In April 2021, the Company adopted the 2021 Employee Stock Purchase Plan (“ESPP”) and the 2021 Equity Incentive Plan (“2021 EIP”), each of which became effective in connection with the IPO. The Company has reserved 421,476 and 3,242,762 shares of Class A common stock for future issuance under the ESPP and 2021 EIP, respectively.

The Company may not grant any additional awards under the 2017 Equity Incentive Plan (“2017 EIP”). The 2017 EIP will continue to govern outstanding equity awards granted thereunder. As of March 31, 2022, there were 1,863,512 shares available for issuance under the 2021 EIP.

Stock option activity under the 2017 EIP and 2021 EIP was as follows:


	NUMBER OF OPTIONS			WEIGHTED- AVERAGE EXERCISE PRICE PER SHARE		WEIGHTED- AVERAGE REMAINING CONTRACTUAL LIFE (YEARS)		AGGREGATE INTRINSIC VALUE (000s)
Balance – December 31, 2021		2,924,521		$	5.62		9.11	$	61,712
Granted		588,002			21.08
Exercised		(17,946	)		3.65
Cancelled and forfeited		—			—
Outstanding as of March 31, 2022		3,494,577			8.23		9.03	$	53,356
Options exercisable as of March 31, 2022		672,992			3.47		8.72	$	13,472
Vested and expected to vest as of March 31, 2022		3,494,577		$	8.23		9.03	$	53,356

The aggregate intrinsic value of stock options exercised during the three months ended March 31, 2022, was $0.3 million. The weighted-average grant date fair value of options granted during the three months ended March 31, 2022, was $14.08 per share.

The ESPP enables eligible employees to purchase shares of the Company's Class A common stock at the end of each offering period at a price equal to 85% of the fair market value of the shares on the first trading day or the last trading day of the offering period, whichever is lower. Eligible employees generally include all employees. Share purchases are funded through payroll deductions of at least 1% and up to 15% of an employee's eligible compensation for each payroll period. The number of shares reserved for issuance under the ESPP increase automatically on the first day of each fiscal year, beginning on January 1, 2022, by a number equal to the lesser of 440,502 shares, 1% of the total number of shares of the Company's capital stock (including all classes of the Company's common stock) outstanding on the last day of the calendar month prior to the date of the increase, or such lower number of shares. (including no shares) approved by the Company's board of directors. As of March 31, 2022, 8,458 shares have been issued pursuant to the ESPP. The ESPP generally provides for six-month consecutive offering periods beginning on September 14, 2021. The ESPP is a compensatory plan as defined by the authoritative guidance for stock compensation. As such, stock-based compensation expense has been recorded for the three months ended March 31, 2022.

The following tables summarize the stock-based compensation expense for stock options and restricted stock awards granted to employees and nonemployees that was recorded in the Company’s statements of operations and comprehensive loss for the three months ended March 31, 2022 and 2021.


	Three Months Ended March 31,
	2022		2021
Research and development	$	902	$	60
General and administrative		760		344
Total stock-based compensation expense	$	1,662	$	404


	Three Months Ended March 31,
	2022		2021
Employees	$	1,014	$	399
Nonemployees		648		5
Total stock-based compensation expense	$	1,662	$	404

As of March 31, 2022, the Company had $17.1 million of unrecognized stock-based compensation expense related to unvested stock options, which is expected to be recognized over a weighted-average period of approximately 2.93 years.

The fair value of stock options granted during the three months ended March 31, 2022 and 2021 was estimated using the Black-Scholes option pricing model based on the following weighted-average assumptions.


	Three Months Ended March 31,
	2022	2021
Expected term (in years)	6.0 – 6.1	6.0 – 6.1
Expected volatility	75.8%	76.3% – 76.4%
Risk-free rate	1.8% –1.9%	0.6% – 0.8%
Dividend yield	—	—

In October 2020, in conjunction with the Series C redeemable convertible preferred stock issuance, the Company restricted 49,636 shares of fully issued and outstanding Class A common stock held by the Company’s Chief Executive Officer and founder. The restriction allowed the Company to repurchase shares that have not vested. The vesting term of restricted stock was one year. Restricted stock awards fully vested in October 2021. The grant date fair value of the restricted shares was $6.37.

For the three months ended March 2022 and 2021, the Company recognized zero and $0.1 million, respectively, of stock-based compensation expense related to restricted stock awards that vested during the period.

The Company grants restricted stock units ("RSU") pursuant to the 2021 EIP and satisfies such grants through the issuance of the Company's common stock. The following table shows RSU activity for the period ending March 31, 2022.


	NUMBER OF OPTIONS			WEIGHTED- AVERAGE GRANT DATE FAIR VALUE PER SHARE
Unvested balance at December 31, 2021		77,719		$	23.99
Granted		—			—
Vested		(19,429	)		23.99
Cancelled and forfeited		—			—
Unvested balance at March 31, 2022		58,290			8.23

As of March 31, 2022, the Company recognized $0.5 million of stock-based compensation for restricted stock units and the Company had $1.3 million of unrecognized stock-based compensation expense related to unvested restricted stock units, which is expected to be recognized over a weighted-average period of approximately 0.72 years.