While most of the pioneer studies showing the anti-cancer efficacy of TH9 cells relied on adoptive transfer settings, TH9 cells were recently shown in two studies to be responsible for anti-cancer immune responses following engagement of glucocorticoid-induced TNFR-related protein (GITR) [31, 32], a costimulatory molecule present on T cells (Fig. 2). This evidence concerns the gene TNFRSF18 and cancer.