4D Molecular Therapeutics (FDMT) 10-Q 12 Aug 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Aug. 05, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
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 Common Stock, Shares Outstanding		26,988,255
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

Condensed Balance Sheets (Unaud

Condensed Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 243,743	$ 276,726
Accounts receivable	1,218	1,486
Prepaid expenses and other current assets (includes $768 and $169 at June 30, 2021 and December 31, 2020, respectively, attributable to related parties)	3,791	4,444
Total current assets	248,752	282,656
Property and equipment, net	5,580	5,073
Other assets	602	602
Total assets	254,934	288,331
Current liabilities
Accounts payable (includes $0 and $173 at June 30, 2021 and December 31, 2020, respectively, attributable to related parties)	1,962	1,787
Accrued and other current liabilities	4,892	8,371
Deferred revenue	3,016	6,586
Total current liabilities	9,870	16,744
Deferred revenue, net of current portion	2,342	13,226
Derivative liability	207	122
Other liabilities	1,869	1,852
Total liabilities	14,288	31,944
Commitments and contingencies (Note 8)	0	0
Stockholders’ equity
Preferred stock, $0.0001 par value, 10,000,000 shares authorized as of June 30, 2021 and December 31, 2020; no shares issued and outstanding as of June 30, 2021 and December 31, 2020	0	0
Common stock, $0.0001 par value, 300,000,000 shares authorized at June 30, 2021 and December 31, 2020; 26,891,857 and 26,681,983 shares issued and outstanding at June 30, 2021 and December 31, 2020, respectively	3	3
Additional paid-in-capital	400,317	392,063
Accumulated deficit	(159,674)	(135,679)
Total stockholders’ equity	240,646	256,387
Total liabilities and stockholders’ equity	$ 254,934	$ 288,331

Condensed Balance Sheets (Una_2

Condensed Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Prepaid expenses to related parties	$ 768	$ 169
Accounts payable to related parties	$ 0	$ 173
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	26,891,857	26,681,983
Common stock, shares, outstanding	26,891,857	26,681,983

Condensed Statements of Operati

Condensed Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue:
Collaboration and license revenue	$ 14,580	$ 3,508	$ 16,580	$ 6,919
Collaboration and license revenue, related parties	0	125	0	249
Total revenue	14,580	3,633	16,580	7,168
Operating expenses:
Research and development (includes $262 and $134 for the three months ended June 30, 2021 and 2020 and $410 and $258 for the six months ended June 30, 2021 and 2020, respectively, attributable to related parties)	15,223	15,720	27,992	28,878
General and administrative	6,953	3,062	12,496	6,716
Total operating expenses	22,176	18,782	40,488	35,594
Loss from operations	(7,596)	(15,149)	(23,908)	(28,426)
Other income (expense):
Interest income	7	14	14	144
Other expense, net	0	(18)	(101)	(31)
Total other income (expense)	7	(4)	(87)	113
Net loss and comprehensive loss	$ (7,589)	$ (15,153)	$ (23,995)	$ (28,313)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.28)	$ (2.92)	$ (0.90)	$ (5.46)
Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, basic and diluted	26,739,149	5,183,955	26,715,014	5,183,900

Condensed Statements of Opera_2

Condensed Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Research and development expense, related party	$ 262	$ 134	$ 410	$ 258

Condensed Statements of Redeema

Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Additional Paid-in CapitalCumulative Effect, Period of Adoption, Adjustment	Accumulated Deficit	Accumulated DeficitCumulative Effect, Period of Adoption, Adjustment
Stockholders’ Equity (Deficit), beginning balances at Dec. 31, 2019	$ (72,970)	$ 1	$ 6,054	$ (39)	$ (79,025)	$ 39
Redeemable Convertible Preferred Stock, beginning balances (in shares) at Dec. 31, 2019	7,375,631
Redeemable Convertible Preferred Stock, beginning balances at Dec. 31, 2019	$ 102,980
Stockholders' Equity (Deficit), beginning balances (in shares) at Dec. 31, 2019		5,178,955
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201807Member
Issuance of common stock upon exercise of stock options	$ 5		5
Issuance of common stock upon exercise of stock options (in shares)		5,000
Stock-based compensation	1,083		1,083
Net loss	(13,160)				(13,160)
Stockholders’ Equity (Deficit), ending balances at Mar. 31, 2020	$ (85,042)	$ 1	7,103		(92,146)
Redeemable Convertible Preferred Stock, ending balances (in shares) at Mar. 31, 2020	7,375,631
Redeemable Convertible Preferred Stock, ending balances at Mar. 31, 2020	$ 102,980
Stockholders' Equity (Deficit), ending balances (in shares) at Mar. 31, 2020		5,183,955
Stockholders’ Equity (Deficit), beginning balances at Dec. 31, 2019	$ (72,970)	$ 1	6,054	$ (39)	(79,025)	$ 39
Redeemable Convertible Preferred Stock, beginning balances (in shares) at Dec. 31, 2019	7,375,631
Redeemable Convertible Preferred Stock, beginning balances at Dec. 31, 2019	$ 102,980
Stockholders' Equity (Deficit), beginning balances (in shares) at Dec. 31, 2019		5,178,955
Net loss	(28,313)
Stockholders’ Equity (Deficit), ending balances at Jun. 30, 2020	$ (99,158)	$ 1	8,140		(107,299)
Redeemable Convertible Preferred Stock, ending balances (in shares) at Jun. 30, 2020	11,575,984
Redeemable Convertible Preferred Stock, ending balances at Jun. 30, 2020	$ 175,448
Stockholders' Equity (Deficit), ending balances (in shares) at Jun. 30, 2020		5,183,955
Stockholders’ Equity (Deficit), beginning balances at Mar. 31, 2020	$ (85,042)	$ 1	7,103		(92,146)
Redeemable Convertible Preferred Stock, beginning balances (in shares) at Mar. 31, 2020	7,375,631
Redeemable Convertible Preferred Stock, beginning balances at Mar. 31, 2020	$ 102,980
Stockholders' Equity (Deficit), beginning balances (in shares) at Mar. 31, 2020		5,183,955
Issuance of redeemable convertible preferred stock, net of $3,138 of issuance cost	$ 72,468
Issuance of redeemable convertible preferred stock, net of $3,138 of issuance cost (in shares)	4,200,353
Stock-based compensation	$ 1,037		1,037
Net loss	(15,153)				(15,153)
Stockholders’ Equity (Deficit), ending balances at Jun. 30, 2020	$ (99,158)	$ 1	8,140		(107,299)
Redeemable Convertible Preferred Stock, ending balances (in shares) at Jun. 30, 2020	11,575,984
Redeemable Convertible Preferred Stock, ending balances at Jun. 30, 2020	$ 175,448
Stockholders' Equity (Deficit), ending balances (in shares) at Jun. 30, 2020		5,183,955
Stockholders’ Equity (Deficit), beginning balances at Dec. 31, 2020	256,387	$ 3	392,063		(135,679)
Stockholders' Equity (Deficit), beginning balances (in shares) at Dec. 31, 2020		26,681,983
Issuance of common stock upon exercise of stock options	99		99
Issuance of common stock upon exercise of stock options (in shares)		12,396
Stock-based compensation	2,329		2,329
Vesting of common stock warrants	22		22
Net loss	(16,406)				(16,406)
Stockholders’ Equity (Deficit), ending balances at Mar. 31, 2021	242,431	$ 3	394,513		(152,085)
Stockholders' Equity (Deficit), ending balances (in shares) at Mar. 31, 2021		26,694,379
Stockholders’ Equity (Deficit), beginning balances at Dec. 31, 2020	$ 256,387	$ 3	392,063		(135,679)
Stockholders' Equity (Deficit), beginning balances (in shares) at Dec. 31, 2020		26,681,983
Issuance of common stock upon exercise of stock options (in shares)	169,874
Net loss	$ (23,995)
Stockholders’ Equity (Deficit), ending balances at Jun. 30, 2021	240,646	$ 3	400,317		(159,674)
Stockholders' Equity (Deficit), ending balances (in shares) at Jun. 30, 2021		26,891,857
Stockholders’ Equity (Deficit), beginning balances at Mar. 31, 2021	242,431	$ 3	394,513		(152,085)
Stockholders' Equity (Deficit), beginning balances (in shares) at Mar. 31, 2021		26,694,379
Issuance of common stock upon exercise of stock options and warrants	820		820
Issuance of common stock upon exercise of stock options and warrants (in shares)		197,478
Stock-based compensation	3,816		3,816
Issuance of common stock warrant	1,146		1,146
Vesting of common stock warrants	22		22
Net loss	(7,589)				(7,589)
Stockholders’ Equity (Deficit), ending balances at Jun. 30, 2021	$ 240,646	$ 3	$ 400,317		$ (159,674)
Stockholders' Equity (Deficit), ending balances (in shares) at Jun. 30, 2021		26,891,857

