Immunosuppressive cells and tumour microenvironment: Focus on mesenchymal stem cells and myeloid derived suppressor cells
Giovanna Bianchi1, Giacomo Borgonovo2, Vito Pistoia1 and Lizzia Raffaghello1
1Laboratory of Oncology, G. Gaslini Institute, Genoa, Italy and 2Department of Integrated Surgical Sciences (DISC), University of Genoa, Genoa, Italy.
Offprint requests to: Lizzia Raffaghello, Laboratory of Oncology, G. Gaslini Children’s Hospital, Largo G. Gaslini 5, 16148 Genova, Italy. e-mail: firstname.lastname@example.org
Summary. Tumours have been compared to unhealed wounds that produce large amounts of inflammatory mediators, including cytokines, chemokines, and growth factors. These molecules participate in the formation of a rich and heterogeneous microenvironment by attracting non malignant cells that promote tumour progression and dissemination. Tumour infiltrating cells include macrophages, myeloid-derived suppressor cells (MDSCs), mesenchymal stromal cells (MSCs) and TIE2-expressing monocytes. Most of them are bone marrow-derived, although MSC are present in virtually every tissue. This review focuses on MDSCs and MSCs, both of which can exert pro-tumorigenic effects through negative regulation of immune responses. MDSCs represent a heterogeneous population of cells of myeloid origin that are expanded and activated in response to growth factors and cytokines released by tumours. Once MDSCs are activated, they accumulate in lymphoid organs and tumours where they exert T cell immunosuppression. Like MDSCs, MSCs can be mobilized from the bone marrow into the bloodstream and home in the tumour stroma, where they either help or hinder tumour growth. Here, we will discuss the origin, the functions and the mechanisms of action of MSCs and MDSCs, as well as the strategies to target these cells for the therapeutic benefit of cancer patients. Histol Histopathol 26, 941-951 (2011)
Key words: Tumour microenvironment, Immuno-suppression, Mesenchymal stem cells, Myeloid-derived suppressor cells