Th176 - MHC II-specific Chimeric Antigen Receptor Regulatory T Cells for Transplantation Tolerance

Andrew Brown, MSc – StemCell Technologies, Vancouver, BC, Canada; Majid Mojibian, MD, PhD – Research Scientist, BC Children's Hospital, Vancouver, BC, Canada; Madeleine Speck, BSc – Research Technician, BC Children's Hospital, Vancouver, BC, Canada; Isaac Rosado-Sánchez, PhD – Post-Doctoral Fellow, BC Children's Hospital, Vancouver, BC, Canada; Qing Huang, MD, PhD – Research Technician, BC Children's Hospital, Vancouver, BC, Canada; Manjurul Haque, DVM, PhD – Post-Doctoral Fellow, BC Children's Hospital, Vancouver, BC, Canada; Ismail Sayin, PhD – Post-Doctoral Fellow, Department of Surgery, University of Chicago, Chicago, IL, USA; Samarth Durgam, MD – Post-Doctoral Fellow, Department of Surgery, University of Chicago, Chicago, IL, USA; Anita Chong, PhD – Principal Investigator, Department of Surgery, University of Chicago, Chicago, IL, USA; Megan Levings, PhD – Principal Investigator, Surgery, University of British Columbia, Vancouver, BC Canada

Abstract Text: Solid organ transplantation is a critical intervention for end-stage organ failure. However, transplant recipients require lifelong immune-suppressive therapy to prevent immune-mediated allograft rejection. Cell therapy with regulatory T cells (Tregs) expressing a donor antigen-specific chimeric antigen receptor (CAR) is a promising alternative approach for promoting allograft tolerance. CAR-Tregs targeting ubiquitously expressed donor MHC I (HLA-A2) have entered clinical trials for transplantation. However, donor MHC II stimulates alloreactive CD4+ T cells, which facilitate B cell and CD8+ T cell responses, promoting allograft rejection. We therefore hypothesize that MHC II-specific CAR-Tregs could also promote allograft tolerance.

To study the effectiveness of MHC II-specific CAR-Tregs in immunocompetent mouse models of C57BL/6xBalb/c (F1) to C57BL/6 skin and heart transplantation, we generated Tregs expressing a CAR specific for the BALB/c MHC II allele I-Ed. I-Ed-CARs selectively bound target I-Ed tetramers, with no cross-reactivity towards their C57BL/6 counterpart I-Eb or other MHC alleles. In response to CD11c+ dendritic cells (DCs) from BALB/c or F1, but not C57BL/6 mice, I-Ed-CAR-Tregs upregulated CD69, LAP and PD-1 and Ki-67, and proliferated. In in vitro suppression assays, I-Ed-specific CAR-Tregs inhibited proliferation of C57BL/6 CD4+ and CD8+ T cells following allogeneic stimulation with BALB/c or F1 DCs, and suppressed CD80, CD86 and MHC II expression on DCs. Preliminary in vivo work demonstrates persistence and sustained FOXP3 expression of I-Ed-specific CAR-Tregs >30 days post-infusion.

Overall, I-Ed-specific CAR-Tregs are antigen-specific and potently suppressive in vitro. Ongoing experiments are testing the in vivo efficacy of I-Ed-specific CAR-Tregs in mouse models of skin allograft transplantation.