Condensed Statements of Redee_2

Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) (Parenthetical) $ in Thousands	3 Months Ended
	Jun. 30, 2020USD ($)
Redeemable Convertible Preferred Stock
Issuance cost for issuance of preferred stock	$ 3,138

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities
Net loss	$ (23,995)	$ (28,313)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	6,145	2,120
Vesting of common stock warrant in return for services	44	0
Change in fair value of derivative liability	85	11
Depreciation and amortization	751	703
Loss on disposition of property and equipment	2	0
Changes in operating assets and liabilities
Accounts receivable	268	250
Prepaid expenses and other current assets	653	(503)
Other assets	0	15
Accounts payable	(172)	2,251
Accrued and other liabilities	(904)	4,019
Deferred revenue	(14,454)	(592)
Net cash used in operating activities	(31,577)	(20,039)
Cash flows from investing activities
Acquisition of property and equipment	(1,379)	(841)
Net cash used in investing activities	(1,379)	(841)
Cash flows from financing activities
Issuance of redeemable convertible preferred stock, net of issuance costs	0	72,468
Proceeds from the exercise of stock options and warrants	919	5
Payments of offering costs	(946)	(368)
Net cash (used in) provided by financing activities	(27)	72,105
Net increase (decrease) in cash and cash equivalents	(32,983)	51,225
Cash and cash equivalents, beginning of period	276,726	49,652
Cash and cash equivalents, end of period	243,743	100,877
Supplemental disclosures of non-cash investing and financing information
Issuance of common stock warrant to settle liability	1,146	0
Purchases of property and equipment in accounts payable and accrued and other liabilities	347	304
Unpaid offering costs	$ 0	$ 10

The Company

The Company	6 Months Ended
	Jun. 30, 2021
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 gene therapy company pioneering the development of product candidates using its targeted and evolved adeno-associated viruses (“AAV”) vectors. 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. Liquidity The Company has incurred significant losses and negative cash flows from operations and had an accumulated deficit of $159.7 million as of June 30, 2021. The Company believes that its cash and cash equivalents as of June 30, 2021 are sufficient for the Company to fund planned operations for at least one year from the issuance date of these 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 currently 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 at 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	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying unaudited 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 footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted. Accordingly, the unaudited 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, 2020 filed with the SEC. The accompanying financial information for the three and six months ended June 30, 2021 and 2020 are unaudited. The unaudited 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, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position as of June 3 0 , 202 1 and its results of operations for the three and six months ended June 30 , 2021 and 2020 and cash flows for the six months ended June 30 , 202 1 and 20 2 0 . 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 The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and judgements 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, as well as estimates of the fair value of stock options and derivative instruments and income tax uncertainties. Actual results could differ from those estimates. Due to the coronavirus (“COVID-19”) pandemic, 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 June 30, 2021. These estimates may change, as new events occur and additional information is obtained, as well as other factors related to the COVID-19 pandemic that could result in material impacts to the financial statements in future reporting periods. Segment Information The Company operates and manages its business as one reportable and operating segment. Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents 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 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 June 30, Six Months Ended June 30, 2021 2020 2021 2020 Customer A 98% 98% 96% 97% Customer B * * * * Total 98% 98% 96% 97% * Less than 10% The Company’s partners in collaboration and license agreements who represent 10% or more of the Company’s total accounts receivable are as follows: June 30, 2021 December 31, 2020 Customer A 100% 74% Customer B * 26% Total 100% 100% * Less than 10% The Company’s total revenues by geographic region, based on the location of the customer, are as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Netherlands $ 267 $ 125 $ 659 $ 249 Switzerland 14,297 3,571 15,902 6,959 United States 16 (63 ) 19 (40 ) $ 14,580 $ 3,633 $ 16,580 $ 7,168 Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. Cash equivalents consist of money market funds. 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). The extent of the impact of the COVID-19 pandemic on the Company’s business will depend upon the duration and spread of the outbreak and the extent and severity of its impact on the Company’s clinical trial activities, research activities and suppliers, all of which are uncertain and cannot be predicted. The extent to which the COVID-19 pandemic may materially impact the Company’s financial condition, liquidity or results of operations is uncertain. Fair Value Measurements The Company applies fair value accounting for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a three-level fair value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows: • Level 1 —Observable inputs, such as quoted prices in active markets for identical assets and liabilities. • Level 2 —Observable inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. • Level 3 —Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. The Company accounts for transfers of financial instruments between levels of the fair value hierarchy on the date of the event or change in circumstance that caused the transfer. Common Stock Warrants The Company accounts for common stock warrants which meet the definition of a derivative as liabilities if the warrant requires net cash settlement or gives the holder the option of net cash settlement. The Company accounts for common stock warrants as equity if the contract requires physical settlement or net physical settlement or if the Company has the option of physical settlement or net physical settlement. Common stock warrants classified as liabilities are initially recorded at fair value and remeasured at fair value each balance sheet date with the offset adjustments recorded in other income (expense), net within the statements of operations and comprehensive loss. Common stock warrants classified as equity are initially measured at fair value on the grant date and are not subsequently remeasured. Revenue Recognition The Company determines revenue recognition for arrangements within the scope of ASC 606 by performing the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company’s revenue is primarily derived through its license, research, development and commercialization agreements. The terms of these types of agreements may include (i) licenses to the Company’s technology, (ii) research and development services, and (iii) services or obligations in connection with participation in research or steering committees. Payments to the Company under these arrangements typically include one or more of the following: nonrefundable upfront and license fees, research funding, milestone and other contingent payments to the Company for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products. Arrangements that include upfront payments are recorded as deferred revenue upon receipt or when due and are recognized as revenue as performance conditions are met. The event-based milestone payments, royalties and cost reimbursements represent variable consideration, and the Company uses the most likely amount method to estimate this variable consideration. Royalty payments are recognized when earned or as the sales occur. The Company records cost reimbursements as accounts receivable when right to consideration is unconditional. A performance obligation is a promise in a contract to transfer a distinct good or service to the customer and is the unit of account in ASC 606. The Company allocates the total transaction price to each performance obligation based on the estimated standalone selling price and recognizes revenue when, or as, the performance obligation is satisfied. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. At the end of each reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Significant management judgment is required to determine the level of effort required under an arrangement and the period over which the Company expects to complete its performance obligations under the arrangement. Changes in these estimates can have a material effect on revenue recognized. Embedded Derivative Embedded derivatives that are required to be bifurcated from the underlying host instrument are accounted for and valued as a separate financial instrument. An embedded derivative exists in the award agreement with the Cystic Fibrosis Foundation (“CFF”). As described in Note 13, the embedded derivative has been bifurcated and is classified as a liability on the balance sheet and separately accounted for at its fair value. The derivative liability is subject to remeasurement to fair value each reporting period. Changes in the fair value of the derivative liability are recognized as a component of other income (expense), net within the statements of operations and comprehensive loss. Net Loss Per Share Attributable to Common Stockholders The Company calculates basic and diluted net loss per share to common stockholders in conformity with the two-class method required for companies with participating securities. The Company considers all series of redeemable convertible preferred stock to be participating securities as the holders are entitled to receive non-cumulative dividends on a pari passu basis in the event the dividend is paid on common shares. Under the two-class method, the net loss attributable to common stockholders is not allocated to the redeemable convertible preferred stock as the holders of redeemable convertible preferred stock do not have a contractual obligation to share in losses. Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period, less shares subject to repurchase. Diluted net loss per share attributable to common stockholders is computed by giving effect to all potentially dilutive common shares outstanding for the period. For purposes of this calculation, redeemable convertible preferred shares, stock options to acquire shares of common stock, common stock warrants, and unvested common stock subject to repurchase, are considered potentially dilutive common shares, but have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect is antidilutive. Upon completion of the Company’s IPO, all outstanding shares of redeemable convertible preferred shares were automatically converted to common stock. As of June 30, 2021 and December 31, 2020, there was no outstanding preferred stock. Recent Accounting Pronouncements New Accounting Pronouncements Recently Adopted In November 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 Revenue from Contracts with Customers Revenue from Contracts with Customers In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes adoption of this ASU did not result in a material impact on the Company's unaudited condensed financial statements and related disclosures. New Accounting Pronouncements Not Yet Adopted As an “emerging growth company,” the Jumpstart Our Business Startups Act (“JOBS Act”) allows the Company to delay adoption of new or revised accounting pronouncements applicable to public companies until such pronouncements are made applicable to private companies. The Company has elected to use this extended transition period under the JOBS Act. The adoption dates discussed below reflect this election. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2021
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 June 30, 2021 and December 31, 2020 (in thousands): Basis for Fair Value Measurements Fair Value as of Level 1 Level 2 Level 3 June 30, 2021 Assets Money market funds $ 243,368 $ — $ — $ 243,368 Total $ 243,368 $ — $ — $ 243,368 Liabilities Derivative liability $ — $ — $ 207 $ 207 Total $ — $ — $ 207 $ 207 Basis for Fair Value Measurements Fair Value as of Level 1 Level 2 Level 3 December 31, 2020 Assets Money market funds $ 276,726 $ — $ — $ 276,726 Total $ 276,726 $ — $ — $ 276,726 Liabilities Derivative liability $ — $ — $ 122 $ 122 Total $ — $ — $ 122 $ 122 Level 3 Inputs The fair value of the derivative liability is based on significant inputs not observable in the market, which represents 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 CFF, 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 13 for further discussion on 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 instruments during the periods ended June 30, 2021 and 2020 (in thousands): Derivative Liability Balance as of December 31, 2020 $ 122 Change in fair value included in other income (expense), net 85 Balance as of June 30, 2021 $ 207 Derivative Liability Balance as of December 31, 2019 $ 101 Change in fair value included in other income (expense), net 11 Balance as of June 30, 2020 $ 112

