0000950170-22-004794 | 10-K | XBRL Viewer | 4D Molecular Therapeutics INC

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Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss	Accumulated Deficit	Accumulated Deficit Cumulative 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]	Accounting Standard Update ("ASU") 2018-07
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
Conversion of redeemable convertible preferred stock into common stock	$ 175,448	$ 1	175,447
Conversion of redeemable convertible preferred stock into common stock (in shares)		11,575,984
Conversion of redeemable convertible preferred stock into common stock	$ (175,448)
Conversion of redeemable convertible preferred stock into common stock (in shares)	(11,575,984)
Issuance of common stock upon initial public offering, net of issuance cost	$ 204,713	$ 1	204,712
Issuance of common stock upon initial public offering, net of issuance cost (in shares)		9,660,000
Issuance of common stock upon exercise of stock options	857		857
Issuance of common stock upon exercise of stock options (in shares)		267,044
Stock-based compensation expense	4,984		4,984
Vesting of common stock warrants issued for services	48		48
Net loss	(56,693)					(56,693)
Stockholders’ Equity (Deficit), ending balances at Dec. 31, 2020	$ 256,387	$ 3	392,063			(135,679)
Redeemable Convertible Preferred Stock, ending balances (in shares) at Dec. 31, 2020	0
Stockholders’ Equity (Deficit), ending balances (in shares) at Dec. 31, 2020		26,681,983
Issuance of common stock upon exercise of stock options and warrants	$ 3,905		3,905
Issuance of common stock upon exercise of stock options and warrants (in shares)		646,417
Issuance of common stock upon initial public offering, net of issuance cost	$ 115,090		115,090
Issuance of common stock upon initial public offering, net of issuance cost (in shares)		4,875,715
Issuance of common stock upon exercise of stock options (in shares)	563,387
Issuance of common stock warrant	$ 1,146		1,146
Stock-based compensation expense	13,799		13,799
Issuance of common stock - 2020 ESPP	433		433
Issuance of common stock - 2020 ESPP (in shares)		20,409
Vesting of common stock warrants issued for services	87		87
Gross unrealized loss on marketable securities	(423)				$ (423)
Net loss	(71,317)				(71,317)	(71,317)
Stockholders’ Equity (Deficit), ending balances at Dec. 31, 2021	$ 319,107	$ 3	$ 526,523		$ (423)	$ (206,996)
Redeemable Convertible Preferred Stock, ending balances (in shares) at Dec. 31, 2021	0
Stockholders’ Equity (Deficit), ending balances (in shares) at Dec. 31, 2021		32,224,524

Commitments and Contingencies - summary of Components of Lease Expense (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Operating lease cost	$ 2,631
Variable lease cost	914
Total	$ 3,545

Stock-based Compensation - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Mar. 25, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Mar. 24, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance		6,151,665	7,123,787	6,151,665
Number of shares available for grant		2,606,546	2,690,097	2,606,546
Number of options outstanding		3,194,113	3,881,274	3,194,113
Number of stock options granted			1,566,150
Fair value of options vested			$ 13,800	$ 5,000
Unrecognized stock-based compensation of unvested options			$ 37,700
Unrecognized stock-based compensation, expected to be recognized over weighted-average period			2 years 8 months 12 days
Stock-based compensation expense			$ 13,799	$ 4,984
Expected dividend yield			0.00%	0.00%
Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock options granted			1,521,150	1,267,743
Weighted-average grant date fair value			$ 34.46	$ 11.84
Stock-based compensation expense			$ 13,300	$ 4,600
Expected dividend yield			0.00%	0.00%
Nonemployee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of stock options granted			45,000	54,000
Weighted-average grant date fair value			$ 47.42	$ 11.05
Stock-based compensation expense			$ 500	$ 400
Expected dividend yield			0.00%	0.00%
2020 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance		2,606,546		2,606,546
Percentage of common stock outstanding increased annually for future issuance			5.00%
Number of shares available for grant			2,690,097
Number of shares authorized and reserved for issuance			1,334,099
2020 Incentive Award Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options exercisable period		10 years
Number of shares available for grant			18,000,000
2015 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options exercisable period			10 years
Number of shares available for grant			0
Number of options outstanding			2,519,217
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]
Percentage of aggregate number of shares of common stock outstanding reserved for future issuance	1.00%
Number of shares authorized and reserved for issuance		252,337		252,337	25,000
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%		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

Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
Statements of Comprehensive Loss - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net loss	$ (71,317)	$ (56,693)
Other comprehensive loss:
Gross unrealized loss on marketable securities	(423)	0
Total comprehensive loss	$ (71,740)	$ (56,693)

- Definition

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

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+ Details

Stock-based Compensation - Summary of Stock Compensation Expense for Employees and Nonemployees by Function (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 13,799	$ 4,984
Research and Development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	6,847	2,670
General and Administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6,952	$ 2,314

Related Party Transactions

12 Months Ended

Dec. 31, 2021

Related Party Transactions

17. Related Party Transactions

During the years ended December 31, 2021 and 2020, the Company paid $85,000 and $93,000, respectively, to David Schaffer, Ph.D., the co-founder, director and Chief Scientific Advisor of the Company for consulting services. In April 2019, the Company entered into two sponsored research agreements (“SRAs”) with the UC Regents to conduct research in a research facility on the U.C. Berkeley campus, under the direction of Dr. Schaffer. The SRAs have a three year term ending in May 2022. Under the SRAs, the Company has an option to license (on a royalty-bearing basis) all intellectual property generated under the SRAs. The total amount the Company is committed to pay to the UC Regents under the SRAs is $1.5 million, which was fully paid as of December 31, 2021. In March 2021, the Company entered into another sponsored research agreement with the UC Regents to conduct research in laboratories on the U.C. Berkeley campus that are under the direction of Dr. Schaffer and another U.C. Berkeley professor covering investigations into how machine learning approaches may enhance AAV capsid engineering (the “Machine Learning SRA”). Pursuant to the Machine Learning SRA, the Company has committed to pay the UC Regents a total of $1.4 million, of which $0.4 million was paid as of December 31, 2021. The Machine Learning SRA has a three-year term ending in 2024. Any patent prosecution costs incurred under the SRAs will also be borne by the Company. The Company can terminate the SRAs for convenience and without cause with 60 days’ notice. While the Machine Learning SRA is between the Company and the UC Regents, the payments under the SRA will be used to fund the lab under the direction of Dr. Schaffer. As of December 31, 2021 and 2020, accounts payable to the UC Regents related to the SRAs and Machine Learning SRA was $0.0 million and $0.2 million, respectively. In the years ended December 31, 2021 and 2020, the Company recorded $0.9 million and $0.5 million, respectively, of expense related to SRAs.

In August 2019, the Company and uniQure entered into the amended uniQure Agreement and the Second uniQure Agreement. Under these agreements, the Company agreed to transfer incremental rights and services to uniQure in exchange for uniQure eliminating the exclusivity clause in the uniQure Agreement and transferring other rights back to the Company. Further details and the accounting for these agreements is discussed in Note 7. As of June 17, 2020, uniQure was no longer a related party of the Company.

Marketable Securities - Summary of Available for Sale Securities (Details) $ in Thousands	Dec. 31, 2021 USD ($)
Short-term Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 94,868
Gross Unrealized Gains	0
Gross Unrealized Losses	(92)
Fair Value	94,776
Short-term Marketable Securities \| Commercial Paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	32,471
Gross Unrealized Gains	0
Gross Unrealized Losses	(4)
Fair Value	32,467
Short-term Marketable Securities \| Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	57,315
Gross Unrealized Gains	0
Gross Unrealized Losses	(79)
Fair Value	57,236
Short-term Marketable Securities \| US Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	5,082
Gross Unrealized Gains	0
Gross Unrealized Losses	(9)
Fair Value	5,073
Long-term Marketable Securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	67,983
Gross Unrealized Gains	0
Gross Unrealized Losses	(331)
Fair Value	67,652
Long-term Marketable Securities \| Commercial Paper
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	5,089
Gross Unrealized Gains	0
Gross Unrealized Losses	(21)
Fair Value	5,068
Long-term Marketable Securities \| Corporate Bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	37,821
Gross Unrealized Gains	0
Gross Unrealized Losses	(193)
Fair Value	37,628
Long-term Marketable Securities \| US Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	25,073
Gross Unrealized Gains	0
Gross Unrealized Losses	(117)
Fair Value	$ 24,956

Commitments and Contingencies - Summary of Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
2022	$ 1,230
2023	3,058
2024	3,149
2025	3,244
2026	3,135
Thereafter	8,686
Total future minimum lease payments	22,502
Less: Amount representing interest	(6,054)
Present value of future minimum lease payments	16,448
Less: Current portion of operating lease liabilities	1,231	$ 2,029	$ 0
Long-term portion of operating lease liabilities	$ 15,217	$ 16,058	$ 0

Stock-based Compensation - Schedule of Assumptions Used in Black-Scholes Valuation Model to Estimate Fair Value of Stock Options (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%
Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, minimum	80.00%	82.10%
Expected volatility, maximum	84.30%	83.80%
Risk-free interest rate, minimum	0.60%	0.40%
Risk-free interest rate, maximum	1.30%	0.70%
Expected dividend yield	0.00%	0.00%
Nonemployee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term	6 years 3 months 18 days	6 years
Expected volatility, minimum		82.10%
Expected volatility, maximum		83.10%
Expected volatility	83.50%
Risk-free interest rate, minimum		0.40%
Risk-free interest rate, maximum		0.70%
Risk-free interest rate	0.60%
Expected dividend yield	0.00%	0.00%
Minimum \| Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term	5 years 9 months 18 days	5 years 6 months
Maximum \| Employee
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term	6 years 3 months 18 days	6 years 3 months 18 days

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 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:


	Year Ended December 31,
	2021	2020
Customer A	95%	95%
Customer B	*	*
Total	95%	95%

* 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:


	December 31,
	2021	2020
Customer A	100%	74%
Customer B	0%	26%
Total	100%	100%

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):


	Year Ended December 31,
	2021		2020
Netherlands	$	736	$	742
Switzerland		17,181		12,897
United States		121		(27	)
Total revenue	$	18,038	$	13,612

Schedule of Impact of Adoption of New Accounting Standard

The impact of adoption of the new lease standard as of January 1, 2021 is summarized as follows:


	December 31, 2020			ASC 842 Adjustments			January 1, 2021
Operating lease right-of-use assets	$	—		$	16,537		$	16,537
Prepaid expenses and other current assets		4,444			(214	)		4,230
Accrued and other current liabilities		(8,371	)		68			(8,303	)
Other liabilities		(1,852	)		1,696			(156	)
Operating lease liabilities, current		—			(2,029	)		(2,029	)
Operating lease liabilities, long-term		—			(16,058	)		(16,058	)

Net Loss Per Share, Basic and Diluted (Tables)

12 Months Ended

Dec. 31, 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 (in thousands, except share and per share data):


	Year Ended December 31,
	2021			2020
Numerator
Net loss attributable to common stockholders	$	(71,317	)	$	(56,693	)
Denominator
Weighted-average shares outstanding		27,730,420			6,430,555
Weighted-average shares outstanding used in computing net loss per share, basic and diluted		27,730,420			6,430,555
Net loss per share, basic and diluted	$	(2.57	)	$	(8.82	)

Outstanding Shares of Potentially Dilutive Securities Excluded from Computation of Diluted Net Loss Per Share

The following outstanding shares of potentially dilutive securities were excluded from the computation of diluted net loss per share for the periods presented because including them would have been antidilutive:


	December 31,
	2021		2020
Options issued and outstanding		3,881,274		3,194,113
Common stock warrants		53,669		98,669
Total		3,934,943		3,292,782

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended						12 Months Ended
	Nov. 30, 2021	Feb. 28, 2021	Dec. 31, 2019	Nov. 30, 2018	Oct. 31, 2018	Jan. 31, 2016	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Commitment And Contingencies [Line Items]
Operating lease right-of-use ("ROU") assets							$ 14,562	$ 16,537	$ 0
Operating lease liability							$ 16,448
Operating lease, discount rate							7.80%
Operating lease expense							$ 2,600
Cash paid for amounts included in the measurement of lease liabilities							2,300
5980 Horton Street Building Lease
Commitment And Contingencies [Line Items]
Lease extended term date						Mar. 31, 2023
Tenant improvement allowance				$ 200
Lease extended term period					2026-09
Operating lease right-of-use ("ROU") assets							1,900
Operating lease liability							$ 2,300
Operating lease, discount rate							7.50%
5858 Horton Street Building Lease and Expansion
Commitment And Contingencies [Line Items]
Tenant improvement allowance	$ 600	$ 2,300	$ 400
Operating lease right-of-use ("ROU") assets							$ 12,600
Operating lease liability							$ 14,200
Operating lease, discount rate							7.80%
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 at market rent.
Lease existence of option to renew term					true
Lease renewal term					5 years
Minimum \| 5980 Horton Street Building Lease
Commitment And Contingencies [Line Items]
Lease renewal term						3 years
Maximum \| 5980 Horton Street Building Lease
Commitment And Contingencies [Line Items]
Lease renewal term						5 years

Common Stock - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 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 vote per share
Common stock dividend	$ 0	$ 0

