STOCK OPTIONS (Tables)

9 Months Ended

Sep. 30, 2021

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


	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020

Research and development expenses	$	986,406	$	1,667,986	$	2,786,486	$	4,555,447
General and administrative expenses		1,612,841		1,963,010		4,900,435		5,561,328
Total stock-based compensation	$	2,599,247	$	3,630,996	$	7,686,921	$	10,116,775

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 nine months ended September 30, 2021 and is presented below:


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		6,788,800			2.50
Exercised		(838,600	)		1.13
Forfeited		(2,987,752	)		4.62
Expired		(3,772	)		0.11
Outstanding at September 30, 2021		17,248,319		$	4.39		6.94	$	2,922,393
Vested at September 30, 2021		9,928,222		$	5.19		5.42	$	2,714,243
Vested and expected to vest at September 30, 2021		16,474,538		$	4.46		6.84	$	2,891,015