Stock-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows:


	Three Months Ended March 31,
	2025		2024
	(In thousands)
Research and development	$	12,626	$	20,161
General and administrative		9,214		14,015
Total	$	21,840	$	34,176

In April 2016, the Company adopted the Amended and Restated 2015 Stock Option and Incentive Plan (the “2015 Plan”). The 2015 Plan provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, restricted stock awards (“RSAs”), restricted stock units (“RSUs”) and other stock-based awards. Recipients of incentive stock options and non-qualified stock options are eligible to purchase shares of the Company’s common stock at an exercise price equal to the fair value of such stock on the grant date. As of March 31, 2025, there were 6,968,448 shares available for future issuance under the 2015 Plan. The number of shares reserved for issuance under the 2015 Plan are subject to cumulative increases on each January 1st by four percent of the number of shares of stock issued and outstanding on the immediately preceding December 31st or such lesser number of shares of stock as determined by the board of directors.

In June 2024, the Company adopted the 2024 Inducement Plan (the “Inducement Plan”). The Inducement Plan provides for the grant of non-qualified stock options, stock appreciation rights, RSAs, RSUs, unrestricted stock awards and dividend equivalent rights to individuals who are not employed by the Company. Recipients of non-qualified stock options are eligible to purchase shares of the Company’s common stock at an exercise price equal to the fair value of such stock on the grant date. In accordance with the Inducement Plan, 850,000 shares of common stock were reserved for future issuance; there were 312,674 shares available for future issuance under the Inducement Plan as of March 31, 2025.

The following table summarizes the Company’s RSU activity for the three months ended March 31, 2025:


	Number of Shares			Weighted Average Grant Date Fair Value per Share
Unvested restricted stock units as of December 31, 2024		5,547,530		$	39.13
Granted		2,240,207			10.67
Vested		(1,510,091	)		42.85
Cancelled		(752,172	)		43.45
Unvested restricted stock units as of March 31, 2025		5,525,474		$	25.99

The Company awards RSUs with a service condition to new employees upon hire, non-employee directors upon appointment, and to existing employees and non-employee directors as part of their annual grant. RSUs with a service condition granted to new and existing employees, and to non-employee directors upon appointment, under the 2015 Plan beginning in 2023 and the Inducement Plan since its inception, generally vest as to one-third on the first anniversary of the original vesting date, with the balance vesting annually over the remaining two years. RSUs granted to non-employee directors with a service condition as part of their annual grant generally vest on the first anniversary of the original vesting date.

In the three months ended March 31, 2025, the Company granted 2,016,607 RSUs with a service condition to new and existing employees and non-employee directors, which have the potential to vest over a period of approximately three years. The weighted average grant date fair value of these RSUs was $10.11.

Unvested restricted stock units as of March 31, 2025 in the table above includes 4,482,087 RSUs that are service-based.

Since 2022, market-based RSUs have been granted to senior executives. These RSUs have the potential to vest after a period of three years, with a vesting start date of January 1 in the year of grant, and the number of shares to be delivered will depend on the Company’s Total Shareholder Return (“TSR”), a market condition, over that period relative to a defined group of biotechnology companies. The number of market-based RSUs granted in the three months ended March 31, 2025 and 2024 was 223,600 and 235,858, respectively. The grant date fair value for the market-based RSUs, calculated using a Monte Carlo valuation model, was $15.76 and $51.12, respectively. The following assumptions were used to determine the grant date fair value for the three months ended March 31, 2025 and 2024, respectively: risk free interest rate: 3.99% and 4.28%; expected volatility: 67.6% and 77.2%. The expected term for all grants was approximately 3.0 years; the expected dividend yield was 0.0%.

Unvested restricted stock units as of March 31, 2025 in the table above includes 616,618 RSUs that are market-based.

In 2024, performance-based RSUs (“PSUs”) with a relative TSR modifier were also granted to senior executives. The number of PSUs with a relative TSR modifier granted in the year ended December 31, 2024 was 486,617. These PSUs, to the extent earned, shall vest on January 1, 2027, and the number of shares to be delivered will be determined based upon the achievement of certain performance goals, which can range from 0% to 200%. Following the determination of the achievement of performance criteria, the amount of shares awarded will be subject to adjustment based on the application of a TSR modifier, which can range from 75% to 125%. The grant date fair value for these PSUs, calculated using a Monte Carlo valuation model, was $36.16. The following assumptions were used to determine the grant date fair value: risk free interest rate: 4.28%; expected volatility: 77.2%; expected term: approximately 3.0 years; expected dividend yield: 0.0%. The Company recognizes compensation expense ratably

over the required service period based on its estimate of the number of shares that will vest based upon the probability of achieving the performance goals.

