Inc.(“Hercules”), that requires the Company to maintain a minimum level of cash of $20 million through January 30, 2025 and a minimum level of cash equal to at least 20% of outstanding borrowings under the Hercules Loan Agreement thereafter. Based on its current operating plan, which includes estimates of anticipated cash inflows from product sales and cash outflows from operating expenses, the Company believes there is a risk that it will not meet the conditions of the Minimum Cash Covenant within the 12-month period from the issuance date of these condensed consolidated financial statements. In such case, Hercules could accelerate the principal payments on the Company’s outstanding loans and the Company potentially would not have sufficient cash, cash equivalents and short-term marketable securities to settle such obligations. Accordingly, management has concluded that this condition meets the ASC 205-40 standard for raising substantial doubt about the Company’s ability to continue as a going concern. The Company does not have adequate financial resources to fund its forecasted operating costs for at least one year after the date that these consolidated financial statements are issued. The accompanying consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty. Accordingly, the consolidated financial statements have been prepared on a basis that assumes the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the ordinary course of business. To alleviate the risk that the Company violates the Minimum Cash Covenant and to finance its future operations, the Company will need to raise additional capital, which cannot be assured, and/or modify such Minimum Cash Covenant. Unless and until the Company reaches profitability in the future, it will require additional capital to fund its operations, which could be raised through a combination of equity offerings, debt financings, other third-party funding, marketing and distribution arrangements, or 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. The Company is subject to risks common to companies in the biopharmaceutical industry including, but not limited to, uncertainties relating to conducting preclinical and clinical research and development, the manufacture and supply of products and product candidates for clinical and commercial use, obtaining and maintaining regulatory approvals and pricing and reimbursement for the Company’s products and product candidates, market acceptance, managing global growth and operating expenses, availability of additional capital, competition, obtaining and enforcing patents, stock price volatility, dependence on collaborative relationships and third-party service providers, dependence on key personnel, and from time to time government investigations, litigation, and potential product liability claims. Principles of Consolidation— The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, including X4 Pharmaceuticals (Austria) GmbH (“X4 Austria”), which is incorporated in Vienna, Austria, and X4 Therapeutics, Inc. All intercompany accounts and transactions have been eliminated. Unaudited Interim Condensed Consolidated Financial Statements— The condensed consolidated balance sheet at December 31, 2023 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, 2023 included in the 2023 Annual Report filed with the SEC on March 21, 2024. 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 comprehensive (loss) income and cash flows have been made. The results of operations for the three and nine months ended September 30, 2024 are not necessarily indicative of the results of operations that may be expected for the year ending December 31, 2024. Use of Estimates— The preparation of the Company’s 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 condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the accrual of operational and financial license milestones (Note 3), the accrual of reserves for variable consideration related to product revenue, and the impairment or lack of impairment of long-lived assets including operating lease right-of-use assets and goodwill. 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 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.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2024
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, 2023 filed with the SEC on March 21, 2024. Since the date of those consolidated financial statements, there have been no material changes to the Company’s significant accounting policies other than as follows: Revenue Recognition— The Company records revenue using the guidance of ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”), as amended. Upon the approval by the FDA of the sales and marketing of the Company’s lead product candidate, revenue related to its sale and distribution is accounted for under ASC 606. The Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the Company determines it expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (1) identify the customer and contract with the customer; (2) identify the performance obligations in the contract; (3) determine the transaction price, adjusted for variable consideration resulting from potential returns, rebates, discounts, and down-stream charges; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when the Company satisfies its performance obligations, which is upon shipment of the finished product to the customer. The Company currently sells its product to one U.S. customer, which is a specialty pharmacy. The specialty pharmacy dispenses the Company’s drug product to patients in the U.S.. The Company records revenue when the specialty pharmacy obtains control over the promised good, which occurs at a point in time, typically upon delivery to the specialty pharmacy. The Company has concluded that it provides one performance obligation in its contract with its customer: the delivery of drug product that has been approved for sale and distribution by the applicable regulatory authority. As part of the accounting for its contract arrangements, the Company makes significant judgments, primarily related to the estimation of the amount of variable consideration to include in the transaction price upon delivery of the Company’s drug product. The variable consideration includes estimates for discounts, product returns, rebates that will be due to U.S. federal and state payors, such as Medicaid, based on agreements that the Company has with these payors who provide medical insurance to the end patient, and estimated co-pay assistance payments for patients who enroll in the Company’s patient assistance program. These variable payments are considered a reduction of the Company’s transaction price with its customer and must be estimated at the time the Company’s product is delivered to the customer. The Company determines the amount of variable consideration by using the expected value method. Net revenue recognized for each period is the amount for which, based on management’s estimate, it is probable that a significant reversal of cumulative revenue recognized will not occur. At the end of each subsequent reporting period, the Company re-evaluates these estimates based on new information and actual operational trends and if necessary, adjusts these variable consideration estimates. Any such adjustments are recorded on a cumulative catch-up basis in the period of the adjustment. Inventory— Prior to receiving approval from the FDA in April 2024 to sell XOLREMDI (mavorixafor) in the United States, the Company expensed all costs incurred related to the manufacture of mavorixafor as research and development expense due to the inherent risks associated with the development of a drug candidate, the uncertainty about the regulatory approval process and the lack of history for the Company in obtaining of regulatory approval of drug candidates. The Company has capitalized inventory-related costs that have been incurred subsequent to FDA approval, such as the bottling, labelling, and packaging of drug product, and the acquisition of raw materials for the production of drug substance to be used in commercial drug product. In connection therewith, the Company values inventories at the lower of cost or estimated net realizable value. The Company determines the cost of inventories on a first-in, first-out (“FIFO”) basis. Raw materials and work in process include all inventory costs prior to packaging, and labelling, including raw materials and the active pharmaceutical ingredient used in the drug product. Finished goods include packaged and labelled drug products designated for commercial distribution. Clinical drug supplies are expensed to research and development. Raw materials and work in process that may be used for either research and development or commercial sale are classified as inventory until the material is consumed or otherwise allocated for research and development. If the material may only be used for research and development, it is expensed as research and development. Cost of Revenue— Cost of revenue consists of drug product costs, amortization of intangible assets associated with license agreements, accrued royalty costs and capitalized internal direct and overhead costs associated with the manufacturing, lot release and distribution of XOLREMDI. Cost of revenue may also include costs related to excess or obsolete inventory adjustment charges and abnormal manufacturing costs. Intangible Assets, Net— Definite-lived intangible assets related to capitalized milestones under license agreements are amortized on a straight-line basis, which aligns with the pattern over which the economic benefit of the intangible assets are consumed, over their remaining useful lives, which are estimated to be the remaining patent life. If the Company’s estimate of the product’s useful life is shorter than the remaining patent life, then a shorter period is used. Amortization expense is recorded as a component of cost of revenue on the consolidated statements of operations and comprehensive (loss) income. Restricted Cash (in thousands) As of September 30, 2024 As of December 31, 2023 Letter of credit security: Waltham lease $ — $ 250 Letter of credit security: Vienna Austria lease 213 211 Letter of credit security: Boston lease 575 571 Total restricted cash $ 788 $ 1,032 Restricted cash included in prepaid expenses and other current assets $ — $ 250 Restricted cash included in other assets $ 788 $ 782 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 Company’s Waltham lease agreement expired in December 2023; however, the letter of credit was in place as of December 31, 2023 pending the landlord’s completion of its lease expiration procedures. The letter of credit was released in the quarter ended March 31, 2024. In accordance with the Company’s Hercules Loan Agreement and as further described in Note 10, the Company at all times must maintain a minimum level of cash of $20.0 million in an account or accounts in which Hercules has a first priority security interest as further described in Note 10. The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets to the sum to the total of amounts shown in the Company’s consolidated statements of cash flows as of September 30, 2024 and December 31, 2023: (in thousands) September 30, 2024 December 31, 2023 Cash and cash equivalents $ 97,412 $ 99,216 Restricted cash, current (included within prepaid expenses and other current assets) — 250 Restricted cash, non-current 788 782 Total cash, cash equivalents and restricted cash $ 98,200 $ 100,248 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 nine months ended September 30, 2024 that necessitated an interim impairment test of goodwill. Recently Issued Accounting Standards In November 2023, the Financial Accounting Standards Board (“FASB”) issued ASU 2023-07, Segment Reporting (Topic 326) Improvements to Reportable Segment Disclosures (“ASU 2023-07”). Among other disclosure enhancements, ASU 2023-07 requires that entities with one reportable segment, such as the Company, disclose general information for its reportable segment, such as the title and position of the individual identified as the Chief Operating Decision Maker (“CODM”), which for the Company is the Chief Executive Officer, the types of products and services provided by the reportable segment, the measure of profit or loss reviewed by the CODM to evaluate performance of the reportable segment and other financial results such as interest income, interest expense, and depreciation associated with the reportable segment. The amendments in ASU 2023-07 will become effective for the Company in its consolidated financial statements as of and for the three years ending December 31, 2024 and must be adopted retrospectively. Although the Company continues to evaluate the impact of ASU 2023-07, these amendments may require additional disclosures in the Company’s annual and interim consolidated financial statements, though such disclosures are not expected to have a material impact on the Company’s consolidated financial states when adopted. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740) Improvements to Income Tax Disclosures (“ASU 2023-09”). The amendments in ASU 2023-09 require that entities on an annual basis disclose specific categories in the income tax rate reconciliation and provide additional information for reconciling items if the effect of those reconciling items that exceed a certain threshold. ASU 2023-09 will also require more disaggregated disclosures related to income taxes paid. The amendments in ASU 2023-09 will become effective for the Company in its December 31, 2024 consolidated financial statements. Although the Company continues to evaluate the impact of ASU 2023-09, the Company expects that these amendments will require further disclosures in the tax footnote of its annual consolidated financial statements and will not have a material impact on its consolidated financial states when adopted. In November 2024, the FASB issued ASU 2024-03, Disaggregation of Income Statement Expenses (Topic 220)

