In July 2020, the Company’s board of directors and stockholders approved and adopted the 2020 Equity Incentive Plan (the “2020 Plan”). Under the 2020 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other stock or cash-based awards to individuals who are current employees, officers, directors or consultants of the Company. A total of 11,183,476 shares of common stock were approved to be initially reserved for issuance under the 2020 Plan. The number of shares that remained available for issuance under the Company’s previous equity incentive plan as of the effective date of the 2020 Plan and shares subject to outstanding awards under the Company’s previous equity incentive plan as of the effective date of the 2020 Plan that are subsequently canceled, forfeited or repurchased by the Company are added to the shares reserved under the 2020 Plan. The number of shares of common stock available for issuance under the 2020 Plan is automatically increased on the first day of each calendar year during the ten-year term of the 2020 Plan, beginning with January 1, 2021 and ending with January 1, 2030, by an amount equal to 5% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors.

In February 2022, the Company’s board of directors approved and adopted the 2022 Inducement Plan (the “Inducement Plan”). Under the Inducement Plan, the Company may grant nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards and other awards to individuals not previously employees or non-employee directors of the Company, as an inducement toward entering into employment with the Company. Under the Inducement Plan approved in February 2022, the maximum number of shares of common stock initially approved to be issued was 2,000,000 shares. In December 2023, the Compensation Committee of the Company’s board of directors approved an amendment to the Inducement Plan which increased the pool to a maximum of 3,517,105 shares.

The following is a summary of the Company’s stock option activity for the three months ended March 31, 2024:


	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (thousands)
Balance at January 1, 2024		14,909,912		$	6.84
Granted		3,143,177			4.00
Exercised		(12,823	)		2.49
Forfeited/Cancelled		(82,284	)		6.21
Balance at March 31, 2024		17,957,982		$	6.35		7.89	$	1,312
Options vested and expected to vest as of March 31, 2024		17,957,982		$	6.35		7.89	$	1,312
Options vested and exercisable as of March 31, 2024		8,780,735		$	7.88		6.92	$	718

The weighted-average grant date fair value of options granted during the three months ended March 31, 2024 and 2023 was $2.90 and $3.92, respectively. The aggregate intrinsic value of options exercised was $13 thousand and $0.1 million during each of the three months ended March 31, 2024 and 2023, respectively, determined as of the date of exercise. The Company received $32 thousand and $0.1 million in cash from options exercised during each of the three months ended March 31, 2024 and 2023, respectively.

As of March 31, 2024, total unrecognized compensation cost related to stock options was $29.4 million, and the weighted-average period over which this cost is expected to be recognized was approximately 2.6 years.

The fair value of options granted is estimated at the date of grant using the Black-Scholes option pricing model. Forfeitures are accounted for as incurred as a reversal of any share-based compensation expense related to options that will not vest. The assumptions that the Company used to determine the fair value of options granted to employees, non-employees and directors were as follows:


	Three Months Ended March 31,
	2024	2023
Risk-free interest rate	4.2%	4.2%
Expected volatility	84.2%	82.8%
Expected term (years)	5.8	6.0
Dividend yield	—	—

The following is a summary of the Company’s restricted stock unit (“RSU”) activity for the three months ended March 31, 2024:


	Shares			Weighted Average Grant Date Fair Value
Balance at January 1, 2024		4,555,099		$	4.35
Granted		2,262,809			4.00
Vested		(990,034	)		4.85
Forfeited/Cancelled		(38,779	)		4.66
Balance at March 31, 2024		5,789,095		$	4.13

RSU awards are share awards that, upon vesting, will deliver to the holder shares of the Company’s common stock. The RSUs granted to employees and non-employee directors vest up to four years from the grant date. The grant-date fair value is recognized as compensation expense over the vesting period. As of March 31, 2024, total unrecognized compensation cost related to RSUs was $22.3 million, and the weighted-average period over which this cost is expected to be recognized was approximately 3.0 years.

In July 2020, the Company’s board of directors and stockholders approved and adopted the 2020 Employee Stock Purchase Plan (the “ESPP”), which became effective as of the pricing of the Company’s initial public offering. A total of 615,000 shares of common stock were approved to be initially reserved for issuance under the ESPP. The number of shares of common stock available for issuance under the ESPP is automatically increased on the first day of each calendar year during the first ten-years of the term of the ESPP, beginning with January 1, 2021 and ending with January 1, 2030, by an amount equal to the lessor of (i) 1% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year, (ii) 1,230,000 shares of common stock or (iii) such lesser amount as determined by the Company’s board of directors. Under the 2020 ESPP, substantially all employees can elect to have up to 15% of their annual compensation withheld to purchase up to 3,000 shares of common stock per purchase period, subject to certain limitations. The shares of common stock can be purchased over an offering period of six months and at a price of 85% of the fair market value per share of common stock on the first trading day of the applicable offering period or on the exercise date of the applicable offering period, whichever is less. Under applicable accounting guidance, the 2020 ESPP is classified as a compensatory plan. During the three months ended March 31, 2024, a total of 310,054 shares were purchased by the Company’s employees under the 2020 ESPP resulting in net proceeds of $0.5 million.

The Company uses the Black-Scholes pricing model to estimate the fair value of the purchase rights issued under the ESPP on each offering date. The assumptions that the Company used to determine the fair value of the purchase rights issued to employees were as follows:


	Three Months Ended March 31,
	2024	2023
Risk-free interest rate	5.4%	5.0%
Expected volatility	95.3%	73.2%
Expected term (years)	0.5	0.5
Dividend yield	—	—

The Company recorded total stock-based compensation expense related to stock options, RSUs and the ESPP in the following expense categories of the accompanying condensed consolidated statements of operations and comprehensive income (loss) (in thousands):


	Three Months Ended March 31,
	2024		2023
Research and development	$	3,006	$	2,749
General and administrative		2,377		4,731
Total stock-based compensation expense	$	5,383	$	7,480