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. As of June 30, 2022, there were 953,596 shares of common stock available for issuance as future equity grants under the 2019 Plan.

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. As of June 30, 2022, there were 731,603 shares of common stock available for issuance under the ESPP.

The following table summarizes stock option activity for the six months ended June 30, 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		956,816			4.19
Exercised		(12,065	)		2.43
Cancelled		(199,145	)		14.49
Balance outstanding as of June 30, 2022		3,152,274		$	12.92		8.1	$	790
Exercisable as of June 30, 2022		1,365,395		$	13.14		7.0	$	642

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

	Six Months Ended
	June 30,
	2022			2021
Expected term (years)	5.5-6.1			5.5-6.1
Expected volatility	89.9-91.0		%	94.0-97.6		%
Risk-free interest rate	1.6-2.8		%	0.7-1.0		%
Expected dividend		—			—

Pursuant to the Company’s 2019 Plan, RSUs are granted to executives and certain employees.

In February 2021 and 2022, the Company granted certain employees service-based RSUs that generally vest annually over a 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 three months ended June 30, 2022 and 2021, the Company recognized $0.2 million and $0.1 million, respectively, in expense related to the service-based RSUs. For the six months ended June 30, 2022 and 2021, the Company recognized $0.4 million and $0.2 million, respectively, in expense 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. Also, in February 2022, the Company granted performance-based RSUs that vest during the performance period, subject to the achievement of certain corporate or department targets and continued service to the Company. Expense was recognized for the performance-based RSUs using the accelerated attribution method because it is probable that the performance conditions will be met. For the three months ended June 30, 2022 and 2021, the Company recognized $0.4 million and $0.2 million, respectively, in expense related to the performance-based RSUs. For the six months ended June 30, 2022 and 2021, the Company recognized $0.7 million and $0.3 million, respectively, in expense related to the performance-based RSUs.

The following table summarizes RSU activity for the six months ended June 30, 2022:

				Weighted Average
	Number of			Grant Date
	RSUs			Fair Value
Balance outstanding as of December 31, 2021		106,394		$	23.10
Granted		596,891			4.44
Vested / released		(22,115	)		23.10
Cancelled / forfeited		(80,522	)		5.64
Balance outstanding as of June 30, 2022		600,648		$	6.51

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

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
Research and development	$	1,014	$	758	$	1,898	$	1,397
General and administrative		1,572		1,659		3,200		2,813
Total stock-based compensation	$	2,586	$	2,417	$	5,098	$	4,210