Oral Therapy with Colonization Factor Antigen I (CFA/I) Activates Stable Regulatory T Cells (Tregs) in the Pancreatic Lymph Nodes (PaLNs) of Non-Obese Diabetic (NOD) Mice

Type 1 diabetes (T1D) is an autoimmune disease in which insulin-producing pancreatic β cells are destroyed by auto-aggressive T cells. Tregs in T1D have been shown to lose their suppressive function and/or become inflammatory, complicating Treg immunotherapy. Oral treatment with the adhesin from enterotoxigenic E. coli, CFA/I fimbriae, protects against autoimmunity. Although CFA/I fimbriae act in a bystander or in an antigen (Ag)-independent fashion, protection is ultimately dependent upon the induction and/or activation of auto-Ag-specific Tregs. Our initial findings showed that oral dosing with a Lactococcus lactis vector expressing CFA/I fimbriae (LL-CFA/I) reduces incidence of T1D in NOD mice by 45%. We hypothesized that dosing NOD mice more frequently would induce Foxp3+ Tregs in the pancreas and PaLNs to provide more robust protection. To test this, 4 wk-old NOD mice were orally dosed with LL-CFA/I varying the dosage and frequency of treatment. When dosed every 2 wks, the frequency of insulitis was reduced by more than half at 11 wks of age, and tetramer staining revealed a 2-fold reduction of insulin-specific CD4+ and CD8+ T cells within the PaLNs. Additional groups were followed until 16 wks of age, and examined for Treg and inflammatory T cell phenotypes. Treatment with LL-CFA/I reduced 2-fold IFN-γ-producing CD8+ T cells in the spleen and PaLNs. PaLN Foxp3+ T cells from the PBS and vector control groups, but not the LL-CFA/I-treated mice, co-expressed Tbet and IFN-γ, suggesting that Tregs from LL-CFA/I treated mice maintained their regulatory function at 16 wks. These data show that orally dosing with LL-CFA/I diminishes or halts T1D progression via activation of stably functional Foxp3+ Tregs. Work supported by AI121745.