In March 2018, the Company adopted the 2018 Equity Incentive Plan (2018 Plan). The 2018 Plan replaced the Company’s 2015 Stock Plan (2015 Plan) and 3,570,000 shares were reserved under the 2018 Plan, along with any shares remaining available for issuance under the Company’s 2015 Plan or outstanding awards under its 2015 Plan that subsequently expire, lapse unexercised or are forfeited to or repurchased by the Company.

Total stock-based compensation expense was recognized in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands):

	Three months ended June 30,				Six months ended June 30,
	2019		2018		2019		2018
Research and development		868	$	701		1,715	$	1,041
General and administrative		1,262		415		2,089		731
Total stock-based compensation	$	2,130	$	1,116	$	3,804	$	1,772

The Company granted 1,311,750 and 3,087,650 stock options during the three and six months ended June 30, 2019, respectively and 210,808 and 1,396,989 for the three and six months ended June 30, 2018, respectively. These options had a weighted average grant-date fair value of $6.28 and $6.63 per share for the three and six months ended June 30, 2019, respectively, and $11.23 and $7.29 for the three and six months ended June 30,2018, respectively.

Under the Company’s stock plans, 18,701 and 18,770 stock options were exercised during the three and six months ended June 30, 2019, respectively, and 5,171 and 713,931 for the three and six months ended June 30, 2018, respectively.

As a result of early exercises under the 2015 Plan, approximately 665,301 and 927,123 shares had not vested and were subject to repurchase as of June 30, 2019 and December 31, 2018, respectively. The Company treats cash received from the exercise of unvested options as a refundable deposit and classifies such amounts as a liability in its condensed consolidated balance sheets. As of June 30, 2019 and December 31, 2018, the Company included cash received from the early exercise of unvested options of $2.3 million and $2.8 million, in its other current and long-term liabilities, respectively based on the timing of their expected vesting. Amounts included in liabilities are transferred into common stock and additional paid-in capital as the shares vest, which is generally over a period of 48 months.