Immunogenicity of 2 serogroup B outer-membrane protein meningococcal vaccines: a randomized controlled trial in Chile

Stability of PorA during a meningococcal disease epidemic

Meningococci causing New Zealand's epidemic, which began in 1991, are defined as group B, serosubtype P1.4 (subtype P1.7-2,4), belonging to the ST-41/ST-44 complex, lineage III. Of the 2,358 group B isolates obtained from disease cases from 1991 through 2003, 85.7% (2,021 of 2,358) were determined to be serosubtype P1.4. Of the remaining isolates, 156 (6.6%) were not serosubtypeable (NST). Molecular analysis of the porA gene from these B:NST meningococcal isolates was used to determine the reason. Most NST isolates (156, 88.5%) expressed a PorA that was distinct from P1.7-2,4 PorA. Fifteen isolates expressed variants of P1.7-2,4 PorA, and a further three expressed P1.7-2,4 PorA without any sequence variation. These three isolates expressed P1.7-2,4 PorA at very low levels, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, and showed variation in the porA promoter region. Among the 15 meningococcal isolates expressing variants of P1.7-2,4 PorA, 11 different sequence variations were found. Compared with the P1.7-2,4 PorA sequence, the sequences of these variants contained deletions, insertions, or single-nucleotide substitutions in the VR2 region of the protein. Multilocus restriction typing was used to assess the clonal derivations of B:NST case isolates. Meningococcal isolates expressing distinct PorA proteins belonged mostly to clonal types that were unrelated to the epidemic strain, whereas all meningococcal isolates expressing variants of P1.7-2,4 PorA belonged to the ST-41/ST-44 complex, lineage III. These results, together with those obtained serologically, demonstrate that the P1.7-2,4 PorA protein of meningococci responsible for New Zealand's epidemic has remained relatively stable over 13 years and support the use of a strain-specific outer membrane vesicle vaccine to control the epidemic.

Effect of a booster dose of serogroup B meningococcal vaccine on antibody response to Neisseria meningitidis in mice vaccinated with different immunization schedules

The generation and maintenance of memory antibody response by different primary immunization schedules with the Cuban-produced outer membrane protein based vaccine was investigated in a murine model. We analyzed the duration of the antibody response (IgG-ELISA and bactericidal titer) and the effect of a booster dose on the antibody response. The IgG avidity index was determined in an attempt to find a marker for memory development. This study also included an analysis of IgG subclasses induced by primary and booster immunization. The specificity of bactericidal antibodies was investigated using local strains of the same serotype/serosubtype (4,7:P1.19,15) as the vaccine strain and mutant strains lacking major outer membrane proteins. A significant recall response was induced by a booster dose given 7 months after a primary series of 2, 3 or 4 doses of vaccine. The primary antibody response showed a positive dose-effect. In contrast, a negative dose-effect was found on the booster bactericidal antibody response. There was a significant increase in IgG1 levels after the fourth and booster doses. Three doses of vaccine were required to induce a significant increase in IgG avidity. Two injections of vaccine induced a significant antibody response to PorA protein, while 4 injections induced a larger range of specificities.

Development and characterisation of outer membrane vesicle vaccines against serogroup A Neisseria meningitidis

Neisseria meningitidis bacteria of serogroup A are causing recurring meningitis epidemics on the African continent. An outer membrane vesicle (OMV) vaccine against serogroup A meningococci made from a subgroup III serogroup A meningococcal strain was previously shown to induce antibodies with serum bactericidal activity (SBA) in mice. We have here further investigated the properties of OMV vaccines made from five different subgroup III serogroup A meningococcal strains grown in a synthetic medium with low iron content. In addition to the major outer membrane proteins (PorA, PorB, RmpM, Opa and OpcA), small amounts of the NadA, TdfH, Omp85, FetA, FbpA and NspA outer membrane proteins, as well as lipooligosaccharides, were detected in the vaccines. The OMV vaccines were used to immunise mice. Anti-meningococcal IgG antibodies in the mouse sera were analysed by immunoblotting and by enzyme-linked immunosorbent assay against OMVs, and against live meningococcal cells in SBA and a flow-cytometric assay. The vaccines induced antibodies with high SBA and opsonophagocytic activity. The strongest IgG responses were directed against PorA. Significant SBA responses were also observed against a subgroup III strain, which did not express PorA, whereas no SBA was observed against a clone IV-1 serogroup A strain. An OMV vaccine from serogroup A meningococci may be an alternative to polysaccharide and conjugate polysaccharide vaccines for Africa.

Interactions of proteoliposomes from serogroup B Neisseria meningitidis with bone marrow-derived dendritic cells and macrophages: adjuvant effects and antigen delivery

Exposure to proteoliposomes from serogroup B Neisseria meningitidis (PL) induced up-regulation of MHC-II, MHC-I, CD40, CD80 and CD86 expression on the surface of murine bone marrow-derived dendritic cells (DC). CD40, CD80 and CD86 were up-regulated on bone marrow-derived macrophages (MPhi) upon stimulation with PL. Both DC and MPhi released TNFalpha, but only DC produced IL12(p70) in response to PL. A small increase in the expression of MHC-II, CD40 and CD86, as well as production of IL12(p70), was observed on the cell surface of DC, but not MPhi from LPS-non-responder C3H/HeJ after exposure to PL. DC, but not MPhi, incubated with PL containing ovalbumin (PL-OVA) presented OVA-specific peptides to CD4+ and CD8+ OVA-specific T-cell hybridomas. These data clearly indicate that PL exert an immunomodulatory effect on DC and MPhi, with some contribution of non-LPS components besides the main role of LPS. The work also shows the potential of PL as a general system to deliver antigens to DC for presentation to CD4+ and CD8+ T-cells.

The region comprising amino acids 100 to 255 of Neisseria meningitidis lipoprotein GNA 1870 elicits bactericidal antibodies

GNA 1870 is a novel surface-exposed lipoprotein, identified by genome analysis of Neisseria meningitidis strain MC58, which induces bactericidal antibodies. Three sequence variants of the protein were shown to be sufficient to induce bactericidal antibodies against a panel of strains representative of the diversity of serogroup B meningococci. Here, we studied the antigenic and immunogenic properties of GNA 1870, which for convenience was divided into domains A, B, and C. The immune responses of mice immunized with each of the three variants were tested using overlapping peptides scanning the entire protein length and using recombinant fragments. We found that while most of the linear epitopes are located in the A domain, the bactericidal antibodies are directed against conformational epitopes located in the BC domain. This was also confirmed by the isolation of a bactericidal murine monoclonal antibody, which failed to recognize linear peptides on the A, B, and C domains separately but recognized a conformational epitope formed only by the combination of the B and C domains. Arginine in position 204 was identified as important for binding of the monoclonal antibody. The identification of the region containing bactericidal epitopes is an important step in the design of new vaccines against meningococci.

Immunogenicity and bactericidal activity in mice of an outer membrane protein vesicle vaccine against Neisseria meningitidis serogroup A disease

Serogroup A Neisseria meningitidis organisms of the subgroup III have caused epidemics of meningitis in sub-Saharan Africa since their introduction into the continent in 1987. The population structure of these bacteria is basically clonal, and these meningococci are strikingly similar in their major outer membrane antigens PorA and PorB. Protein-based vaccines might be an alternative to prevent epidemics caused by these meningococci; thus, we developed an outer membrane vesicle (OMV) vaccine from a serogroup A meningococcal strain of subgroup III. The serogroup A OMV vaccine was highly immunogenic in mice and elicited significant bactericidal activity towards several other serogroup A meningococci of subgroup III. The IgG antibodies generated were in immunoblot shown to be mainly directed towards the PorA outer membrane protein. The results presented demonstrate the potential of an OMV vaccine as an optional strategy to protect against meningococcal disease caused by serogroup A in Africa.