Property and Equipment, Net

Property and Equipment, Net	6 Months Ended
	Jun. 30, 2021
Property Plant And Equipment [Abstract]
Property and Equipment, Net	4. Property and Equipment, Net Property and equipment, net, consisted of the following (in thousands): June 30, 2021 December 31, 2020 Machinery and equipment $ 5,650 $ 4,911 Leasehold improvements 2,527 2,527 Furniture and fixtures 464 473 Office equipment 101 101 Computer equipment and software 366 366 Construction in progress 1,060 539 Total property and equipment 10,168 8,917 Less: Accumulated depreciation and amortization (4,588 ) (3,844 ) Property and equipment, net $ 5,580 $ 5,073 All property and equipment are maintained in the United States. Depreciation expense was $0.4 million for each of the three months ended June 30, 2021 and 2020. Depreciation expense was $0.8 million and $0.7 million for the six months ended June 30, 2021 and 2020, respectively.

Accrued and Other Liabilities,

Accrued and Other Liabilities, Current and Noncurrent	6 Months Ended
	Jun. 30, 2021
Payables And Accruals [Abstract]
Accrued and Other Liabilities, Current and Noncurrent	5. Accrued and Other Liabilities, Current and Noncurrent Accrued liabilities consisted of the following (in thousands): June 30, 2021 December 31, 2020 Payroll and related $ 2,407 $ 3,437 Accrued clinical and preclinical study costs 1,383 869 Consulting and professional 746 3,574 Other accrued expenses 356 491 Total accrued and other current liabilities $ 4,892 $ 8,371 Other liabilities, noncurrent consisted of the following (in thousands): June 30, 2021 December 31, 2020 Deferred rent, noncurrent $ 1,314 $ 1,237 Other payable, noncurrent 555 615 Total other liabilities, noncurrent $ 1,869 $ 1,852

Research and Collaboration Arra

Research and Collaboration Arrangements	6 Months Ended
	Jun. 30, 2021
Research And Collaboration Arrangements [Abstract]
Research and Collaboration Arrangements	6. Research and Collaboration Arrangements Collaboration and license revenue for each period was as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 uniQure $ 267 $ 125 $ 659 $ 249 Roche 14,297 3,571 15,902 6,959 CFF 16 (63 ) 19 (40 ) $ 14,580 $ 3,633 $ 16,580 $ 7,168 Deferred revenue is summarized as follows (in thousands): June 30, 2021 December 31, 2020 uniQure $ 3,736 $ 4,396 Roche 544 14,318 CFF 1,078 1,098 $ 5,358 $ 19,812 The total amount of revenue in the six months ended June 30, 2021, which was included in deferred revenue at January 1, 2021, was $14.0 million. The total amount of revenue in the six months ended June 30, 2020, which was included in deferred revenue at January 1, 2020, was $1.6 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 was three years and uniQure exercised a one-time option to extend the research term for an additional year to January 2018. Once the Company’s research plan concluded, uniQure was solely responsible for the continued development, manufacturing and commercialization of the project variants as potential product candidates. 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. 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 The upfront payment of $0.2 million was recorded as deferred revenue and recognized on a ratable basis over the performance period of four years. The options to purchase uniQure shares were deemed to be a noncash component of the arrangement consideration. The estimated fair value of the uniQure options was $10.6 million and was recognized ratably as revenue over the performance period of four years. The associated compensation expense related to the stock options were 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 but separate 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 determined to be $5.1 million. This intellectual property right is 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. The incremental transaction price described in the paragraph above was recorded as deferred revenue. The Company identified one single combined performance obligation under ASC 606, which includes the licenses to the New Variants, research services and participation in the joint steering committee (“JSC”). Revenue is recognized using the input method based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation. Based on the current estimated timelines, the deferred revenue is expected to be recognized as revenue over approximately one to two years from June 30, 2021. During the three months ended June 30, 2021 and 2020, the Company recognized revenue of $0.3 million and $0.1 million under the Amended uniQure Agreement and the Second uniQure Agreement, respectively. During the six months ended June 30, 2021 and 2020, the Company recognized revenue of $0.7 million and $0.2 million, respectively, under both of the Amended uniQure Agreement and the Second uniQure Agreement. As of June 30, 2021 and December 31, 2020, deferred revenue relating to uniQure was $3.7 million and $4.4 million, respectively. There were no amounts due from uniQure under the uniQure Agreement, Amended uniQure Agreement or Second uniQure Agreement as of June 30, 2021 and December 31, 2020. As of June 30, 2021 and December 31, 2020, the aggregate amount of the transaction price allocated to the remaining performance obligation was $3.7 million and $4.4 million, respectively. CRF In November 2015, the Company entered into a research funding and collaboration agreement (the “CRF Agreement”) with the Choroideremia Research Foundation (“CRF”). The goal of the CRF Agreement is for CRF to contribute funding to help with the advancement of the Company’s choroideremia research program. The Company is responsible for all decision making and execution of any and all of the related activities to be completed in its sole discretion. The initial term of the CRF Research Plan is two years. The agreement includes contribution to CRF of up to $2.5 million upon certain development or approval milestones. The overall arrangement has automatic extensions of up to three additional years. As of June 30, 2021, no milestones have been achieved. Revenue was fully recognized for this agreement in the year ended December 31, 2017. Roche In November 2017, the Company entered into a collaboration and license agreement with F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (together, “Roche”) to discover and develop products containing optimized next generation AAV Vectors focused on ophthalmological diseases and disorders excluding select criteria (the “2017 Roche Agreement”). At the effective date of the 2017 Roche Agreement , choroideremia was designated a Roche product class and the 4D-110 product was licensed to Roche . The Company was responsible for conducting research and development services prior to pivotal clinical studies, and Roche was responsible for conducting subsequent development and commercialization activities. In addition, Roche agreed to pay for research and development services at the agreed upon full-time employee rate for work performed for choroideremia under the 2017 Roche Agreement, and certain external costs , except for the costs associated with the manufacturing work for choroideremia. Under the 2017 Roche Agreement, Roche had an option exercisable prior to pivotal clinical studies, to license 4D-125 (for the treatment of XLRP), which was not exercised. Pursuant to the 2017 Roche Agreement, the Company received a non-refundable upfront payment of $21.0 million as consideration. In addition, the Company was entitled to contingent payments including (i) $1.0 million for each Roche nominated product beyond the first three, (ii) up to $30.0 million upon exercise of the option to convert a product the Company nominated and developed prior to pivotal clinical studies, (iii) development milestone payments of up to $223.0 million, of which $86.0 million related to choroideremia and the rest related to other licensed products; and (iv) sales-based milestones of up to $123.0 million in connection with licensed products. Through June 30, 2021, the Company received $10.0 million for development milestone payments that are non-refundable. The 2017 Roche Agreement also included provisions that entitled the Company to receive royalty payments ranging from the mid-single digits to the mid-teens for the net sales of the licensed products, in each case subject to the reductions in accordance with the terms of the agreement. The Company identified a single combined performance obligation for the license, research services and participation in the JSC and concluded that Roche’s option did not represent a material right. The Company’s contract with Roche did not include a significant financing component. The Company further concluded that the transaction price should not include the variable consideration related to development milestones as they were considered to be constrained as it was probable that the inclusion of such variable consideration could result in a significant reversal of cumulative revenue in the future. The Company excluded any consideration related to sales-based milestones, including royalties, which would be recognized when the related sales occur. The transaction price and estimated period of performance are re-evaluated at each reporting period and adjusted as needed to reflect changes in the scope of the project, reimbursable expenses and other conditions affecting variable consideration. In June 2021, the Company received from Roche notice of termination without cause of the 2017 Roche Agreement. The termination is effective on September 16, 2021. As a result of the termination of the 2017 Roche Agreement, an adjustment of $8.5 million was made to the transaction price to reflect the decrease in expected reimbursable costs for the six months ended June 30, 2021. The decrease in the transaction price and total budgeted costs for the remaining performance obligation resulted in a $10.6 million increase in revenue recognized in the six months ended June 30, 2021 related to performance obligation partially satisfied prior to January 1, 2021. For the six months ended June 30, 2020, an adjustment of $10.1 million was made to the transaction price to reflect a $5.1 million increase in the scope of the project and expected reimbursable costs and the addition of $5.0 million of variable consideration as uncertainty associated with a development milestone was resolved. This adjustment resulted in a $ 3.0 million increase in revenue recognized in the six months ended June 30, 2020 related to the performance obligation partially satisfied in periods prior to January 1, 2020. During the three months ended June 30, 2021 and 2020, the Company recognized revenue of $14.3 million and $3.6 million, respectively. During the six months ended June 30, 2021 and 2020, the Company recognized revenue of $15.9 million and $7.0 million, respectively. As of June 30, 2021 and December 31, 2020, deferred revenue relating to the 2017 Roche Agreement was $0.5 million and $14.3 million, respectively. Accounts receivable from Roche under this agreement as of June 30, 2021 and December 31, 2020 was $1.2 million and $1.1 million, respectively. As of June 30, 2021 and December 31, 2020, the aggregate amount of the transaction price allocated to the remaining performance obligation was $1.5 million and $25.8 million, respectively. 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 CF research program. The agreement was subsequently amended in September 2017, August 2018 and February 2021 (all four agreements are collectively referred to as the “CFF Agreement”). The total amount of the award under the CFF Agreement is $3.5 million. As of June 30, 2021 and December 31, 2020, the Company achieved milestones totaling $1.3 million 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 three times six times 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 date. Revenue recognized during the three and six months ended June 30 , 2021 and June 30 , 2020 was immaterial . As of June 30 , 2021 and December 31, 2020, deferred revenue relating to the CFF Agreement was $ 1.1 million . Accounts receivable from CFF under the CFF Agreement as of June 30 , 2021 and December 31, 2020 w ere $0 and $ 0.4 million , respectively . As of June 30 , 2021 and December 31, 2020, the aggregate amount of the transaction price allocated to the remaining performance obligation was $ 1.1 million. Based on current timelines, the deferred revenue is expected to be recognized as revenue over the next three to four 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 13 for further discussion of the embedded derivative.

