CD4 and graft versus host disease: Some investigators have postulated that this may explain the in vivo ability of MSCs to be effective against very inflammatory diseases such as graft-versus-host-disease (GVHD), in which the production of such activating cytokines as IFN-γ by T and natural killer lymphocytes (NKs) may actually promote MSC immunomodulation, subsequently suppressing the proliferation of CD4+, CD8+ T cells, and NKs themselves [59].