Net Loss Per Share, Basic and Diluted

12 Months Ended

Dec. 31, 2021

Earnings Per Share [Abstract]

Net Loss Per Share, Basic and Diluted

15. Net Loss Per Share, Basic and Diluted

The following table sets forth the computation of basic and diluted net loss per share (in thousands, except share and per share data):


	Year Ended December 31,
	2021			2020
Numerator
Net loss attributable to common stockholders	$	(71,317	)	$	(56,693	)
Denominator
Weighted-average shares outstanding		27,730,420			6,430,555
Weighted-average shares outstanding used in computing net loss per share, basic and diluted		27,730,420			6,430,555
Net loss per share, basic and diluted	$	(2.57	)	$	(8.82	)


	December 31,
	2021		2020
Options issued and outstanding		3,881,274		3,194,113
Common stock warrants		53,669		98,669
Total		3,934,943		3,292,782

Common Stock (Tables)

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Schedule of Common Share Reserved for Future Issuance

As of December 31, 2021 and 2020, the Company has reserved common stock, on an as-converted basis, for future issuance as follows:


	December 31,
	2021		2020
Issuance of common stock under the 2020 Equity Incentive Plan		2,690,097		2,606,546
Issuance of common stock under the Employee Stock Share Purchase Plan		498,747		252,337
Exercise of options issued and outstanding		3,881,274		3,194,113
Exercise of common stock warrants		53,669		98,669
Total common stock reserved		7,123,787		6,151,665

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2021

Commitments and Contingencies Disclosure [Abstract]

Summary of Components of Lease Expense

The following table summarizes the components of lease expense for the year ended December 31, 2021, which are included in operating expenses in the Company’s statements of operations (in thousands):


Operating lease cost	$	2,631
Variable lease cost		914
Total	$	3,545

Summary of Supplemental Information Related to Leases

The following table summarizes supplemental information related to operating leases for the year ended December 31, 2021:


Weighted-average remaining lease term (in years):	7.6
Weighted-average discount rate:	7.8	%

Summary of Maturities of Lease Liabilities

The following table summarizes the maturities of lease liabilities as of December 31, 2021 (in thousands):


2022	$	1,230
2023		3,058
2024		3,149
2025		3,244
2026		3,135
Thereafter		8,686
Total future minimum lease payments		22,502
Less: Amount representing interest		(6,054	)
Present value of future minimum lease payments		16,448
Less: Current portion of operating lease liabilities		1,231
Long-term portion of operating lease liabilities	$	15,217

Stock-based Compensation - Summary of Stock Options Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Share-based Payment Arrangement [Abstract]
Number of Shares Available for Grant, Beginning Balance	2,606,546
Number of Shares Available for Grant, Options authorized	1,334,099
Number of Shares Available for Grant, Options granted	(1,566,150)
Number of Shares Available for Grant, Options expired	4,324
Number of Shares Available for Grant, Options forfeited	311,278
Number of Shares Available for Grant, Ending Balance	2,690,097	2,606,546
Number of Shares Underlying Outstanding Options, Beginning Balance	3,194,113
Number of Shares Underlying Outstanding Options, granted	1,566,150
Number of Shares Underlying Outstanding Options, exercised	(563,387)
Number of Shares Underlying Outstanding Options, expired	(4,324)
Number of Shares Underlying Outstanding Options, forfeited	(311,278)
Number of Shares Underlying Outstanding Options, Ending Balance	3,881,274	3,194,113
Number of Shares Underlying Outstanding Options, Shares exercisable, December 31, 2021	1,592,139
Number of Shares Underlying Outstanding Options, Shares vested and expected to vest, December 31, 2021	3,881,274
Weighted-Average Exercise Price, Beginning Balance	$ 11.05
Options granted	34.83
Options exercised	6.26
Options expired	36.33
Options forfeited	29.17
Weighted-Average Exercise Price, Ending Balance	19.86	$ 11.05
Weighted-Average Exercise Price, Shares exercisable, December 31,2021	12.75
Weighted-Average Exercise Price, Shares vested and expected to vest, December 31,2021	$ 19.86
Weighted-Average Remaining Contractual Term (in years), Outstanding	7 years 11 months 19 days	8 years 5 months 15 days
Weighted-Average Remaining Contractual Term (in years), Shares exercisable, December 31,2021	7 years 25 days
Weighted-Average Remaining Contractual Term (in years), Shares vested and expected to vest, December 31,2021	7 years 11 months 19 days
Aggregate Intrinsic Value, Outstanding Balance	$ 24,666	$ 97,105
Aggregate Intrinsic Value, Shares exercisable, December 31,2021	17,280
Aggregate Intrinsic Value, Shares vested and expected to vest, December 31,2021	$ 24,666

The Company

12 Months Ended

Dec. 31, 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.

Follow On Public Offering

In November 2021, the Company completed its second underwritten public offering ("Follow-on Offering") in which 4,750,000 shares of the Company's common stock were sold at an offering price of $25.00 per share pursuant to an effective Registration Statement on Form S-1. The net proceeds from the Follow-on Offering were $111.1 million, after deducting underwriting discounts and commissions and offering expenses.

Liquidity

The Company has incurred significant losses and negative cash flows from operations and had an accumulated deficit of $207.0 million as of December 31, 2021. The Company believes that its cash and cash equivalents and marketable securities as of December 31, 2021 are sufficient for the Company to fund planned operations for at least one year from the issuance date of these financial statements for the year ended December 31, 2021. The Company has historically financed its operations primarily through the sale of equity securities, and to a lesser extent, from cash received pursuant to its collaboration and license agreements. To date, none of the Company’s product candidates have been approved for sale, and therefore, the Company has not generated any revenue from product sales. Management expects operating losses and negative cash flows from operations to continue for the foreseeable future. The Company plans to raise additional funding as required based on the status of its clinical trials and projected cash flows. There can be no assurance that, in the event the Company requires additional financing, such financing will be available on terms acceptable to the Company, if at all. Failure to generate sufficient cash flows from operations, raise additional capital and reduce discretionary spending should additional capital not become available could have a material adverse effect on the Company’s ability to achieve its business objectives.

Related Party Transactions - Additional Information (Details)	1 Months Ended		12 Months Ended
	Mar. 31, 2021 USD ($)	Apr. 30, 2019 USD ($) Agreement	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
David Schaffer, PhD, \| Consulting Services and Services as Board of Director
Related Party Transaction [Line Items]
Related party expenses			$ 85,000	$ 93,000
UC Regents \| SRAs
Related Party Transaction [Line Items]
Related party expenses			900,000	500,000
Number of sponsored research agreements entered \| Agreement		2
Agreement term		3 years
Amount due to related party		$ 1,500,000
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
UC Regents \| SRAs and Machine Learning SRA
Related Party Transaction [Line Items]
Accounts payable, related party			$ 0.0	$ 200,000

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	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	$ 198,984	$ 276,726
Liabilities	214	122
Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	94,864
US Treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	30,029
Derivative Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	214	122
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	37,535
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	36,556	276,726
Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	36,556	276,726
Level 1 \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	36,556	276,726
Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	162,428
Level 2 \| Corporate Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	94,864
Level 2 \| US Treasuries
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	30,029
Level 2 \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Assets	37,535
Level 3
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	214	122
Level 3 \| Derivative Liability
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Liabilities	$ 214	$ 122

Derivative Liability - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Change in control discount rate	14.00%	14.00%
Estimated fair value of derivative liability	$ 0.2	$ 0.1
Minimum
Derivative [Line Items]
Change of control payment	$ 0.0	$ 0.0
Change in control event percentage	4.80%	3.40%
Maximum
Derivative [Line Items]
Change of control payment	$ 10.6	$ 10.6
Change in control event percentage	17.20%	12.30%

Statements of Operations (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Research and development expense, related party	$ 935	$ 579

Research and Collaboration Arrangements (Tables)

12 Months Ended

Dec. 31, 2021

Research And Collaboration Arrangements [Abstract]

Summary of Collaboration and License Revenue

Collaboration and license revenue for each period was as follows (in thousands):


	Year Ended December 31,
	2021		2020
uniQure	$	736	$	742
Roche		17,181		12,897
CFF		121		(27	)
	$	18,038	$	13,612

Summary of Deferred Revenue

Deferred revenue for each period was as follows (in thousands):


	Deferred Revenue as of December 31,
	2021		2020
uniQure	$	3,661	$	4,396
Roche		—		14,318
CFF		1,429		1,098
	$	5,090	$	19,812

Accrued and Other Liabilities, Current and Noncurrent - Summary of Other Liabilities, Noncurrent (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Deferred rent			$ 1,237
Other payable	$ 120		615
Total other liabilities, noncurrent	$ 120	$ 156	$ 1,852

401(K) Plan

12 Months Ended

Dec. 31, 2021

Retirement Benefits [Abstract]

401(K) Plan

18. 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 $0.5 million and $0.4 million for the years ended December 31, 2021 and 2020, respectively.

Common Stock Warrants

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Common Stock Warrants

14. 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. The fair value of the warrant was determined at the issuance date using the Black-Scholes option pricing model. 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. 45,000 shares of this warrant were exercised in October 2021.

In May 2018, the Company issued a warrant for 23,669 shares of the Company’s common stock to a service provider with an exercise price of $3.19 per share. The fair value of the warrant was determined at the issuance date using the Black-Scholes option pricing model, expires in 2025 and upon issuance was fully vested.

In December 2020, the Company issued a warrant for 30,000 shares of the Company’s common stock to a service provider with an exercise price of $18.00 per share. This warrant vests over a period of four years and expires in 2027. The fair value of the warrant was determined at the issuance date using the Black-Scholes option pricing model.

In 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. The Company previously recorded an accrual within accrued and other current liabilities within the balance sheet at December 31, 2020 to accrue for the settlement and the related expense was recognized in general and administrative expenses for the year ended December 31, 2020. Upon the issuance of the warrant in April 2021 in connection with the settlement, $1.1 million was reclassified from accrued and other current liabilities to additional paid-in capital within the balance sheet as of December 31, 2021.

The Company recorded less than $0.1 million expense for the above warrants, within operating expenses in the statements of operations during each of the years ended December 31, 2021 and 2020.

Net Loss Per Share, Basic and Diluted - Outstanding Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	3,934,943	3,292,782
Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	3,881,274	3,194,113
Common Stock Warrants
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	53,669	98,669

Summary of Significant Accounting Policies - Schedule of Concentration of Risk (Details) (Parenthetical)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Revenue \| Customer Concentration Risk \| Customer B \| Maximum
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%	10.00%

Redeemable Convertible Preferred Stock (Tables)

12 Months Ended

Dec. 31, 2021

Temporary Equity Disclosure [Abstract]

Summary of Redeemable Convertible Preferred Stock

As of December 31, 2019, redeemable convertible preferred stock consisted of the following (in thousands, except per share and share amounts):


	Shares Authorized		Original Issuance price		Shares Issued and Outstanding		Liquidation Value		Proceeds Net of Issuance cost
Series A		909,312	$	7.70		909,312	$	7,001	$	6,960
Series A-1		1,311,687	$	8.84		1,311,687		11,595		11,548
Series B		5,154,639	$	17.46		5,154,632		90,000		84,472
Total		7,375,638				7,375,631	$	108,596	$	102,980

401(K) Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
2014 401(k) Plan
Defined Contribution Plan Disclosure [Line Items]
Employer contribution	$ 0.5	$ 0.4

Income Taxes

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Income Taxes

10. Income Taxes

The Company did not record any income tax expense during the years ended December 31, 2021 and 2020. The Company has a net operating loss and has provided a valuation allowance against net deferred tax assets due to uncertainties regarding the Company’s ability to realize these assets. All losses before income taxes arose in the United States.

The effective tax rate of the Company’s income tax expense (benefit) differs from the federal statutory rate as follows:


	December 31,
	2021			2020
Federal statutory income tax rate		21.0	%		21.0	%
Research tax credit		2.1	%		2.8	%
Permanent differences		0.4	%		(1.7	)%
Valuation allowance		(23.5	)%		(22.1	)%
Provision for income taxes		0.0	%		0.0	%

The tax effects of temporary differences that give rise to significant components of the deferred taxes are as follows (in thousands):


	December 31,
	2021			2020
Deferred Tax Assets
Net operating loss carryforwards	$	37,295		$	21,132
Other accrued liabilities		937			422
Deferred revenue		993			3,111
Research tax credits		8,078			6,018
Stock-based compensation expense		2,618			1,151
Intangible asset basis		907			977
Operating lease liabilities		3,460			—
Total deferred tax assets	$	54,288		$	32,811

Deferred Tax Liabilities
Operating lease right-of-use assets	$	(3,064	)	$	—
Prepaid expenses		(992	)		—
Total deferred tax liabilities	$	(4,056	)	$	—
Less: valuation allowance		(50,232	)		(32,811	)
Total net deferred tax	$	—		$	—

ASC 740, Income Taxes, requires that the tax benefit of net operating losses, temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is “more likely than not.” Realization of the future tax benefits is dependent on the Company’s ability to generate sufficient taxable income within the carryforward period. Because of the Company’s recent history of operating losses, management believes that recognition of the deferred tax assets arising from future tax benefits is currently not likely to be realized and, accordingly, has provided a full valuation allowance. The valuation allowance increased by $17.4 million during 2021 and $12.5 million during the year ended December 31, 2020. The increase in the valuation allowance for each of the years ended December 31, 2021 and 2020 was primarily driven by net losses incurred, stock-based compensation expense and tax credits generated within the U.S.

