Bactericidal antibody responses elicited by a meningococcal outer membrane vesicle vaccine with overexpressed factor H-binding protein and genetically attenuated endotoxin

Background. Outer membrane vesicle (OMV) vaccines from mutant Neisseria meningitidis strains engineered to overexpress factor H-binding protein (fHbp) have elicited broadly protective serum antibody responses in mice. The vaccines investigated were not treated with detergents to avoid extracting fHbp, which is a lipoprotein. Because of their high endotoxin content, the vaccines would not be safe to administer to humans. Methods. We prepared a native OMV vaccine from a strain engineered to overexpress fHbp and in which the gene encoding LpxL1 was inactivated, which reportedly decreases endotoxin activity. Results. The OMV vaccine from the mutant had a similar or lower ability to induce the expression of proinflammatory cytokines by human peripheral blood mononuclear cells, compared with a detergent-extracted wild-type OMV, and 1000-10,000-fold lower activity than a native wild-type OMV. In mice, the OMV vaccine from the mutant elicited higher serum bactericidal antibody responses to a panel of heterologous N. meningitidis strains than did a control multicomponent recombinant protein vaccine or a detergent-extracted OMV vaccine that has been demonstrated to confer protection against meningococcal disease in humans. Conclusions. The data illustrate the potential to develop a broadly immunogenic native OMV vaccine that has decreased endotoxin activity and is potentially suitable for testing in humans.