CD4 and graft versus host disease: However, treatment with hPMSCs significantly downregulated the PD-1 expression on the surface of CD4+IL-10+ T cells in comparison with that of the PBS group (P < 0.05, Fig. 1e) and markedly increased the proportion of CD4+IL-10+ T cells in the liver and spleen in the GVHD mouse model (P < 0.01, Fig. 1d).