The Company had net operating loss (“NOL”) carryforwards of $177.5 million and $100.6 million as of December 31, 2021 and 2020, respectively, available to reduce future taxable income, if any, for federal income tax purposes. $9.5 million of the federal NOL carryforwards expire in 2037 and the remaining $168.0 million carryforward indefinitely.

As of December 31, 2021 and 2020, the Company had federal research and development credit carryforwards of $8.6 million and $5.7 million, respectively, and state research and development credit carryforwards of $5.9 million and $4.3 million, respectively, available to reduce future taxable income, if any, for federal and California state income tax purposes, respectively. The federal credit carryforwards begin expiring in 2035 and the state credits carryforward indefinitely.

Utilization of the NOL carryforwards and research credit carryforwards may be subject to an annual limitation due to the ownership percentage change limitations provided by the Internal Revenue Code and similar state provisions. Annual limitations may result in the expiration of the NOL and tax credit carryforwards before they are utilized. The Company has experienced ownership changes in the past as a result of its Series B redeemable convertible preferred stock financing. As a result of the ownership changes, some of the tax attribute carryforwards may be permanently limited as they will expire unused and such amounts are excluded from our NOLs as of December 31, 2021. Subsequent ownership changes may result in additional limitations.

The reconciliation of the beginning and ending unrecognized tax benefits amounts is as follows (in thousands):


	Unrecognized Income Tax Benefits
Balance as of December 31, 2019	$	1,566
Additions for current year tax positions		1,729
Additions for tax positions of prior years		72
Balance as of December 31, 2020		3,367
Additions for current year tax positions		2,219
Additions for tax positions of prior years		—
Balance as of December 31, 2021	$	5,586

The entire amount of the unrecognized tax benefits would not impact the Company’s effective tax rate if recognized. During the years ended December 31, 2021 and 2020, the Company did not recognize accrued interest and penalties related to unrecognized tax benefits. The Company does not anticipate that the amount of existing unrecognized tax benefits will materially increase or decrease during the next 12 months.

The Company files income tax returns in the U.S. federal and California tax jurisdictions. In general, the Company is no longer subject to tax examination by the Internal Revenue Service or state taxing authorities for years before 2017. Although the federal and state statutes are closed for purposes of assessing additional income tax in those prior years, the taxing authorities may still make adjustments to the NOL and credit carryforwards used in open years. Therefore, the tax statutes should be considered open as it relates to the NOL and credit carryforwards used in open years. The Company has no ongoing income tax examinations by tax authorities at this time.

In March 2020, the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) was signed into law. The CARES Act changed certain provisions of the Tax Act. Under the CARES Act, NOLs arising in taxable years beginning after December 31, 2017 and before January 1, 2021 may be carried back to each of the five taxable years preceding the tax year of such loss, but NOLs arising in taxable years beginning after December 31, 2020 may not be carried back. In addition, the CARES Act eliminated the limitation on the deduction of NOLs to 80% of current year taxable income for taxable years beginning before January 1, 2021 and increased the amount of interest expense that may be deducted to 50% of adjusted taxable income for taxable years beginning in 2019 or 2020. The Company evaluated the impact of the CARES act on its tax provision and concluded that there was not a material impact.

On December 21, 2020, the U.S. president signed into law the Consolidated Appropriations Act, 2021 which includes further COVID-19 economic relief and extension of certain expiring tax provisions. The relief package includes a tax provision clarifying that businesses with forgiven PPP loans can deduct regular business expenses that are paid for with the loan proceeds. Additional pandemic relief tax measures include an expansion of the employee retention credit, enhanced charitable contribution deductions, and a temporary full deduction for business expenses for food and beverages provided by a restaurant. The Company evaluated the impact of the Consolidated Appropriations Act, 2021 on its tax provision and concluded that there was not a material impact.

On March 11, 2021, the American Rescue Plan Act was signed into law and contained provisions relating to extending the Employee Retention Tax Credit, additional funding for the PPP loan and Economic Injury Disaster Loans, as well as expanding the covered employees under Section 162(m) for tax years beginning after December 31, 2026. The Company does not expect the American Rescue Plan will have a material impact to its current income tax provision.

On November 15, 2021, the Infrastructure Investment and Jobs Act was signed into law and contained several tax provisions including changes to the Employee Retention Tax Credit after September 30, 2021. The Company does not expect the Infrastructure Investment and Jobs Act will have a material impact to its income tax provision.

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319

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+ Details

Research and Collaboration Arrangements - Additional Information (Details 1)	Jan. 31, 2014
uniQure \| uniQure Agreement \| Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, estimated performance period	4 years

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
Statements of Cash Flows - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Cash flows from operating activities
Net loss	$ (71,317)	$ (56,693)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	13,799	4,984
Vesting of common stock warrant in return for services	87	48
Change in fair value of derivative liability	92	21
Depreciation and amortization	1,523	1,443
Amortization of right-of-use assets	1,497	0
Net amortization (accretion) of premium (discount) on marketable securities	719	0
Changes in operating assets and liabilities
Accounts receivable	1,439	(508)
Prepaid expenses and other current assets	(4,225)	(2,566)
Other assets	0	75
Accounts payable	2,285	43
Accrued and other liabilities	689	1,899
Deferred revenue	(14,722)	345
Operating lease liabilities	(1,000)	0
Net cash used in operating activities	(69,134)	(50,909)
Cash flows from investing activities
Acquisition of property and equipment	(9,110)	(1,000)
Purchase of marketable securities	(168,570)	0
Maturities of marketable securities	5,000	0
Net cash used in investing activities	(172,680)	(1,000)
Cash flows from financing activities
Issuance of redeemable convertible preferred stock, net of issuance costs	0	72,468
Issuance of common stock upon offerings, net of issuance costs	114,296	205,658
Issuance of common stock upon exercise of stock options and warrants	3,360	857
Issuance of common stock through 2020 ESPP	433	0
Net cash provided by financing activities	118,089	278,983
Net (decrease) increase in cash and cash equivalents	(123,725)	227,074
Cash and cash equivalents, beginning of period	276,726	49,652
Cash and cash equivalents, end of period	153,001	276,726
Supplemental disclosures of noncash investing and financing information
Conversion of redeemable convertible preferred stock into common stock	0	175,448
Purchases of property and equipment in accounts payable and accrued and other liabilities	2,199	466
Unpaid offering costs	152	946
Decrease in right-of-use assets due to reduction in operating lease liabilities upon modification	(478)	0
Issuance of common stock warrant to settle liability	1,146	0
Receivable for common stock issued upon exercise of stock options	$ 545	$ 0

Derivative Liability

12 Months Ended

Dec. 31, 2021

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Liability

16. 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 $0.0 million to $10.6 million at December 31, 2021 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% and 17.2% at December 31, 2021 and 3.4% to 12.3% at December 31, 2020) and the discount rate (14.0% at December 31, 2021 and December 31, 2020). The Company determined the estimated fair value of this liability as of the inception date of the CFF Agreement and concluded that the amount was immaterial. The Company determined the fair value of this derivative liability was $0.2 million and $0.1 million as of December 31, 2021 and 2020, respectively.

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 1.5	$ 1.4

Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2021

Investments, Debt and Equity Securities [Abstract]

Summary of Available for Sale Securities

Marketable securities, which are classified as available-for-sale, consisted of the following as of December 31, 2021 (in thousands):


	Amortized Cost Basis		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value as of December 31, 2021
Short-term marketable securities:
Commercial paper	$	32,471	$	—	$	(4	)	$	32,467
Corporate bonds		57,315		—		(79	)		57,236
US Treasuries		5,082		—		(9	)		5,073
Total short-term marketable securities	$	94,868	$	—	$	(92	)	$	94,776
Long-term marketable securities:
Commercial paper	$	5,089	$	—	$	(21	)	$	5,068
Corporate bonds		37,821		—		(193	)		37,628
US Treasuries		25,073		—		(117	)		24,956
Total long-term marketable securities	$	67,983	$	—	$	(331	)	$	67,652

Fair Value Measurements - Summary of Changes in Fair Value of Level 3 Derivative Liability (Details) - Derivative Liability - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 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	$ 92	$ 21
Fair Value, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Income [Extensible List]	Other income (expense), net	Other income (expense), net
Ending Balance	$ 214	$ 122

Property and Equipment, Net

12 Months Ended

Dec. 31, 2021

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

5. Property and Equipment, Net

Property and equipment, net, consisted of the following (in thousands):


	December 31,
	2021			2020
Machinery and equipment	$	5,971		$	4,911
Leasehold improvements		2,527			2,527
Furniture and fixtures		566			473
Office equipment		165			101
Computer equipment and software		421			366
Construction in progress		10,066			539
Total property and equipment		19,716			8,917
Less: Accumulated depreciation and amortization		(5,325	)		(3,844	)
Property and equipment, net	$	14,391		$	5,073

All property and equipment are maintained in the United States. Depreciation expense was $1.5 million and $1.4 million for the years ended December 31, 2021 and 2020, respectively.

License Arrangements

12 Months Ended

Dec. 31, 2021

License Arrangements [Abstract]

License Arrangements

8. 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 percentage rate royalties on the net sales of its licensed products that consists of a minimum annual royalty of up to $0.1 million per year for the term of the Agreement beginning in the first calendar year after the year in which net sales first occurred and (iii) sublicense consideration in the mid-single digits to the low twenties percentage rate range on any future sublicensing arrangements the Company may enter into with third-party licensees.

During the years ended December 31, 2021 and 2020, the Company incurred expenses of $0.3 million and $0.2 million, respectively, under the provisions of the outstanding license arrangements.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Basis of Presentation

The accompanying financial statements have been prepared in accordance with United States Generally Accepted Accounting Principles (“U.S. GAAP”).

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 common stock (prior to the IPO), 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 December 31, 2021. While there was not a material impact to the Company’s financial statements as of December 31, 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. The Company’s chief executive officer, who is the chief operating decision maker, reviews financial information on a company-wide basis for purposes of allocating resources and assessing financial performance.

As of and for the years ended December 31, 2021 and 2020, all of the Company’s long-lived assets were located in the United States and all revenue was earned in the United States.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents, marketable securities and accounts receivable. The Company’s cash is held at two financial institutions in the United States of America. The Company’s cash equivalents are invested in money market funds. The Company also invests in U.S. Treasuries, commercial paper and corporate bonds. 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:


	Year Ended December 31,
	2021	2020
Customer A	95%	95%
Customer B	*	*
Total	95%	95%

* 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:


	December 31,
	2021	2020
Customer A	100%	74%
Customer B	0%	26%
Total	100%	100%

The Company’s total revenues by geographic region, based on the location of the customer, are as follows (in thousands):


	Year Ended December 31,
	2021		2020
Netherlands	$	736	$	742
Switzerland		17,181		12,897
United States		121		(27	)
Total revenue	$	18,038	$	13,612

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.

Marketable Securities

Marketable securities consist of commercial paper, corporate bonds and U.S. Treasuries and are included in current and noncurrent assets. The Company classifies its marketable securities as available-for-sale and carries them at fair value on its balance sheet. Fair value is estimated using independent pricing sources based on quoted prices in active markets for similar securities. Unrealized gains and losses on the marketable securities are reported as a component of stockholders' equity (deficit) in accumulated other comprehensive loss. The amortized cost of marketable securities is adjusted for amortization of premiums and accretion of discounts to maturity, which is included in interest income on the statements of operations. Realized gains and losses are included in interest income on the statements of operations.

The Company periodically evaluates its marketable securities to assess whether those with unrealized loss positions are other than temporarily impaired. The Company considers various factors in determining whether to recognize an impairment charge. If the Company determines that the decline in an investment's fair value is other-than-temporary, the difference is recognized as an impairment loss in the statements of operations.

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 the 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 coronavirus outbreak 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 nonfinancial 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 on the measurement date. 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 that reflect unadjusted quoted market prices in active markets for identical assets or liabilities that are accessible at the measurement date.

•

Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs 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 supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

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.

Accounts Receivable—Allowance for Doubtful Accounts

The Company regularly reviews accounts receivable for collectability and establishes an allowance for probable credit losses and writes off uncollectible accounts as necessary. The Company has determined that no allowance was required at December 31, 2021 and 2020. The Company did not have any write-offs relating to uncollectible accounts receivable during the years ended December 31, 2021 and 2020.

Property and Equipment, Net

Property and equipment are stated at cost less accumulated depreciation for acquired assets. Depreciation is computed using the straight-line method over the estimated useful lives of assets, ranging from three to five years. Leasehold improvements are amortized over the shorter of the useful life of the assets or the lease term. Upon sale or retirement of assets, the costs and related accumulated depreciation are removed from the balance sheet and the resulting gain or loss is reflected within operating expenses in the statements of operations. Maintenance and repairs are charged to expense as incurred.

Impairment of Long-Lived Assets

The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amount to the future undiscounted net cash flows, which the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is typically measured by the amount by which the carrying amount of the assets exceeds the projected discounted future net cash flows arising from the asset. There have been no such impairments of long-lived assets in the years ended December 31, 2021 and 2020.

