In June 2019, the Company’s board of directors and stockholders approved the 2019 Equity Incentive Plan (the “2019 Plan”) which became effective on June 17, 2019 and replaced the Company’s 2014 Equity Incentive Plan (the “2014 Plan”). In addition to the shares of common stock reserved for future issuance under the 2014 Plan that were added to the 2019 Plan upon its effective date, the Company initially reserved 2,200,000 shares of common stock for issuance under the 2019 Plan. The number of shares reserved for issuance under the Company’s 2019 Plan will increase automatically on January 1 of each of 2020 through 2029 by the number of shares equal to 4% of the aggregate number of outstanding shares of the Company’s common stock as of the immediately preceding December 31, or a lesser number as may be determined by the Company’s board of directors.

As of December 31, 2022 there were no shares available for future issuance under the 2014 Plan and 992,231 shares were available for future issuance under the 2019 Plan.

During the years ended December 31, 2022 and December 31, 2021, the Company granted options to purchase 3,459,500 and 1,311,897 shares of common stock to certain of its employees, and directors, respectively. The options vest up to four years except for certain options granted to members of our board of directors which vest over one or three years and are exercisable at a per share price equal to the fair value of the common stock on the grant date.

	Number of shares			Weighted average exercise price		Weighted average remaining contractual life (years)		Aggregate intrinsic value⁽¹⁾
Outstanding as of December 31, 2021		5,435,304		$	19.77		8.0	$	64,981
Granted		3,459,500			15.97
Exercised		(270,376	)		1.83
Forfeitures		(254,450	)		29.77
Expired		(95,331	)		34.72
Outstanding as of December 31, 2022		8,274,647		$	18.28		7.6	$	20,598
Exercisable as of December 31, 2022		4,286,461		$	14.70		6.4	$	18,454

The weighted average grant date fair value per share of stock options granted during the years ended December 31, 2022 and 2021 was $10.32 and $34.07, respectively. The aggregate grant date fair value of stock options granted during the years ended December 31, 2022 and 2021 was approximately $35.7 million and $44.7 million, respectively. The aggregate intrinsic value of stock options exercised during the year ended December 31, 2022 and 2021 was approximately $3.5 million and $9.9 million, respectively.

The Company recorded stock-based compensation expense of $22.9 million and $16.5 million during the years ended December 31, 2022 and 2021, respectively. As of December 31, 2022, there was $53.3 million of unrecognized compensation cost related to unvested stock-based compensation arrangements granted under the 2014 and the 2019 Plans. The compensation is expected to be recognized over a weighted average period of 2.8 years as of December 31, 2022.

Stock-based compensation expense recorded as research and development and general and administrative expenses in the accompanying consolidated statements of operations and comprehensive loss is as follows:

	Year ended December 31,
	2022		2021
Research and development	$	8,901	$	6,215
General and administrative		13,953		10,235
	$	22,854	$	16,450

The Company uses the Black-Scholes option pricing model to calculate the grant-date fair value of an award. The fair values of the options granted to employees and directors were calculated using the following assumptions for the years ended December 31, 2022 and 2021:

	Year ended December 31,
	2022	2021
Risk-free interest rate	1.82-4.15%	0.78-1.51%
Expected dividend yield	0%	0%
Expected life	5.5-6.25 years	5.5-6.25 years
Expected volatility	70-71%	70-73%

In June 2019, the Company adopted the 2019 Employee Stock Purchase Plan (“ESPP”), which became effective on June 18, 2019. The Company initially reserved 315,000 shares of common stock for sale under the ESPP. At December 31, 2022, the Company had 959,603 shares available for issuance under the plan. The average grant date fair value per share under the plan was $18.39 for 2022. The total ESPP stock-based compensation expense for the year ended December 31, 2022 was $0.3 million and for the year ended December 31, 2021 was $0.3 million. The number of shares reserved for issuance under the ESPP will increase automatically on January 1st of each of the first ten calendar years following the first offering date by the number of shares equal to the lesser of 1% of the total outstanding shares of the Company’s common stock as of the immediately preceding December 31 or a lower amount determined by the Company’s board of directors. The aggregate number of shares issued over the term of the ESPP will not exceed 3,150,000 shares of the Company’s common stock.