Personnel expenses primarily include salary, benefits, stock-based compensation and payroll taxes. The $1.5 million increase in personnel expenses for the three months ended September 30, 2021, as compared to the three months ended September 30, 2020, was primarily due to higher stock-based compensation expense and an increase in employee headcount. We expect personnel expenses increase over the next twelve months as a result of expanded development of CDX-0159, although there may be fluctuations on a quarterly basis.
Laboratory supplies expenses include laboratory materials and supplies, services, and other related expenses incurred in the development of our technology. The $0.5 million increase in laboratory supply expenses for the three months ended September 30, 2021, as compared to the three months ended September 30, 2020, was primarily due to higher laboratory materials and supplies purchases. We expect laboratory supplies expenses to remain relatively consistent over the next twelve months, although there may be fluctuations on a quarterly basis.
Facility expenses include depreciation, amortization, utilities, rent, maintenance and other related expenses incurred at our facilities. The $0.5 million decrease in facility expenses for the three months ended September 30, 2021, as compared to the three months ended September 30, 2020, was primarily due to lower rent as a result of the consolidation of our Massachusetts lab and manufacturing facilities in the second quarter of 2020 and lower repairs expenses. We expect facility expenses to remain relatively consistent over the next twelve months, although there may be fluctuations on a quarterly basis.
Product development expenses include clinical investigator site fees, external trial monitoring costs, data accumulation costs, contracted research and outside clinical drug product manufacturing. The $1.2 million increase in product development expenses for the three months ended September 30, 2021, as compared to the three months ended September 30, 2020, was primarily due to an increase in contract research and clinical trial expenses. We expect product development expenses to increase over the next twelve months as a result of expanded development of CDX-0159, although there may be fluctuations on a quarterly basis.
General and Administrative Expense
The $2.2 million increase in general and administrative expenses for the three months ended September 30, 2021, as compared to the three months ended September 30, 2020, was primarily due to higher personnel and legal expenses. We expect general and administrative expenses to increase over the next twelve months, although there may be fluctuations on a quarterly basis.
Intangible Asset Impairment
We evaluated the TAM program IPR&D asset for potential impairment as a result of a lack of interest in the program from third parties. We concluded that the TAM program IPR&D asset was fully impaired, and a non-cash impairment charge of $3.5 million was recorded in the third quarter of 2021.
(Gain) Loss on Fair Value Remeasurement of Contingent Consideration
The $1.9 million gain on fair value remeasurement of contingent consideration for the three months ended September 30, 2021 was primarily due to updated assumptions for the TAM program. The $0.7 million loss on fair value remeasurement of contingent consideration for the three months ended September 30, 2020 was primarily due to changes in discount rates and the passage of time.
Investment and Other Income, Net
Investment and other income, net for the three months ended September 30, 2021 was consistent with the three months ended September 30, 2020. We expect investment and other income to increase over the next twelve months due to higher levels of cash as a result of our July 2021 underwritten public offering, although there may be fluctuations on a quarterly basis.
Income Tax Benefit
A $0.2 million non-cash income tax benefit was recorded related to the impairment of the TAM program IPR&D asset in the third quarter of 2021.