The Company has outstanding awards under its 2016 Stock Incentive Plan, as amended (the “2016 Plan”), but is no longer granting awards under this plan. The Company’s 2021 Stock Incentive Plan (the “2021 Plan” and, together with the 2016 Plan, the “Plans”) allows the Company to make equity-based and cash-based incentive awards to officers, employees, directors and consultants. The number of shares initially reserved under the 2021 Plan was 3,119,514 shares of the Company’s common stock. Additionally, shares of the Company’s common stock subject to outstanding awards under the 2016 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right will be added back to the shares of common stock available for issuance under the 2021 Plan. The 2021 Plan contains an “evergreen” provision, which allows for an annual increase in the number of shares of common stock available for issuance under the 2021 Plan on the first day of each fiscal year during the period beginning in fiscal year 2022. The annual increase in the number of

shares shall be equal to 4% of the number of shares of common stock outstanding on the immediately preceding December 31, or such lesser number of shares as determined by the Administrator as provided in the 2021 Plan. There was no increase to the shares available for issuance under the 2021 Plan on January 1, 2025. As of June 30, 2025, 6,098,984 shares of common stock remain available for future issuance under the 2021 Plan.

The vesting periods for equity awards, which generally are four years, are determined by the Company’s board of directors. The contractual term for stock option awards is ten years.

The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2025		2024		2025		2024
Research and development	$	45	$	400	$	192	$	1,177
General and administrative		413		879		994		1,840
Restructuring and other charges		—		—		176		263
Total	$	458	$	1,279	$	1,362	$	3,280

As of June 30, 2025, the total unrecognized stock-based compensation balance for outstanding awards was $1.8 million, which is expected to be recognized over a weighted average period of 1.8 years.

The following table summarizes stock option activity for the six months ended June 30, 2025:


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value (thousands)
Outstanding as of December 31, 2024		7,678,058		$	5.02		6.25	$	426
Granted		—			—
Exercised		—			—
Cancelled or forfeited		(1,345,202	)		7.74
Outstanding as of June 30, 2025		6,332,856		$	4.44		6.69	$	22
Vested or expected to vest as of June 30, 2025		6,332,856		$	4.44		6.69	$	22
Options exercisable as of June 30, 2025		4,514,738		$	5.30		6.01	$	22

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. No options were exercised during the three or six months ended June 30, 2025 or 2024.

The fair value of each option award granted is estimated on the date of grant using the Black-Scholes option pricing model and assumptions input into the model. The following table presents, on a weighted average basis, the assumptions used in the model to determine the grant-date fair value of stock options granted:


	Three Months Ended June 30, 2024			Six Months Ended June 30, 2024

Risk-free interest rate		4.43	%		4.19	%
Expected dividend yield		0	%		0	%
Expected option term (in years)	5.58			6.01
Expected stock price volatility		94.04	%		91.32	%

No stock options were granted during the three or six months ended June 30, 2025. The weighted-average grant date fair value of the stock options granted during the six months ended June 30, 2024 was $1.10 per share.