4D Molecular Therapeutics (FDMT) 10-Q 13 Nov 24 2024 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2024	Nov. 12, 2024
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2024
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Document Quarterly Report	true
Document Transition Report	false
Entity Registrant Name	4D Molecular Therapeutics, Inc.
Entity Central Index Key	0001650648
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Interactive Data Current	Yes
Entity File Number	001-39782
Entity Tax Identification Number	47-3506994
Entity Address, Address Line One	5858 Horton Street #455
Entity Address, City or Town	Emeryville
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94608
City Area Code	(510)
Local Phone Number	505-2680
Entity Incorporation, State or Country Code	DE
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	FDMT
Security Exchange Name	NASDAQ
Pre-funded Warrants [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,583,476
PreFunded Warrants Issued in Exchange of Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		5,775,000
Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		46,227,709

Condensed Balance Sheets

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 187,539	$ 249,108
Marketable securities	314,353	39,124
Prepaid expenses and other current assets	8,865	8,356
Total current assets	510,757	296,588
Marketable securities, long-term	48,779	10,954
Property and equipment, net	19,866	20,126
Operating lease right-of-use assets, net	21,762	11,539
Other assets	2,864	684
Total assets	604,028	339,891
Current liabilities
Accounts payable	2,924	3,515
Accrued and other current liabilities	21,415	12,014
Deferred revenue	35	273
Operating lease liabilities, current portion	5,091	3,149
Total current liabilities	29,465	18,951
Deferred revenue, net of current portion	1,280	972
Derivative liability	396	369
Operating lease liabilities, long-term portion	19,743	11,522
Other liabilities	196	248
Total liabilities	51,080	32,062
Commitments and contingencies (Note 9)
Stockholders’ equity
Preferred stock, $0.0001 par value, 10,000,000 shares authorized at September 30, 2024 and December 31, 2023; no shares issued and outstanding at September 30, 2024 and December 31, 2023	0	0
Common stock, $0.0001 par value, 300,000,000 shares authorized at September 30, 2024 and December 31, 2023; 51,996,639 and 43,075,218 shares issued and outstanding at September 30, 2024 and December 31, 2023, respectively	5	4
Additional paid-in-capital	1,078,388	723,136
Accumulated other comprehensive gain	1,079	16
Accumulated deficit	(526,524)	(415,327)
Total stockholders’ equity	552,948	307,829
Total liabilities and stockholders’ equity	$ 604,028	$ 339,891

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares, issued	51,996,639	43,075,218
Common stock, shares, outstanding	51,996,639	43,075,218

Condensed Statements of Operati

Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenue:
Collaboration and license revenue	$ 3	$ 20,204	$ 36	$ 20,742
Operating expenses:
Research and development	38,484	25,066	98,212	71,068
General and administrative	12,651	9,112	33,548	25,889
Total operating expenses	51,135	34,178	131,760	96,957
Loss from operations	(51,132)	(13,974)	(131,724)	(76,215)
Other income (expense):
Interest income	7,290	3,876	20,583	7,831
Other income (expense), net	(1)	(158)	(56)	(170)
Total other income, net	7,289	3,718	20,527	7,661
Net loss	$ (43,843)	$ (10,256)	$ (111,197)	$ (68,554)
Net loss per share, basic	$ (0.79)	$ (0.24)	$ (2.08)	$ (1.81)
Net loss per share, diluted	$ (0.79)	$ (0.24)	$ (2.08)	$ (1.81)
Weighted-average shares outstanding used in computing net loss per share, basic	55,554,476	42,256,629	53,377,712	37,884,363
Weighted-average shares outstanding used in computing net loss per share, diluted	55,554,476	42,256,629	53,377,712	37,884,363

Condensed Statements of Compreh

Condensed Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net loss	$ (43,843)	$ (10,256)	$ (111,197)	$ (68,554)
Other comprehensive loss:
Net unrealized gain (loss) on marketable securities	1,372	189	1,063	1,730
Total comprehensive loss	$ (42,471)	$ (10,067)	$ (110,134)	$ (66,824)

Condensed Statements of Stockho

Condensed Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	ATM Offering Program	Public offering	February / March 2024 Public Offering Sale	Common Stock	Common Stock ATM Offering Program	Common Stock Public offering	Common Stock February / March 2024 Public Offering Sale	Additional Paid-in Capital	Additional Paid-in Capital ATM Offering Program	Additional Paid-in Capital Public offering	Additional Paid-in Capital February / March 2024 Public Offering Sale	Accumulated Other Comprehensive Loss	Accumulated Deficit
Stockholders' Equity, beginning balances at Dec. 31, 2022	$ 231,337				$ 3				$ 547,020				$ (1,196)	$ (314,490)
Stockholders' Equity, beginning balances (in shares) at Dec. 31, 2022					32,626,627
Issuance of common stock upon exercise of stock options	1,135								1,135
Issuance of common stock upon exercise of stock options (in shares)					122,207
Issuance of common stock, net of issuance costs		$ 9,647								$ 9,647
Issuance of common stock, net of issuance costs (in shares)						487,934
Stock-based compensation expense	4,221								4,221
Vesting of common stock warrants issued for services	22								22
Net unrealized gain (loss) on marketable securities	926												926
Net loss	(28,682)													(28,682)
Stockholders' Equity, ending balances at Mar. 31, 2023	218,606				$ 3				562,045				(270)	(343,172)
Stockholders' Equity, ending balances (in shares) at Mar. 31, 2023					33,236,768
Stockholders' Equity, beginning balances at Dec. 31, 2022	231,337				$ 3				547,020				(1,196)	(314,490)
Stockholders' Equity, beginning balances (in shares) at Dec. 31, 2022					32,626,627
Net unrealized gain (loss) on marketable securities	1,730
Net loss	(68,554)
Stockholders' Equity, ending balances at Sep. 30, 2023	329,934				$ 4				712,440				534	(383,044)
Stockholders' Equity, ending balances (in shares) at Sep. 30, 2023					42,752,452
Stockholders' Equity, beginning balances at Mar. 31, 2023	218,606				$ 3				562,045				(270)	(343,172)
Stockholders' Equity, beginning balances (in shares) at Mar. 31, 2023					33,236,768
Issuance of common stock upon exercise of stock options	894								894
Issuance of common stock upon exercise of stock options (in shares)					72,217
Issuance of common stock, net of issuance costs			$ 129,208				$ 1				$ 129,207
Issuance of common stock, net of issuance costs (in shares)							8,625,000
Issuance of common stock - 2020 ESPP	658								658
Issuance of common stock - 2020 ESPP (in shares)					82,637
ATM offering costs		(212)								(212)
Stock-based compensation expense	4,969								4,969
Vesting of common stock warrants issued for services	22								22
Net unrealized gain (loss) on marketable securities	615												615
Net loss	(29,616)													(29,616)
Stockholders' Equity, ending balances at Jun. 30, 2023	325,144				$ 4				697,583				345	(372,788)
Stockholders' Equity, ending balances (in shares) at Jun. 30, 2023					42,016,622
Issuance of common stock upon exercise of stock options	1,040								1,040
Issuance of common stock upon exercise of stock options (in shares)					125,152
Issuance of common stock, net of issuance costs		9,701								9,701
Issuance of common stock, net of issuance costs (in shares)						610,678
ATM offering costs		(468)								(468)
Stock-based compensation expense	4,562								4,562
Vesting of common stock warrants issued for services	22								22
Net unrealized gain (loss) on marketable securities	189												189
Net loss	(10,256)													(10,256)
Stockholders' Equity, ending balances at Sep. 30, 2023	329,934				$ 4				712,440				534	(383,044)
Stockholders' Equity, ending balances (in shares) at Sep. 30, 2023					42,752,452
Stockholders' Equity, beginning balances at Dec. 31, 2023	307,829				$ 4				723,136				16	(415,327)
Stockholders' Equity, beginning balances (in shares) at Dec. 31, 2023					43,075,218
Issuance of common stock upon exercise of stock options and vesting of RSUs	3,113								3,113
Issuance of common stock upon exercise of stock options and vesting of RSUs (in shares)					236,856
Issuance of common stock, net of issuance costs				$ 316,149				$ 1				$ 316,148
Issuance of common stock, net of issuance costs (in shares)								7,845,314
Stock-based compensation expense	5,974								5,974
Vesting of common stock warrants issued for services	22								22
Net unrealized gain (loss) on marketable securities	(125)												(125)
Net loss	(32,401)													(32,401)
Stockholders' Equity, ending balances at Mar. 31, 2024	600,561				$ 5				1,048,393				(109)	(447,728)
Stockholders' Equity, ending balances (in shares) at Mar. 31, 2024					51,157,388
Stockholders' Equity, beginning balances at Dec. 31, 2023	$ 307,829				$ 4				723,136				16	(415,327)
Stockholders' Equity, beginning balances (in shares) at Dec. 31, 2023					43,075,218
Issuance of common stock upon exercise of stock options (in shares)	367,962
Net unrealized gain (loss) on marketable securities	$ 1,063
Net loss	(111,197)
Stockholders' Equity, ending balances at Sep. 30, 2024	552,948				$ 5				1,078,388				1,079	(526,524)
Stockholders' Equity, ending balances (in shares) at Sep. 30, 2024					51,996,639
Stockholders' Equity, beginning balances at Mar. 31, 2024	600,561				$ 5				1,048,393				(109)	(447,728)
Stockholders' Equity, beginning balances (in shares) at Mar. 31, 2024					51,157,388
Issuance of common stock upon exercise of stock options and vesting of RSUs	850								850
Issuance of common stock upon exercise of stock options and vesting of RSUs (in shares)					81,290
Issuance of common stock, net of issuance costs		$ 15,263								$ 15,263
Issuance of common stock, net of issuance costs (in shares)						585,938
Issuance of common stock - 2020 ESPP	707								707
Issuance of common stock - 2020 ESPP (in shares)					89,659
Stock-based compensation expense	6,074								6,074
Vesting of common stock warrants issued for services	22								22
Net unrealized gain (loss) on marketable securities	(184)												(184)
Net loss	(34,953)													(34,953)
Stockholders' Equity, ending balances at Jun. 30, 2024	588,340				$ 5				1,071,309				(293)	(482,681)
Stockholders' Equity, ending balances (in shares) at Jun. 30, 2024					51,914,275
Issuance of common stock upon exercise of stock options and vesting of RSUs	567								567
Issuance of common stock upon exercise of stock options and vesting of RSUs (in shares)					82,364
Stock-based compensation expense	6,490								6,490
Vesting of common stock warrants issued for services	22								22
Net unrealized gain (loss) on marketable securities	1,372												1,372
Net loss	(43,843)													(43,843)
Stockholders' Equity, ending balances at Sep. 30, 2024	$ 552,948				$ 5				$ 1,078,388				$ 1,079	$ (526,524)
Stockholders' Equity, ending balances (in shares) at Sep. 30, 2024					51,996,639

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Cash flows from operating activities
Net loss	$ (111,197)	$ (68,554)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	18,538	13,752
Vesting of common stock warrant in return for services	66	66
Change in fair value of derivative liability	27	157
Depreciation and amortization	3,557	3,102
Amortization of right-of-use assets	1,364	1,134
Net amortization (accretion) of premium (discount) on marketable securities	(5,332)	(765)
Changes in operating assets and liabilities
Prepaid expenses and other current assets	(508)	(1,622)
Other assets	(2,181)	(69)
Accounts payable	(591)	1,984
Accrued and other liabilities	8,890	1,374
Deferred revenue	69	(734)
Operating lease liabilities	(1,424)	(967)
Net cash used in operating activities	(88,722)	(51,142)
Cash flows from investing activities
Purchase of marketable securities	(409,874)	(20,156)
Maturities of marketable securities	103,215	144,777
Acquisition of property and equipment	(2,837)	(2,222)
Net cash provided by (used in) investing activities	(309,496)	122,399
Cash flows from financing activities
Issuance of Common Stock upon Exercise of Stock Options and Warrants	4,530	3,069
Issuance of common stock - 2020 ESPP	707	658
Net cash provided by financing activities	336,649	152,070
Net increase (decrease) in cash and cash equivalents	(61,569)	223,327
Cash and cash equivalents, beginning of period	249,108	52,351
Cash and cash equivalents, end of period	187,539	275,678
Supplemental disclosures of noncash investing and financing information
Deferred ATM costs reclassification		468
Purchases of property and equipment in accounts payable and accrued and other liabilities	694	345
Right-of-use assets obtained in exchange for lease obligations	11,587
Public offering
Cash flows from financing activities
Issuance of common stock for the offering program, net of issuance costs	316,149	129,208
ATM Offering Program
Cash flows from financing activities
Issuance of common stock for the offering program, net of issuance costs	$ 15,263	$ 19,135

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ 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
Pay vs Performance Disclosure
Net Income (Loss)	$ (43,843)	$ (34,953)	$ (32,401)	$ (10,256)	$ (29,616)	$ (28,682)	$ (111,197)	$ (68,554)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	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

