Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2022

Share-based Payment Arrangement [Abstract]

Summary of Stock Options Activity

The following table summarizes the stock options activity for the three months ended March 31, 2022:

	Number of Shares Available for Grant			Number of Shares Underlying Outstanding Options
Balances at December 31, 2021		2,690,097			3,881,274
Options authorized		1,611,226			—
Options granted		(1,167,086	)		1,167,086
Options exercised		—			(39,541	)
Options expired		71,735			(71,735	)
Options forfeited		106,674			(106,674	)
Balances at March 31, 2022		3,312,646			4,830,410
Options exercisable at March 31, 2022					1,697,603
Options vested and expected to vest at March 31, 2022					4,830,410

Schedule of Assumptions Used in Black-Scholes Valuation Model to Estimate Fair Value of Stock Options

The Company estimates the fair value of stock options using the Black-Scholes option pricing model. The fair value of employee and nonemployee options is recognized on a straight-line basis over the requisite service period of the awards. The fair value of the Company’s stock options was estimated using the following assumptions for the three months ended March 31, 2022 and 2021.

	Three Months Ended March 31,
	2022	2021
Expected term	6.0 - 6.1 years	6.0 - 6.3 years
Expected volatility	80.0% - 80.2%	83.1% - 83.5%
Risk-free interest rate	1.5% - 2.0%	0.6% - 1.1%
Expected dividend yield	—%	—%

Summary of Stock-based Compensation Expense for Employees and Nonemployees by Function

The following table is a summary of stock-based compensation expense incurred for employees and nonemployees by function (in thousands):

	Three Months Ended March 31,
	2022		2021
Research and development	$	2,150	$	1,113
General and administrative		1,783		1,216
Total stock-based compensation expense	$	3,933	$	2,329