MDSC: Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immature myeloid cells whose numbers are increased in states of cancer, inflammation, or infection. MDSC are reported to be induced by tumor-produced growth factors in cancer-bearing hosts. Mechanisms of immune suppression by MDSC include production of arginase-1, reactive oxygen species, and nitric oxide and secretion of immunosuppressive cytokines including IL-10. MDSC have been reported to be one of the strongest barriers to cancer immunotherapy because of their extensive suppression of immune functions. Inhibition of MDSC is thus essential for improving anticancer immunotherapy. Several compounds and agents that were reported to inhibit MDSC in mice are now being proven effective for inhibition of MDSC in patients with cancer. In this chapter, mechanisms of MDSC production and MDSC suppression of immune responses are described, and strategies to inhibit MDSC are addressed.