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 induced pluripotent stem cells (iPSCs), from the viewpoint of time and economic cost, the 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 the major histocompatibility complex (MHC) on the iPSC-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 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 conditions. 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 iPSC engraftment. These results suggest for the first time a possibility that DST using donor B cells could induce tolerance against allogeneic iPSC-derived grafts.

Establishment of an experimental model for MHC homo-to-hetero transplantation.

Preventing rejection is a major challenge in transplantation medicine, even when using pluripotent stem cell-derived grafts. In iPS cell (iPSC)-based transplantation, to reduce the risk of rejection, it is thought to be optimal that preparing the cells from donors whose human leukocyte antigen-haplotype are homozygous. Generally, this approach is referred to as major histocompatibility complex (MHC) homo-to-hetero transplantation, which is MHC-matched but minor antigen-mismatched. To investigate the immune response in the MHC homo-to-hetero transplantation, we established a murine experimental system in which MHC-matched but minor antigen-mismatched tissue (skin) grafts were transplanted into MHC-heterozygous recipients. Unexpectedly, only minor antigen-mismatched grafts were rejected at the same time points as rejection of fully allogeneic grafts. A vigorous anti-donor type T cell response was detected in vitro and conventional immunosuppressants targeting T cell activation had limited effects on controlling rejection. However, anti-donor antibodies were not detected only in the minor antigen-mismatched transplantation. This murine transplantation model can be used to further analyze immunological subjects for MHC homo-to-hetero iPSC-based transplantation.

Induction of macrophage-like immunosuppressive cells from common marmoset ES cells by stepwise differentiation with DZNep.

Recent progress in regenerative medicine has enabled the utilization of pluripotent stem cells (PSCs) as the resource of therapeutic cells/tissue. However, immune suppression is still needed when the donor-recipient combination is allogeneic. We have reported previously that mouse PSCs-derived immunosuppressive cells contribute to prolonged survival of grafts derived from the same mouse PSCs in allogeneic recipients. For its clinical application, a preclinical study using non-human primates such as common marmoset must be performed. In this study, we established the induction protocol of immunosuppressive cells from common marmoset ES cells. Although similar immunosuppressive macrophages could not be induced by same protocol as that for mouse PSCs, we employed an inhibitor for histone methyltransferase, DZNep, and succeeded to induce them. The DZNep-treated macrophage-like cells expressed several immunosuppressive molecules and significantly inhibited allogeneic mixed lymphocyte reaction. The immunosuppressive cells from non-human primate ESCs will help to establish an immunoregulating strategy in regenerative medicine using PSCs.

Efficient generation of thymic epithelium from induced pluripotent stem cells that prolongs allograft survival.

The thymus plays a significant role in establishing immunological self-tolerance. Previous studies have revealed that host immune reaction to allogeneic transplants could be regulated by thymus transplantation. However, physiological thymus involution hinders the clinical application of these insights. Here, we report an efficient generation of thymic epithelial-like tissue derived from induced pluripotent stem cells (iPSCs) and its potential to regulate immune reaction in allogeneic transplantation. We established an iPSC line which constitutively expresses mouse Foxn1 gene and examined the effect of its expression during in vitro differentiation of thymic epithelial cells (TECs). We found that Foxn1 expression enhances the differentiation induction of cells expressing TEC-related cell surface molecules along with upregulation of endogenous Foxn1. iPSC-derived TECs (iPSC-TECs) generated T cells in nude recipient mice after renal subcapsular transplantation. Moreover, iPSC-TEC transplantation to immuno-competent recipients significantly prolonged the survival of allogeneic skin. Our study provides a novel concept for allogeneic transplantation in the setting of regenerative medicine.