In June 2025, our stockholders approved an amendment to our Amended and Restated 2019 Equity Incentive Plan (the "2019 EIP") that increased the maximum number of shares of our common stock available for issuance under our 2019 EIP by 7.0 million shares.

We primarily use the Black-Scholes option pricing model to value stock options granted to employees and non-employees, including stock options granted to members of our Board of Directors. However, the fair value of stock option market-based awards is calculated based on a Monte Carlo simulation as of the date of issuance. All stock options have 10-year terms and generally vest ratably over a 3 or 4-year period.

A summary of option activity for the six months ended June 30, 2025 is presented below:


	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2024		5,242,916		$	28.76
Granted		495,564			3.05
Exercised		—			—
Forfeited		(242,539	)		10.45
Expired		(253,738	)		56.68
Outstanding at June 30, 2025		5,242,203		$	25.76		7.83	$	4,044,166
Vested or expected to vest at June 30, 2025		5,242,203		$	25.76		7.83	$	4,044,166
Exercisable at June 30, 2025		2,741,527		$	43.79		6.54	$	317,505

The weighted average grant-date fair values of stock options granted during the six months ended June 30, 2025 and 2024 were $2.90 and $11.53, respectively.

During the six months ended June 30, 2025, all options were granted with exercise prices equal to the market value of the underlying shares of common stock on the grant date other than certain awards dated June 18, 2025. In May 2025, our Board of Directors approved certain awards subject to forfeiture in the event stockholder approval was not obtained for an amendment to our 2019 EIP. This approval was obtained in June 2025. Accordingly, these awards have a grant date of June 2025, with an exercise price as of the date the Board of Director's approved the awards in May 2025.

As of June 30, 2025, there was approximately $8.6 million of total unrecognized share-based compensation expense related to these stock options and stock options granted under subsidiary plans which, if all milestones are achieved, will be recognized over a weighted average period of 1.2 years.

Certain employees and consultants have been granted non-vested stock. The fair value of non-vested market-based awards is calculated based on a Monte Carlo simulation as of the date of issuance. The fair value of other non-vested stock is calculated based on the closing sale price of our common stock on the date of issuance.

A summary of non-vested stock activity for the six months ended June 30, 2025 is presented below:


	Non-vested Shares			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2024		42,222		$	17.30
Granted		1,598,322			4.30
Vested		(316,728	)		3.97
Forfeited		(10,598	)		22.53
Outstanding at June 30, 2025		1,313,218		$	4.65

As of June 30, 2025, there was approximately $1.2 million of unrecognized share-based compensation expense related to these non-vested shares and non-vested shares granted under subsidiary plans which will be recognized over a period of 2.4 years.

During the six months ended June 30, 2025, 18,365 shares were issued under the 2019 Employee Stock Purchase Plan and 94,340 shares were issued as a result of the vesting of non-vested stock.

The impact on our results of operations from share-based compensation for the three and six months ended June 30, 2025 and 2024, was as follows (in thousands):


	Three Months Ended June 30,				Six Months Ended June 30,
	2025		2024		2025		2024
Research and development	$	778	$	4,722	$	1,604	$	6,036
General and administrative		2,663		4,568		5,170		7,450
Total share-based compensation expense	$	3,441	$	9,290	$	6,774	$	13,486