Smoking-associated modulation of gut microbiota shapes response to immune checkpoint inhibitors in non-small cell lung cancer

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BACKGROUND: Smoking status has been associated with differences in immune checkpoint inhibitor (ICI) efficacy in non-small cell lung cancer (NSCLC), though the underlying mechanisms remain unclear. This prospective cohort study evaluated whether smoking-related changes in the gut microbiota are linked to ICI response. METHODS: Baseline fecal samples from 225 patients with NSCLC were analyzed using full-length 16S rRNA sequencing. Microbial composition, predicted functional features, and clinical variables were examined in relation to treatment response and progression-free survival (PFS). Associations with treatment response were assessed using multivariable ordinal logistic regression. PFS was evaluated using Kaplan-Meier analysis and the log-rank test. RESULTS: Smoking was associated with selected taxon-level microbial differences despite no significant differences in alpha or beta diversity. Compared with never-smokers, smokers exhibited reduced abundance of Bifidobacterium longum and enrichment of Gram-negative taxa. Functional prediction indicated increased potential for lipopolysaccharide, Kdo₂-lipid A, and lipid IVA biosynthesis in smokers. Predicted lpxM abundance, encoding a lipid A myristoyltransferase, was positively correlated with the Gram-negative bacterial fraction. Moreover, increased abundance of lpxM-linked Gammaproteobacteria was associated with improved ICI response in the NSCLC cohort. Conversely, lower B. longum abundance was associated with favorable ICI response and prolonged PFS. CONCLUSIONS: These results indicate that smoking-related gut microbial alterations, particularly reduced B. longum abundance, are associated with enhanced ICI efficacy in NSCLC, supporting a role for the gut microbiota in smoking-associated differences in immunotherapy outcomes.