Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recorded related to awards granted to employees and non-employees was as follows (in thousands):

	Year Ended December 31,
	2021		2020		2019
Research and development	$	3,492	$	1,234	$	956
General and administrative		4,745		2,375		1,212
Total stock-based compensation expense	$	8,237	$	3,609	$	2,168

Summary of Activity under Plans

Activity under the Company’s 2015 and 2019 Plans is set forth below:

				Outstanding Options
	Shares available for Grant			Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (in thousands)
Balance, January 1, 2021		975,135			2,591,456		$	7.27		8.36	$	15.70
Additional shares authorized		1,181,488			—
Options granted		(1,560,425	)		1,560,425		$	20.52
Options exercised		—			(211,900	)	$	7.13
Options repurchased		—			—
Options canceled		326,628			(319,315	)	$	14.33
Balance, December 31, 2021		922,826			3,620,666		$	12.36		7.92	$	41.40
Exercisable as of December 31, 2021					1,498,708		$	6.58		6.60	$	25.70
Vested and expected to vest as of    December 31, 2021					3,620,666		$	12.36		7.92	$	41.40

Assumptions Used to Calculate Fair Values of Options

The fair values of options were calculated using the assumptions set forth below:

	Year Ended December 31,
	2021	2020	2019
Expected term	5.5 - 6.1 years	5.5 - 6.1 years	5.4 - 6.1 years
Expected volatility	90.0% - 103.6%	84.9 % - 98.3%	77.2% - 85.5%
Risk-free interest rate	0.6% - 1.4%	0.3% - 1.5%	1.4% - 2.5 %
Dividend yield	0%	0%	0%

Summary of Restricted Stock Activity

Restricted stock activity was as follows:

	Number of Shares Underlying Outstanding Restricted Stock Awards			Weighted Average Grant Date Fair Value
Unvested, December 31, 2020		14,625		$	0.82
Vested		(7,312	)	$	0.82
Repurchased		(7,313	)	$	0.82
Unvested, December 31, 2021		—