Redeemable Convertible Preferred Stock

The Company recorded all shares of redeemable convertible preferred stock at their respective fair values on the date of issuance, net of issuance costs. The redeemable convertible preferred stock was recorded outside of permanent equity because while it was not mandatorily redeemable, in certain events considered not solely within the Company's control, such as a merger or consolidation, sale, lease, or license of substantially all of the Company's assets (each, a "deemed liquidation event"), the convertible preferred stock would become redeemable at the option of the holders of a majority of the outstanding series of redeemable convertible preferred stock. The Company did not adjust the carrying values of the redeemable convertible preferred stock to the liquidation preference of such shares because a deemed liquidation event obligating the Company to pay the liquidation preference did not occur. All outstanding shares of the redeemable convertible preferred stock converted into common stock upon the close of the IPO in December 2020.

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. Common stock warrants classified as equity are initially measured at fair value on the grant date and are not subsequently remeasured.

Leases

On December 31, 2021, the Company adopted Accounting Standards Update (“ASU”) No. 2016-02, Leases (Topic 842), ("ASC 842") using the alternative modified retrospective approach effective as of January 1, 2021 to recognize a cumulative-effect adjustment on the effective date and to not adjust financial information and disclosures required under the new lease standards for comparative prior periods. The Company has elected to apply the package of practical expedients requiring no reassessment of whether any expired or existing contracts are or contain leases, the lease classification of any expired or existing leases, or the capitalization of initial direct costs for any existing leases. Additionally, the Company has elected not to separate lease and non-lease components and not to recognize leases with an initial term of twelve months or less.

Under ASC 842, at contract inception, the Company determines if an arrangement is or contains a lease. A contract is or contains a lease if the contract conveys the right to control the use of an identified asset for a period of time in exchange for consideration. If determined to be or contain a lease, the lease is assessed for classification as either an operating or finance lease at the lease commencement date, defined as the date on which the leased asset is made available for use by the Company, based on the economic characteristics of the lease.

A right-of-use asset represents the economic benefit conveyed to the Company by the right to use the underlying asset over the lease term. A lease liability represents the obligation to make lease payments arising from the lease. Operating lease right-of-use assets represent the Company's right to use an underlying asset for the lease term and operating lease liabilities represent the Company's obligation to make payments arising from the lease. Operating right-of-use assets and liabilities are recognized at the commencement date of the lease and are measured at the present value of the fixed payments due over the expected lease term less the present value of any incentives, rebates, or abatements the Company expects to receive from the lessor. The Company records amortization of operating right-of-use assets and accretion of lease liabilities as a single lease cost on a straight-line basis over the lease term. No lease renewal options are recognized as part of the right-of-use assets and lease liabilities.

The Company's operating leases are presented in the balance sheet as operating lease right-of-use assets, classified as noncurrent assets, and operating lease liabilities, classified as current and noncurrent based on the discounted lease payments to be made within the proceeding twelve months.

As the Company’s leases do not provide an implicit rate , the Company uses its incremental borrowing rate to discount lease payments. The incremental borrowing rate represents an estimated rate of interest that the Company would have to pay to borrow equivalent funds on a collateralized basis at the lease commencement date.

Upon adoption of the new lease standard effective January 1, 2021, the Company recognized operating lease right-of-use assets of $16.5 million, and current and noncurrent operating lease liabilities of $2.0 million and $16.1 million, respectively. In connection with the adoption of this standard, deferred rent of $1.0 million and lease incentive liability of $0.5 million, which were previously recorded in prepaid expenses and other current assets, accrued and other current liabilities and other liabilities on the balance sheet as of December 31, 2020, were derecognized. The adoption of the standard did not have an impact on the Company's statements of operations or comprehensive loss, stockholders' equity or cash flows. The impact of adoption of the new lease standard as of January 1, 2021 is summarized as follows:


	December 31, 2020			ASC 842 Adjustments			January 1, 2021
Operating lease right-of-use assets	$	—		$	16,537		$	16,537
Prepaid expenses and other current assets		4,444			(214	)		4,230
Accrued and other current liabilities		(8,371	)		68			(8,303	)
Other liabilities		(1,852	)		1,696			(156	)
Operating lease liabilities, current		—			(2,029	)		(2,029	)
Operating lease liabilities, long-term		—			(16,058	)		(16,058	)

Revenue Recognition

The Company determines revenue recognition for arrangements within the scope of Accounting Standards Update 2014-09, Revenue from Contracts with Customers (Topic 606) ("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.

Research and Development Expenses

Costs related to research, design and development of programs are charged to research and development expense as incurred. Research and development costs include, but are not limited to, payroll and personnel expenses including stock-based compensation, materials, laboratory supplies, outside services and allocated overhead, including rent, insurance, repairs and maintenance, depreciation and utilities. The Company expenses all research and development costs in the period in which they are incurred.

Costs incurred in obtaining technology licenses are charged to research and development expense as acquired in-process research and development if the technology licensed has not reached technological feasibility and has no alternative future use.

Accrued Research and Development

The Company has entered into various agreements with CROs and CMOs. The Company’s research and development accruals are estimated based on the level of services performed, progress of the studies, including the phase or completion of events, and contracted costs. The estimated costs of research and development provided, but not yet invoiced, are included in accrued and other current liabilities on the balance sheet. If the actual timing of the performance of services or the level of effort varies from the original estimates, the Company will adjust the accrual accordingly. Payments made to CROs or CMOs under these arrangements in advance of the performance of the related services are recorded as prepaid expenses and other current assets until the services are rendered.

Stock-Based Compensation

As of January 1, 2020, the Company adopted ASU 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which aligns the measurement and classification guidance for share-based payments to nonemployees with the guidance for share-based payments to employees. As of January 1, 2020, the Company accounts for stock-based compensation for stock options granted to employees, directors and nonemployees as measured at grant date, based on the fair value of the award. The Company measures the fair value of awards granted using the Black-Scholes option pricing model and recognizes the expense in the statements of operations over the requisite service period, generally four years, using the straight-line method. Forfeitures are accounted for as they occur. The Company’s policy for issuing stock upon stock option exercise is to issue new common stock.

Prior to the adoption of ASU 2018-07 on January 1, 2020, stock-based compensation expense related to stock options granted to nonemployees was recognized based on the vesting date fair value of options as the stock options were earned. The Company remeasured the stock-based compensation at each reporting period end with the resulting change in fair value being recognized in the statements of operations over the period the related services were rendered. The Company estimated the service period for the options based on the time that would be required to satisfy the service condition, assuming the service condition would be satisfied. Stock-based compensation expense was recognized over the estimated service period but was accelerated if the performance condition was achieved earlier than estimated.

Income Taxes

The Company accounts for income taxes under the asset and liability method, which requires, among other things, that deferred income taxes be provided for temporary differences between the tax basis of the Company’s assets and liabilities and their financial statement reported amounts. In addition, deferred tax assets are recorded for the future benefit of utilizing net operating losses and research and development credit carryforwards and are measured using the enacted tax rates and laws that will be in effect when such items are expected to reverse. A valuation allowance is provided against deferred tax assets unless it is more likely than not that they will be realized.

The Company accounts for uncertain tax positions by assessing all material positions taken in any assessment or challenge by relevant taxing authorities. Assessing an uncertain tax position begins with the initial determination of the position’s sustainability and is measured at the largest amount of benefit that is greater than fifty percent likely of being realized upon ultimate settlement. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits.

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 16, 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.

Deferred Offering Costs

The Company capitalizes certain legal, accounting and other third-party fees that are directly related to the Company’s in-process financings, until such financings are consummated. After consummation of the financing, these costs are recorded as a reduction of the proceeds received as a result of the offering. In the event that a planned offering does not occur or is significantly delayed, all related deferred offering costs will be expensed immediately within the Company’s statements of operations.

Net Loss Per Share, Basic and Diluted

The Company calculates basic and diluted net loss per share 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 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 is calculated by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, less shares subject to repurchase. Diluted net loss per share 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 as their effect is antidilutive.

Recent Accounting Pronouncements

New Accounting Pronouncements Recently Adopted

In June 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting. This ASU aligns the measurement and classification guidance for share-based payments to nonemployees with the guidance for share-based payment to employees. Under this ASU, the measurement of equity-classified nonemployee awards is fixed at the grant date, which may lower their cost and reduce volatility in the statements of operations. The transition method provided by this ASU is on a modified retrospective basis, which recognizes a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. This ASU is effective for fiscal years beginning after December 15, 2019, and interim periods within fiscal years beginning after December 15, 2020, with early adoption permitted, but no earlier than a company's adoption date of ASC 606. The Company adopted this guidance effective January 1, 2020 using the modified retrospective method. The Company recorded a less than $0.1 million cumulative-effect adjustment reflected as a decrease to the opening balance of accumulated deficit and a decrease to additional paid-in capital

In November 2018, the FASB issued ASU No. 2018-18, Collaborative Arrangements (Topic 808): Clarifying the Interaction Between Topic 808 and Topic 606. This ASU clarifies that certain transactions between participants in a collaborative arrangement should be accounted for under ASC 606, Revenue from Contracts with Customers, when the counterparty is a customer. This ASU also precludes an entity from presenting consideration received from a transaction as revenue from contracts with customers if the counterparty is not a customer for that transaction. This ASU is effective for fiscal years beginning after December 15, 2020, and interim periods within fiscal years beginning after December 15, 2021. Early adoption is permitted for entities that have adopted ASC 606, Revenue from Contracts with Customers. The Company adopted this ASU on January 1, 2021. The adoption of this ASU did not result in a material impact on the Company’s financial statements and related disclosures.

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This ASU affects general principles within Topic 740 and is meant to simplify the accounting for income taxes by removing certain exceptions to the general framework. The ASU adds guidance to reduce complexity in certain areas, including recognizing a franchise (or similar) tax that is partially based on income as an income-based tax and incremental amounts incurred as a non-income-based tax and recognizing deferred taxes for tax goodwill. ASU 2019-12 also created an exception to the incremental approach for intraperiod tax allocation when there is a loss from continuing operations and income or a gain from other items (for example, other comprehensive income). The amendments in ASU 2019-12 are effective for the Company for fiscal years beginning after December 15, 2021, and interim periods within fiscal years beginning after December 15, 2022. Early adoption of the amendments is permitted. The Company adopted ASU 2019-12 effective January 1, 2021 on a prospective basis. The adoption of this ASU did not result in a material impact on the Company's financial statements and related disclosures.

In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842), as subsequently amended, which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors), and replaces the existing guidance in ASC 840, Leases. The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. The classification will determine the recognition pattern of lease expense over the term of the lease. In addition, a lessee is required to record (i) a right-of-use asset and a lease liability on its balance sheet for all leases with accounting lease terms of more than twelve months regardless of whether it is an operating or financing lease and (ii) lease expense in its statements of operations for operating leases and amortization and interest expense in its statements of operations for financing leases. Leases with a term of twelve months or less may be accounted for similar to existing guidance for operating leases under Topic 840. In July 2018, the FASB issued ASU No. 2018-11, Leases (Topic 842), which added an optional transition method that allows companies to adopt the standard as of the beginning of the year of adoption as opposed to the earliest comparative period presented.

See earlier disclosure in this footnote on the impact on the Company of the adoption of this standard in 2021.

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 June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments, as clarified in subsequent amendments. ASU 2016-13 changes the impairment model for certain financial instruments. The new model is a forward-looking expected loss model and will apply to financial assets subject to credit losses and measured at amortized cost and certain off-balance sheet credit exposures. This includes loans, held-to-maturity debt securities, loan commitments, financial guarantees and net investments in leases, as well as trade receivables. For available-for-sale debt securities with unrealized losses, credit losses will be measured in a manner similar to today, except that the losses will be recognized as allowances rather than reductions in the amortized cost of the securities. In October 2019, the FASB voted to delay the effective date of this standard. Topic 326 will be effective for the Company for fiscal years beginning after December 15, 2022. Early adoption is permitted. The Company is in the process of evaluating the impact of this new guidance on its financial statements.

Fair Value Measurements

12 Months Ended

Dec. 31, 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 December 31, 2021 and 2020 (in thousands):


	Basis for Fair Value Measurements						Fair Value as of
	(Level 1)		(Level 2)		(Level 3)		December 31, 2021
Assets
Money market funds	$	36,556	$	—	$	—	$	36,556
Commercial paper		—		37,535		—		37,535
Corporate bonds		—		94,864		—		94,864
US Treasuries		—		30,029		—		30,029
Total	$	36,556	$	162,428	$	—	$	198,984
Liabilities
Derivative liability	$	—	$	—	$	214	$	214
Total	$	—	$	—	$	214	$	214


	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 16 for further discussion on embedded derivative.

There were no transfers between Level 1, 2 and 3 during the periods presented.

