Immunogenicity of outer membrane vesicles of Fusobacterium nucleatum

Abstract:

[Objective] To evaluate the safety and immunogenicity of outer membrane vesicles (OMVs) of Fusobacterium nucleatum prepared under the pH conditions simulating normal intestinal and tumor microenvironments, and to lay a foundation for the later development of OMV-based vaccines against F. nucleatum. [Methods] Ultra-high-speed centrifugation and density gradient centrifugation were employed to isolate the OMVs of F. nucleatum under different pH conditions. Three models of human colorectal cancer cells (HCT116), human colonic epithelial cells (HCoEpiC), and mouse macrophage Raw264.7 were infected by F. nucleatum. The cell proliferation was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cell counting kit-8 (CCK-8) assay, and the cell apoptosis were evaluated by flow cytometry and in situ fluorescence of adherent cells. The safety in vivo was detected by blood routine and whole blood index of mice. The enzyme-linked immunosorbent assay (ELISA) was employed to examine the cell immunogenicity, and the adhesion inhibition assay was conducted to assess cell immunoprotection. [Results] Acidic outer membrane vesicles (aOMVs) and neutral outer membrane vesicles (nOMVs) had no significant different effects on the proliferation or apoptosis of HCoEpiC, HCT116, and Raw264.7 cells. Both nOMVs and aOMVs at a concentration of 25 μg/mL did not lead to significant hemolysis of red blood cells, and the routine blood and whole blood test results of the mice treated with aOMVs were within the normal ranges. The results demonstrated that both aOMVs and nOMVs exhibited good immunogenicity and reduced the adhesion of F. nucleatum to colon cancer cells DLD-1. The aOMVs outperformed nOMVs regarding immunogenicity. [Conclusion] Both aOMVs and nOMVs had good safety and immunogenicity, and aOMVs were superior to nOMVs.