Stock-based compensation

3 Months Ended

Mar. 31, 2023

Stock-based compensation

Stock-based compensation

9. Stock-based compensation

Stock-Based Compensation Expense

Total compensation cost recognized for all stock-based compensation awards in the condensed consolidated statements of operations and comprehensive income (loss) is as follows:

	Three Months Ended
	March 31,
	2023		2022
	(in thousands)
Research and development	$	863	$	801
General and administrative		1,695		1,518
Total stock-based compensation expense	$	2,558	$	2,319

Stock-based compensation expense by type of award included within the condensed consolidated statements of operations and comprehensive income (loss) was as follows:

	Three Months Ended
	March 31,
	2023		2022
	(in thousands)
Stock options	$	1,663	$	1,477
Restricted stock awards and units		841		792
Employee stock purchase plan awards		54		51
Total stock-based compensation expense	$	2,558	$	2,319

Restricted Stock Units

A summary of the status of and changes in unvested restricted stock unit activity under the Company’s equity award plans for the three months ended March 31, 2023 was as follows:

		Weighted
		Average
		Grant Date
		Fair Value
	Units	Per Unit
Unvested restricted stock units as of December 31, 2022	1,112,563	$	5.27
Granted	622,050	$	7.24
Vested	(374,417)	$	5.44
Forfeited	(24,037)	$	3.80
Unvested restricted stock units as of March 31, 2023	1,336,159	$	6.17

Stock-based compensation of restricted stock units is based on the fair value of the Company’s common stock on the date of grant and is recognized over the vesting period. Restricted stock units granted by the Company typically vest in equal amounts, annually over three years. All of the restricted stock units granted in the three months ended March 31, 2023 vest in equal amounts, annually over three years. The stock-based compensation expense related to restricted stock units and awards was $0.8 million for each of the three months ended March 31, 2023 and 2022.

As of March 31, 2023, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $7.3 million, which is expected to be recognized over the remaining average vesting period of 2.4 years.

Stock Options

The following is a summary of stock option activity for the three months ended March 31, 2023:

		Weighted		Remaining	Aggregate
		Average		Contractual	Intrinsic
		Exercise		Life	Value
	Shares	Price		(in years)	(in thousands)
Outstanding at December 31, 2022	6,199,571	$	8.12	7.9	$	6,095
Granted	1,358,200	$	7.55
Exercised	(51,993)	$	3.56
Cancelled or forfeited	(145,033)	$	5.42
Outstanding at March 31, 2023	7,360,745	$	8.10	8.0	$	10,631
Exercisable at March 31, 2023	3,133,247	$	10.28	6.4	$	4,025

As of March 31, 2023, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $17.9 million which is expected to be recognized over the remaining weighted-average vesting period of 3.0 years.