The Company has two equity incentive plans: the 2006 Stock Plan (“2006 Plan”) and the 2015 Omnibus Equity Incentive Plan (“2015 Plan”).

In 2006, the Company adopted the 2006 Plan, which provided for the granting of stock options to executives, employees, and other service providers under terms and provisions established by the Board of Directors. The Company granted non-statutory stock options (“NSOs”) under the 2006 Plan until May 2015, when the 2006 Plan was terminated as to future awards. The 2006 Plan continues to govern the terms of options that remain outstanding and were issued under the 2006 Plan. The 2015 Plan became effective in May 2015 and all shares that were reserved, but not issued, under the 2006 Plan were assumed by the 2015 Plan. Upon effectiveness, the 2015 Plan had 154,387 shares of common stock reserved for future issuance, which included 10,637 shares under the 2006 Plan that were transferred to and assumed by the 2015 Plan. The 2015 Plan provides for automatic annual increases in shares available for grant. In addition, shares subject to awards under the 2006 Plan that are forfeited or canceled will be added to the 2015 Plan. The 2015 Plan provides for the grant of incentive stock options (“ISOs”), NSOs, restricted stock awards, stock units, stock appreciation rights, and other forms of equity compensation, all of which may be granted to employees, officers, non-employee directors, and consultants. The ISOs and NSOs will be granted at a price per share not less than the fair value at the date of grant. Options granted generally vest over a four-year period, with 25% vesting at the end of one year and the remaining vesting monthly thereafter; however, the options granted in the third quarter of 2018 vest over a two-year period, vesting monthly on a pro-rated basis. Options granted, once vested, are generally exercisable for up to 10 years after grant.

As of March 31, 2019, a total of 538,953 shares of common stock were reserved for issuance under the 2015 Plan, of which 65,872 shares of common stock are available for future grant. As of March 31, 2019, a total of 62,162 and 473,081 options are outstanding under the 2006 and 2015 Plans, respectively.

A summary of activity under the stock incentive plans is as follows (in thousands, except share data and price per share):

	Shares Subject to Outstanding Options			Weighted- Average Exercise Price Per Share		Aggregate Intrinsic Value
Outstanding — Balance at December 31, 2018		530,044		$	35.53	$	—
Options granted		7,500			3.57
Options exercised		—			—
Options forfeited		(1,287	)		4.33
Options expired		(1,014	)	$	24.78
Outstanding — Balance at March 31, 2019		535,243		$	35.13	$	637
Vested and expected to vest — March 31, 2019		526,131		$	35.47	$	623
Exercisable —March 31, 2019		231,086		$	60.40	$	182

As of March 31, 2019, there was $0.9 million of unrecognized compensation cost related to unvested stock-based compensation grants that will be recognized over the weighted-average remaining recognition period of 1.9 years.

The fair value of stock option awards to executives and other service providers was estimated at the date of grant using the Black-Scholes Model with the following weighted-average assumption. There were 7,500 and 10,000 options granted during the three months ended March 31, 2019 and 2018, respectively.

	Three Months Ended March 31,
		2019		2018
Expected term (years)		2.58		6.25
Expected volatility		133	%	100	%
Risk-free interest rate		2.55	%	2.73	%
Dividend yield		—		—

The Company’s 2015 Employee Stock Purchase Plan (“ESPP”) became effective on May 14, 2015. The ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount of up to 15% of their eligible compensation through payroll deductions, subject to any plan limitations. The ESPP provides for six-month offering periods, and 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 on the first trading day of the offering period or on the last trading day of the offering period. As of March 31, 2019, the number of shares of common stock reserved for future issuance under the ESPP is 108,864. The ESPP provides for automatic annual increases in the shares available for purchase beginning on January 1, 2016. As of March 31, 2019, 9,353 shares had been issued under the ESPP. The Company recorded $4,300 and $1,200 of compensation expense for the three months ended March 31, 2019 and 2018, respectively.

As of March 2019, the Company has 2,821,144 common stock warrants outstanding with a weighted average exercise price of $18.15. The expiration of the warrants ranges from April 2019 to June 2023.

On December 2013, the Company issued warrants to Mahyco International to purchase 3,784 shares of common stock, exercisable as of the issuance date, at an exercise price of $330.40 per share. These warrants expired on December 11, 2018.

In connection with the Series D preferred stock financing in the first half of 2014, the Company issued warrants, exercisable as of the issuance date, to the Series D preferred stock investors to purchase an aggregate of 61,397 shares of common stock at an exercise price of $363.20 per share and to the placement agents to purchase 1,674 shares of common stock at $268.80. Of the 61,397 warrants issued to the investors, 1,759 expired on March 28, 2019 and the remaining 59,638 expire in the second quarter of 2019, along with those issued to the placement agents.

As of March 2019, 1,297,870 common stock warrants are outstanding that were issued in the March 2018 Private Placement. The final exercise price for these warrants is $10.7258 as adjusted in accordance with the March 2018 Purchase Agreement’s adjustment provisions. See Note 8.

As of March 2019, 1,461,962 common stock warrants are outstanding in accordance with the June 2018 Offering. Of the total, 1,392,345 shares have a purchase price of $9.94 and the remaining 69,617 common stock warrants have an exercise price of $12.568. See Note 8.