License Arrangements

License Arrangements	6 Months Ended
	Jun. 30, 2021
License Arrangements [Abstract]
License Arrangements	7. License Arrangements 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 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-teens to the mid-twenties-range on any future sublicensing arrangements the Company may enter into with third-party licensees. 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 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-range on any future sublicensing arrangements the Company may enter into with third-party licensees. During each of the three months ended June 30, 2021 and 2020, the Company incurred $0.1 million of expense

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Operating Lease Commitments In May 2015, the Company executed a lease agreement for office and laboratory space in Emeryville, California. In January 2016, the Company executed the first amendment to the lease agreement for additional rentable office and laboratory space which extended the lease to March 31, 2023. In October 2018, the Company executed a second amendment to extend the lease to September 2026. Additionally, the second amendment provided a tenant improvement allowance of $0.2 million, which was paid to the Company in November 2018. The Company amortizes the tenant improvement allowance on a straight-line basis over the remaining term of the lease as a reduction of rent expense. In October 2018, the Company executed a second lease agreement for additional office and laboratory space in Emeryville, California. The new lease has an initial term of 87 months beginning on the rent commencement date with the option to renew the lease for one additional term of five years. The Company did not have to pay rent until October 2019. This lease agreement also provided for a tenant improvement allowance of $0.4 million, which was paid to the Company in December 2019. The Company amortizes the tenant improvement allowance on a straight-line basis over the remaining term of the lease as a reduction of rent expense. In May 2019, the Company amended the second lease agreement executed in October 2018 to add additional office and laboratory space. The amendment extended the term of the lease to December 31, 2029. The Company did not have to pay rent until December 2019. The lease agreement also included a tenant improvement allowance, which was increased to $2.3 million in February 2021 pursuant to a second amendment to the second lease agreement. The Company recognizes rent expense on a straight-line basis over the lease term with the difference between the rent payments and the straight-line rent expense recorded as deferred rent. Rent expense for each of the three months ended June 30, 2021 and 2020 was $0.8 million. Rent expense for each of the six months ended June 30, 2021 and 2020 was $1.5 million. Deferred rent as of June 30, 2021 and December 31, 2020 was $1.6 million. In conjunction with the lease agreements and amendments, the Company paid security deposits of $0.6 million, which is included in other assets within the balance sheets as of June 30, 2021 and December 31, 2020. The following table summarizes the Company’s future minimum commitments under lease contracts as of June 30, 2021 (in thousands): 2021 (remaining 6 months) $ 1,490 2022 3,035 2023 3,115 2024 3,205 2025 3,258 2026 and beyond 11,820 Total $ 25,923 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. In April 2021, the Company executed a settlement with a former employee which resulted in the issuance of a warrant for 40,000 shares of common stock with an exercise price of $9.41 per share. The Company previously recorded an accrual within accrued and other current liabilities within the condensed balance sheet at December 31, 2020 to accrue for the settlement. Upon the issuance of the warrant in April 2021, $1.1 million was reclassified from accrued and other current liabilities to additional paid-in capital within the condensed balance sheet as of June 30, 2021.

Common Stock

Common Stock	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Common Stock	9. Common Stock As of each of June 30, 2021 and December 31, 2020, the Company’s certificate of incorporation authorized the Company to issue 300,000,000 shares of common stock, at a 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 June 30, 2021 and December 31, 2020, the Company has reserved common stock, on an as-converted basis, for future issuance as follows: June 30, 2021 December 31, 2020 Issuance of common stock under the 2020 Equity Incentive Award Plan 2,726,365 2,606,546 Issuance of common stock under the Employee Stock Purchase Plan 519,156 252,337 Exercise of options issued and outstanding 4,238,519 3,194,113 Exercise of common stock warrants 98,669 98,669 Total common stock reserved 7,582,709 6,151,665

Stock-based Compensation

Stock-based Compensation	6 Months Ended
	Jun. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based Compensation	10. 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 our board of directors, provided, however, no more than 18,000,000 shares of our common stock may be issued upon the exercise of incentive stock options. In 2021, an additional 1,334,099 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 June 30, 2021, there were 2,726,365 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 June 30, 2021, options to purchase 3,005,281 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. If an individual owns stock representing more than 10% of the Company’s outstanding shares, the exercise price of each share shall be at least 110% of the fair market value on the date of grant. 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 will become available for grant under the 2020 Plan in accordance with its terms. 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 our common stock were initially reserved for employee purchases of our common stock under terms and provisions established by the Board of Directors and approved by our 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 our board of directors, provided, however, no more than 15,000,000 shares of our common stock may be issued under the plan. On March 25, 2021, an additional 266,819 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 our 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 comprised of four six-month Stock Options The following table summarizes the stock options activity: Number of Shares Available for Grant Number of Shares Underlying Outstanding Options Balances at December 31, 2020 2,606,546 3,194,113 Options authorized 1,334,099 — Options granted (1,240,750 ) 1,240,750 Options exercised — (169,874 ) Options forfeited 26,470 (26,470 ) Balances at June 30, 2021 2,726,365 4,238,519 Options exercisable at June 30, 2021 1,355,297 Options vested and expected to vest at June 30, 2021 4,238,519 The Company estimates the fair value of stock options using the Black-Scholes valuation model. The fair value of stock 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 six months ended June 30, 2021 and 2020. Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Expected term 5.8 - 6.1 years 6.0 - 6.3 years 5.8 - 6.3 years 6.0 - 6.3 years Expected volatility 82.8% - 84.3% 83.5% - 83.5% 82.8% - 84.3% 82.1% - 83.5% Risk-free interest rate 1.0% - 1.1% 0.4% - 0.4% 0.6% - 1.1% 0.4% - 0.7% 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 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 estimated based on a study of publicly traded peer companies as the Company does not have sufficient trading history for its common stock. The Company selects the peer group based on similarities in industry, stage of development, size and financial leverage with the Company’s principal business operations. 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 compensation expense for employees and nonemployees by function (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Research and development $ 1,895 $ 668 $ 3,008 $ 1,304 General and administrative 1,921 369 3,137 816 Total stock-based compensation $ 3,816 $ 1,037 $ 6,145 $ 2,120

