Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2023

Stock-Based Compensation

Summary of stock option activity

	Options Outstanding and Exercisable
				Weighted
		Weighted		Average	Aggregate
		Average		Remaining	Intrinsic
	Number of	Exercise		Contractual	Value(1)
	Shares	Price		Life (Years)	(in thousands)
Outstanding as of December 31, 2022	5,262,179	$	11.44	7.6	$	115
Granted	2,059,250	$	1.55	—		—
Exercised	(5,057)	$	0.99	—		—
Forfeited	(403,024)	$	5.23	—		—
Outstanding as of September 30, 2023	6,913,348	$	8.86	7.5	$	79
Exercisable as of September 30, 2023	3,720,545	$	12.43	6.3	$	79

(1) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at September 30, 2023 and December 31, 2022.

Summary of stock based compensation expense recorded

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
(in thousands)	2023		2022		2023		2022
Research and development	$	721	$	779	$	2,184	$	2,274
General and administrative		1,280		1,533		4,020		4,908
Total stock-based compensation expense	$	2,001	$	2,312	$	6,204	$	7,182

Summary of assumptions used in the Black Scholes option pricing model for stock options granted

	Nine Months Ended
	September 30,
	2023		2022
Expected term	6.1	years	5.5 - 6.1	years
Expected volatility	81.4	%	79.7	%
Risk free interest rate	3.5 - 4.1	%	1.8 - 3.1	%
Expected dividend yield	—	%	—	%