In October 2022, the Board adopted, and in November 2022 its stockholders approved, the 2022 Plan, which replaced the 2019 Plan and became effective immediately prior to and contingent upon the execution of the underwriting agreement related to the Company’s IPO. The 2022 Plan allows the Company to make equity-based and cash-based incentive awards to its officers, employees, directors, and consultants and provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards, restricted stock units (“RSUs”) and other stock-based awards. In addition, the number of shares reserved and available for issuance under the 2022 Plan shall automatically increase beginning on January 1, 2023 and each January 1 thereafter, by five percent of the aggregate number of shares of common stock of all classes issued and outstanding on the immediately preceding December 31 or such lesser number of shares of common stock as determined by the compensation committee.

In October 2022, the Board adopted, and in November 2022 its stockholders approved, the 2022 ESPP, which became effective immediately prior to and contingent upon the execution of the underwriting agreement related to the Company’s IPO. The number of shares of common stock that may be issued under the 2022 ESPP shall cumulatively increase beginning on January 1, 2023 and each January 1 thereafter through January 1, 2032, by one percent 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 compensation committee. No shares of the Company's common stock have been issued and no stock-based compensation expense has been recognized related to the 2022 ESPP.

In June 2023, the Board adopted the Inducement Plan to facilitate the granting of equity awards as an inducement material to new employees joining the Company. The only persons eligible to receive awards under the Inducement Plan are individuals who are new employees and satisfy the standards for inducement grants under Nasdaq Listing Rule 5635(c)(4) or 5635(c)(3), as applicable. The terms of the Inducement Plan are identical to the terms of the 2022 Plan, except that no incentive stock options shall be awarded under the Inducement Plan.

The Company has granted stock options with service-based vesting conditions. Stock options typically vest over four years and have a maximum term of ten years. The Company typically grants stock options to employees and non-employees at exercise prices deemed by the Board to be equal to the fair value of the common stock at the time of grant.

The assumptions that the Company used in the Black-Scholes option-pricing model to determine the grant date fair value of stock options granted were as follows:


	Three Months Ended March 31,
	2024	2023
Risk-free interest rate range	3.93% - 4.33%	3.40% - 4.28%
Dividend yield	0.00%	0.00%
Expected life of options (years)	5.8 - 6.1	6.1
Volatility rate range	81.99% - 82.31%	83.05% - 83.55%
Fair value of common stock range	$3.54 - $6.19	$13.02 - $20.50

The following table summarizes the Company’s stock option activity:


	Number of Shares			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2023		3,117,042		$	7.04		8.34	$	3,409
Granted		1,241,583			5.55
Exercised		(20,277	)		3.88
Forfeited or canceled		(64,875	)		4.76
Outstanding as of March 31, 2024		4,273,473		$	6.65		8.65	$	9,431
Vested and expected to vest as of March 31, 2024		4,273,473		$	6.65		8.65	$	9,431
Vested and exercisable as of March 31, 2024		1,464,984		$	5.42		7.79	$	4,910

The aggregate intrinsic value of options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the common stock as of the end of the reporting period. The aggregate intrinsic value of options exercised during the three months ended March 31, 2024 and 2023 was de minimis.

The weighted-average grant date fair value of the Company’s stock options granted during the three months ended March 31, 2024 and 2023 was $4.03 and $13.54 per option, respectively. As of March 31, 2024, there was $14.3 million of unrecognized stock-based compensation expense related to stock option grants. The Company expects to recognize this amount over a weighted-average period of 2.9 years.

The total fair value of options vested during the three months ended March 31, 2024 and 2023 was $1.0 million and $0.4 million, respectively.

The Company has granted RSUs with service vesting based conditions. Unvested shares of restricted common stock may not be sold or transferred by the holder. They are legally issued and outstanding. These restrictions lapse according to the time-based vesting of each award.

A summary of the RSU activity during the three months ended March 31, 2024 is as follows:


	Restricted Stock Units			Weighted-Average Grant Date Fair Value
Unvested at December 31, 2023		1,759,918		$	12.09
Vested		(143,010	)		12.55
Unvested at March 31, 2024		1,616,908		$	12.05

RSUs typically vest over four years. If and when an RSU vests, the Company will issue one share of common stock for each whole RSU that has vested, subject to satisfaction of the employee's tax withholding obligations. Upon vesting and settlement of RSUs, the Company may withhold the portion of those shares with a fair market value equal to the amount of the minimum statutory withholding taxes due. The withheld shares are accounted for as repurchases of common stock.

No RSUs were granted during the three months ended March 31, 2024. The weighted-average grant date fair value of the Company’s RSUs granted during the three months ended March 31, 2023 was $18.47 per RSU. As of March 31, 2024, there was $17.4 million of unrecognized stock-based compensation expense related to RSUs. The Company expects to recognize this amount over a weighted-average period of 2.1 years.

The total fair value of RSUs vested during the three months ended March 31, 2024 was $1.8 million. No RSUs vested during the three months ended March 31, 2023.

Stock-based compensation expense included in the Company’s condensed consolidated statements of operations and comprehensive loss is as follows (in thousands):


	Three Months Ended March 31,
	2024		2023
General and administrative	$	2,666	$	2,020
Research and development		678		626
Total stock-based compensation expense	$	3,344	$	2,646