Common Stock Warrants

Common Stock Warrants	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Common Stock Warrants	11. Common Stock Warrants In 2016, the Company issued a warrant for 45,000 shares of the Company’s common stock to a service provider with an exercise price of $1.14 per share, of which 15,000 warrant shares become exercisable upon completion of an offering of securities in a private placement by the Company with net proceeds in excess of $25.0 million and 30,000 warrant shares become exercisable upon completion of an IPO by the Company. The warrant expires in 2023. As the services had been completed at the date the warrant had been issued, the fair value of the warrant was determined at the issuance date. 15,000 of these warrant shares became exercisable upon the completion of the Series B financing in 2018 and 30,000 of these warrants became exercisable upon completion of the IPO in 2020. No expense was recognized during the three months and six months ended June 30, 2021 and 2020 with respect to the warrant shares. 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 and recorded $ 0.1 million within additional paid-in-capital upon issuance of the warrant. The warrant expires in 2025 . 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 Model. For the three months and six months ended June 30, 2021, expense related to the vested portion of warrant shares was immaterial and recorded within operating expenses in the statements of operations and comprehensive loss and within additional paid-in-capital on the condensed balance sheets. In April 2021, the Company issued a warrant for 40,000 shares of the Company’s common stock to a former employee with an exercise price of $9.41 per share as a result of a settlement agreement with such former employee. The warrant was exercised in May 2021. See Note 8 for further discussion on the accounting treatment for this warrant.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	12. Net Loss Per Share Attributable to Common Stockholders The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Numerator Net loss attributable to common stockholders $ (7,589 ) $ (15,153 ) $ (23,995 ) $ (28,313 ) Denominator Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, basic and diluted 26,739,149 5,183,955 26,715,014 5,183,900 Net loss per share attributable to common stockholders—basic and diluted $ (0.28 ) $ (2.92 ) $ (0.90 ) $ (5.46 ) The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share attributable to common stockholders for the period presented because including them would have been antidilutive: June 30, 2021 2020 Redeemable convertible preferred stock — 11,575,984 Options issued and outstanding 4,238,519 2,399,276 ESPP shares issuable and outstanding 111,589 — Common stock warrants 98,669 68,669 Total 4,448,777 14,043,929

Derivative Liability

Derivative Liability	6 Months Ended
	Jun. 30, 2021
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivative Liability	13. 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 $ 0 to $ 10.6 million at June 30 , 202 1 and December 31, 2020 ), the probability of a change of control event, the probability of the product achieving development or commercial status at time of change of control (range of 4.8 % to % at June 30 , 202 1 and 3.4 % to 12.3 % at December 31, 2020 ) and the discount rate ( 14 % at June 30 , 202 1 and December 31, 2020 ) . The Company determined the fair value of this derivative liability was $ 0.2 million and $ 0.1 million as of June 30 , 2021 and December 31, 2020 , respectively .

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions	14. Related Party Transactions During the three months ended June 30, 2021 and 2020, the Company paid $31,000 and three-year

401(K) Plan

401(K) Plan	6 Months Ended
	Jun. 30, 2021
Compensation And Retirement Disclosure [Abstract]
401(K) Plan	15. 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 Plan for eligible participants, and recorded contribution expenses of $0.1 million for each of the three month periods ended June 30, 2021 and 2020. For the six months ended June 30, 2021 and 2020, the Company recorded contribution expenses of $0.3 million and $0.2 million, respectively.

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	16. Subsequent Events In July 2021, the Company entered into a license agreement with the UC Regents and the Trustees of the University of Pennsylvania. See Note 7 for further discussion on the license agreement. In July 2021, the Company notified Roche of the Company’s election to continue development of choroideremia. See Note 6 for further discussion on the continuation election notice.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited 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 footnote disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted. Accordingly, the unaudited 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, 2020 filed with the SEC. The accompanying financial information for the three and six months ended June 30, 2021 and 2020 are unaudited. The unaudited 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, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position as of June 3 0 , 202 1 and its results of operations for the three and six months ended June 30 , 2021 and 2020 and cash flows for the six months ended June 30 , 202 1 and 20 2 0 . 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 Judgements The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and judgements 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, as well as estimates of the fair value of stock options and derivative instruments and income tax uncertainties. Actual results could differ from those estimates. Due to the coronavirus (“COVID-19”) pandemic, 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 June 30, 2021. These estimates may change, as new events occur and additional information is obtained, as well as other factors related to the COVID-19 pandemic that could result in material impacts to the financial statements in future reporting periods.
Segment Information	Segment Information The Company operates and manages its business as one reportable and operating segment.
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 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 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 June 30, Six Months Ended June 30, 2021 2020 2021 2020 Customer A 98% 98% 96% 97% Customer B * * * * Total 98% 98% 96% 97% * Less than 10% The Company’s partners in collaboration and license agreements who represent 10% or more of the Company’s total accounts receivable are as follows: June 30, 2021 December 31, 2020 Customer A 100% 74% Customer B * 26% Total 100% 100% * Less than 10% The Company’s total revenues by geographic region, based on the location of the customer, are as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Netherlands $ 267 $ 125 $ 659 $ 249 Switzerland 14,297 3,571 15,902 6,959 United States 16 (63 ) 19 (40 ) $ 14,580 $ 3,633 $ 16,580 $ 7,168
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents. Cash equivalents consist of money market funds.
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). The extent of the impact of the COVID-19 pandemic on the Company’s business will depend upon the duration and spread of the outbreak and the extent and severity of its impact on the Company’s clinical trial activities, research activities and suppliers, all of which are uncertain and cannot be predicted. The extent to which the COVID-19 pandemic may materially impact the Company’s financial condition, liquidity or results of operations is uncertain.
Fair Value Measurements	Fair Value Measurements The Company applies fair value accounting for all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed at fair value in the financial statements on a recurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a three-level fair value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows: • Level 1 —Observable inputs, such as quoted prices in active markets for identical assets and liabilities. • Level 2 —Observable inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. • Level 3 —Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. The Company accounts for transfers of financial instruments between levels of the fair value hierarchy on the date of the event or change in circumstance that caused the transfer.
Common Stock Warrants	Common Stock Warrants The Company accounts for common stock warrants which meet the definition of a derivative as liabilities if the warrant requires net cash settlement or gives the holder the option of net cash settlement. The Company accounts for common stock warrants as equity if the contract requires physical settlement or net physical settlement or if the Company has the option of physical settlement or net physical settlement. Common stock warrants classified as liabilities are initially recorded at fair value and remeasured at fair value each balance sheet date with the offset adjustments recorded in other income (expense), net within the statements of operations and comprehensive loss. Common stock warrants classified as equity are initially measured at fair value on the grant date and are not subsequently remeasured.
Revenue Recognition	Revenue Recognition The Company determines revenue recognition for arrangements within the scope of ASC 606 by performing the following five steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations based on estimated selling prices; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company’s revenue is primarily derived through its license, research, development and commercialization agreements. The terms of these types of agreements may include (i) licenses to the Company’s technology, (ii) research and development services, and (iii) services or obligations in connection with participation in research or steering committees. Payments to the Company under these arrangements typically include one or more of the following: nonrefundable upfront and license fees, research funding, milestone and other contingent payments to the Company for the achievement of defined collaboration objectives and certain preclinical, clinical, regulatory and sales-based events, as well as royalties on sales of any commercialized products. Arrangements that include upfront payments are recorded as deferred revenue upon receipt or when due and are recognized as revenue as performance conditions are met. The event-based milestone payments, royalties and cost reimbursements represent variable consideration, and the Company uses the most likely amount method to estimate this variable consideration. Royalty payments are recognized when earned or as the sales occur. The Company records cost reimbursements as accounts receivable when right to consideration is unconditional. A performance obligation is a promise in a contract to transfer a distinct good or service to the customer and is the unit of account in ASC 606. The Company allocates the total transaction price to each performance obligation based on the estimated standalone selling price and recognizes revenue when, or as, the performance obligation is satisfied. The Company includes the unconstrained amount of estimated variable consideration in the transaction price. At the end of each reporting period, the Company re-evaluates the estimated variable consideration included in the transaction price and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Significant management judgment is required to determine the level of effort required under an arrangement and the period over which the Company expects to complete its performance obligations under the arrangement. Changes in these estimates can have a material effect on revenue recognized.
Embedded Derivative	Embedded Derivative Embedded derivatives that are required to be bifurcated from the underlying host instrument are accounted for and valued as a separate financial instrument. An embedded derivative exists in the award agreement with the Cystic Fibrosis Foundation (“CFF”). As described in Note 13, the embedded derivative has been bifurcated and is classified as a liability on the balance sheet and separately accounted for at its fair value. The derivative liability is subject to remeasurement to fair value each reporting period. Changes in the fair value of the derivative liability are recognized as a component of other income (expense), net within the statements of operations and comprehensive loss.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common Stockholders The Company calculates basic and diluted net loss per share to common stockholders in conformity with the two-class method required for companies with participating securities. The Company considers all series of redeemable convertible preferred stock to be participating securities as the holders are entitled to receive non-cumulative dividends on a pari passu basis in the event the dividend is paid on common shares. Under the two-class method, the net loss attributable to common stockholders is not allocated to the redeemable convertible preferred stock as the holders of redeemable convertible preferred stock do not have a contractual obligation to share in losses. Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period, less shares subject to repurchase. Diluted net loss per share attributable to common stockholders is computed by giving effect to all potentially dilutive common shares outstanding for the period. For purposes of this calculation, redeemable convertible preferred shares, stock options to acquire shares of common stock, common stock warrants, and unvested common stock subject to repurchase, are considered potentially dilutive common shares, but have been excluded from the calculation of diluted net loss per share attributable to common stockholders as their effect is antidilutive. Upon completion of the Company’s IPO, all outstanding shares of redeemable convertible preferred shares were automatically converted to common stock. As of June 30, 2021 and December 31, 2020, there was no outstanding preferred stock.
Recent Accounting Pronouncements	Recent Accounting Pronouncements New Accounting Pronouncements Recently Adopted In November 2018, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606 Revenue from Contracts with Customers Revenue from Contracts with Customers In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes adoption of this ASU did not result in a material impact on the Company's unaudited condensed financial statements and related disclosures. New Accounting Pronouncements Not Yet Adopted As an “emerging growth company,” the Jumpstart Our Business Startups Act (“JOBS Act”) allows the Company to delay adoption of new or revised accounting pronouncements applicable to public companies until such pronouncements are made applicable to private companies. The Company has elected to use this extended transition period under the JOBS Act. The adoption dates discussed below reflect this election. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2021
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 June 30, Six Months Ended June 30, 2021 2020 2021 2020 Customer A 98% 98% 96% 97% Customer B * * * * Total 98% 98% 96% 97% * Less than 10% The Company’s partners in collaboration and license agreements who represent 10% or more of the Company’s total accounts receivable are as follows: June 30, 2021 December 31, 2020 Customer A 100% 74% Customer B * 26% Total 100% 100% * Less than 10%
Schedule of Revenues by Geographic Region	The Company’s total revenues by geographic region, based on the location of the customer, are as follows (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Netherlands $ 267 $ 125 $ 659 $ 249 Switzerland 14,297 3,571 15,902 6,959 United States 16 (63 ) 19 (40 ) $ 14,580 $ 3,633 $ 16,580 $ 7,168

