The impact of protein-conjugate polysaccharide vaccines: an endgame for meningitis?

Antigenic determinants driving serogroup-specific antibody response to Neisseria meningitidis C, W, and Y capsular polysaccharides: Insights for rational vaccine design

Meningococcal glycoconjugate vaccines sourced from capsular polysaccharides (CPSs) of pathogenic Neisseria meningitidis strains are well-established measures to prevent meningococcal disease. However, the exact structural factors responsible for antibody recognition are not known. CPSs of Neisseria meningitidis serogroups Y and W differ by a single stereochemical center, yet they evoke specific immune responses. Herein, we developed specific monoclonal antibodies (mAbs) targeting serogroups C, Y, and W and evaluated their ability to kill bacteria. We then used these mAbs to dissect structural elements responsible for carbohydrate-protein interactions. First, Men oligosaccharides were screened against the mAbs using ELISA to select putative lengths representing the minimal antigenic determinant. Next, molecular interaction features between the mAbs and serogroup-specific sugar fragments were elucidated using STD-NMR. Moreover, X-ray diffraction data with the anti-MenW CPS mAb enabled the elucidation of the sugar-antibody binding mode. Our findings revealed common traits in the epitopes of all three sialylated serogroups. The minimal binding epitopes typically comprise five to six repeating units. Moreover, the O-acetylation of the neuraminic acid moieties was fundamental for mAb binding. These insights hold promise for the rational design of optimized meningococcal oligosaccharides, opening new avenues for novel production methods, including chemical or enzymatic approaches.

MA, Tovar-Rosero YY, Oñate AA, O'Ryan M. Two centuries of vaccination: historical and conceptual approach and future perspectives

Over the past two centuries, vaccines have been critical for the prevention of infectious diseases and are considered milestones in the medical and public health history. The World Health Organization estimates that vaccination currently prevents approximately 3.5-5 million deaths annually, attributed to diseases such as diphtheria, tetanus, pertussis, influenza, and measles. Vaccination has been instrumental in eradicating important pathogens, including the smallpox virus and wild poliovirus types 2 and 3. This narrative review offers a detailed journey through the history and advancements in vaccinology, tailored for healthcare workers. It traces pivotal milestones, beginning with the variolation practices in the early 17th century, the development of the first smallpox vaccine, and the continuous evolution and innovation in vaccine development up to the present day. We also briefly review immunological principles underlying vaccination, as well as the main vaccine types, with a special mention of the recently introduced mRNA vaccine technology. Additionally, we discuss the broad benefits of vaccines, including their role in reducing morbidity and mortality, and in fostering socioeconomic development in communities. Finally, we address the issue of vaccine hesitancy and discuss effective strategies to promote vaccine acceptance. Research, collaboration, and the widespread acceptance and use of vaccines are imperative for the continued success of vaccination programs in controlling and ultimately eradicating infectious diseases.

A Mouse Immunogenicity Model for the Evaluation of Meningococcal Conjugate Vaccines

The identification of an appropriate animal model for use in the development of meningococcal vaccines has been a challenge as humans are the only natural host for Neisseria meningitidis. Small animal models have been developed and are widely used to study the efficacy or immunogenicity of vaccine formulations generated against various diseases. Here, we describe the development and optimization of a mouse model for assessing the immunogenicity of candidate tetravalent meningococcal polysaccharide (MenACYW-TT) protein conjugate vaccines. Three inbred (BALB/c [H-2d], C3H/HeN [H-2k], or C57BL/6 [H-2b]) and one outbred (ICR [H-2g7]) mouse strains were assessed using serial two-fold dose dilutions (from 2 µg to 0.03125 µg per dose of polysaccharide for each serogroup) of candidate meningococcal conjugate vaccines. Groups of 10 mice received two doses of the candidate vaccine 14 days apart with serum samples obtained 14 days after the last dose for the evaluation of serogroup-specific anti-polysaccharide IgG by ELISA and bactericidal antibody by serum bactericidal assay (SBA). C3H/HeN and ICR mice had a more dose-dependent antibody response to all four serogroups than BALB/c and C57Bl/6 mice. In general, ICR mice had the greatest antibody dose-response range (both anti-polysaccharide IgG and bactericidal antibodies) to all four serogroups and were chosen as the model of choice. The 0.25 µg per serogroup dose was chosen as optimal since this was in the dynamic range of the serogroup-specific dose-response curves in most of the mouse strains evaluated. We demonstrate that the optimized mouse immunogenicity model is sufficiently sensitive to differentiate between conjugated polysaccharides, against unconjugated free polysaccharides and, to degradation of the vaccine formulations. Following optimization, this optimized mouse immunogenicity model has been used to assess the impact of different conjugation chemistries on immunogenicity, and to screen and stratify various candidate meningococcal conjugate vaccines to identify those with the most desirable profile to progress to clinical trials.