License, and Funding Agreements

License, and Funding Agreements	9 Months Ended
License, and Funding Agreements	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License, and Funding Agreements	LICENSE 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, 2024, the amount due under the program is $1.1 million, which amount is included in research and development incentive receivable in the condensed consolidated balance sheet. During the nine months ended September 30, 2024 and 2023, the Company recorded $0.5 million and $0.4 million, respectively, of income related to the program within the condensed consolidated statements of operations and comprehensive (loss) income as other income. License 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 has the right to grant sublicenses of the licensed rights that cover mavorixafor to third parties. As of September 30, 2024, the Company is obligated to make future milestone payments in the aggregate amount of up to $13.0 million, contingent upon the achievement by the Company of certain clinical-stage regulatory milestones and sales milestones with respect to licensed products. During the nine months ended September 30, 2024, a $7.0 million regulatory milestone payment was made after receipt of FDA approval of the Company’s NDA on April 26, 2024. The payment was recorded as a definite-lived intangible asset as discussed in Note 8. The remaining regulatory milestones include (i) $3.0 million for the acceptance by the European Medicines Agency (“EMA”) of the Company’s first drug application and (ii) $5.0 million upon the notification by the EMA of regulatory approval of the Company’s first drug application. The Company must also make one-time sales milestone payments of $0.5 million, $1.5 million, and $3.0 million on cumulative net sales of $50.0 million, $150.0 million, and $300.0 million, respectively. As of September 30, 2024 , the Company has accrued $3.0 million of regulatory milestones and $0.5 million of sales-based milestones as a component of the definite-lived intangible asset, as management has concluded that the achievement of these milestones is probable. The Company is also obligated to pay Genzyme tiered royalties based on net sales of licensed products that the Company commercializes under the agreement. Upon the first sale of the Company’s drug product in the U.S., the Company incurred a royalty on annual net sales at a rate of 6% up to $150 million, 10% on the portion of annual net sales between $150 million and $300 million, and 12% thereafter on annual sale over $300 million. The Company includes these royalties in cost of revenue. There were no material modifications of the Company’s license or research and development incentive agreements during the nine months ended September 30, 2024.

Revenue

Revenue	9 Months Ended
Revenue	Sep. 30, 2024
Revenue from Contract with Customer [Abstract]
Revenue	PRODUCT REVENUE, NET During the three and nine months ended September 30, 2024, the Company recorded net revenue $0.6 million and $1.1 million, respectively, for the sale of the Company’s product. The following table summarizes the balances and activity in each of the product reserve accounts for the nine months ended September 30, 2024. (in thousands) Rebates and Discounts Co-Pay Assistance Product Returns Total Beginning balance at December 31, 2023 $ — $ — $ — $ — Provision related to revenue associated with sales processed in the nine month period ended September 30, 2024 59 37 5 101 Credits and payments made during the period (35) (33) — (68) Balance as of September 30, 2024 $ 24 $ 4 $ 5 $ 33 The provision for contractual discounts provided to the Company’s customer is recorded as a reduction of accounts receivable. The provisions for co-pay assistance payments, contractual rebates and product returns are classified within accrued expenses. The following table provides a rollforward of accounts receivable for the nine months ended September 30, 2024. There was no activity in accounts receivable in the nine months ended September 30, 2023. (in thousands) Accounts Receivable Beginning balance at December 31, 2023 $ — Increase in accounts receivable for drug product sales 1,189 Decrease in accounts receivable for cash collections (1,189) Balance as of September 30, 2024 $ —

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	9 Months Ended
Fair Value of Financial Assets and Liabilities	Sep. 30, 2024
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, 2024 Using: (in thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents—money market funds and U.S. Treasury bills $ 68,734 $ 7,993 $ — $ 76,727 Marketable securities— U.S. Treasury notes, U.S. Treasury bills, and federal government agency notes — 37,565 — 37,565 $ 68,734 $ 45,558 $ — $ 114,292 Liabilities: Embedded derivative liability $ — $ — $ 10 $ 10 Class C warrant liability — — 11,087 11,087 $ — $ — $ 11,097 $ 11,097 Fair Value Measurements as of December 31, 2023 Using: (in thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents—money market funds and U.S. Treasury bills $ 76,856 $ 4,985 $ — $ 81,841 Marketable securities—U.S. Treasury notes, U.S. Treasury bills, and federal government agency notes — 15,000 — 15,000 $ 76,856 $ 19,985 $ — $ 96,841 Liabilities: Embedded derivative liability $ — $ — $ 10 $ 10 Class C warrant liability — — 15,683 15,683 $ — $ — $ 15,693 $ 15,693 All marketable securities are classified as short-term investments as all are due within one year and include investments in U.S. Treasury notes, U.S. Treasury bills and federal government agency notes. The Company evaluated each marketable security for impairment that is other-than-temporary and concluded that no marketable security was impaired as of September 30, 2024. The Company’s cash equivalents consisted of money market funds invested in U.S. Treasury securities and direct investments in U.S. Treasury securities. The money market funds were valued based on quoted prices in active markets for identical assets, which represents a Level 1 measurement. U.S. Treasury securities were valued by using inputs observable in active markets for similar securities, which represents a Level 2 measurement in the fair value hierarchy. The following table provides amortized cost, unrealized gains and losses and the carrying amount of available-for-sale debt marketable securities as of September 30, 2024: (in thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. Treasury securities $ 4,193 $ 3 $ — $ 4,196 Federal Government agency securities 33,367 21 (19) 33,369 Total available-for-sale debt securities $ 37,560 $ 24 $ (19) $ 37,565 The following table provides a roll-forward for the nine months ended September 30, 2024, 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, 2023 $ 10 $ 15,683 $ 15,693 Change in fair value — (4,596) (4,596) Balance as of September 30, 2024 $ 10 $ 11,087 $ 11,097 Valuation of Embedded Derivative Liability — The fair value of the embedded derivative liability recognized in connection with the Company’s loan agreement with Hercules (see Note 10), 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 consolidated balance sheets, is estimated by the Company at each reporting date based, in part, on the results of third-party valuations, which were prepared based on a discounted cash flow model that considered 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 17%. 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. The Class C Warrants are accounted for as a liability on the consolidated balance sheet and are adjusted to fair value at period end through “other (expense) income” on the condensed consolidated statements of operations and comprehensive (loss) income. 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, 2024 December 31, 2023 Common stock price $0.67 $0.84 Risk-free interest rate 3.6 % 3.9 % Expected term (in years) 3.2 3.9 Expected volatility 103.5 % 96.2 % Expected dividend yield — % — %

Inventory

Inventory	9 Months Ended
Inventory	Sep. 30, 2024
Inventory Disclosure [Abstract]
Inventory	INVENTORY Inventory consists of the following: (in thousands) September 30, 2024 December 31, 2023 Raw materials $ 1,520 — Work in process 745 — Finished goods 180 — Total inventory $ 2,445 $ —

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
Property and Equipment, Net	Sep. 30, 2024
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, 2024 December 31, 2023 Leasehold improvements $ 228 $ 228 Furniture and fixtures 1,472 1,301 Computer equipment 263 160 Software 24 24 Lab equipment 651 651 2,638 2,364 Less: Accumulated depreciation and amortization (1,818) (1,619) $ 820 $ 745 Depreciation expense related to property and equipment was $211 thousand and $357 thousand for the nine months ended September 30, 2024 and 2023, respectively.

