IL9 and neoplasm: Differently, an increased tumor growth was described in IL-9R deficient mouse; ILC2s together with Th9-cells are an important source of IL-9 in inflammatory conditions and TGF-β is able to induce IL-9 production by ILC2s, thus we cannot exclude that in the tumor microenvironment TGF-β-induced IL-9 release by ILC2s may elicit anti-tumor activity of these cells [89,90,91].