Inhibition of graft-versus-host disease by double-negative regulatory T cells.

Pretransplant infusion of lymphocytes that express a single allogeneic MHC class I Ag has been shown to induce tolerance to skin and heart allografts that express the same alloantigens. In this study, we demonstrate that reconstitution of immunoincompetent mice with spleen cells from MHC class I L(d)-mismatched donors does not cause graft-vs-host disease (GVHD). Recipient mice become tolerant to skin allografts of lymphocyte donor origin while retaining immunity to third-party alloantigens. The mechanism involves donor-derived CD3(+)CD4(-)CD8(-) double-negative T regulatory (DN Treg) cells, which greatly increase and form the majority of T lymphocytes in the spleen of recipient mice. DN Treg cells isolated from tolerant recipient mice can suppress the proliferation of syngeneic antihost CD8(+) T cells in vitro. Furthermore, we demonstrate that DN Treg cells can be generated in vitro by stimulating them with MHC class I L(d)-mismatched lymphocytes. These in vitro generated L(d)-specific DN Treg cells are able to down-regulate the activity of antihost CD8(+) T cells in vitro by directly killing activated CD8(+) T cells. Moreover, infusing in vitro generated L(d)-mismatched DN Treg cells prevented the development of GVHD caused by allogeneic CD8(+) T cells. Together these data demonstrate that infusion of single MHC class I locus-mismatched lymphocytes may induce donor-specific transplantation tolerance through activation of DN Treg cells, which can suppress antihost CD8(+) T cells and prevent the development of GVHD. This finding indicates that using single class I locus-mismatched grafts may be a viable alternative to using fully matched grafts in bone marrow transplantation.