ST8Sia6 expression in beta cells mitigates onset of autoimmune diabetes in the murine NOD model

Abstract

Cell surface hypersialylation is used by malignant cells as a survival mechanism, leveraging interactions with inhibitory Siglec receptors to dampen immune rejection. In this study, we harnessed this mechanism to prevent autoimmune rejection of beta cells in the context of Type 1 Diabetes. Mice were engineered to express the sialyltransferase ST8Sia6 in a beta cell specific manner (βST mice) and crossed to the non-obese diabetic (NOD) mouse model of spontaneous autoimmune diabetes. Both female and male littermates on the NOD background developed diabetes by 300 days (56% and 80.8%, respectively). βST mice, however, demonstrated minimal occurrence of disease (5.3% and 16.6%). Additionally, histologic analysis of pancreas sections from non-diabetic βST and littermate mice suggested a similar degree of immune infiltration at 4 and 8 weeks of age, but the severity of infiltration was drastically reduced only in the βST mice at 20 weeks of age. IHC for various leukocyte markers suggested no difference in composition of immune infiltrates at the 8 week time point. To determine whether protection was due to central or peripheral mechanisms, euglycemic βST and littermate mice at 16 weeks of age were challenged with anti-PD-L1 monoclonal antibodies; both groups resulted in similar induction of disease, suggesting that ST8Sia6 dependent protection occurs peripherally. Physiologically, an insulin tolerance test demonstrated no difference between βST mice and littermates, suggesting no systemic effects of beta cell ST8Sia6 expression. The induced expression of ST8Sia6 has been shown to mitigate autoimmune attack in the NOD mouse and presents a novel path forward for improving the success of curative islet transplant into diabetic patients.