Meningococcal vaccines

Meningococcal disease is one of the most feared and serious infections in the young and its prevention by vaccination is an important goal. The high degree of antigenic variability of the organism makes the meningococcus a challenging target for vaccine prevention. Meningococcal polysaccharide vaccines against serogroup A and C are efficacious and have been widely used, often in combination with serogroup Y and W135 components. Their relative lack of immunogenicity in young children and infants can be overcome by conjugation to a protein carrier. The effectiveness of serogroup C glycoconjugate vaccines in children of all ages has been demonstrated and they have now been introduced into routine vaccination schedules. Conjugate vaccines against other serogroups, including A, Y, and W135 will soon be available and it is hoped they may emulate this success. Prevention of serogroup B disease has proven more elusive. Several serogroup B vaccines based on outer membrane vesicles have been shown to be immunogenic and reasonably effective in adults and older children, but the protection offered by them is chiefly strain-specific. Multivalent recombinant PorA vaccines have been developed to broaden the protective effect, but no efficacy data are available as yet. Intensive efforts have been directed at other outer membrane protein vaccine candidates and lipopolysaccharide, and some of these have been shown to offer protection in experimental animal models. Nonpathogenic Neisseriae spp. such as Neisseria lactamica are also possible vaccine candidates. Previously unknown proteins have been identified from in silico analysis of the meningococcal genome and their vaccine potential explored. However, none of these has yet been presented as the 'universal' protective antigen and work in this field continues to be held back by our limited knowledge concerning the mechanisms of natural protection against serogroup B meningococci.

Expression of heterologous antigens in commensal Neisseria spp.: preservation of conformational epitopes with vaccine potential

Commensal neisseriae share with Neisseria meningitidis (meningococcus) a tendency towards overproduction of the bacterial outer envelope, leading to the formation and release during growth of outer membrane vesicles (OMVs). OMVs from both meningococci and commensal neisseriae have shown promise as vaccines to protect against meningococcal disease. We report here the successful expression at high levels of heterologous proteins in commensal neisseriae and the display, in its native conformation, of one meningococcal outer membrane protein vaccine candidate, NspA, in OMVs prepared from such a recombinant Neisseria flavescens strain. These NspA-containing OMVs conferred protection against otherwise lethal intraperitoneal challenge of mice with N. meningitidis serogroup B, and sera raised against them mediated opsonophagocytosis of meningococcal strains expressing this antigen. This development promises to facilitate the design of novel vaccines containing membrane protein antigens that are otherwise difficult to present in native conformation that provide cross-protective efficacy in the prevention of meningococcal disease.

Biotechnology and vaccines: application of functional genomics to Neisseria meningitidis and other bacterial pathogens

Since its introduction, vaccinology has been very effective in preventing infectious diseases. However, in several cases, the conventional approach to identify protective antigens, based on biochemical, immunological and microbiological methods, has failed to deliver successful vaccine candidates against major bacterial pathogens. The recent development of powerful biotechnological tools applied to genome-based approaches has revolutionized vaccine development, biological research and clinical diagnostics. The availability of a genome provides an inclusive virtual catalogue of all the potential antigens from which it is possible to select the molecules that are likely to be more effective. Here, we describe the use of "reverse vaccinology", which has been successful in the identification of potential vaccines candidates against Neisseria meningitidis serogroup B and review the use of functional genomics approaches as DNA microarrays, proteomics and comparative genome analysis for the identification of virulence factors and novel vaccine candidates. In addition, we describe the potential of these powerful technologies in understanding the pathogenesis of various bacteria.

Distribution of surface protein variants among hyperinvasive meningococci: implications for vaccine design

The bacterium Neisseria meningitidis is a major cause of meningitis and septicemia worldwide. Outer membrane proteins (OMPs) are candidates in the search for comprehensive meningococcal vaccines; however, the formulation of OMP vaccines is complicated by antigenic diversity, which is generated by high levels of genetic reassortment and strong positive selection in the meningococcal antigen genes. The genetic and antigenic diversity of three OMPs (FetA, PorA, and PorB) among a global collection of meningococcal isolates representative of the major hyperinvasive clonal complexes was determined. There was evidence for antigenic structuring among the three OMPs that could not be explained purely by descent. These observations violated the predictions of the clonal and epidemic clonal models of population structure but were in concordance with models of strain structure which propose that host immunity selects for nonoverlapping antigen combinations. The patterns of antigenic variant combinations suggested that an OMP-based vaccine with as few as six PorA and five FetA variant sequences could generate homologous immune responses against all 78 isolates examined.

Adjuvant can improve protection induced by OMV vaccine against Neisseria meningitidis serogroups B/C in neonatal mice

Meningococcal outer membrane vesicle (OMV) vaccines are weak antigens in infants. This study aimed at investigating alternative adjuvants for induction of functional antibodies in newborn mice. Serogroup B/C anti-meningococcal vaccines, consisting of capsular polysaccharide from serogroup C (PSC) conjugated to OMV from one serogroup B serosubtype prevalent in Brazil, combined with OMV from another prevalent serosubtype, were tested in newborn and adult mice with the following adjuvants: aluminum hydroxide, MPL (monophosphoryl lipid A), Titermax and MF59. Total IgG, IgG avidity index determination and bactericidal assay were performed with sera from immunized mice. Antibodies induced against PSC in newborn mice showed avidity and bactericidal titers, similar to those obtained in adult mice, independently of the adjuvant. Evidence is presented that the inclusion of MF59 enhanced the immune response against OMV in newborn mice.

Protective activity of monoclonal antibodies to genome-derived neisserial antigen 1870, a Neisseria meningitidis candidate vaccine

Genome-derived neisserial Ag (GNA) 1870 is a meningococcal vaccine candidate that can be subdivided into three variants based on amino acid sequence variability. Variant group 1 accounts for approximately 60% of disease-producing group B isolates. The Ag went unrecognized until its discovery by genome mining because it is expressed in low copy number by most strains. To investigate the relationship between Ab binding to GNA1870 and complement-mediated protective functions, we prepared a panel of four murine IgG mAbs against rGNA1870 (variant 1) and evaluated their activity against nine genetically diverse encapsulated Neisseria meningitidis strains expressing subvariants of variant 1 GNA1870. Based on flow cytometry with live encapsulated bacteria, surface accessibility of the epitopes recognized by the mAbs appeared to be low in most strains. Yet mAb concentrations <1 to 5 micro g/ml were sufficient to elicit bactericidal activity with human complement and/or activate C3b deposition on the bacterial surface. Certain combinations of mAbs were highly bactericidal against strains that were resistant to bactericidal activity of the respective individual mAbs. The mAbs conferred passive protection against bacteremia in infant rats challenged by strains resistant to bacteriolysis, and the protective activity paralleled the ability of the mAb to activate C3b deposition. Thus, despite low GNA1870 surface exposure, anti-GNA1870 variant 1 Abs are bactericidal and/or elicit C3b deposition and confer protection against bacteremia caused by encapsulated N. meningitidis strains expressing GNA1870 subvariant 1 proteins. The data support GNA1870 as a promising vaccine candidate for prevention of meningococcal group B disease caused by GNA1870 variant 1 strains.

