Stock-Based Awards | Stock-Based Awards 2014 Stock Incentive Plan The Company’s 2014 Stock Incentive Plan (the “2014 Plan”) provides for the Company to grant incentive stock options or nonqualified stock options, restricted stock awards, unrestricted stock awards or restricted stock units to employees, directors and consultants of the Company. The 2014 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board of directors. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of the stock options may not be less than 100% of the fair market value of a share of the Company’s common stock on the date of grant and the term of the stock options may not be greater than ten years. As of December 31, 2018, all remaining shares available under the 2014 Plan were transferred to the Company’s 2018 Stock Option and Incentive Plan (the “2018 Plan”). 2018 Stock Option and Incentive Plan In April 2018, the Company’s 2018 Plan was approved by its stockholders and became effective. The 2018 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, unrestricted stock awards, cash-based awards and dividend equivalent rights to the Company’s officers, employees, non-employee directors and other key persons (including consultants). The number of shares initially reserved for issuance under the 2018 Plan was 1,545,454, plus the shares of common stock remaining available for issuance under the 2014 Plan, which shall be cumulatively increased each January 1 by 4% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 or such lesser number of shares determined by the Company’s board of directors or compensation committee of the board of directors. The shares of common stock underlying any awards that are forfeited, cancelled, held back upon exercise or settlement of an award to satisfy the exercise price or tax withholding, reacquired by the Company prior to vesting, satisfied without the issuance of stock, expire or are otherwise terminated (other than by exercise) under the 2018 Plan and the 2014 Plan will be added back to the shares of common stock available for issuance under the 2018 Plan. As of June 30, 2020, 603,143 shares were available for future issuance under the 2018 Plan. Stock options granted under the 2014 Plan and 2018 Plan to employees generally vest over four years and expire after ten years. Stock Options The following table summarizes the Company’s stock option activity since January 1, 2020: Number of Weighted Weighted Aggregate (in years) Outstanding as of December 31, 2019 5,418,113 $ 6.11 7.69 $ 690 Granted 1,254,000 3.23 Exercised (96,258) 2.82 Forfeited (389,991) 6.61 Outstanding as of June 30, 2020 6,185,864 $ 5.54 7.74 $ 13,419 Options exercisable at June 30, 2020 3,403,399 $ 5.63 6.99 $ 7,397 Vested and expected to vest at June 30, 2020 6,185,864 $ 5.54 7.74 $ 13,419 The weighted average grant-date fair value per share of stock options granted during the six months ended June 30, 2020 and year ended December 31, 2019 was $2.04 and $2.71, respectively. As of June 30, 2020 and December 31, 2019, there were outstanding stock options held by non-employees for the purchase of 267,372 and 272,343 shares of common stock, respectively, with service-based vesting conditions. 2018 Employee Stock Purchase Plan In April 2018, the Company’s 2018 Employee Stock Purchase Plan (the “ESPP”) was approved by its stockholders and became effective. A total of 256,818 shares of common stock were initially reserved for issuance under this plan. In addition, the number of shares of common stock that may be issued under the ESPP automatically increased on January 1, 2019, and shall increase each January 1 thereafter through January 1, 2028, by the lesser of (i) 1% of the number of shares of the Company’s common stock outstanding on the immediately preceding December 31 and (ii) such lesser number of shares as determined by the administrator of the Company’s ESPP. As of June 30, 2020, a total of 764,452 shares of common stock were reserved for issuance under this plan. For the six months ended June 30, 2020, the Company issued 49,025 shares of common stock under the ESPP. For the three months ended June 30, 2020 and three and six months ended June 30, 2019, the Company did not issue any shares of common stock under the ESPP. Restricted Stock Units The Company has granted restricted stock units ("RSUs") with service-based vesting conditions. RSUs represent the right to receive shares of common stock upon meeting specified vesting requirements. Unvested shares of restricted common stock may not be sold or transferred by the holder. These restrictions lapse according to the service-based vesting conditions of each award. In February 2020, the Company granted 1,060,900 RSUs that vest in full after eighteen-months as long as the individual remains an employee of the Company at such time. The table below summarizes the Company’s restricted stock unit activity since December 31, 2019: Number of Weighted Unvested restricted stock units as of December 31, 2019 — $ — Granted 1,060,900 3.18 Vested — — Forfeited (3,300) 3.18 Unvested restricted stock units as of June 30, 2020 1,057,600 $ 3.18 The expense related to RSUs granted to employees was $560 and $990 for the three and six months ended June 30, 2020, respectively. At June 30, 2020, there was $2,373 of total unrecognized compensation cost related to unvested restricted stock units, which is expected to be recognized over the remaining weighted-average vesting period of 1.06 years. Stock-Based Compensation The Company recorded stock-based compensation expense related to stock options and restricted stock unit awards in the following expense categories of its condensed consolidated statements of operations and comprehensive income (loss): Three months ended June 30, Six months ended June 30, 2020 2019 2020 2019 Research and development expenses $ 743 $ 607 $ 1,425 $ 1,172 General and administrative expenses 1,257 878 2,425 1,708 $ 2,000 $ 1,485 $ 3,850 $ 2,880 |