As of March 31, 2025, the Company had five equity compensation plans, each of which was approved by its stockholders: 2006 Equity Incentive Plan, as amended, or the 2006 Plan, 2016 Stock Incentive Plan, or the 2016 Plan, 2017 Stock Incentive Plan, or the 2017 Plan, 2021 Stock Incentive Plan, or the 2021 Plan, and 2017 Employee Stock Purchase Plan, or the 2017 ESPP. The Company also assumed Lung’s 2013 Long-Term Incentive Plan, or the 2013 Plan, as a result of the Lung Acquisition.

As of March 31, 2025, the Company had no shares issuable upon exercise of outstanding options under the 2006 Plan; 8,404 shares to be issued upon exercise of outstanding options under the 2016 Plan, 98,528 shares to be issued upon exercise of outstanding options under the 2017 Plan and 1,432,679 shares to be issued upon exercise of outstanding options under the 2021 Plan. No shares remained available for future awards under the 2006 Plan, the 2016 Plan, and the 2017 Plan as of March 31, 2025.

Under the 2021 Plan, shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards.

The exercise price for stock options granted may not be less than the fair market value of the common stock as of the date of grant.

The Company’s 2021 Plan was approved by the Company’s stockholders on June 15, 2021 and became effective on June 16, 2021. At the 2023 Annual Meeting, the stockholders of the Company approved an amendment, or the Plan Amendment, to the 2021 Plan to increase the number of shares of common stock issuable under the 2021 Plan by 3,000,000 shares to 3,840,254. Other than increasing the number of shares issuable under the 2021 Plan, the Plan Amendment does not make any changes to the 2021 Plan.

Under the 2021 Plan, the Company may grant incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, awards of restricted stock units and other stock-based awards. The Company’s employees, officers, directors, consultants and advisors are eligible to receive awards under the 2021 Plan; however, incentive stock options may only be granted to employees. The 2021 Plan is administered by the Board or, at the discretion of the Board, by a committee of the Board. The number of shares of common stock covered by options and the date those options become exercisable, type of options to be granted, exercise prices, vesting and other restrictions are determined at the discretion of the Board, or its committee if so delegated.

Stock options granted under the 2021 Plan with service-based vesting conditions generally vest over four years and may not have a duration in excess of ten years, although options have been granted with vesting terms of less than four years.

The total number of shares of common stock that may be issued under the 2021 Plan was 3,840,254 as of March 31, 2025, of which 2,389,566 shares remained available for grant. The Company initially reserved 625,000 shares of common stock, plus the number of shares of common stock subject to outstanding awards under the 2017 Plan, the 2016 Plan and the 2006 Plan that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right up to 314,006 shares. As of March 31, 2025, the Company had 1,432,679 shares to be issued upon exercise of outstanding options under the 2021 Plan.

The Company assumed the 2013 Plan as a result of the Lung Acquisition. In October 2013, Lung’s Board of Directors, or the Lung Board, approved the 2013 Plan to provide long-term incentives for its employees, non-employee directors and certain consultants. As of March 31, 2025, 1,540,971 shares were reserved to be issued upon exercise of options outstanding under the 2013 Plan. These options were assumed by the Company in connection with the Lung Acquisition.

Before the Lung Acquisition, the 2013 Plan was administered by the Lung Board or, at the discretion of the Lung Board, by a committee of the Lung Board. The exercise prices, vesting and other restrictions were determined at the discretion of the Lung Board, or its committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. The contractual term for stock option awards is ten years. The vesting periods for equity awards were determined by the Lung Board, but generally were four years. The contractual term for stock option awards is ten years. Following the closing of the Lung Acquisition on October 31, 2023, no further awards can be granted under the 2013 Plan.

There were no stock options granted in the three months ended March 31, 2025. The assumptions that the Company used to determine the grant-date fair value of the stock options granted to employees and directors during the three months ended March 31, 2024 were as follows, presented on a weighted average basis:

The following table summarizes the Company’s stock option activity since January 1, 2025:


	Number of Shares			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at January 1, 2025		3,169,468		$	5.41		7.0	$	1,605
Exercised		(21,533	)		1.05		—		18
Forfeited/Canceled		(59,310	)		2.73		—		—
Expired		(8,043	)		85.03		—		—
Outstanding at March 31, 2025		3,080,582		$	5.28		6.7	$	913

Options exercisable at March 31, 2025		2,040,403		$	6.54		5.4	$	862
Options vested and expected to vest at March 31, 2025		3,040,624		$	5.32		6.7	$	910
Options exercisable at December 31, 2024		2,059,025		$	6.79		5.6	$	1,524
Options vested and expected to vest at December 31, 2024		3,120,812		$	5.45		7.0	$	1,600

There were no stock options granted in the three months ended March 31, 2025. The weighted average grant-date fair value of stock options granted during the three months ended March 31, 2024 was $3.82. The aggregate fair value of stock options that vested during the three months ended March 31, 2025 and 2024, was $46 and $228, respectively.

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. The aggregate intrinsic value of stock options exercised during the three months ended March 31, 2025 was $18. There were no stock options exercised during the three months ended March 31, 2024.

The Company recorded stock-based compensation expense related to stock options in the following expense categories of its statements of operations and comprehensive loss:


	Three Months Ended March 31,
	2025		2024
Research and development expenses	$	64	$	39
General and administrative expenses		200		111
Total stock-based compensation expense	$	264	$	150

As of March 31, 2025, the Company had an aggregate of $2,130 of unrecognized stock-based compensation expense, which it expects to recognize over a weighted average period of 3.15 years. As of March 31, 2024, the Company had an aggregate of $525 of unrecognized stock-based compensation expense, which it expects to recognize over a weighted average period of 1.65 years.