Direct-in-NOD genetic ablation of <i>Bcl3</i> leads to complete type 1 diabetes protection

It was previously reported that genetic ablation of the NF-κB atypical inhibitor Bcl3 through congenic introduction of a 129P2-embryo derived knockout allele (Bcl3tm1Ver) accelerated autoimmune diabetes in the NOD mouse model. Conversely, we found that direct CRISPR-mediated ablation of this gene in the NOD/ShiLtDvs substrain completely inhibited diabetes development. Our CRISPR approach excised exons 3-7 within the NOD Bcl3 gene. These new NOD-Bcl3-/- mice had very low levels of insulitis, indicating protective mechanisms elicited early in the disease process. Dissimilar to reports of Bcl3 ablation in nonautoimmune C57BL/6-background mice, we found that splenic and lymph node B cells were not reduced. However, splenic T2 and MZ cells were increased with a disruption of B-cell follicle formation. Diabetes protection was associated with elevated splenic and lymph node regulatory T cells, and increases in CD4 effector and CD8 central memory T cells in pancreatic lymph nodes. Diabetes protection was overridden by anti-PD-1 administration. Previous studies suggested that Bcl3 may influence diabetes development downstream of Nfkbid, another atypical NF-κB inhibitor. Indeed, co-introduction of this Bcl3 knockout allele also completely blocked diabetes in NOD-Nfkbid-/- mice normally characterized by accelerated disease. Collectively these findings support the possibility that prior findings may have been driven by congenic introduction of linked modifier genes from non-NOD background strains and initiate a critical reevaluation of the role of Bcl3 in type 1 diabetes pathogenesis.