Purine salvage pathway protects CD8⁺ T cells from metabolic stress

Metabolic stress from a high-fat diet (HFD) impairs antitumor immunity through persistent metabolic rewiring, but its effects and long-term impact on CD8⁺ T cell metabolism remain unknown. Here, we found that even temporary exposure to a HFD impaired antitumor immunity 10 weeks after reversion to a normal diet. This was due to lasting metabolome changes that included enrichment in phospholipids sensitive to peroxidation and depletion of antioxidants, affecting the survival and function of CD8⁺ T cells. Under oxidative stress, CD8⁺ T cells utilized the xanthine salvage pathway to produce guanosine triphosphate, enhancing the amount of tetrahydrobiopterin. Xanthine supplementation reduced lipid peroxidation in tumor-draining lymph nodes and improved antitumor immunity in mice previously on a HFD. Our data indicate that metabolic stress in CD8⁺ T cells persists long after restoration of a balanced diet, and manifests as vulnerability to ferroptosis, which could be mitigated by replenishing biopterins through the xanthine salvage pathway.