In December 2015, the Company’s board of directors adopted and approved the 2015 Stock Incentive Plan (the “2015 Plan”). The 2015 Plan provided for the granting of incentive stock options, non-statutory stock options, restricted stock awards and other stock-based awards to eligible employees, officers, directors, consultants and advisors as determined by the Company’s board of directors.

In February 2021, the Company’s board of directors adopted and the stockholders approved the 2021 Equity Incentive Plan (the “2021 Plan”). The 2021 Plan became effective on February 5, 2021, following which no further grants were or will be made under the 2015 Plan. The 2021 Plan provides for the grant of stock options, non-statutory stock options, restricted stock awards, restricted stock unit awards, stock appreciation rights, performance stock awards and other forms of stock compensation to our employees, consultants and directors. As of June 30, 2021, the Company had 2,619,976 shares available for future issuance under the 2021 Plan.

The Company’s stock options generally vest over 48 months with 25% vesting after one year followed by ratable monthly vesting over the remaining three years and have a contractual term of 10 years. The weighted-average assumptions used principally in determining the fair value of options granted were as follows:

	Three Months Ended June 30,						Six Months Ended June 30,
	2021			2020			2021			2020
Fair value of common stock	$	23.38		$	2.18		$	22.66		$	2.18
Expected term (in years)		6.1			6.1			6.0			5.9
Expected volatility		79.7	%		76.3	%		79.7	%		76.0	%
Risk-free interest rate		1.1	%		0.5	%		0.8	%		0.6	%
Dividend yield		—			—			—			—

During the six months ended June 30, 2021 and 2020, the Company granted stock options to purchase 478,434 shares and 696,510 shares, respectively, of its common stock with aggregate grant date fair values of $7.4 million and $1.0 million, respectively.

As of June 30, 2021, total unrecognized compensation expense related to stock options was $14.1 million, which is expected to be recognized over a weighted-average period of 2.88 years.

As of June 30, 2021 options for 257,578 shares with a weighted average exercise price of $1.85 were exercised and unvested. The underlying proceeds from the unvested exercises of $0.5 million is recorded in other current liabilities on the condensed consolidated balance sheet.

	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2021		2020		2021		2020
Research and development	$	542	$	73	$	991	$	120
General and administrative		525		80		967		145
Total stock-based compensation expense	$	1,067	$	153	$	1,958	$	265