Antigen-specific iTreg cells in minor histocompatibility antigen-mismatched islet transplantation model

Abstract

Introduction: Inducing immunological tolerance to transplant is the ultimate goal in transplantation field. It has been reported that the pancreatic islet transplantation across the minor histocompatibility of H-Y (male antigen) could induce immunological tolerance to male antigen in female C57BL/6 mice resulting in the acceptance of male skin graft without any immunological manipulation. In this study, I tried to find out the underlying mechanisms of the immune tolerance. Methods: Female RAG2-/- Marilyn mice having transgenic TCR specific for H-Y peptide were transplanted with male skin on left flank or with male islet underneath the kidney capsule. Before and after the islet transplantation, CD4+ T cells were analyzed for expression of Foxp3 by flow cytometry. Subsequent male skin transplantations were operated to male islet recipients to verify the establishment of immunological tolerance. Results: Female Marilyn mice rejected male skin graft within 24 days, but accepted male islet graft indefinitely and did not reject the subsequently transplanted male skin. Flow cytometric analysis of the peripheral blood of these mice revealed the emergence of CD4+FoxP3+ regulatory T cells (Treg) which are normally absent in naïve Marilyn mice. These induced Treg cells were antigen-specific and played an important role in the prevention of the rejection of male skin graft. The suppressive function of inducible Treg (iTreg) cells was confirmed by in vitro Treg suppression assay. In addition, the positive correlation between the number of iTregs and the passenger leukocytes accompanied by the transplanted male islets provide clues to the role of the passenger leukocytes in the iTreg induction. Conclusions: Pancreatic islet transplantation across H-Y disparity induced iTregs and contributed to the establishment of transplantation tolerance. This model could be an asset for the characterization of de novo induced iTreg cells.