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Stock-Based Compensation (Tables) | 6 Months Ended
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Jun. 30, 2024
Share-Based Payment Arrangement [Abstract] |
Schedule of Total Share Based Compensation Expense | Total stock-based compensation expense related to share-based awards was comprised of the following (in thousands):
|  | Three months ended |  |  | Six months ended |
|  | June 30, |  |  | June 30, |
|  | 2024 |  |  | 2023 |  |  | 2024 |  |  | 2023 |
Research and development |  | $ | 2,574 |  |  | $ | 4,117 |  |  | $ | 5,434 |  |  | $ | 7,331 |
General and administrative |  |  | 3,197 |  |  |  | 3,751 |  |  |  | 6,880 |  |  |  | 7,104 |
Total stock-based compensation expense |  | $ | 5,771 |  |  | $ | 7,868 |  |  | $ | 12,314 |  |  | $ | 14,435 |
Stock-based compensation expense by type of share-based award (in thousands):
|  | Three months ended |  |  | Six months ended |
|  | June 30, |  |  | June 30, |
|  | 2024 |  |  | 2023 |  |  | 2024 |  |  | 2023 |
Stock options |  | $ | 4,885 |  |  | $ | 6,735 |  |  | $ | 10,362 |  |  | $ | 12,239 |
Restricted stock awards |  |  | 10 |  |  |  | 28 |  |  |  | 37 |  |  |  | 55 |
Restricted stock units |  |  | 850 |  |  |  | 1,047 |  |  |  | 1,863 |  |  |  | 2,046 |
Employee Stock Purchase Plan |  |  | 26 |  |  |  | 58 |  |  |  | 52 |  |  |  | 95 |
Total stock-based compensation expense |  | $ | 5,771 |  |  | $ | 7,868 |  |  | $ | 12,314 |  |  | $ | 14,435 |
Summary of Stock Option Activity | The following table summarizes stock option activity for the six months ended June 30, 2024:
|  |  |  |  |  |  |  | Weighted |  |  |  |
|  |  |  |  | Weighted |  |  | Average |  |  |  |
|  |  |  |  | Average |  |  | Remaining |  |  | Aggregate |
|  | Number |  |  | Exercise |  |  | Contractual |  |  | Intrinsic |
|  | of Shares |  |  | Price |  |  | Term |  |  | Value |
Outstanding as of December 31, 2023 |  |  | 10,338,724 |  |  | $ | 14.42 |  |  |  | 8.24 |  |  | $ | 1,737 |
Granted |  |  | 2,044,500 |  |  |  | 3.08 |  |  |  |  |  |  |
Exercised |  |  | (127,996 | ) |  |  | 0.92 |  |  |  |  |  |  |
Forfeited and cancelled |  |  | (1,462,027 | ) |  |  | 17.18 |  |  |  |  |  |  |
Outstanding as of June 30, 2024 |  |  | 10,793,201 |  |  | $ | 12.05 |  |  |  | 7.88 |  |  | $ | 1,142 |
Vested and expected to vest as of June 30, 2024 |  |  | 10,793,201 |  |  | $ | 12.05 |  |  |  | 7.88 |  |  | $ | 1,142 |
Exercisable as of June 30, 2024 |  |  | 4,962,290 |  |  | $ | 12.86 |  |  |  | 6.60 |  |  | $ | 821 |
Summary of Assumptions Used in Black-Scholes Option Pricing Model | The fair value of each option award is estimated on the date of grant using the Black-Scholes option pricing model. The following assumptions were used in the Black-Scholes option pricing model to estimate the fair value of stock options granted to employees under the Company’s Plans during the periods presented:
|  | Six months ended |
|  | June 30, |
|  | 2024 |  |  | 2023 |
Risk-free interest rate |  | 3.9% - 4.7% |  |  | 3.4% - 4.8% |
Expected volatility |  | 99.7% - 102.6% |  |  | 68.4% - 73.5% |
Expected term (in years) |  | 5.5 - 10.0 |  |  | 0.4 - 10.0 |
Expected dividend yield |  |  | — |  |  |  | — |
Summary of Restricted Stock Award Activity | The following table summarizes restricted stock award activity for the six months ended June 30, 2024:
|  |  |  |  | Weighted |
|  |  |  |  | Average |
|  |  |  |  | Grant Date |
|  | Number |  |  | Fair Value |
|  | of Shares |  |  | Per Share |
Unvested balance as of December 31, 2023 |  |  | 13,236 |  |  | $ | 3.45 |
Vested |  |  | (13,236 | ) |  |  | 3.45 |
Unvested balance as of June 30, 2024 |  |  | — |  |  | $ | — |
Summary of Restricted Stock Unit Activity | The following table summarizes restricted stock unit activity for the six months ended June 30, 2024:
|  |  |  |  | Weighted |
|  |  |  |  | Average |
|  |  |  |  | Grant Date |
|  | Number |  |  | Fair Value |
|  | of Shares |  |  | Per Share |
Unvested Balance as of December 31, 2023 |  |  | 530,726 |  |  | $ | 21.11 |
Granted |  |  | — |  |  | $ | — |
Vested |  |  | (51,558 | ) |  | $ | 31.46 |
Forfeited |  |  | (34,450 | ) |  | $ | 28.65 |
Unvested balance as of June 30, 2024 |  |  | 444,718 |  |  | $ | 19.33 |

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- Definition Tabular disclosure for stock option plans. Includes, but is not limited to, outstanding awards at beginning and end of year, grants, exercises, forfeitures, and weighted-average grant date fair value. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 718 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (c)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (d) -SubTopic 10 -Topic 718 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (e) -SubTopic 10 -Topic 718 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-2 + Details
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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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