There were no PSUs with a relative TSR modifier granted in the three months ended March 31, 2025. Unvested restricted stock units as of March 31, 2025 in the table above includes 404,560 PSUs with a TSR multiplier.

In 2022, the Company granted 66,296 performance-based RSUs to certain non-executive employees that would vest upon obtaining certain scientific milestones. There were two separate tranches, each attached to a different set of milestones. The milestone related to the first tranche, made up of 21,878 RSUs, was achieved in the first quarter of 2023 and these RSUs vested. The remaining performance milestones were considered not probable of achievement as of March 31, 2025 and, therefore, no related stock-based compensation expense was recorded during the period then ending.

Unvested restricted stock units as of March 31, 2025 in the table above includes 22,209 performance-based RSUs.

The weighted-average grant date fair value of all RSUs granted during the three months ended March 31, 2025 and 2024 was $10.67 and $34.52, respectively. The total fair value of RSUs vested (measured on the date of vesting) for the three months ended March 31, 2025 and 2024 was $17.5 million and $30.9 million, respectively.

As of March 31, 2025, there was $90.0 million of unrecognized stock-based compensation expense related to all RSUs that are expected to vest. These costs are expected to be recognized over a weighted average remaining vesting period of 1.69 years.

The weighted average grant date fair value of options, estimated as of the grant date using the Black-Scholes option pricing model, was $6.92 and $22.61 per option for those options granted during the three months ended March 31, 2025 and 2024, respectively. Weighted average assumptions used to apply this pricing model were as follows:


	Three Months Ended March 31,
	2025	2024
Risk-free interest rate	4.1%	4.2%
Expected term	6.0 years	6.0 years
Expected volatility of underlying stock	75.4%	76.4%
Expected dividend yield	0.0%	0.0%

Risk-free Interest Rate. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant with maturities approximately equal to the option’s expected term.

Expected Term. The expected term represents the period that stock option awards are expected to be outstanding. For option grants that are considered to be “plain vanilla,” the Company determines the expected term using the simplified method. The simplified method deems the term to be the average of the time-to-vesting and the contractual life of the options. The Company uses the simplified method because it does not have sufficient historical option exercise data to provide a reasonable basis upon which to estimate the expected term.

Expected Volatility. Expected volatility is estimated based on actual movements in the Company’s stock price over the most recent historical periods, over the expected term of their stock option grants.

Expected Dividend Yield. The Company has not paid cash dividends and has no intention to pay cash dividends in the future.

Stock options generally vest as to one-third on the first anniversary of the original vesting date, with the balance vesting monthly over the remaining two years, unless they contain specific vesting provisions. The maximum term of stock options granted under the 2015 Plan and the Inducement Plan is ten years.

The following is a summary of stock option activity for the three months ended March 31, 2025:


	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(In years)		(In thousands)
Outstanding at December 31, 2024		5,412,786		$	47.27		6.18	$	350
Granted		640,751			10.09
Forfeited		(150,340	)		86.88
Outstanding at March 31, 2025		5,903,197		$	42.23		5.92	$	20
Exercisable at March 31, 2025		4,504,464		$	47.42		4.88	$	20

The total intrinsic value (the amount by which the fair market value exceeded the exercise price) of stock options exercised during the three months ended March 31, 2024 was $1.2 million. There were no options exercised during the three months ended March 31, 2025.

As of March 31, 2025, there was $16.6 million of unrecognized compensation cost related to stock options that have not yet vested, which are expected to be recognized over a weighted average remaining vesting period of 1.23 years.

In May 2016, the Company adopted the 2016 Employee Stock Purchase Plan (the “2016 Plan”). The 2016 Plan allows eligible employees to purchase shares of the Company’s common stock on the last day of each predetermined six-month offering period at 85% of the lower of the fair market value per share at the beginning or end of the applicable offering period. The 2016 Plan provides for six-month offering periods beginning in January and July of each year.

As of March 31, 2025, there were 1,356,897 shares available for future issuance under the 2016 Plan. The number of shares reserved for issuance under the 2016 Plan are subject to cumulative increases on each January 1st by the lesser of a) one percent of the number of shares of common stock issued and outstanding on the immediately preceding December 31st, b) 500,000 shares of common stock, or c) such lesser number of shares of common stock as determined by the board of directors. During the three months ended March 31, 2025 and 2024 the Company did not issue any shares of common stock under the 2016 Plan.

The fair value of shares under the 2016 Plan was estimated at the beginning of the offering period using a Black-Scholes option-pricing model with the following assumptions:


	Three Months Ended March 31,
	2025	2024
Risk-free interest rate	4.24%	5.24%
Expected term	0.5 years	0.5 years
Expected volatility of underlying stock	66.2%	56.7%
Expected dividend yield	0.0%	0.0%