Prior to our IPO, we issued warrants to certain employees, board members and advisors (Pre-IPO Plan). Each vested warrant entitled the warrant holder to a single class A ordinary share. Holders of stock warrants were entitled to exercise the vested portion of the stock warrant. Stock warrants generally vest over a three-year period and expire five years from the vest date.

In November 2021, our board of directors adopted, and our stockholders approved, the 2021 Equity Incentive Plan (or the “2021 Plan”), which became effective on November 4, 2021. The 2021 Plan provides for the grant of incentive stock options, nonstatutory stock options, stock appreciation rights, awards of restricted stock, restricted stock units and other stock-based awards. The number of shares of our common stock reserved for issuance under the 2021 Plan is equal to 2,465,150, subject to an annual increase, to be added on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2022 and continuing until, and including, the fiscal year ending December 31, 2031, equal to the lesser of (i) 4% of the number of shares of common stock outstanding on the first day of such fiscal year or (ii) such other amount determined by our board of directors. The 2,396,413 outstanding warrants granted under the Pre-IPO Plan were transferred to the 2021 Equity Plan and no further warrants were available to be issued under the Pre-IPO Plan. As of March 31, 2022, we had 2,277,377 options available for future grant under the 2021 Equity Plan.

The following table summarizes our stock options activity:


	Number of Options		Weighted- average exercise price per share		Weighted- average remaining contractual term (in years)		Aggregate intrinsic value
Outstanding, December 31, 2021		3,071,613	$	13.12		8.5	$	—
Granted		450,078	$	8.42
Outstanding March 31, 2022		3,521,691	$	12.52		8.5	$	—
Exercisable at March 31, 2022		346,575	$	13.93		7.1	$	—

All share-based awards granted are measured based on the fair value on the date of the grant and compensation expense is recognized with respect to those awards over the requisite service period, which is generally the vesting period of the respective award. Forfeitures related to equity-based compensation awards are recognized as they occur, and we reverse any previously recognized compensation cost associated with forfeited awards in the period the forfeiture occurs.

As of March 31, 2022, there was $24.0 million of unrecognized compensation cost related to unvested stock-based compensation arrangements that is expected to be recognized over a weighted average period of 3.5 years.

Equity-based compensation expense recorded as research and development and general and administrative expenses is as follows (in thousands):


	Three Months Ended March 31,
	2022		2021
Research and development	$	685	$	1
General and administrative		935		3
Total equity-based compensation	$	1,620	$	4

We did not recognize any tax benefits for stock-based compensation during the three months ended March 31, 2022 and 2021.