Vaccine and vaccination as a part of human life: In view of COVID-19

Background

Vaccination created a great breakthrough toward the improvement to the global health. The development of vaccines and their use made a substantial decrease and control in infectious diseases. The abundance and emergence of new vaccines has facilitated targeting populations to alleviate and eliminate contagious pathogens from their innate reservoir. However, along with the infections like malaria and HIV, effective immunization remains obscure and imparts a great challenge to science.

Purpose and scope

The novel Corona virus SARS‐CoV‐2 is the reason for the 2019 COVID‐19 pandemic in the human global population, in the first half of 2019. The need for establishing a protected and compelling COVID‐19 immunization is a global prerequisite to end this pandemic.

Summary and conclusion

The different vaccine technologies like inactivation, attenuation, nucleic acid, viral vector, subunit, and viral particle based techniques are employed to develop a safe and highly efficient vaccine. The progress in vaccine development for SARS‐CoV2 is much faster in the history of science. Even though there exist of lot of limitations, continuous efforts has put forward so as to develop highly competent and effective vaccine for many human and animal linked diseases due to its unlimited prospective. This review article focuses on the historical outlook and the development of the vaccine as it is a crucial area of research where the life of the human is saved from various potential diseases.

Molecular diagnostic assays for the detection of common bacterial meningitis pathogens: A narrative review

Bacterial meningitis is a major global cause of morbidity and mortality. Rapid identification of the aetiological agent of meningitis is essential for clinical and public health management and disease prevention given the wide range of pathogens that cause the clinical syndrome and the availability of vaccines that protect against some, but not all, of these. Since microbiological culture is complex, slow, and often impacted by prior antimicrobial treatment of the patient, molecular diagnostic assays have been developed for bacterial detection. Distinguishing between meningitis caused by Neisseria meningitidis (meningococcus), Streptococcus pneumoniae (pneumococcus), Haemophilus influenzae, and Streptococcus agalactiae and identifying their polysaccharide capsules is especially important. Here, we review methods used in the identification of these bacteria, providing an up-to-date account of available assays, allowing clinicians and diagnostic laboratories to make informed decisions about which assays to use.

Immunogenicity and safety of a quadrivalent meningococcal tetanus toxoid-conjugate vaccine (MenACYW-TT) vs. a licensed quadrivalent meningococcal tetanus toxoid-conjugate vaccine in meningococcal vaccine-naïve and meningococcal C conjugate vaccine-primed toddlers: a phase III randomised study

Vaccination remains the best strategy to reduce invasive meningococcal disease. This study evaluated an investigational tetanus toxoid-conjugate quadrivalent meningococcal vaccine (MenACYW-TT) vs. a licensed tetanus toxoid-conjugate quadrivalent meningococcal vaccine (MCV4-TT) (NCT02955797). Healthy toddlers aged 12–23 months were included if they were either meningococcal vaccine-naïve or MenC conjugate (MCC) vaccine-primed (≥1 dose of MCC prior to 12 months of age). Vaccine-naïve participants were randomised 1:1 to either MenACYW-TT (n = 306) or MCV4-TT (n = 306). MCC-primed participants were randomised 2:1 to MenACYW-TT (n = 203) or MCV4-TT (n = 103). Antibody titres against each of the four meningococcal serogroups were measured by serum bactericidal antibody assay using the human complement. The co-primary objectives of this study were to demonstrate the non-inferiority of MenACYW-TT to MCV4-TT in terms of seroprotection (titres ≥1:8) at Day 30 in both vaccine-naïve and all participants (vaccine-naïve and MCC-primed groups pooled). The immune response for all four serogroups to MenACYW-TT was non-inferior to MCV4-TT in vaccine-naïve participants (seroprotection: range 83.6–99.3% and 81.4–91.6%, respectively) and all participants (seroprotection: range 83.6–99.3% and 81.4–98.0%, respectively). The safety profiles of both vaccines were comparable. MenACYW-TT was well-tolerated and demonstrated non-inferior immunogenicity when administered to MCC vaccine-primed and vaccine-naïve toddlers.

Whole-Cell Vaccine Preparation: Options and Perspectives

Vaccines are biological preparations to elicit a specific immune response in individuals against the targetted microorganisms. The use of vaccines has caused the near eradication of many critical diseases and has had an everlasting impact on public health at a relatively low cost. Most of the vaccines developed today are based on techniques which were developed a long time ago. In the beginning, vaccines were prepared from tissue fluids obtained from infected animals or people, but at present, the scenario has changed with the development of vaccines from live or killed whole microorganisms and toxins or using genetic engineering approaches. Considerable efforts have been made in vaccine development, but there are still many diseases that need attention, and new technologies are being developed in vaccinology to combat them. In this chapter, we discuss different approaches for vaccine development, including the properties and preparation of whole-cell vaccines.