Mucosal vaccination against serogroup B meningococci: induction of bactericidal antibodies and cellular immunity following intranasal immunization with NadA of Neisseria meningitidis and mutants of Escherichia coli heat-labile enterotoxin

Conjugated polysaccharide vaccines protect against serogroup C meningococci. However, this approach cannot be applied to serogroup B, which is still a major cause of meningitis. We evaluated the immunogenicity of three surface-exposed proteins from serogroup B Neisseria meningitidis (App, NhhA, and NadA) identified during whole-genome sequencing. Mice were immunized intranasally with individual proteins in the presence of wild-type Escherichia coli heat-labile enterotoxin (LTwt), LTR72, a partially inactivated mutant, or LTK63, a completely nontoxic mutant, as the adjuvant. Each of the meningococcal proteins induced significant cellular responses; NhhA and NadA induced strong antibody responses, but only NadA induced bactericidal antibody when administered intranasally with mucosal adjuvants. In addition, immunoglobulin A and bactericidal antibodies were detected in the respiratory tract following intranasal delivery of NadA. Analysis of antigen-specific cytokine production by T cells from immunized mice revealed that intranasal immunization with NadA alone failed to generate detectable cellular immune responses. In contrast, LTK63, LTR72, and LTwt significantly augmented NadA-specific gamma interferon, interleukin-4 (IL-4), IL-5, and IL-10 production by spleen and lymph node cells, suggesting that both Th1 and Th2 cells were induced in vivo. The strongest cellular responses and highest bactericidal antibody titers were generated with LTR72 as the adjuvant. These findings demonstrate that the quality and magnitude of the immune responses generated by mucosal vaccines are influenced by the antigen as well as the adjuvant and suggest that nasal delivery of NadA with mucosal adjuvants has considerable potential in the development of a mucosal vaccine against serogroup B meningococci.

Meningococcal conjugate vaccines

Neisseria meningitidis is a leading cause of bacterial meningitis and sepsis in the US, Europe and in many other parts of the world, including parts of sub-Saharan Africa (known as the African 'meningitis belt'). There are > 500000 cases of meningococcal disease annually with an estimated death toll of 135000 worldwide. Approximately 10 - 15 % of survivors experience significant morbidity in the form of neurological sequelae, including hearing loss, speech disorders, loss of limbs, mental retardation and paralysis. Disease is usually caused by N. meningitidis serogroups A, B, C, Y or W-135. Prevention of meningococcal disease includes isolation, chemoprophylaxis and vaccination with available polysaccharide vaccines. However, the polysaccharide meningococcal vaccines (i.e., A and C; A, C and W-135; or A, C, Y and W-135) initially developed in the 1970s are generally poorly immunogenic in children or require repeated doses and do not produce long-lasting immunity. Conjugate vaccine technology has been very successfully used in childhood vaccines for the prevention of other bacterial meningitis pathogens, including vaccines against Haemophilus influenzae serotype b (Hib) and more recently, the seven- and nine-valent conjugate pneumococcal vaccines. Newly released meningococcal conjugate vaccines against N. meningitidis serogroup C have been highly efficacious in young children and adolescents, with minimal side effects. Conjugate vaccines targeting other important meningococcal serogroups (e.g., N. meningitidis serogroup A, responsible for the large pandemic outbreaks and the majority of disease in sub-Saharan Africa and serogroups Y and W-135) are under development and together with the serogroup C conjugates, have the potential to significantly impact worldwide sporadic and epidemic meningococcal disease. The search for an effective serogroup B meningococcal vaccine remains elusive. This manuscript reviews the conjugate meningococcal vaccines and their potential for meningococcal disease prevention.

Clinical evaluation of a group B meningococcal N-propionylated polysaccharide conjugate vaccine in adult, male volunteers

The safety and immunogenicity of a group B meningococcal vaccine, consisting of N-propionylated (NPr) B capsular polysaccharide conjugated to tetanus toxoid, was tested for the first time, in 17 healthy male volunteers aged between 18 and 40 years. Four escalating dosages of vaccine were tested and each was given as three intramuscular injections at 4-week intervals. The vaccine was well tolerated and induced only mild and transient, dose-dependent, injection-site reactions. One month after the last injection, there was no evidence of the production of autoantibodies or antibodies binding to PSA-NCAM. The vaccine induced an increase in the pre-existing titres of IgM specific to B polysaccharide and NPr B polysaccharide. Moreover, it induced IgG antibodies specific to NPr B polysaccharide, which were undetectable before vaccination. However, no functional activity of vaccine-induced antibodies was demonstrated in bactericidal assays, opsonophagocytic tests or passive protection tests.

Vaccine potential of the Neisseria meningitidis 2086 lipoprotein

A novel antigen that induces cross-reactive bactericidal antibodies against a number of Neisseria meningitidis strains is described. This antigen, a approximately 28-kDa lipoprotein called LP2086, was first observed within a complex mixture of soluble outer membrane proteins (sOMPs) following a series of fractionation, protein purification, and proteomics steps. Approximately 95 different neisserial isolates tested positive by Western blotting and PCR screening methods for the presence of the protein and the gene encoding LP2086. The strains tested included isolates of N. meningitidis serogroups A, B, C, W135, and Y, Neisseria gonorrhoeae, and Neisseria lactamica. To better understand the microheterogeneity of this protein, the 2086 genes from 63 neisserial isolates were sequenced. Two different subfamilies of LP2086 were identified based on deduced amino acid sequence homology. A high degree of amino acid sequence similarity exists within each 2086 subfamily. The highest degree of genetic diversity was seen between the two subfamilies which share approximately 60 to 75% homology at the nucleic acid level. Flow cytometry (fluorescence-activated cell sorting) analyses and electron microscopy indicated that the LP2086 is localized on the outer surface of N. meningitidis. Antiserum produced against a single protein variant was capable of eliciting bactericidal activity against strains expressing different serosubtype antigens. Combining one recombinant lipidated 2086 (rLP2086) variant from each subfamily with two rPorA variants elicited bactericidal activity against all strains tested. The rLP2086 family of antigens are candidates worthy of further vaccine development.

Opportunities for Control of Meningococcal Disease in the United States

The United States currently has relatively low rates of meningococcal disease caused by Neisseria meningitidis. Serogroups Y, C, and B are most common. Although most cases are sporadic, a minority are associated with outbreaks. Pediatric populations have disproportionately higher rates of disease, but nearly two thirds of all cases occur in persons aged 15 years and older. The major challenge to control of domestic meningococcal disease is the absence of a vaccine to prevent sporadic cases spanning many age groups. The quadrivalent A/C/Y/W-135 meningococcal polysaccharide vaccine is licensed in the United States, but because of its limited efficacy in children under two years of age, it is recommended for high-risk groups and outbreak response rather than routine childhood immunization. New conjugate meningococcal vaccines have successfully reduced endemic disease in the United Kingdom, and similar vaccines promise to have a dramatic impact on the burden of meningococcal disease in the United States.

