In January 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Incentive Award Plan (the “2019 Plan”). The 2019 Plan became effective on February 6, 2019, the day prior to the effectiveness of the registration statement filed in connection with the IPO. Under the 2019 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units, and other stock or cash-based awards to individuals who are then employees, officers, directors or consultants of the Company, and employees and consultants of the Company’s subsidiaries. A total of 5,750,000 shares of common stock were approved to be initially reserved for issuance under the 2019 Plan. The number of shares that remained available for issuance under the 2017 Plan (as defined below) as of the effective date of the 2019 Plan were, and shares subject to outstanding awards under the 2017 Plan as of the effective date of the 2019 Plan that are subsequently canceled, forfeited or repurchased by the Company will be, added to the shares reserved under the 2019 Plan. In addition, the number of shares of common stock available for issuance under the 2019 Plan will be automatically increased on the first day of each calendar year during the ten-year term of the 2019 Plan, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 5% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. As of June 30, 2020, an aggregate of 2,164,523 shares of common stock were available for issuance under the 2019 Plan and 6,853,154 shares of common stock were subject to outstanding awards under the 2019 Plan.

In January 2019, the Company’s board of directors and stockholders approved and adopted the 2019 Employee Stock Purchase Plan (the “ESPP”). The ESPP became effective as of February 6, 2019, the day prior to the effectiveness of the registration statement filed in connection with the IPO. The ESPP permits participants to purchase common stock through payroll deductions of up to 20% of their eligible compensation. A total of 700,000 shares of common stock were approved to be initially reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP will be automatically increased on the first day of each calendar year during the first ten-years of the term of the ESPP, beginning with January 1, 2020 and ending with January 1, 2029, by an amount equal to 1% of the outstanding number of shares of the Company’s common stock on December 31 of the preceding calendar year or such lesser amount as determined by the Company’s board of directors. During the six months ended June 30, 2020, 49,889 shares were issued pursuant to the ESPP. As of June 30, 2020, an aggregate of 1,312,951 shares of common stock were available for issuance under the ESPP.

The Company’s 2017 Equity Incentive Plan (the “2017 Plan”) permitted the granting of incentive stock options, non-statutory stock options, restricted stock, restricted stock units and other stock-based awards. Subsequent to the adoption of the 2019 Plan, no additional equity awards can be made under the 2017 Plan. As of June 30, 2020, 4,135,841 shares of common stock were subject to outstanding options under the 2017 Plan, and 415,293 shares of restricted stock awards granted under the 2017 plan were unvested.

The fair value of each employee and non-employee stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company, prior to the closing of its IPO on February 12, 2019, was a private company and lacked company-specific historical and implied volatility information. Therefore, it estimated its expected volatility based on the historical volatility of a publicly traded set of peer companies. Due to the lack of historical exercise history, the expected term of the Company’s stock options for employees has been determined utilizing the “simplified” method for awards. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is zero based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future.

The following table summarizes stock option activity during the six months ended June 30, 2020:

	Shares Subject to Options Outstanding					Weighted- Average
				Weighted-		Remaining
				Average Exercise		Contractual Life		Aggregate
	Shares			Price		(Years)		Intrinsic Value
								(in thousands)
Outstanding as of December 31, 2019		8,538,060		$	13.67		9.0	$	35,385
Options granted		1,911,222		$	14.30
Option exercised		(44,007	)	$	3.49
Options forfeited/cancelled		(541,572	)	$	12.96
Outstanding as of June 30, 2020		9,863,703		$	13.88		8.6	$	22,225
Options vested and exercisable as of June 30, 2020		2,791,102		$	12.31		8.0	$	9,989

The aggregate intrinsic value in the above table is calculated as the difference between fair value of the Company’s common stock price on June 30, 2020 and the exercise price of the stock options. The aggregate intrinsic value of stock options exercised during the six months ended June 30, 2020 was $0.4 million.

The weighted-average grant date fair value per share for the stock option grants during the six months ended June 30, 2020 was $10.21.

The aggregate fair value of stock options that vested during the six months ended June 30, 2020 was $17.9 million.

	Number of			Weighted-
	Restricted			Average
	Stock Units			Grant Date
	Outstanding			Fair Value
Nonvested at December 31, 2019		4,648,526		$	3.98
Granted		1,176,340		$	11.94
Vested		(809,274	)	$	3.71
Forfeited		(51,048	)	$	14.21
Nonvested at June 30, 2020		4,964,544		$	5.80

At June 30, 2020, the total unrecognized compensation related to unvested restricted stock awards granted was $22.8 million, which the Company expects to recognize over a weighted-average period of approximately 2.4 years.

Stock-based compensation expense has been reported in the Company’s condensed consolidated statements of operations as follows (in thousands):

	Three months ended				Six months ended
	June 30,				June 30,
	2020		2019		2020		2019
Research and development	$	4,782	$	2,463	$	9,368	$	3,756
General and administrative		4,118		2,677		7,776		4,473
Total stock-based compensation	$	8,900	$	5,140	$	17,144	$	8,229

At June 30, 2020, the total unrecognized compensation related to unvested stock option awards granted was $63.4 million, which the Company expects to recognize over a weighted-average period of approximately 2.6 years.

As of June 30, 2020, total unrecognized compensation expense related to the ESPP was $1.7 million, which the Company expects to recognize over a weighted-average period of approximately 1.1 years.