Objective:

To characterize and validate the associations of the 'microbiome-immune axis' in colorectal cancer (CRC) through multi-omics integration analysis and large-scale cohort validation methods.

Approach:

• Microbiome Analysis: Analyzed microbiome cohort GSE163366 to identify gut dysbiosis in CRC using 16S rRNA sequencing.
• Single-Cell Transcriptomics: Characterized tumor immune remodeling using single-cell transcriptomic data from GSE132465, focusing on immune cell types.

Key Findings:

• CRC patients exhibited significantly reduced α diversity (Shannon index, P = 1.29×10-7) and altered community structure (PERMANOVA, P = 0.001).
• Seven key differentially abundant genera were identified, including pathogenic bacteria enriched in CRC and beneficial bacteria depleted.
• The tumor microenvironment showed reduced adaptive immune infiltration, particularly a significant reduction in B-cell proportion (11.5% decrease).
• Pathogenic bacteria positively associated with myeloid cells and negatively with B-cells, while beneficial bacteria showed the opposite pattern.
• Differentially expressed genes were significantly enriched in immune signaling pathways, including Toll-like receptor and NF-κB pathways.
• In the independent validation cohort, six out of seven core bacterial genera exhibited consistent abundance changes.

Interpretation:

The study characterizes gut microbiota dysbiosis and its association with the immunosuppressive microenvironment in CRC, confirming the robustness of microbial abundance changes across cohorts.

Limitations:

• The study may be limited by the specific cohorts analyzed, which may not represent all CRC populations.
• Potential biases in microbiome data collection and analysis methods could affect results, such as sampling techniques and sequencing errors.

Conclusion:

The reproducible abundance changes of six out of seven core microbial genera confirm cross-cohort robustness.