Neisseria meningitidis group B correlates of protection and assay standardization--international meeting report Emory University, Atlanta, Georgia, United States, 16-17 March 2005

Immunogenicity, reactogenicity, and safety of a P1.7b,4 strain-specific serogroup B meningococcal vaccine given to preteens

New Zealand (NZ) has experienced a Neisseria meningitidis serogroup B epidemic since 1991. MeNZB, a strain-specific outer membrane vesicle vaccine made using an NZ epidemic strain isolate, NZ98/254 (B:4:P1.7b,4), from two manufacturing sites, the Norwegian Institute of Public Health (NIPH) and Chiron Vaccines (CV; now Novartis), was evaluated for safety, immunogenicity, and reactogenicity in this observer-blind trial with 8- to 12-year-old children. In year 1, cohort A (n = 302) was randomized 4:1 for receipt of NIPH-MeNZB or MenBvac (Norwegian parent vaccine strain 44/76; B:15:P1.7,16). In year 2, cohort B (n = 313) was randomized 4:1 for receipt of CV-MeNZB or NIPH-MeNZB. Participants all received three vaccinations 6 weeks apart. Local and systemic reactions were monitored for 7 days. Seroresponse was defined as a fourfold or greater rise in the serum bactericidal antibody titer from the baseline titer as measured by a serum bactericidal assay. Those with baseline titers of <1:4 required titers of >/=1:8 to serorespond. Intention-to-treat (ITT) and per protocol (PP) analyses are presented. In cohort A, 74% (ITT) and 73% (PP) of NIPH-MeNZB recipients demonstrated seroresponses against NZ98/254 after three doses, versus 32% (ITT and PP) of MenBvac recipients. In cohort B, seroresponses against NZ98/254 after three doses occurred in 79% (ITT and PP) of CV-MeNZB versus 75% (ITT) and 76% (PP) of NIPH-MeNZB recipients. Vaccines were tolerable, with no vaccine-related serious adverse events. In conclusion, the NZ strain meningococcal B vaccine (MeNZB) from either manufacturing site was immunogenic against New Zealand epidemic vaccine strain meningococci with no safety concerns when given in three doses to these 8- to 12-year-old children.

Comparison of phenotypically indistinguishable but geographically distinct Neisseria meningitidis Group B isolates in a serum bactericidal antibody assay

The "gold standard" assay for measuring serologic protection against Neisseria meningitidis group B (MenB) is the serum bactericidal antibody (SBA) assay. Of vital importance to the outcome of the SBA assay is the choice of the target strain(s), which is often chosen on the basis of phenotype or genotype. We therefore investigated the effect on the results produced by the SBA assay of using phenotypically indistinguishable but geographically distinct MenB isolates. Nine PorA P1.19,15 and 11 PorA P1.7-2,4 MenB isolates were incorporated into the SBA assay using human complement and were assayed against sera obtained either before or after outer membrane vesicle vaccination. Large differences in the results produced by the isolates in the SBA assay were demonstrated. These included differences as great as 5.8-fold in SBA geometric mean titers and in the proportions of subjects with SBA titers of >/=4. Ranges of as many as 9 SBA titers were achieved by individual sera across the panels of isolates. To determine the reasons for the differences observed, investigations into the expression of capsular polysaccharide, PorA, PorB, Opc, and lipooligosaccharide (LOS) and into LOS sialylation were completed. However, minor differences were found between strains, indicating similar expression and no antigen masking. These results have implications for the choice of MenB target strains for inclusion in future studies of MenB vaccines and highlight the requirement for standardization of target strains between laboratories.

Scale-up for bulk production of vaccine against meningococcal disease

At the Netherlands Vaccine Institute (NVI) a vaccine against Neisseria meningitidis serogroup B organisms based on different porA subtypes contained in outer membrane vesicles (OMVs) is in advanced stage of development and will be evaluated in clinical trial studies in the near future. In order to meet the expected demand for product, the current biopharmaceutical production process is being scaled-up. This study describes the scale-up approach for the upstream process and the resulting bioreactor design and operation strategy leading towards a feasible solution for bulk production of a vaccine against meningococcal disease. The technically realized 1.2 m(3) bioreactor, equipped with a turbine impeller for gas dispersion, was complemented with an upward pumping impeller and a rotary plate foam breaker to contain foam inside the bioreactor. Aeration and ventilation in the culture broth were controlled by increasing the stirrer speed and gas flow rate simultaneously at increasing oxygen demand. The scale-up was successful and comparable growth curves and nutrient consumption profiles were reached on 0.06 and 1.2 m(3).