The Company

The Company	9 Months Ended
	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company	1. The Company 4D Molecular Therapeutics, Inc. (the “Company”) was formed as a limited liability company in September 2013 under the name 4D Molecular Therapeutics, LLC. The Company changed its name and converted into a corporation which was incorporated in the state of Delaware in March 2015. The Company is a clinical-stage biotherapeutics company harnessing the power of directed evolution for targeted genetic medicines. Initial Public Offering In December 2020, the Company sold and issued 9,660,000 shares of common stock at a price to the public of $ 23.00 per share, which included shares sold upon the underwriters’ exercise of their overallotment option to purchase 1,260,000 additional shares. The Company received an aggregate of $ 204.7 million in net proceeds, after deducting underwriting discounts and commissions and offering costs. Upon the closing of the Company’s initial public offering in December 2020 (the “IPO”), all outstanding shares of redeemable convertible preferred stock automatically converted into 11,575,984 shares of common stock. Subsequent to the closing of the IPO, there were no shares of redeemable convertible preferred stock outstanding. 2021 Follow On Public Offering In November 2021, the Company completed an underwritten public offering (“2021 Offering”) in which 4,750,000 shares of the Company's common stock were sold at an offering price of $ 25.00 per share pursuant to an effective Registration Statement on Form S-1. The net proceeds from the 2021 Offering were $ 111.1 million, after deducting underwriting discounts and commissions and offering expenses. 2023 Follow On Public Offering In May 2023, the Company completed its third underwritten public offering (the “2023 Offering”) in which 8,625,000 shares of the Company’s common stock were sold at an offering price of $ 16.00 per share pursuant to an effective Registration Statement on Form S-3. The net proceeds from the 2023 Offering were $ 129.2 million, after deducting underwriting discounts and commissions and offering expenses. 2024 Follow On Public Offering In February 2024, the Company completed an underwritten public offering (the “2024 Offering”) in which 6,586,015 shares of the Company’s common stock were sold at an offering price of $ 29.50 per share, as well as pre-funded warrants to purchase 3,583,476 shares of the Company’s common stock at an offering price of $ 29.4999 per underlying share pursuant to an effective Registration Statement on Form S-3. The net proceeds from the 2024 Offering were $ 281.2 million, after deducting underwriting discounts and commissions and other offering expenses. The Company also granted the underwriters the option to purchase up to 1,525,423 additional shares of common stock in connection with the offering. In March 2024, the underwriters exercised their option to purchase 1,259,299 additional shares of common stock resulting in net proceeds of $ 34.9 million, after deducting commissions. Liquidity The Company has incurred significant losses and negative cash flows from operations and had an accumulated deficit of $ 526.5 million as of September 30, 2024. The Company believes that its cash and cash equivalents and marketable securities as of September 30, 2024 are sufficient for the Company to fund planned operations for at least one year from the issuance date of these condensed financial statements. The Company has historically financed its operations primarily through the sale of equity securities, and to a lesser extent, from cash received pursuant to its collaboration and license agreements. To date, none of the Company’s product candidates have been approved for sale, and therefore, the Company has not generated any revenue from product sales. Management expects operating losses and negative cash flows from operations to continue for the foreseeable future. The Company plans to raise additional funding as required based on the status of its clinical trials and projected cash flows. There can be no assurance that, in the event the Company requires additional financing, such financing will be available on terms acceptable to the Company, if at all. Failure to generate sufficient cash flows from operations, raise additional capital and reduce discretionary spending should additional capital not become available could have a material adverse effect on the Company’s ability to achieve its business objectives.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed financial statements have been prepared in accordance with United States Generally Accepted Accounting Principles (“U.S. GAAP”) and the rules and regulations of the United States Securities and Exchange Commission (“SEC”) for interim reporting. Certain information and note disclosures normally included in annual financial statements prepared in accordance with U.S. GAAP have been condensed or omitted. Accordingly, the condensed financial statements should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023 filed with the SEC. The accompanying financial information for the three and nine months ended September 30, 2024 and 2023 is unaudited. The condensed financial statements have been prepared on the same basis as the annual audited financial statements and, in the opinion of management, reflect all adjustments, consisting of only normal recurring adjustments, necessary for a fair statement of the Company’s financial position as of September 30, 2024, and its results of operations and cash flows for the nine months ended September 30, 2024 and 2023. The condensed balance sheet at December 31, 2023 was derived from audited annual financial statements but does not contain all of the footnote disclosures from the annual financial statements. The results for interim periods are not necessarily indicative of the results expected for the full fiscal year or any other periods. Use of Estimates and Judgments The preparation of condensed financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the reported amounts of assets, liabilities, revenue and expenses; and disclosure of contingent assets and liabilities as of the date of the financial statements. Such estimates include the determination of useful lives for property and equipment, the contract term, transaction price and costs of collaboration agreements, stock options and the derivative instrument and income tax uncertainties. Actual results could differ from those estimates. Due to the war in Ukraine, conflicts in the Middle East, any expansion of these conflicts, rising interest rates and inflation, natural disasters and pandemics, there has been uncertainty and disruption in the global economy and financial markets. The Company is not aware of any specific event or circumstance that would require an update to its estimates or judgments or a revision of the carrying value of its assets or liabilities as of September 30, 2024. While there was not a material impact to the Company’s condensed financial statements as of September 30, 2024 , these estimates may change, as new events occur and additional information is obtained, as well as other factors that could result in material impacts to the condensed financial statements in future reporting periods. Segment Information The Company operates and manages its business as one reportable and operating segment. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on a company-wide basis for purposes of allocating resources and assessing financial performance. Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, marketable securities and accounts receivable. The Company’s cash is held at two financial institutions in the United States of America. The Company’s cash equivalents are invested in money market funds. The Company also invests in U.S. Treasuries, U.S. government sponsored agencies, commercial paper, corporate bonds and certificates of deposit. The Company has not experienced any losses on its deposits of cash and cash equivalents. Such deposits may, at times, exceed federally insured limits. The Company’s partners in collaboration and license agreements who represent 10% or more of the Company’s total revenue are as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 Customer A 100 % * 100 % * Customer B 0 % 99 % 0 % 96 % Total 100 % 99 % 100 % 96 % * Less than 10 % The Company did no t have accounts receivable from its partners in collaboration and license agreements as of September 30, 2024 and December 31, 2023. The Company’s total revenue by geographic region, based on the location of the customer, are as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2024 Netherlands $ — $ 41 $ — $ 566 United States 3 20,163 36 20,176 Total revenue $ 3 $ 20,204 $ 36 $ 20,742 Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, protection of proprietary technology, dependence on key personnel, suppliers for key raw materials, contract manufacturing organizations (“CMOs”) and contract research organizations (“CROs”), compliance with government regulations and the need to obtain additional financing to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical studies, clinical trials and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance and reporting. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained or maintained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from other pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees, consultants and other third parties (including for clinical trials and some aspects of research and preclinical testing). Recently Issued Accounting Pronouncements Not Yet Adopted In November 2023, the Financial Accounting Standards Board issued Accounting Standards Update (“ASU”) No. 2023-07, Improvements to Reportable Segment Disclosures. ASU No. 2023-07 is intended to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023, and for interim periods within fiscal years beginning after December 15, 2024, and must be applied retrospectively to all prior periods presented in the financial statements. The Company is currently evaluating the impact of adoption of this ASU and does not expect the adoption to have a material impact on the Company ’ s financial statements and the related notes thereto. In December 2023, the Financial Accounting Standards Board issued ASU No. 2023-09, Improvements to Income Tax Disclosures. The final guidance adds clarifications related to the presentation of rate reconciliation for public business entities and definitions of specific categories in rate reconciliation. These amendments are effective for public business entities for annual periods beginning after December 15, 2024. For other entities, amendments are effective for annual periods beginning after December 15, 2025. The Company expects to make additional disclosures for income taxes upon adoption of ASU No. 2023-09.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements The following tables represent the Company’s fair value hierarchy for financial assets and financial liabilities measured at fair value on a recurring basis as of September 30, 2024 and December 31, 2023 (in thousands): Basis for Fair Value Measurements Fair Value as of Level 1 Level 2 Level 3 September 30, 2024 Assets Money market funds $ 160,546 $ — $ — $ 160,546 Certificates of deposit — 55,872 — 55,872 Commercial paper — 86,712 — 86,712 Corporate bonds — 213,848 — 213,848 U.S. Treasuries — 6,700 — 6,700 Total $ 160,546 $ 363,132 $ — $ 523,678 Liabilities Derivative liability $ — $ — $ 396 $ 396 Total $ — $ — $ 396 $ 396 Basis for Fair Value Measurements Fair Value as of Level 1 Level 2 Level 3 December 31, 2023 Assets Money market funds $ 217,644 $ — $ — $ 217,644 Commercial paper — 18,243 — 18,243 Corporate bonds — 28,939 — 28,939 U.S. government sponsored agencies — 2,896 — 2,896 Total $ 217,644 $ 50,078 $ — $ 267,722 Liabilities Derivative liability $ — $ — $ 369 $ 369 Total $ — $ — $ 369 $ 369 Level 3 Inputs The fair value of the derivative liability is based on significant inputs not observable in the market, which represent a Level 3 measurement within the fair value hierarchy. The fair value of the derivative liability was determined using a present value analysis with multiple scenarios. In determining the fair value of the derivative liability, the inputs impacting fair value include the change of control payment to Cystic Fibrosis Foundation, the probability of a change of control event, the product status at time of a change of control event and the discount rate. See Note 15 for further discussion on the embedded derivative. There were no transfers between Level 1, 2 and 3 during the periods presented. The following tables set forth a summary of the changes in the fair value of the Company’s Level 3 financial instrument during the nine months ended September 30, 2024 and 2023 (in thousands): Derivative Balance as of December 31, 2023 $ 369 Change in fair value included in other income (expense), net 27 Balance as of September 30, 2024 $ 396 Derivative Balance as of December 31, 2022 $ 212 Change in fair value included in other income (expense), net 157 Balance as of September 30, 2023 $ 369

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2024
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities Marketable securities, which are classified as available-for-sale, consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): Amortized Cost Basis Gross Unrealized Gains Gross Unrealized Losses Fair Value as of September 30, 2024 Short-term marketable securities: Certificates of deposit $ 55,750 $ 122 $ — $ 55,872 Commercial paper 85,276 134 ( 1 ) 85,409 Corporate bonds 166,012 366 ( 6 ) 166,372 U.S. Treasuries 6,679 21 — 6,700 Total short-term marketable securities $ 313,717 $ 643 $ ( 7 ) $ 314,353 Long-term marketable securities: Commercial paper $ 1,289 $ 14 $ — $ 1,303 Corporate bonds 47,047 431 ( 2 ) 47,476 Total long-term marketable securities $ 48,336 $ 445 $ ( 2 ) $ 48,779 Amortized Cost Basis Gross Unrealized Gains Gross Unrealized Losses Fair Value as of December 31, 2023 Short-term marketable securities: Commercial paper $ 17,603 $ 1 $ ( 26 ) $ 17,578 Corporate bonds 18,641 12 ( 3 ) 18,650 U.S. government sponsored agencies 2,900 — ( 4 ) 2,896 Total short-term marketable securities $ 39,144 $ 13 $ ( 33 ) $ 39,124 Long-term marketable securities: Commercial paper $ 661 $ 4 $ — $ 665 Corporate bonds 10,257 32 — 10,289 Total long-term marketable securities $ 10,918 $ 36 $ — $ 10,954 All marketable securities held as of September 30, 2024 had contractual maturities of less than two years . There have been no material realized gains or losses on marketable securities for the periods presented. Aggregate fair values of marketable securities with unrealized losses and gains were as follows as of September 30, 2024 and December 31, 2023 (in thousands): September 30, December 31, 2024 2023 Aggregate fair value of marketable securities in a continuous loss position for less than twelve months $ 23,828 $ 20,494 Aggregate fair value of marketable securities in a continuous loss position for more than twelve months — 4,986 Aggregate fair value of marketable securities in unrealized gain position 339,304 24,598 Total marketable securities $ 363,132 $ 50,078 The Company manages credit risk associated with its investment portfolio through its investment policy, which limits purchases to high-quality issuers and also limits the amount of its portfolio that can be invested in a single issuer. The Company did no t record an allowance for credit losses or other impairment charges related to its marketable securities for any period presented. The Company has determined that (i) it does not have the intent to sell any of these investments, and (ii) it is not more likely than not that it will be required to sell any of these investments before recovery of the entire amortized cost basis. The Company further considered the maximum unrealized loss amounts both at the individual instrument level, $ 3 thousand, as well as in aggregate, $ 9 thousand, as of September 30, 2024, as immaterial. These unrealized losses were not attributed to credit risk and were associated with changes in market conditions. The Company periodically reviews its marketable securities for indications of credit losses. The Company anticipates that it will recover the entire amortized cost basis of such securities, and therefore, no credit loss existed as of September 30, 2024.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2024
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net, consisted of the following (in thousands): September 30, December 31, Machinery and equipment $ 14,218 $ 12,996 Leasehold improvements 17,325 16,902 Furniture and fixtures 637 566 Office equipment 239 239 Computer equipment and software 920 805 Construction in progress 2,017 550 Total property and equipment 35,356 32,058 Less: Accumulated depreciation and amortization ( 15,490 ) ( 11,932 ) Property and equipment, net $ 19,866 $ 20,126 All property and equipment are maintained in the United States. Depreciation expense was $ 1.2 million and $ 1.1 million for the three months ended September 30, 2024 and 2023, respectively, and $ 3.6 million and $ 3.1 million for the nine months ended September 30, 2024 and 2023, respectively.

