The Company’s 2020 Performance Incentive Plan (the "2020 Plan"), which was adopted by the Company’s board of directors in June 2020 and approved by the Company’s stockholders in July 2020, became effective upon the consummation of the Company’s initial public offering in July 2020 ("IPO"). Upon the effectiveness of the 2020 Plan, no further grants may be made under the Company’s 2015 Equity Incentive Plan (the "2015 Plan"). The 2020 Plan allows for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, stock bonuses, restricted stock, stock units and other forms of awards including cash awards

As of September 30, 2023, a total of 8,388,917 shares of the Company’s common stock were authorized for issuance with respect to awards granted under the 2020 Plan (this number of shares gives effect to the annual increases in the 2020 Plan share limit, as described in the next sentence, through that date). The share limit will automatically increase on the first trading day in January of each year by an amount equal to the lesser of (1) 5% of the total number of outstanding shares of the Company’s common stock on the last trading day in December in the prior year, or (2) such lesser number as determined by the Company’s board of directors. Any shares subject to awards granted under the 2020 Plan or the 2015 Plan that are not paid, delivered or exercised before they expire or are canceled or terminated, or otherwise fail to vest, as well as shares used to pay the purchase or exercise price of such awards or related tax withholding obligations, will become available for new award grants under the 2020 Plan. A total of 2,177,773 shares were available for issuance under the 2020 Plan as of September 30, 2023.

The following table summarizes the option activity under the 2020 Plan and 2015 Plan during the nine months ended September 30, 2023:


	Number of shares			Weighted- average exercise price		Weighted- average remaining contractual term (in years)
Outstanding at December 31, 2022		5,519,275		$	17.17		8.1
Granted		2,338,828			4.39
Exercised		(6,145	)		3.61
Forfeited		(724,509	)		16.18
Outstanding at September 30, 2023		7,127,449		$	13.09		8.0
Exercisable at September 30, 2023		3,257,376		$	16.28		7.0
Vested and expected to vest at September 30, 2023		7,127,449		$	13.09		8.0

The weighted-average grant date fair value of stock option grants was $3.35 per share for the nine months ended September 30, 2023.

The following table summarizes the restricted stock unit activity under the 2020 Plan during the nine months ended September 30, 2023:


	Number of shares			Weighted-average grant date fair value per share
Outstanding at December 31, 2022		356,728		$	12.66
Granted		503,639			5.57
Vested		(88,543	)		12.66
Forfeited		(76,714	)		7.79
Outstanding at September 30, 2023		695,110		$	8.06

The Company’s 2020 Employee Stock Purchase Plan (the "ESPP"), which was adopted by the Company’s board of directors in June 2020 and approved by the Company’s stockholders in July 2020, became effective upon the consummation of the IPO. A total of 1,441,307 shares of the Company’s common stock were authorized for issuance under the ESPP. The ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their eligible compensation, subject to any plan limitations. The ESPP provides for six-month offering periods, and at the end of each offering period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first trading day of the offering period or on the last trading day of the offering period. The six-month offering periods extend from June to November and December to May. As of September 30, 2023, 156,986 shares had been issued under the ESPP, and 1,284,321 shares remained available for issuance under the ESPP (after giving effect to share purchases under the ESPP through and including the offering period on May 31, 2023). As of September 30, 2023, employee contributions to the ESPP were $0.3 million and included as part of accrued and other current liabilities in the condensed balance sheets.

Share-based compensation expense for the three and nine ended September 30, 2023 and 2022 was as follows (in thousands):


	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development	$	2,077	$	1,947	$	6,283	$	5,404
General and administrative		2,214		2,443		7,404		6,995
Total share-based compensation	$	4,291	$	4,390	$	13,687	$	12,399

The total unrecognized compensation cost related to unvested stock options was $26.4 million, which is expected to be recognized over a weighted-average remaining service period of 2.7 years as of September 30, 2023. The total unrecognized compensation cost related to unvested restricted stock units was $4.7 million, which is expected to be recognized over a weighted-average remaining service period of 3.0 years as of September 30, 2023.

There were no shares subject to repurchase by the Company as of September 30, 2023. Shares subject to repurchase by the Company were 508 shares as of December 31, 2022, and the related liability recorded under other accrued and other current liabilities in the condensed balance sheet was insignificant.