Fusobacterium nucleatum-driven CX3CR1⁺ PD-L1⁺ phagocytes route to tumor tissues and reshape tumor microenvironment

The intracellular bacterium Fusobacterium nucleatum (Fn) mediates tumorigenesis and progression in colorectal cancer (CRC). However, the origin of intratumoral Fn and the role of Fn-infected immunocytes in the tumor microenvironment remain unclear. Here, we observed that Fn-infected neutrophils/macrophages (PMNs/MΦs), especially PMNs, accumulate in tumor tissues and fecal Fn abundance correlates positively with an abundance of blood PD-L1⁺ PMNs in CRC patients. Moreover, Fn accumulates in tumor tissues of tumor-bearing mice via intragingival infection and intravenous injection. Mechanistically, Fn can survive inside PMNs by reducing intracellular ROS levels and producing H₂S. Specifically, the lysozyme inhibitor Fn1792 as a novel virulence factor of Fn suppressed apoptosis of phagocytes by inducing CX3CR1 expression. Furthermore, Fn-driven CX3CR1⁺PD-L1⁺ phagocytes transfer intracellular Fn to tumor cells, which recruit PMNs/MΦs through the CXCL2/8-CXCR2 and CCL5/CCR5 axes. Consequently, CX3CR1⁺PD-L1⁺ PMNs infiltration promotes CRC metastasis and weakens the efficacy of immunotherapy. Treatment with the doxycycline eradicated intracellular Fn, thereby reducing the CX3CR1⁺PD-L1⁺ PMNs populations and slowing Fn-promoted tumor growth and metastasis in mice. These results suggest phagocytes as Fn-presenting cells use mutualistic strategies to home to tumor tissues and induce immunosuppression, and treatment with ROS-enhanced antibiotics can inhibit Fn-positive tumor progression.