Accrued and Other Current Liabi

Accrued and Other Current Liabilities	9 Months Ended
	Sep. 30, 2024
Payables and Accruals [Abstract]
Accrued and Other Current Liabilities	6. Accrued and Other Current Liabilities Accrued and other current liabilities consisted of the following (in thousands): September 30, December 31, Payroll and related expenses $ 9,606 $ 8,149 Accrued clinical and preclinical study costs 9,402 2,180 Consulting and professional 2,282 1,581 Other accrued expenses 125 104 Total accrued and other current liabilities $ 21,415 $ 12,014

Research and Collaboration Arra

Research and Collaboration Arrangements	9 Months Ended
	Sep. 30, 2024
Research And Collaboration Arrangements [Abstract]
Research and Collaboration Arrangements	7. Research and Collaboration Arrangements Collaboration and license revenue for each period was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 uniQure $ — $ 41 $ — $ 566 CFF 3 155 36 168 Astellas — 20,008 — 20,008 Total revenue $ 3 $ 20,204 $ 36 $ 20,742 Deferred revenue is summarized as follows (in thousands): September 30, December 31, CFF $ 1,315 $ 1,245 Total deferred revenue $ 1,315 $ 1,245 The total amount of revenue in the nine months ended September 30, 2024 which was included in deferred revenue at January 1, 2024 was immaterial. The total amount of revenue in the nine months ended September 30, 2023 which was included in deferred revenue at January 1, 2023 was $ 0.7 million. uniQure In January 2014, the Company and uniQure biopharma B.V. (“uniQure”) entered into a Collaboration and License Agreement (the “uniQure Agreement”) to collaborate on the discovery and non-clinical research activities related to the Company’s Therapeutic Vector Evolution platform in order to generate and validate vectors for gene delivery to treat diseases within the central nervous system and liver (together, the “uniQure Field”). The uniQure Agreement provided uniQure with a research license as well as an exclusive development and commercialization license for each project variant selected for further development. The initial research term is three years with an option for uniQure to extend the research term one time for an additional year. Once the Company’s research plan has concluded, uniQure is solely responsible for the continued development, manufacturing and commercialization of the project variants as potential product candidates. In October 2016, uniQure exercised its option to extend the research term for an additional year to January 2018. The Company was also required to work exclusively with uniQure in the uniQure Field (the “uniQure Exclusivity Clause”). Pursuant to the uniQure Agreement, the Company received upfront payments of $ 0.2 million, and was entitled to receive (i) contingent payments for the achievement of research and development milestones of up to $ 5.0 million for each licensed product selected under the arrangement, and (ii) royalties in the single digit range on future sales of the potential product candidates and sublicense consideration in the low teens to low thirties range on any future sublicensing arrangements. The Company also received capped research and development service fees based on contractual full-time employee rates per year. In connection with the performance obligations under the uniQure Agreement, the founders of 4D Molecular Therapeutics, LLC received equity options to purchase an aggregate of 609,744 of uniQure ordinary shares that vested over the initial three-year term of the agreement. The upfront payment of $ 0.2 million was recorded as deferred revenue and was recognized on a ratable basis over the estimated performance period of four years . Payments and reimbursements for research costs were recognized on an as-incurred basis. The options to purchase uniQure shares were deemed to be a noncash component of the arrangement consideration, as the vesting of options is linked to the uniQure Agreement and there is a requirement for the holders of the options to provide services under the agreement. The fair value of the uniQure options, which was estimated to be $ 10.6 million, was recognized ratably as revenue over the estimated performance period of four years and the associated compensation expense related to the stock options was recorded as research and development expense. In August 2019, the Company and uniQure entered into an Amended and Restated Collaboration and License Agreement (the “Amended uniQure Agreement”), which amended and restated the uniQure Agreement, and a separate Collaboration and License Agreement (the “Second uniQure Agreement”). Under these agreements, the Company agreed to transfer incremental rights and services to uniQure in exchange for uniQure eliminating the uniQure Exclusivity Clause and transferring other rights back to the Company. Under the Amended uniQure Agreement, uniQure continues to have an exclusive license to select AAV capsid variants (the “Selected Variants”) in the uniQure Field. uniQure continues to be solely responsible, at its cost, to develop and commercialize the compounds and products containing the Selected Variants. The amended uniQure Agreement eliminated the uniQure Exclusivity Clause in the uniQure Agreement. Furthermore, the contingent payments that the Company was entitled to from uniQure for the achievement of research and development milestones of up to $ 5.0 million for each licensed product selected under the uniQure Agreement were eliminated and sublicense consideration on any future sublicensing arrangements was reduced from the low teens to low thirties percentages to mid-single digit to mid-twenties percentages. Under the Second uniQure Agreement, the parties agreed to research and develop new AAV capsid variants (the “New Variants”) that are not Selected Variants that affect certain targets selected by uniQure (the “uniQure Targets”) in the uniQure Field. The Company is solely responsible, at its cost, for the research of the New Variants. The Company granted uniQure an exclusive license to a certain number of the New Variants (the “uniQure New Variants”) that affect the uniQure Targets. uniQure is solely responsible, at its cost, to develop and commercialize the compounds and products containing the uniQure New Variants that affect the uniQure Targets (the “Licensed Products”). The Company retains all rights to New Variants in the uniQure Field that affect targets other than the uniQure Targets. Under both the Amended uniQure Agreement and the Second uniQure Agreement, uniQure will be required to pay the Company royalties on worldwide annual net sales of Licensed Products at a mid-single digit percentage rate, subject to certain specified reductions. uniQure will also be required to pay the Company sublicensing consideration for sublicensing the Company’s intellectual property rights licensed under the Amended uniQure Agreement or the Second uniQure Agreement to third parties at a rate between the mid-single digit to mid-twenties. The Company has reciprocal obligations, at the same percentage rates as uniQure, to pay uniQure royalties and sublicensing consideration for sublicensing certain intellectual property rights licensed under the Amended uniQure Agreement or the Second uniQure Agreement to third parties. The Company concluded that the Amended uniQure Agreement and the Second uniQure Agreement should be accounted for as one combined contract that should be accounted for as a separate contract from the uniQure Agreement given that the incremental licensed intellectual property rights and research and development services are distinct from the rights and services previously transferred to uniQure under the uniQure Agreement and the transaction price increased by an amount that equals the standalone selling price of the incremental rights and services to be transferred to uniQure under the Amended uniQure Agreement and Second uniQure Agreement. Neither party was required to pay monetary consideration in connection with the execution of the Amended uniQure Agreement or the Second uniQure Agreement or for subsequent performance by the parties under those agreements, notwithstanding the potential future royalty and sublicense consideration described above. The fair value of the non-monetary consideration given by uniQure to the Company, for the intellectual property right was $ 5.1 million. This intellectual property right was considered to be an in-process research and development asset with no alternative future use and, accordingly, was written off as acquired in-process research and development expense in the year ended December 31, 2019. In accordance with Accounting Standards Codification ("ASC") Topic 606, Revenue from Contracts with Customers, the incremental transaction price described in the paragraph above was recorded as deferred revenue given that the Company identified one single combined performance obligation, which includes the licenses to the New Variants, research services and participation in the joint steering committee (“JSC”). Revenue is being recognized using the input method based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation. The Company completed its performance obligation during the third quarter of 2023 and the deferred revenue was recognized as revenue in the same period. The Company determined the transaction price using the risk adjusted net present value analysis (“rNPV”) methodology to value the elimination of the uniQure exclusivity clause and other material rights received by the Company, including the potential royalties the Company would receive from uniQure. The rNPVs incorporate estimates and assumptions including the number of products the Company and uniQure would develop, the risk-adjusted probability of successfully developing a biopharmaceutical product, the probability that uniQure will develop a product, the research and development costs, the potential worldwide sales and associated commercialization costs, corporate tax rate, and discount rate. During each of the three and nine months ended September 30, 2024, the Company recognized no revenue under both of the Amended uniQure Agreement and the Second uniQure Agreement. The Company recognized an immaterial amount and $ 0.6 million during the three and nine months ended September 30, 2023, respectively, under both of the Amended uniQure Agreement and the Second uniQure Agreement. There were no amounts due from uniQure under the uniQure Agreement, Amended uniQure Agreement or Second uniQure Agreement as of September 30, 2024 and December 31, 2023. As of September 30, 2024 and December 31, 2023, deferred revenue relating to uniQure was zero and the aggregate amount of the transaction price allocated to the remaining performance obligation was zero . Cystic Fibrosis Foundation (“CFF”) In September 2016, the Company entered into an award agreement for the Optimized Adeno-Associated Virus for Lung Epithelia Gene Delivery Development Program with CFF, a non-profit organization dedicated to finding a cure for cystic fibrosis, an inherited disorder that causes disease in the pulmonary airways leading to morbidity and mortality. Under this agreement, CFF contributes funding to help advance the Company’s cystic fibrosis research program. The September 2016 grant award agreement was incorporated into a new grant award agreement with CFF in September 2017 with the same objectives, which was subsequently amended in August 2018 and February 2021. In August 2023, the Company executed a third amendment to the agreement (the “August 2023 Amendment”), which modified the research plan, increased the aggregate milestone payments from $ 3.5 million to $ 6.3 million and extended the estimated project completion date. The aforementioned September 2017 agreement and three amendments are collectively referred to as the “CFF Agreement”. The August 2023 Amendment represents a contract modification to an existing contract under ASC Topic 606, given the amendment did not include any additional goods or services, and the remaining research activities are not distinct from those previously provided. The August 2023 Amendment did not impact the transaction price, given the increased award amount relates to variable consideration for future milestones that are fully constrained. Accordingly, the contract modification did not result in a revenue adjustment. As of September 30, 2024 and December 31, 2023, the Company had achieved milestones totaling $ 1.8 million and $ 1.7 million, respectively, under the CFF Agreement. The remaining award amount will be paid by CFF based on achievement of certain development milestones by the Company. The Company expects to make payments to CFF equal to six times the actual award received by the Company in three installments within the first four years of the first commercial sale of a product developed under this agreement. The Company also has agreed to make future sales-based milestone payments to CFF of up to three times the actual award received upon achieving specified commercialization milestones with respect to the first of any product developed utilizing any compound covered under the CFF Agreement. The CFF Agreement also requires the Company to pay to CFF royalties of a mid-single digit percentage, up to six times the actual award received, on any amounts received by the Company from the sale, license or transfer to a third-party of rights in the technology developed as a result of this collaboration. Any such royalty payments shall be credited against the payments owed by the Company upon first commercial sale. In the event of a change of control of the Company, CFF will receive certain payments, depending on the timing of the change of control and the size of the transaction. To date, the Company has not developed a commercial product in connection with the CFF Agreement, and it has not licensed, sold or otherwise transferred to another party the product developed under the CFF Agreement or the underlying technology. If at any time prior to the first commercial sale of a product developed as a result of the CFF Agreement, the Company ceases to use commercially reasonable efforts to develop or commercialize any product under the CFF Agreement for a continuous period of 180 consecutive days and fails to present a reasonable plan to resume commercially reasonable efforts, the Company will grant to CFF an irrevocable, exclusive worldwide interruption license under all of the Company’s interest in the research plan technology to exploit such product. Any third-party license granted by the Company shall be subject to such interruption license. The Company identified one performance obligation within the CFF grant agreement for research activities. The Company’s contract with CFF does not include a significant financing component. The Company concluded that the transaction price should not include the variable consideration related to future research milestones as they were considered to be constrained as it is probable that the inclusion of such variable consideration could result in a significant reversal of cumulative revenue in the future. The Company re-evaluates the transaction price and estimated period of performance at each reporting period. Revenue recognized during each of the three and nine months ended September 30, 2024 was immaterial, while r evenue recognized for each of the three and nine months ended September 30, 2023 was $ 0.2 million . As of September 30, 2024 and December 31, 2023, deferred revenue relating to the CFF Agreement was $ 1.3 million and $ 1.2 million, respectively. There were no accounts receivable from CFF under the CFF Agreement as of September 30, 2024 and December 31, 2023. As of September 30, 2024 and December 31, 2023, the aggregate amount of the transaction price allocated to the remaining performance obligation was $ 1.3 million and $ 1.2 million, respectively. Based on current timelines, the deferred revenue is expected to be recognized as revenue over the next one to three years as the Company performs research services through the completion of IND-enabling studies. The obligation to make payments to CFF upon a change of control meets the definition of an embedded derivative that is required to be bifurcated and separately accounted for as a derivative liability. See Note 15 for further discussion of the embedded derivative. Arbor Biotechnologies, Inc. On December 20, 2023, the Company entered into a co-development and co-commercialization agreement (the “Arbor Agreement”) with Arbor Biotechnologies, Inc. (“Arbor”), pursuant to which the Company and Arbor agreed to co-develop and co-commercialize on a fifty-fifty cost-and-profit-sharing basis up to six genetic medicine products to treat central nervous system (“CNS”) indications, based on combining the Company’s CNS-targeting vectors and Arbor’s Cas enzymes and Guide RNAs. The first product candidate under the Arbor Agreement will address a molecular target implicated in amyotrophic lateral sclerosis. The Company will account for its costs related to the co-development and co-commercialization of product candidates under the Arbor Agreement as research and development expenses in the periods in which they are incurred. As of September 30, 2024, no Shared Product has been designated by the JSC (each as defined in the Arbor Agreement) under the Arbor Agreement, and no research and development expenses were incurred related to the Arbor Agreement during the three and nine months ended September 30, 2024.

