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Stock-based Compensation (Tables)
6 Months Ended
Jun. 30, 2024
Share-Based Payment Arrangement [Abstract]  
Schedule of Stock-based Compensation Expense Recognized
Total stock-based compensation expense recognized in the condensed consolidated statements of operations was as follows:
Three Months Ended
June 30,
Six Months Ended
June 30,
2024202320242023
(in thousands)
Research and development
$1,516 $1,019 $2,698 $2,039 
General and administrative
1,086 911 2,209 1,999 
Total stock-based compensation
$2,602 $1,930 $4,907 $4,038 
Schedule of Restricted Stock Awards Activity The following table summarizes RSU activity during the six months ended June 30, 2024:
Shares/UnitsWeighted-Average
Grant Date Fair
Value Per Share
(in thousands)
Unvested at December 31, 2023361,500 $3.92 
Granted
— $— 
Vested
(211,500)$4.97 
Forfeited
— $— 
Unvested at June 30, 2024150,000 $2.45 
Schedule of Weighted -average Valuation Assumptions
The fair value of stock options granted during the three and six months ended June 30, 2024 and 2023 was calculated on the date of grant using the following weighted-average assumptions:
Three Months Ended
June 30,
Six Months Ended
June 30,
2024202320242023
Risk-free interest rate
4.5 %3.8 %4.0 %3.9 %
Expected term (in years)
5.55.76.06.0
Expected annual dividend yield
— %— %— %— %
Expected volatility
92.6 %82.6 %92.6 %82.6 %
Summary of Stock Option Activity
The following table summarizes stock option activity during the six months ended June 30, 2024: 
Options Outstanding
Number of Options
Weighted-Average Exercise Price per Share
Weighted-Average Remaining
Contractual Life
(in years)
Aggregate Intrinsic Value (in millions)
Outstanding at December 31, 20235,700,070 $6.89 
Granted
2,205,112 $4.66 
Exercised
(6,099)$2.05 
Cancelled
(389,050)$5.06 
Outstanding at June 30, 20247,510,033 $6.33 7.85$0.8 
Exercisable at June 30, 20244,100,266 $7.25 7.09$0.5