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Stockholders’ Equity and Stock Options (Tables) | 12 Months Ended
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Dec. 31, 2023
Stockholders' Equity Note [Abstract] |
Assumptions used to Determine Fair Value of Stock Options Granted | The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the grant-date fair value of stock options granted to employees:
|  | 2023 |  |  | 2022 |
Risk-free interest rate |  | 3.72% |  |  | 2.15% |
Expected term (in years) |  |  | 6.23 |  |  |  | 6.21 |
Expected volatility |  | 94% |  |  | 89% |
Dividend yield |  | 0.00% |  |  | 0.00% |
Summary of Stock Option Activity | The following table summarizes the Company’s stock option activity for the twelve months ended December 31, 2023 (amounts in millions, except for share and per share data):
|  |  |  |  | Weighted |  |  | Weighted Average |  |  | Aggregate |
|  |  |  |  | Average |  |  | Remaining |  |  | Intrinsic |
|  | Number of |  |  | Exercise |  |  | Contractual |  |  | Value (a) |
|  | Shares |  |  | Price |  |  | Term (in years) |  |  | (in millions) |
Outstanding as of December 31, 2022 |  |  | 3,071,528 |  |  | $ | 12.13 |  |  |  | 7.6 |  |  |  |
Granted |  |  | 1,748,200 |  |  |  | 4.68 |  |  |  |  |  |  |
Exercised |  |  | (11,466 | ) |  |  | 2.93 |  |  |  |  |  |  |
Forfeited/Expired |  |  | (534,760 | ) |  |  | 12.52 |  |  |  |  |  |  |
Outstanding as of December 31, 2023 |  |  | 4,273,502 |  |  | $ | 9.06 |  |  |  | 7.8 |  |  | $ | 0.9 |
Exercisable as of December 31, 2023 |  |  | 1,930,100 |  |  | $ | 12.55 |  |  |  | 6.6 |  |  | $ | 0.2 |
Vested and expected to vest as of December 31, 2023 |  |  | 4,273,502 |  |  | $ | 9.06 |  |  |  | 7.8 |  |  | $ | 0.9 |
(a) The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of the common stock for the options that were in the money at December 31, 2023.
Summary of Restricted Stock Units | Activity with respect to the Company's RSUs during the twelve months ended December 31, 2023 was as follows (in millions, except share, contractual term, and per share data):
|  |  |  |  | Weighted |  |  | Weighted Average |  |  | Aggregate |
|  |  |  |  | Average |  |  | Remaining |  |  | Intrinsic |
|  | Number of |  |  | Grant Date |  |  | Contractual |  |  | Value (a) |
|  | Shares |  |  | Fair Value |  |  | Term (in years) |  |  | (in millions) |
Outstanding as of December 31, 2022 |  |  | — |  |  | $ |  |  |  |  | — |  |  |  |
Restricted stock units granted |  |  | 650,000 |  |  |  | 4.94 |  |  |  |  |  |  |
Restricted stock units forfeited |  |  | (35,000 | ) |  |  | 4.94 |  |  |  |  |  |  |
Outstanding as of December 31, 2023 |  |  | 615,000 |  |  | $ | 4.94 |  |  |  | 1.6 |  |  | $ | 2.8 |
Unvested and expected to vest as of December 31, 2023 |  |  | 615,000 |  |  | $ | 4.94 |  |  |  | 1.6 |  |  | $ | 2.8 |
Summary of Stock-Based Compensation Expense | Stock-based compensation expense was classified in the consolidated statements of operations as follows:
|  | Year Ended December 31, |  |
|  | 2023 |  |  | 2022 |  |
|  | (in thousands) |  |
Research and development |  | $ | 3,077 |  |  | $ | 2,771 |  |
General and administrative |  |  | 4,538 |  |  |  | 3,848 |  |
|  | $ | 7,615 |  |  | $ | 6,619 |  |

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