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Equity Incentive Plan (Tables) | 12 Months Ended
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Dec. 31, 2023
Share-Based Payment Arrangement [Abstract] |
Summary of Stock Option Activity | The following table presents stock option activity under the Plans for the period:
|  | Number of Shares |  |  | Weighted- Average Exercise Price Per Share |  |  | Weighted- Average Remaining Contractual Term (in years) |  |  | Aggregate Intrinsic Value (in thousands) |
Balances as of December 31, 2022 |  |  | 8,152,093 |  |  | $ | 11.92 |  |  |  | 8.09 |  |  | $ | 3,329 |
Stock options granted |  |  | 2,602,050 |  |  | $ | 5.17 |  |  |  |  |  |  |
Stock options exercised |  |  | (76,888 | ) |  | $ | 1.89 |  |  |  |  |  |  |
Stock options forfeited |  |  | (1,468,285 | ) |  | $ | 10.61 |  |  |  |  |  |  |
Balances as of December 31, 2023 |  |  | 9,208,970 |  |  | $ | 10.31 |  |  |  | 7.53 |  |  | $ | 2,930 |
Exercisable as of December 31, 2023 |  |  | 5,083,778 |  |  | $ | 12.10 |  |  |  | 6.64 |  |  | $ | 1,299 |
Summary of RSU Activity under Equity Incentive Plan | A summary of RSU activity under our equity incentive plan and related information is as follows:
|  | Number of Shares |  |  | Weighted-Average Grant Date Fair Value Per Share |
Unvested as of December 31, 2022 |  |  | 550,236 |  |  | $ | 5.58 |
Granted |  |  | 249,615 |  |  |  | 5.95 |
Vested |  |  | (172,096 | ) |  |  | 5.73 |
Cancelled |  |  | (132,176 | ) |  |  | 5.67 |
Unvested as of December 31, 2023 |  |  | 495,579 |  |  | $ | 5.69 |
Summary of Stock-Based Compensation Expense | The total stock-based compensation expense recognized was as follows (in thousands):
|  | Year Ended December 31, |  |
|  | 2023 |  |  | 2022 |  |
Research and development |  | $ | 8,878 |  |  | $ | 8,874 |  |
General and administrative |  |  | 9,305 |  |  |  | 9,642 |  |
Total stock-based compensation expense |  | $ | 18,183 |  |  | $ | 18,516 |  |
Summary of Fair Value of Each Stock Option Issued Estimated on the Date of Grant Using the Black-Scholes Option Pricing Model | The fair value of each stock option issued was estimated on the date of grant using the Black-Scholes option pricing model with the following assumptions:
|  | Year Ended December 31,
|  | 2023 |  | 2022
Expected term (in years) |  | 5.50 - 6.08 |  | 5.50 - 6.08
Expected volatility |  | 81.20% - 82.40% |  | 78.80% - 85.90%
Risk-free interest rate |  | 3.47% - 4.85% |  | 1.49% - 4.19%
Dividend yield |  | — |  | —

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- Definition Tabular disclosure of the significant assumptions used during the year to estimate the fair value of stock options, including, but not limited to: (a) expected term of share options and similar instruments, (b) expected volatility of the entity's shares, (c) expected dividends, (d) risk-free rate(s), and (e) discount for post-vesting restrictions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 718 -SubTopic 10 -Subparagraph (f)(2) -Name Accounting Standards Codification -Paragraph 2 -Section 50 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
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