In January 2022 and 2021, the number of shares of common stock available for issuance under the 2013 Stock Option and Incentive Plan (“2013 Plan”) was increased by approximately 2.8 million and 2.7 million shares, respectively, as a result of the automatic increase provision of the 2013 Plan. As of June 30, 2022, the total number of shares of common stock available for issuance under the 2013 Plan was approximately 4.7 million.

The Company recognized stock-based compensation expense totaling $8.9 million and $23.1 million during the three months ended June 30, 2022 and 2021, respectively. The Company recognized stock based compensation expense totaling $21.3 million and $54.4 million on for the six months ended June 30, 2022 and 2021, respectively. Stock-based compensation expense recognized by award type is included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands):


	For the three months ended June 30,				For six months ended June 30,
	2022		2021(1)		2022		2021(1)
Stock options	$	3,685	$	13,863	$	8,945	$	30,289
Restricted stock units	4,850		5,956		11,884		16,173
Employee stock purchase plan and other	372		3,307		469		7,958
	$	8,907	$	23,126	$	21,298	$	54,420

Stock-based compensation expense by classification included within the condensed consolidated statements of operations and comprehensive loss was as follows (in thousands):


	For the three months ended June 30,				For six months ended June 30,
	2022		2021(1)		2022		2021(1)
Research and development	$	5,255	$	10,336	$	11,810	$	22,726
Selling, general and administrative	3,652		12,790		9,488		31,694
	$	8,907	$	23,126	$	21,298	$	54,420

The following table summarizes the stock option activity under the Company’s equity award plans and have been adjusted to reflect the effects of the Separation:


	Shares (in thousands)	Weighted- average exercise price per share
Outstanding at December 31, 2021	3,586	$	39.23
Granted	967	$	7.48
Exercised	(2)	$	1.04
Canceled or forfeited	(1,482)	$	41.11
Outstanding at June 30, 2022	3,069	$	29.48
Exercisable at June 30, 2022	1,296	$	51.24
Vested and expected to vest at June 30, 2022	3,069	$	29.48

During the six months ended June 30, 2022, less than 0.1 million stock options were exercised, resulting in total proceeds to the Company of less than $0.1 million.

The following table summarizes the restricted stock unit activity under the Company’s equity award plans and have been adjusted to reflect the effects of the Separation:


	Shares (in thousands)	Weighted- average grant date fair value
Unvested at December 31, 2021	3,193	$	16.21
Granted	1,451	$	7.51
Vested	(293)	$	25.65
Forfeited	(1,076)	$	12.67
Unvested at June 30, 2022	3,275	$	12.70

In June 2013, the Company adopted its 2013 Employee Stock Purchase Plan (“2013 ESPP”), which authorized the initial issuance of up to a total of 0.2 million shares of the Company’s common stock to participating employees. In June 2021, the Company amended the 2013 ESPP to authorize an additional 1.4 million shares of the Company’s common stock available to participating employees. During each of the six months ended June 30, 2022 and 2021, no shares and less than 0.1 million shares, respectively, of common stock were issued under the 2013 ESPP.