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Induction of FoxP3+CD4+25+ Regulatory T Cells Following Hemopoietic Stem Cell Transplantation: Role of Bone Marrow-Derived Facilitating Cells12

The establishment of donor cell lineages following allogeneic bone marrow transplantation is frequently associated with the development of graft-vs-host disease (GVHD). The identification of cell populations that are capable of supporting allogeneic stem cell (SC) engraftment and the induction of tolerance without inducing GVHD could expand the use of this therapy. CD8+TCR− facilitating cells (FC) have been shown to promote allogeneic SC engraftment with resulting transplantation tolerance across complete MHC barriers without inducing GVHD. Although donor reconstitution in SC plus FC recipients is associated with the induction of regulatory T cell-associated factors, it is not known whether an induction of regulatory T cells and subsequent tolerance is a direct effect of the FC. The current study demonstrates that 1) SC plus FC transplantation results in the induction of donor CD4+25+ regulatory T cells and that FC are present in the spleen of recipients before the induction of these cells, 2) activation of FC with CpG-oligodeoxynucleotide promotes CD4+25− T cell differentiation into CD4+25+ regulatory T cells in vitro, as demonstrated by cytokine and forkhead/winged helix transcription factor (FoxP3) gene and protein expression, and 3) direct contact between FC and CD4+25− T cells is required for FoxP3+CD4+25+ regulatory T cell induction and is dependent on CD86 expression on FC. This is the first report to demonstrate a mechanism for FC in the induction of regulatory T cells following allogeneic SC plus FC transplantation. The transplantation of donor FC may provide an alternative approach to permit clinical SC engraftment and induction of transplantation tolerance in the future.