Objective

T cells coordinate immune function by differentiating into highly specialised cellular lineages. Whereas effector CD4+ and CD8+ T cells promote immune activation and drive clearance of infections and cancer, CD4+ regulatory T (Treg) cells, dependent upon the transcription factor Foxp3, suppress their function, preventing excessive autoimmune and allergic reactions. The suppressive function of Treg cells also powerfully prevents immune responses against cancer. We are interested in understanding general principles and specific mechanisms which promote T cell immunosuppression within tumours. We will discuss recent experimental data evidencing mechanisms by which immunosuppressive gene expression programmes are driven within tumours, and extracellular environmental factors such as hyperoxia and hyperkalaemia that promote immunosuppressive T cell differentiation.