Project Summary: 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 effect...