Background: Upon activation, CD8+ T cells undergo distinct metabolic changes that support their rapid proliferation and increased biosynthetic demands. Specifically, nutrients are now widely recognised as the ‘fourth signal’ involved in shaping the T cell response. While the transcriptional and epigenetic signatures of different T cell fates have been thoroughly characterised, much remains unexplored regarding the specific metabolic changes that T cells undergo during differentiation.
Aim: Here, we aimed to mechanistically characterise the effect of metabolic changes on T cell fitness, phenotype and function.
Methods: Though in vivo models are widely employed to study different T cell states, the variability of the metabolic composition in different tissue microenvironments presents a challenge in investigating how specific nutrients may alter T cell phenotypes and function. Hence, in vitro models are advantageous due to the ease of manipulating the extracellular nutrient composition. Using physiological media which mimic the metabolic composition of human and mouse plasma, we established more biologically relevant in vitro models of effector T cell differentiation.
Results: T cells in physiological media exhibited attenuated proliferation and an altered phenotype characterised by higher CD69 and PD-1 expression. Physiological media also altered T cell function, with higher production of IFNg, TNFa and IL-2. Though the higher concentration of calcium in physiological media appeared to be a driver of augmented IFNg and TNFa production, elevated IL-2 secretion was attributed to other nutrients in physiological media.
Conclusion: Thus, T cells acutely stimulated in physiological media are phenotypically and functionally altered. These in vitro cultures allow for the profiling of the molecular and metabolic pathways that may be altered by specific nutrients and can be used to model other T cell states, such as exhaustion. Further understanding of how nutrients shape the T cell response may improve therapy-induced reinvigoration of anti-tumour immunity within patients.