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Equity Incentive Plans | 12 Months Ended
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Dec. 31, 2024
Share-Based Payment Arrangement [Abstract] |
Equity Incentive Plans | Equity Incentive Plans 2023 Equity Inducement Incentive Plan In November 2023, the Company approved the 2023 Employment Inducement Incentive Plan (the "2023 Inducement Plan"). The terms of the 2023 Inducement Plan are substantially similar to the terms of the Company’s 2019 Incentive Award Plan (as described below) with the exception that incentive stock options may not be issued under the 2023 Inducement Plan and awards under the 2023 Inducement Plan may only be issued to eligible recipients under the applicable Nasdaq rules. The 2023 Inducement Plan was adopted without stockholder approval pursuant to Rule 5635(c)(4) of the Nasdaq Listing Rules. In accordance with Rule 5635(c)(4) of the Nasdaq Listing Rules, awards under the 2023 Inducement Plan may only be made to an employee who has not previously been an employee or member of the board of directors of the Company or any parent or subsidiary, or following a bona fide period of non-employment by the Company or a parent or subsidiary, if he or she is granted such award in connection with his or her commencement of employment with the Company or a subsidiary and such grant is an inducement material to his or her entering into employment with the Company or such subsidiary. The Company has initially reserved 6,762,279 shares of the Company’s common stock for issuance pursuant to awards granted under the 2023 Inducement Plan. As of December 31, 2024, an aggregate of 4,152,779 shares of common stock were available for issuance under the 2023 Inducement Plan, and 2,609,500 shares of common stock were subject to outstanding awards under the 2023 Inducement Plan. 2019 Equity Incentive Plan In January 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Incentive Award Plan (the “2019 Plan”). The 2019 Plan became effective on February 6, 2019, the day prior to the effectiveness of the registration statement filed in connection with the IPO. Under the 2019 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units, and other stock or cash-based awards to individuals who are then employees, officers, directors or consultants of the Company, and employees and consultants of the Company’s subsidiaries. A total of 5,750,000 shares of common stock were approved to be initially reserved for issuance under the 2019 Plan. The number of shares that remained available for issuance under the 2017 Plan (as defined below) as of the effective date of the 2019 Plan were, and shares subject to outstanding awards under the 2017 Plan as of the effective date of the 2019 Plan that are subsequently canceled, forfeited or repurchased by the Company will be added to the shares reserved under the 2019 Plan. In addition, the number of shares of common stock available for issuance under the 2019 Plan will be automatically increased on the first day of each calendar year during the ten-year term of the 2019 Plan, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 5% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. As of December 31, 2024, an aggregate of 2,308,197 shares of common stock were available for issuance under the 2019 Plan and 29,747,623 shares of common stock were subject to outstanding awards under the 2019 Plan. 2019 Employee Stock Purchase Plan In January 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Employee Stock Purchase Plan (the "ESPP"). The ESPP became effective as of February 6, 2019, the day prior to the effectiveness of the registration statement filed in connection with the IPO. The ESPP permits participants to purchase common stock through payroll deductions of up to 20% of their eligible compensation. A total of 700,000 shares of common stock were approved to be initially reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP will be automatically increased on the first day of each calendar year during the first ten-years of the term of the ESPP, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 1% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. During the years ended December 31, 2024 and 2023, 767,125 shares and 336,795 shares were issued pursuant to the ESPP, respectively. As of December 31, 2024, an aggregate of 4,545,812 shares of common stock were available for issuance under the ESPP. 2017 Equity Incentive Plan The Company’s 2017 Equity Incentive Plan (the “2017 Plan”) permitted the granting of incentive stock options, non-statutory stock options, restricted stock, restricted stock units and other stock-based awards. Subsequent to the adoption of the 2019 Plan, no additional equity awards can be made under the 2017 Plan. As of December 31, 2024, 2,059,214 shares of common stock were subject to outstanding options under the 2017 Plan, and no shares of restricted stock awards granted under the 2017 Plan were unvested. Stock Options The fair value of each employee and non-employee time-vested stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company uses its own volatility to the extent it has sufficient trading history, and for awards in which sufficient trading history is not available, a peer group is used to calculate the expected volatility. Due to the lack of historical exercise history, the expected term of the Company’s stock options for employees has been determined utilizing the “simplified” method for awards. