Stock-based compensation

6 Months Ended

Jun. 30, 2022

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 loss is as follows:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
	(in thousands)
Research and development	$	781	$	1,336	$	1,582	$	2,706
General and administrative		1,709		2,655		3,227		4,886
Total stock-based compensation expense	$	2,490	$	3,991	$	4,809	$	7,592

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

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2022		2021		2022		2021
	(in thousands)
Stock options	$	1,618	$	2,480	$	3,095	$	5,002
Restricted stock awards and units		842		1,392		1,634		2,366
Employee stock purchase plan awards		30		120		81		223
Total stock-based compensation expense	$	2,490	$	3,991		4,809		7,592

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 six months ended June 30, 2022 was as follows:

		Weighted
		Average
		Grant Date
		Fair Value
	Units	Per Unit
Unvested restricted stock units as of December 31, 2021	806,379	$	7.26
Granted	739,080	$	3.79
Vested	(344,255)		7.45
Forfeited	(169,839)	$	5.06
Unvested restricted stock units as of June 30, 2022	1,031,365	$	5.08

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 six months ended June 30, 2022 vest in equal amounts, annually over three or four years. The stock-based compensation expense related to restricted stock units and awards was $0.8 million and $1.6 million for the three and six months ended June 30, 2022, respectively. The stock-based compensation expense related to restricted stock units and awards was $1.4 million and $2.4 million for the three and six months ended June 30, 2021, respectively.

As of June 30, 2022, the Company had unrecognized stock-based compensation expense related to its unvested restricted stock units of $4.0 million, which is expected to be recognized over the remaining average vesting period of 2.0 years.

Stock Options

The following is a summary of stock option activity for the six months ended June 30, 2022:

		Weighted		Remaining	Aggregate
		Average		Contractual	Intrinsic
		Exercise		Life	Value
	Shares	Price		(in years)	(in thousands)
Outstanding at December 31, 2021	5,013,193	$	12.69	5.6	$	1,165
Granted	2,965,075	$	4.95
Exercised	(74,496)	$	7.90
Cancelled or forfeited	(1,274,172)	$	12.42
Outstanding at June 30, 2022	6,629,600	$	9.33	7.2	$	5,914
Exercisable at June 30, 2022	3,378,945	$	12.29	5.3	$	1,575

As of June 30, 2022, the Company had unrecognized stock-based compensation expense related to its unvested stock options of $13.0 million which is expected to be recognized over the remaining weighted-average vesting period of 3.1 years.