Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2021
Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity during the twelve months ended December 31, 2021:

 

 

NUMBER
OF
SHARES

 

 

WEIGHTED
AVERAGE
EXERCISE
PRICE
PER
SHARE

 

 

WEIGHTED
AVERAGE
REMAINING
CONTRACTUAL
TERM

 

 

AGGREGATE
INTRINSIC
VALUE (1)

 

 

 

 

 

 

 

 

 

(In years)

 

 

(In thousands)

 

Outstanding as of December 31, 2020

 

 

4,543,318

 

 

$

8.52

 

 

 

7.22

 

 

$

108,048

 

Granted

 

 

1,449,400

 

 

 

23.26

 

 

 

 

 

 

 

Exercised

 

 

(433,751

)

 

 

8.62

 

 

 

 

 

 

 

Forfeited/Cancelled

 

 

(795,478

)

 

 

11.10

 

 

 

 

 

 

 

  Outstanding as of December 31, 2021

 

 

4,763,489

 

 

 

12.56

 

 

 

6.44

 

 

 

10,370

 

  Exercisable as of December 31, 2021

 

 

2,688,532

 

 

 

8.02

 

 

 

5.41

 

 

 

9,372

 

  Vested and expected to vest as of December 31, 2021

 

 

4,763,489

 

 

 

12.56

 

 

 

6.44

 

 

 

10,370

 

 

(1)
Aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock as of December 31, 2021 and 2020.
Schedule of Components and Classification of Stock-Based Compensation Expense

The following table presents the components and classification of stock-based compensation expense (in thousands):

 

 

 

YEAR ENDED
DECEMBER 31,

 

 

 

2021

 

 

2020

 

Research and development

 

$

4,733

 

 

$

3,563

 

General and administrative

 

 

5,409

 

 

 

3,517

 

Gain on disposition

 

 

535

 

 

 

-

 

 

 

$

10,677

 

 

$

7,080

 

 

 

 

 

 

 

 

Employee

 

$

9,862

 

 

$

6,547

 

Non-employee

 

 

815

 

 

 

533

 

 

 

$

10,677

 

 

$

7,080

 
Service-Based Awards  
Summary of Key Assumptions Used for Stock Option Valuation

The key assumptions used in the Black-Scholes option pricing model on the date of grant for options with service-based vesting conditions granted to employees, directors and non-employees, were as follows, presented on a weighted average basis:

 

 

 

YEAR ENDED
DECEMBER 31,

 

 

 

2021

 

 

2020

 

Risk-free interest rate

 

 

0.83

%

 

 

0.68

%

Expected term (in years)

 

 

6.20

 

 

6.18

 

Expected volatility

 

 

68.21

%

 

 

68.75

%

Expected dividend yield

 

 

0.00

%

 

 

0.00

%

Fair value per share of common stock

 

$

14.37

 

 

$

13.52