The Company previously maintained the 2010 Stock Incentive Plan (the “2010 Plan”) for employees, consultants, advisors, and directors, as amended in March 2013, June 2014 and June 2017.

In April 2019, the Company’s board of directors adopted the 2019 Equity Incentive Plan (the “2019 Plan”) and on June 12, 2019 the stockholders approved the 2019 Plan at the Annual Meeting of Stockholders. The 2019 Plan provides similar terms as the 2010 Plan, including: (i) a provision for the grant of equity awards such as stock options and restricted stock, (ii) that the exercise price of incentive stock options cannot be less than 100% of the fair market value of the common stock on the date of the grant for participants who own less than 10% of the total combined voting power of stock of the Company and not less than 110% for participants who own more than 10% of the total combined voting power of the stock of the Company, (iii) that options and restricted stock granted under the 2019 Plan vest over periods as determined by the board of directors, which generally are equal to four years, and (iv) that options granted under the 2019 Plan expire over periods as determined by the board of directors, which generally are ten years from the date of grant. In April 2020, the board of directors adopted an amendment to the 2019 Plan to increase the total number of shares reserved under the Plan by 1,300,000 shares, among other things. The amendment was approved by stockholders at the Annual Meeting of Stockholders held on June 10, 2020.

Awards may be made under the 2019 Plan for up to the sum of (i) 2,300,000 shares of common stock and (ii) such additional number of shares of common stock (up to 1,068,901 shares) as is equal to (x) the number of shares of common stock reserved for issuance under the 2010 Plan that were available for grant under the 2010 Plan immediately prior to the date the 2019 Plan was approved by the Company’s stockholders and (y) the number of shares of common stock subject to awards outstanding under the 2010 Plan, which awards expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company pursuant to a contractual repurchase right. As of March 31, 2021, there were 292,420 shares of common stock available for future issuance under the 2019 Plan and no shares of common stock available for future issuance under the 2010 Plan.

The following table summarizes stock option activity during the three months ended March, 31, 2021:

	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at January 1, 2021		1,816,690		$	11.04	7.53		$	170,000
Granted		1,308,138		$	9.02
Exercised		—		$	—
Forfeited		(57,276	)	$	8.73
Outstanding at March 31, 2021		3,067,552		$	10.22		8.16	$	1,634,000
Exercisable at March 31, 2021		1,061,401		$	13.79		5.67	$	566,000

The aggregate intrinsic value is based upon the Company’s closing stock price of $7.32 on March 31, 2021.

The fair value of stock options subject only to service or performance conditions that are granted to employees is estimated on the date of grant using the Black-Scholes option-pricing model using the assumptions noted in the table below.

	Three Months Ended March 31,
	2021		2020
Volatility factor	56.17% - 102.66%		94.37% - 94.51
Expected term (in years)	0.25 - 6.25		6.25
Risk-free interest rates	0.06% - 1.13%		1.52% - 1.67%
Dividend yield		—		—

The risk-free interest rate is determined based upon the United States Treasury’s rates for United States Treasury zero-coupon bonds with maturities similar to those of the expected term of the options being valued. The Company does not expect to pay dividends in the foreseeable future.

Based upon these assumptions, the weighted-average grant date fair value of stock options granted during the three months ended March 31, 2021 and 2020 was $7.03 and $4.50, respectively.

As of March 31, 2021, there was $12.7 million of total unrecognized stock-based compensation expense related to stock options granted to employees under the Plan. The expense is expected to be recognized over a weighted-average period of 3.4 years.