According to Puwar (28), the antitumor effect of Th9 cells mainly relied on the activation of mast cells through IL-9 but not adaptive immunity since they found that anti-IL-9 treatment inhibited tumor growth in Rag1−/− C57BL/6 mice, which lacked T and B cells, whereas anti-IL-9 treatment had no influence on tumor progression in mast-cell-deficient mice injected with B16F10 melanoma cells and LLC-1 cells (Figure 2). Here, IL9 is linked to melanoma.