Intangible Assets, Goodwill and

Intangible Assets, Goodwill and Other	9 Months Ended
Intangible Assets, Goodwill and Other	Sep. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets, Net	INTANGIBLE ASSET, NET As of September 30, 2024 , the Company’s net definite-lived intangible asset, which resulted from the capitalization of certain milestone payments made or accrued related to its license agreement for the intellectual property contained in its drug product, totaled $10.2 million . The Company amortizes the intangible asset to cost of revenue over the remaining life of the underlying patent protecting the intellectual property through 2038. As of September 30, 2024 , amortization expense for the next five years and beyond is summarized as follows (in thousands): Year Amortization expense 2024 (remainder of year) $ 188 2025 750 2026 750 2027 750 2028 750 Thereafter 7,000 Total $ 10,188 The Company began amortizing its finite-lived intangible assets in April 2024 over a 14-year period based on the expected patent exclusivity period for XOLREMDI. Amortization expense totaled $0.2 million and $0.3 million for the three and nine months ended September 30, 2024, respectively

Accrued Expenses

Accrued Expenses	9 Months Ended
Accrued Expenses	Sep. 30, 2024
Payables and Accruals [Abstract]
Accrued Expenses	ACCRUED EXPENSES Accrued expenses consisted of the following: (in thousands) September 30, December 31, Accrued employee compensation and benefits $ 9,212 8,195 Accrued external research and development expenses 3,327 2,804 Accrued royalty and milestone payments . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,033 — Accrued professional fees 2,134 1,195 Other 1,753 622 $ 19,459 $ 12,816

Long-Term Debt

Long-Term Debt	9 Months Ended
Long-Term Debt	Sep. 30, 2024
Debt Disclosure [Abstract]
Long-Term Debt	LONG-TERM DEBT Long-term debt consisted of the following: (in thousands) September 30, December 31, Principal amount of long-term debt $ 75,000 $ 55,000 Debt discount, net of accretion (706) (917) Cumulative accretion of end of term payments 930 487 Long-term debt $ 75,224 $ 54,570 Hercules Loan Agreement The Company entered into a Loan and Security Agreement, as most recently amended in August 2023 with Hercules Capital, Inc. The Hercules Loan Agreement provides for an aggregate term loan facility of up to $115.0 million, under which the Company has borrowed an aggregate of $75.0 million of term loans, representing the maximum borrowings allowable as of September 30, 2024. During the nine months ended September 30, 2024, the Company borrowed an additional $20.0 million term loan, which became available based on the achievement of an operational milestone. The Hercules Loan Agreement allows for $40.0 million of additional borrowings: (i.) an additional tranche of $7.5 million is now available following achievement of a certain clinical development-related milestone through 45 days following achievement of such milestone. Such tranche is not included in the $75.0 million of borrowings outstanding as of September 30, 2024; and (ii.) an additional tranche of up to $32.5 million, which will be available subject to approval by Hercules in its sole discretion. 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 July 1, 2027, which is the maturity date of the loans. 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 2% during the 12-month period ending January 5, 2025 and 1% thereafter. In addition, the Hercules Loan Agreement provides for payment of end-of-term fees of $2.8 million plus 3.5% of the aggregate principal amount of future loans drawn, if any, 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 (a) the Company maintains a market capitalization (as defined in the Hercules Loan Agreement) of at least $450.0 million and (b) the Company maintains Qualified Cash, as defined in the Hercules Loan Agreement, 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, 2024 2023 2024 2023 Total interest expense $ 2,414 $ 1,397 $ 6,463 $ 3,210 Non-cash interest expense $ 194 $ 237 $ 655 $ 681 The annual effective interest rate of the Hercules Loan Agreement as of September 30, 2024 is 12.2%. There were no principal payments due or paid under the Hercules Loan Agreement during the nine months ended September 30, 2024. During the nine months ended September 30, 2024, the Company borrowed an additional $20.0 million term loan, which became available based on the achievement of an operational milestone. As of September 30, 2024, future principal and accrued end-of-term payments of $75.9 million under the Hercules Loan Agreement are due on July 1, 2027. (in thousands), Year Ending December 31, Total 2024 $ — 2025 — 2026 — 2027 75,930 Long-term debt $ 75,930

Leases

Leases	9 Months Ended
Leases	Sep. 30, 2024
Leases [Abstract]
Leases	LEASES The Company has lease agreements for its facilities in Boston, Massachusetts, which is the Company’s principal executive office, and Vienna, Austria, which is the Company’s research and development center. There are no restrictions or financial covenants associated with any of the lease agreements. The Company has an operating lease for approximately 1,200 square meters of laboratory and office space in Vienna, Austria (“Vienna Lease”), that commenced in February 2021 for a term of 7 years. The annual base rent for the Vienna Lease is approximately $282 thousand. The Company also 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 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. 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, 2024 and 2023 were as follows: (dollars in thousands) Three Months Ended September 30, Nine Months Ended September 30, Lease Cost 2024 2023 2024 2023 Fixed operating lease cost $ 495 $ 518 $ 1,473 $ 1,561 Total lease expense $ 495 $ 518 $ 1,473 $ 1,561 Other information Operating cash outflows from operating leases $ 345 $ 345 $ 1,032 $ 1,037 Sublease income $ — $ 49 $ — $ 97 Weighted-average remaining lease term—operating leases 2.5 3.4 2.5 3.4 Weighted-average discount rate—operating leases 11.5 % 11.5 % 11.5 % 11.5 % Maturities of lease liabilities due under lease agreements that have commenced as of September 30, 2024 are as follows (in thousands): Maturity of lease liabilities Operating 2024 (remainder of the year) $ 349 2025 1,414 2026 1,344 2027 292 2028 49 Total lease payments 3,448 Less: interest (469) Total operating lease liabilities as of September 30, 2024 $ 2,979

Commitment and Contingencies

Commitment and Contingencies	9 Months Ended
Commitment and Contingencies	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitment and Contingencies	COMMITMENTS AND CONTINGENCIES The Company has agreements with clinical research organizations (“CROs”) pursuant to which the Company and the CROs are conducting clinical trials. The Company may terminate these agreements by providing notice pursuant to the contractual provisions of such agreements and would incur early termination fees. The Company has agreements with contract manufacturing organizations (“CMOs”) for the production of mavorixafor for use in clinical trials and for the commercial supply of XOLREMDI. The Company’s agreement with the CMO who produces batches of drug substance for use in the Company’s clinical and commercial drug supply contains cancellation provisions that would require the Company to pay up to the full contract value upon cancellation. As of September 30, 2024, the Company has approximately $1.9 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, 2024 or December 31, 2023. 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.

