In this study, human PBMCs including lymphocytes and APCs were stimulated by anti-CD3/CD28 beads in vitro and MSCs-exo blocked Th17 differentiation and improved Treg phenotype in PBMCs obtained from both healthy donors and patients with active cGVHD, indicating the regulatory effect of MSCs-exo on GVHD effector T cells in the presence of APCs. The gene discussed is CD28; the disease is graft versus host disease.