STOCK OPTIONS (Tables)

6 Months Ended

Jun. 30, 2021

Stock-based compensation expense was classified in the consolidated statements of operations and comprehensive loss as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020

Research and development expenses	$	913,003	$	1,522,571	$	1,800,080	$	2,887,461
General and administrative expenses		1,594,269		1,825,689		3,287,594		3,598,318
Total stock-based compensation	$	2,507,272	$	3,348,260	$	5,087,674	$	6,485,779

The weighted average assumptions used principally in determining the fair value of options granted to employees were as follows:

A summary of option activity for the six months ended June 30, 2021 and is presented below:

SUMMARY OF OPTION ACTIVITY

Options	Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term in Years		Aggregate Intrinsic Value
Outstanding at December 31, 2020		14,289,643		$	5.15
Granted		6,613,800			2.53
Exercised		(838,600	)		1.13
Forfeited		(1,588,014	)		5.25
Outstanding at June 30, 2021		18,476,829		$	4.38		7.31	$	2,805,174
Vested at June 30, 2021		9,568,928		$	5.23		5.54	$	2,710,024
Vested and expected to vest at June 30, 2021		17,440,115		$	4.47		7.19	$	2,793,225