License Arrangements

License Arrangements	9 Months Ended
	Sep. 30, 2024
License Arrangements [Abstract]
License Arrangements	8. License Arrangements Astellas Gene Therapies, Inc. On July 5, 2023, the Company entered into a licensing agreement (the “Astellas License Agreement”) with Astellas Gene Therapies, Inc. (“AGT”), pursuant to which the Company granted to AGT a license to utilize its intravitreal R100 vector (“4D Vector”) to develop and commercialize licensed compounds and licensed products for one genetic target implicated in rare monogenic ophthalmic disease(s), with options to add up to two additional targets implicated in rare monogenic ophthalmic diseases after paying additional option exercise fees. Under the terms of the Astellas License Agreement, the Company has provided its 4D vector technology to AGT to deliver AGT’s genetic payloads for the treatment of rare monogenic diseases. AGT will conduct all subsequent research, development, manufacturing, and commercialization activities. As partial consideration for the rights and licenses granted to AGT by the Company under this Astellas License Agreement, AGT paid the Company an upfront amount of $ 20 million, which was received in July 2023. The Company may receive potential future option fees and milestones of up to $ 942.5 million. In addition, the Company is entitled to receive mid-single digit to double-digit, sub-teen royalties on net sales of all licensed products. Under the Astellas License Agreement, the Company’s performance obligation is to grant and make available to AGT the Licensed IP and Licensed Know-How (each as defined in the Astellas License Agreement) with respect to the 4D Vector. In connection with the grant of the license, in July 2023, the Company delivered to AGT the Transferred Material (as defined in the Astellas License Agreement). As of September 30, 2024, there was no deferred revenue and no accounts receivable relating to the Astellas License Agreement. Aevitas Therapeutics, Inc. and The Trustees of the University of Pennsylvania On April 21, 2023, the Company entered into an agreement (the “Aevitas Agreement”) with Aevitas Therapeutics, Inc. (“Aevitas”), pursuant to which the Company acquired all of Aevitas’ worldwide rights to short-form human complement factor H (sCFH), which the Company plans to use for its 4D-175 product candidate research program. The asset purchase was accounted for as an asset acquisition. As consideration for the Aevitas Agreement, the Company shall pay Aevitas up to approximately $ 144 million in cash upon certain late-stage development, regulatory and sales milestones being achieved plus royalties in the low single digits range on sales of 4D-175. In addition, as part of the Aevitas Agreement, the Company was assigned a License Agreement for sCFH with the Trustees of the University of Pennsylvania, under which the Company shall pay the University of Pennsylvania up to approximately $ 42 million in cash upon certain late-stage development, regulatory and sales milestones being achieved plus royalties in the low single digits range on sales of 4D-175. No upfront consideration was paid under the Aevitas Agreement. As of September 30, 2024, the Company has no t recorded a liability related to contingent consideration for future milestone and royalty payments to either Aevitas or the University of Pennsylvania, as the achievement of such milestones has not occurred and was not deemed probable and product sales have not commenced. Regents of the University of California The Company has exclusive, worldwide license agreements (the “UC Agreements”) with the Regents of the University of California (the “UC Regents”) relating to the use of certain patents and intellectual property surrounding its core technologies, including Therapeutic Vector Evolution. Pursuant to each of the UC Agreements executed prior to January 2019, the Company was obligated to pay a (i) non-refundable license fee of $ 5,000 upon execution, (ii) a non-refundable license fee of $ 5,000 each year thereafter, until sales of a licensed product are made and royalties are paid to the UC Regents, (iii) reimbursement of domestic and foreign patent filing, prosecution and maintenance fees, and (iv) either $ 50,000 or issuance of a 3 % equity interest in the Company upon the closing of the first qualified financing at the option of the UC Regents. The Company’s first qualified financing occurred in 2015 and at the election of the UC Regents, the Company issued the UC Regents in January 2016 an amount of common stock equal to 6 % of the equity interests in the Company pursuant to the applicable clause in each of the UC Agreements. Pursuant to an agreement with the UC Regents executed in January 2019 the Company paid a non-refundable license fee of $ 50,000 to the UC Regents upon execution of the agreement. The Company is obligated to pay a non-refundable license fee of $ 5,000 on the one-year anniversary of the contract effective date and each year thereafter, until sales of a licensed product are made and royalties are paid to the UC Regents. In addition, the Company is obligated to make certain contingent payments including (i) development milestones up to $ 3.1 million, (ii) low single digit royalties on the net sales of its developed products that consist of a minimum annual royalty of up to $ 0.1 million per year for the term of the agreement beginning in the first calendar year after the year in which net sales first occurred, and (iii) sublicense consideration in the mid-teens to the mid-twenties-range on any future sublicensing arrangements the Company may enter into with third-party licensees. Regents of the University of California and The Trustees of the University of Pennsylvania In July 2021, the Company entered into an exclusive license agreement with the UC Regents and the Trustees of the University Pennsylvania to license intellectual property related to certain vectors. In July 2021, the Company paid a non-refundable license fee of $ 100,000 to the UC Regents upon execution of the agreement. The Company is obligated to pay a non-refundable license maintenance fee of $ 10,000 on the one-year anniversary of the contract effective date and each year thereafter, except years for which the Company has paid royalties on the net sales of a licensed product. In addition, the Company is obligated to make certain contingent payments including (i) development milestones up to $ 3.9 million, (ii) low single digit percentage rate royalties on the net sales of its licensed products that consists of a minimum annual royalty of up to $ 0.1 million per year for the term of the agreement beginning in the first calendar year after the year in which net sales first occurred and (iii) sublicense consideration in the mid-single digits to the low twenties percentage rate range on any future sublicensing arrangements the Company may enter into with third-party licensees. On February 22, 2023, the Company provided 90 days written notice to the UC Regents and the Trustees of the University Pennsylvania to terminate said agreement in its entirety at-will. Accordingly, the effective termination date of this agreement is May 23, 2023. The Company did no t incur any expense under the provisions of the outstanding license agreements during each of the three and nine months ended September 30, 2024 and 2023.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies The Company’s lease obligations relate primarily to leased office, laboratory and warehouse facilities under noncancelable operating leases. Operating Lease Commitments 5980 Horton Street Building Lease In May 2015, the Company executed a lease agreement (the “5980 Horton Lease”) for office and laboratory space in Emeryville, California. The 5980 Horton Lease, as amended, expires in August 2026 . As of September 30, 2024, the right-of-use asset and lease liability related to the 5980 Horton Lease were $ 0.9 million and $ 1.1 million, respectively. As of December 31, 2023, the right-of-use asset and lease liability related to the 5980 Horton Lease were $ 1.2 million and $ 1.4 million, respectively. 5858 Horton Street Lease and Expansion In October 2018, the Company executed a lease agreement (the “5858 Horton Lease”) for office and laboratory facilities in Emeryville, California. The 5858 Horton Lease, as amended in 2019, 2021 and 2022, consists of approximately 40,802 square feet of space and has a lease term through December 31, 2029. In July 2024, the Company extended the term of the 5858 Horton Lease for a period of twelve months to December 31, 2030 . In accordance with ASC Topic 842, Leases , the Company accounted for the extension as a modification and remeasured the lease liability based on the new lease term and an updated, estimated incremental borrowing rate of 10.75 %. The modification resulted in an increase to the lease liability of $ 0.8 million and a corresponding increase to the carrying value of the right-of-use asset. No gain or loss was recognized upon the modification. As of September 30, 2024, the right-of-use asset and lease liability related to the 5858 Horton Lease was $ 10.2 million and $ 12.9 million, respectively. As of December 31, 2023, the right-of-use asset and lease liability related to the 5858 Horton Lease were $ 10.3 million and $ 13.2 million, respectively. In July 2024, the Company also entered into a lease agreement for additional office and laboratory space in Emeryville, California (the “5858 Horton Expansion Lease”) . The 5858 Horton Expansion Lease consists of approximately 32,038 square feet of space and commenced on September 1, 2024 and has a lease term through December 31, 2030 . As of September 30, 2024, the right-of-use asset and lease liability related to the 5858 Horton Expansion Lease were $ 9.2 million and $ 9.4 million , respectively. The discount rate used to measure the lease liability was 11.02 %. Emeryville Warehouse Lease In January 2024, the Company entered into a lease agreement for warehouse space in Emeryville, California (the “Warehouse Lease”). The Warehouse Lease commenced on August 1, 2024 . The Warehouse Lease consists of approximately 7,800 square feet of warehouse space and has a lease term through December 31, 2029 . As of September 30, 2024, the right-of-use asset and lease liability related to the Warehouse Lease were each $ 1.5 million . The discount rate used to measure the lease liability related to the Warehouse Lease was 10.69 %. The following table summarizes the components of lease expense for the three and nine months ended September 30, 2024 and 2023, which are included in operating expenses in the Company’s condensed statements of operations (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Operating lease cost $ 955 $ 698 $ 2,352 $ 2,095 Variable lease cost 455 311 1,268 933 Total $ 1,410 $ 1,009 $ 3,620 $ 3,028 Variable lease payments include amounts relating to common area maintenance and are recognized in the condensed statements of operations as incurred. Cash paid for amounts included in the measurement of the Company’s operating lease liabilities and presented within cash used in operating activities in the statements of cash flows was $ 2.4 million and $ 2.3 million for the nine months ended September 30, 2024 and 2023, respectively. The following table summarizes supplemental information related to operating leases: September 30, December 31, Weighted-average remaining lease term (in years): 6.0 5.7 Weighted-average discount rate: 10.7 % 7.8 % The following table summarizes the maturities of lease liabilities as of September 30, 2024 (in thousands): 2024 (remaining three months) $ 883 2025 5,638 2026 5,601 2027 5,350 2028 5,510 Thereafter 11,130 Total future minimum lease payments 34,112 Less: Amount representing interest ( 9,278 ) Present value of future minimum lease payments 24,834 Less: Current portion of operating lease liabilities 5,091 Long-term portion of operating lease liabilities $ 19,743 Indemnification Agreements In the ordinary course of business, the Company enters into agreements that may include indemnification provisions, such as with vendors and other parties. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors and officers that require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. The Company currently maintains directors’ and officers’ liability insurance that would generally enable it to recover a portion of any future amounts paid. The Company believes the estimated fair value of its indemnification agreements in excess of applicable insurance coverage is not material. Legal Proceedings From time to time, the Company may become involved in legal proceedings arising from the ordinary course of its business. If applicable, the Company records a legal liability when it believes that it is both probable that a liability may be imputed, and the amount of the liability can be reasonably estimated. Significant judgment by the Company is required to determine both probability and the estimated amount. There are no material legal proceedings outstanding at September 30, 2024.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2024
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes For the three and nine months ended September 30, 2024 and 2023, the Company did no t record a federal or state income tax provision due to its recurring net losses. In addition, the Company has taken a full valuation allowance against its net deferred tax assets as the Company believes it is not more likely than not that the benefit will be realized.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2024
Equity [Abstract]
Common Stock	11. Common Stock As of September 30, 2024 and December 31, 2023, the Company’s certificate of incorporation authorized the Company to issue 300,000,000 shares of common stock, at the par value of $ 0.0001 per share. The holder of each share of common stock is entitled to one vote per share . Common stockholders are entitled to dividends, if and when declared by the board of directors. To date, no dividends on common stock have been declared by the board of directors. As of September 30, 2024 and December 31, 2023, the Company has reserved common stock, on an as-converted basis, for future issuance as follows: September 30, December 31, Issuance of common stock under the 2020 Equity Incentive Award Plan 1,546,593 524,078 Issuance of common stock under the 2020 Employee Stock Purchase Plan 273,375 313,034 Exercise of options issued and outstanding and future vesting of restricted stock units 9,153,990 8,423,481 Exercise of common stock warrants 3,637,145 53,669 Total common stock reserved for future issuance 14,611,103 9,314,262 Funding Agreement with CFF — In April 2020, CFF made a $ 10.0 million investment in the Company’s Series C redeemable convertible preferred stock financing. In return for the investment, CFF received shares of Series C redeemable convertible preferred stock, and the Company and CFF entered into a Funding Agreement (the “Funding Agreement”). Pursuant to the terms of the Funding Agreement, except in the event of a technical failure, the $ 10.0 million received from CFF will be used to advance the development program for 4D-710, the Company’s lead product in cystic fibrosis, or any other therapeutic approved by the Program Advisory Group (“PAG”) to alleviate pulmonary complications of cystic fibrosis (the “Funding Agreement Product”). CFF committed to provide an additional $ 4.0 million of funding upon acceptance of an IND application or its equivalent to allow for human testing of the Funding Agreement Product (“Acceptance”). In October 2021, the IND was cleared by the U.S. Food and Drug Administration and CFF made the additional investment of $ 4.0 million in cash for the issuance of 125,715 shares of the Company’s common stock to CFF. The Company was committed to providing an amount equal to the funding provided by CFF to be used solely to advance the Funding Agreement Product. As of September 30, 2024, the funding commitment has been fulfilled. Under the terms of the Funding Agreement, neither the $ 10.0 million investment in the Series C redeemable convertible preferred stock, which converted to common stock as of December 31, 2020, nor the $ 4.0 million of funding upon Acceptance are restricted as to withdrawal or usage.

