As of March 31, 2023, there were 2,418,516 shares available for future issuance under the 2020 Equity Incentive Plan and 330,861 shares available for future issuance under the 2022 Inducement Equity Incentive Plan. The 2020 Equity Incentive Plan provides for the grants of stock options and other equity-based awards to employees, non-employee directors and consultants of the Company. The 2022 Inducement Equity Incentive Plan provides for the grants of equity-based awards to individuals not previously employees or non-employee directors of the Company.

The table below summarizes the total stock-based compensation expense included in the Company’s statements of operations and comprehensive loss for the periods presented (in thousands):


	Three Months Ended March 31,
	2023		2022
Research and development	$	1,475	$	1,568
General and administrative		2,139		2,377
Total stock-based compensation expense	$	3,614	$	3,945

On June 21, 2022, the Company filed with the SEC a Tender Offer Statement on Schedule TO defining the terms and conditions of a one-time voluntary stock option exchange of certain eligible options for its employees (the Option Exchange). On July 20, 2022, the completion date of the Option Exchange, stock options covering an aggregate of 4,406,732 shares of common stock were tendered by eligible employees, and the Company granted new options at an exercise price of $4.36, the Company’s closing stock price on July 20, 2022, covering an aggregate of 4,406,732 shares of common stock under the 2020 Equity Incentive Plan in exchange for the tendered options. As a result of the Option Exchange, the Company will recognize incremental stock-based compensation expense of $3.7 million over the requisite service period of the new stock options, which is three or four years. The Company will recognize the sum of the incremental stock-based compensation expense and the remaining unrecognized compensation expense for the original awards on the modification date, over the requisite service period of the new stock options.

The following table summarizes the stock option activity for the three months ended March 31, 2023:


	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2022		6,690,492		$	4.27
Granted		1,796,570		$	6.00
Exercised		(16	)	$	1.60
Forfeited and cancelled		(12,647	)	$	5.37
Outstanding at March 31, 2023		8,474,399		$	4.64		8.7	$	12,929
Exercisable at March 31, 2023		1,755,709		$	3.92		5.7	$	5,938

The fair value of stock option awards to employees, executives, directors, and other service providers was estimated at the date of grant using the Black-Scholes-Merton option pricing model with the following assumptions:


	Three Months Ended March 31,
	2023	2022
Risk-free interest rate	3.45%	1.47% - 1.70%
Expected volatility	87.68%	82.98% - 83.59%
Expected term (in years)	6.08	6.08
Expected dividend yield	0%	0%

The Company recognized stock-based compensation expense related to the vesting of stock options of $3.1 million and $3.7 million during the three months ended March 31, 2023 and 2022, respectively. Total unrecognized compensation expense related to outstanding unvested stock-option awards as of March 31, 2023, was $38.3 million, which is expected to be recognized over a weighted-average remaining service period of 3.1 years.

The following table summarizes the restricted stock unit activity for the three months ended March 31, 2023:


	Number of Shares			Weighted- Average Grant-Date Fair Value
Outstanding at December 31, 2022		191,925		$	7.83
Granted		297,323		$	6.00
Vested		(1,662	)	$	7.97
Forfeited		(1,644	)	$	6.37
Outstanding at March 31, 2023		485,942		$	6.72

The Company recognized stock-based compensation expense related to the vesting of restricted stock units of $0.3 million and $0.1 million during the three months ended March 31, 2023 and 2022, respectively. Total unrecognized compensation expense related to restricted stock units as of March 31, 2023, was $2.9 million, which is expected to be recognized over a weighted-average remaining service period of 2.4 years.

The company recognized stock-based compensation expense related to the Employee Stock Purchase Plan (ESPP) of $0.2 million and $0.1 million during the three months ended March 31, 2023 and 2022, respectively.

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


	Three Months Ended March 31,
	2023		2022
Options to purchase common stock		8,474,399		6,424,324
Non-vested restricted stock units		485,942		217,730
Total		8,960,341		6,642,054