Cholera toxin subunit B peptide fusion proteins reveal impaired oral tolerance induction in diabetes‐prone but not in diabetes‐resistant mice

The cholera toxin B subunit (CTB) has been used as adjuvant to improve oral vaccine delivery in type 1 diabetes. The effect of CTB/peptide formulations on Ag‐specific CD4⁺ T cells has remained largely unexplored. Here, using tetramer analysis, we investigated how oral delivery of CTB fused to two CD4⁺ T‐cell epitopes, the BDC‐2.5 T‐cell 2.5mi mimotope and glutamic acid decarboxylase (GAD) 286–300, affected diabetogenic CD4⁺ T cells in nonobese diabetic (NOD) mice. When administered i.p., CTB‐2.5mi activated 2.5mi⁺ T cells and following intragastric delivery generated Ag‐specific Foxp3⁺ Treg and Th2 cells. While 2.5mi⁺ and GAD‐specific T cells were tolerized in diabetes‐resistant NODxB6.Foxp3^EGFP F1 and nonobese resistant (NOR) mice, this did not occur in NOD mice. This indicated that NOD mice had a recessive genetic resistance to induce oral tolerance to both CTB‐fused epitopes. In contrast to NODxB6.Foxp3^EGFP F1 mice, oral treatment in NOD mice lead to strong 2.5mi⁺ T‐cell activation and the sequestration of these cells to the effector‐memory pool. Oral treatment of NOD mice with CTB‐2.5mi failed to prevent diabetes. These findings underline the importance of investigating the effect of oral vaccine formulations on diabetogenic T cells as in selected cases they may have counterproductive consequences in human patients.