STOCK BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2022

Stock-based compensation

Schedule of stock-based compensation expenses

Total stock-based compensation expense recorded for employees, directors and non-employees (in thousands):

	Year Ended
	December 31,
(in thousands)	2022		2021
Research and development	$	3,619	$	2,759
General and administrative		5,543		8,418
Total stock-based compensation expense	$	9,162	$	11,177

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		1.39
Options exercised	(47,602)		1.04			21
Forfeited	(377,378)		19.90
Expired	(173,774)		26.82
Outstanding at December 31, 2022	4,874,047	$	1.97	6.9	$	—
Exercisable at December 31, 2022	3,859,880	$	2.21	6.6	$	—
Nonvested at December 31, 2022	1,014,167	$	1.05	8.3	$	—

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	605,600		2.33
Released	(50,242)		24.57
Forfeited	(209,334)		18.10
Outstanding at December 31, 2022	815,509	$	5.96	$	620
Nonvested at December 31, 2022	815,509	$	5.73	$	582
Weighted Average Remaining Recognition Period (in years)	3.2

Stock options - Service conditions only

Stock-based compensation

Schedule of valuation assumptions

	Year Ended
	December 31,
	2022			2021
Expected term (in years)		5.7			5.8
Volatility		75.83	%		71.92	%
Risk-free interest rate		2.13	%		1.08	%
Dividend yield		—	%		—	%