14. Income Taxes

The income tax provision for the years ended December 31, 2020 and 2019 are as follows (in thousands):

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Deferred tax assets and liabilities reflect the net effects of net operating losses, or NOLs, and tax credit carryovers and temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Realization of the deferred tax assets is contingent on future taxable income and based upon the level of historical losses, management has concluded that the deferred tax assets do not meet the more-likely-than-not threshold for realizability. Accordingly, a full valuation allowance continues to be recorded against the Company's deferred tax assets as of December 31, 2020 and 2019. The Company’s valuation allowance increased by $5.9 million and $9.0 million for the years ended December 31, 2020 and 2019, respectively.

Significant components of the Company’s net deferred tax assets as of December 31, 2020 and 2019 are as follows (in thousands):

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A reconciliation of income tax expense computed at the statutory federal income tax rate to income taxes as reflected in the financial statements is as follows:

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As of December 31, 2020, the Company had U.S. federal and state NOLs of $90.2 million and $88.8 million, respectively, that begin to expire starting in 2027. As of December 31, 2020, the Company had federal research and development tax credit carryforwards of $14.9 million that begin to expire in 2027. Net operating loss and tax credit carryforwards may become subject to annual limitations in the event of certain cumulative changes in the ownership interest of significant stockholders over a three-year period in excess of 50%, as defined by Sections 382 and 383 of the Internal Revenue Code as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities.

The Company files income tax returns in the U.S. and the Commonwealth of Pennsylvania. Tax years for 2017 and thereafter are open and potentially subject to examination by the federal and state taxing authorities. The Company is currently not under examination by the Internal Revenue Service or any other jurisdictions for any tax years. To the extent the Company utilizes any tax attributes from a tax period that may otherwise be closed due to statute expiration, the Internal Revenue Service, state tax authorities, or other governing parties may still adjust the tax attributes upon their examination of the future period in which the attribute was utilized. There are no uncertain tax positions recorded for any federal or state positions. The Company’s policy is to record interest and penalties related to tax matters in income tax expense.