Stock-based Compensation

Stock-based Compensation	9 Months Ended
	Sep. 30, 2024
Share-Based Payment Arrangement [Abstract]
Stock-based Compensation	12. Stock-based Compensation 2020 Equity Incentive Award Plan In December 2020, the Company adopted the 2020 Incentive Award Plan (“2020 Plan”), which became effective on December 10, 2020. The 2020 Plan initially reserved 2,606,546 shares of common stock for the issuance of stock options, stock appreciation rights, restricted stock awards, restricted stock units, performance bonus awards, performance stock units, dividend equivalents or other stock or cash based award granted to employees, directors and consultants of the Company. The number of shares reserved for future issuance under the 2020 Plan will increase annually on the first day of each fiscal year beginning in 2021 and ending in 2030 by the lesser of (i) 5 % of the shares of common stock outstanding (on an as converted basis) on the last day of the immediately preceding fiscal year and (ii) such number of shares of common stock as determined by the Company's board of directors, provided, however, no more than 18,000,000 shares of the Company’s common stock may be issued upon the exercise of incentive stock options. On February 29, 2024, an additional 2,153,533 shares of common stock became available for issuance under the 2020 Plan, as a result of the operation of the automatic annual increase provision. All options are exercisable over a period not to exceed the contractual term of ten years from the date the stock options were issued. As of September 30, 2024 there were 1,210,988 shares available for grant under the 2020 Plan. Following the effectiveness of the 2020 Plan, the Company will not make any further grants under the 2015 Equity Incentive Plan (the “2015 Plan”). However, the 2015 Plan continues to govern the terms of options that remain outstanding under the 2015 Plan. 2015 Equity Incentive Plan The 2015 Plan provided for grants of stock options, stock appreciation rights, restricted stock and restricted stock unit awards to employees, directors and consultants of the Company. As of September 30, 2024, options to purchase 1,518,923 shares of common stock were outstanding under the 2015 Plan. All options are exercisable over a period not to exceed the contractual term of ten years from the date the stock options were issued and are granted at prices not less than the estimated fair market value of the Company’s common stock on the grant date as determined by the board of directors. No additional grants will be made under the 2015 Plan, and all outstanding grants under the 2015 Plan that are repurchased, forfeited, expire or are cancelled are returned to the 2015 Plan and are not available for grant under the 2020 Plan. Employee Stock Purchase Plan In December 2020, the Company adopted the 2020 Employee Stock Purchase Plan (the “2020 ESPP”). Under the 2020 ESPP, 252,337 shares of the Company’s common stock were initially reserved for employee purchases of the Company’s common stock under terms and provisions established by the Company’s board of directors and approved by the Company’s stockholders. The number of shares reserved for future issuance under the 2020 ESPP will increase annually on the first day of each fiscal year beginning in 2021 and ending in 2030 by the lesser of (i) 1 % of the shares of common stock outstanding (on an as converted basis) on the last day of the immediately preceding fiscal year and (ii) such number of shares of common stock as determined by the Company’s board of directors, provided, however, no more than 15,000,000 shares the Company’s common stock may be issued under the 2020 ESPP. On February 29, 2024, an additional 50,000 shares of common stock became available for future issuance under the 2020 ESPP, as a result of the operation of this automatic annual increase provision. Under the 2020 ESPP the Company’s employees may purchase common stock through payroll deductions at a price equal to 85 % of the lower of the fair market value of the stock at the beginning of the offering period or at the end of each applicable purchase period. The 2020 ESPP provides for a series of overlapping 24-month offering periods comprising four six-month purchase periods. The initial offering period under the 2020 ESPP is longer than 24 months, commencing February 15, 2021 and ending on May 14, 2023. Contributions under the 2020 ESPP are limited to a maximum of 15 % of an employee’s eligible compensation. Restricted Stock Units The Company has granted restricted stock unit (RSU) awards under the 2020 Equity Incentive Award Plan that vest over a period of four years . The following table summarizes the RSU activity for the nine months ended September 30, 2024: Number of Unvested balance at December 31, 2023 181,181 Issued 214,025 Vested ( 32,548 ) Canceled/Forfeited ( 33,991 ) Unvested balance at September 30, 2024 328,667 Stock Options The following table summarizes the stock options activity for the nine months ended September 30, 2024: Number of Balances at December 31, 2023 8,240,154 Options granted 1,179,750 Options exercised ( 367,962 ) Options expired ( 11,395 ) Options forfeited ( 215,224 ) Balances at September 30, 2024 8,825,323 Options exercisable at September 30, 2024 4,136,974 Options vested and expected to vest at September 30, 2024 8,825,323 The Company estimates the fair value of stock options using the Black-Scholes option pricing model. The fair value of employee and nonemployee options is recognized on a straight-line basis over the requisite service period of the awards. The fair value of the Company ’ s stock options was estimated using the following assumptions for the three and nine months ended September 30, 2024 and 2023: Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Expected term 6.0 - 6.1 years 6.0 - 6.1 years 6.0 - 6.1 years 6.0 - 6.1 years Expected volatility 85.3 % - 87.3 % 80.6 % - 82.2 % 85.3 % - 87.3 % 80.6 % - 84.4 % Risk-free interest rate 4.4 % - 4.5 % 4.1 % - 4.4 % 4.3 % - 4.5 % 3.5 % - 4.4 % Expected dividend yield —% —% —% —% Expected Term . The expected term for employee options is calculated using the simplified method as the Company does not have sufficient historical information to provide a basis for this estimate. The simplified method is based on the average of the vesting tranches and the contractual life of each grant. The expected term for nonemployee options is the contractual term of the options. Expected Volatility . The expected volatility is based on a mix of the Company ’ s historical volatility and the historical volatility of comparable companies with similar attributes to the Company, including industry, stage of life cycle, size and financial leverage. For each grant, the Company measured historical volatility over a period equivalent to the expected term. Risk-free Interest Rate. The risk-free interest rate is based on the yield available on U.S. Treasury zero-coupon issues whose term is similar in duration to the expected term of the respective stock option. Expected Dividend Yield . The Company has not paid and does not anticipate paying any dividends on its common stock in the future. Accordingly, the Company has estimated the dividend yield to be zero . Stock-Based Compensation Expense The following table is a summary of stock-based compensation expense incurred for employees and nonemployees by function (in thousands): Three Months Ended Nine Months Ended 2024 2023 2024 2023 Research and development $ 3,650 $ 2,314 $ 9,881 $ 7,463 General and administrative 2,840 2,248 8,657 6,289 Total stock-based compensation expense $ 6,490 $ 4,562 $ 18,538 $ 13,752

Common Stock Warrants

Common Stock Warrants	9 Months Ended
	Sep. 30, 2024
Equity [Abstract]
Common Stock Warrants	13. Common Stock Warrants In May 2018, the Company issued a warrant for 23,669 shares of the Company’s common stock to a service provider with an exercise price of $ 3.19 per share. The fair value of the warrant was determined at the issuance date using the Black-Scholes option pricing model. The warrant expires in 2025 and upon issuance was fully vested. In December 2020, the Company issued a warrant for 30,000 shares of the Company ’ s common stock to a service provider with an exercise price of $ 18.00 per share. This warrant vests over a period of four years and expires in 2027 . The fair value of the warrant was determined at the issuance date using the Black-Scholes option pricing model. In February 2024, the Company completed an underwritten public follow-on offering which included the sale of pre-funded warrants (the “Pre-funded Warrants”) to purchase 3,583,476 shares of the Company’s common stock at an offering price of $ 29.4999 . The exercise price of each Pre-funded Warrant is $ 0.0001 per share, and each Pre-funded Warrant is exercisable from the date of issuance. The Pre-funded Warrants are classified as a component of stockholders’ equity within additional paid-in-capital. The Company valued the Pre-funded Warrants at issuance and recorded net proceeds of $ 99.4 million after deducting underwriters fees during the nine months ended September 30, 2024 related to the sale of the Pre-funded Warrants. There was no material expense related to the above warrant shares during each of the three and nine months ended September 30, 2024 and 2023.

Net Loss Per Share, Basic and D

Net Loss Per Share, Basic and Diluted	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Net Loss Per Share, Basic and Diluted	14. Net Loss Per Share, Basic and Diluted The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Numerator Net loss $ ( 43,843 ) $ ( 10,256 ) $ ( 111,197 ) $ ( 68,554 ) Denominator Weighted-average shares outstanding used in computing net loss per share, basic and diluted 55,554,476 42,256,629 53,377,712 37,884,363 Net loss per share, basic and diluted $ ( 0.79 ) $ ( 0.24 ) $ ( 2.08 ) $ ( 1.81 ) In February 2024, the Company issued and sold Pre-funded Warrants to purchase 3,583,476 shares of common stock at a nominal exercise price of $ 0.0001 (see Note 13). The shares of common stock into which the Pre-funded Warrants may be exercised are considered outstanding for the purposes of computing earnings per share, because the shares may be issued for little or no consideration, they are fully vested and the Pre-funded Warrants are immediately exercisable upon their issuance date. The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: September 30, 2024 2023 Options issued and outstanding 8,825,323 6,021,383 Restricted stock units subject to future vesting 328,667 — 2020 ESPP 244,622 269,102 Common stock warrants 53,669 53,669 Total 9,452,281 6,344,154

Derivative Liability

Derivative Liability	9 Months Ended
	Sep. 30, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Liability	15. Derivative Liability The Company identified an embedded derivative resulting from the change of control provision in the CFF Agreement. Embedded derivatives that are required to be bifurcated from the underlying host instrument are accounted for and valued as separate financial instruments. At the inception of the derivative in 2017, the Company recognized this derivative as a liability and revenue was reduced by the initial fair value of the derivative liability. The Company remeasures the derivative liability to fair value at each reporting period and records the change in fair value of the derivative liability as other income (expense), net. The Company uses a present value analysis with multiple scenarios, which incorporates assumptions and estimates to value the derivative instrument. The Company assesses these assumptions and estimates on a periodic basis as additional information impacting the assumptions is obtained. Estimates and assumptions impacting the fair value measurement include the change of control payment to CFF (range of zero to $ 18.9 million at September 30, 2024 and December 31, 2023), the probability of a change of control event (range of 5.0 % to 37.5 % at September 30, 2024 and December 31, 2023), the probability of the product achieving development or commercial status at time of change of control (range of 4.8 % to 17.2 % at September 30, 2024 and December 31, 2023) and the discount rate ( 15 % at September 30, 2024 and December 31, 2023). The Company determined the estimated fair value of this liability as of the inception date of the CFF Agreement and concluded that the amount was immaterial. The Company determined the fair value of this derivative liability was $ 0.4 million as of September 30, 2024 and December 31, 2023.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2024
Related Party Transactions [Abstract]
Related Party Transactions	16. Related Party Transactions In March 2024, the Company entered into a research and option agreement (the “Reignite Agreement”) with Reignite Therapeutics Inc. (“Reignite”), which was founded by David Kirn, M.D., Chief Executive Officer of the Company. Reignite has the expertise to develop high-capacity, helper-dependent adenovirus capsids which the Company plans to utilize as they expand their therapeutic capsid evolution platform. Reignite and the Company plan to collaborate on a one-to-two year program to develop these high capacity, helper-dependent adenovirus capsids. Under the Reignite Agreement, the Company shall have the final authority to amend and make updates to the plan and budget of the program. Further, the Company is responsible for the funding of the related research which includes the budgeted full-time employees and CRO costs, equipment costs not to exceed $ 60 thousand and all other costs, in total not to exceed $ 1.5 million in any year of the program. The Company will have an option to acquire up to three capsids resulting from the program. The Company shall pay to Reignite an option exercise fee of $ 1.0 million per selected capsid for which the Company has exercised its option. The maximum total amount payable is $ 3.0 million. During the three and nine months ended September 30, 2024, the Company paid Reignite $ 0.3 million and $ 0.7 million, respectively, for research and development expenses. As of September 30, 2024, the Company owes $ 0.1 million to Reignite for unpaid research and development expense. No option exercise fees were incurred during the three and nine months ended September 30, 2024.

