Th9 Cells Represent a Unique Subset of CD4+ T Cells Endowed with the Ability to Eradicate Advanced Tumors

The antitumor effector T helper 1 (Th1) and Th17 cells represent two T cell paradigms: short-lived cytolytic Th1 cells and "stem cell-like'' memory Th17 cells. We report that Th9 cells represent a third paradigmthey are less-exhausted, fully cytolytic, and hyperproliferative. Only tumor-specific Th9 cells completely eradicated advanced tumors, maintained a mature effector cell signature with cytolytic activity as strong as Th1 cells, and persisted as long as Th17 cells in vivo. Th9 cells displayed a unique Pu. 1-Traf6-NF-kappa B activation-driven hyperproliferative feature, suggesting a persistence mechanism rather than an antiapoptotic strategy. Th9 antitumor efficacy depended on interleukin-9 and upregulated expression of Eomes and Traf6. Thus, tumor-specific Th9 cells are a more effective CD4(+) T cell subset for adoptive cancer therapy.