Vaccines against bacterial meningitis

Meningitis remains an important cause of morbidity and mortality among children >5 years of age and is especially prevalent in developing countries. Effective routine immunization against Hib, pneumococcus and serogroupC meningococcus has had a significant impact on both invasive disease and carriage caused by these encapsulated bacteria. The major challenge in prevention of meningitis remains the delivery of vaccines worldwide, especially to resource-poor regions with the greatest disease burden.

Serosubtipos de meningococo B causantes de enfermedad invasiva en Cantabria y concordancia con la cepa de la vacuna cubana

OBJECTIVE

To determine the serosubtypes of meningococcus B causing invasive disease in Cantabria and the percentage of agreement with the Cuban vaccine strain, VA-MENGOC-BC.

METHODS

We performed a retrospective review of all cases of invasive disease due to meningococcus B declared through the Diseases of Mandatory Reporting System between 1st January 1998 and 28th February 2003. The bacteriological isolates of the "Marqués de Valdecilla" University Hospital, and the serosubtyping performed in the Majadahonda reference laboratory (Madrid, Spain) were also analyzed.

RESULTS

Of the 117 declared cases, serosubtype was identified in 79 (67.5%). The agreement with the Cuban vaccine strain was 67%, 71% and 76% in the age groups of newborn to 19 years, 18 months to 19 years, and 4 to 19 years, respectively. When strains with cross-protection were included, these percentages increased to 83%, 83% and 84%, respectively, in the same age groups.

CONCLUSIONS

The percentage of agreement between the Cuban vaccine strain and heterologous strains with cross-protection was high. Therefore, this vaccine could be useful in Cantabria.

Relative immunogenicity of PorA subtypes in a multivalent Neisseria meningitidis vaccine is not dependent on presentation form

The hexavalent meningococcal vaccine HexaMen, containing six PorAs on two vesicles, was tested in clinical studies. Although fourfold increases in serum bactericidal activity (SBA) titers against all of the PorAs were observed, there were significant differences between PorA-specific SBA titers. SBA titers were mainly directed against one PorA from each vesicle, P1.5-2,10 and P1.5-1,2-2, and were lower against the other PorAs, especially P1.7-2,4 and P1.19,15-1. We investigated whether these differences were due to immunological interference that resulted in competition between the three PorAs on the same vesicle or whether they were caused by a difference in the immunogenicities of the separate PorAs. Therefore, mice were immunized either with HexaMen, with six monovalent outer membrane vesicles (OMVs) representing the same six PorAs simultaneously (HexaMix), or with only one of the monovalent OMVs. The immunoglobulin G and SBA titers after HexaMen immunization in mice resembled the results obtained in clinical studies. Although immunization with HexaMix gave higher titers than immunization with HexaMen for some PorAs, the pattern of high and low titers was the same. Similar differences in immunogenicity between subtypes were seen after monovalent immunization when interference was eliminated as a cause of the differences. Monovalent immunization resulted in higher titers for P1.5-1,2-2 and P1.7,16 than immunization with HexaMen. However, no significant differences were found for the weakly immunogenic PorAs, P1.7-2,4 and P1.19,15-1. Since immunization with the six PorAs in the trivalent presentation form (HexaMen) and in the mixture of monovalent vesicles (HexaMix) resulted in the same pattern of high and low titers, we concluded that the differences between the PorA-specific responses are due to differences in the immunogenicities of the various PorAs and not due to interference that results in competition between different PorAs.

Critical analysis of old and new vaccines against N. meningitidis serogroup C, considering the meningococcal disease epidemiology in Brazil

Worldwide, the impact of meningococcal disease is substantial, and the potential for the introduction and spread of more virulent strains of N. meningitidis or strains with increased resistance to current antibiotics causes concern, making prevention essential.

OBJECTIVES

Review the indications for meningococcal disease vaccines, considering the epidemiological status in Brazil.

METHODS

A critical literature review on this issue using the Medline and Lilacs databases.

RESULTS

In Brazil, MenB and MenC were the most important serogroups identified in the 1990s. Polysaccharide vaccines available against those serogroups can offer only limited protection for infants, the group at highest risk for meningococcal disease. Additionally, polysaccharide vaccines may induce a hypo-responsive state to MenC. New meningococcal C conjugate vaccines could partially solve these problems, but it is unlikely that in the next few years a vaccine against MenB that can promote good protection against multiple strains of MenB responsible for endemic and epidemic diseases will become available.

CONCLUSIONS

In order to make the best decision about recommendations on immunization practices, better quality surveillance data are required. In Brazil, MenC was responsible for about 2,000 cases per year during the last 10 years. New conjugate vaccines against MenC are very effective and immunogenic, and they should be recommended, especially for children less than 5 years old. Polysaccharide vaccines should be indicated only in epidemic situations and for high-risk groups. Until new vaccines against MenC and MenB are available for routine immunization programs, the most important measure for controlling meningococcal disease is early diagnosis of these infections in order to treat patients and to offer chemoprophylaxis to contacts.

Liposomal meningococcal B vaccination: role of dendritic cell targeting in the development of a protective immune response

The effect of targeting strategies for improving the interaction of liposomal PorA with dendritic cells (DC) on the immunogenicity of PorA was investigated. PorA, a major antigen of Neisseria meningitidis, was purified and reconstituted in different types of (targeted) liposomes, i.e., by using mannose or phosphatidylserine as targeting moieties, or with positively charged liposomes. We studied the efficiency of liposome uptake and its effect on the maturation of and interleukin 12 (IL-12) production by murine DC. Moreover, mice were immunized subcutaneously to study the localization and immunogenicity of PorA liposomes. Uptake of liposomes by DC was significantly increased for targeted liposomes and resulted in the maturation of DC, but to various degrees. Maturation markers (i.e., CD80, CD86, major histocompatibility complex class II, and CD40) showed enhanced expression on DC incubated with targeted PorA liposomes relative to those incubated with nontargeted PorA liposomes. Moreover, only the uptake of targeted PorA liposomes induced production of IL-12 by DC, with levels similar to those produced by lipopolysaccharide (LPS)-pulsed DC. Mannose-targeted PorA liposomes administered subcutaneously had an increased localization in draining lymph nodes compared to nontargeted PorA liposomes. Liposomes in draining lymph nodes interacted preferentially with antigen-presenting cells, an effect that was enhanced with targeted PorA liposomes. Immunization studies showed an improvement of the bactericidal antibody response (i.e., increased number of responders) generated by targeted PorA liposomes compared to that generated by nontargeted ones or LPS-containing outer membrane vesicles. In conclusion, the use of targeted PorA liposomes results in an improved uptake by and activation of DC and an increased localization in draining lymph nodes. These effects correlate with an enhanced immune response toward the vaccine.