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. On May 5, 2023, the Company granted to its Chairman and Chief Executive Officer 750,000 options with an exercise price of $1.36 per share. This grant contains both service and market based vesting conditions. The awards vest on the later of the date of achievement and the one-year anniversary of the grant date. The market condition becomes satisfied in 50%, 25% and 25% tranches upon achieving the average per-share closing price of the Company's common stock over any 30 consecutive calendar days following the grant date equal to or exceeding $5.00, $7.50 and $10.00, respectively. In the event a stock price tranche has not vested prior to the fourth anniversary of the grant date, any portion of the option attributable to such tranche will be forfeited. Due to the market condition included in this grant, the Company used the Geometric Brownian Motion/Monte Carlo model to value this award. The total stock-based compensation expense related to this award is $0.4 million, which is included in general and administrative expense on the consolidated statements of operations and comprehensive loss. The Company expects to recognize this expense over a weighted average period of approximately 2.2 years. Effective May 5, 2023, and in accordance with the terms of the 2019 Plan, the Company's board of directors approved a stock option repricing (the “Option Repricing”) whereby the exercise price of each Eligible Option (as defined below) was immediately reduced to $1.36 per share, the closing stock price on May 5, 2023. For purposes of the Option Repricing, “Eligible Options” are 6,817,057 outstanding stock options as of May 5, 2023 (vested or unvested) granted under the 2019 Plan prior to November 30, 2022 and held by those eligible employees of the Company identified by the Company's board of directors, including the Company’s executive officers, except for the Company’s Chairman and Chief Executive Officer. The participation of the executive officers of the Company in the Option Repricing was subject to their agreement to cancel a portion of their Eligible Options effective immediately (the “Cancelled Options”). Each executive was required to agree to cancel one-third of his or her Eligible Options, on a grant-by-grant basis. The Cancelled Options were deducted proportionately from the vested and unvested portions of each Repriced Option grant. To the extent an Eligible Option is exercised prior to the Premium End Date (as defined below), or the eligible employee’s employment terminates prior to the Premium End Date, the eligible employee will be required to pay the original exercise price per share of the Eligible Options in connection with any exercise of the Eligible Option. The “Premium End Date” means the earliest of (i) May 5, 2024, (ii) the date of a change in control, (iii) the eligible employee’s death or disability, or (iv) if an eligible employee is an executive subject to the cancellation of a portion of Eligible Options and is terminated under circumstances giving rise to severance under his or her employment agreement, the date of such termination. Except for the reduction in the exercise prices of the Eligible Options as described above, the Eligible Options will retain their existing terms and conditions as set forth in the 2019 Plan and the applicable award agreements. The repricing resulted in $3.4 million of incremental cost, which was calculated using the Black-Scholes option-pricing model, of which $2.0 million of the incremental cost was recognized immediately, and $1.4 million of the incremental cost will be recognized on the straight-line basis over the remaining vesting period of the repriced options. The incremental cost is included in general and administrative expense and research and development expense on the consolidated statements of operations and comprehensive loss. The following assumptions were used to estimate the fair value of stock option awards granted to employees under the Company’s equity incentive plans and the shares purchasable under the ESPP during the periods presented:
| Year Ended December 31,
| 2024 |  | 2023 |  | 2022
Employee Stock Options |  |  |  |  |
Expected term (in years) | 4.6 - 6.1 |  | 1.0 - 7.0 |  | 4.4 - 6.1
Risk-free interest rate | 3.59% - 4.50% |  | 3.36% - 4.73% |  | 1.31% - 4.35%
Volatility | 100.72% - 104.51% |  | 70.01% - 170.69% |  | 71.10% - 89.87%
Dividend yield | — |  | — |  | —
Employee Stock Purchase Plan |  |  |  |  |
Expected term (in years) | 0.5 - 2.0 |  | 0.5 - 2.0 |  | 0.5 - 2.0
Risk-free interest rate | 3.88% -5.27% |  | 4.87% - 5.47% |  | 0.60% - 3.51%
Volatility | 83.96% - 151.54% |  | 115.19% - 216.45% |  | 64.98% - 121.43%