Structural and mechanistic basis of capsule O-acetylation in Neisseria meningitidis serogroup A

O-Acetylation of the capsular polysaccharide (CPS) of Neisseria meningitidis serogroup A (NmA) is critical for the induction of functional immune responses, making this modification mandatory for CPS-based anti-NmA vaccines. Using comprehensive NMR studies, we demonstrate that O-acetylation stabilizes the labile anomeric phosphodiester-linkages of the NmA-CPS and occurs in position C3 and C4 of the N-acetylmannosamine units due to enzymatic transfer and non-enzymatic ester migration, respectively. To shed light on the enzymatic transfer mechanism, we solved the crystal structure of the capsule O-acetyltransferase CsaC in its apo and acceptor-bound form and of the CsaC-H228A mutant as trapped acetyl-enzyme adduct in complex with CoA. Together with the results of a comprehensive mutagenesis study, the reported structures explain the strict regioselectivity of CsaC and provide insight into the catalytic mechanism, which relies on an unexpected Gln-extension of a classical Ser-His-Asp triad, embedded in an α/β-hydrolase fold.

Meningococcal disease surveillance in the Asia-Pacific region (2020): The global meningococcal initiative

The degree of surveillance data and control strategies for invasive meningococcal disease (IMD) varies across the Asia-Pacific region. IMD cases are often reported throughout the region, but the disease is not notifiable in some countries, including Myanmar, Bangladesh and Malaysia. Although there remains a paucity of data from many countries, specific nations have introduced additional surveillance measures. The incidence of IMD is low and similar across the represented countries (<0.2 cases per 100,000 persons per year), with the predominant serogroups of Neisseria meningitidis being B, W and Y, although serogroups A and X are present in some areas. Resistance to ciprofloxacin is also of concern, with the close monitoring of antibiotic-resistant clonal complexes (e.g., cc4821) being a priority. Meningococcal vaccination is only included in a few National Immunization Programs, but is recommended for high-risk groups, including travellers (such as pilgrims) and people with complement deficiencies or human immunodeficiency virus (HIV). Both polysaccharide and conjugate vaccines form part of recommendations. However, cost and misconceptions remain limiting factors in vaccine uptake, despite conjugate vaccines preventing the acquisition of carriage.

Immunogenicity and safety of a quadrivalent meningococcal tetanus toxoid-conjugate vaccine (MenACYW-TT) in healthy toddlers: a Phase II randomized study

Neisseria meningitidis

can lead to invasive meningococcal disease to which young children are particularly vulnerable. We assessed the immunogenicity and safety of Sanofi Pasteur’s investigational quadrivalent (serogroups A, C, Y, and W) meningococcal tetanus-toxoid conjugate vaccine, MenACYW-TT, as a single dose, in healthy meningococcal vaccine-naïve toddlers versus a licensed conjugate vaccine MCV4-TT (NCT03205358). In this Phase II study conducted in Finland, 188 toddlers aged 12–24 months were randomized 1:1 to MenACYW-TT or MCV4-TT. Serum bactericidal antibody assays using human complement (hSBA) and baby rabbit complement (rSBA) measured antibodies against each serogroup before and 30 days after vaccination. Participants were monitored for immediate adverse events (AEs) and post-vaccination AEs for 30 days. All analyses were descriptive. All 188 participants completed the study. The Day 30 hSBA seroresponses (hSBA titer <8 at baseline and post-vaccination titer ≥8, or ≥8 at baseline and ≥4-fold increase post-vaccination) were comparable between participants receiving MenACYW-TT (96.7–100%), and MCV4-TT (86.0–100.0%) for each serogroup. Most unsolicited AEs were of Grade 1 or Grade 2 intensity. There were no immediate hypersensitivity reactions, and no AEs or serious AEs leading to discontinuation from the study. In this exploratory study, MenACYW-TT vaccine was well tolerated and immunogenic. If confirmed in Phase III, a single dose of the MenACYW-TT vaccine may show promise as an alternative vaccine option for toddlers receiving meningococcal vaccination for the first time.

