On April 10, 2019, our Board of Directors adopted, and on June 19, 2019, our stockholders approved, our 2019 Equity Incentive Plan (the “2019 EIP”). On June 11, 2024, June 8, 2022 and June 15, 2021, our stockholders approved amendments to the 2019 EIP, increasing the number of shares available for issuance. The 2019 EIP provides for the grant of incentive stock options intended to qualify under Section 422 of the Code, nonstatutory stock options, restricted stock, unrestricted stock and other equity-based awards, such as stock appreciation rights, phantom stock awards, and restricted stock units, which we refer to collectively as Awards, for up to 6.5 million shares of our common stock (subject to adjustment in the event of stock splits and other similar events).

The Board of Directors appointed the Compensation Committee to administer the 2019 EIP. No awards will be granted under the 2019 EIP after June 19, 2029.

In the second quarter of 2019, our Board of Directors adopted, and on June 16, 2020, our stockholders approved the 2019 Employee Stock Purchase Plan (the “2019 ESPP”) to provide eligible employees the opportunity to acquire our common stock in a program designed to comply with Section 423 of the Code. On June 12, 2023 and June 15, 2021, our stockholders approved

amendments to the 2019 ESPP, increasing the number of shares available for issuance. There are 0.1 million shares reserved for issuance under the 2019 ESPP.

Our Directors’ Deferred Compensation Plan, as amended, permits each outside director to defer all, or a portion of, their cash compensation until their service as a director ends or until a specified date into a cash account or a stock account. On June 11, 2024 and June 8, 2022, our stockholders approved amendments to this plan, increasing the number of shares available for issuance. There are 63,750 shares of our common stock reserved for issuance under this plan. As of December 31, 2024, 16,363 shares had been issued. Amounts deferred to a cash account will earn interest at the rate paid on one-year Treasury bills with interest added to the account annually. Amounts deferred to a stock account will be converted on a quarterly basis into a number of units representing shares of our common stock equal to the amount of compensation which the participant has elected to defer to the stock account divided by the applicable price for our common stock. The applicable price for our common stock has been defined as the average of the closing price of our common stock for all trading days during the calendar quarter preceding the conversion date as reported by The Nasdaq Capital Market. Pursuant to this plan, a total of 63,750 units, each representing a share of our common stock at a weighted average common stock price of $46.74, had been credited to participants’ stock accounts as of December 31, 2024. The compensation charges for this plan were immaterial for all periods presented.

On November 4, 2015, our Board of Directors adopted and approved our 2015 Inducement Equity Plan (the “2015 IEP”) in compliance with and in reliance on Nasdaq Listing Rule 5635(c)(4), which exempts inducement grants from the general requirement of the Nasdaq Listing Rules that equity-based compensation plans and arrangements be approved by stockholders. In October 2023, our Board of Directors approved an increase to the number of shares available for issuance. There are 175,000 shares of our common stock reserved for issuance under the 2015 IEP.

We primarily use the Black-Scholes option pricing model to value options granted to employees and non-employees, as well as options granted to members of our Board of Directors. All stock option grants have 10-year terms and generally vest ratably over a 3 or 4-year period.

The fair value of each option granted during the periods was estimated on the date of grant using the following weighted average assumptions:


	2024			2023			2022
Expected volatility		86	%		72	%		68	%
Expected term in years		6			6			6
Risk-free interest rate		3.8	%		3.3	%		1.8	%
Dividend yield		0	%		0	%		0	%

Expected volatility is based exclusively on historical volatility data of our common stock. The expected term of stock options granted is based on historical data and other factors and represents the period of time that stock options are expected to be outstanding prior to exercise. The risk-free interest rate is based on U.S. Treasury strips with maturities that match the expected term on the date of grant.

A summary of option activity for 2024 is presented below:


	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2023		2,141,360		$	65.00
Granted		3,334,887			6.91
Exercised		(16,668	)		12.26
Forfeited		(93,758	)		26.87
Expired		(122,905	)		63.56
Outstanding at December 31, 2024		5,242,916			28.76		8.06	$	—
Vested or expected to vest at December 31, 2024		5,242,916			28.76		8.06	$	—
Exercisable at December 31, 2024		2,534,682		$	50.07		6.52	$	—

The weighted average grant-date fair values of options granted during the years ended December 31, 2024, 2023, and 2022, was $10.75, $28.20, and $35.00, respectively.

The aggregate intrinsic value in the table above represents the difference between our closing stock price on the last trading day of fiscal 2024 and the exercise price, multiplied by the number of in-the-money options that would have been received by the option holders had all option holders exercised their options on December 31, 2024 (the intrinsic value is considered to be zero if the exercise price is greater than the closing stock price). This amount changes based on the fair market value of our stock. The total intrinsic value of options exercised during the years ended December 31, 2024, 2023, and 2022, determined on the dates of exercise, was $64,000, $13,000, and $70,000, respectively.

During 2024, 2023, and 2022, 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 January 16, 2024 and January 17, 2024. In January 2024, 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 2024. Accordingly, these awards have a grant date of June 2024, with an exercise price as of the date the Board of Director's approved the awards in January 2024.

As of December 31, 2024, there was $13.1 million of unrecognized share-based compensation expense related to these stock options and stock options granted under a subsidiary plan which, if all milestones are achieved, will be recognized over a weighted average period of 1.4 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 2024 is presented below:


	Nonvested Shares			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2023		27,163		$	37.20
Granted		48,561			11.96
Vested		(17,002	)		29.11
Forfeited		(16,500	)		21.82
Outstanding at December 31, 2024		42,222		$	17.30

As of December 31, 2024, there was $1.1 million of unrecognized share-based compensation expense related to these non-vested shares and non-vested shares granted under a subsidiary plan which will be recognized over a weighted average period of 3.1 years. The total intrinsic value of shares vested during the years ended December 31, 2024, 2023, and 2022, was $0.2 million, $11.5 million, and $10.9 million, respectively.

Cash received from option exercises and purchases under our 2019 ESPP for the years ended December 31, 2024, 2023, and 2022, was $0.6 million, $0.8 million, and $0.9 million, respectively.

We issue new shares upon option exercises, purchases under our 2019 ESPP, vesting of non-vested stock and under the Directors’ Deferred Compensation Plan. During the years ended December 31, 2024, 2023, and 2022, 16,668 shares, 2,337 shares, and 5,166 shares, respectively, were issued as a result of stock option exercises. During the years ended December 31, 2024, 2023, and 2022, 30,637 shares, 22,469 shares, and 16,310 shares, were issued under the 2019 ESPP, respectively. During the years ended December 31, 2024, 2023, and 2022, 17,002 shares, 4,804 shares, and 11,524 shares, respectively, were issued as a result of the vesting of non-vested stock. Additionally, during the years ended December 31, 2023, and 2022, 232,190 shares and 204,504 shares were issued as payment for certain employee bonuses, with 83,438 and 72,342 of those shares being withheld to cover taxes, resulting in a net share issuance of 148,752 and 132,162, respectively.

The impact on our results of operations from share-based compensation for the years ended December 31, 2024, 2023, and 2022, was as follows (in thousands).


	Year Ended
	2024		2023		2022
Research and development	$	11,998	$	6,237	$	4,847
General and administrative		15,329		16,114		13,391
Total share-based compensation expense	$	27,327	$	22,351	$	18,238