Dividend yield | — |  | — |  | —
The following table summarizes stock option activity for the years ended December 31, 2024, 2023 and 2022:
| Shares Subject to Options Outstanding |  | Weighted- Average Remaining Contractual Life (Years) |  | Aggregate Intrinsic Value
| Shares |  | Weighted- Average Exercise Price |  |
|  |  |  |  |  |  | (in thousands)
Outstanding as of December 31, 2021 | 9,434,660 |  |  | $ | 12.24 |  |  | 7.4 |  | $ | 15,822 |
Options granted | 9,271,272 |  |  | $ | 6.75 |  |  |  |  |
Options exercised | (270,707) |  |  | $ | 6.41 |  |  |  |  |
Options forfeited/cancelled | (948,060) |  |  | $ | 15.69 |  |  |  |  |
Outstanding as of December 31, 2022 | 17,487,165 |  |  | $ | 9.24 |  |  | 8.1 |  | $ | 47 |
Options granted | 17,159,617 |  |  | $ | 1.16 |  |  |  |  |
Options exercised | — |  |  | $ | — |  |  |  |  |
Options forfeited/cancelled | (11,020,667) |  |  | $ | 11.07 |  |  |  |  |
Outstanding as of December 31, 2023 | 23,626,115 |  |  | $ | 2.52 |  |  | 7.9 |  | $ | 369 |
Options granted | 13,006,228 |  |  | $ | 0.96 |  |  |  |  |
Options exercised | — |  |  | $ | — |  |  |  |  |
Options forfeited/cancelled | (2,216,006) |  |  | $ | 2.25 |  |  |  |  |
Outstanding as of December 31, 2024 | 34,416,337 |  |  | $ | 1.95 |  |  | 7.5 |  | $ | 598 |
Options vested and expected to vest as of December 31, 2024 | 34,416,337 |  |  | $ | 1.95 |  |  | 7.5 |  | $ | 598 |
Options exercisable as of December 31, 2024 | 14,126,062 |  |  | $ | 3.20 |  |  | 6.1 |  | $ | 100 |
The weighted-average grant date fair value per share for the stock options granted during the year ended December 31, 2024, 2023 and 2022 was $0.78, $3.88 and $4.77, respectively. The aggregate fair value of stock options that vested during the years ended December 31, 2024, 2023 and 2022 was $15.7 million, $22.7 million and $20.7 million, respectively. The aggregate intrinsic value in the above table is calculated as the difference between fair value of the Company’s common stock price and the exercise price of the stock options. There were no options exercised during the years ended December 31, 2024 and 2023. The aggregate intrinsic value of stock options exercised during the year ended December 31, 2022 was $1.5 million. Warrants On July 24, 2023, the Company completed a private placement of 129,869,440 shares of the Company’s common stock and accompanying warrants to purchase up to 32,467,360 shares of the Company's common stock at a combined purchase price of $1.63125 per share and accompanying warrant, or with respect to any purchaser that was an officer, director, employee or consultant of the Company, $1.85125 per share and accompanying warrant. Each warrant has an exercise price per share of $2.04, was immediately exercisable on the date of issuance and will expire five years from the closing of the private placement. Given that the warrants are indexed to the Company's shares of common stock (and otherwise meet the requirements to be classified in equity), the Company recorded the consideration received from the issuance of the warrants as additional paid-in capital on the Company's consolidated balance sheets. As of December 31, 2024, there were 32,467,360 warrants outstanding. Restricted Stock The summary of the Company’s restricted stock activity during the years ended December 31, 2024, 2023 and 2022 is as follows:
| Number of Restricted Stock Units Outstanding |  | Weighted- Average Grant Date Fair Value
Nonvested at December 31, 2021 | 2,561,219 |  |  | $ | 8.67 |
Granted | 572,901 |  |  | 11.94 |
Vested | (1,592,588) |  |  | 7.78 |
Forfeited / cancelled | (191,497) |  |  | 10.68 |
Nonvested at December 31, 2022 | 1,350,035 |  |  | $ | 10.83 |
Granted | — |  |  | — |
Vested | (779,900) |  |  | 10.67 |
Forfeited / cancelled | (142,437) |  |  | 11.39 |
Nonvested at December 31, 2023 | 427,698 |  |  | $ | 10.92 |
Granted | — |  |  | — |
Vested | (427,698) |  |  | 10.92 |
Forfeited / cancelled | — |  |  | — |
Nonvested at December 31, 2024 | — |  |  | $ | — |
As of December 31, 2024, there was no unrecognized stock-based compensation expense related to the unvested restricted stock awards. Stock-Based Compensation Expense Stock-based compensation expense has been reported in the Company’s consolidated statements of operations and comprehensive loss as follows (in thousands):
| Year Ended December 31,
| 2024 |  | 2023 |  | 2022
Research and development | $ | 10,172 |  |  | $ | 15,871 |  |  | $ | 24,415 |
General and administrative | 10,447 |  |  | 12,647 |  |  | 18,138 |
Total stock-based compensation expense | $ | 20,619 |  |  | $ | 28,518 |  |  | $ | 42,553 |
At December 31, 2024, the total unrecognized compensation related to unvested stock option awards granted was $14.0 million, which the Company expects to recognize over a weighted-average period of approximately 2.6 years. As of December 31, 2024, total unrecognized compensation expense related to the ESPP was $0.8 million, which the Company expects to recognize over a weighted-average period of approximately 0.8 years.

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