Figure 1: MSCs interact with immune cells, representing potential cellular therapy to enhance allogeneic hematopoietic engraftment and prevent GVHD. MSCs reduced the expression of activation markers CD25, CD38 and CD69 on PHA-stimulated lymphocytes, making allogeneic HSCs and MSCs escape from recognition of alloreactive T-cells. MSCs suppressed the proliferation of PHA-stimulated CD3+, CD4+ and CD8+ lymphocytes. MSCs inhibit naïve and memory T-cell responses to their cognate antigens by the engagement of the inhibitory molecule PD-1. MSCs inhibit the proliferation of B-cells and the differentiation of mature DCs from HSCs. MSCs induce DC apoptosis by downregulate TNF-α and TGF-β1 levels and upregulated IL-6 levels. MSCs inhibit the IL-2-induced proliferation of NK cells by producing PGE2. IFN-γ can stimulate MSCs to exhibit induction of class II molecule expression to prevent GVHD.