The first human studies of Treg cell therapy explored its potential in the regulation of GVHD and tested HLA-matched sibling donor-derived expanded CD4+CD25+CD127low/− (second generation) Treg to combat the difficulty in treating GVHD, following allogeneic bone marrow or stem cell transplantation (80, 81). This evidence concerns the gene IL2RA and graft versus host disease.