Common Stock Warrants

Common Stock Warrants	9 Months Ended
Common Stock Warrants	Sep. 30, 2024
Equity [Abstract]
Common Stock Warrants	COMMON STOCK AND COMMON STOCK WARRANTS As of September 30, 2024, 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. 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. There were no warrant exercises during the three or nine months ended September 30, 2024. As of September 30, 2024, the Company’s outstanding warrants and pre-funded warrants to purchase shares of common stock consisted of the following: Issuance Date Number of Exercise 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 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 18, 2023 8,263,157 $ 1.52 (g) n/a 108,792,939 (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

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
Stock-Based Compensation	Sep. 30, 2024
Share-Based Payment Arrangement [Abstract]
Stock-Based Compensation	STOCK-BASED COMPENSATION As of September 30, 2024, there is an aggregate of approximately 3.9 million shares of common stock available for issuance under the Company’s equity incentive plans. Approximately 4.7 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, 2024 2023 2024 2023 Risk-free interest rate 3.8 % 4.2 % 4.1 % 4.0 % Expected term (in years) 6.1 6.1 6.1 6.0 Expected volatility 101.4 % 94.7 % 97.6 % 93.5 % 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, 2024: Number of Weighted Weighted Aggregate Outstanding as of December 31, 2023 6,008,541 $ 2.97 8.6 $ 24 Granted 6,245,756 0.98 Forfeited and Expired (670,641) 1.87 $ — Outstanding as of September 30, 2024 11,583,656 $ 1.96 8.8 $ — Exercisable as of September 30, 2024 2,418,389 $ 5.26 6.7 $ — Vested and expected to vest as of September 30, 2024 9,206,078 $ 2.19 8.6 $ — The weighted average grant-date fair value per share of stock options granted during the nine months ended September 30, 2024 and 2023 was $0.78 and $1.02, respectively. Restricted Stock Units— The following table summarizes the Company’s restricted stock unit activity for the nine months ended September 30, 2024: Number of Unvested as of December 31, 2023 3,118,824 Granted 6,292,459 Vested (842,351) Forfeited (452,712) Unvested as of September 30, 2024 8,116,220 During the nine months ended September 30, 2024, 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, 2024, neither of the two performance criteria had been met. Stock-based compensation expense has been recognized for awards for which vesting is considered probable 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 the probable 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, 2024, total unrecognized compensation expense related to unvested stock options and restricted stock units was $7.9 million, which is expected to be recognized over a weighted average period of 2.3 years. Stock-based compensation expense was classified in the condensed consolidated statements of operations and comprehensive (loss) income as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2024 2023 2024 2023 Research and development expense $ 1,143 $ 1,259 $ 3,108 $ 3,210 Selling, general and administrative expense 677 1,102 2,879 2,938 Total stock-based compensation $ 1,820 $ 2,361 $ 5,987 $ 6,148

Income Taxes

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2024
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The income tax provision recorded for the three and nine months ended September 30, 2024 and 2023 is primarily related to the Company’s Austrian subsidiary and its Security Corporation subsidiary that holds a portion of its investment portfolio. The Company did not record a U.S. federal or state provision or benefit for income taxes in its consolidated statement of operations and comprehensive (loss) income for the three and nine month periods ended September 30, 2024 and 2023. For the nine months ended September 30, 2024, the Company generated net income and ordinary income. However, as the Company is projecting an ordinary loss before income taxes for the full year and as the Company has a full valuation allowance on its net operating loss carryforwards, the Company has not recorded a U.S. federal or state income tax expense or benefit for the three month and nine months ended September 30, 2024.

Net Loss per Share

Net Loss per Share	9 Months Ended
Net Loss per Share	Sep. 30, 2024
Earnings Per Share [Abstract]
Net Loss per Share	NET (LOSS) INCOME PER SHARE Basic and diluted net (loss) income per share was calculated as follow: Three Months Ended September 30, Nine Months Ended September 30, (in thousands, except share and per share data) 2024 2023 2024 2023 Numerator: Net (loss) income $ (36,696) $ (2,305) $ 2,371 $ (82,037) Denominator: Weighted average shares of common stock outstanding—basic 200,865,276 196,987,827 200,434,027 170,751,244 Net (loss) income per share— basic $ (0.18) $ (0.01) $ 0.01 $ (0.48) Effective of dilutive securities Restricted stock units — 110,947 Employee stock purchase plan — 66,258 Dilutive potential common shares — — 177,205 — Weighted average shares of common stock outstanding—diluted 200,865,276 196,987,827 200,611,232 170,751,244 Net (loss) income per share— diluted $ (0.18) $ (0.01) $ 0.01 $ (0.48) Basic and diluted weighted average shares of common stock outstanding for the three and nine months ended September 30, 2024 and September 30, 2023 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. 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, 2024 and 2023. For the three and nine months ended September 30, 2023, and for the three months ended September 30, 2024, during which the Company recorded a net loss, 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.” For these periods, the weighted average number of shares of common stock outstanding used to calculate both basic and diluted net loss per share of common stock is the same. For the nine months ended September 30, 2024, the Company reported net income. For this period, the dilutive effect of outstanding stock options, restricted stock units, warrants, and estimated common shares issuable under the Company’s employee stock purchase plan was calculated using the treasury stock method, whereby all such awards were assumed to be exercised at the later of the beginning of the period or the grant date. The hypothetical proceeds from such exercises, including the average unrecognized stock compensation expense for outstanding stock options and restricted stock units, was assumed to be used to purchase outstanding common stock at the average price during the period. The net share impact of dilutive securities was added to the weighted average basic common shares outstanding to calculate weighted average diluted shares outstanding. 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) income per share for the periods indicated because including them would have had an anti-dilutive effect: Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Options to purchase shares of common stock 11,583,656 5,568,734 11,583,656 5,568,734 Unvested restricted stock units 8,116,220 5,574,839 7,976,220 5,574,839 Warrants to purchase shares of common stock (excluding prefunded warrants, which are included in basic shares outstanding) 76,378,805 80,244,959 76,378,805 80,244,959 96,078,681 91,388,532 95,938,681 91,388,532

Gain on Sale of Non-Financial A

Gain on Sale of Non-Financial Asset	9 Months Ended
Gain on Sale of Non-Financial Asset	Sep. 30, 2024
Discontinued Operations and Disposal Groups [Abstract]
Gain on Sale of Non-Financial Asset	GAIN ON SALE OF NON-FINANCIAL ASSET During the nine months ended September 30, 2024, the Company entered into contractual arrangement with a third party that transferred the rights to a Priority Review Voucher (“PRV”) awarded to the Company as a result of the FDA’s approval of XOLREMDI. The PRV was accounted for as an intangible asset with no accounting cost basis. The third party purchased the PRV for $105.0 million. There were no fees associated with the sale and the Company has no continuing obligations with respect to the PRV. The Company concluded that the third party is “non-customer” as the underlying PRV is not an output of the Company’s ordinary commercial activities. Accordingly, the Company accounted for this transaction under ASC Topic 610-20, Gains and Losses from the Derecognition of Nonfinancial Assets

