Stromal MTHFD2 orchestrates a fibrotic–inflammatory niche driving tumor growth and immune evasion

Cancer-associated fibroblasts (CAFs) are key drivers of fibrosis and immune suppression; however, the molecular basis linking these processes remains unclear. Here, we identified methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) as a stromal metabolic regulator that integrates fibrotic activation with inflammatory signaling. Fibrotic cues, such as TGF-β and matrix stiffening, induced MTHFD2 expression in fibroblasts, whereas its knockdown reduced α-SMA expression and IL-6/IL-8 secretion. Overexpression enhanced IL-6 production, even without fibrotic stimulation. Single-cell RNA-seq data from non-small-cell lung cancer revealed elevated MTHFD2 levels across CAF subsets, independent of their myofibroblastic or inflammatory states. Mechanistically, MTHFD2 sustained NAD+–ROS signaling and induced mitochondrial stress with DNA release, activating the cGAS–STING–NF-κB pathway and promoting IL-6-dependent PD-L1 expression. Fibroblast-specific deletion of MTHFD2 suppressed tumor growth and reduced PD-L1 expression in vivo. These findings define MTHFD2 as a stromal metabolic–inflammatory switch and highlight stromal metabolism as a potential therapeutic target in desmoplastic cancers.