Monoclonal Antibody Blockade of CD226 Decreases Spontaneous Diabetes in the NDO Mouse by Augmenting Treg and Diminishing Effector Functionality

Immunotherapeutics that modulate T cell activation represent a crucial component for inhibiting the autoimmune pathogenesis of type 1 diabetes (T1D) and improving the efficacy of β-cell replacement therapy. Here, we present a novel strategy for reducing diabetes incidence in the NOD mouse using monoclonal antibodies (mAbs) to block the T cell costimulatory receptor, CD226. Notably, female NOD mice treated with 600 µg of ⍺-CD226 mAbs between 7-8 weeks of age showed decreased disease incidence at 30 weeks and reduced insulitis severity compared to mice treated with an isotype control. Ex vivo analysis performed five weeks post-treatment revealed ⍺-CD226 mAbs persist in vivo, reducing the availability of CD226 on CD8+ T cells and Tregs. Flow cytometric analysis demonstrates that ⍺-CD226 mAbs inhibit the proliferation of both CD4+ and CD8+ T cells in vitro. Similarly, ex vivo samples had reduced CD4+ and CD8+ effector memory T cell proliferation following ⍺-CD226 mAb treatment. Splenocytes treated with ⍺-CD226 mAbs exhibited a more immunoregulatory cytokine profile with decreased IFN-γ and increased IL-10 production. This phenotype was further corroborated by 51Cr-release assays demonstrating reduced cell-mediated lympholysis (CML) of murine β-cells by ⍺-CD226 mAb-treated autoreactive cytotoxic lymphocytes. Ex vivo phenotyping of FOXP3+Helios+ Tregs revealed increased CD25 expression following ⍺-CD226 mAb treatment, with Tregs displaying augmented suppressive capacity of CD4+ responders during in vitro suppression assays. These data suggest that ⍺-CD226 mAbs both reduce T cell cytotoxicity and improve Treg function, with important therapeutic implications for the prevention or suspension of T1D.