Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income taxes

Schedule of components of Income tax expense

For the years ended December 31, 2021, 2020, and 2019 income tax expense consisted of the following (in thousands):

	Year ended December 31,
	2021		2020		2019
Current tax expense:
Federal	$	—	$	—	$	—
State		—		194		—
Current income tax expense		—		194		—
Deferred
Federal		—		—		—
State		—		—		—
Deferred income tax expense		—		—		—
Total income tax expense	$	—	$	194	$	—

Schedule of reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations

	December 31,
	2021		2020
Income tax benefit using U.S. federal statutory rate	21.00	%	21.00	%
State tax benefit, net of federal benefit	3.01	%	(8.55)	%
Research and development tax credits	2.71	%	2.84	%
Permanent items	(0.44)	%	(0.60)	%
Change in the valuation allowance	(21.23)	%	35.09	%
NOL and tax credit expiration under Section 382	(4.34)	%	(52.67)	%
Other	(0.71)	%	2.60	%
	—	%	(0.29)	%

Schedule of principal components of deferred tax assets and liabilities

The principal components of the Company’s deferred tax assets and liabilities are as follows (in thousands):

	December 31,
	2021		2020
Deferred tax assets:
Net operating loss carryforwards	$	98,777	$	86,665
Capitalized research and development		1,276		1,565
Research and development credits		4,516		2,043
Stock-based compensation		4,200		4,041
Installment sale		8,819		9,981
Lease liability		730		950
Other deferred tax assets		411		680
Total deferred tax assets		118,729		105,925
Deferred tax liabilities:
Right-of-use asset		(574)		(742)
Debt discount		(11)		(2,245)
Other deferred tax liability		(91)		—
Total deferred tax liabilities		(676)		(2,987)
Net deferred tax asset prior to valuation allowance		118,053		102,938
Valuation allowance		(118,053)		(102,938)
Net deferred tax asset	$	—	$	—