Antibody specificities and effect of meningococcal carriage in icelandic teenagers receiving the Norwegian serogroup B outer membrane vesicle vaccine

Antibody specificities of pre- and postvaccination serum samples from 40 (53%) teenagers who received three doses of the Norwegian Neisseria meningitidis serogroup B vaccine (B:15:P1.7,16) during a previous trial in Iceland (Perkins et al., J. Infect. Dis. 177:683-691, 1998) were analyzed with serum bactericidal activity (SBA) and immunoblotting assays with reference and isogenic meningococcal H44/76 vaccine strains. The H44/76 variants demonstrated significant vaccine-induced SBA to P1.7,16 PorA and Opc but not to PorB, Opa5.5, and a heterologous PorA protein. On blots, immunoglobulin G levels to all these proteins increased significantly after vaccination. Measurement of SBA to the two main variable regions (P1.7 and P1.16) on the P1.7,16 PorA with PorA deletion mutants revealed significantly higher activity to the P1.7,- and P1.-,16 mutants compared to the P1.7,16 strain, indicating exposure of new accessible epitopes. Only 12 (30%) serum samples showed distinct decreases with these or the P1.-,- mutant, with most samples containing SBA to the P1.7 and P1.16 combination. In contrast, P1.16-specific antibodies were mainly found on blots. Thirteen of the vaccinees (32.5%) were carriers of meningococci at the time of the third dose, of whom four (30.8%) harbored strains of the ET-5 complex. Carriage of P1.15 strains was generally reflected in > or =4-fold increases in SBA and distinct immunoglobulin G binding to the P1.19,15 PorA on blots. Although vaccination did not elicit bactericidal activity to the serotype 15 PorB, most carriers of serotype 15 strains showed > or =4-fold increases in SBA to this antigen.

Comparison of PorA VR types and porA promoter sequence from Neisseria meningitidis B isolated from non-immunised children and vaccine failures immunised with a serogroup B outer membrane protein vaccine

PorA protein is an important component of group B meningococcal protein-based vaccines. The goals of this study were: (i) to classify the non-serosubtypable strains recovered from vaccine failures and controls by porA variable region (VR) type; (ii) to investigate if point mutations of VRs of the porA gene are present in P1.19,15 strains recovered from vaccine failures and controls; (iii) to investigate if nucleotide sequence variation in the promoter region of porA gene is related to low expression of PorA protein. VR type P1.19,15 predominated in younger vaccine failures (3-47 months) compared to older failures (48-83 months). No changes in VRs of porA were observed in 46 P1.19,15 strains studied. A promoter spacer of 16bp and 10 guanidine residues in the polymeric G tract was detected in five of six strains with weak PorA expression. Overall, this study indicated that lack of antibody response was probably the major cause of low vaccine efficacy in young children.

Analysis of PorA variable region 3 in meningococci: implications for vaccine policy?

Outer membrane protein (OMP) vaccines are being developed against Neisseria meningitidis serogroup B which may provide protection against common circulating serotypes and serosubtypes in some countries. However, limited data is available in Europe from genosubtyping meningococci. We therefore undertook a retrospective analysis of the three main variable regions, VR1, VR2 as well as VR3, of the porA gene from N. meningitidis isolated from different countries, mainly from Scotland and Sweden. Analysis of this gene showed that, amongst 226 strains studied, there were a total of 78 different strains. No new VR1 or VR2 alleles were found but five new VR3 alleles are described. Our data indicates the importance of analysing the VR3 region of PorA in addition to VR1 and VR2 and also highlights, in general terms, the need for genosubtyping meningococci. Such analyses have major implications for the design of new meningococcal vaccines.

Meningococcal vaccines: a progress report

Neisseria meningitidis causes a wide range of human disease and remains a common cause of septicaemia and meningitis. Meningococcal serogroups A, B, C and Y cause the majority of cases of invasive disease in the US and throughout the world, with epidemics usually caused by serogroups A and C. Most patients with meningococcaemia, with or without meningitis, respond to standard antimicrobial therapy with either penicillin or ampicillin, but the recent emergence of meningococcal strains that are intermediately resistant to penicillin may alter these recommendations in the future. Given the devastating nature of meningococcal disease and emergence of these resistant strains, prevention (specifically through vaccination) remains the best approach to control this serious infection. A polysaccharide meningococcal vaccine is efficacious against disease caused by serogroups A, C, Y and W135, but is not effective in infants and children aged <2 years, and the duration of efficacy decreases markedly during the first 3 years after a single dose of the vaccine. Conjugate meningococcal vaccines have been developed to address these concerns. Initial studies with the meningococcal C conjugate vaccine have shown that the vaccine is safe and immunogenic and provides a T cell-dependent antigen that can be boosted by further doses of vaccine, or following exposure to the homologous organism or cross-reacting antigens. The UK recently implemented routine vaccination with the meningococcal C conjugate vaccine to all infants, and to all persons aged >1 year in a catch-up programme to immunise all school-aged children and young adults up to 20 years of age. Early postlicensure data indicate that this vaccine has shown significant efficacy in reduction of invasive meningococcal disease in these age groups. The full impact of vaccination will be determined once all age groups are immunised.

Rational antibacterial vaccine design through genomic technologies

After 200 years of practice, vaccinology has proved to be very effective in preventing infectious diseases. However, several human and animal pathogens exist for which vaccines have not yet been discovered. As for other fields of medical sciences, it is expected that vaccinology will greatly benefit from the emerging genomics technologies such as bioinformatics, proteomics and DNA microarrays. In this review, the potential of these technologies will be illustrated taking into account part of the research activities currently in progress in our laboratories. In particular, I will describe the identification of new vaccine candidates against Meningococcus B through high-throughput cloning and expression of meningococcal antigens selected by: (i) in silico analysis of genome sequence; and (ii) transcriptome analysis of bacteria adherent to epithelial cells. In addition, I will show how the combination of high-throughput cloning and expression technology with two-dimensional gel/mass spectrometry led us to the elucidation of Chlamydia pneumoniae surface protein subproteome and to the identification of potential vaccine candidates.

Cross-reactivity of antibodies against PorA after vaccination with a meningococcal B outer membrane vesicle vaccine

The cross-reactivity of PorA-specific antibodies induced by a monovalent P1.7-2,4 (MonoMen) and/or a hexavalent (HexaMen) meningococcal B outer membrane vesicle vaccine (OMV) in toddlers and school children was studied by serum bactericidal assays (SBA). First, isogenic vaccine strains and PorA-identical patient isolates were compared as a target in SBA, to ensure that the vaccine strains are representative for patient isolates. Geometric mean titers (GMTs) in SBA against patient isolates with subtypes P1.5-2,10 and P1.5-1,2-2 after vaccination with HexaMen were generally lower than those against vaccine strains with the same subtype, although the percentage of vaccine responders (> or =4-fold increase in SBA after vaccination) was not affected. Using various P1.7-2,4 patient isolates, GMTs as well as the number of vaccine responders were higher than for the P1.7-2,4 vaccine strain, indicating that the use of the P1.7-2,4 vaccine strain may have underestimated the immunogenicity of this subtype in HexaMen. Secondly, the cross-reactivity of antibodies induced by MonoMen and HexaMen was studied using several patient isolates that differed from the vaccine subtypes by having minor antigenic variants of one variable region (VR), by having a completely different VR or by having a different combination of VRs. MonoMen induced P1.4-specific antibodies that were cross-reactive with P1.4 variants P1.4-1 and P1.4-3. HexaMen induced a broader cross-reactive antibody response against various patient isolates with one VR identical to a vaccine subtype or a combination of VRs included in HexaMen. Cross-reactivity, measured by a fourfold increase in SBA after vaccination, against these strains ranged from 23 to 92% depending on the subtype of the tested strain and was directed against both VR1 and VR2. The extended cross-reactivity of vaccinee sera induced by HexaMen against antigenic variants has important favorable implications for meningococcal B OMV vaccine coverage.

