Early clinical experience with a candidate meningococcal B recombinant vaccine (rMenB) in healthy adults.

BACKGROUND: The development of a broadly protective vaccine against meningococcal serogroup B is a well-recognized public health need. Whole-genome sequencing was used to identify meningococcal surface proteins that are conserved across strains. These proteins were incorporated into two investigational vaccines. METHODS: Three randomized studies were performed to evaluate a three-component recombinant meningococcal serogroup B vaccine (rMenB) and rMenB plus outer membrane vesicles from the Norwegian outbreak strain 44/76 (rMenB+OMVNW). Participants were randomized to receive 3 or 4 doses of rMenB or rMenB+OMVNW or control vaccines and provided sera for exploratory immunogenicity testing against a panel of meningococcal serogroup B strains. A booster dose was administered 12 months after the initial primary series in one of the studies. The control cohort received a licensed quadrivalent meningococcal polysaccharide vaccine against serogroups A, C, W-135 and Y as well as hepatitis B vaccine as safety comparators. Solicited reactions within 7 days of any vaccination and adverse events throughout the studies were recorded. RESULTS: One hundred four participants enrolled into the clinical trials. Both rMenB and rMenB+OMVNW induced immune responses to multiple serogroup B strains in the majority of participants. Compared with rMenB, rMenB+OMVNW appeared somewhat more immunogenic and reactogenic; the study was not adequately powered for statistical assessment of these small differences. Both investigational vaccines were more reactogenic than the licensed vaccines. Few vaccinees discontinued any study due to reactogenicity to any study vaccine administered. CONCLUSION: Based on the immunogenicity and reactogenicity results in these participants, both rMenB and rMenB+OMVNW were promising candidates for further investigation.

Development of an automated, high-throughput bactericidal assay that measures cellular respiration as a survival readout for Neisseria meningitidis.

Complement-mediated bactericidal activity has long been regarded as the serological correlate of protective immunity against Neisseria meningitidis. This was affirmed in 2005 at a WHO-sponsored meningococcal serology standardization workshop. The assay currently employed by most laboratories involves determining surviving bacterial colony counts on agar as a readout which is labor-intensive, time-consuming, and not amendable to rapid data analysis for clinical trials. Consequently, there is an acute need to develop a sensitive, high-throughput bactericidal assay to enable a rapid and robust assessment of the effectiveness of vaccine candidates. To this end, we have developed an automated, kinetic assay based on the fluorescent respiration product of resazurin which reduces assay volume, shortens assay time, and facilitates automation of data analysis. We demonstrate proof of concept for applicability of this high-throughput system with multiple meningococcal strains and utilizing different lots of human complement. The assay is robust and highly reproducible. Titers obtained by the fluorescence readout method are strongly correlated with the data obtained using the conventional, agar plate-based assay. These results demonstrate that the detection of bacteria that have survived the bactericidal reaction by measuring metabolic activity using a fluorescent dye as an alternative readout is a promising approach for the development of a high-throughput bactericidal assay.

Investigation on the effect of immune selection on resistance to bactericidal antibodies to group B meningococci in vitro.

The induction of resistance by immune selective pressure to bactericidal antibodies from humans immunized with Novartis recombinant meningococcal group B vaccines was assessed. Serum bactericidal antibody titers against selected bacteria were within assay variability through a selection event frequency of 1 in 10(-5). No change in antigen expression was observed by Western blotting.

Interlaboratory standardization of the measurement of serum bactericidal activity by using human complement against meningococcal serogroup b, strain 44/76-SL, before and after vaccination with the Norwegian MenBvac outer membrane vesicle vaccine.

There is currently no standardized serum bactericidal antibody (SBA) assay for evaluating immune responses to meningococcal outer membrane vesicle or protein vaccines. Four laboratories, Manchester Health Protection Agency (MC HPA), New Zealand Institute of Environmental Science and Research Limited (NZ ESR), Norwegian Institute of Public Health (NIPH), and Chiron Vaccines (Chiron), measured SBA titers in the same panel of human sera (n=76) from laboratory staff (n=21) vaccinated with MenBvac. Blood samples were collected prevaccination, prior to each of the three doses of MenBvac given at 6-week intervals, and 6 weeks following the third dose. Initial results showed a number of discrepancies in results between the four participating laboratories. The greatest effect on titers appeared to be due to differences among laboratories in the maintenance of the meningococcal serogroup B test strain, 44/76-SL. A repeat study was conducted using the same frozen isolate (meningococcal serogroup B test strain 44/76-SL), freshly distributed to all four laboratories. Using SBA titers from the tilt method for all samples, and using MC HPA as the comparator, the results were as follows for NZ ESR, NIPH, and Chiron, respectively, using log(10) titers: correlation coefficients (r) were 0.966, 0.967, and 0.936; intercepts were 0.08, 0.15, and 0.17; and slopes were 0.930, 0.851, and 0.891. In both prevaccination and postvaccination samples from 15 subjects assayed by all four laboratories, similar increases in SBA (fourfold or greater) were observed (for 11, 11, 9, and 9 subjects for MC HPA, NZ ESR, NIPH, and Chiron, respectively), and similar percentages of subjects with SBA titers of>or=4 p revaccination and 6 weeks following each dose were found. The SBA assay has been harmonized between the four different laboratories with good agreement on seroconversion rates, n-fold changes in titers, and percentages of subjects with SBA titers of >or=4.