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Pay vs Performance Disclosure
Net income	$ (36,696)	$ 90,833	$ (51,766)	$ (2,305)	$ (55,712)	$ (24,020)	$ 2,371	$ (82,037)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Sep. 30, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2024
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation— The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, including X4 Pharmaceuticals (Austria) GmbH (“X4 Austria”), which is incorporated in Vienna, Austria, and X4 Therapeutics, Inc. All intercompany accounts and transactions have been eliminated.
Use of Estimates	Use of Estimates— The preparation of the Company’s 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 condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the accrual of operational and financial license milestones (Note 3), the accrual of reserves for variable consideration related to product revenue, and the impairment or lack of impairment of long-lived assets including operating lease right-of-use assets and goodwill. 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 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.
Revenue Recognition	Revenue Recognition— The Company records revenue using the guidance of ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”), as amended. Upon the approval by the FDA of the sales and marketing of the Company’s lead product candidate, revenue related to its sale and distribution is accounted for under ASC 606. The Company recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the Company determines it expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that the Company determines are within the scope of ASC 606, the Company performs the following five steps: (1) identify the customer and contract with the customer; (2) identify the performance obligations in the contract; (3) determine the transaction price, adjusted for variable consideration resulting from potential returns, rebates, discounts, and down-stream charges; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when the Company satisfies its performance obligations, which is upon shipment of the finished product to the customer. The Company currently sells its product to one U.S. customer, which is a specialty pharmacy. The specialty pharmacy dispenses the Company’s drug product to patients in the U.S.. The Company records revenue when the specialty pharmacy obtains control over the promised good, which occurs at a point in time, typically upon delivery to the specialty pharmacy. The Company has concluded that it provides one performance obligation in its contract with its customer: the delivery of drug product that has been approved for sale and distribution by the applicable regulatory authority.
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 nine months ended September 30, 2024 that necessitated an interim impairment test of goodwill.
Recently Adopted Accounting Pronouncements	Recently Issued Accounting Standards In November 2023, the Financial Accounting Standards Board (“FASB”) issued ASU 2023-07, Segment Reporting (Topic 326) Improvements to Reportable Segment Disclosures (“ASU 2023-07”). Among other disclosure enhancements, ASU 2023-07 requires that entities with one reportable segment, such as the Company, disclose general information for its reportable segment, such as the title and position of the individual identified as the Chief Operating Decision Maker (“CODM”), which for the Company is the Chief Executive Officer, the types of products and services provided by the reportable segment, the measure of profit or loss reviewed by the CODM to evaluate performance of the reportable segment and other financial results such as interest income, interest expense, and depreciation associated with the reportable segment. The amendments in ASU 2023-07 will become effective for the Company in its consolidated financial statements as of and for the three years ending December 31, 2024 and must be adopted retrospectively. Although the Company continues to evaluate the impact of ASU 2023-07, these amendments may require additional disclosures in the Company’s annual and interim consolidated financial statements, though such disclosures are not expected to have a material impact on the Company’s consolidated financial states when adopted. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740) Improvements to Income Tax Disclosures (“ASU 2023-09”). The amendments in ASU 2023-09 require that entities on an annual basis disclose specific categories in the income tax rate reconciliation and provide additional information for reconciling items if the effect of those reconciling items that exceed a certain threshold. ASU 2023-09 will also require more disaggregated disclosures related to income taxes paid. The amendments in ASU 2023-09 will become effective for the Company in its December 31, 2024 consolidated financial statements. Although the Company continues to evaluate the impact of ASU 2023-09, the Company expects that these amendments will require further disclosures in the tax footnote of its annual consolidated financial statements and will not have a material impact on its consolidated financial states when adopted. In November 2024, the FASB issued ASU 2024-03, Disaggregation of Income Statement Expenses (Topic 220)
Research and Development Expense, Policy
Inventory	Inventory— Prior to receiving approval from the FDA in April 2024 to sell XOLREMDI (mavorixafor) in the United States, the Company expensed all costs incurred related to the manufacture of mavorixafor as research and development expense due to the inherent risks associated with the development of a drug candidate, the uncertainty about the regulatory approval process and the lack of history for the Company in obtaining of regulatory approval of drug candidates. The Company has capitalized inventory-related costs that have been incurred subsequent to FDA approval, such as the bottling, labelling, and packaging of drug product, and the acquisition of raw materials for the production of drug substance to be used in commercial drug product. In connection therewith, the Company values inventories at the lower of cost or estimated net realizable value. The Company determines the cost of inventories on a first-in, first-out (“FIFO”) basis. Raw materials and work in process include all inventory costs prior to packaging, and labelling, including raw materials and the active pharmaceutical ingredient used in the drug product. Finished goods include packaged and labelled drug products designated for commercial distribution. Clinical drug supplies are expensed to research and development. Raw materials and work in process that may be used for either research and development or commercial sale are classified as inventory until the material is consumed or otherwise allocated for research and development. If the material may only be used for research and development, it is expensed as research and development.
Intangible Assets	Intangible Assets, Net— Definite-lived intangible assets related to capitalized milestones under license agreements are amortized on a straight-line basis, which aligns with the pattern over which the economic benefit of the intangible assets are consumed, over their remaining useful lives, which are estimated to be the remaining patent life. If the Company’s estimate of the product’s useful life is shorter than the remaining patent life, then a shorter period is used. Amortization expense is recorded as a component of cost of revenue on the consolidated statements of operations and comprehensive (loss) income.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
Summary of Significant Accounting Policies (Tables)	Sep. 30, 2024
Accounting Policies [Abstract]
Schedule of Restricted Cash	Restricted Cash (in thousands) As of September 30, 2024 As of December 31, 2023 Letter of credit security: Waltham lease $ — $ 250 Letter of credit security: Vienna Austria lease 213 211 Letter of credit security: Boston lease 575 571 Total restricted cash $ 788 $ 1,032 Restricted cash included in prepaid expenses and other current assets $ — $ 250 Restricted cash included in other assets $ 788 $ 782
Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the consolidated balance sheets to the sum to the total of amounts shown in the Company’s consolidated statements of cash flows as of September 30, 2024 and December 31, 2023: (in thousands) September 30, 2024 December 31, 2023 Cash and cash equivalents $ 97,412 $ 99,216 Restricted cash, current (included within prepaid expenses and other current assets) — 250 Restricted cash, non-current 788 782 Total cash, cash equivalents and restricted cash $ 98,200 $ 100,248

Revenue (Tables)

Revenue (Tables)	9 Months Ended
Revenue (Tables)	Sep. 30, 2024
Revenue from Contract with Customer [Abstract]
Schedule of Product Reserve Accounts	The following table summarizes the balances and activity in each of the product reserve accounts for the nine months ended September 30, 2024. (in thousands) Rebates and Discounts Co-Pay Assistance Product Returns Total Beginning balance at December 31, 2023 $ — $ — $ — $ — Provision related to revenue associated with sales processed in the nine month period ended September 30, 2024 59 37 5 101 Credits and payments made during the period (35) (33) — (68) Balance as of September 30, 2024 $ 24 $ 4 $ 5 $ 33
Schedule of Accounts, Notes, Loans and Financing Receivable	The following table provides a rollforward of accounts receivable for the nine months ended September 30, 2024. There was no activity in accounts receivable in the nine months ended September 30, 2023. (in thousands) Accounts Receivable Beginning balance at December 31, 2023 $ — Increase in accounts receivable for drug product sales 1,189 Decrease in accounts receivable for cash collections (1,189) Balance as of September 30, 2024 $ —

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
Fair Value of Financial Assets and Liabilities (Tables)	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value	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, 2024 Using: (in thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents—money market funds and U.S. Treasury bills $ 68,734 $ 7,993 $ — $ 76,727 Marketable securities— U.S. Treasury notes, U.S. Treasury bills, and federal government agency notes — 37,565 — 37,565 $ 68,734 $ 45,558 $ — $ 114,292 Liabilities: Embedded derivative liability $ — $ — $ 10 $ 10 Class C warrant liability — — 11,087 11,087 $ — $ — $ 11,097 $ 11,097 Fair Value Measurements as of December 31, 2023 Using: (in thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents—money market funds and U.S. Treasury bills $ 76,856 $ 4,985 $ — $ 81,841 Marketable securities—U.S. Treasury notes, U.S. Treasury bills, and federal government agency notes — 15,000 — 15,000 $ 76,856 $ 19,985 $ — $ 96,841 Liabilities: Embedded derivative liability $ — $ — $ 10 $ 10 Class C warrant liability — — 15,683 15,683 $ — $ — $ 15,693 $ 15,693
Debt Securities, Available-for-Sale	The following table provides amortized cost, unrealized gains and losses and the carrying amount of available-for-sale debt marketable securities as of September 30, 2024: (in thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. Treasury securities $ 4,193 $ 3 $ — $ 4,196 Federal Government agency securities 33,367 21 (19) 33,369 Total available-for-sale debt securities $ 37,560 $ 24 $ (19) $ 37,565
Summary of Aggregate Fair Values of Warrant Liability and Derivative Liability	The following table provides a roll-forward for the nine months ended September 30, 2024, 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, 2023 $ 10 $ 15,683 $ 15,693 Change in fair value — (4,596) (4,596) Balance as of September 30, 2024 $ 10 $ 11,087 $ 11,097
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	September 30, 2024 December 31, 2023 Common stock price $0.67 $0.84 Risk-free interest rate 3.6 % 3.9 % Expected term (in years) 3.2 3.9 Expected volatility 103.5 % 96.2 % Expected dividend yield — % — %

Inventory (Tables)

Inventory (Tables)	9 Months Ended
Inventory (Tables)	Sep. 30, 2024
Inventory Disclosure [Abstract]
Schedule of Inventory, Current	Inventory consists of the following: (in thousands) September 30, 2024 December 31, 2023 Raw materials $ 1,520 — Work in process 745 — Finished goods 180 — Total inventory $ 2,445 $ —

