WARRANTS (Tables)

9 Months Ended

Sep. 30, 2021

Warrant [Abstract]

Summary of Assumptions using Black- Scholes Option Pricing Model to estimate fair value

The aggregate fair value of the 2018 Offering Warrants of $7.4 million was estimated using the Black-Scholes option-pricing model with the following assumptions:

	Upon Issuance
Common Stock Warrants:
Expected term (in years)	7.0
Expected volatility (%)	62.5%
Risk-free interest rate (%)	2.8%
Expected dividend yield (%)	0%

The fair value of the 2017 and 2016 Placement Warrants at September 30, 2021 and December 31, 2020, respectively, was estimated using the Black-Scholes option-pricing model and the following weighted-average assumptions:

	2017 Placement Warrants				2016 Placement Warrants
	September 30, 2021		December 31, 2020		September 30, 2021		December 31, 2020
Expected term (in years)	2.3		3.0		1.9		2.6
Expected volatility	87.1	%	86.9	%	86.6	%	86.3	%
Risk-free interest rate	0.4	%	0.2	%	0.3	%	0.2	%
Expected dividend yield	—	%	—	%	—	%	—	%

Schedule of Key Terms of Placement Warrants

The key terms of the 2017 and 2016 Placement Warrants are as follows:

	Issuance Date	Term	Exercise Price Per Share		Warrants Exercised during the nine months ended September 30, 2021	Warrants Outstanding at September 30, 2021
2017 Placement Warrants	January 2017	7 years	$	3.17	118,868	1,500,022
2016 Placement Warrants	August and September 2016	7 years	$	2.95	552	536,711
Total					119,420	2,036,733