Vaccine prevention of meningococcal disease, coming soon?

Discovery of Semi- and Fully-Synthetic Carbohydrate Vaccines Against Bacterial Infections Using a Medicinal Chemistry Approach

The glycocalyx, a thick layer of carbohydrates, surrounds the cell wall of most bacterial and parasitic pathogens. Recognition of these unique glycans by the human immune system results in destruction of the invaders. To elicit a protective immune response, polysaccharides either isolated from the bacterial cell surface or conjugated with a carrier protein, for T-cell help, are administered. Conjugate vaccines based on isolated carbohydrates currently protect millions of people against Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitides infections. Active pharmaceutical ingredients (APIs) are increasingly discovered by medicinal chemistry and synthetic in origin, rather than isolated from natural sources. Converting vaccines from biologicals to pharmaceuticals requires a fundamental understanding of how the human immune system recognizes carbohydrates and could now be realized. To illustrate the chemistry-based approach to vaccine discovery, I summarize efforts focusing on synthetic glycan-based medicinal chemistry to understand the mammalian antiglycan immune response and define glycan epitopes for novel synthetic glycoconjugate vaccines against Streptococcus pneumoniae, Clostridium difficile, Klebsiella pneumoniae, and other bacteria. The chemical tools described here help us gain fundamental insights into how the human system recognizes carbohydrates and drive the discovery of carbohydrate vaccines.

Construction and assessment of the immunogenicity and bactericidal activity of fusion protein porin A from Neisseria meningitidis serogroups A and B admixed with OMV adjuvant as a novel vaccine candidate

Objectives

The porins A and B and also outer membrane vesicles (OMVs) of Neisseria meningitidis are used for vaccine purposes. In the present study, we aimed to design a new vaccine candidate based on a fusion of PorA of serogroups A and B of N. meningitidis admixed with OMV and evaluate it in an animal model.

Materials and Methods

After bioinformatic studies, a fusion protein composed of porin A from both serogroups A and B of N. meningitidis was constructed, expressed, and purified by nickel resins. Extraction of OMV of N. meningitidis was performed using a chemical method. The mice were vaccinated subcutaneously in different groups with mixtures of PorA proteins, OMV, and Freund's adjuvants. Then, the immune responses were measured using the ELISA method. Finally, serum bactericidal activity (SBA) procedure was applied to assay the activity of the immune responses in mice.

Results

Mice received the PorA protein plus Freund's adjuvant. Mice vaccinated with PorA fusion of serogroups A+B plus Freund's adjuvant produced more IgG, IgG1, and IgG2a than combinations admixed with OMV. Furthermore, the vaccinated mice tended to direct the IgG responses toward IgG1. Sera of the mice that received PorA+Freund's and those that received PorA+OMV produced higher bactericidal activity than the controls.

Conclusion

Fusion protein porin A could be a valuable target for developing vaccines against N. meningitidis. Although, Freund's adjuvant induced the strongest IgG responses, given that Freund's adjuvant has no human use, and OMV is a human adjuvant, OMV could be considered in vaccine design against N. meningitidis.

Mechanistic research holds promise for bacterial vaccines and phage therapies for Pseudomonas aeruginosa

Vaccines for Pseudomonas aeruginosa have been of longstanding interest to immunologists, bacteriologists, and clinicians, due to the widespread prevalence of hospital-acquired infection. As P. aeruginosa becomes increasingly antibiotic resistant, there is a dire need for novel treatments and preventive vaccines. Despite intense efforts, there currently remains no vaccine on the market to combat this dangerous pathogen. This article summarizes current and past vaccines under development that target various constituents of P. aeruginosa. Targeting lipopolysaccharides and O-antigens have shown some promise in preventing infection. Recombinant flagella and pili that target TLR5 have been utilized to combat P. aeruginosa by blocking its motility and adhesion. The type 3 secretion system components, such as needle-like structure PcrV or exotoxin PopB, are also potential vaccine targets. Outer membrane proteins including OprF and OprI are newer representatives of vaccine candidates. Live attenuated vaccines are a focal point in this review, and are also considered for novel vaccines. In addition, phage therapy is revived as an effective option for treating refractory infections after failure with antibiotic treatment. Many of the aforementioned vaccines act on a single target, thus lacking a broad range of protection. Recent studies have shown that mixtures of vaccines and combination approaches may significantly augment immunogenicity, thereby increasing their preventive and therapeutic potential.

Synthesis and immunochemical evaluation of a novel Neisseria meningitidis serogroup A tetrasaccharide and its conjugate

A tetrameric repeating unit of capsular polysaccharide of Neisseria meningitidis serogroup A was synthesized which mimicked natural polysaccharide in immunochemical analysis.

Immunoinformatics Approach in Designing Epitope-based Vaccine Against Meningitis-inducing Bacteria (Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae Type b)

Meningitis infection is one of the major threats during Hajj season in Mecca. Meningitis vaccines are available, but their uses are limited in some countries due to religious reasons. Furthermore, they only give protection to certain serogroups, not to all types of meningitis-inducing bacteria. Recently, research on epitope-based vaccines has been developed intensively. Such vaccines have potential advantages over conventional vaccines in that they are safer to use and well responded to the antibody. In this study, we developed epitope-based vaccine candidates against various meningitis-inducing bacteria, including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae type b. The epitopes were selected from their protein of polysaccharide capsule. B-cell epitopes were predicted by using BCPred, while T-cell epitope for major histocompatibility complex (MHC) class I was predicted using PAProC, TAPPred, and Immune Epitope Database. Immune Epitope Database was also used to predict T-cell epitope for MHC class II. Population coverage and molecular docking simulation were predicted against previously generated epitope vaccine candidates. The best candidates for MHC class I- and class II-restricted T-cell epitopes were MQYGDKTTF, MKEQNTLEI, ECTEGEPDY, DLSIVVPIY, YPMAMMWRNASNRAI, TLQMTLLGIVPNLNK, ETSLHHIPGISNYFI, and SLLYILEKNAEMEFD, which showed 80% population coverage. The complexes of class I T-cell epitopes–HLA-C*03:03 and class II T-cell epitopes–HLA-DRB1*11:01 showed better affinity than standards as evaluated from their ΔGbinding value and the binding interaction between epitopes and HLA molecules. These peptide constructs may further be undergone in vitro and in vivo testings for the development of targeted vaccine against meningitis infection.

