STOCK BASED COMPENSATION (Tables)
12 Months Ended
Dec. 31, 2021
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)

    

2021

    

2020

Research and development

$

2,759

$

2,580

General and administrative

 

8,418

 

5,446

Total stock-based compensation expense

$

11,177

$

8,026

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, 2020

 

4,529,675

$

12.87

8.49

$

51,103

Options granted

 

406,752

13.74

Options exercised

 

(191,436)

2.67

2,990

Forfeited

 

(40,008)

21.43

Expired

 

(95)

44.02

Outstanding at December 31, 2021

 

4,704,888

$

13.29

7.7

$

10,305

Exercisable at December 31, 2021

 

3,168,679

$

9.83

7.3

$

10,258

Nonvested at December 31, 2021

 

1,536,209

$

20.40

8.6

$

48

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, 2020

 

206,529

$

36.08

$

4,546

Awarded

 

348,536

11.03

Released

 

(52,562)

33.52

Forfeited

 

(33,018)

32.07

Outstanding at December 31, 2021

 

469,485

$

18.05

$

4,202

Nonvested at December 31, 2021

 

469,485

$

18.05

$

4,202

Weighted Average Remaining Recognition Period (in years)

3.4

Stock options - Service conditions only  
Stock-based compensation  
Schedule of valuation assumptions

Year Ended

 

December 31, 

    

2021

 

2020

Expected term (in years)

5.8

6.1

Volatility

 

71.92

%

69.70

%

Risk-free interest rate

 

1.08

%

0.51

%

Dividend yield

%

%