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Equity Incentive Plans (Tables)
12 Months Ended
Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]  
Summary of Stock-based Compensation Expense

The Company recorded stock-based compensation expense as research and development and general and administrative expenses in the consolidated statements of operations and comprehensive loss as follows (in thousands):

 

 

 

Year ended December 31,

 

 

 

2023

 

 

2022

 

Research and development

 

$

4,269

 

 

$

4,026

 

General and administrative

 

 

4,524

 

 

 

3,727

 

Total stock-based compensation expense

 

$

8,793

 

 

$

7,753

 

 

Summary of Assumptions Used in Black-Scholes Option-pricing Model for Stock Options

The assumptions used in the Black-Scholes option-pricing model for stock options granted were as follows:

 

 

 

Year ended December 31,

 

 

 

2023

 

 

2022

 

Expected volatility

 

74.65% - 77.06%

 

 

76.09% - 77.62%

 

Weighted-average risk-free interest rate

 

4.16%

 

 

2.69%

 

Expected dividend yield

 

0.00%

 

 

0.00%

 

Weighted-average expected term (in years)

 

 

6.08

 

 

 

6.11

 

 

Summary of Option Activity

A summary of option activity under the Company’s equity incentive plans during the year ended December 31, 2023 was as follows:

 

 

 

 

 

 

Weighted

 

 

Weighted
average
remaining

 

 

Aggregate
intrinsic

 

 

 

Number
of options

 

 

average
exercise price

 

 

contractual
life (years)

 

 

value (1)
(in thousands)

 

Outstanding as of January 1, 2023

 

 

8,438,573

 

 

$

6.00

 

 

 

8.40

 

 

$

12,976

 

Granted

 

 

1,586,002

 

 

 

5.74

 

 

 

 

 

 

 

Exercised

 

 

(152,050

)

 

 

3.21

 

 

 

 

 

 

 

Forfeited

 

 

(964,787

)

 

 

7.96

 

 

 

 

 

 

 

Expired

 

 

(127,001

)

 

 

12.73

 

 

 

 

 

 

 

Outstanding as of December 31, 2023

 

 

8,780,737

 

 

 

5.69

 

 

 

7.52

 

 

 

5,033

 

Vested and expected to vest as of December 31, 2023

 

 

8,780,737

 

 

 

5.69

 

 

 

7.52

 

 

 

5,033

 

Exercisable as of December 31, 2023

 

 

4,837,051

 

 

$

4.79

 

 

 

6.71

 

 

$

4,599

 

 

(1) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money as of December 31, 2023.