Fusobacterium Nucleatum-Derived Outer Membrane Vesicles Promote Immunotherapy Resistance

To explore whether the F. nucleatum-derived outer membrane vesicles (F.n-OMVs) promote immune escape and malignant phenotype formation of HNSCC. Fluorescence in situ hybridization/immunofluorescence analyzed F. nucleatum abundance and immune cell infiltration in HNSCC. F.n-OMVs were administered to immunocompetent C3H and immunodeficient NOD-SCID tumor-bearing mice to assess immune-dependent tumorigenesis. Flow cytometry and macrophage-depletion models identified tumor-associated macrophage (TAM) roles. RNA-seq, LC/MS, and molecular assays elucidated F.n-OMV-induced immunosuppressive mechanisms. TDO2 inhibitor 680C91 and PD-1 antibody combinational therapy was tested in mice models. Clinical samples from immunotherapy-treated HNSCC patients were analyzed for F. nucleatum/TDO2 correlations with survival. F. nucleatum levels were elevated in HNSCC vs. healthy tissues (p<0.05), correlating with tumor size, TNM stage, and metastasis (p<0.05). F.n-OMVs promoted HNSCC progression via TAM-mediated immunosuppression, mediated by vesicle-derived tryptophanase that activated the TDO2/AHR pathway, inducing IL-10 and checkpoint molecule expression. Combined TDO2 inhibition and PD-1 blockade reduced tumor volume by 81% vs. controls (0.1343±0.1058 vs. 0.7142±0.2382 cm³; p<0.05). Non-responders to PD-1 therapy exhibited higher F. nucleatum loads and TDO2 expression than responders (p<0.05). F.n-OMVs drive HNSCC progression via TAM immunosuppression and immunotherapy resistance. F. nucleatum abundance and TDO2 levels serve as predictive biomarkers and therapeutic targets for optimizing HNSCC immunotherapy.