A Critical Threshold of Meningococcal Factor H Binding Protein Expression Is Required for Increased Breadth of Protective Antibodies Elicited by Native Outer Membrane Vesicle Vaccines

Abstract

Native outer membrane vesicles (NOMV) (not detergent treated), which are prepared from recombinant strains with attenuated endotoxin activity and overexpressed factor H binding protein (fHbp), elicited broad serum bactericidal antibody responses in mice. The amount of overexpressed fHbp required for optimal immunogenicity is not known. In this study we prepared NOMV vaccines from LpxL1 knockout (⌬LpxL1) mutants with penta-acylated lipooligosaccharide and attenuated endotoxin activity. The recombinant strains had wild-type (1؋) fHbp expression or were engineered for 3-fold-or 10-fold-increased fHbp expression (3؋ or 10؋ fHbp). Control vaccines included NOMV from ⌬LpxL1/⌬fHbp mutants or recombinant fHbp. In mice, only the 10؋ fHbp NOMV vaccine elicited significantly higher serum IgG anti-fHbp antibody titers than the corresponding 1؋ fHbp NOMV or recombinant fHbp vaccine. The 10؋ fHbp NOMV vaccine also elicited higher bactericidal responses (P < 0.05) against five group B strains with heterologous PorA than the recombinant fHbp or 1؋ fHbp NOMV vaccine. The 3؋ fHbp NOMV vaccine gave higher bactericidal titers against only one strain. Serum bactericidal titers in mice immunized with the control ⌬fHbp NOMV vaccines were <1:10, and bactericidal titers in mice immunized with the 10؋ fHbp NOMV vaccine were <1:10 after adsorption of anti-fHbp antibodies. Mixing antiserum to NOMV vaccines from fHbp knockout mutants with antiserum to recombinant fHbp did not increase anti-fHbp bactericidal titers. Thus, a critical threshold of increased fHbp expression is required for NOMV vaccines to elicit broad serum bactericidal responses, and the antibodies conferring protection are directed primarily at fHbp.

Next-generation outer membrane vesicle vaccines againstNeisseria meningitidisbased on nontoxic LPS mutants

“…Koeberling et al 17 showed that it is fully retained in lpxL1 nOMVs, and they further engineered strains for 3-to 10-fold higher expression by using plasmid constructs of either fHbp itself or its regulator. This higher fHbp expression turned out to be critical for getting an increased breadth of protective antibodies.…”

A Burkholderia pseudomallei Outer Membrane Vesicle Vaccine Provides Protection against Lethal Sepsis

“…Mice were challenged i.p. with approximately 50ϫ LD 50 of B. pseudomallei strain K96243. Two independent experiments were performed; survival was monitored up to day 14.…”

“…It may also be necessary to enrich the OMV cargo with virulence determinants specific to the intracellular stage of infection (44,45) or with antigens that induce strong T cell responses (46)(47)(48). A number of studies have shown that expression and delivery of homologous and heterologous antigens with OMVs are feasible (45,49,50). We previously showed that immunization with B. pseudomallei OMVs stimulates memory T cell responses and gamma interferon (IFN-␥) production (14).…”

Current Trends In Research, Development And Production Of Prophylactic Vaccines: Report of Vaccipharma 2015 Congress

“…Issues to be studied more carefully are duration of protection in various age groups, mucosal immunity and herd protection. Of particular note, a substantial difference in immunogenicity has been observed with recombinant fHbp versus the experimental formulations of native OMV vaccines where fHbp has been included as over-expressed vaccine antigen (NOMV-OEfHbp with 3-6 times the ordinary level found in wild type strains) [89][90][91]. The total amount of fHbp in the two formulations can be more than 100 times different, and the NOMV formulation induces better anti-fHbp immunity than the recombinant vaccine.…”