The Company’s 2018 Equity Incentive Plan (the “2018 Plan”) provided for the grant of incentive stock options intended to qualify under Section 422 of the IRC, nonstatutory stock options, restricted stock, unrestricted stock and other equity-based awards, such as stock appreciation rights, and stock units including restricted stock units for up to approximately 13.9 million shares of the Company’s common stock (subject to adjustment in the event of stock splits and other similar events). As of December 31, 2023, no shares remain available for issuance under the 2018 Plan.

In connection with the Company’s initial public offering (“IPO”), MiNK’s board of directors adopted the MiNK Therapeutics, Inc. 2021 Equity Incentive Plan (the “2021 Plan”). The 2021 Plan 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, for an initial share pool of approximately 6.1 million shares of the Company’s common stock (subject to adjustment in the event of stock splits and other similar events). The initial share pool will automatically increase on January 1st of each year from 2024 to 2031 by the lesser of (i) four percent of the number of shares of the Company’s common stock outstanding as of the close of business on the immediately preceding December 31st and (ii) the number of shares determined by the Company’s board of directors on or prior to such date for such year. In January 2022 and 2023, the 2021 Plan share pool increased by approximately 1.3 million shares and 1.4 million shares, respectively. As of December 31, 2023, there were approximately 8.8 million shares reserved for issuance under the 2021 Plan.

In connection with the Company’s IPO, MiNK’s board of directors adopted the MiNK Therapeutics, Inc. 2021 Employee Stock Purchase Plan (the “ESPP”). The ESPP provides eligible employees the opportunity to acquire the Company’s common stock in a program designed to comply with Section 423 of the Code. There are approximately 1.0 million shares reserved for issuance under the ESPP, plus an automatic annual increase on January 1st of each year from 2024 to 2031 equal to the lesser of (i) one percent of the number of shares of the Company’s common stock outstanding as of the close of business on the immediately preceding December 31st and (ii) the number of shares determined by the Company’s board of directors on or prior to such date for such year, up to a maximum of approximately 3.5 million shares in the aggregate.

The Company primarily uses the Black-Scholes option pricing model to value options granted to employees and non-employees, as well as options granted to members of the Company’s Board of Directors. All stock option grants have 10-year terms, service conditions, and generally vest ratably over a 3 or 4-year period.

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


	2023			2022
Expected volatility		92	%		81	%
Expected term in years		6			6
Risk-free interest rate		3.6	%		1.7	%
Dividend yield		0	%		0	%

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 2023 is presented below:


	Options			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2022		6,148,447		$	1.97
Granted		1,002,743			2.28
Exercised		(105,187	)		0.22
Forfeited		(61,883	)		2.94
Expired		(38,404	)		3.01
Outstanding at December 31, 2023		6,945,716			2.03		7.32	$	2,227,555
Vested or expected to vest at December 31, 2023		6,945,716			2.03		7.32	$	2,227,555
Exercisable at December 31, 2023		3,999,908		$	1.44		6.56	$	2,227,545

The weighted average grant-date fair values of options granted during the years ended December 31, 2023 and 2022, was $1.78 and $2.20, respectively. During both 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.

The aggregate intrinsic value in the table above represents the difference between the Company's closing stock price on the last trading day of fiscal 2023 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, 2023 (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 the Company's stock. The total intrinsic value of options exercised during the year ended December 31, 2023, determined on the dates of exercise, was approximately $0.2 million.

As of December 31, 2023, there was $3.6 million of unrecognized share-based compensation expense related to stock options granted to employees, consultants and directors which, if all milestones are achieved on outstanding performance based awards, will be recognized over a weighted average period of 1.9 years. For awards with performance conditions, expense is recognized if the achievement of underlying performance conditions is deemed probable.

A summary of non-vested stock activity for 2023 is presented below:


	Nonvested Shares			Weighted Average Grant Date Fair Value
Outstanding at December 31, 2022		726,163		$	3.01
Granted		1,563,324			1.66
Vested		(804,234	)		2.15
Forfeited		(695,750	)		3.03
Outstanding at December 31, 2023		789,503		$	1.18

As of December 31, 2023, there was $0.8 million of unrecognized share-based compensation expense related to these non-vested shares which will be recognized over a weighted average period of 4.7 years. The total intrinsic value of shares vested during the year ended December 31, 2023 was $1.7 million.

The Company issues new shares upon option exercises the vesting of non-vested stock and purchases under the ESPP. During the years ended December 31, 2023 and 2022, 105,187 shares and 258,648 shares, respectively, were issued as a result of stock option exercises. During the years ended December 31, 2023 and 2022, 175,196 shares and 60,595 shares, respectively, were issued as a result of the vesting of non-vested stock. During the year ended December 31, 2023, 39,340 shares were issued under the ESPP. Additionally, during the years ended December 31, 2023 and 2022, 603,830 shares and 125,199 shares were issued as payment for certain employee bonuses, with 205,879 shares and 43,665 of those shares being withheld to cover taxes, resulting in a net share issuance of 397,951 and 81,534, respectively.

Stock based compensation expense also includes expense related to awards granted to employees of the Company from the Agenus 2019 Equity Incentive Plan. The impact on the Company’s results of operations from share-based compensation for the year ended December 31, 2023 and 2022, was as follows (in thousands):


	2023		2022
Research and development	$	541	$	435
General and administrative		3,289		2,592
Total share-based compensation expense	$	3,830	$	3,027