Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense

The following table summarizes the components of our income tax expense (in thousands):

	Year ended December 31,
	2022		2021
Current:
Federal	$	—	$	—
State	1		1
	1		1
Deferred:
Federal	—		—
State	—		—
	—		—
Income tax expense	$	1	$	1

Schedule of Effective Income Tax Rate Reconciliation

The following is a reconciliation of the expected statutory federal income tax provision to our actual income tax provision (in thousands):

	Year ended December 31,
	2022		2021
Expected income tax benefit at federal statutory tax rate	$	(5,948)	$	(5,840)
State income taxes, net of federal benefit	1		1
Tax credits	(1,850)		(1,180)
Change in valuation allowance	7,327		6,659
Return to provision adjustments	(18)		80
Stock compensation	236		243
Reserve for uncertain tax positions	253		176
Other	—		(138)
Income tax expense	$	1	$	1

Schedule of Deferred Tax Assets and Liabilities

The following table summarizes the significant components of our deferred tax assets and liabilities (in thousands):

	December 31,
	2022		2021
Deferred tax assets:
Net operating loss carryovers	$	90,085	$	87,877
Research and development and other tax credits	36,963		35,344
Intangibles and property and equipment basis difference	496		607
Section 174 research and development	3,302		—
Stock compensation expense	818		587
Lease liability	508		631
Other	597		564
Total deferred tax assets	132,769		125,610
Total deferred tax liabilities	(611)		(782)
Gross deferred tax asset	132,158		124,828
Valuation allowance	(132,158)		(124,828)
Net deferred tax asset	$	—	$	—

Summary of Income Tax Contingencies

The following table summarizes the changes in the amount of our unrecognized tax benefits (in thousands):

	Year Ended December 31,
	2022		2021
Beginning balance of unrecognized tax benefits	$	16,953	$	17,939
Decrease for prior year tax positions	(11,463)		(1,174)
Increase for current year tax positions	295		188
Total	$	5,785	$	16,953