Epidemiologic Trends, Global Shifts in Meningococcal Vaccination Guidelines, and Data Supporting the Use of MenACWY-TT Vaccine: A Review

Neisseria meningitidis is a major cause of meningitis and septicemia with cases, outbreaks, and epidemics reported globally in industrialized and non-industrialized countries. N. meningitidis is categorized into 12 serogroups; however, only 5 serogroups (A, B, C, W, Y) are responsible for the majority of disease. Invasive meningococcal disease (IMD) occurs unpredictably; protection is therefore best achieved by initiating proactive vaccination strategies. Vaccines are currently available for the five main disease-causing serogroups. With the evolution of meningococcal vaccines and changes in IMD epidemiology, different vaccination strategies have been used. Recently, the rapid clonal expansion of meningococcal serogroup W (MenW) has been associated with a change in the national and regional vaccination recommendations from monovalent meningococcal serogroup C vaccines to meningococcal serogroup A, C, W, Y (MenACWY) vaccines in several countries. This review highlights these and other changes in IMD epidemiology and meningococcal vaccination recommendations, summarizes information available for currently available conjugate MenACWY vaccines, and focuses on clinical study data for the most recently approved MenACWY conjugate vaccine, MenACWY vaccine conjugated to tetanus toxoid (MenACWY-TT). MenACWY-TT studies spanned multiple age groups and generally demonstrated safety and immunogenicity in comparison with other meningococcal vaccines and under concomitant administration of other routine vaccines. Continuous updates to meningococcal vaccine recommendations in response to changing epidemiology, as have been undertaken for MenW, are necessary to ensure optimal population protection. FUNDING: Pfizer, Inc.

Inhibition ELISA as a putative tool for the identification and quantification of meningococcal A and X polysaccharides at various stages of vaccine development

The multivalent glycoconjugate vaccines against Neisseria meningitidis are extremely high-priced for the developing world. The high cost is due to the manufacturing set-up required to produce an effective vaccine and other inflators like complex production steps including the production and purification of the polysaccharide and consequently its conjugation with a protein and finally formulating the finished multivalent product. There is an urgent need for assays which are simple, precise, can be applicable at multiple steps and contribute in reducing the overall manufacturing cost, thereby making the vaccines more equitable to the developing world. WHO recommends serological tests for polysaccharide identification and quantitation at different stages of conjugate vaccine production. We report development of inhibition ELISAs for the identification and quantification of N. meningitidis serogroup A (MenA) and N. meningitidis serogroup X (MenX) polysaccharides (PSs) in samples from stage of cell banking till production of finished product. The method was qualified on various parameters such as specificity, intermediate precision, sensitivity and accuracy. Our results provide a proof of concept for the use of an inhibition ELISA as a common tool for the identification and quantification of PS at various stages of vaccine development and manufacture.

Typing complex meningococcal vaccines to understand diversity and population structure of key vaccine antigens

Background: Protein-conjugate capsular polysaccharide vaccines can potentially control invasive meningococcal disease (IMD) caused by five (A, C, W, X, Y) of the six IMD-associated serogroups.  Concerns raised by immunological similarity of the serogroup B capsule to human neural cell carbohydrates, meant that 'serogroup B substitute' vaccines target more variable subcapsular protein antigens.  A successful approach using outer membrane vesicles (OMVs) as major vaccine components had limited strain coverage. In 4CMenB (Bexsero ^®), recombinant proteins have been added to ameliorate this problem.  Methods: Scalable, portable, genomic techniques were used to investigate the Bexsero ^® OMV protein diversity in meningococcal populations. Shotgun proteomics identified 461 proteins in the OMV, defining a complex proteome. Amino acid sequences for the 24 proteins most likely to be involved in cross-protective immune responses were catalogued within the PubMLST.org/neisseria database using a novel OMV peptide Typing (OMVT) scheme. Results: Among these proteins there was variation in the extent of diversity and association with meningococcal lineages, identified as clonal complexes (ccs), ranging from the most conserved peptides (FbpA, NEISp0578, and putative periplasmic protein, NEISp1063) to the most diverse (TbpA, NEISp1690).  There were 1752 unique OMVTs identified amongst 2492/3506 isolates examined by whole-genome sequencing (WGS). These OMVTs were grouped into clusters (sharing ≥18 identical OMVT peptides), with 45.3% of isolates assigned to one of 27 OMVT clusters. OMVTs and OMVT clusters were strongly associated with cc, genogroup, and Bexsero ^® antigen variants, demonstrating that combinations of OMV proteins exist in discrete, non-overlapping combinations associated with genogroup and Bexsero ^® Antigen Sequence Type. This highly structured population of IMD-associated meningococci is consistent with strain structure models invoking host immune and/or metabolic selection. Conclusions: The OMVT scheme facilitates region-specific WGS investigation of meningococcal diversity and is an open-access, portable tool with applications for vaccine development, especially in the choice of antigen combinations, assessment and implementation.

Typing complex meningococcal vaccines to understand diversity and population structure of key vaccine antigens

Background: Protein-conjugate capsular polysaccharide vaccines can potentially control invasive meningococcal disease (IMD) caused by five (A, C, W, X, Y) of the six IMD-associated serogroups.  Concerns raised by immunological similarity of the serogroup B capsule to human neural cell carbohydrates, meant that ‘serogroup B substitute’ vaccines target more variable subcapsular protein antigens.  A successful approach using outer membrane vesicles (OMVs) as major vaccine components had limited strain coverage. In 4CMenB (Bexsero ^®), recombinant proteins have been added to ameliorate this problem. 

