During the years ended December 31, 2020 and 2019, the Company recorded no income tax benefits due to the losses incurred due to the uncertainty of future taxable income.

A reconciliation of the expected income tax (benefit) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows for the year ended December 31, 2020 and 2019:

	December 31,
	2020			2019
Income tax computed at federal statutory rate		21	%		21.0	%
State taxes, net of federal benefit		5.7	%		7.0	%
Change in valuation allowance		(27.3	)%		(31.0	)%
R&D credit carryovers		7.6	%		4.1	%
Stock-based compensation		(6.7	)%		(0.9	)%
Permanent differences		(0.3	)%		(0.2	)%
Total		0.0	%		0.0	%

The Company’s deferred tax assets at December 31, 2020 and 2019, consist of the following:

	December 31,
	2020			2019
Deferred tax assets:
Net operating losses	$	48,832		$	42,647
Tax credit carryforwards		10,270			6,309
Lease liability		6,430			6,542
Intangibles		1,469			1,498
Stock-based compensation		4,496			534
Depreciation and amortization		230			188
Other		14			13
Total gross deferred tax asset		71,741			57,731
Valuation allowance		(65,813	)		(51,537	)
Net deferred tax asset		5,928			6,194
Deferred tax liability
Operating lease assets		(5,928	)		(6,194	)
Total deferred tax liability		(5,928	)		(6,194	)
	$	—		$	—

The Company has incurred net operating losses (“NOL”) since inception. As of December 31, 2020, the Company had federal NOL carryforwards of $174,028 available to reduce taxable income, of which $43,127 expire beginning in 2035 and $130,901 do not expire. The Company has state NOL carryforwards of $192,346 as of December 31, 2020 available to reduce future state taxable income, which expire at various dates beginning in 2035.

As of December 31, 2020, the Company also had available federal research and development tax credit carryforwards of $8,139 available to reduce future tax liabilities, which begin to expire beginning in 2035. The Company also has state research and development tax credit carryforwards of $2,699 available to reduce future state tax liabilities, which expire at various dates beginning in 2030.

Utilization of the NOL carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 (“Section 382”) due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain stockholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.

The Company recorded a valuation allowance against its deferred tax assets for the years ended December 31, 2020 and 2019 because the Company’s management believes that it is more likely than not that these assets will not be realized. The valuation allowance increased by approximately $14,276 and $23,307 for the years ended December 31, 2020 and 2019, respectively, primarily as a result of operating losses generated with no corresponding financial statement benefit.

The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations. The Company’s tax years are still open under statute from inception to the present.

In response to the COVID-19 pandemic, the Coronavirus Aid, Relief and Economic Security Act (CARES Act) was signed into law in March 2020. The CARES Act lifts certain deduction limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (“2017 Tax Act”). Corporate taxpayers may carryback NOLs originating during 2018 through 2020 for up to five years, which was not previously allowed under the 2017 Tax Act. The CARES Act also eliminates the 80% of taxable income limitations by allowing corporate entities to fully utilize NOL carryforwards to offset taxable income in 2018, 2019 or 2020. Taxpayers may generally deduct interest up to the sum of 50% of adjusted taxable income plus business interest income (30% limit under the 2017 Tax Act) for tax years beginning January 1, 2019 and 2020. The CARES Act allows taxpayers with alternative minimum tax credits to claim a refund in 2020 for the entire amount of the credits instead of recovering the credits through refunds over a period of years, as originally enacted by the 2017 Tax Act.

In addition, the CARES Act raises the corporate charitable deduction limit to 25% of taxable income and makes qualified improvement property generally eligible for 15-year cost-recovery and 100% bonus depreciation. The enactment of the CARES Act did not result in any adjustments to the Company’s income tax provision for the year ended December 31, 2020, or to the Company’s net deferred tax assets as of December 31, 2020, since the Company has not recorded any U.S. federal or state income tax benefits for the net losses incurred in any year due to the uncertainty of realizing a benefit from those items.