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Stock-Based Compensation | 12 Months Ended
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Dec. 31, 2025
Share-Based Payment Arrangement [Abstract] |
Stock-Based Compensation | 9. Stock-Based Compensation 2021 Equity Incentive Plan and 2021 Employee Stock Purchase Plan In January 2021, the Company’s board of directors adopted the 2021 Equity Incentive Plan (the “2021 Plan”) and the Company’s stockholders approved the 2021 Plan. The 2021 Plan authorized issuance of up to 403,750 shares of common stock and it became effective upon the execution of the underwriting agreement for the Company’s IPO. In addition, the number of shares of common stock reserved for issuance under the 2021 Plan automatically increases on the first day of January of each calendar year that commences after the 2021 Plan became effective and continuing through and including January 1, 2031, in an amount equal to 5% of the total number of shares of the Company’s common stock outstanding on December 31, or a lesser number of shares determined by the Company's board of directors or compensation committee. As a result, common stock reserved for issuance under the 2021 Plan was increased by 95,849 shares on January 1, 2025. In connection with the workforce reduction described in Note 7 “Restructuring”, the Company entered into consulting agreements with certain officers of the Company, pursuant to which a total of 80,785 stock options previously granted to the officers were canceled on July 15, 2024. In addition, in January 2021, the Company’s board of directors and stockholders adopted the 2021 Employee Stock Purchase Plan (the “ESPP”). The ESPP authorized issuance of up to 21,000 shares of common stock and it became effective upon the execution of the underwriting agreement for the Company’s IPO. The ESPP permits participants to purchase common stock through payroll deductions of up to 15% of their eligible compensation. Employees purchase shares of common stock at a price per share equal to 85% of the lower of the fair market value at the start or end of six-month purchase periods within the two-year offering period. In addition, the number of shares of common stock reserved for issuance under the ESPP automatically increases on January 1 of each calendar year that commences after the ESPP became effective and continuing through and including January 1, 2031, by the lesser of (1) 1% of the total number of shares of the Company's common stock outstanding on December 31 of the preceding calendar year, (2) 42,000 shares, and (3) a number of shares determined by the Company's board of directors. As a result, common stock reserved for issuance under the 2021 ESPP was increased by 19,169 shares on January 1, 2025. During the years ended December 31, 2025 and 2024, 3,623 and 9,161 shares were issued under the ESPP, respectively. Performance and Service-Based Stock Options In September 2020, the compensation committee of the Company’s board of directors granted 26,300 options to employees that would commence vesting upon the closing of the Series C-2 financing and generally vest monthly over 48 months (the “Performance Awards”). The Company recognizes expense based on the fair value of the Performance Awards over the estimated service period (under the graded vesting method) to the extent the achievement of the related performance criteria is estimated to be probable. The Company determined that the financing milestone was achieved during January 2021. Accordingly, the Company recognized stock-based compensation expenses related to the Performance Awards of approximately zero and $35,000 for the years ended December 31, 2025 and 2024, respectively. The weighted-average grant date fair value of the Performance Awards was $64.80 per share. The following table summarizes the stock option activity during the year ended December 31, 2025:
|  | Options Outstanding |  |  | Weighted-average Exercise Price |  |  | Weighted-average Remaining Contractual Term (in years) |  |  | Weighted-average Grant Date Fair Value |  |  | Aggregate Intrinsic Value (in thousands) |
Outstanding at December 31, 2024 |  |  | 571,308 |  |  | $ | 50.09 |  |  |  | 5.7 |  |  |  |  |  | $ | — |
Granted |  |  | 130,963 |  |  | $ | 6.95 |  |  |  |  |  | $ | 5.14 |  |  |  |
Exercised |  |  | — |  |  |  |  |  |  |  |  |  |  |  |  |
Canceled/forfeited |  |  | (242,496 | ) |  | $ | 36.84 |  |  |  |  |  |  |  |  |  |
Outstanding at December 31, 2025 |  |  | 459,775 |  |  | $ | 6.93 |  |  |  | 6.1 |  |  |  |  |  | $ | 12 |
Exercisable at December 31, 2025 |  |  | 354,334 |  |  | $ | 7.37 |  |  |  | 5.2 |  |  |  |  |  | $ | 9 |
Vested or expected to vest at December 31, 2025 |  |  | 459,775 |  |  | $ | 6.93 |  |  |  | 6.1 |  |  |  |  |  | $ | 12 |
The intrinsic value of options exercised was zero for both years ended December 31, 2025 and 2024, respectively. As of December 31, 2025, there was approximately $0.8 million of unrecognized stock-based compensation related to unvested stock options, which the Company expects to recognize over a weighted-average period of 1.8 years. The fair value of each option grant was estimated on the date of grant using the Black-Scholes option-pricing model with the following assumptions:
| Years Ended December 31,
| 2025 |  |  | 2024
Expected volatility |  | 87-91 |  | % | 98-105 |  | %
Risk-free interest rate |  | 3.8-4.2 |  | % | 3.7-4.7 |  | %
Expected option life (in years) |  | 5.2-6.1 |  |  | 5.2-6.1 |  |
Expected dividend yield |  |  | — |  | % |  | — |  | %
Fair value per share of common stock |  | $5.44 - $9.76 |  |  | $11.22-$25.40 |  |
