Cutting Edge: Dual TCRα Expression Poses an Autoimmune Hazard by Limiting Regulatory T Cell Generation

Despite accounting for 10-30% of the T cell population in mice and humans, the role of dual TCR-expressing T cells in immunity remains poorly understood. It has been hypothesized that dual TCR T cells pose an autoimmune hazard by allowing self-reactive TCRs to escape thymic selection. We revisited this hypothesis using the NOD murine model of type 1 diabetes. We bred NOD mice hemizygous at both TCRa and beta (TCR alpha(+/-) beta(+/-)) loci, rendering them incapable of producing dual TCR T cells. We found that the lack of dual TCR alpha expression skewed the insulin-specific thymocyte population toward greater regulatory T (T-reg) cell commitment, resulting in a more tolerogenic T-reg to conventional T cell ratio and protection from diabetes. These data support a novel hypothesis by which dual TCR expression can promote autoimmunity by limiting agonist selection of self-reactive thymocytes into the T-reg cell lineage.