Paired comparison of tumor core and airway lumen (BALF) microbiomes in lung adenocarcinoma: deciphering specific Bacillus enrichment and immunomodulation.

BACKGROUND: Lung adenocarcinoma (LUAD) is the leading cause of cancer mortality. While the lung microbiome influences tumorigenesis, the spatial heterogeneity between the airway reservoir (bronchoalveolar lavage fluid, BALF) and the actual intratumoral niche remains underexplored. Understanding this distinction is critical for identifying true tumor-resident drivers.

METHODS: Paired tumor tissue and BALF samples were collected from 77 LUAD patients. 16S rRNA gene sequencing targeting V3-V4 regions was performed to characterize microbial diversity. Host transcriptomics were integrated to explore host-microbe interactions. Bioinformatics analyses utilized UPARSE for OTU clustering, PICRUSt2 for functional prediction, and CIBERSORTx for immune cell deconvolution. Differential abundance was assessed using LEfSe and Random Forest algorithms to identify discriminatory biomarkers.

RESULTS: Comparative analysis revealed distinct ecological architectures, with tumor tissues exhibiting significantly reduced alpha-diversity compared to BALF. The genus Bacillus was identified as a key tumor-enriched biomarker (LDA > 2.0), distinct from airway colonizers. Clinically, elevated Bacillus abundance significantly correlated with tumor invasiveness. Immunologically, Bacillus load was inextricably linked to an immunosuppressive microenvironment, characterized by the upregulation of inhibitory checkpoints (VSIR, TIGIT, PD-L1) and a reduction in M1 macrophage infiltration. Functional analysis suggested Bacillus involvement in metabolic pathways facilitating tumor adaptation.

CONCLUSION: This study delineates the spatial disparity between intratumoral and airway microbiomes, identifying Bacillus as a potential driver of malignant progression and immune evasion. Targeting intratumoral microbiota offers novel diagnostic and therapeutic avenues for lung cancer.