Stock-Based Compensation | Note 7. Stock-Based Compensation On December 4, 2014, the Company’s stockholders approved the 2014 Stock Plan (“2014 Plan”), and most recently amended the 2014 Plan on April 25, 2019. The 2014 Plan was amended, restated and re-named the 2019 Equity Incentive Plan (the “2019 Plan”), which became effective as of May 7, 2019, the day prior to the effectiveness of the registration statement filed in connection with the IPO. The remaining shares available for issuance under the 2014 Plan were added to the shares reserved for issuance under the 2019 Plan. The 2019 Plan provides for the grant of stock options (including incentive stock options and non-qualified stock options), stock appreciation rights, restricted stock, RSUs, performance units, and performance shares to the Company’s employees, directors, and consultants. The maximum aggregate number of shares that may be issued under the 2019 Plan is 7,388,053 shares of the Company’s common stock. In addition, the number of shares available for issuance under the 2019 Plan will be annually increased on the first day of each fiscal years beginning with fiscal 2020, by an amount equal to the least of (i) 2,146,354 shares of common stock; (ii) 4% of the outstanding shares of its common stock as of the last day of its immediately preceding fiscal year; and (iii) such other amount as the Company’s Board of Directors may determine . The 2019 Plan may be amended, suspended or terminated by the Company’s Board of Directors at any time, provided such action does not impair the existing rights of any participant, subject to stockholder approval of any amendment to the 2019 Plan as required by applicable law or listing requirements. Unless sooner terminated by the Company’s Board of Directors, the 2019 Plan will automatically terminate on April 23, 2029. As of March 31, 2021, the Company had 1,352,165 shares available for future issuance under the 2019 Plan. Stock Options Activity for service-based stock options under the 2019 Plan is as follows: Number of Options and Unvested Shares Weighted Average Exercise Price Weighted average remaining contractual life (years) Aggregate intrinsic value (In thousands) Balance at December 31, 2020 4,790,327 $ 25.47 8.69 $ 49,723 Options granted 126,000 39.27 Options exercised (32,722 ) 13.48 Options cancelled / forfeited (27,084 ) 28.90 Balance at March 31, 2021 4,856,521 $ 25.89 8.48 $ 73,413 Options vested and expected to vest as of March 31, 2021 4,856,521 25.89 8.48 73,413 Options exercisable as of March 31, 2021 1,713,563 $ 12.43 7.56 $ 45,006 For the three months ended March 31, 2021 and 2020, the Company recognized stock-based compensation expense of $6,077,000 and $1,955,000, respectively, related to options granted to employees and non-employees. The compensation expense is allocated on a departmental basis, based on the classification of the option holder. No income tax benefits have been recognized in the statement of operations for stock-based compensation arrangements. As of March 31, 2021, total unamortized employee stock-based compensation was $70.1 million, which is expected to be recognized over the remaining estimated vesting period of 1.62 years. Performance Stock Options (“PSOs”) The following table summarizes activity under the Company’s PSOs from the 2019 Plan and related information: Shares Subject to Outstanding PSOs Weighted Average Exercise Price Weighted average remaining contractual life (years) Balance at December 31, 2020 675,000 $ 29.60 9.94 Balance at March 31, 2021 675,000 29.60 9.69 Outstanding 675,000 $ 29.60 9.69 Vested — — — For the three months ended March 31, 2021 and 2020, the Company recognized stock-based compensation expense of $914,000 and $0, respectively, related to these PSOs. As of March 31, 2021, total unamortized stock-based compensation related to PSOs was $8.9 million, which is expected to be recognized over the remaining estimated vesting period of 2.51 years. Stock-Based Compensation Expense The following table summarizes employee and non-employee stock-based compensation expense for the three months ended March 31, 2021 and 2020 and the allocation within the condensed consolidated statements of operations and comprehensive loss (in thousands): March 31, 2021 2020 General and administrative expense $ 3,478 $ 1,038 Research and development expense 3,513 917 Total stock-based compensation $ 6,991 $ 1,955 Employee Stock Purchase Plan On April 24, 2019, the Company’s Board of Directors adopted its 2019 Employee Stock Purchase Plan (“2019 ESPP”), which was subsequently approved by the Company’s stockholders and became effective on May 7, 2019, the day immediately prior to the effectiveness of the registration statement filed in connection with the IPO. The 2019 ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the Internal Revenue Code (the “Code”) for U.S. employees. In addition, the 2019 ESPP authorizes grants of purchase rights that do not comply with Section 423 of the Code under a separate non-423 component for non-U.S. employees and certain non-U.S. service providers. The Company has reserved 832,421 |