Stock-Based Compensation |
(8) Stock-Based Compensation A summary of stock option activity for the six months ended June 30, 2022 is as follows: | | | | | | | | | | | | Weighted | | Weighted | | | | | Average | | Average | | | | | Exercise | | Remaining | | | | | Price | | Contractual | | | Shares | | Per Share | | Term (In Years) | Options outstanding at December 31, 2021 | | 4,077,667 | | $ | 30.02 | | 8.0 | Granted
| | 1,570,900 | | $ | 22.79 | | | Exercised
| | (29,910) | | $ | 8.05 | | | Canceled
| | (28,444) | | $ | 36.24 | | | Options outstanding at June 30, 2022 | | 5,590,213 | | $ | 28.07 | | 8.20 | Options vested and expected to vest at June 30, 2022 | | 5,428,921 | | $ | 28.25 | | 8.17 | Options exercisable at June 30, 2022 | | 2,135,506 | | $ | 39.84 | | 6.76 | Shares available for grant under the 2021 Plan | | 1,761,761 | | | | | |
The weighted average grant-date fair value of stock options granted during the three and six ended June 30, 2022 was $17.20 and $17.29, respectively. The aggregate intrinsic value of stock options vested and expected to vest at June 30, 2022 was $48.6 million. The aggregate intrinsic value of stock options exercisable at June 30, 2022 was $26.2 million. As of June 30, 2022, total compensation cost related to non-vested employee, consultant and non-employee director stock options not yet recognized was approximately $51.2 million, net of estimated forfeitures, which is expected to be recognized as expense over a weighted average period of 3.0 years. Stock-based compensation expense for the three and six months ended June 30, 2022 and 2021 was recorded as follows: | | | | | | | | | | | | | | | Three months ended June 30, | | Six months ended June 30, | | | 2022 | | 2021 | | 2022 | | 2021 | | | | (In thousands) | | (In thousands) | Research and development
| | $ | 1,798 | | $ | 762 | | $ | 3,412 | | $ | 1,423 | General and administrative
| | | 1,656 | | | 747 | | | 3,195 | | | 1,361 | Total stock-based compensation expense
| | $ | 3,454 | | $ | 1,509 | | $ | 6,607 | | $ | 2,784 |
The fair values of employee, consultant and non-employee director stock options granted during the three and six months ended June 30, 2022 and 2021 were valued using the Black-Scholes option pricing model with the following assumptions: | | | | | | | | | | | Three months ended June 30, | | Six months ended June 30, | | | 2022 | | 2021 | | 2022 | | 2021 | Expected stock price volatility
| | 90 – 91% | | 97 – 98% | | 90 – 97% | | 97 – 98% | Expected option term
| | 6.0 Years | | 6.0 Years | | 6.0 Years | | 6.0 Years | Risk-free interest rate
| | 2.7 – 3.6% | | 1.2 – 1.3% | | 1.7 – 3.6% | | 0.8 – 1.3% | Expected dividend yield
| | None | | None | | None | | None |
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