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Stock-Based Compensation (Tables)
3 Months Ended
Mar. 31, 2024
Summary of Assumptions Used in Black-Scholes Option Pricing Model

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Three Months Ended

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March 31, 

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2024

    

2023

    

Risk-free interest rate

 

4.12%

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3.62% - 4.22%

 

Expected volatility

 

89.6%

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76.3% - 81.3%

 

Expected dividend yield

 

0%

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0%

 

Expected life of employee and Board options (in years)

 

6.25

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6.25

 

Summary of Stock Option Activity

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Weighted

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Number of

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Average Exercise

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Shares

    

 Price

    

Outstanding, December 31, 2023

 

7,897,647

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$

12.99

 

Granted

 

1,875,125

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0.99

 

Exercised

 

—

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—

 

Forfeited

 

(679,165)

​

 

10.87

 

Expired

 

(277,075)

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13.36

 

Outstanding, March 31, 2024

 

8,816,532

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$

10.59

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Options exercisable, March 31, 2024

 

4,827,562

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Employees And Non-Employee Members Of Board Of Directors [Member]  
Summary of Restricted Stock Unit Activity

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Weighted

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Number of

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Average Grant

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Units

    

Date Fair Value

Outstanding, December 31, 2023

 

566,324

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$

9.27

Awarded

 

—

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—

Vested and released

 

(186,375)

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11.04

Forfeited

 

(129,682)

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10.57

Outstanding, March 31, 2024

 

250,267

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$

7.28

Restricted stock units exercisable (vested and deferred), March 31, 2024

 

—

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Employee Stock Option [Member]  
Summary of Compensation Expense Recognized

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Three Months Ended

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March 31, 

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2024

    

2023

    

Research and development

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$

504

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$

1,480

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General and administrative

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1,229

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1,241

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Total stock option expense

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$

1,733

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$

2,721

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Restricted Stock Units [Member]  
Summary of Compensation Expense Recognized

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Three Months Ended

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March 31, 

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2024

    

2023

Research and development

 

$

255

 

$

179

General and administrative

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​

1,357

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​

453

Total restricted stock unit expense

 

$

1,612

 

$

632