The Company’s 2017 Stock Option and Incentive Plan (the “2017 Stock Plan”) became effective in November 2017, upon the closing of the Company’s initial public offering and will expire in October 2027. Under the 2017 Stock Plan, the Company may grant incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units (“RSUs”) and other stock-based awards. The Company’s 2014 Stock Incentive Plan (the “2014 Stock Plan”) was terminated in November 2017 upon the completion of the Company’s initial public offering and no further options were granted under the 2014 Stock Plan. At June 30, 2020, there were 703,636 options outstanding under the 2014 Stock Plan.

As of June 30, 2020, there were 3,894,270 shares of the Company’s common stock authorized for issuance under the 2017 Stock Plan, including 265,203 options that have been forfeited from the 2014 Stock Plan.

At June 30, 2020, there were 2,466,174 options available for issuance under the 2017 Stock Plan, 1,326,207 options outstanding and 80,450 RSUs outstanding. Awards granted under the 2017 Stock Plan have a term of ten years. Vesting of awards under the 2017 Stock Plan is determined by the board of directors, but is generally over one to four-year terms.

The fair value of options at date of grant was estimated using the Black-Scholes option-pricing model with the following assumptions:

	Six Months Ended June 30,
	2019		2020
Risk-free interest rate	1.85%-2.51%		0.41% - 1.71%
Expected dividend yield	0%		0%
Expected life	5.5-6.0 years		5.5-6.6 years
Expected volatility	73%-74%		72%-75%
Weighted-average grant date fair value	$	2.14	$	4.06

The following table summarizes information about stock option activity during the six months ended June 30, 2020 (in thousands, except share and per share data):

	NUMBER OF SHARES			WEIGHTED- AVERAGE EXERCISE PRICE		WEIGHTED- AVERAGE REMAINING CONTRACTUAL TERM		AGGREGATE INTRINSIC VALUE
Outstanding, December 31, 2019		1,439,518		$	6.09
Granted		763,702			6.32
Exercised		(115,671	)		6.18
Forfeited		(57,706	)		9.97
Outstanding, June 30, 2020		2,029,843		$	6.06		8.08	$	4,128
Vested and exercisable, June 30, 2020		956,575		$	5.69		7.00	$	2,435
Vested and expected to vest, June 30, 2020		1,669,947		$	6.01		7.80	$	3,605

Of the options granted in the six months ended June 30, 2020, 226,110 were performance-based options. Vesting of these performance-based options is contingent on the occurrence of certain regulatory and commercial milestones. The Company is recognizing the expense as straight-line over the expected performance achievement term.

The following table summarizes information about RSU activity during the six months ended June 30, 2020:

	RSUs			AVERAGE GRANT DATE FAIR VALUE (IN DOLLARS PER SHARE)
Outstanding, December 31, 2019		160,900		$	3.25
Granted		—			—
Vested		(80,450	)		3.25
Forfeited		—			—
RSUs outstanding at June 30, 2020		80,450		$	3.25

The number of RSUs vested includes shares of common stock withheld on behalf of employees to satisfy the minimum statutory tax withholding requirements. On June 30, 2020, 42,250 RSUs vested as a result of a regulatory milestone. 31,962 common shares were issued on July 2, 2020 related to the vesting event.

Unrecognized compensation expense related to unvested options as of June 30, 2020 was $2.6 million and will be recognized over the remaining vesting periods of the underlying awards. The weighted-average period over which such compensation is expected to be recognized is 2.0 years. Unrecognized compensation expense related to unvested RSUs as of June 30, 2020 was $177,000 and will be recognized over the remaining vesting periods of the underlying awards. The weighted-average period over which such compensation is expected to be recognized is 0.6 years.

The Company recorded stock-based compensation expense in the following expense categories of its accompanying condensed consolidated statements of operations and comprehensive loss for the three and six months ended June 30, 2019 and 2020 (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2020		2019		2020
Research and development	$	72	$	177	$	140	$	321
General and administrative		254		444		541		808
Total	$	326	$	621	$	681	$	1,129