Cancer competition for vitamin B2 creates metabolic checkpoint for T cell ferroptosis.

Metabolic competition between tumors and T cells drives immune evasion, but the transporters and mechanisms remain largely elusive. Here, we establish the CareSLCs platform and identify that SLC52A3-mediated vitamin B2 (VB2) uptake is indispensable for T cell antitumor immunity. Mechanistically, VB2 deficiency impairs mitochondrial respiration and glutathione regeneration, leading to mitophagy, labile iron accumulation, and lipid peroxidation that trigger T cell ferroptosis. Unexpectedly, tumors preferentially employ SLC52A2, not SLC52A3, to scavenge VB2 and outcompete T cells. Tumor SLC52A2 ablation enhances T cell function in immunocompetent hosts without appreciably affecting intrinsic tumor growth. Clinically, high tumoral SLC52A2 correlates with T cell dysfunction and poor survival, whereas dietary VB2 intake is associated with reduced cancer risks. Thus, VB2 supplementation or SLC52A3 overexpression augments CAR-T cell antitumor efficacy. Our results suggest that tumoral VB2 competition establishes a metabolic checkpoint driving T cell ferroptosis and that enhancing VB2 uptake reinvigorates T cells to improve cancer immunotherapy.