Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2022

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Stock-based Compensation Expense for Employees and Non-employees

In the accompanying condensed consolidated statements of operations, the Company recognized stock-based compensation expense for its employees and non-employees as follows:

	Three Months Ended March 31,
	2022		2021
	(in thousands)
Research and development	$	1,594	$	1,663
General and administrative		1,738		1,268
Total stock-based compensation	$	3,332	$	2,931

Schedule of Estimated Grant-date Fair Value of Stock-based Awards Using Black-Scholes Option Pricing Model Assumptions

The fair values of the Company’s stock-based awards granted during the three months ended March 31, 2022 and 2021 were estimated as of the grant date using the Black-Scholes option pricing model, based on assumptions as follows:

	Three Months Ended March 31,
	2022			2021
Expected term (in years)	6.0 – 6.1			5.5 – 7.0
Expected volatility		81 – 84	%		84 – 85	%
Risk-free interest rate		1.5 – 2.1	%		0.5 – 1.1	%
Expected dividend rate		—	%		—	%

Summary of Stock-Based Compensation Activity

A summary of activity under the 2008 Plan, 2015 Plan and 2018 Plan and related information is as follows:

				Options Outstanding
	Shares Available for Grant			Number of Shares Outstanding			Weighted- Average Exercise Price Per Share		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value of Outstanding Options (in thousands)
Outstanding — December 31, 2021		1,207,827			4,937,189		$	19.23		8.14	$	36,080
Awards authorized		1,122,866
Options granted		(995,380	)		995,380			30.87
Options exercised		—			(348,201	)		13.13
Options forfeited/cancelled		117,546			(117,546	)		22.36
Outstanding — March 31, 2022		1,452,859			5,466,822		$	21.67	8.37		$	76,739
Exercisable — March 31, 2022					1,625,633		$	28.54		7.28	$	25,331
Vested and expected to vest — March 31, 2022					4,957,332		$	22.65		8.40	$	66,600