Cancer Immunotherapy

Immune escape and inflammation are now recognized as hallmarks of tumor onset and progression. Myeloid-derived suppressor cells (MDSC), a heterogeneous population of immature myeloid cells that are present in virtually all patients and mice with advanced cancer, are a major contributor to immune escape through their inhibition of innate and adaptive antitumor immunity. Immature myeloid cells with the phenotype of MDSC are present in low levels in healthy individuals; however, chronic inflammation perturbs normal myelopoiesis and mobilizes MDSC, thereby facilitating tumor growth. This chapter reviews the experimental and patient findings that identified MDSC as an immune suppressive cell population mediating tumor immune escape, the phenotypic characteristics and heterogeneity of MDSC from cancer patients and mice, the diversity of mechanisms used by MDSC to facilitate tumor progression and metastasis, the pro-inflammatory mediators that drive the induction and accumulation of MDSC, and therapeutic approaches that have been developed to reduce MDSC levels and/or impair MDSC function.