Iron overload in the tumor microenvironment induces CD8+ T cell ferroptosis and dysfunction.

While iron homeostasis in cancer cells is well-established, its role in mediating crosstalk between tumors and CD8+ T cells within the tumor microenvironment (TME) remains largely elusive. In this study, we compare iron levels across primary tissues populated by CD8+ T cells. Contrary to the systemic iron deficiency commonly found in cancer patients, the TME exhibits marked iron enrichment compared to lymphatic fluid and peripheral blood, a phenomenon primarily attributed to tumor necrosis. However, this iron-overloaded TME is detrimental to CD8+ T cells, triggering their ferroptosis and dysfunction. Mechanistically, tumoral T cell receptor (TCR) hyperactivation and tumor-derived hepcidin cooperatively downregulate the iron exporter SLC40A1 in CD8+ T cells, leading to intracellular iron accumulation and ferroptosis. Both genetic restoration of SLC40A1 and iron chelation inhibit CD8+ T cell ferroptosis and restore their cytotoxic activity, thereby suppressing tumor growth. Finally, to enhance chimeric antigen receptor T (CAR-T) cell adaptability to the iron-overloaded TME, we engineer SLC40A1-overexpressing CAR-T cells. These engineered cells resist ferroptosis induced by the TME and elicit potent anti-tumor immunity.