Fully Synthetic Self-Adjuvanting α-2,9-Oligosialic Acid Based Conjugate Vaccines against Group C Meningitis

α-2,9-Polysialic acid is an important capsular polysaccharide expressed by serotype C Neisseria meningitidis. Its protein conjugates are current vaccines against group C meningitis. To address some concerns about traditional protein conjugate vaccines, a new type of fully synthetic vaccines composed of oligosialic acids and glycolipids was explored. In this regard, α-2,9-linked di-, tri-, tetra-, and pentasialic acids were prepared and conjugated with monophosphoryl lipid A (MPLA). Immunological studies of the conjugates in C57BL/6J mouse revealed that they alone elicited robust immune responses comparable to that induced by corresponding protein conjugates plus adjuvant, suggesting the self-adjuvanting properties of MPLA conjugates. The elicited antibodies were mainly IgG2b and IgG2c, suggesting T cell dependent immunities. The antisera had strong and specific binding to α-2,9-oligosialic acids and to group C meningococcal polysaccharide and cell, indicating the ability of antibodies to selectively target the bacteria. The antisera also mediated strong bactericidal activities. Structure-activity relationship analysis of the MPLA conjugates also revealed that the immunogenicity of oligosialic acids decreased with elongated sugar chain, but all tested MPLA conjugates elicited robust immune responses. It is concluded that tri- and tetrasialic acid-MPLA conjugates are worthy of further investigation as the first fully synthetic and self-adjuvanting vaccines against group C meningitis.

Synthesis and immunological study of α-2,9-oligosialic acid conjugates as anti-group C meningitis vaccines

α-2,9-Di-, tri-, tetra-, and pentasialic acids were prepared and conjugated with a carrier protein. The resultant glycoconjugates elicited robust T cell-mediated immunity in mice. α-2,9-Trisialic acid was identified as a promising antigen for developing glycoconjugate vaccines against group C Neisseria meningitidis.

Synthesis and immunological evaluation of protein conjugates of Neisseria meningitidis X capsular polysaccharide fragments

A vaccine to prevent infections from the emerging Neisseria meningitidis X (MenX) is becoming an urgent issue. Recently MenX capsular polysaccharide (CPS) fragments conjugated to CRM197 as carrier protein have been confirmed at preclinical stage as promising candidates for vaccine development. However, more insights about the minimal epitope required for the immunological activity of MenX CPS are needed. We report herein the chemical conjugation of fully synthetic MenX CPS oligomers (monomer, dimer, and trimer) to CRM197. Moreover, improvements in some crucial steps leading to the synthesis of MenX CPS fragments are described. Following immunization with the obtained neoglycoconjugates, the conjugated trimer was demonstrated as the minimal fragment possessing immunogenic activity, even though significantly lower than a pentadecamer obtained from the native polymer and conjugated to the same protein. This finding suggests that oligomers longer than three repeating units are possibly needed to mimic the activity of the native polysaccharide.

CanNeisseria lactamicaantigens provide an effective vaccine to prevent meningococcal disease?

Neisseria lactamica is a commensal organism that is closely related to Neisseria meningitidis, the causative agent of meningococcal disease. N. lactamica has many antigens in common with N. meningitidis, but it lacks a polysaccharide capsule and the serosubtyping antigen PorA. Carriage studies have demonstrated that N. lactamica is carried in the nasopharynx of young children at a time when meningococcal carriage is rare. However, natural immunity to meningococcal disease develops during this period and carriage of commensal Neisseria is implicated in the development of this immunity. Recent studies have characterized the antigens which may be responsible for inducing a crossreactive antibody response and have demonstrated that N. lactamica-based vaccines can protect in experimental models of meningococcal disease. The potential for these vaccines to be effective in preventing meningococcal disease is discussed.

An epidemiological review of changes in meningococcal biology during the last 100 years

AIM

The aim of this study was to assess changes in trends of meningococcal disease and strain diversity of Neisseria meningitidis in Europe, South America, and Africa over the last 100 years.

METHODS

Healthcare databases and sources of grey literature were searched in 2012 and records were screened against the protocol eligibility criteria using a three-stage sifting process. Studies included in the review were subject to data extraction. Results were summarised using a narrative approach.

RESULTS

Serogroup A was the dominant cause of invasive meningococcal disease in Europe before and during World Wars I and II. Whilst serogroup B has been dominant from the 1970s in Europe and the 1980s in South America, outbreaks have emerged associated with serogroups W135 and Y in the twenty-first century. There has been a shift in the age groups affected by invasive meningococcal disease with an increase in incidence among the elderly associated with serogroup Y and a decline in serogroup C among adolescent populations. Recent outbreaks of serogroup W135 have occurred in some countries in South America. The epidemiological trend of invasive meningococcal disease has remained largely static across Africa and dominated by serogroup A although recently serogroups X and W135 have accounted for a large proportion of morbidity and mortality.

CONCLUSION

The epidemiology of N. meningitidis has been dynamic in Europe and South America especially over the last 30 years. Routine vaccination with serogroup C vaccines has led to reduced carriage and incidence of invasive meningococcal disease and herd immunity.

Pseudomonas aeruginosa outer membrane vesicles modulate host immune responses by targeting the Toll-like receptor 4 signaling pathway

Bacteria can naturally secrete outer membrane vesicles (OMVs) as pathogenic factors, while these vesicles may also serve as immunologic regulators if appropriately prepared. However, it is largely unknown whether Pseudomonas aeruginosa OMVs can activate inflammatory responses and whether immunization with OMVs can provide immune protection against subsequent infection. We purified and identified OMVs, which were then used to infect lung epithelial cells in vitro as well as C57BL/6J mice to investigate the immune response and the underlying signaling pathway. The results showed that OMVs generated from P. aeruginosa wild-type strain PAO1 were more cytotoxic to alveolar epithelial cells than those from quorum-sensing (QS)-deficient strain PAO1-ΔlasR. The levels of Toll-like receptor 4 (TLR4) and proinflammatory cytokines, including interleukin-1β (IL-1β) and IL-6, increased following OMV infection. Compared with lipopolysaccharide (LPS), lysed OMVs in which the membrane structures were broken induced a weak immune response. Furthermore, expression levels of TLR4-mediated responders (i.e., cytokines) were markedly downregulated by the TLR4 inhibitor E5564. Active immunization with OMVs or passive transfer of sera with a high cytokine quantity acquired from OMV-immunized mice could protect healthy mice against subsequent lethal PAO1 challenges (1.5 × 10(11) CFU). Collectively, these findings indicate that naturally secreted P. aeruginosa OMVs may trigger significant inflammatory responses via the TLR4 signaling pathway and protect mice against pseudomonal lung infection.

