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Stock-Based Compensation Plans (Tables)
9 Months Ended
Sep. 30, 2024
Share-Based Payment Arrangement [Abstract]  
Schedule of Stock Option Activity
The following table summarizes stock option activity for the nine months ended September 30, 2024 and 2023, respectively, for the 2019 Plan:
OptionsWeighted-
Average
Exercise
Price
Weighted-
Average
Remaining
Contractual
Term (Years)
Aggregate
Intrinsic
Value
Outstanding as of January 1, 20246,196,140 $7.15 
Granted5,715,349 $1.23 
Exercised— $— — 
Repricing modification— $9.55 
Forfeited or expired(365,351)$2.08 
Outstanding as of September 30, 202411,546,138 $1.63 8.33$2,794,286 
Options vested and expected to vest as of September 30, 202411,546,138 $1.63 8.33$2,794,286 
Options exercisable as of September 30, 20244,171,969 $2.09 7.07$329,830 
OptionsWeighted-
Average
Exercise
Price
Weighted-
Average
Remaining
Contractual
Term (Years)
Aggregate
Intrinsic
Value
Outstanding as of January 1, 20233,791,688 $11.33 
Granted2,740,564 $1.71 
Exercised— $— 
Forfeited or expired(268,342)$7.80 
Outstanding as of September 30, 20236,263,910 $7.27 8.27$119,691 
Options vested and expected to vest as of September 30, 20236,263,910 $7.27 8.27$119,691 
Options exercisable as of September 30, 20232,393,294 $11.67 7.12$6,160 
Schedule of Valuation Assumptions Used The following are the underlying assumptions used in the Black-Scholes-Merton option pricing model to determine the fair value of stock options granted to employees and to non-employees under this stock plan:
Nine Months Ended September 30,
20242023
Risk-free interest rate4.11%4.00%
Expected dividend yield0%0%
Expected volatility100.0%96.0%
Expected term of options (years)5.956.01
Schedule of Stock-based Compensation Expense for Stock Awards Recognized
Total stock-based compensation expense for all stock awards recognized in the accompanying unaudited condensed consolidated statements of operations is as follows:
 Three Months
 Ended September 30,
Nine Months
 Ended September 30,
 2024202320242023
Research and development$811,000 $815,000 $2,816,000 $2,607,000 
General and administrative1,099,000 872,000 3,726,000 2,857,000 
Total$1,910,000 $1,687,000 $6,542,000 $5,464,000