Methods: Scalable, portable, genomic techniques were used to investigate the Bexsero ^® OMV protein diversity in meningococcal populations. Shotgun proteomics identified 461 proteins in the OMV, defining a complex proteome. Amino acid sequences for the 24 proteins most likely to be involved in cross-protective immune responses were catalogued within the PubMLST.org/neisseria database using a novel OMV peptide Typing (OMVT) scheme.

Results: Among these proteins there was variation in the extent of diversity and association with meningococcal lineages, identified as clonal complexes (ccs), ranging from the most conserved peptides (FbpA, NEISp0578, and putative periplasmic protein, NEISp1063) to the most diverse (TbpA, NEISp1690).  There were 1752 unique OMVTs identified amongst 2492/3506 isolates examined by whole-genome sequencing (WGS). These OMVTs were grouped into clusters (sharing ≥18 identical OMVT peptides), with 45.3% of isolates assigned to one of 27 OMVT clusters. OMVTs and OMVT clusters were strongly associated with cc, genogroup, and Bexsero ^® antigen variants, demonstrating that combinations of OMV proteins exist in discrete, non-overlapping combinations associated with genogroup and Bexsero ^® Antigen Sequence Type. This highly structured population of IMD-associated meningococci is consistent with strain structure models invoking host immune and/or metabolic selection.

Conclusions:The OMVT scheme facilitates region-specific WGS investigation of meningococcal diversity and is an open-access, portable tool with applications for vaccine development, especially in the choice of antigen combinations, assessment and implementation.

The Impact of Nucleotide Sequence Analysis on Meningococcal Vaccine Development and Assessment

Since it became available as a routine tool in biology, the determination and analysis of nucleotide sequences has been applied to the design of vaccines and the investigation of their effectiveness. As vaccination is primarily concerned with the interaction of biological molecules with the immune system, the utility of sequence data is not immediately obvious and, indeed, nucleotide sequence data are most effective when used to complement more conventional immunological approaches. Here, the impact of sequencing on the field of vaccinology will be illustrated with reference to the development and implementation of vaccines against Neisseria meningitidis (the meningococcus) over the 30-year period from the late-1980s to the late-2010s. Nucleotide sequence-based studies have been important in the fight against this aggressive pathogen largely because of its high genetic and antigenic diversity, properties that were only fully appreciated because of sequence-based studies. Five aspects will be considered, the use of sequence data to: (i) discover vaccine antigens; (ii) assess the diversity and distribution of vaccine antigens; (iii) determine the evolutionary and population biology of the organism and their implications for immunization; and (iv) develop molecular approaches to investigate pre- and post-vaccine pathogen populations to assess vaccine impact. One of the great advantages of nucleotide sequence data has been its scalability, which has meant that increasingly large data sets have been available, which has proved invaluable in the investigation of an organism as diverse and enigmatic as the meningococcus.

Diversity-Generating Machines: Genetics of Bacterial Sugar-Coating

Bacterial pathogens and commensals are surrounded by diverse surface polysaccharides which include capsules and lipopolysaccharides. These carbohydrates play a vital role in bacterial ecology and interactions with the environment. Here, we review recent rapid advancements in this field, which have improved our understanding of the roles, structures, and genetics of bacterial polysaccharide antigens. Genetic loci encoding the biosynthesis of these antigens may have evolved as bacterial diversity-generating machines, driven by selection from a variety of forces, including host immunity, bacteriophages, and cell-cell interactions. We argue that the high adaptive potential of polysaccharide antigens should be taken into account in the design of polysaccharide-targeting medical interventions like conjugate vaccines and phage-based therapies.

A Three Component Synthetic Vaccine Containing a β-Mannan T-Cell Peptide Epitope and a β-Glucan Dendritic Cell Ligand

Glycoconjugates prepared from the capsular polysaccharide of several pathogenic bacteria and carrier proteins, such as CRM 197 or tetanus toxoid, have been one of the most successful public health measures to be implemented in the last quarter century. A crucial element in the success of conjugate vaccines has been the recruitment of T-cell help and systematic induction of a secondary immune response. The seminal discovery, that degraded polysaccharide fragments with attached peptide are presented to the T-cell receptor of carbohydrate specific T-cells by MHC-II molecules that bind to the peptide component of degraded vaccine, suggests potentially novel designs for conjugate vaccines. A fully synthetic conjugate vaccine was constructed from a 1,2-linked β-mannose trisaccharide conjugated to a T-cell peptide, previously shown to afford protection against Candida albicans. This combined B- and T-cell epitope was synthesized with a C-terminal azidolysine residue for subsequent conjugation by click chemistry. Four copies of a β-1,3 linked hexaglucan dendritic cell epitope were conjugated to an asymmetric dendrimer bearing an alkyne terminated tether. Click chemistry of these two components created a conjugate vaccine that induced antibodies to all three epitopes of the fully synthetic construct.