401(K) Plan

401(K) Plan	9 Months Ended
	Sep. 30, 2024
Retirement Benefits [Abstract]
401(K) Plan	17. 401(k) Plan In 2014, the Company adopted a 401(k) plan for all employees who have met certain eligibility requirements. The 401(k) plan allows employees to make pre-tax and post-tax contributions up to the maximum allowable amount set by the Internal Revenue Service. The Company made contributions to the 401(k) plan for all eligible participants and recorded contribution expenses of $ 0.4 million and $ 0.2 million for the three months ended September 30, 2024 and 2023, respectively. For the nine months ended September 30, 2024 and 2023, the Company recorded contribution expenses of $ 1.2 million and $ 0.9 million, respectively.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2024
Subsequent Events [Abstract]
Subsequent Events	18. Subsequent Events On November 8, 2024, the Company entered into an Exchange Agreement (the “Exchange Agreement”) with Biotechnology Value Fund, L.P. and certain of its affiliates (“BVF”), pursuant to which BVF exchanged 5,775,000 shares of the Company ’s common stock for pre-funded warrants to acquire the same number of shares of the Company’ s common stock. The pre-funded warrants have an exercise price of $ 0.0001 per underlying share of common stock, are exercisable at any time until they are fully exercised and will not expire until they are fully exercised. The number of shares of the Company ’s common stock issuable upon exercise of each pre-funded warrant is subject to appropriate adjustment in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting shares of the Company’s common stock, as well as upon any distribution of assets, including cash, stock or other property, to the Company’s stockholders. The pre-funded warrants include a beneficial ownership blocker that provides that the holder may not exercise (nor may the Company allow the exercise) if upon giving effect to such exercise, it would cause the aggregate number of shares of the Company’s common stock beneficially owned by the holder (together with affiliates and any other persons whose beneficial ownership of the Company’ s common stock would be aggregated for the purposes of Section 13(d) of the Exchange Act) to exceed 9.99 % of the total number of then issued and outstanding shares of the Company ’ s common stock as determined in accordance with the terms of the pre-funded warrant.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed financial statements have been prepared in accordance with United States Generally Accepted Accounting Principles (“U.S. GAAP”) and the rules and regulations of the United States Securities and Exchange Commission (“SEC”) for interim reporting. Certain information and note disclosures normally included in annual financial statements prepared in accordance with U.S. GAAP have been condensed or omitted. Accordingly, the condensed financial statements should be read in conjunction with the audited financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023 filed with the SEC. The accompanying financial information for the three and nine months ended September 30, 2024 and 2023 is unaudited. The condensed financial statements have been prepared on the same basis as the annual audited financial statements and, in the opinion of management, reflect all adjustments, consisting of only normal recurring adjustments, necessary for a fair statement of the Company’s financial position as of September 30, 2024, and its results of operations and cash flows for the nine months ended September 30, 2024 and 2023. The condensed balance sheet at December 31, 2023 was derived from audited annual financial statements but does not contain all of the footnote disclosures from the annual financial statements. The results for interim periods are not necessarily indicative of the results expected for the full fiscal year or any other periods.
Use of Estimates and Judgements	Use of Estimates and Judgments The preparation of condensed financial statements in conformity with U.S. GAAP requires management to make estimates and judgments that affect the reported amounts of assets, liabilities, revenue and expenses; and disclosure of contingent assets and liabilities as of the date of the financial statements. Such estimates include the determination of useful lives for property and equipment, the contract term, transaction price and costs of collaboration agreements, stock options and the derivative instrument and income tax uncertainties. Actual results could differ from those estimates. Due to the war in Ukraine, conflicts in the Middle East, any expansion of these conflicts, rising interest rates and inflation, natural disasters and pandemics, there has been uncertainty and disruption in the global economy and financial markets. The Company is not aware of any specific event or circumstance that would require an update to its estimates or judgments or a revision of the carrying value of its assets or liabilities as of September 30, 2024. While there was not a material impact to the Company’s condensed financial statements as of September 30, 2024 , these estimates may change, as new events occur and additional information is obtained, as well as other factors that could result in material impacts to the condensed financial statements in future reporting periods.
Segment Information	Segment Information The Company operates and manages its business as one reportable and operating segment. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on a company-wide basis for purposes of allocating resources and assessing financial performance.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, marketable securities and accounts receivable. The Company’s cash is held at two financial institutions in the United States of America. The Company’s cash equivalents are invested in money market funds. The Company also invests in U.S. Treasuries, U.S. government sponsored agencies, commercial paper, corporate bonds and certificates of deposit. The Company has not experienced any losses on its deposits of cash and cash equivalents. Such deposits may, at times, exceed federally insured limits. The Company’s partners in collaboration and license agreements who represent 10% or more of the Company’s total revenue are as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 Customer A 100 % * 100 % * Customer B 0 % 99 % 0 % 96 % Total 100 % 99 % 100 % 96 % * Less than 10 % The Company did no t have accounts receivable from its partners in collaboration and license agreements as of September 30, 2024 and December 31, 2023. The Company’s total revenue by geographic region, based on the location of the customer, are as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2024 Netherlands $ — $ 41 $ — $ 566 United States 3 20,163 36 20,176 Total revenue $ 3 $ 20,204 $ 36 $ 20,742
Other Risks and Uncertainties	Other Risks and Uncertainties The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, protection of proprietary technology, dependence on key personnel, suppliers for key raw materials, contract manufacturing organizations (“CMOs”) and contract research organizations (“CROs”), compliance with government regulations and the need to obtain additional financing to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical studies, clinical trials and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance and reporting. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained or maintained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from other pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees, consultants and other third parties (including for clinical trials and some aspects of research and preclinical testing).
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In November 2023, the Financial Accounting Standards Board issued Accounting Standards Update (“ASU”) No. 2023-07, Improvements to Reportable Segment Disclosures. ASU No. 2023-07 is intended to improve reportable segment disclosure requirements, primarily through enhanced disclosures about significant segment expenses. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023, and for interim periods within fiscal years beginning after December 15, 2024, and must be applied retrospectively to all prior periods presented in the financial statements. The Company is currently evaluating the impact of adoption of this ASU and does not expect the adoption to have a material impact on the Company ’ s financial statements and the related notes thereto. In December 2023, the Financial Accounting Standards Board issued ASU No. 2023-09, Improvements to Income Tax Disclosures. The final guidance adds clarifications related to the presentation of rate reconciliation for public business entities and definitions of specific categories in rate reconciliation. These amendments are effective for public business entities for annual periods beginning after December 15, 2024. For other entities, amendments are effective for annual periods beginning after December 15, 2025. The Company expects to make additional disclosures for income taxes upon adoption of ASU No. 2023-09.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2024
Accounting Policies [Abstract]
Schedule of Concentration of Risk	The Company’s partners in collaboration and license agreements who represent 10% or more of the Company’s total revenue are as follows: Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2023 Customer A 100 % * 100 % * Customer B 0 % 99 % 0 % 96 % Total 100 % 99 % 100 % 96 % * Less than 10 % The Company did no t have accounts receivable from its partners in collaboration and license agreements as of September 30, 2024 and December 31, 2023.
Schedule of Revenues by Geographic Region	The Company’s total revenue by geographic region, based on the location of the customer, are as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2024 2023 2024 2024 Netherlands $ — $ 41 $ — $ 566 United States 3 20,163 36 20,176 Total revenue $ 3 $ 20,204 $ 36 $ 20,742

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Fair Value Hierarchy for Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis	The following tables represent the Company’s fair value hierarchy for financial assets and financial liabilities measured at fair value on a recurring basis as of September 30, 2024 and December 31, 2023 (in thousands): Basis for Fair Value Measurements Fair Value as of Level 1 Level 2 Level 3 September 30, 2024 Assets Money market funds $ 160,546 $ — $ — $ 160,546 Certificates of deposit — 55,872 — 55,872 Commercial paper — 86,712 — 86,712 Corporate bonds — 213,848 — 213,848 U.S. Treasuries — 6,700 — 6,700 Total $ 160,546 $ 363,132 $ — $ 523,678 Liabilities Derivative liability $ — $ — $ 396 $ 396 Total $ — $ — $ 396 $ 396 Basis for Fair Value Measurements Fair Value as of Level 1 Level 2 Level 3 December 31, 2023 Assets Money market funds $ 217,644 $ — $ — $ 217,644 Commercial paper — 18,243 — 18,243 Corporate bonds — 28,939 — 28,939 U.S. government sponsored agencies — 2,896 — 2,896 Total $ 217,644 $ 50,078 $ — $ 267,722 Liabilities Derivative liability $ — $ — $ 369 $ 369 Total $ — $ — $ 369 $ 369
Summary of Changes in Fair Value of Level 3 Financial Instruments	The following tables set forth a summary of the changes in the fair value of the Company’s Level 3 financial instrument during the nine months ended September 30, 2024 and 2023 (in thousands): Derivative Balance as of December 31, 2023 $ 369 Change in fair value included in other income (expense), net 27 Balance as of September 30, 2024 $ 396 Derivative Balance as of December 31, 2022 $ 212 Change in fair value included in other income (expense), net 157 Balance as of September 30, 2023 $ 369

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2024
Investments, Debt and Equity Securities [Abstract]
Summary of Available for Sale Securities	Marketable securities, which are classified as available-for-sale, consisted of the following as of September 30, 2024 and December 31, 2023 (in thousands): Amortized Cost Basis Gross Unrealized Gains Gross Unrealized Losses Fair Value as of September 30, 2024 Short-term marketable securities: Certificates of deposit $ 55,750 $ 122 $ — $ 55,872 Commercial paper 85,276 134 ( 1 ) 85,409 Corporate bonds 166,012 366 ( 6 ) 166,372 U.S. Treasuries 6,679 21 — 6,700 Total short-term marketable securities $ 313,717 $ 643 $ ( 7 ) $ 314,353 Long-term marketable securities: Commercial paper $ 1,289 $ 14 $ — $ 1,303 Corporate bonds 47,047 431 ( 2 ) 47,476 Total long-term marketable securities $ 48,336 $ 445 $ ( 2 ) $ 48,779 Amortized Cost Basis Gross Unrealized Gains Gross Unrealized Losses Fair Value as of December 31, 2023 Short-term marketable securities: Commercial paper $ 17,603 $ 1 $ ( 26 ) $ 17,578 Corporate bonds 18,641 12 ( 3 ) 18,650 U.S. government sponsored agencies 2,900 — ( 4 ) 2,896 Total short-term marketable securities $ 39,144 $ 13 $ ( 33 ) $ 39,124 Long-term marketable securities: Commercial paper $ 661 $ 4 $ — $ 665 Corporate bonds 10,257 32 — 10,289 Total long-term marketable securities $ 10,918 $ 36 $ — $ 10,954
Summary of Aggregate Fair Values of Marketable Securities with Unrealized Losses and Gains	Aggregate fair values of marketable securities with unrealized losses and gains were as follows as of September 30, 2024 and December 31, 2023 (in thousands): September 30, December 31, 2024 2023 Aggregate fair value of marketable securities in a continuous loss position for less than twelve months $ 23,828 $ 20,494 Aggregate fair value of marketable securities in a continuous loss position for more than twelve months — 4,986 Aggregate fair value of marketable securities in unrealized gain position 339,304 24,598 Total marketable securities $ 363,132 $ 50,078

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2024
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net, consisted of the following (in thousands): September 30, December 31, Machinery and equipment $ 14,218 $ 12,996 Leasehold improvements 17,325 16,902 Furniture and fixtures 637 566 Office equipment 239 239 Computer equipment and software 920 805 Construction in progress 2,017 550 Total property and equipment 35,356 32,058 Less: Accumulated depreciation and amortization ( 15,490 ) ( 11,932 ) Property and equipment, net $ 19,866 $ 20,126

Accrued and Other Current Lia_2

Accrued and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2024
Payables and Accruals [Abstract]
Summary of Accrued and Other Current Liabilities	Accrued and other current liabilities consisted of the following (in thousands): September 30, December 31, Payroll and related expenses $ 9,606 $ 8,149 Accrued clinical and preclinical study costs 9,402 2,180 Consulting and professional 2,282 1,581 Other accrued expenses 125 104 Total accrued and other current liabilities $ 21,415 $ 12,014

Research and Collaboration Ar_2

Research and Collaboration Arrangements (Tables)	9 Months Ended
	Sep. 30, 2024
Research And Collaboration Arrangements [Abstract]
Summary of Collaboration and License Revenue	Collaboration and license revenue for each period was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 uniQure $ — $ 41 $ — $ 566 CFF 3 155 36 168 Astellas — 20,008 — 20,008 Total revenue $ 3 $ 20,204 $ 36 $ 20,742
Summary of Deferred Revenue	Deferred revenue is summarized as follows (in thousands): September 30, December 31, CFF $ 1,315 $ 1,245 Total deferred revenue $ 1,315 $ 1,245

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Summary of Components of Lease Expense	The following table summarizes the components of lease expense for the three and nine months ended September 30, 2024 and 2023, which are included in operating expenses in the Company’s condensed statements of operations (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Operating lease cost $ 955 $ 698 $ 2,352 $ 2,095 Variable lease cost 455 311 1,268 933 Total $ 1,410 $ 1,009 $ 3,620 $ 3,028
Summary of Supplemental Information Related to Operating Leases	The following table summarizes supplemental information related to operating leases: September 30, December 31, Weighted-average remaining lease term (in years): 6.0 5.7 Weighted-average discount rate: 10.7 % 7.8 %
Summary of Maturities of Lease Liabilities	The following table summarizes the maturities of lease liabilities as of September 30, 2024 (in thousands): 2024 (remaining three months) $ 883 2025 5,638 2026 5,601 2027 5,350 2028 5,510 Thereafter 11,130 Total future minimum lease payments 34,112 Less: Amount representing interest ( 9,278 ) Present value of future minimum lease payments 24,834 Less: Current portion of operating lease liabilities 5,091 Long-term portion of operating lease liabilities $ 19,743

Common Stock (Tables)

Common Stock (Tables)	9 Months Ended
	Sep. 30, 2024
Equity [Abstract]
Schedule of Common Shares Reserved for Future Issuance	As of September 30, 2024 and December 31, 2023, the Company has reserved common stock, on an as-converted basis, for future issuance as follows: September 30, December 31, Issuance of common stock under the 2020 Equity Incentive Award Plan 1,546,593 524,078 Issuance of common stock under the 2020 Employee Stock Purchase Plan 273,375 313,034 Exercise of options issued and outstanding and future vesting of restricted stock units 9,153,990 8,423,481 Exercise of common stock warrants 3,637,145 53,669 Total common stock reserved for future issuance 14,611,103 9,314,262

Stock-based Compensation (Table

Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2024
Share-Based Payment Arrangement [Abstract]
Summary of Restricted Stock Units (RSU)	The Company has granted restricted stock unit (RSU) awards under the 2020 Equity Incentive Award Plan that vest over a period of four years . The following table summarizes the RSU activity for the nine months ended September 30, 2024: Number of Unvested balance at December 31, 2023 181,181 Issued 214,025 Vested ( 32,548 ) Canceled/Forfeited ( 33,991 ) Unvested balance at September 30, 2024 328,667
Summary of Stock Options Activity	The following table summarizes the stock options activity for the nine months ended September 30, 2024: Number of Balances at December 31, 2023 8,240,154 Options granted 1,179,750 Options exercised ( 367,962 ) Options expired ( 11,395 ) Options forfeited ( 215,224 ) Balances at September 30, 2024 8,825,323 Options exercisable at September 30, 2024 4,136,974 Options vested and expected to vest at September 30, 2024 8,825,323
Summary of Assumptions Used in Black-Scholes Valuation Model to Estimate Fair Value of Stock Options	The Company estimates the fair value of stock options using the Black-Scholes option pricing model. The fair value of employee and nonemployee options is recognized on a straight-line basis over the requisite service period of the awards. The fair value of the Company ’ s stock options was estimated using the following assumptions for the three and nine months ended September 30, 2024 and 2023: Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Expected term 6.0 - 6.1 years 6.0 - 6.1 years 6.0 - 6.1 years 6.0 - 6.1 years Expected volatility 85.3 % - 87.3 % 80.6 % - 82.2 % 85.3 % - 87.3 % 80.6 % - 84.4 % Risk-free interest rate 4.4 % - 4.5 % 4.1 % - 4.4 % 4.3 % - 4.5 % 3.5 % - 4.4 % Expected dividend yield —% —% —% —%
Summary of Stock-based Compensation Expense for Employees and Nonemployees by Function	The following table is a summary of stock-based compensation expense incurred for employees and nonemployees by function (in thousands): Three Months Ended Nine Months Ended 2024 2023 2024 2023 Research and development $ 3,650 $ 2,314 $ 9,881 $ 7,463 General and administrative 2,840 2,248 8,657 6,289 Total stock-based compensation expense $ 6,490 $ 4,562 $ 18,538 $ 13,752

