Exploring Foxp3+ CD4+ Treg cell-stimulating vaccines to inhibit preproinsulin-specific effector CD8+ T cells and autoimmune diabetes

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Vaccines that induce or restore peripheral tolerance and inhibit T cell-mediated autoimmune diabetes in a controlled and antigen-specific manner would be a goal in combating type 1 diabetes. We have established a novel diabetes model in PD-L1-/- and PD-1-/- mice to characterize preproinsulin/(ppins)-specific expression requirements that induce (or prevent) autoreactive CD8+ T cells by plasmid-DNA vaccination. A single injection of pCI/ppins-DNA efficiently induced insulin A-chain (Kb/A12-21)-monospecific CD8+ T cells and severe diabetes in PD-L1/PD-1-deficient mice within 3-5 weeks. In contrast, ppins designer antigens targeted to the cytosol and/or the nucleus (and excluded from direct processing in the Endoplasmatic Reticulum) did not induce this autoreactive CD8+ T-cell response, but efficiently induced Foxp3+ CD25+ CD4+ regulatory T cells (Treg) that suppressed inducible diabetes in PD-L1/PD-1-deficient mice by a subsequent injection of pCI/ppins. These antigens also inhibited spontaneous diabetes development in NOD mice expressing the diabetes-susceptible H-2g7 haplotype (Kd; Db; I-Ag7). The proposal aims to elucidate systemic and local (in the pancreas) mechanisms that inhibit CD8+ T cell-mediated destruction of beta-cells in inducible and spontaneous diabetes models. We will establish vaccination protocols that induce and sustain ppins-specific Treg. In particular, we are interested in (i) the characterization of Treg responses in PD1/PD-L1-competent (B6) versus PD-1/PD-L1-deficient animals; (ii) the identification of I-Ab-restricted epitope(s) and the conditions under which CD4+ T and/or Treg cells are stimulated in vitro and/or in vivo; (iii) the characterization of surface marker and cytokine expression profiles of vaccine-induced Treg populations in distinct tissues. To determine the general applicability of ppins designer antigens, we will analyse if (and which specificities of) vaccine-induced Treg inhibit pCI/ppins-inducible diabetes in PD-1/PD-L1-deficient B6.g7 (Kd; Db; I-Ag7) mice and spontaneous diabetes development in B6.g7/RIP-B7.1 tg and diabetes-susceptible NOD mice. These studies may help to design specific immune intervention protocols that attenuate autoreactive immune responses by Treg.