Structure-based design of chimeric antigens for multivalent protein vaccines

There is an urgent need to develop vaccines against pathogenic bacteria. However, this is often hindered by antigenic diversity and difficulties encountered manufacturing membrane proteins. Here we show how to use structure-based design to develop chimeric antigens (ChAs) for subunit vaccines. ChAs are generated against serogroup B Neisseria meningitidis (MenB), the predominant cause of meningococcal disease in wealthy countries. MenB ChAs exploit factor H binding protein (fHbp) as a molecular scaffold to display the immunogenic VR2 epitope from the integral membrane protein PorA. Structural analyses demonstrate fHbp is correctly folded and the PorA VR2 epitope adopts an immunogenic conformation. In mice, immunisation with ChAs generates fHbp and PorA antibodies that recognise the antigens expressed by clinical MenB isolates; these antibody responses correlate with protection against meningococcal disease. Application of ChAs is therefore a potentially powerful approach to develop multivalent subunit vaccines, which can be tailored to circumvent pathogen diversity.

Factor H binding protein (fHbp) and PorA are components of experimental serogroup B N. meningitidis vaccines. Here the authors graft the VR2 loop of PorA onto an fHBp-based scaffold to demonstrate proof-of-principle of a chimeric antigen strategy and vaccination against meningococcal disease.

Effect of Vaccine-Elicited Antibodies on Colonization of Neisseria meningitidis Serogroup B and C Strains in a Human Bronchial Epithelial Cell Culture Model

Capsular polysaccharide-protein conjugate vaccines protect individuals from invasive disease and decrease carriage, which reduces spread of the organism in the population. In contrast, antibodies elicited by plain polysaccharide or protein antigen-based meningococcal (Men) vaccines have little or no effect on decreasing carriage. In this study, we investigated the mechanism by which vaccine-induced human immunoglobulin G (IgG) antibodies affect colonization by meningococcal serogroup B (MenB) or C (MenC) strains using a human bronchial epithelial cell culture model (16HBE14o-). Fluorescence microscopy showed that bacteria colonizing the apical side of 16HBE14o- monolayers had decreased capsular polysaccharide on the bacterial surface that resulted from shedding the capsule and not decreased production of polysaccharide. Capsular polysaccharide shedding depended on the presence of 16HBE14o- cells and bacteria but not direct adherence of the bacteria to the cells. Treatment of bacteria and cells with postimmunization MenC-conjugate IgG or murine anti-MenB polysaccharide monoclonal antibodies (MAbs) inhibited capsule shedding, microcolony dispersal, and invasion of the 16HBE14o- cell monolayer. In contrast, the IgG responses elicited by immunization with MenC polysaccharide (PS), MenB outer membrane vesicle (OMV)-based, or factor H binding protein (FHbp)-based vaccines were not different than preimmune IgG or no-treatment response. The results provide new insights on the mechanism by which high-avidity anticapsular antibodies elicited by polysaccharide-conjugate vaccines affect meningococcal colonization. The data also suggest that any effect on colonization by IgG elicited by OMV- or FHbp-based vaccines may involve a different mechanism.

Seroprevalence of antibodies against serogroup C meningococci in the region of Valencia, Spain: Impact of meningococcal C conjugate vaccination

BACKGROUND AND AIMS

Meningococcal C conjugate (MCC) vaccination programs provide direct and indirect protection against meningococcal disease. However, a decrease in the antibodies could affect herd immunity. We conducted a seroprevalence study to assess the immunity in subjects 8-12years after different MCCV vaccination programs were launched and evaluated the impact of vaccination on seroprotection.

METHODS

Seroepidemiological study conducted from October 2010 to April 2012 in the region of Valencia, Spain. Sample size was not proportional to the population but to the expected seroprotection by age group. Sera from subjects that were≥3years old were tested using a standardized complement-mediated serum bactericidal antibodies (SBA) assay. Age-stratified proportions of subjects with SBA titers≥8 were considered seroprotected and evaluated. A multivariate logistic regression model was performed to evaluate the impact of vaccination on the seroprotection.

RESULTS

Serum samples from 1880 subjects were collected. In total, 523 (27.8%) of the 1880 subjects and 446 (31.2%) of the 1430 subjects<30years (targeted to any vaccination campaign) showed protective SBA titers. The highest percentage of seroprotected subjects (67.8%, 95%CI 56.9-77.4) was observed in those that were vaccinated in a catch-up campaign at 10-13years of age (20-21years old at the time of blood sampling). Those scheduled for immunization in infancy at 2, 4 and 6months of age (7-8years at blood sample) represented the lowest (7.1%, 95% CI 3.3-13.1) number of seroprotected subjects. Having received one vaccine dose after 12months of age was associated with increased seroprotection. The present study revealed a positive correlation between the increasing age at vaccination and longer duration of seroprotection.

