CD40 engagement of CD4+ CD40+ T cells in a neo-self antigen disease model ablates CTLA-4 expression and indirectly impacts tolerance

Biomarkers defining pathogenic effector T (Teff) cells slowly have been forthcoming and towards this we identified CD4⁺ T cells that express CD40 (CD4⁺CD40⁺) as pathogenic in the NOD type 1 diabetes (T1D) model. CD4⁺CD40⁺ T cells rapidly and efficiently transfer T1D to NOD.scid recipients. To study the origin of CD4⁺CD40⁺ T cells and disease pathogenesis, we employed a dual transgenic model expressing OVA_323–339 peptide as a neo‐self antigen on islet β cells and medullary thymic epithelial cells (mTECs) and a transgenic TCR recognizing the OVA_323–339 peptide. CD4⁺CD40⁺ T cells and Treg cells each recognizing the cognate neo‐antigen, rather than being deleted through central tolerance, drastically expanded in the thymus. In pancreatic lymph nodes of DO11.RIPmOVA mice, CD4⁺CD40⁺ T cells and Treg cells are expanded in number compared with DO11 mice and importantly, Treg cells remain functional throughout the disease process. When exposed to neo‐self antigen, CD4⁺CD40⁺ T cells do not express the auto‐regulatory CTLA‐4 molecule while naïve CD4⁺CD40⁺ T cells do. DO11.RIPmOVA mice develop autoimmune‐type diabetes. CD40 engagement has been shown to prevent CTLA‐4 expression and injecting anti‐CD40 in DO11.RIPmOVA mice significantly exacerbates disease. These data suggest a unique means by which CD4⁺CD40⁺ T cells thwart tolerance.