	As of December 31, 2019
	Estimated Useful Lives	Gross Carrying Value		Accumulated Amortization			Impairment			Net Book Value
Internally developed patents	6 – 10 years	$	746,323	$	(448,874	)	$	—		$	297,449
Acquired licenses	16 – 20 years		285,000		(269,221	)		—			15,779
Total intangible assets subject to amortization		$	1,031,323	$	(718,095	)	$	—		$	313,228
IPR&D assets	Indefinite		13,418,967		—			(1,000,000	)		12,418,967
Total		$	14,450,290	$	(718,095	)	$	(1,000,000	)	$	12,732,195

	As of December 31, 2018
	Estimated Useful Lives	Gross Carrying Value		Accumulated Amortization			Impairment			Net Book Value
Internally developed patents	6 – 10 years	$	718,559	$	(317,172	)	$	—		$	401,387
Acquired licenses	16 – 20 years		285,000		(253,430	)		—			31,570
Total intangible assets subject to amortization		$	1,003,559	$	(570,602	)	$	—		$	432,957
IPR&D assets	Indefinite		37,868,978		—			(24,450,011	)		13,418,967
Total		$	38,872,537	$	(570,602	)	$	(24,450,011	)	$	13,851,924

Amortization expense of intangible assets subject to amortization totaled $147,500 and $83,652 for the years ended December 31, 2019 and 2018, respectively, and was classified as research and development expenses in the accompanying consolidated statements of operations and comprehensive loss.

The above future estimated amortization expense does not include potential amortization charges related to the remaining carrying value of IPR&D assets as of December 31, 2019. Those assets, which represent incomplete technologies, will be amortized to expense once the underlying technologies are substantially complete over their estimated useful lives, expected to be 15 to 18 years. In the event that in the future the Company ceases the development of these assets, the remaining carrying value would be written off at that time. IPR&D assets are periodically assessed for impairment by considering the state of completion of the projects, the remaining activities required to complete development, the anticipated market for the completed products, and anticipated future cash required to complete development.

During the fourth quarter of 2018, based on the continued decline of the Company’s market capitalization following the completion of the equity offerings and a strategic review of the development pipeline at the direction of a new CEO, the Company concluded under the qualitative assessment that an impairment indicator was present as it related to three IPR&D assets. Based on the Company’s strategic review, management concluded it would discontinue development of the Oncosyn cancer immunotherapy program and accordingly the entire amount of this IPR&D asset, or $3,061,011 was charged to expense. For the remaining two IPR&D assets related to HepTcell and SparVax-L, the Company calculated fair value using an excess earnings method or discounted cash flow model and compared the fair value to the carrying amount of the indefinite lived asset. Based on the analysis, the fair value of the Company’s HepTcell IPR&D asset exceeded its carrying value by an amount greater than 10%. However, during 2018, the Company concluded that the fair value of the SparVax-L IPR&D intangible asset was approximately $1,000,000 as compared to the current carrying value of the asset of $22,389,000, which resulted in an impairment charge of $21,389,000. Key assumptions used in the analysis included projected cash flows, a probability of success of the ultimate project, and the discount rate.

During 2019, as a result of the SparVax-L NIAID contract completion and the US government’s funding prioritization of only single dose anthrax vaccine candidates, we abandoned the project and concluded that the full remaining net book value of the SparVax-L IPR&D asset was impaired. As a result, of $1,000,000 was written off as an impairment charge which was classified as a component of operating expenses during the year ended December 31, 2019.

During the year ended December 31, 2018, an additional $490,676 of goodwill was written off as an impairment charge. The impairment was an adjustment to reduce the tax refund receivable acquired in connection with a 2017 business combination.

Changes in the carrying amounts of IPR&D assets and goodwill for the years ended December 31, 2019 and 2018 were:

	IPR&D			Goodwill
Balance, January 1, 2018	$	38,245,871		$	—
Additions		—			490,676
Foreign currency translation adjustments		(376,893	)		—
Impairment charges		(24,450,011	)		(490,676	)
Balance, December 31, 2018	$	13,418,967		$	—
Impairment charges		(1,000,000	)
Balance, December 31, 2019	$	12,418,967		$	—