The Board of Directors, at its sole discretion, shall determine the exercise price. Stock options expire 7 to 10 years from the date of grant. The stock options generally vest 25% upon the one-year anniversary of the service inception date and then ratably each month over the remaining 36 months. Upon termination of service, any unvested stock options are automatically returned to Company. Vested stock options that are not exercised within the specified period, according to the terms and conditions of the option plan, following the termination as an employee, consultant, or service provider to the Company are surrendered back to the Company. Those stock options are added back to the pool and made available for future grants.

The Company’s 2019 Stock Option and Grant Plan (the "2019 Plan") provided for the Company to grant stock options and other stock-based awards to employees and non-employees to purchase the Company’s common stock. Total authorized options under the 2019 Stock Option and Grant Plan is 3,464,316. Upon the effectiveness of the 2020 Plan (as defined below), no further issuances will be made under the 2019 Plan.

On July 15, 2020, the Company’s Board of Directors approved an amendment to stock options outstanding under the 2019 Stock Option and Grant Plan to provide for immediate 100% vesting for all outstanding options under the plan upon the consummation of a Sale Event, as defined by the amendment.

The 2020 Stock Option and Incentive Plan (the "2020 Plan") was approved by the Company’s board of directors on July 15, 2020, and the Company’s stockholders on July 20, 2020 and became effective on July 22, 2020, the date immediately prior to the date on which the registration statement for the Company’s IPO became effective. The 2020 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights to the Company’s officers, employees, directors and consultants. The number of shares of common stock reserved for issuance as of December 31, 2021 under the 2020 Plan was 5,562,055 and will be increased each January 1 by 5% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares as determined by the Company’s compensation committee of the board of directors. Accordingly, on January 1, 2022, the number of shares of common stock reserved and available for issuance under the 2020 Plan increased by 1,773,300. The number of shares of common stock reserved for issuance as of June 30, 2022 under the 2020 Plan was 7,335,355. The 2020 Plan replaced the 2019 Plan, as the Company’s board of directors is not expected to make additional awards under the 2019 Plan following the completion of the IPO. However, the 2019 Plan will continue to govern outstanding equity awards granted thereunder.

The 2020 Employee Stock Purchase Plan (the "2020 ESPP") was approved by the Company’s board of directors on July 15, 2020, and the Company’s stockholders on July 20, 2020, and became effective on July 22, 2020, the date immediately prior to the date on which the registration statement for the Company’s IPO was declared effective. The number of shares of common stock reserved for issuance as of June 30, 2022 under the 2020 ESPP was 667,931. The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1 thereafter by the lesser of 634,969 shares of common stock, 1% of the outstanding number of shares of common stock on the immediately preceding December 31, or such lesser number of shares as determined by the Company’s compensation committee. There was no increase to the number of shares of common stock reserved and available for issuance under the 2020 ESPP on January 1, 2022. As of June 30, 2022, no shares had been issued under the 2020 ESPP.

Stock-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive income (loss) as follows:


	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2022		2021		2022		2021
Research and development	$	1,148	$	496	$	1,756	$	771
General and administrative		4,612		2,731		8,197		5,040
Total stock-based compensation expense	$	5,760	$	3,227	$	9,953	$	5,811

The following table summarizes stock option activity for the six months ended June 30, 2022:


	Stock Options
	Shares			Weighted average exercise price		Weighted average remaining contractual life (in years)		Aggregate intrinsic value (in thousands)
Outstanding as of December 31, 2021		5,207,084		$	14.35	7.7
Granted		1,237,467			33.79
Forfeited		(26,831	)		6.80
Exercised		(109,322	)		5.58
Outstanding as of June 30, 2022		6,308,398		$	18.35		7.7	$	45,432
Exercisable at June 30, 2022		2,649,909		$	12.20		6.7	$	27,105

The weighted-average grant-date fair value of options awarded during the six month periods ended June 30, 2022 and 2021 was approximately $24.57 per share and $26.56 per share, respectively. As of June 30, 2022, there was a total of $58.4 million of unrecognized employee compensation costs related to non-vested stock option awards expected to be recognized over a weighted average period of 2.9 years.

The Company estimates the fair value of stock-based compensation utilizing the Black-Scholes option pricing model, which is dependent upon several variables, such as expected term, volatility, risk-free interest rate, and expected dividends. Each of these inputs is subjective and generally requires significant judgment to determine.

The following table summarizes the range of key assumptions used to determine the fair value of stock options granted during:


	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Risk-free interest rate	1.96% - 3.07%		0.84% to 0.90%		1.37% - 3.07%		0.42% - 0.90%
Expected term (in years)	5.5 - 6		6		5.5 - 6		6
Expected volatility	86% - 93%		94% to 99%		86% - 93%		94% - 100%
Expected dividend yield		—		—		—		—
Estimated fair value of common stock	$17.50 - $36.21		$23.19 to $34.18		$17.50 - $46.56		$23.19 - $41.58

The Company issued restricted stock units in 2022, which vest over a four year period. The following table summarizes the Company’s restricted stock unit activity:


	Shares		Weighted average grant date fair value
Unvested as of December 31, 2021		—	$	—
Issued		10,000		35.86
Vested		—		—
Cancelled		—		—
Unvested as of June 30, 2022		10,000	$	35.86

As of June 30, 2022, there was approximately $0.3 million of unrecognized stock-based compensation expense related to restricted stock units that are expected to vest. These costs are expected to be recognized over a weighted-average period of approximately 3.7 years.