Induction of allograft tolerance by adoptive transfer of donor B cells: an immune regulatory strategy for transplantation using MHC-matched iPS cells.

For cellular or tissue transplantation using iPS cells (iPSCs), from the viewpoint of time and economic cost, an use of allogeneic ones is being considered. Immune regulation is one of the key issues in successful allogeneic transplantation. To reduce the risk of rejection, several attempts have been reported to eliminate effects of major histocompatibility complex (MHC) on the iPSCs-derived grafts. On the other hand, we have shown that minor antigen-induced rejection is not negligible even when the MHC's impact is mitigated. In organ transplantation, it is known that donor-specific blood transfusion (DST) can specifically control immune responses to the donor. However, whether DST could control the immune response in iPSC-based transplantation was not clarified. In this study, using a mouse skin transplantation model, we demonstrate that infusion of donor splenocytes can promote allograft tolerance in the MHC-matched but minor antigen-mismatched condition. When narrowing down the cell types, we found that infusion of isolated splenic B cells was sufficient to control rejection. As a mechanism, the administration of donor B cells induced unresponsiveness but not deletion in recipient T cells, suggesting that the tolerance was induced in the periphery. The donor B cell transfusion induced allogeneic iPSCs engraftment. These results suggest for the first time a possibility that DST using donor B cells could induce tolerance against allogeneic iPSC-derived grafts.