Stock-based compensation (Tables)

9 Months Ended

Sep. 30, 2023

Stock-based compensation

Compensation cost recognized for all stock-based compensation awards

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2023		2022		2023		2022
	(in thousands)
Research and development	$	919	$	588	$	2,472	$	2,170
General and administrative		1,959		1,601		5,636		4,828
Total stock-based compensation expense	$	2,878	$	2,189	$	8,108	$	6,998

Summary of stock-based compensation expense by type of award

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2023		2022		2023		2022
	(in thousands)
Stock options	$	2,021	$	1,357	$	5,587	$	4,452
Restricted stock awards and units		774		748		2,339		2,382
Employee stock purchase plan awards		83		84		182		164
Total stock-based compensation expense	$	2,878	$	2,189	$	8,108	$	6,998

Summary of status and changes in unvested restricted stock

		Weighted
		Average
		Grant Date
		Fair Value
	Units	Per Unit
Unvested restricted stock units as of December 31, 2022	1,112,563	$	5.27
Granted	725,550	$	7.52
Vested	(459,745)	$	5.68
Forfeited	(65,641)	$	4.65
Unvested restricted stock units as of September 30, 2023	1,312,727	$	6.40

Summary of stock option activity

		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	2,250,400	$	8.64
Exercised	(377,593)	$	5.02
Cancelled or forfeited	(326,785)	$	9.60
Outstanding at September 30, 2023	7,745,593	$	8.42	7.9	$	9,348
Exercisable at September 30, 2023	3,527,536	$	9.66	6.7	$	4,355