STOCK OPTIONS (Tables)

3 Months Ended

Mar. 31, 2021

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

	Three Months Ended March 31,
	2021		2020

Research and development expenses	$	887,077	$	1,364,890
General and administrative expenses		1,693,325		1,772,629
Total stock-based compensation	$	2,580,402	$	3,137,519

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 three months ended March 31, 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		5,996,800			2.58
Exercised		(788,600	)		1.13
Forfeited		(1,069,648	)		5.57
Outstanding at March 31, 2021		18,428,195		$	4.46		7.48	$	2,841,774
Vested at March 31, 2021		9,412,878		$	5.16		5.68	$	2,758,524
Vested and expected to vest at March 31, 2021		17,222,580		$	4.56		7.33	$	2,830,060