Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Taxes

Schedule of components of deferred tax assets

(in thousands)	2021		2020
Operating loss carryforwards	$	90,550	$	90,895
Tax credit carryforwards		28,226		26,550
Stock-based compensation		6,902		6,820
Capitalized research and development		7,818		—
Lease liabilities		220		276
Other		70		162
Total deferred tax assets		133,786		124,703
Right-of-use asset		(213)		(270)
Valuation allowance		(133,573)		(124,433)
Net deferred tax assets	$	—	$	—

Schedule of difference between U.S. federal corporate tax rate and Company effective tax rate

	2021		2020		2019
Expected federal income tax rate	(21.0)	%	(21.0)	%	(21.0)	%
Expiring credits and NOLs	—		—		—
Change in valuation allowance	(9.3)		10.6		26.2
Federal and state credits	1.7		(3.1)		(8.1)
State income taxes, net of federal benefit	2.1		(1.9)		(4.7)
Warrant and future tranche right revaluation loss	26.9		14.2		4.3
Stock-based compensation	—		0.2		0.5
Other	(0.4)		1.0		2.8
Effective tax rate	0.0	%	0.0	%	0.0	%