Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2022

Summary of Assumptions Used in Black-Scholes Option Pricing Model

The fair values of stock options granted during the three and six months ended June 30, 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		Six Months Ended
	June 30,		June 30,
	2022	2021	2022	2021
Risk-free interest rate	2.83% - 3.54%	1.07% - 1.23%	1.70% - 3.54%	0.66% - 1.23%
Expected volatility	77.77% - 81.45%	71.78% - 83.48%	77.77% - 81.93%	71.62% - 83.48%
Expected dividend yield	0%	0%	0%	0%
Expected life of employee and Board options (in years)	6.25	6.25	6.25	6.25

Summary of Compensation Expense Relating to Stock Options

During the three and six months ended June 30, 2022 and 2021, the Company recognized compensation expense relating to stock options as follows:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
Research and development	$	1,744	$	1,805	$	3,661	$	3,395
General and administrative		1,958		1,225		3,988		2,239
Total stock option expense	$	3,702	$	3,030	$	7,649	$	5,634

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 six months ended June 30, 2022 is presented below:

		Weighted
	Number of	Average Exercise
	Shares	Price
Outstanding, December 31, 2021	6,512,280	$	15.58
Granted	1,302,419		10.21
Exercised	(30,470)		6.09
Forfeited	(293,143)		14.85
Expired	(72,059)		19.42
Outstanding, June 30, 2022	7,419,027	$	14.67
Options exercisable, June 30, 2022	4,694,573

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 six months ended June 30, 2022 is presented below:

		Weighted
	Number of	Average Grant
	Units	Date Fair Value
Outstanding, December 31, 2021	576,544	$	17.50
Awarded	466,926		10.11
Vested and released	(199,018)		17.07
Forfeited	(196,002)		17.06
Outstanding, June 30, 2022	648,450	$	12.45
Restricted stock units exercisable (vested and deferred), June 30, 2022	—