CD4 and graft versus host disease: On the other hand, in spite of several murine studies successfully achieving a protocol to improve the induction of Treg cells from naive CD4+ T cells, using TGF-β, RA, and/or rapamycin (26, 45, 46), its translation to human Treg has not been effective enough, as shown in studies in which human Treg generated in vitro fail to retain Foxp3 expression and suppress graft versus-host disease (47).