The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 derivative liability (in thousands):


Balance as of December 31, 2019	$	101
Change in fair value included in other income (expense), net		21
Balance as of December 31, 2020	$	122
Change in fair value included in other income (expense), net		92
Balance as of December 31, 2021	$	214

- Definition

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

+ References + Details

Marketable Securities

12 Months Ended

Dec. 31, 2021

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

4. Marketable Securities

Marketable securities, which are classified as available-for-sale, consisted of the following as of December 31, 2021 (in thousands):


	Amortized Cost Basis		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value as of December 31, 2021
Short-term marketable securities:
Commercial paper	$	32,471	$	—	$	(4	)	$	32,467
Corporate bonds		57,315		—		(79	)		57,236
US Treasuries		5,082		—		(9	)		5,073
Total short-term marketable securities	$	94,868	$	—	$	(92	)	$	94,776
Long-term marketable securities:
Commercial paper	$	5,089	$	—	$	(21	)	$	5,068
Corporate bonds		37,821		—		(193	)		37,628
US Treasuries		25,073		—		(117	)		24,956
Total long-term marketable securities	$	67,983	$	—	$	(331	)	$	67,652

All marketable securities held as of December 31, 2021, had contractual maturities of less than two years. There have been no realized gains or losses on marketable securities for the periods presented. None of the Company's investments in marketable securities has been in an unrealized loss position for more than one year. The Company determined that it has the ability and intent to hold all marketable securities that have been in a continuous loss position until maturity or recovery, thus there has been no recognition of any other-than-temporary impairment in the year ended December 31, 2021.

As of December 31, 2020, the Company had no marketable securities.

Redeemable Convertible Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		6 Months Ended	12 Months Ended
	Oct. 31, 2021	Apr. 30, 2020	Jun. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2021	Dec. 31, 2019
Temporary Equity [Line Items]
Temporary equity, shares issued							7,375,631
Net proceeds from issuance of convertible preferred stock				$ 0	$ 72,468
Outstanding shares of redeemable convertible preferred stock				0	0	0	7,375,631
Common Stock
Temporary Equity [Line Items]
Purchase shares of common stock				4,875,715	9,660,000
Series C Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Temporary equity, shares issued			4,200,353
Temporary equity, shares issued price per share			$ 18.00
Net proceeds from issuance of convertible preferred stock			$ 72,500
Funding Agreement Product \| CFF
Temporary Equity [Line Items]
Additional funding upon acceptance of investigational New Drug application		$ 4,000
Additional investment in cash	$ 4,000
Funding Agreement Product \| CFF \| Common Stock
Temporary Equity [Line Items]
Purchase shares of common stock	125,715
Funding Agreement Product \| CFF \| Series C Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Investment in redeemable convertible preferred stock financing		$ 10,000

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 153,001	$ 276,726
Marketable securities	94,776	0
Accounts receivable	47	1,486
Prepaid expenses and other current assets (includes $285 and $169 at December 31, 2021 and 2020, respectively, attributable to related parties)	8,456	4,444
Total current assets	256,280	282,656
Marketable securities, long-term	67,652	0
Property and equipment, net	14,391	5,073
Operating lease, right-of-use assets, net	14,562	0
Other assets	602	602
Total assets	353,487	288,331
Current liabilities
Accounts payable (includes $0 and $173 at December 31, 2021 and 2020, respectively, attributable to related parties)	4,764	1,787
Accrued and other current liabilities	7,744	8,371
Deferred revenue	2,599	6,586
Operating lease liabilities, current portion	1,231	0
Total current liabilities	16,338	16,744
Deferred revenue, net of current portion	2,491	13,226
Derivative liability	214	122
Operating lease liabilities, long -term portion	15,217	0
Other liabilities	120	1,852
Total liabilities	34,380	31,944
Commitments and contingencies (Note 9)
Stockholders' equity
Preferred stock, $0.0001 par value, 10,000,000 shares authorized at December 31, 2021 2020; no shares issued and outstanding at December 31, 2021 and 2020, respectively.	0	0
Common stock, $0.0001 par value, 300,000,000 shares authorized at December 31, 2021 and 2020; 32,224,524 and 26,681,983 shares issued and outstanding at December 31, 2021 and 2020, respectively.	3	3
Additional paid-in-capital	526,523	392,063
Accumulated other comprehensive loss	(423)	0
Accumulated deficit	(206,996)	(135,679)
Total stockholders' equity	319,107	256,387
Total liabilities and stockholders' equity	$ 353,487	$ 288,331

Redeemable Convertible Preferred Stock - Summary of Redeemable Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Shares Authorized				7,375,638
Shares Issued				7,375,631
Shares Outstanding	0	0	0	7,375,631
Liquidation Value				$ 108,596
Proceeds Net of Issuance Cost				$ 102,980
Series A Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Shares Authorized				909,312
Original Issuance Price				$ 7.70
Shares Issued				909,312
Shares Outstanding				909,312
Liquidation Value				$ 7,001
Proceeds Net of Issuance Cost				$ 6,960
Series A-1 Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Shares Authorized				1,311,687
Original Issuance Price				$ 8.84
Shares Issued				1,311,687
Shares Outstanding				1,311,687
Liquidation Value				$ 11,595
Proceeds Net of Issuance Cost				$ 11,548
Series B Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Shares Authorized				5,154,639
Original Issuance Price				$ 17.46
Shares Issued				5,154,632
Shares Outstanding				5,154,632
Liquidation Value				$ 90,000
Proceeds Net of Issuance Cost				$ 84,472

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Total property and equipment	$ 19,716	$ 8,917
Less: Accumulated depreciation and amortization	(5,325)	(3,844)
Property and equipment, net	14,391	5,073
Machinery and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	5,971	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	566	473
Office Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	165	101
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Total property and equipment	421	366
Construction in Progress
Property Plant And Equipment [Line Items]
Total property and equipment	$ 10,066	$ 539

Accrued and Other Liabilities, Current and Noncurrent - Summary of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Payroll and related expenses	$ 3,994		$ 3,437
Accrued clinical and preclinical study costs	407		869
Consulting and professional	1,573		3,574
Other accrued expenses	1,770		491
Total accrued and other current liabilities	$ 7,744	$ 8,303	$ 8,371

Research and Collaboration Arrangements - CRF Agreement - Additional Information (Details) - CRF - CRF Agreement - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2015	Dec. 31, 2021	Dec. 31, 2020
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
Deferred revenue		0	$ 0
Due from related parties		0	0
Amount due to related party		$ 0	$ 0

License Arrangements - Additional Information (Details) - UC Agreements - USD ($)	1 Months Ended		12 Months Ended
	Jul. 31, 2021	Jan. 31, 2016	Dec. 31, 2021	Dec. 31, 2020	Jan. 31, 2019	Dec. 31, 2018
Research And Development Arrangement Contract To Perform For Others [Line Items]
Non-refundable license fee payable upon execution						$ 5,000
Non-refundable license fee payable upon execution every year thereafter until sales of a licensed product and payment of royalties						5,000
Amount obligated to pay upon closing first qualified financing at option of UC Regents						$ 50,000
Percentage of equity interest upon closing of first qualified financing at option of UC Regents						3.00%
Percentage of equity interests issued as common stock		6.00%
Amount paid non-refundable license fees	$ 100,000				$ 50,000
Non-refundable license fee payable annually	10,000				$ 5,000
Incurred expenses			$ 300,000	$ 200,000
Maximum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Development milestones	3,900,000		3,100,000
Minimum
Research And Development Arrangement Contract To Perform For Others [Line Items]
Annual royalty	$ 100,000		$ 100,000

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Prepaid expenses to related parties	$ 285	$ 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	32,224,524	26,681,983
Common stock, shares, outstanding	32,224,524	26,681,983

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Income tax expense	$ 0	$ 0
Increase in valuation allowance, deferred tax asset	17,400,000	12,500,000
Net operating loss carryforwards	177,500,000	100,600,000
Accrued interest and penalties related to unrecognized tax benefits	$ 0	0
CARES Act, relief description	The CARES Act changed certain provisions of the Tax Act. Under the CARES Act, NOLs arising in taxable years beginning after December 31, 2017 and before January 1, 2021 may be carried back to each of the five taxable years preceding the tax year of such loss, but NOLs arising in taxable years beginning after December 31, 2020 may not be carried back. In addition, the CARES Act eliminated the limitation on the deduction of NOLs to 80% of current year taxable income for taxable years beginning before January 1, 2021 and increased the amount of interest expense that may be deducted to 50% of adjusted taxable income for taxable years beginning in 2019 or 2020.
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 9,500,000
Net operating loss carryforwards, expiration year	2037
Net operating loss carryforward indefinitely	$ 168,000,000.0
Research and development credit carryforward	$ 8,600,000	5,700,000
Tax credit carryforward beginning expiration year	2035
State
Operating Loss Carryforwards [Line Items]
Research and development credit carryforward	$ 5,900,000	$ 4,300,000
Tax credit carryforward, expiration description	indefinitely

Statements of Operations - USD ($) $ in Thousands	12 Months Ended
Statements of Operations - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Revenue:
Collaboration and license revenue	$ 18,038	$ 13,363
Collaboration and license revenue, related parties		249
Total revenue	18,038	13,612
Operating expenses:
Research and development (includes $935 and $579 for the years ended December 31, 2021, and 2020, respectively, attributable to related parties)	61,360	53,038
General and administrative	28,011	17,238
Total operating expenses	89,371	70,276
Loss from operations	(71,333)	(56,664)
Other income (expense):
Interest income	137	152
Other income (expense), net	(121)	(181)
Total other income (expense)	16	(29)
Net loss	$ (71,317)	$ (56,693)
Net loss per share, basic and diluted	$ (2.57)	$ (8.82)
Weighted-average shares outstanding used in computing net loss per share, basic and diluted	27,730,420	6,430,555

Commitments and Contingencies

12 Months Ended

Dec. 31, 2021

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

9. Commitments and Contingencies

Operating Lease Commitments

Prior to the adoption of ASC 842, the Company recognized rent expense for its operating leases on a straight-line basis over the noncancelable lease term and recorded the difference between rent payments and the straight-line rent expense was recorded as a deferred rent liability. As of December 31, 2020, the Company performed an evaluation of its other contracts with customers and suppliers in accordance with ASC 842 and determined that, except for the leases described below, none of the Company’s contracts contain a material lease.

5980 Horton Street Building Lease

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 term to March 31, 2023 and updated the option to renew the lease at market rent from the prior additional term of three years to five years. 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 5980 Horton Street Building Lease is considered an operating lease under ASC 842 as it does not meet the criteria of a finance lease. As of December 31, 2021, the operating lease right-of-use asset and operating lease liability was $1.9 million and $2.3 million, respectively. The discount rate used to determine the lease liability was 7.5%.

5858 Horton Street Building Lease and Expansion

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 at market rent. 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 "Expansion"). 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. In November 2021, the Company received the first installment of this tenant improvement allowance of $0.6 million. The tenant improvement allowance funds improvements to the additional office and laboratory space, which the Company has determined to be lessee owned. The allowance is treated as a reduction of lease payments used to measure the lease liability.

The 5858 Horton Street Building Lease and Expansion is considered an operating lease under ASC 842 as it does not meet the criteria of a finance lease. As of December 31, 2021, the operating lease right-of-use asset and operating lease liability was $12.6 million and $14.2 million, respectively. The discount rate used to determine the lease liability was 7.8%.

Total operating lease expense for the year ended December 31, 2021 was $2.6 million. Cash paid for amounts included in the measurement of lease liabilities was $2.3 million for the year ended December 31, 2021.

Neither of the leases include a general option for the Company to terminate the leases.


Operating lease cost	$	2,631
Variable lease cost		914
Total	$	3,545

Variable lease payments include amounts relating to common area maintenance and are recognized in the statements of operations as incurred.

The following table summarizes supplemental information related to operating leases for the year ended December 31, 2021:


Weighted-average remaining lease term (in years):	7.6
Weighted-average discount rate:	7.8	%

The following table summarizes the maturities of lease liabilities as of December 31, 2021 (in thousands):


2022	$	1,230
2023		3,058
2024		3,149
2025		3,244
2026		3,135
Thereafter		8,686
Total future minimum lease payments		22,502
Less: Amount representing interest		(6,054	)
Present value of future minimum lease payments		16,448
Less: Current portion of operating lease liabilities		1,231
Long-term portion of operating lease liabilities	$	15,217

Indemnification Agreements

In the ordinary course of business, the Company enters into agreements that may include indemnification provisions, such as with vendors and other parties. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. The Company has never incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors and officers that require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. The Company currently maintains directors’ and officers’ liability insurance that would generally enable it to recover a portion of any future amounts paid. The Company believes the estimated fair value of its indemnification agreements in excess of applicable insurance coverage is not material.

Legal Proceedings

From time to time, the Company may become involved in legal proceedings arising from the ordinary course of its business. If applicable, the Company records a legal liability when it believes that it is both probable that a liability may be imputed, and the amount of the liability can be reasonably estimated. Significant judgment by the Company is required to determine both probability and the estimated amount. There are no material legal proceedings outstanding at December 31, 2021. See Note 14 for details of a settlement with a former employee in April 2021.

Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) Financial_Institution Segment	Dec. 31, 2020 USD ($)	Jan. 01, 2021 USD ($)	Dec. 31, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of reportable segments \| Segment	1
Number of operating segments \| Segment	1
Number of financial institutions cash is held \| Financial_Institution	2
Allowance for doubtful accounts	$ 0	$ 0
Write-offs relating to uncollectible accounts receivable	0	0
Impairments of long-lived assets	$ 0	0
Award requisite service period	4 years
Operating lease, right-of-use assets	$ 14,562,000	0	$ 16,537,000
Operating lease liabilities, current	1,231,000	0	2,029,000
Operating lease liabilities, long -term portion	15,217,000	0	16,058,000
Deferred rent			1,000,000.0
Lease incentive liability			$ 500,000
Stockholders' equity attributable to parent	319,107,000	256,387,000		$ (72,970,000)
Additional Paid-in Capital
Summary Of Significant Accounting Policies [Line Items]
Stockholders' equity attributable to parent	$ 526,523,000	392,063,000		6,054,000
Additional Paid-in Capital \| Cumulative Effect, Period of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Stockholders' equity attributable to parent				$ (39,000)
Accounting Standard Update ("ASU") 2016-02
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. 01, 2021
Change in accounting principle accounting standards update, immaterial effect	true
Accounting Standard Update ("ASU") 2018-07
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. 01, 2020
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. 01, 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. 01, 2021
Change in accounting principle accounting standards update, immaterial effect	true
Minimum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	3 years
Maximum
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	5 years
Maximum \| Accounting Standard Update ("ASU") 2018-07 \| Additional Paid-in Capital \| Cumulative Effect, Period of Adoption, Adjustment
Summary Of Significant Accounting Policies [Line Items]
Stockholders' equity attributable to parent		$ 100,000

Redeemable Convertible Preferred Stock

12 Months Ended

Dec. 31, 2021

Temporary Equity Disclosure [Abstract]

Redeemable Convertible Preferred Stock

11. Redeemable Convertible Preferred Stock

As of December 31, 2019, redeemable convertible preferred stock consisted of the following (in thousands, except per share and share amounts):


	Shares Authorized		Original Issuance price		Shares Issued and Outstanding		Liquidation Value		Proceeds Net of Issuance cost
Series A		909,312	$	7.70		909,312	$	7,001	$	6,960
Series A-1		1,311,687	$	8.84		1,311,687		11,595		11,548
Series B		5,154,639	$	17.46		5,154,632		90,000		84,472
Total		7,375,638				7,375,631	$	108,596	$	102,980

In April and June of 2020, the Company issued a total of 4,200,353 shares of Series C redeemable convertible preferred stock at $18.00 per share for net proceeds of $72.5 million. Upon the closing of the Company's IPO on December 15, 2020, all outstanding redeemable convertible preferred stock automatically converted into shares of common stock and the related carrying value was reclassified to common stock and additional paid-in capital. There were no shares of redeemable convertible preferred stock outstanding as of December 31, 2021 and 2020.

Funding Agreement with CFF — In April 2020, CFF made a $10.0 million investment in the Company's Series C redeemable convertible preferred stock financing. In return for the investment, CFF received shares of Series C redeemable convertible preferred stock, and the Company and CFF entered into a Funding Agreement ("the Funding Agreement"). Pursuant to the terms of the Funding Agreement, except in the event of a technical failure, the $10.0 million received from CFF will be used to advance the development program for 4D-710, the Company's lead product in cystic fibrosis, or any other therapeutic approved by the Program Advisory Group ("PAG") to alleviate pulmonary complications of cystic fibrosis ("the Funding Agreement Product").

CFF committed to provide an additional $4.0 million of funding upon acceptance of an Investigational New Drug ("IND") application or its equivalent to allow for human testing of the Funding Agreement Product ("Acceptance").

The IND was cleared by the U.S. Food and Drug Administration in October 2021, and CFF made the additional investment of $4.0 million in cash for the issuance of 125,715 shares of the Company's common stock to CFF.

Except in the event of a technical failure, the Company is committed to providing an amount equal to the funding provided by CFF to be used solely to advance the Funding Agreement Product. A technical failure is defined as a determination by the Company, after consultation with and approval of the PAG that (i) the Funding Agreement Product has failed to reach its intended endpoints due to safety issues, lack of sufficient transgene expression and/or efficacy, each despite commercially reasonable efforts and (iii) the exercise of further commercially reasonable efforts is unlikely to correct such failure. Under the terms of the Funding Agreement, neither the $10.0 million investment in the Series C redeemable convertible preferred stock, which converted to common stock as of December 31, 2020, nor the $4.0 million of funding upon Acceptance are restricted as to withdrawal or usage.

Accrued and Other Liabilities, Current and Noncurrent (Tables)

12 Months Ended

Dec. 31, 2021

Payables and Accruals [Abstract]

Summary of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):


	December 31,
	2021		2020
Payroll and related expenses	$	3,994	$	3,437
Accrued clinical and preclinical study costs		407		869
Consulting and professional		1,573		3,574
Other accrued expenses		1,770		491
Total accrued and other current liabilities	$	7,744	$	8,371

Summary of Other Liabilities, Noncurrent

Other liabilities, noncurrent consisted of the following (in thousands):


	December 31,
	2021		2020
Deferred rent	$	—	$	1,237
Other payable		120		615
Total other liabilities, noncurrent	$	120	$	1,852

Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Summary of Stock Options Activity

The following table summarizes the stock options activity for the year ended December 31, 2021:


				Options Outstanding
	Number of Shares Available for Grant			Number of Shares Underlying Outstanding Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Balances at December 31, 2020		2,606,546			3,194,113		$	11.05		8.46	$	97,105
Options authorized		1,334,099			—
Options granted		(1,566,150	)		1,566,150			34.83
Options exercised		—			(563,387	)		6.26
Options expired		4,324			(4,324	)		36.33
Options forfeited		311,278			(311,278	)		29.17
Balances at December 31, 2021		2,690,097			3,881,274		$	19.86	$	7.97	$	24,666
Shares exercisable, December 31, 2021					1,592,139		$	12.75	$	7.07	$	17,280
Shares vested and expected to vest, December 31, 2021					3,881,274		$	19.86	$	7.97	$	24,666

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):


	Year Ended December 31,
	2021		2020
Research and development	$	6,847	$	2,670
General and administrative		6,952		2,314
Total stock-based compensation expense	$	13,799	$	4,984

Schedule of Assumptions Used in Black-Scholes Valuation Model to Estimate Fair Value of Stock Options

The Company estimates the fair value of employee and nonemployee stock options using the Black-Scholes option pricing model. The fair value of employee and nonemployee options is recognized on a straight-line basis over the requisite service period of the awards. The fair value of the Company's stock options was estimated using the following assumptions for the years ended December 31, 2021 and 2020.


	Year Ended December 31, 2021		Year Ended December 31, 2020
	Employee	Nonemployee	Employee	Nonemployee
Expected term	5.8 – 6.3 years	6.3 years	5.5 – 6.3 years	6.0 years
Expected volatility	80.0% – 84.3%	83.5%	82.1% – 83.8%	82.1% – 83.1%
Risk-free interest rate	0.6% – 1.3%	0.6%	0.4% – 0.7%	0.4% – 0.7%
Expected dividend yield	0%	0%	0%	0%

Income Taxes - Schedule of Tax Effects of Temporary Differences to Significant Components of Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred Tax Assets
Net operating loss carryforwards	$ 37,295	$ 21,132
Other accrued liabilities	937	422
Deferred revenue	993	3,111
Research tax credits	8,078	6,018
Stock-based compensation expense	2,618	1,151
Intangible asset basis	907	977
Operating lease liabilities	3,460
Total deferred tax assets	54,288	32,811
Deferred Tax Liabilities, Net [Abstract]
Operating lease right-of-use assets	(3,064)
Prepaid expenses	(992)
Total deferred tax liabilities	(4,056)
Less: valuation allowance	$ (50,232)	$ (32,811)

Common Stock - Schedule of Common Share Reserved for Future Issuance (Details) - shares	Dec. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock reserved	7,123,787	6,151,665
2020 Equity Incentive Plan
Class Of Stock [Line Items]
Common stock reserved	2,690,097	2,606,546
Employee Stock Share Purchase Plan
Class Of Stock [Line Items]
Common stock reserved	498,747	252,337
Options Issued and Outstanding
Class Of Stock [Line Items]
Common stock reserved	3,881,274	3,194,113
Common Stock Warrants
Class Of Stock [Line Items]
Common stock reserved	53,669	98,669

Summary of Significant Accounting Policies - Schedule of Concentration of Risk (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Revenue \| Customer Concentration Risk \| Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	95.00%	95.00%
Revenue \| Customer Concentration Risk \| Customer
Concentration Risk [Line Items]
Concentration risk, percentage	95.00%	95.00%
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	0.00%	26.00%
Accounts Receivable \| Credit Concentration Risk \| Customer
Concentration Risk [Line Items]
Concentration risk, percentage	100.00%	100.00%

Income Taxes - Reconciliation of Beginning and Ending Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Balance at beginning of year	$ 3,367	$ 1,566
Additions for current year tax positions	2,219	1,729
Additions for tax positions of prior years	0	72
Balance at end of year	$ 5,586	$ 3,367

Fair Value Measurements - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 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

Common Stock

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Common Stock

12. Common Stock

As of each of December 31, 2021 and 2020, the Company’s certificate of incorporation authorized the Company to issue 300,000,000 shares of common stock, at the par value of $0.0001 per share. The holder of each share of common stock is entitled to one vote per share.

Common stockholders are entitled to dividends if and when declared by the board of directors, subject to the prior rights of the redeemable preferred stockholders. As of December 31, 2021 and 2020, no dividends on common stock had been declared by the board of directors.

As of December 31, 2021 and 2020, the Company has reserved common stock, on an as-converted basis, for future issuance as follows:


	December 31,
	2021		2020
Issuance of common stock under the 2020 Equity Incentive Plan		2,690,097		2,606,546
Issuance of common stock under the Employee Stock Share Purchase Plan		498,747		252,337
Exercise of options issued and outstanding		3,881,274		3,194,113
Exercise of common stock warrants		53,669		98,669
Total common stock reserved		7,123,787		6,151,665

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

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+ Details

Research and Collaboration Arrangements - Summary of Collaboration and License Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 18,038	$ 13,612
Collaboration and License Revenue
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	18,038	13,612
Collaboration and License Revenue \| uniQure
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	736	742
Collaboration and License Revenue \| Roche
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	17,181	12,897
Collaboration and License Revenue \| CFF
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 121	$ (27)

- Definition

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

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Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e9054-108599

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 942
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
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Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Subparagraph (SX 210.13-02(a)(4)(iii)(B))
-URI http://asc.fasb.org/extlink&oid=124359900&loc=SL124442552-122756

Reference 22: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(ii))
-URI http://asc.fasb.org/extlink&oid=124359900&loc=SL124442526-122756

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(1))
-URI http://asc.fasb.org/extlink&oid=123367319&loc=SL114868664-224227

+ Details

Stock-based Compensation

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Stock-based Compensation

13. Stock-based Compensation

2020 Incentive Award Plan

In December 2020, the Company adopted the 2020 Incentive Award Plan (“2020 Plan”), which became effective on December 10, 2020. The 2020 Plan initially reserved 2,606,546 shares of common stock for the issuance of stock options, stock appreciation rights, restricted stock awards, restricted stock units, performance bonus awards, performance stock units, dividend equivalents or other stock or cash based award granted to employees, directors and consultants of the Company. The number of shares reserved for future issuance under the 2020 Plan will increase annually on the first day of each fiscal year beginning in 2021 and ending in 2030 by the lesser of (i) 5% of the shares of common stock outstanding (on an as converted basis) on the last day of the immediately preceding fiscal year and (ii) such number of shares of common stock as determined by the Company's board of directors, provided, however, no more than 18,000,000 shares of the Company's common stock may be issued upon the exercise of incentive stock options. 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 December 31, 2021, there were 2,690,097 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 December 31, 2021, options to purchase 2,519,217 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 are returned back to the 2015 Plan and are not available for grant under the 2020 Plan.

Employee Stock Purchase Plan

In December 2020, the Company adopted the 2020 Employee Stock Purchase Plan (the “2020 ESPP”). Under the 2020 ESPP, 252,337 shares of the Company's common stock were initially reserved for employee purchases of the Company's common stock under terms and provisions established by the Company's board of directors and approved by the Company's stockholders. The number of shares reserved for future issuance under the 2020 ESPP will increase annually on the first day of each fiscal year beginning in 2021 and ending in 2030 by the lesser of (i) 1% of the shares of common stock outstanding (on an as converted basis) on the last day of the immediately preceding fiscal year and (ii) such number of shares of common stock as determined by the Company's board of directors, provided, however, no more than 15,000,000 shares the Company's common stock may be issued under the 2020 ESPP. On March 28, 2022, an additional 25,000 shares of common stock became available for future issuance under the 2020 ESPP, as a result of the operation of this automatic annual increase provision.

Under the 2020 ESPP the Company's employees may purchase common stock through payroll deductions at a price equal to 85% of the lower of the fair market value of the stock at the beginning of the offering period or at the end of each applicable purchase period. The 2020 ESPP provides for a series of overlapping 24-month offering periods comprising four six-month purchase periods. The initial offering period under the 2020 ESPP is longer than 24 months, commencing February 15, 2021 and ending on May 14, 2023. Contributions under the 2020 ESPP are limited to a maximum of 15% of an employee's eligible compensation.