Immunogenicity and safety of the quadrivalent meningococcal serogroups A, C, W-135 and Y tetanus toxoid conjugate vaccine (MenACWY-TT) in 2-10-year-old children: results of an open, randomised, controlled study

In Europe, the introduction of monovalent meningococcal serogroup C (MenC) conjugate vaccines has resulted in a significant decline in MenC invasive disease. However, given the potential for strain evolution and increasing travel to areas of high endemicity, protection against additional serogroups is needed. In this study, the immunogenicity, measured by a serum bactericidal activity assay using rabbit complement (rSBA), and the safety of a quadrivalent meningococcal serogroups A, C, W-135 and Y tetanus toxoid conjugate vaccine (MenACWY-TT) were compared to that of a licensed monovalent MenC conjugate vaccine (MenC-CRM₁₉₇) in children 2-10 years of age. Children were randomised (3:1) to receive a single dose of either MenACWY-TT or MenC-CRM₁₉₇. Non-inferiority of the immunogenicity of MenACWY-TT versus MenC-CRM₁₉₇ in terms of rSBA-MenC vaccine response was demonstrated. Exploratory analyses suggested that rSBA-MenC geometric mean titres adjusted for pre-vaccination titres were lower in children vaccinated with MenACWY-TT compared to MenC-CRM₁₉₇. Nevertheless, at 1 month post-vaccination, ≥99.3 % of the children who received MenACWY-TT had rSBA titres ≥1:128 for each of the four vaccine serogroups, which is the more conservative correlate of protection. The reactogenicity and safety profile of MenACWY-TT was clinically acceptable and no serious adverse events considered related to vaccination were reported throughout the study.

CONCLUSION

When administered to European school-age children, MenACWY-TT has a clinically acceptable safety profile and, when compared with MenC-CRM₁₉₇, the potential to broaden protection against meningococcal disease caused by serogroups A, W-135 and Y while maintaining protection against MenC. This study has been registered at www.clinicaltrials.gov NCT00674583.

Synthetic neoglycoconjugates of cell-surface phosphoglycans of Leishmania as potential anti-parasite carbohydrate vaccines

Leishmania are a genus of sandfly-transmitted protozoan parasites that cause a spectrum of debilitating and often fatal diseases in humans throughout the tropics and subtropics. During the parasite life cycle, Leishmania survive and proliferate in highly hostile environments. Their survival strategies involve the formation of an elaborate and dense cell-surface glycocalyx composed of diverse stage-specific glycoconjugates that form a protective barrier. Phosphoglycans constitute the variable structural and functional domain of major cell-surface lipophosphoglycan and secreted proteophosphoglycans. In this paper, we discuss structural aspects of various phosphoglycans from Leishmania with the major emphasis on the chemical preparation of neoglycoconjugates (neoglycoproteins and neoglycolipids) based on Leishmania lipophosphoglycan structures as well as the immunological evaluation for some of them as potential anti-leishmaniasis vaccines.

Prediction and characterization of T-cell epitopes for epitope vaccine design from outer membrane protein of Neisseria meningitidis serogroup B

Neisseria meningitidis serogroup B (MC58) is a leading cause of meningitis and septicaemia, principally infects the infants and adolescents. No vaccine is available for the prevention of these infections because the serogroup B capsular polysaccharide is unable to stimulate an immune response, due to its similarity with polysialic acid. To overcome these obstacles, we proposed to develop a peptide based epitope vaccine from outer membrane protein contained in outer membrane vesicles (OMV) based on our computational analysis. In OMV a total of 236 proteins were identified, only 15 (6.4%) of which were predicted to be located in outer membrane. The major requirement is the identification and selection of T-cell epitopes that act as a vaccine target. We have selected 13 out of 15 outer membrane proteins from OMV proteins. Due to similarity of the fkpA and omp85 with the human FKBP2 and SAMM50 protein, we removed these two sequences from the analysis as their presence in the vaccine is likely to elicit an autoimmune response. ProPred and ProPred1 were used to predict promiscuous helper T Lymphocytes (HTL) and cytotoxic T Lymphocytes (CTL) epitopes and MHCPred for their binding affinity in N. meningitidis serogroup B (MC58), respectively. Binding peptides (epitopes) are distinguished from nonbinding peptides in properties such as amino acid preference on the basis of amino acid composition. By using this dataset, we compared physico-chemical and structural properties at amino acid level through amino acid composition, computed from ProtParam server. Results indicate that porA, porB, opc, rmpM, mtrE and nspA are more suitable vaccine candidates. The predicted peptides are expected to be useful in the design of multi-epitope vaccines without compromising the human population coverage.

Assessment of vaccine potential of the Neisseria-specific protein NMB0938

The availability of complete genome sequence of Neisseria meningitidis serogroup B strain MC58 and reverse vaccinology has allowed the discovery of several novel antigens. Here, we have explored the potential of N. meningitidis lipoprotein NMB0938 as a vaccine candidate, based on investigation of gene sequence conservation and the antibody response elicited after immunization in mice. This antigen was previously identified by a genome-based approach as an outer membrane lipoprotein unique to the Neisseria genus. The nmb0938 gene was present in all 37 Neisseria isolates analyzed in this study. Based on amino acid sequence identity, 16 unique sequences were identified which clustered into three variants with identities ranging from 92 to 99%, with one cluster represented by the Neisseria lactamica strains. Recombinant protein NMB0938 (rNMB0938) was expressed in Escherichia coli and purified after solubilization of the insoluble fraction. Antisera produced in mice against purified rNMB0938 reacted with a range of meningococcal strains in whole-cell ELISA and western blotting. Using flow cytometry, it was also shown that anti-rNMB0938 antibodies bound to the surface of the homologous meningococcal strain and activated complement deposition. Moreover, antibodies against rNMB0938 elicited complement-mediated killing of meningococcal strains from both sequence variants and conferred passive protection against meningococcal bacteremia in infant rats. According to our results, NMB0938 represents a promising candidate to be included in a vaccine to prevent meningococcal disease.

Quest for a broad-range vaccine against Neisseria meningitidis serogroup B: implications of genetic variations of the surface-exposed proteins

Despite the development of new vaccine formulations using new biotechnology resources to combat emerging and re-emerging diseases, serogroup B meningococcal disease is still a worldwide burden, accounting for many deaths and disabilities every year. The successful approach of coupling a polysaccharide (PS) with a carrier protein in order to increase long-lasting immunity could not be exploited againstNeisseria meningitidisB because of the limitations of using the capsular PS of serogroup B meningococci. Tailor-made vaccines based on exposed proteins were shown to be a promising approach to overcome these flaws. However, the continuous adaptation of surface meningococcal structures to the external environment has led to genetic shifts of potential vaccine-target epitopes, hampering the quest for a broad-range vaccine that could be used against all serogroups, especially against serogroup B.