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2021
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 June 30, 2021 and December 31, 2020 (in thousands): Basis for Fair Value Measurements Fair Value as of Level 1 Level 2 Level 3 June 30, 2021 Assets Money market funds $ 243,368 $ — $ — $ 243,368 Total $ 243,368 $ — $ — $ 243,368 Liabilities Derivative liability $ — $ — $ 207 $ 207 Total $ — $ — $ 207 $ 207 Basis for Fair Value Measurements Fair Value as of Level 1 Level 2 Level 3 December 31, 2020 Assets Money market funds $ 276,726 $ — $ — $ 276,726 Total $ 276,726 $ — $ — $ 276,726 Liabilities Derivative liability $ — $ — $ 122 $ 122 Total $ — $ — $ 122 $ 122
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 instruments during the periods ended June 30, 2021 and 2020 (in thousands): Derivative Liability Balance as of December 31, 2020 $ 122 Change in fair value included in other income (expense), net 85 Balance as of June 30, 2021 $ 207 Derivative Liability Balance as of December 31, 2019 $ 101 Change in fair value included in other income (expense), net 11 Balance as of June 30, 2020 $ 112

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	6 Months Ended
	Jun. 30, 2021
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net, consisted of the following (in thousands): June 30, 2021 December 31, 2020 Machinery and equipment $ 5,650 $ 4,911 Leasehold improvements 2,527 2,527 Furniture and fixtures 464 473 Office equipment 101 101 Computer equipment and software 366 366 Construction in progress 1,060 539 Total property and equipment 10,168 8,917 Less: Accumulated depreciation and amortization (4,588 ) (3,844 ) Property and equipment, net $ 5,580 $ 5,073

Accrued and Other Liabilities_2

Accrued and Other Liabilities, Current and Noncurrent (Tables)	6 Months Ended
	Jun. 30, 2021
Payables And Accruals [Abstract]
Summary of Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): June 30, 2021 December 31, 2020 Payroll and related $ 2,407 $ 3,437 Accrued clinical and preclinical study costs 1,383 869 Consulting and professional 746 3,574 Other accrued expenses 356 491 Total accrued and other current liabilities $ 4,892 $ 8,371
Summary of Other Liabilities, Noncurrent	Other liabilities, noncurrent consisted of the following (in thousands): June 30, 2021 December 31, 2020 Deferred rent, noncurrent $ 1,314 $ 1,237 Other payable, noncurrent 555 615 Total other liabilities, noncurrent $ 1,869 $ 1,852

Research and Collaboration Ar_2

Research and Collaboration Arrangements (Tables)	6 Months Ended
	Jun. 30, 2021
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 June 30, Six Months Ended June 30, 2021 2020 2021 2020 uniQure $ 267 $ 125 $ 659 $ 249 Roche 14,297 3,571 15,902 6,959 CFF 16 (63 ) 19 (40 ) $ 14,580 $ 3,633 $ 16,580 $ 7,168
Summary of Deferred Revenue	Deferred revenue is summarized as follows (in thousands): June 30, 2021 December 31, 2020 uniQure $ 3,736 $ 4,396 Roche 544 14,318 CFF 1,078 1,098 $ 5,358 $ 19,812

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Summary of Future Minimum Commitments Under Lease Contracts	The following table summarizes the Company’s future minimum commitments under lease contracts as of June 30, 2021 (in thousands): 2021 (remaining 6 months) $ 1,490 2022 3,035 2023 3,115 2024 3,205 2025 3,258 2026 and beyond 11,820 Total $ 25,923

Common Stock (Tables)

Common Stock (Tables)	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Schedule of Common Share Reserved for Future Issuance	As of June 30, 2021 and December 31, 2020, the Company has reserved common stock, on an as-converted basis, for future issuance as follows: June 30, 2021 December 31, 2020 Issuance of common stock under the 2020 Equity Incentive Award Plan 2,726,365 2,606,546 Issuance of common stock under the Employee Stock Purchase Plan 519,156 252,337 Exercise of options issued and outstanding 4,238,519 3,194,113 Exercise of common stock warrants 98,669 98,669 Total common stock reserved 7,582,709 6,151,665

Stock-based Compensation (Table

Stock-based Compensation (Tables)	6 Months Ended
	Jun. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Options Activity	The following table summarizes the stock options activity: Number of Shares Available for Grant Number of Shares Underlying Outstanding Options Balances at December 31, 2020 2,606,546 3,194,113 Options authorized 1,334,099 — Options granted (1,240,750 ) 1,240,750 Options exercised — (169,874 ) Options forfeited 26,470 (26,470 ) Balances at June 30, 2021 2,726,365 4,238,519 Options exercisable at June 30, 2021 1,355,297 Options vested and expected to vest at June 30, 2021 4,238,519
Schedule 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 valuation model. The fair value of stock 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 six months ended June 30, 2021 and 2020. Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Expected term 5.8 - 6.1 years 6.0 - 6.3 years 5.8 - 6.3 years 6.0 - 6.3 years Expected volatility 82.8% - 84.3% 83.5% - 83.5% 82.8% - 84.3% 82.1% - 83.5% Risk-free interest rate 1.0% - 1.1% 0.4% - 0.4% 0.6% - 1.1% 0.4% - 0.7% Expected dividend yield —% —% —% —%
Summary of Stock Compensation Expense for Employees and Nonemployees by Function	The following table is a summary of stock compensation expense for employees and nonemployees by function (in thousands): Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Research and development $ 1,895 $ 668 $ 3,008 $ 1,304 General and administrative 1,921 369 3,137 816 Total stock-based compensation $ 3,816 $ 1,037 $ 6,145 $ 2,120

Net Loss Per Share Attributab_2

Net Loss Per Share Attributable to Common Stockholders (Tables)	6 Months Ended
	Jun. 30, 2021
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 attributable to common stockholders (in thousands, except share and per share data): Three Months Ended June 30, Six Months Ended June 30, 2021 2020 2021 2020 Numerator Net loss attributable to common stockholders $ (7,589 ) $ (15,153 ) $ (23,995 ) $ (28,313 ) Denominator Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, basic and diluted 26,739,149 5,183,955 26,715,014 5,183,900 Net loss per share attributable to common stockholders—basic and diluted $ (0.28 ) $ (2.92 ) $ (0.90 ) $ (5.46 )
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 attributable to common stockholders for the period presented because including them would have been antidilutive: June 30, 2021 2020 Redeemable convertible preferred stock — 11,575,984 Options issued and outstanding 4,238,519 2,399,276 ESPP shares issuable and outstanding 111,589 — Common stock warrants 98,669 68,669 Total 4,448,777 14,043,929

The Company - Additional Inform

The Company - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended
	Dec. 31, 2020	Jun. 30, 2021	Jan. 01, 2021	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Organization And Nature Of Business [Line Items]
Outstanding shares of redeemable convertible preferred stock			0	11,575,984	7,375,631	7,375,631
Accumulated deficit	$ 135,679	$ 159,674
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	1,260,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Details)	6 Months Ended
	Jun. 30, 2021SegmentFinancial_Institutionshares	Dec. 31, 2020shares
Summary Of Significant Accounting Policies [Line Items]
Number of reportable segments	1
Number of operating segments	1
Number of financial institutions cash is held | Financial_Institution	2
Preferred stock, shares outstanding | shares	0	0
Accounting Standard Update ("ASU") 2018-18
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle accounting standards update, adopted	true
Change in accounting principle accounting standards update, adoption date	Jan. 1, 2021
Change in accounting principle accounting standards update, immaterial effect	true
Accounting Standard Update ("ASU") 2019-12
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle accounting standards update, adopted	true
Change in accounting principle accounting standards update, adoption date	Jan. 1, 2021
Change in accounting principle accounting standards update, immaterial effect	true