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
Property and Equipment, Net (Tables)	Sep. 30, 2024
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment, net consisted of the following: (in thousands) September 30, 2024 December 31, 2023 Leasehold improvements $ 228 $ 228 Furniture and fixtures 1,472 1,301 Computer equipment 263 160 Software 24 24 Lab equipment 651 651 2,638 2,364 Less: Accumulated depreciation and amortization (1,818) (1,619) $ 820 $ 745

Intangible Assets, Net (Tables)

Intangible Assets, Net (Tables)	9 Months Ended
Intangible Assets, Net (Tables)	Sep. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	As of September 30, 2024 , amortization expense for the next five years and beyond is summarized as follows (in thousands): Year Amortization expense 2024 (remainder of year) $ 188 2025 750 2026 750 2027 750 2028 750 Thereafter 7,000 Total $ 10,188

Accrued Expenses (Tables)

Accrued Expenses (Tables)	9 Months Ended
Accrued Expenses (Tables)	Sep. 30, 2024
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following: (in thousands) September 30, December 31, Accrued employee compensation and benefits $ 9,212 8,195 Accrued external research and development expenses 3,327 2,804 Accrued royalty and milestone payments . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,033 — Accrued professional fees 2,134 1,195 Other 1,753 622 $ 19,459 $ 12,816

Long-Term Debt (Tables)

Long-Term Debt (Tables)	9 Months Ended
Long-Term Debt (Tables)	Sep. 30, 2024
Debt Disclosure [Abstract]
Summary of Long Term Debt	Long-term debt consisted of the following: (in thousands) September 30, December 31, Principal amount of long-term debt $ 75,000 $ 55,000 Debt discount, net of accretion (706) (917) Cumulative accretion of end of term payments 930 487 Long-term debt $ 75,224 $ 54,570
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, 2024 2023 2024 2023 Total interest expense $ 2,414 $ 1,397 $ 6,463 $ 3,210 Non-cash interest expense $ 194 $ 237 $ 655 $ 681
Schedule of Future Principal Payments and the Final Payments Due	As of September 30, 2024, future principal and accrued end-of-term payments of $75.9 million under the Hercules Loan Agreement are due on July 1, 2027. (in thousands), Year Ending December 31, Total 2024 $ — 2025 — 2026 — 2027 75,930 Long-term debt $ 75,930

Leases (Tables)

Leases (Tables)	9 Months Ended
Leases (Tables)	Sep. 30, 2024
Leases [Abstract]
Schedule of Components of Lease Expense	The components of lease expense for the three and nine months ended September 30, 2024 and 2023 were as follows: (dollars in thousands) Three Months Ended September 30, Nine Months Ended September 30, Lease Cost 2024 2023 2024 2023 Fixed operating lease cost $ 495 $ 518 $ 1,473 $ 1,561 Total lease expense $ 495 $ 518 $ 1,473 $ 1,561 Other information Operating cash outflows from operating leases $ 345 $ 345 $ 1,032 $ 1,037 Sublease income $ — $ 49 $ — $ 97 Weighted-average remaining lease term—operating leases 2.5 3.4 2.5 3.4 Weighted-average discount rate—operating leases 11.5 % 11.5 % 11.5 % 11.5 %
Schedule of Maturities of Lease Liabilities	Maturities of lease liabilities due under lease agreements that have commenced as of September 30, 2024 are as follows (in thousands): Maturity of lease liabilities Operating 2024 (remainder of the year) $ 349 2025 1,414 2026 1,344 2027 292 2028 49 Total lease payments 3,448 Less: interest (469) Total operating lease liabilities as of September 30, 2024 $ 2,979

Common Stock Warrants (Tables)

Common Stock Warrants (Tables)	9 Months Ended
Common Stock Warrants (Tables)	Sep. 30, 2024
Equity [Abstract]
Schedule of Warrants	As of September 30, 2024, the Company’s outstanding warrants and pre-funded warrants to purchase shares of common stock consisted of the following: Issuance Date Number of Exercise 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 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 18, 2023 8,263,157 $ 1.52 (g) n/a 108,792,939 (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

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
Stock-Based Compensation (Tables)	Sep. 30, 2024
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, 2024 2023 2024 2023 Risk-free interest rate 3.8 % 4.2 % 4.1 % 4.0 % Expected term (in years) 6.1 6.1 6.1 6.0 Expected volatility 101.4 % 94.7 % 97.6 % 93.5 % 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, 2024: Number of Weighted Weighted Aggregate Outstanding as of December 31, 2023 6,008,541 $ 2.97 8.6 $ 24 Granted 6,245,756 0.98 Forfeited and Expired (670,641) 1.87 $ — Outstanding as of September 30, 2024 11,583,656 $ 1.96 8.8 $ — Exercisable as of September 30, 2024 2,418,389 $ 5.26 6.7 $ — Vested and expected to vest as of September 30, 2024 9,206,078 $ 2.19 8.6 $ —
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, 2024: Number of Unvested as of December 31, 2023 3,118,824 Granted 6,292,459 Vested (842,351) Forfeited (452,712) Unvested as of September 30, 2024 8,116,220
Summary of Stock-Based Compensation Expense Classification	Stock-based compensation expense was classified in the condensed consolidated statements of operations and comprehensive (loss) income as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2024 2023 2024 2023 Research and development expense $ 1,143 $ 1,259 $ 3,108 $ 3,210 Selling, general and administrative expense 677 1,102 2,879 2,938 Total stock-based compensation $ 1,820 $ 2,361 $ 5,987 $ 6,148
Share-Based Payment Arrangement, Option and Stock Appreciation Rights, Activity	Stock Appreciation Rights

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
Net Loss per Share (Tables)	Sep. 30, 2024
Earnings Per Share [Abstract]
Summary of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	Basic and diluted net (loss) income per share was calculated as follow: Three Months Ended September 30, Nine Months Ended September 30, (in thousands, except share and per share data) 2024 2023 2024 2023 Numerator: Net (loss) income $ (36,696) $ (2,305) $ 2,371 $ (82,037) Denominator: Weighted average shares of common stock outstanding—basic 200,865,276 196,987,827 200,434,027 170,751,244 Net (loss) income per share— basic $ (0.18) $ (0.01) $ 0.01 $ (0.48) Effective of dilutive securities Restricted stock units — 110,947 Employee stock purchase plan — 66,258 Dilutive potential common shares — — 177,205 — Weighted average shares of common stock outstanding—diluted 200,865,276 196,987,827 200,611,232 170,751,244 Net (loss) income per share— diluted $ (0.18) $ (0.01) $ 0.01 $ (0.48)
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) income per share for the periods indicated because including them would have had an anti-dilutive effect: Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Options to purchase shares of common stock 11,583,656 5,568,734 11,583,656 5,568,734 Unvested restricted stock units 8,116,220 5,574,839 7,976,220 5,574,839 Warrants to purchase shares of common stock (excluding prefunded warrants, which are included in basic shares outstanding) 76,378,805 80,244,959 76,378,805 80,244,959 96,078,681 91,388,532 95,938,681 91,388,532

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Business Acquisition [Line Items]
Cash, Cash Equivalents, and Short-Term Investments	$ 135,000
Accumulated deficit	(475,534)		$ (477,905)
Net cash used in operating activities	(97,906)	$ (68,765)
Min Cash Test Date 1 \| Hercules Second Amended Loan Agreement
Business Acquisition [Line Items]
Line of Credit, Covenant, Minimum Cash	$ 20,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Schedule of Compensating Balance Arrangements (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Cash and Cash Equivalents [Line Items]
Restricted Cash	$ 788	$ 1,032
Restricted cash, current (included within prepaid expenses and other current assets)	0	250
Total restricted cash	788	782
Letter of Credit \| Waltham Lease
Cash and Cash Equivalents [Line Items]
Restricted Cash	0	250
Letter of Credit \| Vienna Austria Lease
Cash and Cash Equivalents [Line Items]
Restricted Cash	213	211
Letter of Credit \| Allston Lease Agreement
Cash and Cash Equivalents [Line Items]
Restricted Cash	$ 575	$ 571

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 97,412	$ 99,216
Restricted cash, current (included within prepaid expenses and other current assets)	0	250
Restricted cash, non-current	788	782
Total cash, cash equivalents and restricted cash	$ 98,200	$ 100,248	$ 132,604	$ 123,028

