In November 2019, the Company entered into a sales agreement, the 2019 Sales Agreement, with Cowen and Company, LLC (“Cowen”) to sell shares of its common stock with aggregate gross sales proceeds of up to $25,000, from time to time, through an ATM under which Cowen acts as sales agent. On March 18, 2020, in connection with filing an updated Registration Statement on Form S-3 (File No. 333-237033), the Company entered into a new sales agreement, the 2020 Sales Agreement, with Cowen on substantially the same terms as the 2019 Sales Agreement and terminated the 2019 Sales Agreement. From January 1, 2020 to March 31, 2020 the Company sold approximately 1,230,531 shares of common stock under the 2019 Sales Agreement and the 2020 Sales Agreement, as applicable, at an average price of approximately $3.50 per share, raising aggregate net proceeds of approximately $4,178 after deducting an aggregate commission of approximately 3%.

The following table summarizes the Company’s stock option activity since December 31, 2019:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2019		8,310,683		$	10.36		7.01	$	3,427
Granted		2,957,750			3.30
Exercised		(110,967	)		0.48
Forfeited		(401,873	)		8.62
Outstanding as of March 31, 2020		10,755,593		$	8.58		7.38	$	4,055
Options vested and expected to vest as of March 31, 2020		10,755,593		$	8.58		7.38	$	4,055
Options exercisable as of March 31, 2020		5,080,248		$	12.41		5.38	$	3,110

The weighted average grant-date fair value of stock options granted during the three months ended March 31, 2020 and 2019 was $2.06 and $4.60 per share, respectively.

During the three months ended March 31, 2019, the Company granted performance-based stock options to employees for the purchase of an aggregate of 1.1 million shares of common stock with a grant date fair value of $4.58 per share. These stock options are exercisable only upon achievement of specified performance targets. As of March 31, 2020, none of these options were exercisable because none of the specified performance targets had been achieved. Because achievement of the specified performance targets was not deemed probable as of March 31, 2020, the Company did not record any expense for these stock options from the dates of issuance through March 31, 2020.

The Company has granted restricted stock units with time-based vesting conditions. The table below summarizes the Company’s restricted stock unit activity since December 31, 2019:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2019		130,000		$	8.86
Granted		—			—
Forfeited		—			—
Vested		(110,000	)		9.98
Unvested restricted stock units as of March 31, 2020		20,000		$	2.69

The Company recorded stock-based compensation expense in the following expense categories of its condensed consolidated statements of operations and comprehensive loss:

	Three Months Ended March 31,
	2020		2019
Research and development expenses	$	1,004	$	1,448
General and administrative expenses		955		617
	$	1,959	$	2,065