The Company maintains the 2010 Stock Incentive Plan (the “Plan”) for employees, consultants, advisors, and directors, as amended in March 2013, June 2014 and June 2017. The Plan provides for the grant of equity awards such as stock options and restricted stock. The Plan provides 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 award 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. Options and restricted stock granted under the Plan vest over periods as determined by the Board of Directors, which generally are equal to four years. Options generally expire ten years from the date of grant. A total of 12,000,000 shares has been reserved under the Plan and as of March 31, 2019, there were 499,196 shares of common stock available for future issuance.

The following table summarizes stock option activity during the three months ended March 31, 2019:

	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term		Aggregate Intrinsic Value
Outstanding at January 1, 2019		9,583,349		$	2.28
Granted		712,500		$	0.60
Exercised		—		$	—
Forfeited		(106,030	)	$	2.28
Outstanding at March 31, 2019		10,189,819		$	2.17		7.37	$	524,000
Exercisable at March 31, 2019		5,926,360		$	2.21		6.54	$	228,000

Stock options to purchase 487,759 shares of common stock contain performance-based vesting conditions, which were not deemed probable of vesting at March 31, 2019.

The aggregate intrinsic value is based upon the Company’s closing stock price of $0.82 on March 29, 2019, the last trading day of the quarter.

In February 2019, as part of the Company’s annual individual performance evaluations of its executive officers, the Board of Directors, upon the recommendation of the Compensation Committee, granted to the Company’s executive officers options to purchase an aggregate of 3,303,600 shares of the Company’s common stock, contingent on the approval of the 2019 Equity Incentive Plan by the Company’s stockholders as the Company did not have enough shares under the Plan to make these stock option grants (“Contingent Option Awards”). The Contingent Option Awards to such executive officers were granted with a term of 10 years and an exercise price of $0.62 per share, which was the closing price of the Company’s common stock on the date of grant. The Contingent Option Awards vest in equal monthly installments over four years, subject to the officer’s continued employment with the Company; provided, that the Contingent Option Awards will automatically terminate and be forfeited if the Company’s stockholders do not approve the 2019 Equity Incentive Plan within 12 months of the grant date of the options, and further provided that the options will not be exercisable, and no common stock will be issuable thereunder, before the approval of the 2019 Equity Incentive Plan by the Company’s stockholders. The Contingent Option Awards are excluded from the option table above and no expense was recognized for these awards during the three months ended March 31, 2019 because the grant date criteria under ASC 718 had not been met as of March 31, 2019.

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 the following table:

	Three Months Ended March 31,
	2019		2018
Volatility factor	88.27% - 90.49%		80.18% - 83.40%
Expected term (in years)	5.50 - 6.25		5.50 - 6.25
Risk-free interest rates	2.24% - 2.55%		2.64%
Dividend yield		—		—

Based upon these assumptions, the weighted-average grant date fair value of stock options granted during the three months ended March 31, 2019 and 2018 was $0.46 and $2.18, respectively.

On January 1, 2017, the Company adopted ASU No. 2016-09, Compensation–Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting and elected to account for forfeitures as they occur.

As of March 31, 2019, there was $5.4 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 2.6 years.