Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2022

Summary of Stock Option Activity

A summary of stock option award activity related to employees, non-employee members of the Company’s Board of Directors and non-employee consultants as of and for the three months ended March 31, 2022 is presented below:

		Weighted
	Number of	Average Exercise
	Shares	Price
Outstanding, December 31, 2021	6,512,280	$	15.58
Granted	977,438		10.63
Exercised	(470)		6.50
Forfeited	(37,241)		15.22
Expired	(21,378)		25.16
Outstanding, March 31, 2022	7,430,629	$	14.91
Options exercisable, March 31, 2022	4,357,399

Summary of Assumptions Used in Black-Scholes Option Pricing Model

The fair values of stock options granted during the three months ended March 31, 2022 and 2021 were estimated as of the dates of grant using the Black-Scholes option pricing model with the following assumptions:

	Three Months Ended
	March 31,
	2022	2021
Risk-free interest rate	1.70% - 2.35%	0.66% - 1.21%
Expected volatility	81.4% - 81.9%	71.6% - 71.8%
Expected dividend yield	0%	0%
Expected life of employee and Board options (in years)	6.25	6.25

Summary of Compensation Expense Relating to Stock Options

During the three months ended March 31, 2022 and 2021, the Company recognized compensation expense relating to stock options as follows:

	Three Months Ended
	March 31,
	2022		2021
Research and development	$	1,917	$	1,590
General and administrative		2,030		1,014
Total stock option expense	$	3,947	$	2,604

Employees And Non-Employee Members Of Board Of Directors [Member]

Summary of Restricted Stock Unit Activity

A summary of restricted stock unit activity related to employees and non-employee members of the Company’s Board of Directors as of and for the three months ended March 31, 2022 is presented below:

		Weighted
	Number of	Average Grant
	Units	Date Fair Value
Outstanding, December 31, 2021	576,544	$	17.50
Awarded	388,170		10.46
Vested and released	(109,943)		19.13
Forfeited	(118,499)		19.72
Outstanding, March 31, 2022	736,272	$	13.19
Restricted stock units exercisable (vested and deferred), March 31, 2022	—