Net Loss Per Share, Basic and_2

Net Loss Per Share, Basic and Diluted (Tables)	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss Per Share	The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share data): Three Months Ended September 30, Nine Months Ended September 30, 2024 2023 2024 2023 Numerator Net loss $ ( 43,843 ) $ ( 10,256 ) $ ( 111,197 ) $ ( 68,554 ) Denominator Weighted-average shares outstanding used in computing net loss per share, basic and diluted 55,554,476 42,256,629 53,377,712 37,884,363 Net loss per share, basic and diluted $ ( 0.79 ) $ ( 0.24 ) $ ( 2.08 ) $ ( 1.81 )
Outstanding Shares of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share	The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive: September 30, 2024 2023 Options issued and outstanding 8,825,323 6,021,383 Restricted stock units subject to future vesting 328,667 — 2020 ESPP 244,622 269,102 Common stock warrants 53,669 53,669 Total 9,452,281 6,344,154

The Company - Additional Inform

The Company - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended
	Mar. 31, 2024	Feb. 29, 2024	May 31, 2023	Nov. 30, 2021	Dec. 31, 2020	Sep. 30, 2024	Dec. 31, 2023	Jan. 01, 2021
Organization And Nature Of Business [Line Items]
Outstanding shares of redeemable convertible preferred stock								0
Accumulated deficit						$ 526,524	$ 415,327
Common Stock | Initial Public Offering
Organization And Nature Of Business [Line Items]
Number of shares sold and issued					9,660,000
Stock sold and issued price per share					$ 23
Aggregate net proceeds, after deducting underwriting discounts and commissions and offering costs					$ 204,700
Number shares issued upon conversion of redeemable convertible preferred shares					11,575,984
Common Stock | Exercise of Overallotment Option
Organization And Nature Of Business [Line Items]
Number of shares sold and issued	1,259,299				1,260,000
Aggregate net proceeds, after deducting underwriting discounts and commissions and offering costs	$ 34,900
Common Stock | 2021 Follow On Public Offering
Organization And Nature Of Business [Line Items]
Number of shares priced under public offering				4,750,000
Stock sold and issued price per share				$ 25
Aggregate net proceeds, after deducting underwriting discounts and commissions and offering costs				$ 111,100
Common Stock | 2023 Follow On Public Offering
Organization And Nature Of Business [Line Items]
Number of shares priced under public offering			8,625,000
Stock sold and issued price per share			$ 16
Aggregate net proceeds, after deducting underwriting discounts and commissions and offering costs			$ 129,200
Common Stock | 2024 Follow On Public Offering
Organization And Nature Of Business [Line Items]
Number of shares priced under public offering		6,586,015
Stock sold and issued price per share		$ 29.5
Aggregate net proceeds, after deducting underwriting discounts and commissions and offering costs		$ 281,200
Warrants to purchase shares of common stock		3,583,476
Common Stock | 2024 Follow On Public Offering | Pre-funded Warrants
Organization And Nature Of Business [Line Items]
Warrants to purchase shares of common stock		3,583,476
Common stock offering price		$ 29.4999
Common Stock | Maximum | Exercise of Overallotment Option
Organization And Nature Of Business [Line Items]
Number of shares sold and issued		1,525,423

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2024 USD ($) Segment	Dec. 31, 2023 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of reportable segments	1
Number of operating segments	1
Collaboration and License Agreements
Summary Of Significant Accounting Policies [Line Items]
Accounts receivable | $	$ 0	$ 0

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Concentration of Risk (Details) - Revenue - Customer Concentration Risk	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	100%		100%
Customer B
Concentration Risk [Line Items]
Concentration risk, percentage	0%	99%	0%	96%
Customer
Concentration Risk [Line Items]
Concentration risk, percentage	100%	99%	100%	96%

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Concentration of Risk (Details) (Parenthetical) - Revenue - Customer Concentration Risk	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	100%		100%
Customer B
Concentration Risk [Line Items]
Concentration risk, percentage	0%	99%	0%	96%
Maximum | Customer A
Concentration Risk [Line Items]
Concentration risk, percentage			10%

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Schedule of Revenues by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation Of Revenue [Line Items]
Total revenue	$ 3	$ 20,204	$ 36	$ 20,742
Netherlands
Disaggregation Of Revenue [Line Items]
Total revenue	0	41	0	566
United States
Disaggregation Of Revenue [Line Items]
Total revenue	$ 3	$ 20,163	$ 36	$ 20,176

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Hierarchy for Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value on Recurring Basis - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	$ 523,678	$ 267,722
Liabilities	396	369
Derivative Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	396	369
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	86,712	18,243
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	213,848	28,939
U.S. Treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	6,700
U.S. Government Sponsored Agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets		2,896
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	160,546	217,644
Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	55,872
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	160,546	217,644
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	160,546	217,644
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	363,132	50,078
Level 2 | Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	86,712	18,243
Level 2 | Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	213,848	28,939
Level 2 | U.S. Treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	6,700
Level 2 | U.S. Government Sponsored Agencies
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets		2,896
Level 2 | Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	55,872
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	396	369
Level 3 | Derivative Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	$ 396	$ 369

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	Sep. 30, 2024	Dec. 31, 2023
Fair Value Disclosures [Abstract]
Assets, Level 1 and Level 2 transfers	$ 0	$ 0
Liabilities, Level 1 and Level 2 transfers	$ 0	$ 0

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Changes in Fair Value of Level 3 Financial Instruments (Details) - Derivative Liability - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 369	$ 212
Change in fair value included in other income (expense), net	$ 27	$ 157
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Income [Extensible List]	Other income (expense), net	Other income (expense), net
Ending Balance	$ 396	$ 369

Marketable Securities - Summary

Marketable Securities - Summary of Available for Sale Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Short-term Marketable Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Basis	$ 313,717	$ 39,144
Gross Unrealized Gains	643	13
Gross Unrealized Losses	(7)	(33)
Fair Value	314,353	39,124
Long-term Marketable Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Basis	48,336	10,918
Gross Unrealized Gains	445	36
Gross Unrealized Losses	(2)	0
Fair Value	48,779	10,954
Commercial Paper | Short-term Marketable Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Basis	85,276	17,603
Gross Unrealized Gains	134	1
Gross Unrealized Losses	(1)	(26)
Fair Value	85,409	17,578
Commercial Paper | Long-term Marketable Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Basis	1,289	661
Gross Unrealized Gains	14	4
Gross Unrealized Losses	0	0
Fair Value	1,303	665
Corporate Bonds | Short-term Marketable Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Basis	166,012	18,641
Gross Unrealized Gains	366	12
Gross Unrealized Losses	(6)	(3)
Fair Value	166,372	18,650
Corporate Bonds | Long-term Marketable Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Basis	47,047	10,257
Gross Unrealized Gains	431	32
Gross Unrealized Losses	(2)	0
Fair Value	47,476	10,289
U.S. Treasuries | Short-term Marketable Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Basis	6,679
Gross Unrealized Gains	21
Gross Unrealized Losses	0
Fair Value	6,700
U.S. Government Sponsored Agencies | Short-term Marketable Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Basis		2,900
Gross Unrealized Gains		0
Gross Unrealized Losses		(4)
Fair Value		$ 2,896
Certificates of Deposit | Short-term Marketable Securities
Debt Securities, Available-for-Sale [Line Items]
Amortized Cost Basis	55,750
Gross Unrealized Gains	122
Gross Unrealized Losses	0
Fair Value	$ 55,872

Marketable Securities - Summa_2

Marketable Securities - Summary of Aggregate fair values of marketable securities with unrealized losses and gains (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale [Line Items]
Aggregate fair value of securities held in a continuous unrealized loss position for less than twelve months	$ 23,828	$ 20,494
Aggregate fair value of marketable securities in a continuous loss position for more than twelve months	0	4,986
Aggregate fair value of marketable securities in unrealized gain position	339,304	24,598
Total marketable securities	$ 363,132	$ 50,078

Marketable Securities - Additio

Marketable Securities - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Debt Securities, Available-for-Sale [Line Items]
Realized gains or losses on marketable securities	$ 0	$ 0
Maximum unrealized loss at individual instrument level	3,000
Aggregate unrealized loss	9,000
Allowance for credit loss	0	0
Other impairment charges related to marketable securities	$ 0	$ 0
Maximum
Debt Securities, Available-for-Sale [Line Items]
Maturity period of marketable securities	2 years

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Property Plant And Equipment [Line Items]
Total property and equipment	$ 35,356	$ 32,058
Less: Accumulated depreciation and amortization	(15,490)	(11,932)
Property and equipment, net	19,866	20,126
Machinery and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	14,218	12,996
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	17,325	16,902
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	637	566
Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	239	239
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Total property and equipment	920	805
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 2,017	$ 550

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 1.2	$ 1.1	$ 3.6	$ 3.1

Accrued and Other Current Lia_3

Accrued and Other Current Liabilities - Summary of Accrued and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Payables and Accruals [Abstract]
Payroll and related expenses	$ 9,606	$ 8,149
Accrued clinical and preclinical study costs	9,402	2,180
Consulting and professional	2,282	1,581
Other accrued expenses	125	104
Total accrued and other current liabilities	$ 21,415	$ 12,014

Research and Collaboration Ar_3

Research and Collaboration Arrangements - Summary of Collaboration and License Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue	$ 3	$ 20,204	$ 36	$ 20,742
Collaboration and License Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue	3	20,204	36	20,742
Collaboration and License Revenue | uniQure
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue	0	41	0	566
Collaboration and License Revenue | Cystic Fibrosis Foundation
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue	3	155	36	168
Collaboration and License Revenue | Astellas
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total revenue	$ 0	$ 20,008	$ 0	$ 20,008

Research and Collaboration Ar_4

Research and Collaboration Arrangements - Summary of Deferred Revenue (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total deferred revenue	$ 1,315	$ 1,245
Cystic Fibrosis Foundation
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total deferred revenue	$ 1,315	$ 1,245

Research and Collaboration Ar_5

Research and Collaboration Arrangements - Additional Information (Details) - USD ($)		1 Months Ended	3 Months Ended	9 Months Ended
	Jul. 05, 2023	Jan. 31, 2014	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Aug. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized					$ 700,000
Deferred revenue			$ 1,315,000	$ 1,315,000		$ 1,245,000
Astellas GeneTherapies Inc
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront payments received	$ 20,000,000
uniQure
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts receivable			0	0		0
uniQure | uniQure Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangement, initial research term		3 years
Upfront payments received		$ 200,000
Options to purchase ordinary shares		609,744
Ordinary shares vesting period		3 years
Fair value of options		$ 10,600,000
Fair value of non monetary consideration of intellectual property right							$ 5,100,000
uniQure | uniQure Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments entitled to receive for achievement of research and development milestones		$ 5,000,000
uniQure | Amended uniQure Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments eliminated							$ 5,000,000
uniQure | Amended uniQure Agreement and Second uniQure Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized			0	0	$ 600,000
Deferred revenue			0	0		0
Remaining performance obligations			0	0		$ 0
Arbor Biotechnologies Inc | Arbor Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shared product designated by JSC			0	0
Research and development expenses			$ 0	$ 0

Research and Collaboration Ar_6

Research and Collaboration Arrangements - Additional Information (Details 1)	Jan. 31, 2014
uniQure | uniQure Agreement | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-10-01
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, estimated performance period	4 years

Research and Collaboration Ar_7

Research and Collaboration Arrangements - CFF - Additional Information (Details)	1 Months Ended		3 Months Ended	9 Months Ended		12 Months Ended
	Aug. 31, 2023 USD ($)	Sep. 30, 2016 USD ($) Installment	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized					$ 700,000
CFF Agreement | Cystic Fibrosis Foundation
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangement total amount of award	$ 6,300,000	$ 3,500,000
Collaborative arrangement achieved milestones				$ 1,800,000		$ 1,700,000
Expected payments multiples to equal actual award received		6
Number of installments to pay actual award | Installment		3
Actual award payment period upon first commercial sale of product		4 years
Continuous period where the Company ceases to develop or commercialize any product		180 days
Collaborative arrangements special term		If at any time prior to the first commercial sale of a product developed as a result of the CFF Agreement, the Company ceases to use commercially reasonable efforts to develop or commercialize any product under the CFF Agreement for a continuous period of 180 consecutive days and fails to present a reasonable plan to resume commercially reasonable efforts, the Company will grant to CFF an irrevocable, exclusive worldwide interruption license under all of the Company’s interest in the research plan technology to exploit such product. Any third-party license granted by the Company shall be subject to such interruption license.
Revenue recognized			$ 200,000		$ 200,000
Deferred revenue				1,300,000		1,200,000
Accounts receivable				0		0
Aggregate amount of transaction price allocated to remaining performance obligation				$ 1,300,000		$ 1,200,000
CFF Agreement | Cystic Fibrosis Foundation | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future sales-based milestone payments multiples		3
Royalties multiples on actual award received		6

Research and Collaboration Ar_8

Research and Collaboration Arrangements - CFF - Additional Information (Details 1) - Cystic Fibrosis Foundation - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2024-10-01	Sep. 30, 2024
Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, estimated performance period	1 year
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, estimated performance period	3 years

