Compared with other CD4 T-cell subsets, murine TH9 cells elicit the highest antitumor response upon adoptive transfer because of their superior persistence, cytolytic functions and resistance to T-cell dysfunction.4 Importantly, human chimeric antigenic receptor (CAR) T cells cultured under TH9-polarizing conditions exert enhanced antitumor activity compared with cells cultured with IL-2, underscoring the clinical relevance of TH9 cells for cancer therapy.56 Previous studies reported that cell-extrinsic signals could favor TH9 cell differentiation. This evidence concerns the gene CD4 and cancer.