Figure 3

The conflicting roles of mesenchymal stem cells in tumor progression may be explained by their functional heterogeneity on immunoregulation. The differentiation potential of mesenchymal stem cells (MSCs) is affected by cytokines in the tumor environment. MSCs demonstrate a capacity for hematopoietic lineage differentiation in the tumor microenvironment. They may have the ability to differentiate into macrophages or cytokine-induced killer (CIK) cells. The roles of macrophages on tumor progression are also heterogeneous. MSCs represent a heterogeneous subset of cells, indicated by a distinct color. Some subsets of MSCs suppress graft-versus-host disease (GVHD) and the graft-versus-tumor (GVT) effect, while other subsets of MSCs elicit these. An important determinant that switches whether MSCs promote or inhibit tumor progression may be related to the immunoregulation of different subsets of MSCs. It will be important to balance the impact of MSCs on GVHD and the GVT effect. Selective allodepletion may be used to dissociate GVHD and the GVT effect before the advancement of MSCs as a vehicle for cancer therapy.