IL21 and cancer: A reduced Th1/Th2 ratio is associated with poor patient prognosis.156,157 The differentiation of Th17 is mainly triggered by IL-1β, IL-6, IL-21, IL-23 and TGF-β.154,158,159 Th17 cells primarily secrete IL-17, IL-21, IL-22, IL-10, IL-23, and CCL20, with their roles remaining a subject of debate in cancer.149,160