Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2023

Share-Based Payment Arrangement [Abstract]

Summary of Stock Options Activity

The following table summarizes the stock options activity for the six months ended June 30, 2023:

	Number of Shares Available for Grant			Number of Shares Underlying Outstanding Options
Balances at December 31, 2022		2,112,039			5,778,929
Options authorized		1,631,331			—
Options granted		(1,128,679	)		1,128,679
Options exercised		—			(194,424	)
Options expired		18,259			(18,259	)
Options forfeited		272,049			(272,049	)
Balances at June 30, 2023		2,904,999			6,422,876
Options exercisable at June 30, 2023					2,936,369
Options vested and expected to vest at June 30, 2023					6,422,876

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 and six months ended June 30, 2023 and 2022:

	Three Months Ended June 30,		Six Months Ended June 30,
	2023	2022	2023	2022
Expected term	6.0 - 6.1 years	5.9 - 6.1 years	6.0 - 6.1 years	5.9 - 6.1 years
Expected volatility	81.1% - 82.2%	80.6% - 81.3%	80.9% - 84.4%	80.0% - 81.3%
Risk-free interest rate	3.5% - 4.0%	2.7% - 3.6%	3.5% - 4.0%	1.5% - 3.6%
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 June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Research and development	$	2,678	$	2,343	$	5,148	$	4,493
General and administrative		2,291		1,979		4,042		3,762
Total stock-based compensation expense	$	4,969	$	4,322	$	9,190	$	8,255