Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2022

Equity [Abstract]

Summary of Stock Option Activity

Stock option activity for employee and nonemployee awards and related information is as follows (in thousands, except per share data):

	Number of Options			Weighted- Average Exercise Price Per Share
Outstanding at December 31, 2021		5,778		$	14.49
Granted		3,028			14.95
Exercised		(12	)		1.19
Forfeited/expired		(158	)		22.02
Outstanding at June 30, 2022		8,636		$	14.53

Schedule of Assumptions Used in Black-Scholes Model Pricing Model to to Determine Fair Value of Stock Option and Shares Purchasable Under ESPP

The assumptions used in the Black-Scholes model to determine the fair value of stock option grants and shares purchasable under the ESPP were as follows:

	Six Months Ended June 30,
Stock Option Grants	2022	2021
Risk-free interest rate	1.5%-3.4%	0.5% - 1.2%
Expected volatility	85%	87%-88%
Expected term (in years)	5.5-6.1	5.5 - 6.1
Expected dividend yield	—%	—%

	Six Months Ended June 30,
ESPP	2022	2021
Risk-free interest rate	2.2%	0.1%
Expected volatility	79%	75%
Expected term (in years)	0.5	0.5
Expected dividend yield	—%	—%

Schedule of Allocated Stock-based Compensation Expense

The allocation of stock-based compensation expense was as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development expense	$	3,531	$	2,487	$	6,797	$	4,497
General and administrative expense		2,977		1,802		5,949		3,493
Total stock-based compensation expense	$	6,508	$	4,289	$	12,746	$	7,990