License, and Funding Agreemen_2

License, and Funding Agreements - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Collaboration License And Funding Arrangements [Line Items]
Other income, net	$ 226,000	$ 17,000	$ 475,000	$ 342,000
Research and Development Incentive
Collaboration License And Funding Arrangements [Line Items]
Grant receivable	1,100,000		1,100,000
Other income, net			500,000	$ 400,000
Genzyme Agreement
Collaboration License And Funding Arrangements [Line Items]
Milestone Payments			13,000,000
Collaborative arrangement, rights and obligations, maximum aggregate milestone payments, per product	$ 7,000,000		7,000,000
Collaborative arrangement, rights and obligations, maximum aggregate milestone payments, remaining			3,000,000
Collaborative arrangement, rights and obligations, maximum aggregate milestone payments			5,000,000
Collaborative arrangement, rights and obligations, one time payment one			500,000
Collaborative arrangement, rights and obligations, one time payment two			1,500,000
Collaborative arrangement, rights and obligations, one time payment three			3,000,000
Collaborative arrangement, rights and obligations, cumulative threshold one			50,000,000
Collaborative arrangement, rights and obligations, cumulative threshold two			150,000,000
Collaborative arrangement, rights and obligations, cumulative net sales threshold three			$ 300,000,000
Genzyme Agreement \| 6% Net Sales
Collaboration License And Funding Arrangements [Line Items]
Revenue, performance obligation, percentage of net sale	0.06		0.06
Revenue from collaborative arrangement, excluding revenue from contract with customer			$ 150,000,000
Genzyme Agreement \| 10% Net Sales
Collaboration License And Funding Arrangements [Line Items]
Revenue, performance obligation, percentage of net sale	0.10		0.10
Genzyme Agreement \| 10% Net Sales \| Minimum
Collaboration License And Funding Arrangements [Line Items]
Revenue from collaborative arrangement, excluding revenue from contract with customer			$ 150,000,000
Genzyme Agreement \| 10% Net Sales \| Maximum
Collaboration License And Funding Arrangements [Line Items]
Revenue from collaborative arrangement, excluding revenue from contract with customer			$ 300,000,000
Genzyme Agreement \| 12% Net Sales
Collaboration License And Funding Arrangements [Line Items]
Revenue, performance obligation, percentage of net sale	0.12		0.12
Revenue from collaborative arrangement, excluding revenue from contract with customer			$ 300,000,000

Revenue - Narrative (Details)

Revenue - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Revenue - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenue from Contract with Customer [Abstract]
Product revenue, net	$ 560	$ 0	$ 1,123	$ 0

Revenue (Details)

Revenue (Details)	6 Months Ended
Revenue (Details)	Jun. 30, 2024 USD ($)
Disaggregation of Revenue [Line Items]
Beginning balance at December 31, 2023	$ 0
Provision related to revenue associated with sales processed in the nine month period ended September 30, 2024	101,000
Credits and payments made during the period	(68,000)
Balance as of September 30, 2024	33,000
Rebates and Discounts
Disaggregation of Revenue [Line Items]
Beginning balance at December 31, 2023	0
Provision related to revenue associated with sales processed in the nine month period ended September 30, 2024	59,000
Credits and payments made during the period	(35,000)
Balance as of September 30, 2024	24,000
Co-Pay Assistance
Disaggregation of Revenue [Line Items]
Beginning balance at December 31, 2023	0
Provision related to revenue associated with sales processed in the nine month period ended September 30, 2024	37,000
Credits and payments made during the period	(33,000)
Balance as of September 30, 2024	4,000
Product Returns
Disaggregation of Revenue [Line Items]
Beginning balance at December 31, 2023	0
Provision related to revenue associated with sales processed in the nine month period ended September 30, 2024	5,000
Credits and payments made during the period	0
Balance as of September 30, 2024	$ 5,000

Revenue (Details)_2

Revenue (Details) - USD ($) $ in Thousands	9 Months Ended
Revenue (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Accounts Receivable, after Allowance for Credit Loss, Current	$ 0	$ 0
Accounts Receivable, after Allowance for Credit Loss, Current, Increase During Period	1,189
Accounts Receivable, after Allowance for Credit Loss, Current, Decrease During Period	$ (1,189)

Fair Value of Financial Asset_3

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, 2024	Dec. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	$ 114,292	$ 96,841
Fair value of derivative liability	11,097	15,693
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	76,727	81,841
US Treasury Bill Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	37,565	15,000
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	11,087	15,683
Level 1
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	68,734	76,856
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	68,734
Level 1 \| US Treasury Bill Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	0	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	45,558	19,985
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	7,993	4,985
Level 2 \| US Treasury Bill Securities
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	37,565	15,000
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	11,097	15,693
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	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	$ 11,087	$ 15,683

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Debt Securities Available-for-Sale (Details) $ in Thousands	Sep. 30, 2024 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	$ 37,560
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	24
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(19)
Debt Securities, Available-for-Sale	37,565
U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	4,193
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	3
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	0
Debt Securities, Available-for-Sale	4,196
Federal Government Agency Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-Sale, Amortized Cost	33,367
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax	21
Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax	(19)
Debt Securities, Available-for-Sale	$ 33,369

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities - Aggregate Fair Values Financial Instruments (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2024 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 15,693
Change in fair value	(4,596)
Ending balance	11,097
Embedded Derivative Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	10
Change in fair value	0
Ending balance	10
Class C Warrant Liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	15,683
Change in fair value	(4,596)
Ending balance	$ 11,087

Fair Value of Financial Asset_6

Fair Value of Financial Assets and Liabilities - Narrative (Details)	Sep. 30, 2024 USD ($)
Measurement Input, Discount Rate
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Fair value of derivative liability	$ 0.17

Fair Value of Financial Asset_7

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, 2024	Dec. 31, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (in percentage)			3.80%	4.20%	4.10%	4%
Expected term (in years)			6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days	6 years
Expected volatility (in percentage)			101.40%	94.70%	97.60%	93.50%
Expected dividend yield (in percentage)			0%	0%	0%	0%
Fair value of warrant liability	$ 11,097	$ 15,693	$ 11,097		$ 11,097
Class C Warrant Liability
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Price (in dollars per share)	$ 0.67	$ 0.84	$ 0.67		$ 0.67
Risk-free interest rate (in percentage)	3.60%	3.90%
Expected term (in years)	3 years 2 months 12 days	3 years 10 months 24 days
Expected volatility (in percentage)	103.50%	96.20%
Expected dividend yield (in percentage)	0%	0%

Inventory (Details)

Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Inventory Disclosure [Abstract]
Raw materials	$ 1,520	$ 0
Work in process	745	0
Finished goods	180	0
Inventory	$ 2,445	$ 0

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,638	$ 2,364
Less: Accumulated depreciation and amortization	(1,818)	(1,619)
Property and equipment, net	820	745
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	1,472	1,301
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	263	160
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	$ 651

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Depreciation	$ 211	$ 357
Amortization	$ 211	$ 357

Intangible Assets, Net (Details

Intangible Assets, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
2024 (remainder of year)	$ 188
2025	750
2026	750
2027	750
2028	750
Thereafter	7,000
Total	$ 10,188	$ 0

Intangible Assets, Net - Narrat

Intangible Assets, Net - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2024	Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Finite-Lived Intangible Assets, Net	$ 10,188	$ 10,188	$ 0
Finite-Lived Intangible Asset, Useful Life	14 years	14 years
Amortization of Intangible Assets	$ 200	$ 300

Accrued Expenses - Schedule of

Accrued Expenses - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Accrued employee compensation and benefits	$ 9,212	$ 8,195
Accrued external research and development expenses	3,327	2,804
Accrued royalty and milestone payments . . . . . . . . . . . . . . . . . . . . . . . . . . .	3,033	0
Accrued professional fees	2,134	1,195
Other	1,753	622
Total accrued expenses	$ 19,459	$ 12,816

Long-Term Debt - Summary of Lon

Long-Term Debt - Summary of Long Term Debt (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Debt Disclosure [Abstract]
Principal amount of long-term debt	$ 75,000	$ 55,000
Debt discount, net of accretion	(706)	(917)
Cumulative accretion of end of term payments	930	487
Long-term debt	$ 75,224	$ 54,570

