Autoreactive CD4 Tscm Development in Type 1 Diabetes

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PROJECT SUMMARY Autoimmune type 1 diabetes (T1D) results from T cell-mediated destruction of pancreatic beta cells in the islet, leading to lifelong dependence on exogenous insulin and risk of life-threatening glycemic events. As a result, deletion or immune deviation of islet-autoreactive T cells is a major therapeutic goal in the prevention and treatment of T1D. The existence of memory T cells with stem cell properties (Tscm) raises the possibility that they serve as an ongoing reservoir of autoreactive T cells in T1D. However, little is known about the presence of islet-specific CD4 Tscm cells in T1D. We have made the novel observation that there is an increased frequency of Tscm within the CD4 T cell compartment in peripheral blood from T1D patients compared with healthy donors (HD). Importantly, we also detected increased islet-specific CD4 T cells with a Tscm phenotype in the peripheral blood of T1D subjects relative to HD, both immediately and up to 7 years following diagnosis. Transcript analysis of islet-specific CD4 T cells showed increased expression of TCR, Wnt-β-catenin, and IL-7 signaling gene sets in cells from T1D subjects compared to HD, pathways known to play a central role in CD4 Tscm development. Further study is required to confirm that islet-specific CD4 Tscm in T1D have functional Tscm properties and to determine the mechanism leading to increased Tscm cell frequency in T1D. We hypothesize that islet-specific CD4 Tscm in T1D have the capacity for self-renewal and differentiation into central and effector memory T cells, and are increased in T1D due to elevated TCR, Wnt-β-catenin, and/or cytokine signaling. We will address our hypothesis in two specific aims. Aim 1 will investigate whether islet-specific CD4 Tscm cells in T1D subjects have phenotypic and functional properties of a memory stem cell population. We will evaluate the transcript profile, telomere length, survival, and the potential for self-renewal and differentiation of islet-specific CD4 Tscm compared to total CD4 naïve, Tscm, central memory (Tcm) and effector memory (Tem) populations in peripheral blood from T1D patients. The characteristics of CD8 Tscm cells will serve as a reference. As a control for disease, we will compare transcript profiles and function of total CD4 naïve, Tscm, Tcm, and Tem populations in peripheral blood from matched HD. Aim 2 will test the hypothesis that signaling pathways supporting the development of CD4 Tscm are elevated in T1D subjects versus HD, contributing to increased islet-specific CD4 Tscm cells in T1D. We will compare TCR, Wnt-β-catenin, and IL-7R pathway expression and signaling in CD4 naïve T cells from T1D subjects and HD. In parallel, we will determine if these pathways contribute to superior differentiation or survival of CD4 Tscm cells in T1D subjects vs. HD in response to islet peptides or polyclonal stimulation in the presence or absence of Wnt inhibitors/agonists and IL-7. The proposed study is appropriate for the R21 mechanism because it is an exploratory investigation of a novel autoreactive cell type in T1D. The results will open new areas of inquiry for targeting autoreactivity to prevent and treat T1D.