ReviewThe Role and Regulation of Human Th17 Cells in Tumor Immunity

T helper 17 (Th17) cells play critical roles in the pathogenesis of inflammatory and autoimmune diseases, as well as in host protection against pathogens. The contribution of Th17 cells to human tumor immunity, however, remains largely unknown. Since their identification in 2005, Th17 cells have been extensively studied in mouse tumor models and human cancer patients. Although accumulating data suggest the importance of Th17 cells to tumor immunity, conclusions regarding the functional role of Th17 cells remain controversial. In this review, we summarize current knowledge regarding the regulation and functional role of Th17 cells in human cancers. In particular, we emphasize several recently identified characteristics of Th17 cells, including plasticity, their relationship with regulatory T cells, and Th17 cell heterogeneity in the tumor microenvironment. Improved understanding of these issues is critical to elucidating the role of Th17 cells in antitumor immunity and for the design of novel therapeutic approaches specifically targeting Th17 cells.