Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

17.Income Taxes

The components of loss before provision for income taxes for the periods presented were as follows (in thousands):

	Year Ended December 31,
	2023			2022			2021
Domestic	$	(225,335	)	$	(200,427	)	$	(207,314	)
Foreign		31			59			16
Total loss before provision for income taxes	$	(225,304	)	$	(200,368	)	$	(207,298	)

Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes.

The significant components of our deferred tax assets and liabilities as of the dates presented were as follows (in thousands):

	December 31,
	2023			2022
Deferred tax assets
Net operating losses	$	251,724		$	210,609
Tax credit carryforward		43,528			36,848
Nonqualifying stock options		29,166			23,885
Operating lease liabilities		25,357			27,199
Deferred revenue		18,874			26,170
Capitalized research and development		42,134			40,957
Other		6,146			5,859
Total deferred tax assets		416,929			371,527
Less: Valuation allowance		(402,424	)		(346,578	)
Deferred tax assets, net of valuation allowance		14,505			24,949
Deferred tax liabilities
Tangible and intangible assets		(1,281	)		(4,897	)
Right-of-use assets		(13,224	)		(20,052	)
Net deferred taxes	$	—		$	—

ASC Topic 740, Income Taxes, requires that the tax benefit of net operating losses ("NOLs"), temporary differences and credit carryforwards be recorded as an asset to the extent that management assesses that realization is “more likely than not.” Realization of the future tax benefits is dependent on our ability to generate sufficient taxable income within the carryforward period. Because of our history of operating losses, management believes that recognition of the deferred tax assets arising from the above-mentioned future tax benefits is currently not likely to be realized and, accordingly, has provided a valuation allowance. The valuation allowance increased by $55.8 million and $49.6 million during the year ended December 31, 2023 and 2022, respectively.

Federal tax laws impose substantial restrictions on the utilization of NOL and credit carryforwards in the event of an ownership change, as defined in Section 382 of the Internal Revenue Code of 1986. Accordingly, our ability to utilize these carryforwards may be limited due to such ownership changes. We have completed a Section 382 analysis for changes in ownership through June 30, 2023 and continue to monitor for changes that could trigger a limitation. Based on this analysis, we do not expect to have any permanent limitations on the utilization of our federal NOLs. Under the Tax Cuts and Jobs Act of 2017 federal income tax law, federal NOLs incurred in 2018 and future years may be carried forward indefinitely, but the deductibility of such federal NOLs is subject to an annual limitation. NOLs generated prior to 2018 are eligible to be carried forward up to 20 years. As of December 31, 2023, we had U.S. federal NOLs of $192.5 million and U.S. federal tax credits of $47.2 million that will begin to expire in 2028. We also had $768.2 million of NOLs as of December 31, 2023 that do not expire.

The effective tax rate of our provision for income taxes differs from the federal statutory rate for the periods presented as follows:

	Year Ended December 31,
	2023	2022	2021
Statutory rate	21.0%	21.0%	21.0%
State tax, net of federal tax benefit	4.0	3.8	8.3
Share-based compensation	(2.9)	(2.0)	14.1
Permanent items	(0.1)	(0.2)	(0.1)
Credits	2.3	3.0	4.7
Other	1.0	(1.2)	(0.3)
Change in valuation allowance	(25.3)	(24.4)	(47.7)
Total	0.0%	0.0%	0.0%

We account for global intangible low-taxed income as period costs when incurred.

We recognize, in the consolidated financial statements, the effect of a tax position when it is more likely than not, based on the technical merits, that the position will be sustained upon examination. We had unrecognized tax benefits of $9.3 million as of December 31, 2023.

A reconciliation of the beginning and ending amounts of unrecognized tax benefits for the dates presented are as follows (in thousands):

Balance at December 31, 2020	$	3,489
Additions in 2021		3,426
Balance at December 31, 2021		6,915
Additions in 2022		1,202
Balance at December 31, 2022		8,117
Additions in 2023		1,186
Balance at December 31, 2023	$	9,303

During the year ended December 31, 2023, 2022 and 2021, we recognized uncertain tax positions of $1.2 million, $1.2 million and $3.4 million, respectively, related to a reduction of the research and development credit deferred tax asset. Unrecognized tax benefits may change during the next twelve months for items that arise in the ordinary course of business. We do not expect a material change to our unrecognized tax benefits over the next twelve months that would have an adverse effect on our operating results.

We recognize interest and penalties accrued on any unrecognized tax benefits as a component of income tax expense. We had no accrued interest or penalties related to uncertain tax positions as of December 31, 2023 and 2022.

We file federal and certain state income tax returns, which provide varying statutes of limitations on assessments. However, because of NOL carryforwards, substantially all tax years since inception remain open to federal and state tax examination.