Relationship between Fusobacterium nucleatum and antitumor immunity in colorectal cancer liver metastasis.

Fusobacterium nucleatum has been detected in 8-13% of human colorectal cancer, and shown to inhibit immune responses against primary colorectal tumours in animal models. Thus, we hypothesised that the presence of F. nucleatum might be associated with reduced T-cell density in colorectal cancer liver metastases (CRLMs). We quantified F. nucleatum DNA in 181 CRLM specimens using quantitative polymerase chain reaction assay. The densities of CD8+ T cells, CD33+ cells (marker for myeloid-derived suppressor cells (MDSCs)), and CD163+ cells (marker for tumour-associated macrophages (TAMs)) in CRLM tissue were determined by immunohistochemical staining. F. nucleatum was detected in eight (4.4%) of 181 CRLM specimens. Compared with F. nucleatum-negative CRLMs, F. nucleatum-positive CRLMs exhibited significantly lower density of CD8+ T cells (P = 0.033) and higher density of MDSCs (P = 0.001). The association of F. nucleatum with the density of TAMs was not statistically significant (P = 0.70). The presence of F. nucleatum is associated with a lower density of CD8+ T cells and a higher density of MDSCs in CRLM tissue. Upon validation, our findings may provide insights to develop strategies that involve targeting microbiota and immune cells for the prevention and treatment of CRLMs.