Vaccination against Neisseria meningitidis using three variants of the lipoprotein GNA1870

Sepsis and meningitis caused by serogroup B meningococcus are devastating diseases of infants and young adults, which cannot yet be prevented by vaccination. By genome mining, we discovered GNA1870, a new surface-exposed lipoprotein of Neisseria meningitidis that induces high levels of bactericidal antibodies. The antigen is expressed by all strains of N. meningitidis tested. Sequencing of the gene in 71 strains representative of the genetic and geographic diversity of the N. meningitidis population, showed that the protein can be divided into three variants. Conservation within each variant ranges between 91.6 to 100%, while between the variants the conservation can be as low as 62.8%. The level of expression varies between strains, which can be classified as high, intermediate, and low expressors. Antibodies against a recombinant form of the protein elicit complement-mediated killing of the strains that carry the same variant and induce passive protection in the infant rat model. Bactericidal titers are highest against those strains expressing high yields of the protein; however, even the very low expressors are efficiently killed. The novel antigen is a top candidate for the development of a new vaccine against meningococcus.

The future of meningitis vaccines

Without effective vaccines meningitis remains a substantial worldwide threat with major health-care implications. A number of advances have been made in vaccine design and implementation over the last decade, with new vaccine initiatives providing substantial promise for the future reduction of global disease burden.

La inmunización activa frente a Neisseria meningitidis serogrupo B

Serogroup B Neisseria meningitidis causes high morbidity and mortality rates over the world. This article reviews the current vaccination strategies against this microorganism, including vaccines already tested on a large scale, particularly those based on class 1 outer membrane proteins, and vaccines in different stages of development. The latter involve several approaches, such as modification of the polysaccharide capsule composition or conjugation with proteins, and the use of recombinant DNA techniques to obtain vaccines that express the prevalent sero-subtypes in a particular geographical area. The challenges that have emerged with the sequencing of the meningococcus B genome are also addressed.

Sequential immunization with vesicles prepared from heterologous Neisseria meningitidis strains elicits broadly protective serum antibodies to group B strains

The capsular polysaccharide of Neisseria meningitidis group B is an autoantigen, whereas noncapsular antigens are highly variable. These factors present formidable challenges for development of a broadly protective and safe group B vaccine. Mice and guinea pigs were sequentially immunized with three doses of micovesicles or outer membrane vesicles prepared from three meningococcal strains that were each antigenically heterologous with respect to the two major porin proteins, PorA and PorB, and the group capsular polysaccharide. The resulting antisera conferred passive protection against meningococcal group B bacteremia in infant rats and elicited complement-mediated bactericidal activity against genetically diverse group B strains that were either homologous or heterologous with respect to PorA of the strains used to prepare the vaccine. By using knockout strains, a portion of the bactericidal antibody was directed against the highly conserved protein, neisserial surface protein A (NspA). Further, an anti-NspA monoclonal antibody elicited by the sequential immunization was highly bactericidal against strains that were previously shown to be resistant to bacteriolysis by anti-NspA antibodies produced by immunization with recombinant NspA. Sequential immunization with heterologous vesicle preparations offers a novel approach to eliciting broadly protective immunity against N. meningitidis strains. An NspA-based vaccine prepared from protein expressed by Neisseria also may be more effective than the corresponding recombinant protein made in Escherichia coli.

Meningococcal vaccine use in college students

OBJECTIVE

To discuss the role of meningococcal vaccine in prevention of meningococcal disease.

DATA SOURCES

A MEDLINE search (1966-June 2001) was performed to identify key literature. Search terms included, but were not limited to, meningococcal vaccines, meningococcal meningitis, meningococcal infection, and meningococcus. The search was limited to English-language literature and references dealing with humans. The MEDLINE search was supplemented by a hand search of various bibliographies.

DATA SYNTHESIS

The impact of meningococcal disease has caused national and regional organizations to develop recommendations for use of meningococcal vaccine. Even though the meningococcal vaccine can provide benefit, limitations exist. The available vaccine does not cover all meningococcal strains and is not useful in all age groups. The appropriate target groups for prevention of disease through vaccination have been difficult to determine; vaccine use in college students is especially controversial.

CONCLUSIONS

Although a meningococcal vaccine is available, meningococcus causes significant morbidity and mortality. Controversy exists over the meningococcal vaccine and its use. Students entering college who will be living in dormitories should be informed of the increased risk of meningococcal disease and be offered vaccination.

Neisseria meningitidis serogroup B: laboratory correlates of protection

Meningococcal disease in the Western countries is frequently caused by Neisseria meningitidis serogroup B. Major efforts have been made to develop a safe and efficacious vaccine against this serogroup which is suitable for use in infants and young children. To assess the quality of the immune response after vaccination with candidate vaccines, laboratory correlates of protection are needed. For serogroups A and C, serum bactericidal activity (SBA) is a well established predictor for protection, but for serogroup B other mechanisms besides SBA may also be involved in conferring protection from disease. Several laboratory methods for identification and evaluation of the immunogenicity of possible vaccine antigens are described in this review.

The meningococcus tamed?

Serogroup B Neisseria meningitidis is a frequent cause of invasive meningococcal disease, yet there are no effective vaccines suitable for routine immunisation. Limited efficacy has been shown with meningococcal outer membrane vacccines in children 4 years and older. Here we review the status of current research and consider new approaches to development of meningococcal serogroup B vaccines.

Complement activation and formation of the membrane attack complex on serogroup B Neisseria meningitidis in the presence or absence of serum bactericidal activity

Encapsulated meningococci are complement sensitive only in the presence of bactericidal antibodies by yet-unexplored mechanisms. The objective of this study was to investigate the involvement of major bacterial surface constituents on complement activation and membrane attack complex (MAC) formation on serogroup B meningococci in the presence or absence of antibody-dependent serum bactericidal activity (SBA). The strains used were the encapsulated H44/76, five of its variants differing in capsulation and expression of the class 1 porin (PorA), and its lipopolysaccharide (LPS)-deficient isogenic mutant (LPS(-)) pLAK33. Two normal sera, one with high SBA (SBA(+)) and one with no bactericidal activity (SBA(-)) against H44/76 as well as an a-gamma-globulinemic serum were used for sensibilization of the bacteria. C3b and iC3b deposition on H44/76, its unencapsulated variant v24, and pLAK33 was similar in SBA(+) and SBA(-) serum, and no difference was present between the strains. MAC deposition on H44/76 was higher in SBA(+) serum than in SBA(-) serum and the a-gamma-globulinemic serum. The amounts of C3b on H44/76, v24, and pLAK33 in the a-gamma-globulinemic serum were also not different, indicating immunoglobulin G (IgG)- and LPS-independent complement activation. H44/76 PorA(+) and its PorA(-) variant and the v24 PorA(+) and its PorA(-) variant incubated in SBA(-) serum induced comparable amounts of MAC, despite their different serum sensitivities. Complement formation on the surface of the bacteria occurred almost exclusively via the classical pathway, but the considerable amounts of Bb measured in the serum indicated alternative pathway activation in the fluid phase. We conclude that complement deposition on meningococci is, for the most part, independent of classical pathway IgG and is not influenced by the presence of PorA or LPS on the meningococcal surface. Addition of an anti-PorA chimeric antibody to the nonbactericidal normal serum, while promoting a dose-related bacterial lysis, did not influence the amounts of C3b, iC3b, and MAC formed on the bacterial surface. These findings support the hypothesis that proper MAC insertion rather than the quantity of MAC formed on the bacterial surface is of importance for efficient lysis of meningococci.

