T cell exhaustion and Interleukin 2 downregulation.

T cells reactive to tumor antigens and viral antigens lose their reactivity when exposed to the antigen-rich environment of a larger tumor bed or viral load. Such non-responsive T cells are termed exhausted. T cell exhaustion affects both CD8+ and CD4+ T cells. T cell exhaustion is attributed to the functional impairment of T cells to produce cytokines, of which the most important may be Interleukin 2 (IL2). IL2 performs functions critical for the elimination of cancer cells and virus infected cells. In one such function, IL2 promotes CD8+ T cell and natural killer (NK) cell cytolytic activities. Other functions include regulating naïve T cell differentiation into Th1 and Th2 subsets upon exposure to antigens. Thus, the signaling pathways contributing to T cell exhaustion could be linked to the signaling pathways contributing to IL2 loss. This review will discuss the process of T cell exhaustion and the signaling pathways that could be contributing to T cell exhaustion.