Long Term Debt - Hercules Loan

Long Term Debt - Hercules Loan Agreement - Additional Information (Detail) - USD ($)		3 Months Ended	9 Months Ended	30 Months Ended
	Jul. 01, 2024	Sep. 30, 2024	Sep. 30, 2024	Mar. 31, 2021
Hercules Loan Agreement
Debt Instrument [Line Items]
Proceeds from lines of credit				$ 75,000,000
Debt instrument variable percentage		10.15%
Interest rate increase percentage		4%
Line of credit facility periodic payment	$ 2,800,000
Effective interest rate of loan		12.20%	12.20%
Principal payments			$ 0
Maximum term loan borrowing capacity		$ 115,000,000	115,000,000
Hercules Loan Agreement \| Share-Based Payment Arrangement, Tranche One
Debt Instrument [Line Items]
Maximum term loan borrowing capacity		32,500,000	32,500,000
Hercules Loan Agreement \| Share-Based Payment Arrangement, Tranche Two
Debt Instrument [Line Items]
Maximum term loan borrowing capacity		20,000,000	20,000,000
Hercules Loan Agreement \| Share-Based Payment Arrangement, Tranche Three
Debt Instrument [Line Items]
Maximum term loan borrowing capacity		7,500,000	$ 7,500,000
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

Long-Term Debt - Summary of Int

Long-Term Debt - Summary of Interest Expense (Details) - Hercules Loan Agreement - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Interest expense, debt	$ 2,414	$ 1,397	$ 6,463	$ 3,210
Amortization of debt discount	$ 194	$ 237	$ 655	$ 681

Long-Term Debt - Schedule of Fu

Long-Term Debt - Schedule of Future Principal Payments and the Final Payments Due (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Aug. 02, 2023
Debt Disclosure [Abstract]
2024	$ 0
2025	0
2026	0
2027		$ 75,930
Principal amount of long-term debt	$ 75,930

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands		9 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Nov. 11, 2019 USD ($)	Sep. 30, 2024 USD ($) m²	Dec. 31, 2023 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease, liability		$ 2,979
Right-of-use assets		$ 4,471	$ 5,650
Vienna Lease
Lessee, Lease, Description [Line Items]
Office space \| m²		1,200
Lease not yet commenced, term of contract		7 years
Annual base rent		$ 282
Allston Lease
Lessee, Lease, Description [Line Items]
Lease not yet commenced	$ 1,100

Leases - Schedule of Components

Leases - Schedule of Components of Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Leases [Abstract]
Fixed operating lease cost	$ 495	$ 518	$ 1,473	$ 1,561
Total lease expense	495	518	1,473	1,561
Operating cash outflows from operating leases	345	345	1,032	1,037
Sublease income	$ 0	$ 49	$ 0	$ 97
Weighted-average remaining lease term-operating leases (in years)	2 years 6 months	3 years 4 months 24 days	2 years 6 months	3 years 4 months 24 days
Weighted-average discount rate-operating leases	11.50%	11.50%	11.50%	11.50%

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Lease Liabilities (Detail) $ in Thousands	Sep. 30, 2024 USD ($)
Leases [Abstract]
2024 (remainder of the year)	$ 349
2025	1,414
2026	1,344
2027	292
2028	49
Total lease payments	3,448
Less: interest	(469)
Operating lease, liability	$ 2,979

Commitment and Contingencies -

Commitment and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Contingencies And Commitments [Line Items]
Loss Contingency Accrual	$ 1.9
Indemnification Agreements
Contingencies And Commitments [Line Items]
Accrued liabilities	$ 0	$ 0

Common Stock Warrants - Additio

Common Stock Warrants - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2024	Dec. 31, 2023	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

Common Stock Warrants - Summary

Common Stock Warrants - Summary of Outstanding Warrants to Purchase Shares of Common Stock (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2024	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)	108,792,939
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 November 29, 2019 One
Class of Warrant or Right [Line Items]
Exercise Price (usd per share)	$ 12
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

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
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	$ 0.78
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost of stock based awards	$ 7,900
Unrecognized compensation cost of stock based awards, recognition period	2 years 3 months 18 days
2019 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance	3,900,000
Two Thousand Seventeen Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance	4,700,000

Stock-Based Compensation - Sche

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, 2024	Dec. 31, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (in percentage)			3.80%	4.20%	4.10%	4%
Expected term (in years)			6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days	6 years
Expected volatility (in percentage)			101.40%	94.70%	97.60%	93.50%
Expected dividend yield (in percentage)			0%	0%	0%	0%
Class C Warrant Liability
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate (in percentage)	3.60%	3.90%
Expected term (in years)	3 years 2 months 12 days	3 years 10 months 24 days
Expected volatility (in percentage)	103.50%	96.20%
Expected dividend yield (in percentage)	0%	0%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Number of Shares
Beginning balance (in shares)	6,008,541
Granted (in shares)	6,245,756
Forfeited (in shares)	(670,641)
Ending balance (in shares)	11,583,656	6,008,541
Number of shares Options, Exercisable (in shares)	2,418,389
Number of shares Options, Vested and expected to vest (in shares)	9,206,078
Weighted Average Exercise Price
Beginning balance (in usd per share)	$ 2.97
Granted (in usd per share)	0.98
Forfeited (in usd per share)	1.87
Ending balance (in usd per share)	1.96	$ 2.97
Weighted average exercise price, Exercisable (in usd per share)	5.26
Weighted average exercise price, Vested and expected to vest (in usd per share)	$ 2.19
Weighted average contractual term outstanding (in years)	8 years 9 months 18 days	8 years 7 months 6 days
Weighted average contractual term outstanding, Exercisable (in years)	6 years 8 months 12 days
Weighted average contractual term outstanding, Vested and expected to vest (in years)	8 years 7 months 6 days
Aggregate intrinsic value, Beginning balance	$ 24
Aggregate intrinsic value, Ending balance	0	$ 24
Aggregate intrinsic value, exercisable	0
Aggregate intrinsic value, vested and expected to vest	0
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Forfeitures in Period, Intrinsic Value	$ 0

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Units (Details) - Restricted Stock Units (RSUs)	9 Months Ended
	Sep. 30, 2024 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)	3,118,824
Granted (in shares)	6,292,459
Vested (in shares)	(842,351)
Forfeited (in shares)	(452,712)
Nonvested ending balance (in shares)	8,116,220

Stock-Based Compensation Summar

Stock-Based Compensation Summary of Stock-Based Compensation Expense Classification (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 1,820	$ 2,361	$ 5,987	$ 6,148
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	1,143	1,259	3,108	3,210
Selling, general and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 677	$ 1,102	$ 2,879	$ 2,938

Net Loss per Share - Summary of

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, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator:
Net income	$ (36,696)	$ 90,833	$ (51,766)	$ (2,305)	$ (55,712)	$ (24,020)	$ 2,371	$ (82,037)
Denominator:
Weighted average shares of common stock outstanding—basic	200,865,276			196,987,827			200,434,027	170,751,244
Net loss per share attributable to common stockholders—basic	$ (0.18)			$ (0.01)			$ 0.01	$ (0.48)
Dilutive potential common shares	0			0			177,205	0
Weighted average shares of common stock outstanding—diluted	200,865,276			196,987,827			200,611,232	170,751,244
Net loss per share attributable to common stockholders—diluted	$ (0.18)			$ (0.01)			$ 0.01	$ (0.48)
Stock Options
Denominator:
Effective of dilutive securities (in shares)	0						110,947
Employee Stock
Denominator:
Effective of dilutive securities (in shares)	0						66,258

Net Loss per Share - Additional

Net Loss per Share - Additional Information (Detail)	Sep. 30, 2024 $ / 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

Net Loss per Share - Schedule o

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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
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)	96,078,681	91,388,532	95,938,681	91,388,532
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)	11,583,656	5,568,734	11,583,656	5,568,734
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)	8,116,220	5,574,839	7,976,220	5,574,839
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)	76,378,805	80,244,959	76,378,805	80,244,959

Gain on Sale of Non-Financial_2

Gain on Sale of Non-Financial Asset (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Discontinued Operations and Disposal Groups [Abstract]
Gain (Loss) on Disposition of Assets	$ 0	$ 0	$ 105,000	$ 0