9. Stock-Based Compensation

2018 Equity Incentive Plan

In connection with the consummation of the Reverse Merger and Recapitalization, our board of directors adopted, and our stockholders approved, the 2018 Equity Incentive Plan (the "2018 Plan"). The purposes of the 2018 Plan are to attract and retain the best available personnel for positions of substantial responsibility, to provide additional incentives to employees, directors and consultants who perform services to the Company, and to promote the success of our business. These incentives are provided through the grant of stock options, stock appreciation rights, restricted stock, restricted stock units, performance units and performance shares.

The number of shares of common stock available for issuance under the 2018 Plan will also include an annual increase on the first day of each fiscal year, equal to the lesser of: (i) 10% of the post-closing outstanding shares of common stock; (ii) 5% of the outstanding shares of common stock on the last day of the immediately preceding fiscal year; or (iii) such other amount as our board of directors may determine.

In addition, the shares of common stock reserved for issuance under the 2018 Plan also will include any shares of common stock subject to stock options, restricted stock units or similar awards granted under the 2009 Equity Incentive Plan (the "2009 Plan"), that, on or after the Reverse Merger and Recapitalization, are assumed in connection with the Reverse Merger and Recapitalization, expire or otherwise terminate without having been exercised in full and shares of common stock issued pursuant to awards granted under the 2009 Plan that, on or after the Reverse Merger and Recapitalization, are forfeited to or repurchased by us. As of March 31, 2019, the maximum number of shares of common stock that may be added to the 2018 Plan pursuant to the foregoing equals 2,077,555.

As of March 31, 2019, no awards have been granted under the 2018 Plan. The 2018 Plan had 3,001,620 and 2,729,416 shares of common stock reserved for issuance as of March 31, 2019 and December 31, 2018, respectively.

2018 Employee Stock Purchase Plan

Also, in connection with the consummation of the Reverse Merger and Recapitalization, our board of directors adopted, and our stockholders approved, the 2018 Employee Stock Purchase Plan (the "2018 ESPP"). The 2018 ESPP will be administered by our board of directors or a committee appointed by the board (the "administrator"). The purpose of the 2018 ESPP is to provide eligible employees with an opportunity to purchase shares of our common stock through accumulated contributions. The 2018 ESPP permits participants to purchase shares of common stock through contributions (generally in the form of payroll deductions) of up to an amount of their eligible compensation determined by the administrator. Subject to certain other limitations or unless otherwise determined by the administrator, a participant may purchase a maximum of 2,000 shares of common stock during a purchase period. The offering periods under the 2018 ESPP will begin on such date as determined by the administrator and expire on the earliest to occur of (a) the completion of the purchase of shares on the last exercise date occurring within 27 months of the applicable enrollment date of the offering period on which the purchase right was granted, or (b) a shorter period established by the administrator prior to an enrollment date for all options to be granted on such enrollment date. Amounts deducted and accumulated by the participant are used to purchase shares of common stock on each exercise date. The purchase price of the shares will be determined by the administrator but in no event will be less than 85% of the lower of the fair market value of common stock on the enrollment date or on the exercise date. Participants may end their participation at any time during an offering period and will be paid their accrued contributions that have not yet been used to purchase shares of common stock. Participation ends automatically upon termination of employment with the Company.

The number of shares of common stock that may be made available for sale under the 2018 ESPP also includes an annual increase on the first day of each fiscal year beginning for the fiscal year following the fiscal year in which the first enrollment date (if any) occurs equal to the lesser of (i) 3% of the expected post-closing outstanding shares of common stock; (ii) 1.5% of the outstanding shares of common stock on the last day of the immediately preceding fiscal year; or such other amount as the administrator may determine.

As of March 31, 2019, the Company has not consummated an enrollment or offering period related to the 2018 ESPP. The 2018 ESPP had 1,228,237 shares of common stock available for sale and reserved for issuance as of March 31, 2019 and December 31, 2018.

2009 Equity Incentive Plan

In 2009, the Company adopted its 2009 Equity Incentive Plan (the "Plan"), which allowed for the granting of incentive and non-statutory stock options, as defined by the Internal Revenue Code, to employees, directors, and consultants. The exercise price of the options granted is generally equal to the value of the Company's common stock on the date of grant, as determined by the Company's board of directors. The awards are exercisable and vest, generally over four years, in accordance with each option agreement. The term of each option is no more than ten years from the date of the grant. The Plan allows for options to be immediately exercisable, subject to the Company's right of repurchase for unvested shares at the original exercise price. The total amount received in exchange for these shares has been included in accrued expenses on the accompanying consolidated balance sheets and is reclassified to equity as the shares vest. As of March 31, 2019 and December 31, 2018, 33,102 and 40,707 shares were unvested amounting to $30 and $34 in accrued expenses, respectively. Effective with the Reverse Merger and Recapitalization, no additional grants will be made under the Plan.

Stock-Based Compensation

A summary of the Company's stock option activity under the Plan and related information is as follows:

The aggregate intrinsic value of options exercised was $7,128 and $16 for the three months ended March 31, 2019 and 2018, respectively. The total fair value of options vested was $45 and $124 for the three months ended March 31, 2019 and 2018, respectively.

The fair value of stock options granted is estimated on the date of grant using the Black-Scholes option-pricing model. The following table sets forth information relating to stock options granted:

The Company did not grant any options during the three months ended March 31, 2019.

Compensation costs that have been included on the Company's consolidated statements of operations and comprehensive loss for all stock-based compensation arrangements are detailed as follows:

The Company recognizes forfeitures as they occur. Unrecognized stock comp expense was $456 and $475 as of March 31, 2019 and 2018, respectively.