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Concentration of Risk (Details)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	98.00%	98.00%	96.00%	97.00%
Revenue | Customer Concentration Risk | Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	98.00%	98.00%	96.00%	97.00%
Accounts Receivable | Credit Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage			100.00%		100.00%
Accounts Receivable | Credit Concentration Risk | Customer A
Concentration Risk [Line Items]
Concentration risk, percentage			100.00%		74.00%
Accounts Receivable | Credit Concentration Risk | Customer B
Concentration Risk [Line Items]
Concentration risk, percentage					26.00%

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Schedule of Concentration of Risk (Details) (Parenthetical)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Revenue | Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage	98.00%	98.00%	96.00%	97.00%
Revenue | Customer Concentration Risk | Maximum
Concentration Risk [Line Items]
Concentration risk, percentage			10.00%
Accounts Receivable | Credit Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage			100.00%		100.00%
Accounts Receivable | Credit Concentration Risk | Maximum
Concentration Risk [Line Items]
Concentration risk, percentage			10.00%

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Schedule of Revenues by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation Of Revenue [Line Items]
Revenues	$ 14,580	$ 3,633	$ 16,580	$ 7,168
Netherlands
Disaggregation Of Revenue [Line Items]
Revenues	267	125	659	249
Switzerland
Disaggregation Of Revenue [Line Items]
Revenues	14,297	3,571	15,902	6,959
United States
Disaggregation Of Revenue [Line Items]
Revenues	$ 16	$ (63)	$ 19	$ (40)

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	Jun. 30, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	$ 243,368	$ 276,726
Liabilities	207	122
Derivative Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	207	122
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	243,368	276,726
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	243,368	276,726
Level 1 | Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	243,368	276,726
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	207	122
Level 3 | Derivative Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	$ 207	$ 122

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Assets, Level 1 to Level 2 transfers	$ 0	$ 0
Assets, Level 2 to Level 1 Transfers	0	0
Assets, Transfers into Level 3	0	0
Assets, Transfers out of Level 3	0	0
Liabilities, Level 1 to Level 2 transfers	0	0
Liabilities, Level 2 to Level 1 transfers	0	0
Liabilities, Transfers into Level 3	0	0
Liabilities, Transfers out of Level 3	$ 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	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 122	$ 101
Change in fair value included in other income (expense), net	$ 85	$ 11
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Income [Extensible List]	Other expense, net	Other expense, net
Ending Balance	$ 207	$ 112

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment	$ 10,168	$ 8,917
Less: Accumulated depreciation and amortization	(4,588)	(3,844)
Property and equipment, net	5,580	5,073
Machinery and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	5,650	4,911
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	2,527	2,527
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment	464	473
Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	101	101
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Total property and equipment	366	366
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 1,060	$ 539

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Property Plant And Equipment [Abstract]
Depreciation expense	$ 0.4	$ 0.4	$ 0.8	$ 0.7

Accrued and Other Liabilities_3

Accrued and Other Liabilities, Current and Noncurrent - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Payroll and related	$ 2,407	$ 3,437
Accrued clinical and preclinical study costs	1,383	869
Consulting and professional	746	3,574
Other accrued expenses	356	491
Total accrued and other current liabilities	$ 4,892	$ 8,371

Accrued and Other Liabilities_4

Accrued and Other Liabilities, Current and Noncurrent - Summary of Other Liabilities, Noncurrent (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Deferred rent, noncurrent	$ 1,314	$ 1,237
Other payable, noncurrent	555	615
Total other liabilities, noncurrent	$ 1,869	$ 1,852

Research and Collaboration Ar_3

Research and Collaboration Arrangements - Summary of Collaboration and License Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 14,580	$ 3,633	$ 16,580	$ 7,168
Collaboration and License Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	14,580	3,633	16,580	7,168
Collaboration and License Revenue | uniQure
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	267	125	659	249
Collaboration and License Revenue | Roche
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	14,297	3,571	15,902	6,959
Collaboration and License Revenue | CFF
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 16	$ (63)	$ 19	$ (40)

Research and Collaboration Ar_4

Research and Collaboration Arrangements - Summary of Deferred Revenue (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 5,358	$ 19,812
uniQure
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	3,736	4,396
Roche
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	544	14,318
CFF
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue	$ 1,078	$ 1,098

Research and Collaboration Ar_5

Research and Collaboration Arrangements - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2014	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Aug. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue included in deferred revenue at the beginning of the current year				$ 14,000,000	$ 1,600,000
Deferred revenue		$ 5,358,000		5,358,000		$ 19,812,000
uniQure
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue		3,736,000		3,736,000		4,396,000
Due from related parties		$ 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
Deferred revenue, estimated performance period		2 years		2 years
uniQure | uniQure Agreement | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, estimated performance period		1 year		1 year
uniQure | Amended uniQure Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue included in deferred revenue at the beginning of the current year		$ 300,000	$ 100,000	$ 700,000	$ 200,000
Remaining performance obligation		$ 3,700,000		$ 3,700,000		$ 4,400,000
uniQure | Amended uniQure Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments eliminated							$ 5,000,000

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: 2021-07-01
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, estimated performance period	4 years

Research and Collaboration Ar_7

Research and Collaboration Arrangements - CRF Agreement - Additional Information (Details) - CRF Agreement - CRF - USD ($)	1 Months Ended	6 Months Ended
	Nov. 30, 2015	Jun. 30, 2021
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangement, initial research term	2 years
Collaborative arrangement contribution upon development milestone	$ 2,500,000
Collaborative arrangement additional research term	3 years
Collaborative arrangement achieved milestones		$ 0

Research and Collaboration Ar_8

Research and Collaboration Arrangements - Roche Agreement - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Nov. 30, 2017	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total Revenue		$ 14,580	$ 3,633	$ 16,580	$ 7,168
Roche | 2017 Roche Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-refundable upfront payments received	$ 21,000
Contingent payment for each nominated product beyond the first three	1,000
Maximum contingent payment upon exercise of the option to convert a product	30,000
Maximum development milestone payments	223,000
Development milestone payments relating to Choroideremia	86,000
Maximum sales-based milestone payments	$ 123,000
Non-refundable development milestone payments				10,000
Collaborative arrangement adjustment to transaction price				8,500	10,100
Collaborative arrangement increase in project scope and expected reimbursable costs					5,100
Collaborative arrangement addition of variable consideration					5,000
Increase (decrease) in revenue recognized				10,600	3,000
Total Revenue		14,300	$ 3,600	15,900	$ 7,000
Deferred revenue		500		500		$ 14,300
Accounts receivable		1,200		1,200		1,100
Remaining performance obligation		$ 1,500		$ 1,500		$ 25,800

Research and Collaboration Ar_9

Research and Collaboration Arrangements - CFF - Additional Information (Details) - CFF	1 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2016USD ($)Installment	Jun. 30, 2021USD ($)	Dec. 31, 2020USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangement total amount of award	$ 3,500,000
Collaborative arrangement achieved milestones		$ 1,300,000	$ 1,300,000
Expected payments percentage to equal actual award received	600.00%
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
Deferred revenue		1,100,000	1,100,000
Accounts receivable		0	400,000
Remaining performance obligation		$ 1,100,000	$ 1,100,000
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future sales-based milestone payments percentage	300.00%
Royalties percentage on actual award received	600.00%

Research and Collaboration A_10

Research and Collaboration Arrangements - CFF - Additional Information (Details 1) - CFF - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-07-01	Jun. 30, 2021
Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, estimated performance period	3 years
Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, estimated performance period	4 years

License Arrangements - Addition

License Arrangements - Additional Information (Details) - UC Agreements - USD ($)	1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2021	Jan. 31, 2016	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2018	Jan. 31, 2019
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 first qualified financing at option of UC Regents							3.00%
Percentage of equity interests issued as common stock		6.00%
Amount paid non-refundable license fee	$ 100,000							$ 50,000
Non-refundable license fee payable annually	10,000							$ 5,000
Incurred expenses			$ 100,000	$ 100,000	$ 100,000	$ 100,000
Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Development milestones	3,900,000				3,100,000
Minimum [Member]
Research And Development Arrangement Contract To Perform For Others [Line Items]
Annual royalty	$ 100,000				$ 100,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands

1 Months Ended

3 Months Ended

6 Months Ended

Apr. 30, 2021

Feb. 28, 2021

Dec. 31, 2019

May 31, 2019

Nov. 30, 2018

Oct. 31, 2018

May 31, 2018

Jan. 31, 2016

Jun. 30, 2021

Jun. 30, 2020

Jun. 30, 2021

Jun. 30, 2020

Dec. 31, 2020

Dec. 31, 2016

Commitment And Contingencies [Line Items]

Lease extended term date

Dec. 31, 2029

Mar. 31, 2023

Tenant improvement allowance

$ 2,300

$ 400

$ 200

Lease extended term period

2026-09

Lease initial term

87 months

Lease option to renew term description

The new lease has an initial term of 87 months beginning on the rent commencement date with the option to renew the lease for one additional term of five years.