Structural Basis for the Immunogenic Properties of the Meningococcal Vaccine Candidate LP2086

LP2086 is a family of outer membrane lipoproteins from Neisseria meningitidis, which elicits bactericidal antibodies and are currently undergoing human clinical trials in a bivalent formulation where each antigen represents one of the two known LP2086 subfamilies. Here we report the NMR structure of the recombinant LP2086 variant B01, a representative of the LP2086 subfamily B. The structure reveals a novel fold composed of two domains: a "taco-shaped" N-terminal beta-sheet and a C-terminal beta-barrel connected by a linker. The structure in micellar solution is consistent with a model of LP2086 anchored to the outer membrane bilayer through its lipidated N terminus. A long flexible chain connects the folded part of the protein to the lipid anchor and acts as spacer, making both domains accessible to the host immune system. Antibodies broadly reactive against members from both subfamilies have been mapped to the N terminus. A surface of subfamily-defining residues was identified on one face of the protein, offering an explanation for the induction of subfamily-specific bactericidal antibodies.

Comparative immunogenicity evaluations of influenza A virus M2 peptide as recombinant virus like particle or conjugate vaccines in mice and monkeys

Immunization against M2 peptide, also called M2e, from influenza A virus is an innovative vaccine approach for induction of cross-strain protective immunity. Two promising M2 vaccine compositions reported to date are M2 peptide chemically conjugated to carrier proteins or M2 peptide recombinantly expressed on the surface of virus like particles (VLPs) of hepatitis B virus core antigen (HBVc). To conduct a head-to-head comparison of these approaches, we constructed two recombinant HBVc VLPs expressing M2 peptide and prepared two conjugate vaccines with M2 peptide chemically coupled to Neisseria meningitidis outer membrane complex (OMPC) or HBVc VLP, respectively. Here, we showed superior immunogenicity of M2 peptide conjugated to OMPC and M2 peptide expressed on the surface of HBVc antigen based on dose-titration responses in mice. Surprisingly, HBVc expressing M2 peptide was an inferior vaccine in rhesus monkeys, whether as a primary vaccine or as a booster vaccine, when compared with M2-OMPC conjugate vaccine.

Modeling Neisseria meningitidis B metabolism at different specific growth rates

Neisseria meningitidis is a human pathogen that can infect diverse sites within the human host. The major diseases caused by N. meningitidis are responsible for death and disability, especially in young infants. At the Netherlands Vaccine Institute (NVI) a vaccine against serogroup B organisms is currently being developed. This study describes the influence of the growth rate of N. meningitidis on its macro-molecular composition and its metabolic activity and was determined in chemostat cultures. In the applied range of growth rates, no significant changes in RNA content and protein content with growth rate were observed in N. meningitidis. The DNA content in N. meningitidis was somewhat higher at the highest applied growth rate. The phospholipid and lipopolysaccharide content in N. meningitidis changed with growth rate but no specific trends were observed. The cellular fatty acid composition and the amino acid composition did not change significantly with growth rate. Additionally, it was found that the PorA content in outer membrane vesicles was significantly lower at the highest growth rate. The metabolic fluxes at various growth rates were calculated using flux balance analysis. Errors in fluxes were calculated using Monte Carlo Simulation and the reliability of the calculated flux distribution could be indicated, which has not been reported for this type of analysis. The yield of biomass on substrate (Y(x/s)) and the maintenance coefficient (m(s)) were determined as 0.44 (+/-0.04) g g(-1) and 0.04 (+/-0.02) g g(-1) h(-1), respectively. The growth associated energy requirement (Y(x/ATP)) and the non-growth associated ATP requirement for maintenance (m(ATP)) were estimated as 0.13 (+/-0.04) mol mol(-1) and 0.43 (+/-0.14) mol mol(-1) h(-1), respectively. It was found that the split ratio between the Entner-Doudoroff and the pentose phosphate pathway, the sole glucose utilizing pathways in N. meningitidis, had a minor effect on ATP formation rate but a major effect on the fluxes going through for instance the citric-acid cycle. For this reason, we presented flux ranges for underdetermined parts of metabolic network rather than presenting single flux values, which is more commonly done in literature.

Modeling Neisseria meningitidis metabolism: from genome to metabolic fluxes

A genome-scale flux model for primary metabolism of Neisseria meningitidis was constructed; a minimal medium for growth of N. meningitidis was designed using the model and tested successfully in batch and chemostat cultures.

Background

Neisseria meningitidis is a human pathogen that can infect diverse sites within the human host. The major diseases caused by N. meningitidis are responsible for death and disability, especially in young infants. In general, most of the recent work on N. meningitidis focuses on potential antigens and their functions, immunogenicity, and pathogenicity mechanisms. Very little work has been carried out on Neisseria primary metabolism over the past 25 years.

Results

Using the genomic database of N. meningitidis serogroup B together with biochemical and physiological information in the literature we constructed a genome-scale flux model for the primary metabolism of N. meningitidis. The validity of a simplified metabolic network derived from the genome-scale metabolic network was checked using flux-balance analysis in chemostat cultures. Several useful predictions were obtained from in silico experiments, including substrate preference. A minimal medium for growth of N. meningitidis was designed and tested succesfully in batch and chemostat cultures.

Conclusion

The verified metabolic model describes the primary metabolism of N. meningitidis in a chemostat in steady state. The genome-scale model is valuable because it offers a framework to study N. meningitidis metabolism as a whole, or certain aspects of it, and it can also be used for the purpose of vaccine process development (for example, the design of growth media). The flux distribution of the main metabolic pathways (that is, the pentose phosphate pathway and the Entner-Douderoff pathway) indicates that the major part of pyruvate (69%) is synthesized through the ED-cleavage, a finding that is in good agreement with literature.

Meningococcal A, C, Y and W-135 polysaccharide-protein conjugate vaccines

Serogroup C meningococcal conjugate vaccines, first launched in the UK in 1999, have been used successfully in Australia, Canada and several other European countries. Combination conjugate vaccines, containing more than one meningococcal polysaccharide, have been developed to broaden protection against the disease. A tetravalent meningococcal A, C, Y and W-135 conjugate vaccine was licensed for use in 11-55 year old adolescents and adults in the US in January 2005, and subsequently also in 2-11 year old children in Canada in May 2006. This article discusses the different glycoconjugate meningococcal vaccines which have been developed and the potential for their use to control disease caused by serogroups A, C, Y and W-135 of Neisseria meningitidis.

