Mesenchymal Stem/Stromal Cells and the Tumor Immune System

Stroma of solid tumors contains immune-suppressive cells such as regulatory T-cells, type 2 macrophages, myeloid-derived suppressor cells, and fibroblasts. The supporting cells within the tumor produce growth-supporting factors similar to those involved in tissue remodeling. Tumor formation and progression is a multistep process that includes tumor initiation at the primary sites followed by invasion to secondary metastatic sites. At the secondary site, the cells that initiated the tumor could comprise of cancer stem cells that sustain the tumor. Here we review the mechanistic functions of mesenchymal stem/stromal cells (MSCs) and their association with immune cells during tissue homeostasis compared to tumorigenesis. This chapter discusses how cancer cells interact within a network created by MSCs in communication with other microenvironment cells, especially those belonging to the immune system. The information presented in this chapter can be extrapolated to the crosstalk between MSCs and other cells inside the stromal compartment.