License Arrangements - Addition

License Arrangements - Additional Information (Details) - USD ($)			1 Months Ended			3 Months Ended		9 Months Ended
	Jul. 05, 2023	Apr. 21, 2023	Jul. 31, 2021	Jan. 31, 2019	Jan. 31, 2016	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2018
Astellas GeneTherapies Inc
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront payments received	$ 20,000,000
Deferred revenue						$ 0		$ 0
Accounts receivable						0		0
Astellas GeneTherapies Inc | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Future option fees and milestones	$ 942,500,000
Aevitas Therapeutics, Inc. Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront consideration payment		$ 0
Liability related to contingent consideration						0		0
Aevitas Therapeutics, Inc. Agreement | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Potential cash payment upon achievement of certain late-stage development, regulatory and sales milestones		144,000,000
License Agreement for sCFH with University of Pennsylvania | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Potential cash payment upon achievement of certain late-stage development, regulatory and sales milestones		$ 42,000,000
UC Regents and the Trustees of the University of Pennsylvania
Research And Development Arrangement Contract To Perform For Others [Line Items]
Amount paid non-refundable license fee			$ 100,000
Non-refundable license fee payable annually			10,000
Incurred expenses						$ 0	$ 0	$ 0	$ 0
UC Regents and the Trustees of the University of Pennsylvania | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Contingent payments development milestones			3,900,000
UC Regents and the Trustees of the University of Pennsylvania | Minimum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Annual royalty			$ 100,000
UC Agreements
Research And Development Arrangement Contract To Perform For Others [Line Items]
Non-refundable license fee payable upon execution										$ 5,000
Non-refundable license fee payable upon execution every year thereafter until sales of a licensed product and payment of royalties										5,000
Amount obligated to pay upon closing first qualified financing at option of UC Regents										$ 50,000
Percentage of equity interest upon closing of first qualified financing at option of UC Regents										3%
Percentage of equity interests issued as common stock					6%
Amount paid non-refundable license fee				$ 50,000
Non-refundable license fee payable annually				5,000
UC Agreements | Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Contingent payments development milestones				3,100,000
UC Agreements | Minimum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Annual royalty				$ 100,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)		1 Months Ended	9 Months Ended
	Jan. 01, 2024 ft²	Jul. 31, 2024 USD ($) ft²	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Oct. 31, 2018 ft²
Commitment And Contingencies [Line Items]
Operating lease right-of-use ("ROU") assets			$ 21,762,000		$ 11,539,000
Operating lease liability			24,834,000
Increase lease liability			(1,424,000)	$ (967,000)
Cash used in operating activities			2,400,000	$ 2,300,000
5980 Horton Street Building Lease
Commitment And Contingencies [Line Items]
Operating lease right-of-use ("ROU") assets			900,000		1,200,000
Operating lease liability			$ 1,100,000		1,400,000
Amended lease expiry date			August 2026
5858 Horton Street Lease and 2018 Expansion
Commitment And Contingencies [Line Items]
Lease extended term date		Dec. 31, 2030
Operating lease right-of-use ("ROU") assets			$ 10,200,000		10,300,000
Operating lease liability			12,900,000		$ 13,200,000
Lease renewal term		12 months
Area of office and warehouse space | ft²						40,802
Increase lease liability		$ 800,000
Increase in right-of-use asset		800,000
Gain or loss on increase in carrying value of right of use asset		$ 0
Incremental borrowing rate		10.75%
5858 Horton Street Lease and 2024 Expansion
Commitment And Contingencies [Line Items]
Lease extended term date		Dec. 31, 2030
Operating lease right-of-use ("ROU") assets			9,200,000
Operating lease liability			$ 9,400,000
Operating lease, discount rate			11.02%
Lease commencement date		Sep. 01, 2024
Area of office and warehouse space | ft²		32,038
Warehouse Lease Agreement
Commitment And Contingencies [Line Items]
Lease extended term date	Dec. 31, 2029
Operating lease right-of-use ("ROU") assets			$ 1,500,000
Operating lease liability			$ 1,500,000
Operating lease, discount rate			10.69%
Lease commencement date	Aug. 01, 2024
Area of office and warehouse space | ft²	7,800

Commitments and Contingencies-

Commitments and Contingencies- Summary of Components of Lease Expense - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Commitments and Contingencies Disclosure [Abstract]
Operating lease cost	$ 955	$ 698	$ 2,352	$ 2,095
Variable lease cost	455	311	1,268	933
Total	$ 1,410	$ 1,009	$ 3,620	$ 3,028

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Supplemental Information Related to Leases - (Details)	Sep. 30, 2024	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
Weighted-average remaining lease term (in years)	6 years	5 years 8 months 12 days
Weighted-average discount rate	10.70%	7.80%

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Commitments and Contingencies Disclosure [Abstract]
2024 (remaining six months)	$ 883
2025	5,638
2026	5,601
2027	5,350
2028	5,510
Thereafter	11,130
Total future minimum lease payments	34,112
Less: Amount representing interest	(9,278)
Present value of future minimum lease payments	24,834
Less: Current portion of operating lease liabilities	5,091	$ 3,149
Long-term portion of operating lease liabilities	$ 19,743	$ 11,522

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Tax Disclosure [Abstract]
Provision for income tax	$ 0	$ 0	$ 0	$ 0

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($)	1 Months Ended		9 Months Ended	12 Months Ended
	Oct. 31, 2021	Apr. 30, 2020	Sep. 30, 2024	Dec. 31, 2023
Class of Stock [Line Items]
Common stock, shares authorized			300,000,000	300,000,000
Common stock, par value			$ 0.0001	$ 0.0001
Common stock voting rights			one vote per share
Common stock dividend			$ 0	$ 0
Funding Agreement | Cystic Fibrosis Foundation
Class of Stock [Line Items]
Additional funding upon acceptance of investigational New Drug application	$ 4,000,000	$ 4,000,000
Additional investment in cash	$ 4,000,000
Funding Agreement | Cystic Fibrosis Foundation | Common Stock
Class of Stock [Line Items]
Number of shares sold and issued	125,715
Funding Agreement | Cystic Fibrosis Foundation | Series C Redeemable Convertible Preferred Stock
Class of Stock [Line Items]
Investment in redeemable convertible preferred stock financing		$ 10,000,000

Common Stock - Schedule of Comm

Common Stock - Schedule of Common Share Reserved for Future Issuance (Details) - shares	Sep. 30, 2024	Dec. 31, 2023	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock reserved	14,611,103	9,314,262
2020 Equity Incentive Award Plan
Class Of Stock [Line Items]
Common stock reserved	1,546,593	524,078	2,606,546
2020 Employee Stock Purchase Plan
Class Of Stock [Line Items]
Common stock reserved	273,375	313,034	252,337
Exercise of Options Issued and Outstanding and Future Vesting of Restricted Stock Units
Class Of Stock [Line Items]
Common stock reserved	9,153,990	8,423,481
Common Stock Warrants
Class Of Stock [Line Items]
Common stock reserved	3,637,145	53,669

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details)	9 Months Ended
	Sep. 30, 2024 Period shares	Feb. 29, 2024 shares	Dec. 31, 2023 shares	Dec. 31, 2020 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance	14,611,103		9,314,262
Number of options outstanding	8,825,323		8,240,154
Expected dividend yield	0%
2020 Equity Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance	1,546,593		524,078	2,606,546
Percentage of common stock outstanding increased annually for future issuance	5%
Number of shares available for grant	1,210,988	2,153,533
2020 Equity Incentive Award Plan | Restricted Stock Units (RSU)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	4 years
2020 Equity Incentive Award Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized	18,000,000
Options exercisable period	10 years
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options exercisable period	10 years
Number of options outstanding	1,518,923
Number of additional shares available for grant	0
2020 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance	273,375		313,034	252,337
Number of shares available for grant		50,000
Increase in shares available for issuance percentage	1%
Employee purchase price of common stock as percentage of fair market value	85%
Common stock overlapping offering period	24 months
Number of duration purchase period | Period	4
Percentage of maximum contributions of employee's eligible compensation	15%
2020 ESPP | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized	15,000,000

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Restricted Stock Units (RSU) (Details) - Restricted Stock Units (RSU)	9 Months Ended
	Sep. 30, 2024 shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Number of Shares, Unvested Beginning Balance	181,181
Issued	214,025
Vested	(32,548)
Canceled/Forfeited	(33,991)
Number of Shares, Unvested Ending Balance	328,667

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Stock Options Activity (Details)	9 Months Ended
	Sep. 30, 2024 shares
Share-Based Payment Arrangement [Abstract]
Number of Shares Underlying Outstanding Options, Balances at December 31, 2023	8,240,154
Number of Shares Underlying Outstanding Options, granted	1,179,750
Number of Shares Underlying Outstanding Options, exercised	(367,962)
Number of Shares Underlying Outstanding Options, expired	(11,395)
Number of Shares Underlying Outstanding Options, forfeited	(215,224)
Number of Shares Underlying Outstanding Options, Balances at September 30, 2024	8,825,323
Number of Shares Underlying Outstanding Options, Options exercisable at September 30, 2024	4,136,974
Number of Shares Underlying Outstanding Options, Options vested and expected to vest at September 30, 2024	8,825,323

Stock-based Compensation - Sche

Stock-based Compensation - Schedule of Assumptions Used in Black-Scholes Valuation Model to Estimate Fair Value of Stock Options (Details)	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]
Expected volatility, minimum	85.30%	80.60%	85.30%	80.60%
Expected volatility, maximum	87.30%	82.20%	87.30%	84.40%
Risk-free interest rate, minimum	4.40%	4.10%	4.30%	3.50%
Risk-free interest rate, maximum	4.50%	4.40%	4.50%	4.40%
Expected dividend yield			0%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term	6 years	6 years	6 years	6 years
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days

Stock-based Compensation - Su_3

Stock-based Compensation - Summary of Stock-based Compensation Expense for Employees and Nonemployees by Function (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6,490	$ 4,562	$ 18,538	$ 13,752
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	3,650	2,314	9,881	7,463
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,840	$ 2,248	$ 8,657	$ 6,289

Common Stock Warrants - Additio

Common Stock Warrants - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Dec. 31, 2020	May 31, 2018	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Feb. 29, 2024
Class Of Warrant Or Right [Line Items]
Number of warrant shares issued	30,000	23,669
Exercise price	$ 18	$ 3.19
Warrant expiration year	2027	2025
Warrant vesting period	4 years
Warrant expense			$ 0	$ 0	$ 0	$ 0
2024 Follow On Public Offering | Common Stock
Class Of Warrant Or Right [Line Items]
Warrant shares become exercisable							3,583,476
2024 Follow On Public Offering | Common Stock | Pre-funded Warrants
Class Of Warrant Or Right [Line Items]
Exercise price							$ 0.0001
Warrant shares become exercisable							3,583,476
Common stock offering price							$ 29.4999
Issuance of pre-funded warrants					$ 99,400,000

Net Loss Per Share, Basic and_3

Net Loss Per Share, Basic and Diluted - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Numerator
Net loss	$ (43,843)	$ (10,256)	$ (111,197)	$ (68,554)
Denominator
Weighted-average shares outstanding used in computing net loss per share, basic	55,554,476	42,256,629	53,377,712	37,884,363
Weighted-average shares outstanding used in computing net loss per share, diluted	55,554,476	42,256,629	53,377,712	37,884,363
Net loss per share, basic	$ (0.79)	$ (0.24)	$ (2.08)	$ (1.81)
Net loss per share, diluted	$ (0.79)	$ (0.24)	$ (2.08)	$ (1.81)

Net Loss Per Share, Basic and_4

Net Loss Per Share, Basic and Diluted - Additional Information (Details) - $ / shares	Feb. 29, 2024	Dec. 31, 2020	May 31, 2018
Class of Warrant or Right [Line Items]
Exercise price		$ 18	$ 3.19
Common Stock | 2024 Follow On Public Offering
Class of Warrant or Right [Line Items]
Warrants to purchase shares of common stock	3,583,476
Common Stock | Pre-funded Warrants | 2024 Follow On Public Offering
Class of Warrant or Right [Line Items]
Warrants to purchase shares of common stock	3,583,476
Exercise price	$ 0.0001

Net Loss Per Share, Basic and_5

Net Loss Per Share, Basic and Diluted - Outstanding Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss Per Share (Details) - shares	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	9,452,281	6,344,154
Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	8,825,323	6,021,383
Restricted Stock Units Subject to Future Vesting
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	328,667	0
2020 ESPP
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	244,622	269,102
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	53,669	53,669

Derivative Liability - Addition

Derivative Liability - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Derivative [Line Items]
Change in control discount rate	15%	15%
Estimated fair value of derivative liability	$ 0.4	$ 0.4
Minimum
Derivative [Line Items]
Change of control payment	$ 0	$ 0
Change in control event percentage	5%	5%
Maximum
Derivative [Line Items]
Change of control payment	$ 18.9	$ 18.9
Change in control event percentage	37.50%	37.50%
Product Achieving Development or Commercial Status | Minimum
Derivative [Line Items]
Change in control event percentage	4.80%	4.80%
Product Achieving Development or Commercial Status | Maximum
Derivative [Line Items]
Change in control event percentage	17.20%	17.20%

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details) - Reignite Agreement $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	Mar. 31, 2024 USD ($) Product	Sep. 30, 2024 USD ($)	Sep. 30, 2024 USD ($)
Related Party Transaction [Line Items]
Research and development expenses		$ 300	$ 700
Option exercise fee		0	0
Option exercise fees per selected capsid	$ 1,000
Research and Development
Related Party Transaction [Line Items]
Unpaid research and development expense		$ 100	$ 100
Maximum
Related Party Transaction [Line Items]
Related party expenses	1,500
Equipment costs	$ 60
Number of capsids | Product	3
Option exercise fee	$ 3,000

401(K) Plan - Additional Inform

401(K) Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
2014 401(k) Plan
Defined Contribution Plan Disclosure [Line Items]
Employer contribution	$ 0.4	$ 0.2	$ 1.2	$ 0.9

Subsequent Events (Additional I

Subsequent Events (Additional Information) (Details) - $ / shares	Nov. 08, 2024	Dec. 31, 2020	May 31, 2018
Subsequent Event [Line Items]
Exercise price		$ 18	$ 3.19
Common Stock | Pre-funded Warrants | Subsequent Event
Subsequent Event [Line Items]
Beneficial ownership percentage of common stock	9.99%
Common Stock | Pre-funded Warrants | Exchange Agreement | Biotechnology Value Fund, L.P. | Subsequent Event
Subsequent Event [Line Items]
Warrants shares exercised	5,775,000
Exercise price	$ 0.0001