Stock Options

The following table summarizes the stock options activity for the year ended December 31, 2021:


				Options Outstanding
	Number of Shares Available for Grant			Number of Shares Underlying Outstanding Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Balances at December 31, 2020		2,606,546			3,194,113		$	11.05		8.46	$	97,105
Options authorized		1,334,099			—
Options granted		(1,566,150	)		1,566,150			34.83
Options exercised		—			(563,387	)		6.26
Options expired		4,324			(4,324	)		36.33
Options forfeited		311,278			(311,278	)		29.17
Balances at December 31, 2021		2,690,097			3,881,274		$	19.86	$	7.97	$	24,666
Shares exercisable, December 31, 2021					1,592,139		$	12.75	$	7.07	$	17,280
Shares vested and expected to vest, December 31, 2021					3,881,274		$	19.86	$	7.97	$	24,666

The following table is a summary of stock compensation expense for employees and nonemployees by function (in thousands):


	Year Ended December 31,
	2021		2020
Research and development	$	6,847	$	2,670
General and administrative		6,952		2,314
Total stock-based compensation expense	$	13,799	$	4,984

During the years ended December 31, 2021 and 2020 the Company granted 1,521,150 and 1,267,743 stock options to employees with a weighted-average grant date fair value of $34.46 and $11.84 per share, respectively and 45,000 and 54,000 stock options to nonemployees with a weighted-average grant date fair value of $47.42 and $11.05 per share, respectively. The total fair value of options vested during the years ended December 31, 2021 and 2020 was $13.8 million and $5.0 million, respectively. As of December 31, 2021, the unrecognized stock-based compensation expense of unvested options was $37.7 million and is expected to be recognized over a weighted-average period of 2.7 years.

Stock-based compensation expense recorded for employee options was $13.3 million and $4.6 million for the years ended December 31, 2021 and 2020, respectively. Stock-based compensation expense recorded for nonemployee consultants was $0.5 million and $0.4 million for the years ended December 31, 2021 and 2020, respectively.

Prior to the Company’s IPO, the fair value of the shares of common stock underlying the stock options was estimated by the board of directors at various dates considering the Company’s most recently available third-party valuations of common stock as well as a number of objective and subjective factors including valuation of comparable companies, sales of redeemable convertible preferred stock, operating and financial performance and general and industry specific economic outlook, amongst other factors. The fair value was determined in accordance with the guidance provided by the American Institute of Certified Public Accountants’ Practice Guide, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. Subsequent to the Company’s IPO, the fair value of the Company’s common stock is determined based on its closing market price on the respective grant date.


	Year Ended December 31, 2021		Year Ended December 31, 2020
	Employee	Nonemployee	Employee	Nonemployee
Expected term	5.8 – 6.3 years	6.3 years	5.5 – 6.3 years	6.0 years
Expected volatility	80.0% – 84.3%	83.5%	82.1% – 83.8%	82.1% – 83.1%
Risk-free interest rate	0.6% – 1.3%	0.6%	0.4% – 0.7%	0.4% – 0.7%
Expected dividend yield	0%	0%	0%	0%

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 was estimated based on a study of publicly traded peer companies as the Company did not have sufficient trading history for its common stock. The Company selected 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.

Summary of Significant Accounting Policies - Schedule of Revenues by Geographic Region (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Disaggregation Of Revenue [Line Items]
Total revenues	$ 18,038	$ 13,612
Netherlands
Disaggregation Of Revenue [Line Items]
Total revenues	736	742
Switzerland
Disaggregation Of Revenue [Line Items]
Total revenues	17,181	12,897
United States
Disaggregation Of Revenue [Line Items]
Total revenues	$ 121	$ (27)

- Definition

+ References

+ Details

Accrued and Other Liabilities, Current and Noncurrent

12 Months Ended

Dec. 31, 2021

Payables and Accruals [Abstract]

Accrued and Other Liabilities, Current and Noncurrent

6. Accrued and Other Liabilities, Current and Noncurrent

Accrued liabilities consisted of the following (in thousands):


	December 31,
	2021		2020
Payroll and related expenses	$	3,994	$	3,437
Accrued clinical and preclinical study costs		407		869
Consulting and professional		1,573		3,574
Other accrued expenses		1,770		491
Total accrued and other current liabilities	$	7,744	$	8,371

Other liabilities, noncurrent consisted of the following (in thousands):


	December 31,
	2021		2020
Deferred rent	$	—	$	1,237
Other payable		120		615
Total other liabilities, noncurrent	$	120	$	1,852

The Company - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Nov. 30, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2021	Dec. 31, 2019
Organization And Nature Of Business [Line Items]
Aggregate net proceeds, after deducting underwriting discounts and commissions and offering costs			$ 114,296	$ 205,658
Outstanding shares of redeemable convertible preferred stock		0	0	0	0	7,375,631
Accumulated deficit		$ 135,679	$ 206,996	$ 135,679
Common Stock
Organization And Nature Of Business [Line Items]
Number of shares sold and issued			4,875,715	9,660,000
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		$ 23.00		$ 23.00
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		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
Common Stock \| Follow-On Offering
Organization And Nature Of Business [Line Items]
Stock sold and issued price per share	$ 25.00
Aggregate net proceeds, after deducting underwriting discounts and commissions and offering costs	$ 111,100
Number of shares priced under public offering	4,750,000

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Fair Value Hierarchy for Financial Assets and Financial Liabilities Measured at Fair Value on Recurring Basis


	Basis for Fair Value Measurements						Fair Value as of
	(Level 1)		(Level 2)		(Level 3)		December 31, 2021
Assets
Money market funds	$	36,556	$	—	$	—	$	36,556
Commercial paper		—		37,535		—		37,535
Corporate bonds		—		94,864		—		94,864
US Treasuries		—		30,029		—		30,029
Total	$	36,556	$	162,428	$	—	$	198,984
Liabilities
Derivative liability	$	—	$	—	$	214	$	214
Total	$	—	$	—	$	214	$	214


	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 Derivative Liability

The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 derivative liability (in thousands):


Balance as of December 31, 2019	$	101
Change in fair value included in other income (expense), net		21
Balance as of December 31, 2020	$	122
Change in fair value included in other income (expense), net		92
Balance as of December 31, 2021	$	214

Research and Collaboration Arrangements - Roche Agreement - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2017	Dec. 31, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenues		$ 18,038	$ 13,612
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		8,700	17,000
Collaborative arrangement adjustment to transaction price due to increase in project scope and expected reimbursable costs			7,000
Collaborative arrangement adjustment to transaction price due to variable consideration			10,000
Increase in revenue recognized related to performance obligations partially satisfied in the beginning of the current year		11,100	4,600
Revenues		17,200	12,900
Deferred revenue		0	14,300
Accounts receivable		0	1,100
Aggregate amount of transaction price allocated to remaining performance obligation		$ 0	$ 25,800

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Schedule of Effective Tax Rate of Income Tax Expense (Benefit) Differs from Federal Statutory Rate

The effective tax rate of the Company’s income tax expense (benefit) differs from the federal statutory rate as follows:


	December 31,
	2021			2020
Federal statutory income tax rate		21.0	%		21.0	%
Research tax credit		2.1	%		2.8	%
Permanent differences		0.4	%		(1.7	)%
Valuation allowance		(23.5	)%		(22.1	)%
Provision for income taxes		0.0	%		0.0	%

Schedule of Tax Effects of Temporary Differences to Significant Components of Deferred Taxes

The tax effects of temporary differences that give rise to significant components of the deferred taxes are as follows (in thousands):


	December 31,
	2021			2020
Deferred Tax Assets
Net operating loss carryforwards	$	37,295		$	21,132
Other accrued liabilities		937			422
Deferred revenue		993			3,111
Research tax credits		8,078			6,018
Stock-based compensation expense		2,618			1,151
Intangible asset basis		907			977
Operating lease liabilities		3,460			—
Total deferred tax assets	$	54,288		$	32,811

Deferred Tax Liabilities
Operating lease right-of-use assets	$	(3,064	)	$	—
Prepaid expenses		(992	)		—
Total deferred tax liabilities	$	(4,056	)	$	—
Less: valuation allowance		(50,232	)		(32,811	)
Total net deferred tax	$	—		$	—

Reconciliation of Beginning and Ending Unrecognized Tax Benefits

The reconciliation of the beginning and ending unrecognized tax benefits amounts is as follows (in thousands):


	Unrecognized Income Tax Benefits
Balance as of December 31, 2019	$	1,566
Additions for current year tax positions		1,729
Additions for tax positions of prior years		72
Balance as of December 31, 2020		3,367
Additions for current year tax positions		2,219
Additions for tax positions of prior years		—
Balance as of December 31, 2021	$	5,586

Research and Collaboration Arrangements - CFF - Additional Information (Details 1) - CFF - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-01-01	Dec. 31, 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

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying financial statements have been prepared in accordance with United States Generally Accepted Accounting Principles (“U.S. GAAP”).

Use of Estimates and Judgements

Segment Information

As of and for the years ended December 31, 2021 and 2020, all of the Company’s long-lived assets were located in the United States and all revenue was earned in the United States.

Concentration of Credit Risk

The Company’s partners in collaboration and license agreements who represent 10% or more of the Company’s total revenue are as follows:


	Year Ended December 31,
	2021	2020
Customer A	95%	95%
Customer B	*	*
Total	95%	95%

* 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:


	December 31,
	2021	2020
Customer A	100%	74%
Customer B	0%	26%
Total	100%	100%

The Company’s total revenues by geographic region, based on the location of the customer, are as follows (in thousands):


	Year Ended December 31,
	2021		2020
Netherlands	$	736	$	742
Switzerland		17,181		12,897
United States		121		(27	)
Total revenue	$	18,038	$	13,612

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.

Marketable Securities

Other Risks and Uncertainties

Fair Value Measurements

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 that reflect unadjusted quoted market prices in active markets for identical assets or liabilities that are accessible at the measurement date.

•

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

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.

Accounts Receivable—Allowance for Doubtful Accounts

Property and Equipment, Net

Impairment of Long-Lived Assets

Redeemable Convertible Preferred Stock

Common Stock Warrants

Leases


	December 31, 2020			ASC 842 Adjustments			January 1, 2021
Operating lease right-of-use assets	$	—		$	16,537		$	16,537
Prepaid expenses and other current assets		4,444			(214	)		4,230
Accrued and other current liabilities		(8,371	)		68			(8,303	)
Other liabilities		(1,852	)		1,696			(156	)
Operating lease liabilities, current		—			(2,029	)		(2,029	)
Operating lease liabilities, long-term		—			(16,058	)		(16,058	)

Revenue Recognition

Research and Development Expenses

Accrued Research and Development

Stock-Based Compensation

Income Taxes

Embedded Derivative

Deferred Offering Costs

Net Loss Per Share, Basic and Diluted

Recent Accounting Pronouncements

New Accounting Pronouncements Recently Adopted

See earlier disclosure in this footnote on the impact on the Company of the adoption of this standard in 2021.

New Accounting Pronouncements Not Yet Adopted

Income Taxes - Schedule of Effective Tax Rate of Income Tax Expense (Benefit) Differs from Federal Statutory Rate (Details)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	21.00%
Research tax credit	2.10%	2.80%
Permanent differences	0.40%	(1.70%)
Valuation allowance	(23.50%)	(22.10%)
Provision for income taxes	0.00%	0.00%

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2021

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net, consisted of the following (in thousands):


	December 31,
	2021			2020
Machinery and equipment	$	5,971		$	4,911
Leasehold improvements		2,527			2,527
Furniture and fixtures		566			473
Office equipment		165			101
Computer equipment and software		421			366
Construction in progress		10,066			539
Total property and equipment		19,716			8,917
Less: Accumulated depreciation and amortization		(5,325	)		(3,844	)
Property and equipment, net	$	14,391		$	5,073

Summary of Significant Accounting Policies - Schedule of Impact of Adoption of New Accounting Standard (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Jan. 01, 2021	Dec. 31, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use assets	$ 14,562	$ 16,537	$ 0
Prepaid expenses and other current assets	8,456	4,230	4,444
Accrued and other current liabilities	(7,744)	(8,303)	(8,371)
Other liabilities	(120)	(156)	(1,852)
Operating lease liabilities, current	(1,231)	(2,029)	0
Operating lease liabilities, long-term	$ (15,217)	(16,058)	0
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other current assets			4,444
Accrued and other current liabilities			(8,371)
Other liabilities			$ (1,852)
Revision of Prior Period, Accounting Standards Update, Adjustment \| ASC 842 Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use assets		16,537
Prepaid expenses and other current assets		(214)
Accrued and other current liabilities		68
Other liabilities		1,696
Operating lease liabilities, current		(2,029)
Operating lease liabilities, long-term		$ (16,058)

Marketable Securities (Additional Information) (Details)	12 Months Ended
	Dec. 31, 2021 USD ($) Security	Dec. 31, 2020 USD ($)
Debt Securities, Available-for-sale [Line Items]
Realized gains on marketable securities	$ 0
Realized losses on marketable securities	$ 0
Number of marketable securities unrealized loss position more than one year \| Security	0
Other-than-temporary impairment on investment in debt securities available-for-sale	$ 0
Maximum Maturity Period of Marketable Securities	2 years
Marketable securities		$ 0

Research and Collaboration Arrangements - Summary of Deferred Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total deferred revenue	$ 5,090	$ 19,812
uniQure
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total deferred revenue	3,661	4,396
Roche
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total deferred revenue		14,318
CFF
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Total deferred revenue	$ 1,429	$ 1,098

