Analysis of Immune Tolerance Mechanisms in T1D patients Receiving Sequential B Cell Depletion and T Cell Costimulatory Blockade

About This Grant

Project Summary Type 1 diabetes (T1D) is caused by an autoimmune attack on insulin-producing β-cells in the pancreatic islets of Langerhans. Although T cells drive β-cell destruction, B cells are important for disease pathogenesis. T1D patients with high T cell counts who are treated with B cell depletion therapy (Rituximab, RTX) tend to progress more quickly. Conversely, patients with elevated B cell counts who are treated with CTLA-4-Ig (Abatacept, ABA, which blocks T cell co-stimulation), progress more rapidly. These findings prompted the TN-25 TrialNet trial, in which sequential therapy with RTX and ABA is being compared to therapy with RTX and placebo. This design provides a unique opportunity to analyze T cell and B cell compartments before and after treatment and characterize tolerance mechanisms that may be restored by this potentially synergistic combination therapy. We hypothesize that sequential RTX and ABA treatment abrogates key co-stimulation signals delivered by (self)- antigen-presenting B cells to autoreactive T cells and vice versa. In Aim 1 we will determine if sequential RTX and ABA abrogates co-stimulation signals delivered by B cells to T cells. We will analyze islet-reactive T cells in tetramer binding and activation-induced marker assays. Simultaneously, we will measure cell surface protein expression and clonotypes using single cell RNA-seq and TCR-seq and evaluate CD4 and CD8 T cell populations as well as a novel population of KIR+CD8+ regulatory T cells for alterations in activation, specificity and gene signatures. In aim 2, we will determine if ABA-mediated limitation of T cell help leads to more profound B cell tolerance through clonal deletion. We will analyze recombinant antibodies cloned from autoreactive B cells at naïve and memory stages of development to evaluate defects in clonal recruitment, expansion and evolution. We will also investigate the trajectory of serum IgM and IgG autoantibodies over time and potential blocking effects of IgM on IgG. Taken together, these studies will identify how this novel combination therapy contributes to T cell and B cell tolerance in T1D.