CD8lowCD28– T Cells: A Human CD8 T-Suppressor Subpopulation with Alloantigen Specificity Induced by Soluble HLA-A2 Dimer in Vitro

CD8+ suppressor T cells have been demonstrated to provide protection of allografts from rejection. We previously reported that soluble peptide/HLA-A2 dimer shows peptide-specific inhibitory effects on alloresponse in a coculture of peptide-pulsed T2 cells with HLA-A2 negative lymphocytes in vitro. Here we found a subset of CD8lowCD28– T cells that was induced in the dimer-treated coculture. Importantly, this population showed hyporesponsiveness to the alloantigen restimulation as well as alloantigen-specific suppression on alloreactive T cells in a cell–cell contact-dependent fashion. The suppressive mechanisms of CD8lowCD28– T cells involved an elevated expression of membrane-bound TGF-β1, but not Foxp3, CTLA-4, or IL-10. Furthermore, an over-represention of CD8lowCD28– T cells was observed in the patients after allogeneic platelet transfusion and positively correlated with the elevated concentrations of plasma HLA class I antigens. Our findings demonstrated that soluble HLA-A2 dimer could efficiently induce the tolerant CD8lowCD28– T cells with alloantigen-specific suppression on alloreactive T cells. This study might provide a new strategy for preparation of donor-specific suppressor T cells and represent an attractive alternative for induction of allograft tolerance.