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

The intracellular bacterium <i>Fusobacterium nucleatum</i> (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 <i>via</i> 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.