Net Loss Per Share, Basic and Diluted - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Numerator
Net loss attributable to common stockholders	$ (71,317)	$ (56,693)
Denominator
Weighted-average shares outstanding	27,730,420	6,430,555
Weighted-average shares outstanding used in computing net loss per share, basic and diluted	27,730,420	6,430,555
Net loss per share, basic and diluted	$ (2.57)	$ (8.82)

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=124431687&loc=d3e22595-107794

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=125511455&loc=d3e1448-109256

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124431687&loc=d3e22694-107794

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=125511455&loc=d3e1377-109256

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Research and Collaboration Arrangements - CFF - Additional Information (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2016 USD ($) Installment	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized		$ 18,038	$ 13,363
Estimated fair value of derivative liability		200	100
CFF
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangement total amount of award	$ 3,500
Collaborative arrangement achieved milestones		1,800	1,300
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
Royalties percentage on actual award received	600.00%
Continuous period where the Company ceases to develop or commercialize any product	180 days
Collaborative arrangement transaction price adjustment		500
Revenue recognized		100	100
Deferred revenue		1,400	1,100
Accounts receivable		0	400
Remaining performance obligations		$ 1,400	$ 1,100
CFF \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Future sales-based milestone payments percentage	300.00%

Research and Collaboration Arrangements - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2021	Dec. 31, 2020	Aug. 31, 2019
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue		$ 5,090,000	$ 19,812,000
Revenue recognized		15,100,000	3,200,000
uniQure
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue		3,661,000	4,396,000
Due from related parties		$ 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 \| Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, estimated performance period		1 year
uniQure \| uniQure Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments entitled to receive for achievement of research and development milestones	$ 5,000,000.0
Deferred revenue, estimated performance period		2 years
uniQure \| Amended uniQure Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized		$ 700,000	700,000
Remaining performance obligations		$ 3,700,000	$ 4,400,000
uniQure \| Amended uniQure Agreement \| Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent payments eliminated				$ 5,000,000.0

Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Initial Public Offering
Issuance of common stock upon initial public offering, issuance cost	$ 7,660	$ 17,468
Redeemable Convertible Preferred Stock
Issuance cost for issuance of preferred stock		$ 3,138

Commitments and Contingencies - Summary of Supplemental Information Related to Leases (Details)	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Weighted-average remaining lease term (in years)	7 years 7 months 6 days
Weighted-average discount rate	7.80%

Common Stock Warrants - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Apr. 30, 2021	May 31, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2016	Oct. 31, 2021	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		$ 18.00	$ 1.14
Warrant shares exercisable						45,000
Issuance of common stock warrant in connection with settlement			$ 1,146
Proceeds from offering of securities in a private placement					$ 25,000
Warrant expiration year		2025		2027	2023
Warrant vesting period				4 years
Warrant exercised month and year	2021-05
Additional Paid-in Capital
Class Of Warrant Or Right [Line Items]
Issuance of common stock warrant in connection with settlement	$ 1,100
Maximum
Class Of Warrant Or Right [Line Items]
Fair value of warrant shares			$ 100	$ 100
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

Research and Collaboration Arrangements

12 Months Ended

Dec. 31, 2021

Research And Collaboration Arrangements [Abstract]

Research and Collaboration Arrangements

7. Research and Collaboration Arrangements

Collaboration and license revenue for each period was as follows (in thousands):


	Year Ended December 31,
	2021		2020
uniQure	$	736	$	742
Roche		17,181		12,897
CFF		121		(27	)
	$	18,038	$	13,612

Deferred revenue for each period was as follows (in thousands):


	Deferred Revenue as of December 31,
	2021		2020
uniQure	$	3,661	$	4,396
Roche		—		14,318
CFF		1,429		1,098
	$	5,090	$	19,812

The total amount of revenue in the year ended December 31, 2021, which was included in deferred revenue at January 1, 2021, was $15.1 million. The total amount of revenue in the year ended December 31, 2020, which was included in deferred revenue at January 1, 2020, was $3.2 million.

uniQure

In January 2014, the Company and uniQure biopharma B.V. (“uniQure”) entered into a Collaboration and License Agreement (the “uniQure Agreement”) to collaborate on the discovery and non-clinical research activities related to the Company’s Therapeutic Vector Evolution platform in order to generate and validate vectors for gene delivery to treat diseases within the central nervous system and liver (together, the “uniQure Field”).

The uniQure Agreement provided uniQure with a research license as well as an exclusive development and commercialization license for each project variant selected for further development. The initial research term is three years with an option for uniQure to extend the research term one time for an additional year. Once the Company’s research plan has concluded, uniQure is solely responsible for the continued development, manufacturing and commercialization of the project variants as potential product candidates. In October 2016, uniQure exercised its option to extend the research term for an additional year to January 2018. The Company was also required to work exclusively with uniQure in the uniQure Field (the “uniQure Exclusivity Clause”).

Pursuant to the uniQure Agreement, the Company received upfront payments of $0.2 million, and was entitled to receive (i) contingent payments for the achievement of research and development milestones of up to $5.0 million for each licensed product selected under the arrangement, and (ii) royalties in the single digit range on future sales of the potential product candidates and sublicense consideration in the low teens to low thirties range on any future sublicensing arrangements. The Company also received capped research and development service fees based on contractual full-time employee rates per year. In connection with the performance obligations under the uniQure Agreement, the founders of 4D Molecular Therapeutics, LLC received equity options to purchase an aggregate of 609,744 of uniQure ordinary shares that vest over the initial three-year term of the agreement.

The upfront payment of $0.2 million was recorded as deferred revenue and was recognized on a ratable basis over the estimated performance period of four years. Payments and reimbursements for research costs were recognized on an as-incurred basis. The options to purchase uniQure shares were deemed to be a noncash component of the arrangement consideration, as the vesting of options is linked to the uniQure Agreement and there is a requirement for the holders of the options to provide services under the agreement. The fair value of the uniQure options, which was estimated to be $10.6 million, was recognized ratably as revenue over the estimated performance period of four years and the associated compensation expense related to the stock options 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 that should be accounted for as a separate contract from the uniQure Agreement given that the incremental licensed intellectual property rights and research and development services are distinct from the rights and services previously transferred to uniQure under the uniQure Agreement and the transaction price increased by an amount that equals the standalone selling price of the incremental rights and services to be transferred to uniQure under the Amended uniQure Agreement and Second uniQure Agreement.

Neither party was required to pay monetary consideration in connection with the execution of the Amended uniQure Agreement or the Second uniQure Agreement or for subsequent performance by the parties under those agreements, notwithstanding the potential future royalty and sublicense consideration described above. The fair value of the non-monetary consideration given by uniQure to the Company, for the intellectual property right is $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 given that 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 being recognized using the input method based on actual costs incurred as a percentage of total budgeted costs as the Company completes its performance obligation. Based on the current estimated timelines, the deferred revenue is expected to be recognized as revenue over approximately one to two years from December 31, 2021.

The Company determined the transaction price using the risk adjusted net present value analysis (“rNPV”) methodology to value the elimination of the uniQure exclusivity clause and other material rights received by the Company, including the potential royalties the Company would receive from uniQure. The rNPVs incorporate estimates and assumptions including the number of products the Company and uniQure would develop, the risk-adjusted probability of successfully developing a biopharmaceutical product, the probability that uniQure will develop a product, the research and development costs, the potential worldwide sales and associated commercialization costs, corporate tax rate, and discount rate.

During each of the years ended December 31, 2021 and 2020 the Company recognized revenue of $0.7 million under the Amended uniQure Agreement and the Second uniQure Agreement. As of December 31, 2021 and 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 December 31, 2021 and 2020. As of December 31, 2021 and 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”), a non-profit organization dedicated to finding a cure for choroideremia, a rare inherited disorder that causes progressive vision loss, ultimately leading to complete blindness. 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 by the Company 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 December 31, 2021, no milestones have been achieved.

Revenue was fully recognized for this agreement in the year ended December 31, 2017. There was no deferred revenue relating to the CRF Agreement as of December 31, 2021 and 2020. No amount was due from or to CRF under the CRF Agreement as of December 31, 2021 and 2020.

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”). The Company and Roche both have the ability to nominate products to discover, develop and commercialize.

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 December 31, 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 licenses granted by the Company to Roche under the 2017 Roche Agreement terminated in their entirety on September 16, 2021. Therefore, as of September 16, 2021, Roche no longer has a license for 4D-110 for the treatment of choroideremia or any other product class, and the Company is no longer entitled to receive any further milestones or royalties from Roche. In July 2021, the Company notified Roche of the Company’s election to continue development of choroideremia. As a result, in accordance with the terms of the agreement, all rights to 4D-110 data and intellectual property generated under the collaboration reverted to the Company. Under the 2017 Roche Agreement, if the Company is required to initiate a new Phase 1/2a clinical trial for 4D-110, the Company would not owe any royalty to Roche on net sales of 4D-110. If, however, the Company moves directly to a pivotal trial of 4D-110, without first being required to conduct a new Phase 1/2a clinical trial, the Company must pay Roche a mid-single digits percentage royalty on the net sales of 4D-110.

As a result of the termination of the 2017 Roche Agreement, an adjustment of $8.7 million was made to the transaction price to reflect the decrease in reimbursable costs for the year ended December 31, 2021. The decrease in the transaction price and total budgeted costs for the remaining performance obligation resulted in an $11.1 million increase in revenue recognized in the year ended December 31, 2021 related to the performance obligation partially satisfied prior to January 1, 2021. For the year ended December 31, 2020, an adjustment of $17.0 million was made to the transaction price to reflect an increase of $7.0 million in the scope of the project and expected reimbursable costs and the addition of $10.0 million of variable consideration as the uncertainty associated with two development milestones was resolved. The adjustments to the transaction price and total budgeted costs in 2020 resulted in a $4.6 million increase in revenue recognized in the year ended December 31, 2020 related to performance obligations partially satisfied in periods prior to January 1, 2020.

During the years ended December 31, 2021 and 2020, the Company recognized revenue of $17.2 million and $12.9 million from Roche, respectively. As of December 31, 2021 and 2020, deferred revenue relating to the Roche Agreement was $0.0 million and $14.3 million, respectively. Accounts receivable from Roche under this agreement as of December 31, 2021 and 2020 was $0.0 million and $1.1 million, respectively. As of December 31, 2021 and 2020, the aggregate amount of the transaction price allocated to the remaining performance obligation was $0.0 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 December 31, 2021 and 2020, the Company achieved milestones totaling $1.8 million and $1.3 million under the CFF Agreement, respectively. The remaining award amount will be paid by CFF based on achievement of certain development milestones by the Company.

The Company expects to make payments to CFF equal to six times the actual award received by the Company in three installments within the first four years of the first commercial sale of a product developed under this agreement. The Company also has agreed to make future sales-based milestone payments to CFF of up to three times the actual award received upon achieving specified commercialization milestones with respect to the first of any product developed utilizing any compound covered under the CFF Agreement. The CFF Agreement also requires the Company to pay to CFF royalties of a mid-single digit percentage, up to six times the actual award received, on any amounts received by the Company from the sale, license or transfer to a third-party of rights in the technology developed as a result of this collaboration. Any such royalty payments shall be credited against the payments owed by the Company upon first commercial sale. In the event of a change of control of the Company, CFF will receive certain payments, depending on the timing of the change of control and the size of the transaction.

To date, the Company has not developed a commercial product in connection with the CFF Agreement, and it has not licensed, sold or otherwise transferred to another party the product developed under the CFF Agreement or the underlying technology.

If at any time prior to the first commercial sale of a product developed as a result of the CFF Agreement, the Company ceases to use commercially reasonable efforts to develop or commercialize any product under the CFF Agreement for a continuous period of 180 consecutive days and fails to present a reasonable plan to resume commercially reasonable efforts, the Company will grant to CFF an irrevocable, exclusive worldwide interruption license under all of the Company’s interest in the research plan technology to exploit such product. Any third-party license granted by the Company shall be subject to such interruption license.

Under ASC 606, the Company identified one performance obligation within the CFF grant agreement for research activities. The Company’s contract with CFF does not include a significant financing component.

The Company concluded that the transaction price should not include the variable consideration related to future research milestones as they were considered to be constrained as it is probable that the inclusion of such variable consideration could result in a significant reversal of cumulative revenue in the future. The Company re-evaluates the transaction price and estimated period of performance at each reporting period. For the year ended December 31, 2021, an adjustment of $0.5 million was made to the transaction price to reflect the achievement of the fourth milestone related to demonstrating GFP expression and determining a cell specific expression profile in human and NHP upper airway ALI cultures following apical transduction under the CFF Agreement.

During the years ended December 31, 2021 and 2020, the Company recognized revenue of $0.1 million and $(0.1) million, respectively. As of December 31, 2021 and 2020, deferred revenue relating to the CFF Agreement was $1.4 million and $1.1 million, respectively. Accounts receivable from CFF under the CFF Agreement as of December 31, 2021 and 2020 was $0.0 million and $0.4 million, respectively. As of December 31, 2021 and 2020, the aggregate amount of the transaction price allocated to the remaining performance obligation was $1.4 million and $1.1 million, respectively. 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 16 for further discussion of the embedded derivative.