The Company has two equity incentive plans: the 2016 Equity Incentive Plan, as amended, and the 2020 Equity Incentive Plan. New awards can only be granted under the 2020 Equity Incentive Plan (the “Plan”). The total number of shares initially authorized under the Plan was 4,680,000, which was increased on January 1, 2021 and will automatically increase on January 1st of each year, continuing for ten years, in an amount equal to five percent of the total number of shares of the Company’s common stock outstanding on December 31st of the preceding calendar year, subject to the discretion of the board of directors or compensation committee to determine a lesser number of shares shall be added for such year. At December 31, 2021, 5,314,849 shares were available for future grants and on January 1, 2022, 2,380,116 shares were added to the Plan. The Plan provides for the granting of common stock, incentive stock options, nonqualified stock options, restricted stock awards, restricted stock units and/or stock appreciation rights to employees, directors, and other persons, as determined by the Company’s board of directors. The Company’s stock options vest based on the terms in each award

agreement, generally over four-year periods with 25% of options vesting after 1 year and then monthly thereafter, and have a term of ten years.

The Company measures stock-based awards at their grant-date fair value and records compensation expense on a straight-line basis over the vesting period of the awards. The Company recorded stock-based compensation expense in the following expense categories in its accompanying statements of operations:

	Year Ended December 31,
(in thousands)	2021		2020
Research and development	$	9,469	$	2,585
General and administrative		11,462		2,998
	$	20,931	$	5,583

The following table summarizes stock option activity for the Plan in the years indicated:

	Number of shares			Weighted average exercise price per share		Weighted average remaining contractual term (years)
Outstanding at January 1, 2020		2,269,742		$	1.66		9.20
Granted		4,785,630		$	11.35
Exercised		(100,545	)	$	0.99
Forfeited		(115,736	)	$	1.37
Outstanding at December 31, 2020		6,839,091		$	8.46		9.17
Granted		2,600,231		$	31.14
Exercised		(995,950	)	$	3.52
Forfeited		(1,263,890	)	$	19.79
Outstanding at December 31, 2021		7,179,482		$	15.36		8.66
Exercisable at December 31, 2021		2,057,975		$	6.99		8.04

At December 31, 2021, the aggregate intrinsic value of outstanding options and exercisable options was $25.1 million and $13.2 million, respectively.

The following table summarizes information about stock options outstanding and exercisable at December 31, 2021 under the Plan:

	Options Outstanding						Options Exercisable
Range of Exercise Prices	Number Outstanding		Weighted Average Remaining Contractual Life (in years)		Weighted Average Exercise Price		Number Exercisable		Weighted Average Exercise Price
$0.31 - $7.37		2,352,647		7.76	$	1.80		1,233,638	$	1.75
$7.38 - $13.08		2,465,488		8.67		12.85		777,587		12.85
$13.09 - $31.30		1,760,632		9.61		27.58		4,219		17.99
$31.31 - $88.98		600,715		9.35		43.02		42,531		50.79
		7,179,482						2,057,975

The weighted-average grant date fair value of options granted was $22.80 and $10.12 per share for the years ended December 31, 2021 and 2020, respectively. The aggregate intrinsic value of options exercised was $26.9 million for the year

ended December 31, 2021. The Company recorded stock-based compensation expense of $19.9 million and $4.8 million for the years ended December 31, 2021 and 2020, respectively, related to stock options. As of December 31, 2021, the total unrecognized compensation expense related to unvested stock option awards was $68.4 million, which the Company expects to recognize over a weighted-average period of 3.03 years.

The fair value of each option was estimated on the date of grant using the weighted average assumptions in the table below:

	Year Ended December 31,
	2021			2020
Expected volatility		87.46	%		115.17	%
Risk-free interest rate		0.94	%		0.43	%
Expected life (in years)		6.04			6.25
Expected dividend yield		—			—

The Company issues restricted stock awards (“RSA”) to employees that generally vest over a four-year period with 25% of awards vesting after 1 year and then monthly thereafter. Any unvested shares will be forfeited upon termination of services. The fair value of an RSA is equal to the fair market value price of the Company’s common stock on the date of grant. RSA expense is recorded on a straight-line basis over the vesting period.

The following table summarizes activity related to RSA stock-based payment awards:

	Number of shares			Weighted- average grant date fair value
Unvested balance at January 1, 2020		1,335,349		$	1.42
Granted		432,301		$	3.26
Vested		(552,883	)	$	1.37
Unvested balance at December 31, 2020		1,214,767		$	2.09
Vested		(603,159	)	$	1.89
Unvested balance at December 31, 2021		611,608		$	2.29

The Company recorded stock-based compensation expense of $0.9 million and $0.8 million for the years ended December 31, 2021 and 2020, respectively, related to RSAs. As of December 31, 2021, the total unrecognized expense related to all RSAs was $1.3 million, which the Company expects to recognize over a weighted-average period of 1.83 years.

The Company issues restricted stock units (“RSU”) to employees that generally vest over a four-year period with 25% of awards vesting after 1 year and then quarterly thereafter. Any unvested shares will be forfeited upon termination of services.

The following table summarizes activity related to RSU stock-based payment awards:

	Number of shares			Weighted- average grant date fair value
Outstanding at January 1, 2021		—
Granted		45,000		$	26.91
Forfeited		(25,000	)	$	33.78
Outstanding at December 31, 2021		20,000		$	18.32

The Company recorded stock-based compensation expense of $20 thousand for the year ended December 31, 2021 related to RSUs. At December 31, 2021 the total unrecognized expense related to the RSUs was $0.3 million, which the Company expects to recognize over 3.76 years.

The Company has an Employee Stock Purchase Plan (the “ESPP”), which as of December 31, 2021 had 931,342 shares of common stock reserved for future issuance. The Company issued 25,714 shares under the ESPP in 2021. The number of shares of the Company’s common stock that may be issued pursuant to rights granted under the ESPP shall automatically increase on January 1st of each year and continuing for ten years beginning in 2021, in an amount equal to one percent of the total number of shares of all classes of the Company’s common stock outstanding on December 31st of the preceding calendar year, subject to the discretion of the board of directors or compensation committee to determine a lesser number of shares shall be added for such year. As such, on January 1, 2022, 476,023 shares were added to the ESPP.

Under the ESPP, eligible employees can purchase the Company’s common stock through accumulated payroll deductions at such times as are established by the compensation committee. Eligible employees may purchase the Company’s common stock at 85% of the lower of the fair market value of the Company’s common stock on the first day of the offering period or on the last day of the offering period. Eligible employees may contribute up to 15% of their eligible compensation. Under the ESPP, a participant may not accrue rights to purchase more than $25,000 worth of the Company’s common stock for each calendar year in which such right is outstanding.

The ESPP is considered compensatory under the FASB stock compensation rules. Accordingly, share-based compensation expense is determined based on the option’s grant-date fair value as estimated by applying the Black Scholes option-pricing model and is recognized over the withholding period. The Company recognized share-based compensation expense of $0.2 million for the year ended December 31, 2021 related to the ESPP.