Synthesis and biological evaluation of phosphono analogues of capsular polysaccharide fragments from Neisseria meningitidis A

Neisseria meningitidis type A (MenA) is a Gram-negative encapsulated bacterium that may cause explosive epidemics of meningitis, especially in the sub-Saharan region of Africa. The development and manufacture of an efficient glycoconjugate vaccine against Neisseria meningitidis A is greatly hampered by the poor hydrolytic stability of its capsular polysaccharide, which is made up of (1-->6)-linked 2-acetamido-2-deoxy-alpha-D-mannopyranosyl phosphate repeating units. Since this chemical lability is a product of the inherent instability of the phosphodiester bridges, here we report the synthesis of phosphonoester-linked oligomers of N-acetyl mannosamine as candidates for stabilised analogues of the corresponding phosphate-bridged saccharides. The installation of each interglycosidic phosphonoester linkage was achieved by Mitsunobu coupling of a glycosyl C-phosphonate building block with the 6-OH moiety of a mannosaminyl residue. Each of the synthesised compounds contains an O-linked aminopropyl spacer at its reducing end (alpha- or beta-oriented) to allow for protein conjugation. The relative affinities of the synthetic molecules were investigated by a competitive ELISA assay and showed that a human polyclonal anti-MenA serum can recognise both the phosphonoester-bridged fragments 1-3 and their monomeric subunits, glycosides 20 and 21. Moreover, the biological results suggest that the abilities of these compounds to inhibit the binding of a specific antibody to MenA polysaccharide are dependent on the chain lengths of the molecules, but independent on the orientations of the anomeric linkers.

Age-specific seroprevalence of serogroup C meningococcal serum bactericidal antibody activity and serogroup A, C, W135 and Y-specific IgG concentrations in the Turkish population during 2005

Like many other developing countries; there is no accurate information about the antibody levels against Neisseria meningitidis in Turkey. We collected serum samples from four health centers located in different geographic regions and stratified according to age in order to obtain a baseline seroprevalence of protective antibodies to meningococcal serogroup C and provide data on seroprevalence of IgG antibodies to serogroups A, C, W135 and Y. Sera were tested for serum bactericidal antibodies (SBA) to serogroup C meningococci using rabbit serum as the complement source and by a bead based assay for serogroup A, C, W135 and Y-specific IgG. It was observed that 30% and 12% of individuals within the study population had SBA titers of > or =8 and > or =128, respectively. Overall; at least 70% of the population are susceptible (SBA titer <8) to meningococcal serogroup C disease. The rate of susceptibility was highest in infants aged 7-12 months and young children (1-4 years). Regardless of age, for serogroup A, C, W135 and Y, 60.5%, 27.2%, 12.3% and 19.2% of subjects, respectively, had serogroup-specific IgG concentrations > or =2 microg/mL. These data highlight that a large proportion of the Turkish population are susceptible to serogroups C, W135 and Y and should be considered, along with serogroup-specific disease incidence data, in future decisions on possible meningococcal vaccination programmes.

Neisserial outer membrane vesicles bind the coinhibitory receptor carcinoembryonic antigen-related cellular adhesion molecule 1 and suppress CD4+ T lymphocyte function

Pathogenic Neisseria bacteria naturally liberate outer membrane "blebs," which are presumed to contribute to pathology, and the detergent-extracted outer membrane vesicles (OMVs) from Neisseria meningitidis are currently employed as meningococcal vaccines in humans. While the composition of these vesicles reflects the bacteria from which they are derived, the functions of many of their constituent proteins remain unexplored. The neisserial colony opacity-associated Opa proteins function as adhesins, the majority of which mediate bacterial attachment to human carcinoembryonic antigen-related cellular adhesion molecules (CEACAMs). Herein, we demonstrate that the Opa proteins within OMV preparations retain the capacity to bind the immunoreceptor tyrosine-based inhibitory motif-containing coinhibitory receptor CEACAM1. When CD4(+) T lymphocytes were exposed to OMVs from Opa-expressing bacteria, their activation and proliferation in response to a variety of stimuli were effectively halted. This potent immunosuppressive effect suggests that localized infection will generate a "zone of inhibition" resulting from the diffusion of membrane blebs into the surrounding tissues. Moreover, it demonstrates that OMV-based vaccines must be developed from strains that lack CEACAM1-binding Opa variants.

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).

Use of meningococcal vaccines in the United States

In January 2005, Food and Drug Administration licensed a new tetravalent (serogroups A, C, Y, W-135) meningococcal conjugate vaccine ([MCV4] Menactra) for use in persons 11-55 years of age. In February 2005, CDC's Advisory Committee on Immunization Practices (ACIP) recommended routine vaccination of adolescents and college freshmen living in dormitories with MCV4. The manufacturer started shipments of MCV4 in March 2005. MCV4 should become a key addition to existing meningococcal disease prevention measures.

Peptide Mimics of the Group B Meningococcal Capsule Induce Bactericidal and Protective Antibodies after Immunization

Neisseria meningitidis serogroup B (MenB) is a leading cause of sepsis and meningitis in children. No vaccine is available for the prevention of these infections because the group B capsular polysaccharide (CP) (MenB CP) is unable to stimulate an immune response, due to its similarity with human polysialic acid. Because the MenB CP bears both human cross-reactive and non-cross-reactive determinants, we developed immunogenic peptide mimics of the latter epitopes. Peptides were selected from phage display libraries for their ability to bind to a protective anti-MenB CP mAb. One of these peptides (designated 9M) induced marked elevations in serum bactericidal activity, but not polysialic acid cross-reacting Abs, after gene priming followed by carrier-conjugate boosting. Moreover, the occurrence of bacteremia was prevented in infant rats by administration of immune sera before MenB challenge. 9M is a promising lead candidate for the development of an effective and affordable anti-MenB vaccine.

Persisting immune responses indicating long-term protection after booster dose with meningococcal group B outer membrane vesicle vaccine

MenBvac is an outer membrane vesicle vaccine against systemic meningococcal disease caused by serogroup B Neisseria meningitidis. In this placebo-controlled double-blind study including 374 healthy adolescents, the safety and immunogenicity of a schedule of three primary doses 6 weeks apart followed by a fourth dose a year later were evaluated. Antibody responses to the vaccine strain and heterologous strains (non-vaccine-type strains) and the persistence of these antibodies were measured by the serum bactericidal assay (SBA) and enzyme-linked immunosorbent assay up to 1 year after the last dose. The proportion of subjects with SBA titers of > or = 4 against the vaccine strain increased from 3% prevaccination to 65% after the third dose. Ten months later, this proportion had declined to 28%. The fourth dose induced a booster response demonstrated by 93% of subjects achieving a titer of > or = 4. One year after the booster dose, 64% still showed SBA titers of > or = 4. Cross-reacting antibodies were induced against all heterologous strains tested, although the magnitude of SBA titers differed widely between the different strains. All four doses of MenBvac were safe. Both MenBvac and the placebo had reactogenicity profiles of mild to moderate local and systemic reactions. Pain, the most common reaction, was reported with similar frequencies in both groups. No serious adverse events occurred in the MenBvac group. This study confirmed the good immunogenicity of the primary course of MenBvac and demonstrated prolonged persistence and increased cross-reactivity of functional antibodies elicited by a booster dose.

