Stock-Based Compensation

6 Months Ended

Jun. 30, 2023

Share-Based Payment Arrangement [Abstract]

Stock-Based Compensation

12. Stock-based Compensation

Stock-based Compensation Expense

Total stock-based compensation expense recognized was as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Research and development	$	2,381	$	1,888	$	4,587	$	3,574
General and administrative		2,642		2,447		5,201		5,111
Total stock-based compensation	$	5,023	$	4,335	$	9,788	$	8,685

Stock Options

A summary of stock option activity for the six months ended June 30, 2023 is set forth below:

	Number of Shares Underlying Outstanding Options			Weighted Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2022		6,203,020		$	14.44		8.4	$	780
Options granted		2,561,200		$	7.53
Options exercised		(946	)	$	4.76
Options forfeited or cancelled		(424,242	)	$	12.68
Outstanding, June 30, 2023		8,339,032		$	12.41		8.4	$	20
Options exercisable, June 30, 2023		3,181,499		$	13.92		7.7	$	20
Vested and expected to vest, June 30, 2023		8,339,032		$	12.41		8.4	$	20

The assumptions used in the Black Scholes Model to calculate stock-based compensation are as follows:

	Three Months Ended June 30,		Six Months Ended June 30,
	2023	2022	2023	2022
Fair value of common stock	$2.43 - $5.84	$11.49 - $14.74	$2.43 - $9.15	$11.49 - $19.97
Expected term (years)	5.5 - 6.1	5.5 - 6.1	5.5 - 6.1	5.5 - 6.1
Volatility	84.6% - 86.5%	77.4% - 79.8%	83.3% - 86.5%	77.4% - 79.8%
Risk free rates	3.5% - 4.1%	2.8% - 3.0%	3.5% - 4.2%	1.6% - 3.0%
Dividend rate	0.0%	0.0%	0.0%	0.0%

Restricted Stock Units

In October 2021, the Company granted 560,000 Restricted Stock Units (RSUs) with service and performance conditions to certain employees, none of which vested during the three months ended June 30, 2023. Vesting of these awards is contingent on the occurrence of certain milestone events and fulfilment of any remaining service condition. As a result, the related compensation cost is recognized as an expense when achievement of the milestone is considered probable. The expense

recognized for these awards is based on the grant date fair value of the Company's common stock multiplied by the number of units granted. The Company recognized $0.2 million of related expense during the three months ended June 30, 2023.

The summary of RSU activity and related information for the six months ended June 30, 2023 is set forth below:

	Number of Units Outstanding			Weighted Average Grant Date Fair Value
Outstanding, December 31, 2022		197,580		$	7.8
RSUs granted		513,700		$	7.6
RSUs vested		(3,205	)	$	17.2
RSUs forfeited		(38,225	)	$	7.4
Outstanding, June 30, 2023		669,850		$	7.6