Rapamycin-Conditioned Donor Dendritic Cells Differentiate CD4+CD25+Foxp3+ T Cells In Vitro with TGF-β 1 for Islet Transplantation

Dendritic cells (DCs) conditioned with the mammalian target of rapamycin (mTOR) inhibitor rapamycin have been previously shown to expand naturally existing regulatory T cells (nTregs). This work addresses whether rapamycin-conditioned donor DCs could effectively induce CD4 + CD25 + Foxp3 + Tregs (iTregs) in cell cultures with alloantigen specificities, and whether such in vitro- differentiated CD4 + CD25 + Foxp3 + iTregs could effectively control acute rejection in allogeneic islet transplantation. We found that donor BALB/c bone marrow-derived DCs (BMDCs) pharmacologically modified by the mTOR inhibitor rapamycin had significantly enhanced ability to induce CD4 + CD25 + Foxp3 + iTregs of recipient origin (C57BL/6 (B6)) in vitro under Treg driving conditions compared to unmodified BMDCs. These in vitro- induced CD4 + CD25 + Foxp3 + iTregs exerted donor-specific suppression in vitro , and prolonged allogeneic islet graft survival in vivo in RAG −/− hosts upon coadoptive transfer with T-effector cells. The CD4 + CD25 + Foxp3 + iTregs expanded and preferentially maintained Foxp3 expression in the graft draining lymph nodes. Finally, the CD4 + CD25 + Foxp3 + iTregs were further able to induce endogenous naïve T cells to convert to CD4 + CD25 + Foxp3 + T cells. We conclude that rapamycin-conditioned donor BMDCs can be exploited for efficient in vitro differentiation of donor antigen-specific CD4 + CD25 + Foxp3 + iTregs. Such in vitro- generated donor-specific CD4 + CD25 + Foxp3 + iTregs are able to effectively control allogeneic islet graft rejection.