Outer membrane vesicles of the VA-MENGOC-BC vaccine against serogroup B of Neisseria meningitidis: Analysis of protein components by two-dimensional gel electrophoresis and mass spectrometry

Neisseria meningitidis is a Gram-negative bacterium responsible for significant mortality worldwide. While effective polysaccharides-based vaccines exist against serogroups A, C, W135, and Y, no similar vaccine is suitable for children under 4 years against disease caused by serogroup B strains. Therefore, major vaccine efforts against this serogroup are based on outer membrane vesicles (OMVs), containing major outer membrane proteins. The OMV-based vaccine produced by the Finlay Institute in Cuba (VA-MENGOC-BC) contributed to the rapid decline of the epidemic in this Caribbean island. While the content of major proteins in this vaccine has been discussed, no detailed work of an outer membrane proteomic map of this, or any other, commercially available OMV-derived product has been published so far. Since OMVs exhibit a large bias toward a few major proteins and usually contain a high content of lipids, establishing the adequate conditions for high resolution, 2-DE of this kind of preparation was definitely a technical challenge. In this work, 2-DE and MS have been used to generate a proteomic map of this product, detailing the presence of 31 different proteins, and it allows the identification of new putative protective protein components it contains.

Characterization of MspA, an immunogenic autotransporter protein that mediates adhesion to epithelial and endothelial cells in Neisseria meningitidis

A novel putative autotransporter protein (NMB1998) was identified in the available genomic sequence of meningococcal strain MC58 (ET-5; ST-32). The mspA gene is absent from the genomic sequences of meningococcal strain Z2491 (ET-IV; ST-4) and the gonococcal strain FA1090. An orthologue is present in the meningococcal strain FAM18 (ET-37; ST-11), but the sequence contains a premature stop codon, suggesting that the protein may not be expressed in this strain. MspA is predicted to be a 157-kDa protein with low cysteine content, and it exhibits 36 and 33% identity to the meningococcal autotransporter proteins immunoglobulin A1 (IgA1) protease and App, respectively. Search of the Pfam database predicts the presence of IgA1 protease and autotransporter beta-barrel domains. MspA was cloned, and a recombinant protein of the expected size was expressed and after being affinity purified was used to raise rabbit polyclonal monospecific antiserum. Immunoblot studies showed that ca. 125- and 95-kDa fragments of MspA are secreted in meningococcal strain MC58, which are absent from the isogenic mutant. Secretion of MspA was shown to be modified in an AspA isogenic mutant. A strain survey showed that MspA is expressed by all ST-32 and ST-41/44 (lineage 3) strains, but none of the ST-8 (A4) strains examined. Sera from patients convalescing from meningococcal disease were shown to contain MspA-specific antibodies. In bactericidal assays, anti-MspA serum was shown to kill the homologous strain (MC58) and another ST-32 strain. Escherichia coli-expressing recombinant MspA was shown to adhere to both human bronchial epithelial cells and brain microvascular endothelial cells.

Structural variation and immune recognition of the P1.2 subtype meningococcal antigen

Neisseria meningitidis is a globally important cause of bacterial meningitis and septicemia. No comprehensive antimeningococcal vaccine is available, largely as a consequence of the high sequence diversity of those surface proteins that could function as components of a vaccine. One such component is the protein PorA, a major surface porin of this Gram-negative organism that has been used in a number of experimental and licensed vaccines. Here we describe a series of experiments designed to investigate the consequences for antibody recognition of sequence diversity within a PorA antigen. The binding of a 14-residue peptide, corresponding to the P1.2 subtype antigen, to the MN16C13F4 monoclonal antibody was sensitive to mutation of five out of the six residues within the epitope sequence. The crystal structure of the antibody Fab fragment, determined in complex with the peptide antigen, shows a remarkably hydrophobic binding site and interactions between the antigen and antibody are dominated by apolar residues. Nine intrachain hydrogen bonds are formed within the antigen which maintain the beta-hairpin conformation of the peptide. These hydrogen bonds involve residues that are highly conserved amongst different P1.2 sequence variants, suggesting that some positions may be conserved for structural reasons in these highly polymorphic regions. The sensitivity of antibody recognition of the antigen towards mutation provides a structural explanation for the widespread sequence variation seen in different PorA sequences in this region. Single point mutations are sufficient to remove binding capability, providing a rationale for the manner in which different meningococcal PorA escape variants arise.

Proteomic analysis of Neisseria lactamica and N eisseria meningitidis outer membrane vesicle vaccine antigens

Vaccines to prevent meningococcal disease have been developed from the outer membrane vesicles (OMVs) of Neisseria meningitidis and the related commensal organism Neisseria lactamica. In addition to lipopolysaccharide and the major porins, these vaccines contain a large number of proteins that are incompletely characterised. Here we describe comparative proteomic analyses of the N. lactamica OMV vaccine and OMVs from a serogroup B strain of N. meningitidis. Tandem mass-spectrometry data for trypsinised N. lactamica OMV vaccine were matched to an incompletely assembled genome sequence from the same strain to give 65 robust protein identifications and a further 122 single- or two-peptide matches. Fifty-seven N. meningitidis K454 proteins were identified robustly (and a further 68 from single- or two-peptide matches) by inference from the N. meningitidis MC58 genome. The results suggest that OMVs have a hitherto unappreciated complexity and pinpoint novel candidate antigens for further characterisation.

Antiidiotypic DNA vaccination induces serum bactericidal activity and protection against group B meningococci

No vaccine is available for preventing infections by serogroup B Neisseria meningitidis (MenB), which accounts for a major portion of meningococcal cases in developed countries, because of the poor immunogenicity of the capsular polysaccharide (CP) even after protein conjugation. We have previously induced anticapsular antibodies by immunization with a single chain variable fragment (scFv), which mimics a protective CP epitope. This surrogate antigen, however, was ineffective at inducing serum bactericidal activity, an accepted marker of protection in humans. Serum bactericidal activity was consistently achieved by immunizing mice with the scFv-encoding gene. Immunization with vectors without a secretory signal sequence before the scFv resulted in markedly higher bactericidal activity relative to those with such a sequence. The induced antibodies were capsule specific, as shown by complete inhibition of bactericidal activity by purified MenB CP and by resistance to killing of MenA or MenC. Moreover, these antibodies were predominantly of the IgG2a isotype, reflecting a T helper type 1 response. Administration of sera from scFv gene–vaccinated animals protected infant rats against MenB bacteremia. These data illustrate the potential of vaccination with genes encoding capsular mimics in providing protection against MenB and other encapsulated bacteria.

