Great interest has been focused on CD4+ Tregs [1], and cell therapies using adoptive transfer of in vitro generated CD4+ Treg cells have demonstrated promising efficacy for immunomodulation in animal models of allogeneic transplantation as well as in clinical trials of human allogeneic bone marrow transplantation for the control of graft versus host disease [2], [3], [4]. The gene discussed is CD4; the disease is graft versus host disease.