In Vivo Costimulation Blockade-induced Regulatory T Cells Demonstrate Dominant and Specific Tolerance to Porcine Islet Xenografts

Background. Although islet xenotransplantation is a promising therapy for type 1 diabetes, its clinical application has been hampered by cellular rejection and the requirement for high levels of immunosuppression. The aim of this study was to determine the role of Foxp3(+) regulatory T (Treg) cells in costimulation blockade-induced dominant tolerance to porcine neonatal islet cell cluster (NICC) xenografts in mice. Methods. Porcine-NICC were transplanted under the renal capsule of BALB/c or C57BL/6 recipients and given a single dose of CTLA4-Fc at the time of transplant and 4doses of anti-CD154 mAb to day 6. Depletion of Foxp3(+)Treg cell was performed in DEpletion of REGulatory T cells mice at day 80 posttransplantation. Foxp3(+)Treg cell from spleens of treated BALB/c mice (tolerant Treg cell), and splenocytes were cotransferred into islet transplanted nonobese diabetic background with severe combined immunodeficiency mice to assess suppressive function. Results. In treated mice, increased numbers of Foxp3(+)Treg cell were identified in the porcine-NICC xenografts, draining lymph node, and spleen. Porcine-NICC xenografts from treated mice expressed elevated levels of TGF-beta, IL-10 and IFN-gamma. Porcine-NICC xenograft tolerance was abrogated after depletion of Foxp3(+)Treg cell. Tolerant Treg cell produced high levels of IL-10 and had diverse T cell receptor V beta repertoires with an oligoclonal expansion in CDR3 of Tcell receptor V beta 14. These tolerant Treg cells had the capacity to transfer dominant tolerance and specifically exhibited more potent regulatory function to porcine-NICC xenografts that naive Treg cell. Conclusions. This study demonstrated that short-term costimulation blockade-induced dominant tolerance and that Foxp3(+)Treg cell played an essential role in itsmaintenance. Foxp3(+)Treg cells were activated and had more potent regulatory function in vivo than naive Treg cells.