Synthesis of stable C-phosphonate analogues of Neisseria meningitidis group A capsular polysaccharide structures using modified Mitsunobu reaction conditions

Examples of synthetic C-phosphonate analogues of microbial polysaccharide structures containing inter-residue phosphodiester linkages are most rare. The successful construction of such analogues of the Neisseria meningitidis Group A capsular polysaccharide is described. Using a modified Mitsunobu reaction (tris(4-chlorophenyl)phosphine, DIAD, excess of Et3N) between an anomeric C-phosphonate monoester and a 6-OH ManNAc acceptor a high yield (88%) of a dimer was obtained. Transformation of the dimer into a new 6-OH acceptor through deacetylation and further reaction with the elongating C-phosphonate monomer employing the same conditions afforded the trimer in 92% yield. Iteration of the procedure then afforded the tetramer with a coupling yield of 85%. The di-, tri- and tetramer were deprotected to give target structures ready for conjugation to a carrier protein and subsequent immunological evaluation.

The immunogenicity of a conformationally restricted peptide mimetic of meningococcal lipooligosaccharide

Life-threatening meningitis and septicaemia caused by Neisseria meningitidis are a public health priority, and their prevention by vaccination is a major objective. Meningococcal capsular polysaccharide-based vaccines are effective against the major invasive serogroups, except for serogroup B, the capsule of which mimics human polysaccharides and is poorly immunogenic. An alternative vaccine candidate that has the potential to offer cross-protection against antigenically diverse meningococci is the lipooligosaccharide (LOS). The structurally constrained peptide mimetic, C22, of a bactericidal antibody epitope within LOS was previously shown to elicit cross-reactive antibodies to meningococcal LOS when complexed to NeutrAvidintrade mark as a carrier protein. The immunogenicity of this antigen in H-2(d) (BALB/c) and H-2(k) (C3H/HeN) haplotype mice was further investigated. Anti-LOS immunoglobulin G (IgG) antibody titres increased with the vaccine dose and correlated with the anti-C22 peptide antibody titres in both haplotypes. Antigen-stimulated Th1/Th2 cytokine secretion by splenocytes and antibody isotypes indicated a Th2-type immune response with IgG1 antibodies and a low titre of IgG2b. There was no serum bactericidal activity observed against the meningococcus.

Towards an improved serogroup BNeisseria meningitidisvaccine

Meningococcal disease, presenting primarily as septicaemia and meningitis, continues to be a devastating problem around the world. Over the last century, vaccine development has been undertaken in earnest for the prevention of this disease. Polysaccharide vaccines have been available for almost 40 years, yet they are poorly immunogenic in young children who are at the highest risk. Since their introduction into some routine immunisation schedules in 1999, polysaccharide-protein conjugate vaccines for the prevention of serogroup C meningococcal infection have proven efficacious. A quadrivalent polysaccharide-protein conjugate vaccine against serogroups A, C, W135 and Y, which is being introduced in the US this year, is hoped to control disease caused by these serogroups. To date, however, the development of a universally safe, immunogenic and effective serogroup B Neisseria meningitidis vaccine has remained a challenge. This review details the many conventional vaccine strategies and the more recent genome-derived technological approaches being used in serogroup B vaccine development. The future prevention of serogroup B disease will rely on both outer membrane vesicle vaccines being used for serosubtype-specific outbreaks and new vaccines containing multiple other antigens. Investment by the pharmaceutical industry in preclinical research and development provides hope that an efficacious serogroup B meningococcal vaccine can be developed.

Phenotypic and transcriptional characterization of the meningococcal PhoPQ system, a magnesium-sensing two-component regulatory system that controls genes involved in remodeling the meningococcal cell surface

We previously identified and characterized a two-component regulatory system in the meningococcus with homology to the phoP-phoQ system in salmonella and showed that allele replacement of the NMB0595 regulator gene led to loss of virulence, sensitivity to antimicrobial peptides, perturbed protein expression, and magnesium-sensitive growth. On the basis of these findings we proposed that the system should be designated the meningococcal PhoPQ system. Here we further characterized the NMB0595 mutant and demonstrated that it had increased membrane permeability and was unable to form colonies on solid media with low magnesium concentrations, features that are consistent with disruption of PhoPQ-mediated modifications to the lipooligosaccharide structure. We examined the transcriptional profiles of wild-type and NMB0595 mutant strains and found that magnesium-regulated changes in gene expression are completely abrogated in the mutant, indicating that, similar to the salmonella PhoPQ system, the meningococcal PhoPQ system is regulated by magnesium. Transcriptional profiling of the mutant indicated that, also similar to the salmonella PhoPQ system, the meningococcal system is involved in control of virulence and remodeling of the bacterial cell surface in response to the host environment. The results are consistent with the hypothesis that the PhoP homologue plays a role in the meningococcus similar to the role played by PhoP in salmonella. Elucidating the role that the PhoPQ system and PhoPQ-regulated genes play in the response of the meningococcus to the host environment may provide new insights into the pathogenic process.

Molecular analysis of anti-N-propionyl Neisseria meningitidis group B polysaccharide monoclonal antibodies

The capsular polysaccharide of Neisseria meningitidis group B (MBPS) is a polymer of alpha (2-->8) N-acetyl neuraminic acid, which is chemically identical to polysialic acid (PSA) expressed in human tissues. Antibodies from mice immunized with a MBPS-protein conjugate vaccine in which N-acetyl groups have been replaced by propionyl groups (N-Pr MBPS) can be bactericidal and show minimal or no cross-reactivity with human PSA. To investigate the molecular basis for antigen recognition, we cloned and sequenced the variable region (V) genes of five bactericidal anti-N-Pr MBPS murine mAbs and produced computer models of the combining sites. The results were compared to those reported in the literature for two autoreactive anti-MBPS. The V region genes of the anti-N-Pr MBPS mAbs and the anti-MBPS autoreactive mAbs are derived from a limited set of germline V, J, and D genes. However, the anti-N-Pr MBPS mAbs are more mutated than the anti-MBPS mAbs and the former use V-D-J editing that introduces arginine in H-CDR3. Models of the respective combining sites indicate that the anti-MBPS or anti-N-Pr MBPS mAbs that react with host PSA have relatively wide and shallow grooves with a high overall positive charge, consistent with recognition of extended helical polysaccharide structures recognized by the autoreactive mAbs. In contrast, anti-N-Pr MBPS mAbs that do not react with host PSA contain pockets and deep clefts that are consistent with recognition of discrete structural features of individual residues.

