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Abstract

CD8 T cells are a part of the adaptive immune system and are capable of eliminating cancer cells. It is well established that CD8 T cell function can be regulated by T cell metabolism. Upon activation, T cells increase the breakdown of glucose (glycolysis) and increase mitochondrial metabolism. The increase in glycolysis promotes rapid energy production and increases the levels of glycolytic intermediates to be used for nucleotide, amino acid, and lipid synthesis. T cells that have a high glycolytic rate also have increased expression of pro-inflammatory cytokines: interferon gamma (IFNγ) and tumour necrosis factor alpha (TNFα). In addition, exogenous pyruvate in other cell types has been associated with increased glycolysis. In light of this, we were interested in determining if extracellular availability of pyruvate could improve CD8 T cell anti-tumor function. We hypothesize that supplementing CD8 T cells with sodium pyruvate (NaPyr) will improve CD8 T cell ability to sustain the production of cytokines and cytotoxins to kill cancer cells. We found that CD8 T cells restimulated in the presence of exogenous pyruvate had increased expression of IFNγ, TNFα, and perforin compared to NaCl-exposed T cells due to differences in posttranscriptional regulation. In addition, CD8 T cells exposed to NaPyr had improved tumour cell killing. We then mechanistically explored how exogenous pyruvate improves T cell function. We found that NaPyr supplemented CD8 T cells had an increase pyruvate uptake and a decrease in glucose uptake compared to NaCl-exposed CD8 T cells. We then performed GC-MS on CD8 T cells cultured in labelled or unlabelled glucose to assess how NaPyr supplementation alters metabolite levels, as well as glucose metabolism. We found that NaPyr supplementation increases levels of 3-phosphoglycerate and phosphoenolpyruvate, TCA cycle metabolites, and many amino acids. We used activators/inhibitors of metabolic enzymes/transporters to determine if specific metabolic node(s) were important for the NaPyr supplementation phenotype. We found some interesting observations but were unable to determine a specific mechanism. Determining how extracellular pyruvate alters metabolism could provide insight into metabolic pathways that may be important for CD8 T cell function and potentially use this knowledge to improve immunotherapies against cancer.