CONCLUSION

Only one in three subjects who were vaccinated with MCC vaccine was seroprotected after 8-12years. These findings emphasize that seroprevalence studies are essential to identify susceptible cohorts and to inform vaccine policy.

Applying Central Composite Design and Response Surface Methodology to Optimize Growth and Biomass Production of Haemophilus influenzae Type b

Background

Haemophilus influenzae type b (Hib) is the leading cause of bacterial meningitis, otitis media, pneumonia, cellulitis, bacteremia, and septic arthritis in infants and young children. The Hib capsule contains the major virulence factor, and is composed of polyribosyl ribitol phosphate (PRP) that can induce immune system response. Vaccines consisting of Hib capsular polysaccharide (PRP) conjugated to a carrier protein are effective in the prevention of the infections. However, due to costly processes in PRP production, these vaccines are too expensive.

Objectives

To enhance biomass, in this research we focused on optimizing Hib growth with respect to physical factors such as pH, temperature, and agitation by using a response surface methodology (RSM).

Materials and Methods

We employed a central composite design (CCD) and a response surface methodology to determine the optimum cultivation conditions for growth and biomass production of H. influenzae type b. The treatment factors investigated were initial pH, agitation, and temperature, using shaking flasks. After Hib cultivation and determination of dry biomass, analysis of experimental data was performed by the RSM-CCD.

Results

The model showed that temperature and pH had an interactive effect on Hib biomass production. The dry biomass produced in shaking flasks was about 5470 mg/L, which was under an initial pH of 8.5, at 250 rpm and 35° C.

Conclusions

We found CCD and RSM very effective in optimizing Hib culture conditions, and Hib biomass production was greatly influenced by pH and incubation temperature. Therefore, optimization of the growth factors to maximize Hib production can lead to 1) an increase in bacterial biomass and PRP productions, 2) lower vaccine prices, 3) vaccination of more susceptible populations, and 4) lower risk of Hib infections.

Higher Tetanus Toxoid Immunity 2 Years After PsA-TT Introduction in Mali

Background. In 2010, mass vaccination with a then-new meningococcal A polysaccharide–tetanus toxoid protein conjugate vaccine (PsA-TT, or MenAfriVac) was undertaken in 1- to 29-year-olds in Bamako, Mali. Whether vaccination with PsA-TT effectively boosts tetanus immunity in a population with heterogeneous baseline tetanus immunity is not known. We assessed the impact of PsA-TT on tetanus toxoid (TT) immunity by quantifying age- and sex-specific immunity prior to and 2 years after introduction.

Methods. Using a household-based, age-stratified design, we randomly selected participants for a prevaccination serological survey in 2010 and a postvaccination survey in 2012. TT immunoglobulin G (IgG) antibodies were quantified and geometric mean concentrations (GMCs) pre- and postvaccination among all age groups targeted for vaccination were compared. The probability of TT IgG levels ≥0.1 IU/mL (indicating short-term protection) and ≥1.0 IU/mL (indicating long-term protection) by age and sex was determined using logistic regression models.

Results. Analysis of 793 prevaccination and 800 postvaccination sera indicated that while GMCs were low pre–PsA-TT, significantly higher GMCs in all age–sex strata were observed 2 years after PsA-TT introduction. The percentage with short-term immunity increased from 57.1% to 88.4% (31.3-point increase; 95% confidence interval [CI], 26.6–36.0;, P < .0001) and with long-term immunity increased from 20.0% to 58.5% (38.5-point increase; 95% CI, 33.7–43.3; P < .0001) pre- and postvaccination.

Conclusions. Significantly higher TT immunity was observed among vaccine-targeted age groups up to 2 years after Mali's PsA-TT mass vaccination campaign. Our results, combined with evidence from clinical trials, strongly suggest that conjugate vaccines containing TT such as PsA-TT should be considered bivalent vaccines because of their ability to boost tetanus immunity.