T-cell-stimulating protein A elicits immune responses during meningococcal carriage and human disease

In recognition of the need for immunological memory-inducing components for future Neisseria meningitidis group B vaccines, we previously searched the proteome of N. meningitidis and identified T-cell-stimulating protein A (TspA). This study was designed to confirm the immunogencity of TspA and to examine the subset of T-helper cell responses to the protein in patients and nasopharyngeal carriers. The tspA gene was reconstructed, cloned, and expressed in Escherichia coli, and the recombinant TspA (rTspA) protein was affinity purified. T-cell proliferative responses to rTspA were detected in the peripheral blood mononuclear cells (PBMCs) of convalescent patients and carriers, confirming that TspA-specific T-cell responses were stimulated by invasive disease and nasopharyngeal colonization. Following stimulation of PBMCs with meningococcal lysate, increased frequencies of both Th1 and Th2 cells were observed, indicating that, as during carriage, invasive meningococcal disease induced an unbiased T-helper subset response. A similar unbiased T-helper response was also detected against rTspA in the PBMCs of convalescent patients. The response of PBMCs from the carriers to TspA stimulation, however, was very weak, and the frequencies of cytokine-positive CD4 cells were not significantly greater than the frequencies in unstimulated control cultures. All of the patients and carriers responded with serum antimeningococcal immunoglobulin G (IgG) antibodies, while four of six samples from patients and 5 of 14 samples from carriers contained detectable anti-rTspA IgG antibodies. Taken together, the results of this study confirmed the immunogenicity of TspA in humans during natural meningococcal infection, and therefore, TspA is worthy of further investigation as a possible T-cell stimulating component of future vaccines.

Analysis of human serum immunoglobulin G against O-acetyl-positive and O-acetyl-negative serogroup W135 meningococcal capsular polysaccharide

The capsular polysaccharide of Neisseria meningitidis serogroup W135 is expressed in both O-acetyl-positive (OA+) and O-acetyl-negative (OA-) forms. This study investigates the impact of OA status (OA+ versus OA-) on serological measurements of anti-W135 immunoglobulin G (IgG) antibodies in immunized adults. W135-specific serum antibody assignments were made for 28 postimmunization sera from adults by enzyme-linked immunosorbent assay using the meningococcal standard reference serum CDC1992. The established IgG concentration in micrograms per milliliter ([IgG]microg/ml) for CDC1992 against OA+ antigen (16.2 microg/ml) was used as a reference to assign a concentration of 10.13 microg/ml IgG against OA- antigen by cross-standardization. Overall, the IgG assignments for these sera were higher against OA+ antigen (geometric mean concentration [GMC] = 7.16 microg/ml) than against OA- antigen (GMC = 2.84 microg/ml). However, seven sera showed higher specific [IgG]microg/ml values against the OA+ antigen than against the OA- antigen. These sera were also distinguished by the inability of fluid-phase OA- antigen to compete for antibody binding to OA+ solid-phase antigen. Although there was no overall difference in functional activity measured by complement-mediated serum bactericidal assay (SBA) against OA+ and OA- target bacteria (geometric mean titers of 9,642 and 9,045, respectively), three serum specimens showed a large difference in SBA antibody titers against OA+ versus OA- W135 target bacteria, which may reflect different epitope specificities for these sera. Our data indicate that, for some sera, the agreement in anti-OA+ versus anti-OA- W135 IgG assignments is serum specific and does not reflect the functional (killing) activity in vitro.

Epitopes recognized by a nonautoreactive murine anti-N-propionyl meningococcal group B polysaccharide monoclonal antibody

The capsular polysaccharide of Neisseria meningitidis group B (MBPS) is a polymer of alpha (2-->8) N-acetyl neuraminic acid. The polysaccharide is chemically identical to an autoantigen, polysialic acid (PSA), and is a poor immunogen, even when conjugated to protein carriers. Immunization of mice with MBPS-protein conjugate vaccines, in which N-acetyl groups have been replaced by propionyl groups (N-Pr MBPS), elicits serum bactericidal antibodies. A subpopulation of these antibodies do not cross-react with human PSA. The reasons for the increased immunogenicity of N-Pr MBPS and the antigenic targets of the bactericidal nonautoreactive antibodies are unknown. In this study, we investigated the antigenic targets of a protective murine monoclonal antibody (MAb) prepared against a N-Pr MBPS-tetanus toxoid conjugate vaccine. Binding of the MAb to N-Pr MBPS (as demonstrated by an enzyme-linked immunosorbent assay) and bactericidal activity were inhibited by de-N-acetylated MBPS and re-N-acetylated MBPS, which indicate that N-propionyl groups are not obligatory determinants for binding. The results of affinity selection from a preparation of N-Pr MBPS and matrix-assisted laser desorption ionization-time of flight mass spectroscopic analysis indicated that the minimal epitope recognized by the MAb is a MBPS disaccharide containing one de-N-acetylated residue. Thus, the bacterial capsular epitope recognized by this bactericidal, nonautoreactive, anti-group-B MAb likely contains de-N-acetyl residues.

Booster vaccination with hexavalent DTPa-HBV-IPV/Hib vaccine in the second year of life is as safe as concomitant DTPa-IPV/Hib + HBV administered separately

The safety and reactogenicity of a booster dose of GSK Biologicals' hexavalent DTPa-HBV-IPV/Hib vaccine (N=4725) was compared with the separate administration of GSK Biologicals' DTPa-IPV/Hib and HBV vaccines (N=4474) in two open, randomized multicenter studies (A and B). Solicited symptoms occurring within 4 days of vaccination were recorded on diary cards and serious adverse events (SAEs) were collected throughout the study period. In Study A (N=1149), incidences of solicited symptoms were similar in both groups; there were no SAEs either reported within 4 days of vaccination or considered to be causally related to vaccination. In study B (N=8050), where fever was the only solicited symptom, rectal temperature > or =39.5 degrees C was observed in 2.5% and 2.8% of the subjects, respectively. Fever > or =40.0 degrees C was rare (0.6%), and only two cases of febrile convulsions were recorded during the 4 days following vaccination both in the control group. Large swelling reactions (defined as local injection site swelling with diameter >50 mm, noticeable diffuse injection site swelling or noticeable increased circumference of the injected limb) were reported following 2.3% of the booster vaccine doses, regardless of the vaccine used. Extensive swelling reactions involving an adjacent joint were reported in 0.1% of the subjects. Two SAEs, both reported after booster doses of DTPa-IPV/Hib and HBV vaccines administered separately, were considered by the investigators to be related to vaccination. Both resolved completely without sequelae. The hexavalent DTPa-HBV-IPV/Hib vaccine and the DTPa-IPV/Hib and HBV vaccines administered separately have similar good reactogenicity and safety profiles when given as booster doses in the second year of life.