Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2022

Share-Based Payment Arrangement [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):

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	1,603	$	873	$	2,901	$	1,669
General and administrative		1,441		1,185		2,748		2,307
Total stock-based compensation expense	$	3,044	$	2,058	$	5,649	$	3,976

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 (Millions)
Balance, January 1, 2022		922,826			3,620,666		$	12.36		7.92	$	41.40
Additional shares authorized		1,541,322			—
Options granted		(1,552,180	)		1,552,180		$	12.72
Options exercised		—			(122,913	)	$	6.38
Options canceled		127,709			(127,709	)	$	12.84
Balance, June 30, 2022		1,039,677			4,922,224		$	12.61		8.26	$	14.60
Exercisable as of June 30, 2022					1,994,118		$	9.36		6.99	$	11.00
Vested and expected to vest as of    June 30, 2022					4,922,224		$	12.61		8.26	$	14.60

Assumptions Used to Calculate Fair Values of Options

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

	Three Months Ended June 30,		Six months Ended June 30,
	2022	2021	2022	2021
Expected term	6.1 years	5.5 - 6.1 years	6.1 years	5.5 - 6.1 years
Expected volatility	87.5% - 87.8%	96.0% - 102.8%	87.5% - 89.9%	96.0% - 103.6%
Risk-free interest rate	2.7% - 3.0%	0.8% - 1.1%	1.6% - 3.0%	0.6% - 1.1%
Dividend yield	0%	0%	0%	0%