IL9 and neoplasm: Th9 cells can stimulate epithelial cells by IL-9 to produce CCR6 ligand CCL20, which recruits immature DCs (iDCs) and other APCs into tumor region (Shumin et al., 2015), and then these APCs present antigen to activate CD8 cytotoxic T lymphocyte (CTLs) to kill tumor cells (Rumbo et al., 2004; Kim et al., 2015).