Human CD4+HLA-G+ regulatory T cells are potent suppressors of graft-versus-host disease in vivo

CD4(+) T cells expressing the immunotolerizing molecule HLA-G have been described as a unique human thymus-derived regulatory T (tT(reg)) cell subset involved in immunoregulation and parenchymal homeostasis during infectious and autoimmune inflammation. We compared properties and molecular characteristics of human CD4(+) HLA-G(+) with those of CD4(+) CD25(+) FoxP3-expressing tT(reg) cells using in vitro studies of T-cell receptor (TCR) signaling, single-cell electrophysiology, and functional in vivo studies. Both tT(reg) populations are characterized by alterations in proximal-signaling pathways on TCR stimulation and a hyperpolarization of the plasma membrane when compared to conventional CD4(+) T cells. However, both clearly differ in phenotype and pattern of secreted cytokines, which results in distinct mechanisms of suppression: While CD4(+) HLA-G(+) cells secrete high levels of inhibitory molecules (IL-10, soluble HLA-G, IL-35), CD4(+) CD25(+) FoxP3(+) cells express these molecules at significantly lower levels and seem to exert their function mainly in a contact-dependent manner via cyclic adenosine-monophosphate. Finally we demonstrate that human CD4(+) HLA-G(+) tT(reg) cells significantly ameliorated graft-versus-host disease in a humanized mouse model as a first proof of their in vivo relevance. Our data further characterize and establish CD4(+) HLA-G(+) cells as a potent human tT(reg) population that can modulate polyclonal adaptive immune responses in vivo and thus being a promising candidate for potential clinical applications in the future.