Th17 Cells in Cancer

T helper (Th)17 cells regulate host defense and exacerbate autoimmune diseases, yet their role in tumor immunity remains controversial with reports that Th17 cells could either promote or suppress tumor growth, depending on the type of malignancy or means of therapeutic intervention. This review discusses how inflammatory signals (such as cytokines and co-stimulatory/co-inhibitory molecules) induced in the tumor milieu regulate the functional fate of Th17 cells, which ultimately affect the cells’ capacity to mount immune responses against cancer. We review recent findings regarding the factors that influence the generation, plasticity, and memory phenotype of Th17 cells and their relevance to cancer immunotherapy. Further, we discuss recent reports concerning the interaction of Th17 cells with regulatory T lymphocytes and cytotoxic cluster of differentiation 8 (CD8+) T cells present in tumor tissue. Unraveling the mysteries surrounding basic and translational aspects of Th17 cell biology promises to have important implications for patients with advanced malignancies.