STOCK BASED COMPENSATION (Tables)

9 Months Ended

Sep. 30, 2022

Stock-based compensation

Schedule of stock-based compensation expenses

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
(in thousands)	2022		2021		2022		2021
Research and development	$	1,178	$	642	$	2,822	$	1,974
General and administrative		1,678		2,003		4,342		6,354
Total stock-based compensation expense	$	2,856	$	2,645	$	7,164	$	8,328

Schedule of options outstanding

				Weighted-Average
		Weighted-		Remaining	Aggregate
	Options	Average		Contractual	Intrinsic
(in thousands, except for share data)	Outstanding	Exercise Price		Term (in years)	Value
Outstanding at December 31, 2021	4,704,888	$	13.29	7.7	$	10,305
Options granted	767,913		2.80
Options exercised	(47,602)		1.04			21
Forfeited	(357,833)		20.93
Expired	(141,688)		31.65
Outstanding at September 30, 2022	4,925,678	$	1.99	7.2	$	—
Exercisable at September 30, 2022	3,711,517	$	2.30	6.7	$	—
Nonvested at September 30, 2022	1,214,161	$	1.05	8.5	$	—

Schedule of restricted stock units outstanding

		Weighted-Average
		Grant Date		Aggregate
(in thousands, except for share data)	Shares	Fair Value		Intrinsic Value
Outstanding at December 31, 2021	469,485	$	18.05	$	4,202
Awarded	305,600		3.78
Released	(45,840)		25.57
Forfeited	(196,131)		18.36
Outstanding at September 30, 2022	533,114	$	9.10	$	496
Nonvested at September 30, 2022	528,712	$	9.06	$	492
Weighted Average Remaining Recognition Period (in years)	3.1

Stock options - Service conditions only

Stock-based compensation

Schedule of valuation assumptions

	Nine Months Ended
	September 30,
	2022			2021
Expected term (in years)		5.7			5.6
Volatility		75.83	%		70.99	%
Risk-free interest rate		2.13	%		0.91	%
Dividend yield		—	%		—	%