Lease existence of option to renew term

true

Lease renewal term

5 years

Annual rent

$ 800

$ 800

$ 1,500

$ 1,500

Deferred rent

1,600

1,600

$ 1,600

Exercise price

$ 9.41

$ 3.19

$ 18

$ 1.14

Reclassified to additional paid-in capital

$ 100

1,146

Former Employee

Commitment And Contingencies [Line Items]

Number of warrants issued

40,000

Exercise price

$ 9.41

Other Assets [Member]

Commitment And Contingencies [Line Items]

Security deposit

600

$ 600

$ 600

Accrued And Other Current Liabilities

Commitment And Contingencies [Line Items]

Reclassified to additional paid-in capital

$ 1,100

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Future Minimum Commitments Under Lease Contracts (Details) $ in Thousands	Jun. 30, 2021USD ($)
Commitments And Contingencies Disclosure [Abstract]
2021 (remaining 6 months)	$ 1,490
2022	3,035
2023	3,115
2024	3,205
2025	3,258
2026 and beyond	11,820
Total	$ 25,923

Common Stock - Additional Infor

Common Stock - Additional Information (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Equity [Abstract]
Common stock, shares authorized	300,000,000	300,000,000
Common stock, par value	$ 0.0001	$ 0.0001
Common stock voting rights	one
Common stock dividend	$ 0	$ 0

Common Stock - Schedule of Comm

Common Stock - Schedule of Common Share Reserved for Future Issuance (Details) - shares	Jun. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock reserved	7,582,709	6,151,665
2020 Equity Incentive Award Plan
Class Of Stock [Line Items]
Common stock reserved	2,726,365	2,606,546
Employee Stock Purchase Plan
Class Of Stock [Line Items]
Common stock reserved	519,156	252,337
Options Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved	4,238,519	3,194,113
Common Stock Warrants
Class Of Stock [Line Items]
Common stock reserved	98,669	98,669

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Details) - shares	Mar. 25, 2021	Dec. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance		6,151,665	7,582,709		7,582,709
Number of shares available for grant		2,606,546	2,726,365		2,726,365
Number of options outstanding		3,194,113	4,238,519		4,238,519
Expected dividend yield			0.00%	0.00%	0.00%	0.00%
2020 Equity Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance		2,606,546	2,726,365		2,726,365
Number of shares available for grant			2,726,365		2,726,365
2020 Equity Incentive Award Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options exercisable period		10 years
2020 Equity Incentive Award Plan | Forecast
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized and reserved for issuance							1,334,099
Percentage of aggregate number of shares of common stock outstanding reserved for future issuance							5.00%
2020 Equity Incentive Award Plan | Forecast | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant							18,000,000
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant			0		0
Options exercisable period					10 years
Number of options outstanding			3,005,281		3,005,281
Minimum percentage of outstanding shares held by individual					10.00%
Exercise price as percentage of fair market value, minimum					110.00%
2020 ESPP
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized and reserved for issuance	266,819	252,337
Percentage of aggregate number of shares of common stock outstanding reserved for future issuance	1.00%
Employee purchase price of common stock as percentage of fair market value		85.00%
Common stock overlapping offering period		24 months
Duration of purchase period		6 months
Percentage of maximum contributions of employee's eligible compensation		15.00%
2020 ESPP | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares available for grant	15,000,000

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Stock Options Activity (Details)	6 Months Ended
	Jun. 30, 2021shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares Available for Grant,Balances at December 31, 2020	2,606,546
Number of Shares Available for Grant, Options authorized	1,334,099
Number of Shares Available for Grant, Options granted	(1,240,750)
Number of Shares Available for Grant, Options forfeited	26,470
Number of Shares Available for Grant, Balances at June 30, 2021	2,726,365
Number of Shares Underlying Outstanding Options, Balances at December 31, 2020	3,194,113
Number of Shares Underlying Outstanding Options, granted	1,240,750
Number of Shares Underlying Outstanding Options, exercised	(169,874)
Number of Shares Underlying Outstanding Options, forfeited	(26,470)
Number of Shares Underlying Outstanding Options, Balances at June 30, 2021	4,238,519
Number of Shares Underlying Outstanding Options, Options exercisable at June 30, 2021	1,355,297
Number of Shares Underlying Outstanding Options, Options vested and expected to vest at June 30, 2021	4,238,519

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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	82.80%	83.50%	82.80%	82.10%
Expected volatility, maximum	84.30%	83.50%	84.30%	83.50%
Risk-free interest rate, minimum	1.00%	0.40%	0.60%	0.40%
Risk-free interest rate, maximum	1.10%	0.40%	1.10%	0.70%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term	5 years 9 months 18 days	6 years	5 years 9 months 18 days	6 years
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term	6 years 1 month 6 days	6 years 3 months 18 days	6 years 3 months 18 days	6 years 3 months 18 days

Stock-based Compensation - Su_2

Stock-based Compensation - Summary of Stock Compensation Expense for Employees and Nonemployees by Function (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 3,816	$ 1,037	$ 6,145	$ 2,120
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	1,895	668	3,008	1,304
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation	$ 1,921	$ 369	$ 3,137	$ 816

Common Stock Warrants - Additio

Common Stock Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 30, 2021	May 31, 2018	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2016	Dec. 31, 2018
Class Of Warrant Or Right [Line Items]
Number of warrants issued	40,000	23,669					30,000	45,000
Exercise price	$ 9.41	$ 3.19					$ 18	$ 1.14
Issuance of common stock warrant		$ 100	$ 1,146
Proceeds from offering of securities in a private placement								$ 25,000
Warrant expiration year		2025					2027	2023
Warrant shares, expense recognized			0	0	0	0
Warrant vesting period							4 years
Warrant exercised month and year	2021-05
Series B Financing
Class Of Warrant Or Right [Line Items]
Warrant shares exercisable									15,000
Private Placement
Class Of Warrant Or Right [Line Items]
Warrant shares exercisable								15,000
Initial Public Offering
Class Of Warrant Or Right [Line Items]
Warrant shares exercisable							30,000	30,000

Net Loss Per Share Attributab_3

Net Loss Per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator
Net loss attributable to common stockholders	$ (7,589)	$ (15,153)	$ (23,995)	$ (28,313)
Denominator
Weighted-average shares outstanding used in computing net loss per share attributable to common stockholders, basic and diluted	26,739,149	5,183,955	26,715,014	5,183,900
Net loss per share attributable to common stockholders, basic and diluted	$ (0.28)	$ (2.92)	$ (0.90)	$ (5.46)

Net Loss Per Share Attributab_4

Net Loss Per Share Attributable to Common Stockholders - Outstanding Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss Per Share (Details) - shares	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	4,448,777	14,043,929
Redeemable Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	0	11,575,984
Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	4,238,519	2,399,276
ESPP Shares Issuable and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	111,589	0
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	98,669	68,669

Derivative Liability - Addition

Derivative Liability - Additional Information (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Change in control discount rate	14.00%	14.00%
Estimated fair value of derivative liability	$ 200,000	$ 100,000
Minimum [Member]
Derivative [Line Items]
Change of control payment	$ 0	$ 0
Change in control event percentage	4.80%	3.40%
Maximum
Derivative [Line Items]
Change of control payment	$ 10,600,000	$ 10,600,000
Change in control event percentage	17.20%	12.30%

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Details)	1 Months Ended		3 Months Ended		6 Months Ended
	Mar. 31, 2021USD ($)	Apr. 30, 2019USD ($)agreement	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Dec. 31, 2020USD ($)
UC Regents | SRAs
Related Party Transaction [Line Items]
Number of sponsored research agreements entered | agreement		2
Agreement term		3 years
Amount due to related party		$ 1,500,000
UC Regents | SRAs and Machine Learning SRA
Related Party Transaction [Line Items]
Accounts payable, related party			$ 0		$ 0		$ 200,000
UC Regents | Machine Learning SRA
Related Party Transaction [Line Items]
Agreement term	3 years
Amount due to related party	$ 1,400,000
Payment to related party					400,000
David Schaffer, PhD, | Consulting Services and Services as Board of Director
Related Party Transaction [Line Items]
Related party expenses			$ 31,000	$ 0	$ 63,000	$ 13,000

401(K) Plan - Additional Inform

401(K) Plan - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
2014 Plan
Defined Contribution Plan Disclosure [Line Items]
Employer contribution	$ 0.1	$ 0.1	$ 0.3	$ 0.2