In contrast to the inhibitory action of fumaric acid on the activity of CD8+ T cells, ketoglutaric acid, an intermediate metabolite of the TCA cycle in renal cell carcinoma, is able to enhance the antitumor activity of CD8+ T cells by increasing the expression of major histocompatibility complex I (MHC-I) molecules in cancer cells. The gene discussed is CD8A; the disease is cancer.