Seroprevalence of bactericidal and anti-outer membrane vesicle antibodies to Neisseria meningitidis group B in England

Outer membrane vesicle (OMV) and recombinant protein-based vaccines targeted against multiple strains of group B meningococci are under development. The serum bactericidal antibody (SBA) assay has been designated the surrogate of protection, but the exact cutoff has not been determined. We measured the SBA titers in 2,415 serum samples and the anti-OMV IgG antibody concentrations in 2,672 serum samples representative of the English population to establish a baseline of natural immunity. SBA and anti-OMV IgG antibody titers are high in infants in the first 3 months of life, declining thereafter, presumably as maternal immunity wanes. About 6% of the subjects in the 1- to 11-year-old age group had SBA titers >or=4. During the teenage years, there was a marked increase in the percentage of subjects with SBA titers >or=4, rising to over 50% in 19-year-olds, with about 20% of older adults achieving this titer. The peak in SBA and anti-OMV IgG titers coincided with the peak in meningococcal carriage. Simple mathematical models confirm that the relationship between observed seroprevalence and carriage by age is consistent with carriage inducing SBA and that following an episode of carriage, SBA levels may remain elevated for many months. With the exception of children aged 3 to 11 months, there was no clear relationship between disease incidence and seroprevalence.

Conquering the meningococcus

Since the first outbreaks of meningococcal meningitis were first described in Geneva in 1804 and in New England in 1806, and since the discovery of the causative agent by Weichselbaum in 1887 and the beginning of epidemics of meningococcal meningitis in the sub-Saharan Africa approximately 100 years ago, Neisseria meningitidis has been recognized as the cause worldwide of epidemic meningitis and meningococcemia. The massive epidemic outbreaks in sub-Saharan Africa in the 1990's, the emergence since 1995 of serogroups Y, W-135 and X and the prolonged outbreak of serogroup B meningococcal disease in New Zealand over the last decade serve to remind us of the continued potential of the meningococcus to cause global morbidity and mortality. This report reviews new discoveries impacting prevention and future prospects for conquering the meningococcus as a human pathogen.

Inadequacy of colominic acid as an absorbent intended to facilitate use of complement-preserved baby rabbit serum in the Neisseria meningitidis serogroup B serum bactericidal antibody assay

The surrogate of protection against Neisseria meningitidis serogroup B (MenB) is the serum bactericidal antibody (SBA) assay, which measures the functional activity of antibody by using an exogenous complement source. Despite baby rabbit complement having been used in meningococcal serogroup A, C, Y, and W135 SBA assays, it is not recommended for use in the MenB SBA assay due to elevated SBA titers caused by low-avidity anti-MenB capsular antibody in test sera. Therefore, the possibility of absorbing anti-MenB capsular antibody from test sera to enable the use of baby rabbit complement in the MenB SBA assay was investigated by comparing the results with those gained using human complement. Colominic acid from Escherichia coli K1, which shares the same linkage residue as MenB polysaccharide, was used as an absorbent due to the commercial unavailability of purified MenB polysaccharide. Inclusion of soluble colominic acid as an absorbent with baby rabbit complement resulted in a general reduction in SBA titers compared with those obtained using baby rabbit complement alone. However, these were not comparable to human SBA titers for all samples. Further optimization and investigations demonstrated that for some samples, colominic acid reduced titers to less than those achieved with human complement, and for others, it was not possible to inhibit titers by using colominic acid. The results suggested that the use of colominic acid will not result in the ability to use baby rabbit complement in the MenB SBA assay, thus not alleviating the difficulties in procuring human complement. However, alternative absorbents, such as purified MenB polysaccharide, may warrant further evaluation.

Vaccination against meningococcal disease in Europe: review and recommendations for the use of conjugate vaccines

At the end of 2005, six European countries had implemented public immunization campaigns with serogroup C conjugate vaccines, and all had experienced substantial declines in the incidence of serogroup C disease. A quadrivalent ACWY meningococcal vaccine is in use in the USA, but serogroup A is extremely rare in Europe and serogroups Y and W135 are infrequent causes of disease. This paper outlines recommendations on the use of conjugate vaccines in Europe based on the experience with meningococcal C conjugate (MCC) vaccines so far.