Loss of YTHDF2 enhances Th9 programming and CAR-Th9 cell antitumor efficacy

CD4+ T cells differentiate into various subsets, including T helper 1 (Th1), Th2, Th9, Th17, and regulatory T cells, which are essential in immune responses and cancer immunotherapy. However, the role of RNA N6-methyladenosine (m6A) modification in this differentiation remains unclear. Here, we demonstrate that YTHDF2, a key m6A reader protein known to destabilize m6A-modified mRNA, negatively regulates Th9 cell differentiation. Ablation of Ythdf2 in both mouse and human naïve CD4+ T cells significantly promotes Th9 differentiation by stabilizing Gata3 and Smad3 mRNA under IL-4 and TGF-β signaling. Ythdf2-deficient Th9 cells produce higher levels of IL-9 and IL-21, leading to increased tumor infiltration and cytotoxicity by CD8+ T and NK cells, thereby improving antitumor activity versus wild-type Th9 cells. Moreover, YTHDF2 depletion in CAR-Th9 cells enhances immune activation, reduces terminal differentiation, and augments antitumor efficacy. Targeting YTHDF2 thus represents a promising strategy for enhancing Th9 and CAR-Th9 cell-based cancer immunotherapies.