A Meningococcal Native Outer Membrane Vesicle Vaccine With Attenuated Endotoxin and Overexpressed Factor H Binding Protein Elicits Gonococcal Bactericidal Antibodies

Abstract

Background: Meningococcal outer membrane vesicle (OMV) vaccines are prepared with detergents to remove endotoxin, which also remove desirable antigens such as factor H binding protein (FHbp). Native OMV (NOMV) vaccines with genetically attenuated endotoxin do not require detergent treatment and elicit broader serum bactericidal antibody (SBA) responses than OMV or recombinant FHbp (rFHbp) vaccines.

Methods: We measured human complement-mediated SBA responses in mice immunized with NOMV with overexpressed FHbp subfamily B (NOMV-FHbp), NOMV with FHbp genetically inactivated (NOMV-KO), and/or a control rFHbp vaccine against meningococcal and gonococcal strains.

Results: Despite having 36-fold less FHbp per dose, the NOMV-FHbp vaccine elicited a ≥3-fold higher serum IgG anti-FHbp geometric mean titer than control vaccines containing rFHbp (P ≤ .003). Against 2 meningococcal outbreak strains with mismatched PorA and heterologous FHbp subfamily B sequence variants, the NOMV-FHbp vaccine produced ≥30-fold higher SBA titers than control vaccines. Mice immunized with NOMV-FHbp and NOMV-KO vaccines also elicited SBA against a gonococcal strain (P < .0001 vs the adjuvant-only control group). In contrast, 2 licensed meningococcal serogroup B vaccines, including one containing detergent-extracted OMV, did not produce gonococcal SBA in humans.

Conclusions: A meningococcal NOMV vaccine elicits SBA against gonococci and with overexpressed FHbp elicits SBA against meningococci.

Keywords: Neisseria gonorrhoeae; FHbp; NOMV; OMV; gonococcus; meningococcus; vaccine.

Figure 1.

Immunoglobulin G (IgG) anti-FHbp antibody titers elicited in mice by native meningococcal outer membrane vesicle (NOMV) and/or recombinant factor H binding protein (rFHbp). Each symbol represents pooled serum from 3–4 mice. Values less than the lowest dilution tested (1:500) were assigned half that value. ***P = .0006 and **P = .003, by a 2-tailed t test, compared with NOMV-FHbp. KO, knockout.

Figure 2.

Human complement-mediated serum bactericidal activity (SBA) against 4 meningococcal strains. Each symbol represents the titer of a serum pool from 3 to 4 mice. A, SBA against wild-type strain H44/76, which has PorA and factor H binding protein (FHbp) ID 1 antigens matched to the vaccine. ***P = .0002 and *P = .005, by a 2-tailed t test, compared with native meningococcal outer membrane vesicle (NOMV)–FHbp. B, SBA against SK106, which has a mismatched PorA antigen and a matched FHbp ID 1 antigen. #P = .79 and *P = .052, compared with NOMV-FHbp. C, SBA against outbreak strain CH819, which has a mismatched PorA and a mismatched FHbp ID 276 (96% sequence identity with ID 1). ****P < .0001 and **P = .004, compared with NOMV-FHbp. D, SBA against outbreak strain CH860, which has mismatched PorA and a mismatched FHbp ID 15 (87% sequence identity with ID 1). ***P = .0008 and **P = .009, compared with NOMV-FHbp. KO, knockout.

Figure 3.

Serum bactericidal activity (SBA) measured against Neisseria gonorrhoeae strain FA1090. Bacteria were incubated with individual mouse serum samples at a 1:5 dilution, after which normal human serum (20%) was added as a complement source. SBA was defined by <50% survival of bacteria after incubation for 30 minutes at 37°C. A total of 12 of 16 mice immunized with native meningococcal outer membrane vesicle–knockout (NOMV-KO) and 11 of 15 mice immunized with NOMV–factor H binding protein (FHbp) had SBA titers of ≥1:5, compared with 0 of 14 mice immunized with aluminum hydroxide (Al(OH)₃) given without an antigen (P < .0001, by the χ² test).

Figure 4.

Serum bactericidal activity (SBA) measured against Neisseria gonorrhoeae strain FA1090. Bacteria were incubated with heat-inactivated individual human serum samples at a 1:5 dilution and with normal human serum (20%) as a source of complement. A, Sera obtained before dose 1 or after dose 2 from humans immunized with 2 doses of MenB-4C in a previous study [22]. B, Sera from humans immunized with 3 doses of MenB–factor H binding protein (FHbp) in previous studies [23]. None of the immunized humans had gonococcal SBA titers of ≥1:5 in sera obtained before immunization dose 1 or 1 month after dose 2 or dose 3. C, Positive control monoclonal antibody (MAb) 2C7 (50 µg/mL) showing bactericidal activity against strain FA1090.