IL-9/STAT3/fatty acid oxidation-mediated lipid peroxidation contributes to Tc9 cell longevity and enhanced antitumor activity

CD8⁺ T cell longevity regulated by metabolic activity plays important roles in cancer immunotherapy. Although in vitro-polarized, transferred IL-9-secreting CD8⁺ Tc9 (cytotoxic T lymphocyte subset 9) cells exert greater persistence and antitumor efficacy than Tc1 cells, the underlying mechanism remains unclear. Here, we show that tumor-infiltrating Tc9 cells display significantly lower lipid peroxidation than Tc1 cells in several mouse models, which is strongly correlated with their persistence. Using RNA-sequence and functional validation, we found that Tc9 cells exhibited unique lipid metabolic programs. Tc9 cell-derived IL-9 activated STAT3, upregulated fatty acid oxidation and mitochondrial activity, and rendered Tc9 cells with reduced lipid peroxidation and resistance to tumor- or ROS-induced ferroptosis in the tumor microenvironment. IL-9 signaling deficiency, inhibiting STAT3, or fatty acid oxidation increased lipid peroxidation and ferroptosis of Tc9 cells, resulting in impaired longevity and antitumor ability. Similarly, human Tc9 cells also exhibited lower lipid peroxidation than Tc1 cells and tumor-infiltrating CD8⁺ T cells expressed lower IL9 and higher lipid peroxidation- and ferroptosis-related genes than circulating CD8⁺ T cells in patients with melanoma. This study indicates that lipid peroxidation regulates Tc9 cell longevity and antitumor effects via the IL-9/STAT3/fatty acid oxidation pathway and regulating T cell lipid peroxidation can be used to enhance T cell-based immunotherapy in human cancer.