Expected Term–The expected term of options granted represents the period of time that the options are expected to be outstanding. Due to the lack of historical exercise history, the expected term of the Company’s employee stock options has been determined utilizing the simplified method for awards that qualify as plain-vanilla options, which use the midpoint between the vesting date and the expiration date of each option. Expected Volatility–The estimated volatility was based on the historical volatility of the common stock of a group of publicly traded companies deemed comparable to the Company. Risk-Free Interest Rate–The risk-free interest rate is the implied yield in effect at the time of the option grant based on U.S. Treasury securities with contract maturities equal to the expected term of the Company’s stock options. Dividend Rate–The Company has not paid any cash dividends on common stock since inception and does not anticipate paying any dividends in the foreseeable future. Consequently, an expected dividend yield of zero was used. Fair Value of Common Stock– The fair value of the Company’s common stock is determined by the closing price, on the date of grant, of its common stock, which is traded on the Nasdaq Capital Market. Stock-Based Compensation Expense The following table summarizes the components of stock-based compensation expense recognized in the Company’s statement of operations and comprehensive loss (in thousands):
|  | Years Ended December 31, |
|  | 2025 |  |  | 2024 |
Research and development |  | $ | 1,162 |  |  | $ | 3,152 |
General and administrative |  |  | 1,620 |  |  |  | 4,255 |
Total |  | $ | 2,782 |  |  | $ | 7,407 |
Repricing of Stock Options On December 12, 2025, the Board of Directors of the Company approved amendments to certain outstanding stock options to purchase shares of the Company’s common stock to reduce the per-share exercise price of such options to the closing price of the Company’s common stock on the Nasdaq Capital Market on December 12, 2025, which was $5.44 (the “Repricing”). The Repricing applied to (i) outstanding stock options granted under the Company’s 2015 Equity Incentive Plan that were held by eligible employees and service providers who affirmatively consented to the Repricing and (ii) outstanding stock options granted under the Company’s 2021 Equity Incentive Plan, which were repriced without requiring participant consent (collectively, the “Eligible Options”). The Eligible Options included options held by certain executive officers and non-employee directors. Only options with an exercise price per share greater than $5.44 immediately prior to the Repricing were eligible to participate. Except as described below, the Eligible Options remain subject to their original terms and conditions following the Repricing, including the number of shares underlying the options, vesting schedules and expiration dates. With respect to Eligible Options that were incentive stock options (“ISOs”), the Repricing resulted in the following consequences under U.S. federal income tax rules governing ISOs: (i) the two-year holding period for ISO qualification restarted on the date of the Repricing, and (ii) the $100,000 annual ISO exercisability limitation was recalculated as of the Repricing Date. To the extent the aggregate fair market value of shares underlying ISOs that first become exercisable in any calendar year exceeds $100,000 (determined based on the applicable exercise prices), the portion of such options in excess of the limit will be treated as non-statutory stock options. As of the date of the Repricing, the total number of shares underlying all Eligible Options was approximately 438,000 shares. For the year ended December 31, 2025, the Company recognized incremental stock-based compensation expense totaling $0.5 million associated with the Repricing, which is included in research and development and general and administrative expense on the statement of operations. The change was treated as a modification under ASC 718, Stock Compensation, in which the fair value of the Eligible Options was remeasured at the modification date and compared to the fair value of the modified award immediately prior to the modification, with the difference resulting in incremental stock-based compensation expense. The incremental stock-based compensation expense was calculated using the Black-Scholes option-pricing model. Restricted Stock Units In December 2021, the Company issued 16,800 restricted stock units ("RSUs") under the 2021 Plan at a grant date fair value of $90.20 per share. These RSUs vested in equal quarterly installments over three years, subject to the employee's continued employment with, or services to, the Company on each vesting date. Each RSU represented the right to receive one share of the Company's common stock if the applicable vesting conditions were satisfied. As of December 31, 2024, all such RSUs had vested and the shares thereunder issued. In October 2025, the Company issued 249,500 RSUs under the 2021 Plan at a grant date fair value of $5.61 per share. These RSUs vest on September 15, 2026, subject to the employee's continued employment with, or services to, the Company on the vesting date. Each RSU represents the right to receive one share of the Company's common stock when and if the applicable vesting conditions are satisfied. The following table summarizes the activity of the restricted stock units during the year ended December 31, 2025:
|  | RSU Outstanding |  |  | Weighted-average Grant Date Fair Value |
Outstanding at December 31, 2024 |  |  | — |  |  | $ | — |
Granted |  |  | 249,500 |  |  | $ | 5.61 |
Vested |  |  | — |  |  | $ | — |
Canceled/forfeited |  |  | — |  |  | $ | — |
Outstanding at December 31, 2025 |  |  | 249,500 |  |  | $ | 5.61 |
The intrinsic value of RSUs was $1.4 million and zero during years ended December 31, 2025 and 2024, respectively. As of December 31, 2025, total unrecognized stock-based compensation expense relating to unvested restricted stock units was $1.1 million and the weighted-average remaining vesting period was 0.7 years. As of December 31, 2025, 249,500 RSUs were unvested and outstanding.

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