CD4 and graft versus host disease: IL-10 producing regulatory T cells, termed Tr1 cells, are another subset of CD4 T cells, which produce the anti-inflammatory cytokines IL-10 (49) and transforming growth factor-β (TGF-β), and are involved in down regulating immune responses toward allergens and various antigens such as nickel and insect venom, as well as controlling autoimmunity, and preventing allograft rejection and graft versus host disease (GvHD) (50).