Chronic stimulation through the T cell receptor (TCR) drives T cells to progressively lose their ability to exert their effector functions in a process termed exhaustion. T cell exhaustion occurs during both cancer and persistent infections contributing to the failure of the adaptive immune response to control the tumor or infection. CD8 T cell exhaustion was initially described during chronic lymphocytic choriomeningitis virus (LCMV) infection. However, CD4 T cells control the delicate balance between the maintenance of effector CD8 T cell responses versus the development of CD8 T cell exhaustion during chronic infection. Despite their critical role in maintaining the antiviral CD8 T cell response, much less is known about the specific signaling defects and metabolic changes that occur within exhausted CD4 T cells. Gene expression studies examining LCMV-specific CD4 T cells have indicated that hundreds of genes are differentially expressed between CD4 T cells isolated during an acute versus chronic LCMV infection and that these genetic changes are different for CD4 T cells versus CD8 T cells. Many of the differentially expressed genes in CD4 T cells are related to TCR signaling and metabolic pathways, but how these alterations lead to specific defects in TCR signaling and cellular metabolism has not been defined. Our long-term goal is to understand the mechanisms that mediate CD4 T cell dysfunction during chronic viral infections and cancer progression. The objective of this application is to determine the specific defects in CD4 T cell signaling and metabolic pathways that develop during chronic LCMV infection. Our central hypothesis is that virus-specific CD4 T cells develop multiple defects in critical signaling pathways downstream of the TCR and metabolic pathways, resulting in the impaired ability of the CD4 T cell to mediate effector activity and proliferate during a chronic viral infection. Our hypothesis is based our own preliminary data, in conjunction with published genetic studies, indicating that expression of multiple signaling and metabolic proteins are reduced in virus-specific CD4 T cells following a persistent LCMV Clone 13 infection. The rationale for the proposed research is that, once the principal signaling and metabolic defects affecting exhausted CD4 T cells are identified, new and innovative therapeutic approaches can be targeted to restore CD4 T cell effector activity and enhance clearance of chronic viral infections and human cancers. We will achieve the goals of this proposal by pursuing the following two specific aims: 1) Examine the effects of viral exhaustion on early TCR signaling and function in CD4 T cells and 2) Investigate the impact of viral exhaustion on metabolism in CD4 T cells. The completion of these aims will determine if T cell exhaustion after infection with a chronic virus results in CD4 T cell intrinsic changes in the signaling capacity and metabolic function that would impact effector functions. Our results will provide insight into the molecular mechanism of CD4 T cell exhaustion and highlight potential avenues to modulate either signaling or metabolism to enhance the function of exhausted CD4 T cells during either chronic viral infection or cancer immunotherapy.
Some viruses and human cancers have evolved mechanisms that inhibit critical aspects of the immune response that prevent effective elimination of the infection or malignant cell. The proposed research is relevant to public health because identifying the mechanisms that control immune system dysfunction during a chronic viral infection or cancer progression will increase understanding and treatment of the pathogenesis of chronic viral infections and human malignancies. Thus, the proposed research is relevant to the part of the NIH's mission that pertains to developing new therapeutic interventions aimed at reducing disease burden due to chronic viral infections and cancer.
