Ferroptosis, a major mechanism of non-apoptotic programmed cell death, critically regulates the homeostasis and functionality of peripheral CD4+ and CD8+ T cells1–6. Here we demonstrate that in mouse, resistance of T cells to ferroptosis depends critically on the composition of standard rodent diets, and that dietary effects on ferroptosis (DEFs) have a crucial role in regulation of T cell homeostasis and immune responses. DEFs are microbiota-independent and are driven by variations in dietary polyunsaturated and monounsaturated fatty acids (PUFAs and MUFAs) that lead to variations in abundance of lipid species in lymphoid tissues and T cells. Consistently, ferroptosis resistance of human T cells also correlated with plasma lipid profiles across multiple healthy cohorts, exhibiting negative associations with PUFA/MUFA ratios in major lipid classes. DEFs dictate T cell resilience in the absence of the essential lipid peroxide scavenger GPX4 and broadly modulate T cell-dependent humoral immunity and T cell-mediated anti-tumour immunity, including in chimeric antigen receptor T cell therapy. Mechanistically, ACSL4, which preferentially biosynthezises PUFA-containing phospholipids7, is highly expressed in T cells and underpins DEF-mediated regulation of follicular helper T (TFH) cell generation and function. Our findings reveal the physiological significance of lipid metabolism in driving DEFs in immunity and suggest strategies targeting lipid metabolism to enhance vaccine efficacy and T cell-mediated immunotherapy.