Vaccines for the prevention of meningococcal disease in children

Neisseria meningitidis is one of the most feared infections in pediatrics as the result of its rapid progression, high fatality rate, and frequent occurrence of sequelae. The 5 major meningococcal serogroups associated with disease are A, B, C, Y, and W-135. Currently available polysaccharide vaccines are effective in preventing disease caused by serogroups A, C, Y, and W-135 in older children and adults but do not elicit good long-term protection in young children. Vaccines that protect against serogroup B disease are still in development. As with the Haemophilus influenzae type b and pneumococcal polysaccharide vaccines, conjugation of the polysaccharide vaccine to a protein carrier dramatically changes vaccine characteristics, with resulting efficacy in infants. New meningococcal conjugate vaccines against serogroups A, C, Y, and W-135 are being developed. A serogroup C conjugate vaccine has been introduced successfully into the routine childhood schedule in the United Kingdom. New meningococcal conjugate vaccines are likely to have a dramatic effect on the burden of meningococcal disease within the next decade.

Meningococcal disease: how to prevent and how to manage

Meningococcal disease is a significant problem in the paediatric population. The diagnosis of meningococcal disease can be problematic and progression of the disease can rapidly lead to a life-threatening illness. Despite the success of antibiotic treatment, mortality rates remain high. The development of protein-polysaccharide conjugate vaccines has significantly improved the success of vaccination in reducing the incidence of meningococcal disease. However, a comprehensive vaccine conferring protection against disease-associated serogroups remains elusive. The aim of this review is to highlight recent significant improvements in the prevention and management of meningococcal disease.

Development of vaccines against meningococcal disease

Neisseria meningitidis is a major cause of bacterial meningitis and sepsis. Polysaccharide-protein conjugate vaccines for prevention of group C disease have been licensed in Europe. Such vaccines for prevention of disease caused by groups A (which is associated with the greatest disease burden worldwide), Y, and W135 are being developed. However, conventional approaches to develop a vaccine for group B strains, which are responsible for most cases in Europe and the USA, have been largely unsuccessful. Capsular polysaccharide-based vaccines can elicit autoantibodies to host polysialic acid, whereas the ability of most non-capsular antigens to elicit broad-based immunity is limited by their antigenic diversity. Many new membrane proteins have been discovered during analyses of genomic sequencing data. These antigens are highly conserved and, in mice, elicit serum bactericidal antibodies, which are the serological hallmark of protective immunity in man. Therefore, there are many promising new vaccine candidates, and improved prospects for development of a broadly protective vaccine for group B disease, and for control of all meningococcal disease.

Vaccine prevention of meningococcal disease, coming soon?

The past century has seen the use of a number of vaccines for prevention and control of meningococcal disease with varied success. The use of polysaccharide vaccines for the control of outbreaks of serogroup C infections in teenagers and young adults and epidemic serogroup A disease has been established for 30 years and an effective protein-polysaccharide conjugate vaccine against serogroup C was introduced into the UK infant immunisation schedule in 2000. The next generation of these glycoconjugate vaccines will be on the shelf soon, eventually offering the prospect of eradication of serogroups A, C, Y and W135 through routine infant immunisation. Despite these exciting prospects, serogroup B meningococci still account for a majority of infections in industrialised nations but development of safe, immunogenic and effective serogroup B meningococcal vaccines has been an elusive goal. Outer membrane vesicle vaccines for B disease are already used in some countries, and will likely be used more widely in the next few years, but efficacy for endemic disease in children has so far been disappointing. However, the innovations arising from the availability of the meningococcal genome sequence, public and scientific interest in the disease and recent pharmaceutical company investment in development of serogroup B vaccines may have started the countdown to the end of meningococcal infection in children.

A novel mimetic antigen eliciting protective antibody to Neisseria meningitidis

Molecular mimetic Ags are of considerable interest as vaccine candidates. Yet there are few examples of mimetic Ags that elicit protective Ab against a pathogen, and the functional activity of anti-mimetic Abs has not been studied in detail. As part of the Neisseria meningitidis serogroup B genome sequencing project, a large number of novel proteins were identified. Herein, we provide evidence that genome-derived Ag 33 (GNA33), a lipoprotein with homology to Escherichia coli murein transglycosylase, elicits protective Ab to meningococci as a result of mimicking an epitope on loop 4 of porin A (PorA) in strains with serosubtype P1.2. Epitope mapping of a bactericidal anti-GNA33 mAb using overlapping peptides shows that the mAb recognizes peptides from GNA33 and PorA that share a QTP sequence that is necessary but not sufficient for binding. By flow cytometry, mouse antisera prepared against rGNA33 and the anti-GNA33 mAb bind as well as an anti-PorA P1.2 mAb to the surface of eight of nine N. meningitidis serogroup B strains tested with the P1.2 serosubtype. Anti-GNA33 Abs also are bactericidal for most P1.2 strains and, for susceptible strains, the activity of an anti-GNA33 mAb is similar to that of an anticapsular mAb but less active than an anti-P1.2 mAb. Anti-GNA Abs also confer passive protection against bacteremia in infant rats challenged with P1.2 strains. Thus, GNA33 represents one of the most effective immunogenic mimetics yet described. These results demonstrate that molecular mimetics have potential as meningococcal vaccine candidates.

Serum bactericidal activity and isotype distribution of antibodies in toddlers and schoolchildren after vaccination with RIVM hexavalent PorA vesicle vaccine

A clinical phase II trial with the RIVM hexavalent OMV vaccine containing six different PorAs was carried out in toddlers (2-3 years) and schoolchildren (7-8 years) in The Netherlands. Children were vaccinated three times (0, 2, 8 months). Sera after two and three vaccinations were analysed for serum bactericidal activity (SBA) and isotype distribution in whole cell enzyme linked immunosorbent assay (ELISA). The SBA after vaccination against the six PorAs was significantly different. We investigated whether the age specific and PorA specific differences in SBA titers correlated with differences in PorA specific IgG isotype distribution. The SBA titers were higher in toddlers compared with schoolchildren. After vaccination, IgG1 antibodies dominated the response followed by IgG3 antibodies. IgG2 levels were low, whereas IgG4 was not detected. Irrespective of PorA, IgG total and isotype specific titers after two and three vaccinations were significantly higher in toddlers than in schoolchildren. A weak correlation was found between IgG total or IgG1 and SBA. Although the immunogenicity of the six PorAs is very different, the isotype distribution was similar for all six tested PorAs. We conclude that the RIVM hexavalent PorA vesicle vaccine induces bactericidal antibodies mainly of the IgG1 and IgG3 isotypes that are considered to be most important for protection against disease. The isotype distribution of the response is not age-dependent.

Immunogenicity of a serogroup B meningococcal vaccine against multiple Neisseria meningitidis strains in infants

BACKGROUND

The serogroup B meningococcus is responsible for the majority of cases of meningococcal disease in temperate countries. Infants and young children <2 years of age are at greatest risk of disease. This study assessed the immunogenicity in infants of a serogroup B meningococcal outer membrane protein vaccine that has been used extensively in disease outbreaks in Cuba and several Latin American countries and shown to be efficacious in teenagers.

