In September 2019, the Company’s board of directors adopted the 2019 Equity Incentive Plan (the “2019 Plan”), which also became effective in September 2019. The Company initially reserved 2,844,193 shares of common stock for issuance under the 2019 Plan. In addition, the number of shares of common stock reserved for issuance under the 2019 Plan will automatically increase on the first day of January for a period of up to ten years in an amount equal to 4% of the total number of shares of the Company’s capital stock outstanding on the immediately preceding December 31, or a lesser number of shares determined by the Company’s board of directors.

The board of directors determines the period over which options become exercisable and options generally vest over a four-year period, with 25% of options vesting on the first anniversary of employment, and thereafter, the remaining options vesting quarterly, over the following 36-month period. The options expire within ten years from

In October 2019, the Company’s board of directors adopted the 2019 Employee Stock Purchase Plan (“ESPP”), which became effective in November 2019. The Company initially reserved 225,188 shares of common stock for purchase under the ESPP. The number of shares of common stock reserved for issuance under the ESPP will automatically increase on the first day of January for a period of up to ten years in an amount equal to 1% of the total number of shares of the Company’s common stock outstanding on the immediately preceding December 31, or a lesser number of shares determined by the Company’s board of directors. Purchases are accomplished through the participation of discrete offering periods and each offering is expected to be six months in duration. For each offering period, ESPP participants will purchase shares of common stock at a price per share equal to 85% of the lesser of the fair market value of the Company’s common stock on (1) the first trading day of the applicable offering period or (2) the last trading day of the applicable offering period.

The following table summarizes stock option activity for the year ended December 31, 2022:


						Weighted
				Weighted		Average
				Average		Remaining		Aggregate
	Number of			Exercise		Contractual		Intrinsic
	Options			Price		Term		Value
						(In years)		(In thousands)
Balance outstanding as of December 31, 2021		2,406,668		$	16.46		8.1	$	9,970
Granted		1,149,816			4.48
Exercised		(151,061	)		2.09
Cancelled and forfeited		(243,506	)		16.34
Balance outstanding as of December 31, 2022		3,161,917		$	12.80		7.9	$	16,612
Exercisable as of December 31, 2022		1,460,685		$	14.60		7.0	$	7,320

The fair value of stock options granted for the periods presented was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions:


	Year Ended December 31,
	2022	2021
Expected term (years)	5.5-6.3	5.5-6.1
Expected volatility	89.9-91.0%	86.9-91.9%
Risk-free interest rate	1.6-3.9%	0.7-1.3%
Expected dividend	—	—

The weighted-average grant date fair value of stock options that were granted during the year ended December 31, 2022 and 2021 was $3.38 and $16.18 per share, respectively. As of December 31, 2022, there was $12.2 million of unrecognized stock-based compensation related to stock options granted under the 2019 Plan, which is expected to be recognized over a weighted-average period of 2.2 years.

The Company has granted certain employees service-based RSUs that generally vest annually over a two or three-year period. The restrictions lapse over time for these service-based RSUs. In the event of termination of the holder’s continuous service to the Company, any unvested portion of the service-based RSUs are cancelled. For the year ended December 31, 2022 and 2021, the Company recognized expense of $1.2 million and $0.3 million, respectively, related to the service-based RSUs.

In February 2021, the Company granted performance-based RSUs that vest as to one-third on each one-year anniversary date, subject to achievement of a development milestone and continued service to the Company. In February 2022, a portion of the performance-based RSUs vested upon achievement of the development milestone and satisfaction of the continued service condition.

In February and September 2022, the Company granted performance-based RSUs that vest during the applicable performance period, subject to the achievement of certain corporate or department targets and continued service to the Company. In September 2022, a portion of the performance-based RSUs that were granted in February 2022 vested upon achievement of specific targets and satisfaction of the continued service condition.

As of December 31, 2022, it was probable that the remaining performance conditions would be met for the Company’s performance-based RSUs and expense was recognized using the accelerated attribution method. For the year ended December 31, 2022 and 2021, the Company recognized expense of $1.5 million and $0.8 million, respectively, related to performance-based RSUs.

The following table summarizes RSU activity for the year ended December 31, 2022:


	Number of RSUs			Weighted Average Fair Value at Date of Grant per Unit
Balance outstanding as of December 31, 2021		106,394		$	23.10
Granted		1,224,391			4.61
Vested / released		(103,703	)		8.61
Cancelled / forfeited		(131,344	)		5.53
Balance outstanding as of December 31, 2022		1,095,738			5.77

As of December 31, 2022, there was $3.9 million of total unrecognized expense related to RSUs, which is expected to be recognized over a weighted-average period of 1.4 years.

The Company recorded stock-based compensation for the periods indicated as follows (in thousands):


	Year Ended December 31,
	2022		2021
Research and development	$	4,094	$	2,966
General and administrative		6,262		5,712
Total stock-based compensation	$	10,356	$	8,678