On May 7, 2018, the Company established and adopted the 2018 Equity Incentive Plan (the “2018 Plan”) providing for the granting of stock awards for employees, directors and consultants to purchase shares of the Company’s common stock. Upon the effectiveness of the 2020 Plan (as defined below), the 2018 Plan was terminated and no further issuances were made under the 2018 Plan, although it continues to govern the terms of any equity grants that remain outstanding under the 2018 Plan.

The 2020 Equity Incentive Plan (the “2020 Plan”) was approved by the Company's Board of Directors and the Company’s stockholders and became effective on July 29, 2021. Upon the effectiveness of the 2023 Plan (as defined below), the 2020 Plan was terminated and no further issuances were made under the 2020 Plan, although it continues to govern the terms of any equity grants that remain outstanding under the 2020 Plan.

The Amended and Restated 2023 Equity Incentive Plan (the “2023 Plan”) was approved by the Company's Board of Directors and the Company’s stockholders and became effective on June 15, 2023. The Board of Directors, or a committee thereof, is authorized to administer the 2023 Plan. The 2023 Plan provides for the grant of Incentive Stock Options ("ISO") within the meaning of Section 422 of the Internal Revenue Code ("IRC") as amended, to employees, and for the grant of non-statutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards and other forms of awards to the Company’s employees, directors and consultants and any Company affiliates’ employees and consultants. The number of shares initially reserved for issuance under the 2023 Plan was 7,400,000, which automatically increases on January 1 of each year for a period of 10 years, beginning on January 1, 2024 and continuing through January 1, 2033, in an amount equal to 5% of the total number of shares of common stock outstanding on the last day of the immediately preceding year, or a lesser number of shares determined by the Board of Directors no later than the last day of the immediately preceding year. The maximum number of shares of common stock that may be issued upon the exercise of ISOs under the 2023 Plan is 41,000,000 shares. Pursuant to the terms of the 2023 Plan, the number of shares available under the 2023 Plan was increased by 2,164,366 shares effective January 1, 2024. As of March 31, 2024, 7,227,415 shares were available for grant pursuant to the 2023 Plan, including the increase effective January 1, 2024.

The 2020 Employee Stock Purchase Plan (the “ESPP”) was approved by the Company’s Board of Directors and the Company’s stockholders and became effective on July 29, 2021. A total of 200,000 shares of common stock were initially reserved for issuance under this plan, which automatically increases on January 1 of each year by the lesser of (i) 1% of the outstanding number of shares of common stock on the immediately preceding December 31 and (ii) 400,000, or such lesser number of shares as determined by the Board of Directors. As of March 31, 2024, no shares of common stock had been issued under the ESPP and 787,812 shares remained available for future issuance under the ESPP. The Company’s Board of Directors or designated committee has not set an offering period. Pursuant to the terms of the ESPP, the number of shares available under the ESPP increased by 400,000 shares, effective January 1, 2024.

The following is a summary of the stock option award activity during the three months ended March 31, 2024:


	Number of Stock Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2023		6,695,933		$	3.52		8.32	$	361
Granted		1,690,675			1.24
Exercised		—			—
Forfeited		(50,335	)		4.43
Outstanding at March 31, 2024		8,336,273		$	3.05		8.49	$	40
Exercisable at March 31, 2024		2,797,539		$	5.04		7.45	$	17
Options expected to vest as of March 31, 2024		5,538,734		$	2.05		9.02	$	23

The weighted-average grant date fair value of options granted during the three months ended March 31, 2024 and 2023 was $1.24 and $2.00, respectively. The aggregate intrinsic value is calculated as the difference between the exercise price and the market price of the Company’s common stock at March 31, 2024 and December 31, 2023.

For the three months ended March 31, 2024 and 2023, the Company utilized the Black-Scholes option-pricing model for estimating the fair value of the stock options. The following table presents the assumptions and the Company’s methodology for developing each of the assumptions used:


	March 31, 2024	March 31, 2023
Volatility	94.20% - 102.54%	91.91%
Expected life (years)	6.08	6.08
Risk-free interest rate	3.98% - 4.16%	3.99%
Dividend rate	—	—

Stock-based compensation expense was recorded in the following line items in the condensed statements of operations for the three months ended March 31, 2024 and 2023 (in thousands):


	Three Months Ended March 31,
	2024		2023
Research and development	$	532	$	389
General and administrative		708		470
Total stock-based compensation expense	$	1,240	$	859

No related tax benefits from stock-based compensation expense were recognized for the three months ended March 31, 2024 and 2023. As of March 31, 2024, there was $7.5 million in unrecognized stock-based compensation expense, which is expected to be recognized over a weighted-average period of 2.63 years.