METHOD

One hundred five healthy infants entering the routine vaccination schedule in Havana, Cuba, were given either 2 or 3 doses of the serogroup B meningococcal vaccine VA-MENGOC-BC at 3.5, 5.5 and 7.5 months of age. Immune response pre- and postvaccination was determined by the conventional serum bactericidal assay (SBA), a more sensitive novel whole blood bactericidal assay (WBA) and immunoglobulin ELISA.

RESULTS

In 52 and 46% of infants >50% killing of the vaccine serogroup B strain (B:4:P1.19,15) and serogroup C strain, respectively, was demonstrated by the WBA after 2 doses of the vaccine. Serum bactericidal activity (4-fold increase in titer) was induced in only 27% against the vaccine serogroup B strain and in 14% against the serogroup C strain. The changes in WBA and SBA were mirrored by the serogroup B and C immunoglobulin ELISA. Cross-reactive immunogenicity against other (heterologous) serogroup B strains was demonstrated for one of the four further strains assessed by WBA. By age 16 to 18 months SBA, WBA and ELISA responses had declined considerably. The addition of a third dose of vaccine did not appear to significantly influence immunogenicity at 17 months of age.

CONCLUSION

The serogroup B outer membrane protein vaccine VA-MENGOC-BC induces a demonstrable immune response in infants against both the serogroup B vaccine strain and against a serogroup C strain. Cross-reactive immunogenicity against other (heterologous) serogroup B strains is limited in this age group.

Meningococcal Vaccines: Expanding Protection from Infants to College

With the rapid pace of immunologic research, it is more important than ever for readers to understand rational immunodiagnosis, immunopro-phylaxis, and immunotherapy. This column is intended to help you ensure proper immunologic drug use in your practice.

Active immunization in the United States: developments over the past decade

The Centers for Disease Control and Prevention has identified immunization as the most important public health advance of the 20th century. The purpose of this article is to review the changes that have taken place in active immunization in the United States over the past decade. Since 1990, new vaccines have become available to prevent five infectious diseases: varicella, rotavirus, hepatitis A, Lyme disease, and Japanese encephalitis virus infection. Improved vaccines have been developed to prevent Haemophilus influenzae type b, pneumococcus, pertussis, rabies, and typhoid infections. Immunization strategies for the prevention of hepatitis B, measles, meningococcal infections, and poliomyelitis have changed as a result of the changing epidemiology of these diseases. Combination vaccines are being developed to facilitate the delivery of multiple antigens, and improved vaccines are under development for cholera, influenza, and meningococcal disease. Major advances in molecular biology have enabled scientists to devise new approaches to the development of vaccines against diseases ranging from respiratory viral to enteric bacterial infections that continue to plague the world's population.

Serosubtypes and PorA types of Neisseria meningitidis serogroup B isolated in Brazil during 1997--1998: overview and implications for vaccine development

Meningococcal disease caused by N. meningitidis serogroup B (MenB) has been endemic in Brazil since 1997. In this study, we determined the prevalence of serosubtypes of MenB isolated in 10 Brazilian states and the Federal District during 1997 and 1998 and investigated the extent of PorA VR sequence variation among the most prevalent serosubtypes to evaluate the possible use of an outer membrane vesicle (OMV)-, PorA-based vaccine to prevent meningococcal disease in Brazil. During this period, a total of 8,932 cases of meningococcal disease were reported. Only 42% (n = 3,751) of the reported cases were laboratory confirmed, and about 60% (n = 2,255) of those were identified as MenB. Among 1,297 MenB strains selected for this study, the most prevalent serosubtypes were P1.19,15 (66%), P1.7,1 (11%), and P1.7,16 (4%). PorA VR typing showed that 91% of the P1.19,15 strains analyzed had VR1 and VR2 sequences identical to those of the prototype strain. No sequence variation was detected among the 40 strains representing all isolated MenB P1.7,16 strains in the three southern states, where this serosubtype accounts for 75% of the serosubtypes identified. Similarly, all P1.7,1 strains were identified by PorA typing as P1.7-1,1. Although further improvements in the reporting of cases and collection of strains in Brazil are needed, our data suggest that a trivalent OMV-based vaccine prepared with PorA types P1.19,15, P1.7-1,1, and P1.7,16 may be appropriate to control serogroup B meningococcal disease in most of the Brazilian states.

New therapies and vaccines for meningococcal disease

Meningococcal disease (MCD) is an important cause of morbidity and mortality. The pathophysiology consists of a complex interaction of bacterial and host factors, triggered by the release of endotoxin which initiates the inflammatory cascade, resulting in multi-organ failure, coagulopathy, capillary leak, metabolic derangement and eventually death. Prompt recognition and aggressive management are essential in reducing mortality. Over the past decade, there has been intense research into novel therapies and vaccines, with largely disappointing results. Therapies have been broadly divided into anti-endotoxin and anti-TNF-alpha therapies, treatment aimed at correcting coagulopathy and at blood purification and anti-inflammatory cytokine therapy. The reasons for the disappointing results in the search for new therapeutic strategies are difficult to identify. The disordered physiology in MCD results from a complex interaction of several mediators; therefore attempts to correct this by altering just one step represents a gross oversimplification of the process. In addition, the experimental model of endotoxaemia, which is often used, is a poor representation of an acutely ill patient with rapidly progressive shock. There have been several small or poorly designed trials, which have failed to reach definite conclusions. In order to yield conclusive results any future trials must be multicentre, randomised, controlled trials, but these are expensive and, in practice, difficult to conduct. The BPI trial (vide infra) was a significant step forward in this regard and demonstrated the ability to organise a large multicentred trial which can act as a template for future trials. Although the results were not significant there was an overall trend towards improved outcome in the treatment arm. Whilst the development of effective therapies and vaccines are awaited, the priorities at present must be the prompt recognition and aggressive management of disease.

Functional activity of anti-Neisserial surface protein A monoclonal antibodies against strains of Neisseria meningitidis serogroup B

Neisserial surface protein A (NspA) is currently being investigated with humans as a candidate vaccine for the prevention of meningococcal disease. Although NspA is highly conserved, the ability of anti-NspA antibodies to bind to or elicit complement-mediated bactericidal activity against diverse Neisseria meningitidis serogroup B strains is controversial. To evaluate strain differences in NspA surface accessibility and susceptibility to bactericidal activity, we prepared murine immunoglobulin G2a anti-NspA monoclonal antibodies (MAbs) and evaluated their functional activity against 10 genetically diverse N. meningitidis serogroup B strains. By colony Western blot, all 10 strains expressed NspA as detected by one or more MAbs. By flow cytometry, two MAbs were found to bind to the bacterial surface of 6 of the 10 strains. In addition, two strains showed variable NspA surface accessibility for the MAbs despite being uniformly positive for NspA expression by colony Western blotting. Only 4 of the 10 strains were susceptible to anti-NspA complement-mediated bacteriolysis. Passively administered MAb protected infant rats from developing bacteremia after challenge with N. meningitidis serogroup B strain 8047 (surface binding positive, susceptible to anti-NspA bacteriolysis), was poorly protective against strain BZ232 (surface binding variable, resistant to bacteriolysis), and did not protect against strain M986 (surface binding negative, resistant to bacteriolysis). Finally, NspA does not appear to be critical for causing bacteremia, as an NspA knockout from strain 8047 was highly virulent in infant rats. Taken together, these findings suggest that an NspA-based vaccine will need to incorporate additional antigens to elicit broad protection against N. meningitidis serogroup B.