Efficacy and limitations of combined A2.CAR Treg and anti-CD154 therapy in a mouse model of haplo-mismatched heart transplantation

The ability to induce allograft specific tolerance would reduce the need for daily pharmacological immunosuppression, improve post-transplant quality of life and transplant outcomes. Adoptive cell therapy with regulatory T cells expressing donor-specific Chimeric Antigen Receptors (CAR-Tregs) is a promising strategy, but monotherapy has not resulted in prolonged survival of grafts with multiple MHC mismatches. We used a clinically-relevant, haplo-mismatched model of heart transplantation in immune-competent C57BL/6 recipients to test the ability of HLA-A2-specific (A2) CAR Tregs to synergize with CD154 blockade to enhance graft survival. We found that in combination with a single low dose of anti-CD154, A2.CAR Tregs significantly prolonged heart allograft survival. Through use of grafts expressing the 2W-OVA transgene, tetramer tracking of 2W- and OVA-specific cells revealed that in mice with accepted grafts, the effects of A2.