The Company’s Board of Directors adopted and the Company’s stockholders approved, effective on the day prior to the effectiveness of the registration statement on Form S-1 related to the IPO, an amendment and restatement of the 2018 Omnibus Incentive Plan (the 2018 Plan) which provides for the grant of incentive stock options, within the meaning of Section 422 of the Code to employees, and for the grant of nonstatutory stock options, restricted stock, restricted stock units (RSUs), stock appreciation rights, performance units, and performance shares to employees, directors, and consultants of the Company.

Options granted under the 2018 Plan expire no later than 10 years from the date of grant. The exercise price of options granted under the 2018 Plan must at least be equal to the fair market value of the Company’s common stock on the date of grant. With respect to any participant who owns more than 10% of the voting power of all classes of the Company’s outstanding stock, the term of an incentive stock option granted to such participant must not exceed five years and the exercise price must equal at least 110% of the fair market value on the grant date. Employee stock options generally vest 25% upon one year of continued service to the Company, with the remainder in monthly increments over three additional years.

Subject to an annual evergreen increase and adjustment in the case of certain capitalization events, the Company initially reserved 4,384,000 shares of the Company’s common stock for issuance pursuant to awards under the 2018 Plan. The 2018 Plan is administered by the Compensation Committee of the Company’s Board of Directors. The number of shares of the Company’s common stock available for issuance under the 2018 Plan will also include an annual increase on the first day of each fiscal year beginning with the 2020 fiscal year, equal to the least of (i) 8,768,800 shares, (ii) 4% of the Company’s common stock and non-voting common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Company’s Board of Directors.

On July 30, 2020, the Company’s Board of Directors adopted and the Company’s stockholders approved an amendment and restatement of the 2018 Plan which clarified the number of outstanding shares of common stock used to calculate the annual evergreen provision to include both voting and non-voting shares of common stock. Upon adoption of the amended and restated 2018 Plan, the number of shares of common stock available under the 2018 Plan increased by 257,248 shares.

As of December 31, 2020, 3,054,127 shares of common stock remained available for issuance under the 2018 Plan. Effective January 1, 2021, the number of shares of common stock available under the 2018 Plan increased by 1,278,965 shares pursuant to the evergreen provision of the 2018 Plan.

The 2010 Stock Plan (the 2010 Plan) was originally adopted by the Company’s Board of Directors and approved by the Company’s stockholders in November 2010. The 2010 Plan was amended and restated in December 2017 and April 2019. The 2010 Plan allowed the Company to provide incentive stock options, within the meaning of Section 422 of the Code, nonstatutory stock options and stock purchase rights to eligible employees, consultants and directors and any parent or subsidiary of the Company. The 2010 Plan was terminated in 2019 and the Company will not grant any additional awards under the 2010 Plan. However, the 2010 Plan will continue to govern the terms and conditions of the outstanding awards previously granted under the 2010 Plan.

The Company’s Board of Directors adopted and the Company’s stockholders approved, effective on the day prior to the effectiveness of the registration statement on Form S-1 related to the IPO, the 2019 Employee Stock Purchase Plan (ESPP). However, no offering period or purchase period under the ESPP will begin unless and until determined by the Company’s Board of Directors. The ESPP is intended to have two components: a component that is intended to qualify as an “employee stock purchase plan” under Section 423 of the Code (the 423 Component) and a component that is not intended to qualify (the Non-423 Component). 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. 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 at the beginning of the offering period or at the end of each applicable purchase period.

Subject to adjustment in the case of certain capitalization events, a total of 280,000 common shares of the Company were available for purchase at adoption of the ESPP. Pursuant to the ESPP, the annual share increase pursuant to the evergreen provision is determined based on the least of (i) 560,000 shares, (ii) 1% of the Company’s common stock and non-voting common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Company’s Board of Directors.

On July 30, 2020, the Company’s Board of Directors adopted and the Company’s stockholders approved an amendment and restatement of the ESPP which clarified the number of outstanding shares of common stock used to calculate the annual evergreen provision to include both voting and non-voting shares of common stock. Upon adoption of the amended and restated ESPP, the number of shares of common stock available under the ESPP was increased by 64,312 shares. During the year ended December 31, 2020, the Company issued 31,345 shares of common stock under the ESPP.

As of December 31, 2020, 554,088 shares of common stock remained available for issuance under the ESPP. Effective January 1, 2021, the number of shares of common stock available under the ESPP increased by 319,741 shares pursuant to the evergreen provision of the ESPP.

Total stock-based compensation expense recorded related to the 2010 Plan, 2018 Plan, and ESPP was recorded in the statements of operations and allocated as follows (in thousands):

	Year Ended December 31,
	2020		2019		2018
Research and development	$	4,160	$	522	$	51
General and administrative		4,294		492		132
Total stock-based compensation expense	$	8,454	$	1,014	$	183

	Outstanding Options
	Shares			Weighted- Average Exercise		Weighted- Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
								(in thousands)
Balance—December 31, 2019		2,289,209		$	3.36		8.1	$	79,656
Granted		893,875		$	44.66
Exercised		(203,192	)	$	2.27
Cancelled		(53,332	)	$	31.44
Balance—December 31, 2020		2,926,560		$	15.54		7.8	$	212,906
Exercisable—December 31, 2020		1,462,376		$	6.60		6.8	$	119,459

The fair value of employee stock options was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2020			2019			2018
Expected term in years		6.0			6.0			5.9
Expected volatility		84.3	%		79.3	%		77.5	%
Risk-free interest rate		1.0	%		2.2	%		2.9	%
Expected dividend yield		—			—			—
Weighted average fair value of share-based awards granted per share	$	31.70		$	4.36		$	0.94

As of December 31, 2020, there was $23.6 million of total unrecognized compensation cost related to stock options under the Plans. The unrecognized stock-based compensation cost is expected to be recognized over a weighted-average period of 2.5 years. The aggregate intrinsic value of options exercised for the years ended December 31, 2020 and December 31, 2019 was $12.5 million and $0.3 million, respectively. Intrinsic values are calculated as the difference between the exercise price of the underlying options and the fair value of the common stock on the date of exercise.

The fair value of ESPP was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2020			2019			2018
Expected term in years		0.5			0.7			—
Expected volatility		85.5	%		74.3	%		—
Risk-free interest rate		0.1	%		1.9	%		—
Expected dividend yield		—			—			—

During December 2018, the Company issued 116,518 shares of common stock to an executive officer under a restricted stock agreement at a grant date fair value of $1.39 per share that vested over two years. Any unvested shares were subject to forfeiture in the case that the grantee’s service terminated. As of December 31, 2020, all shares of restricted stock were vested. For the years ended December 31, 2020 and 2019, the related stock-based compensation was not material.

During the year ended December 31, 2020, the Company granted 8,312 shares of RSUs, of which 7,645 shares were issued upon vesting. These RSUs were granted to a consultant and certain members of the Company’s Board of Directors under the Company’s Outside Director Compensation Policy, as amended, and had a weighted-average fair value of $69.30 per share. The stock-based compensation expense related to these awards was $0.5 million, which was recognized over the service period of the awards. As of December 31, 2020, the remaining amount of unrecognized stock-based compensation related to these awards was not material. During the years ended December 31, 2020 and 2019, there were no RSUs cancelled.