Temporal Changes in BEXSERO® Antigen Sequence Type Associated with Genetic Lineages of Neisseria meningitidis over a 15-Year Period in Western Australia

Neisseria meningitidis is the causative agent of invasive meningococcal disease (IMD). The BEXSERO^® vaccine which is used to prevent serogroup B disease is composed of four sub-capsular protein antigens supplemented with an outer membrane vesicle. Since the sub-capsular protein antigens are variably expressed and antigenically variable amongst meningococcal isolates, vaccine coverage can be estimated by the meningococcal antigen typing system (MATS) which measures the propensity of the strain to be killed by vaccinated sera. Whole genome sequencing (WGS) which identifies the alleles of the antigens that may be recognised by the antibody response could represent, in future, an alternative estimate of coverage. In this study, WGS of 278 meningococcal isolates responsible for 62% of IMD in Western Australia from 2000–2014 were analysed for association of genetic lineage (sequence type [ST], clonal complex [cc]) with BEXSERO^® antigen sequence type (BAST) and MATS to predict the annual vaccine coverage. A hyper-endemic period of IMD between 2000–05 was caused by cc41/44 with the major sequence type of ST-146 which was not predicted by MATS or BAST to be covered by the vaccine. An increase in serogroup diversity was observed between 2010–14 with the emergence of cc11 serogroup W in the adolescent population and cc23 serogroup Y in the elderly. BASTs were statistically associated with clonal complex although individual antigens underwent antigenic drift from the major type. BAST and MATS predicted an annual range of 44–91% vaccine coverage. Periods of low vaccine coverage in years post-2005 were not a result of the resurgence of cc41/44:ST-146 but were characterised by increased diversity of clonal complexes expressing BASTs which were not predicted by MATS to be covered by the vaccine. The driving force behind the diversity of the clonal complex and BAST during these periods of low vaccine coverage is unknown, but could be due to immune selection and inter-strain competition with carriage of non-disease causing meningococci.

Hajj vaccinations-facts, challenges, and hope

Vaccination is an effective preventive measure that has been used in the unique Hajj pilgrimage setting to control the transmission of infectious diseases. The current vaccination policy applied during Hajj is reviewed herein, highlighting the effectiveness of the approaches applied and identifying research gaps that need to be filled in order to improve the development and dissemination of Hajj vaccination strategies.

Genetic and Molecular Basis of Kingella kingae Encapsulation

Kingella kingae is a common cause of invasive disease in young children and was recently found to produce a polysaccharide capsule containing N-acetylgalactosamine (GalNAc) and β-3-deoxy-d-manno-octulosonic acid (βKdo). Given the role of capsules as important virulence factors and effective vaccine antigens, we set out to determine the genetic determinants of K. kingae encapsulation. Using a transposon library and a screen for nonencapsulated mutants, we identified the previously identified ctrABCD (ABC transporter) operon, a lipA (kpsC)-like gene, a lipB (kpsS)-like gene, and a putative glycosyltransferase gene designated csaA (capsule synthesis type a gene A). These genes were found to be present at unlinked locations scattered throughout the genome, an atypical genetic arrangement for Gram-negative bacteria that elaborate a capsule dependent on an ABC-type transporter for surface localization. The csaA gene product contains a predicted glycosyltransferase domain with structural homology to GalNAc transferases and a predicted capsule synthesis domain with structural homology to Kdo transferases, raising the possibility that this enzyme is responsible for alternately linking GalNAc to βKdo and βKdo to GalNAc. Consistent with this conclusion, mutation of the DXD motif in the GalNAc transferase domain and of the HP motif in the Kdo transferase domain resulted in a loss of encapsulation. Examination of intracellular and surface-associated capsule in deletion mutants and complemented strains further implicated the lipA (kpsC)-like gene, the lipB (kpsS)-like gene, and the csaA gene in K. kingae capsule production. These data define the genetic requirements for encapsulation in K. kingae and demonstrate an atypical organization of capsule synthesis, assembly, and export genes.

A Synthetic Disaccharide Analogue from Neisseria meningitidis A Capsular Polysaccharide Stimulates Immune Cell Responses and Induces Immunoglobulin G (IgG) Production in Mice When Protein-Conjugated

Some new phosphonoester-linked oligomers, stabilized analogues of the corresponding phosphate-bridged oligomers of Neisseria meningitidis A (MenA) capsular polysaccharide (CPS), were conjugated to human serum albumin (HSA), as a protein carrier model, and studied for immunological activities. We determined (i) in vitro, their biocompatibility (CAM test) and activity in inducing both T cell proliferation (CFSE method) and IL-2 release (ELISA), and (ii) in vivo, their ability to stimulate specific IgG antibody production (ELISA). All HSA-conjugated compounds induce T cell proliferation (40% of proliferation at 10(2) μM), whereas only the phosphonodisaccharide was effective (28% of proliferation at 10(2) μM) among the unconjugated forms. IL-2 release confirmed these results. In addition, the HSA-conjugated showed in vivo the capacity of eliciting the production of specific IgG antibodies. In conclusion, we obtained novel biocompatible, water-stable, and immunoactive MenA CPS analogues. A short disaccharide fragment showed the unusual behavior of triggering T cell proliferation in vitro.

Epidemiological and Molecular Characterization of Invasive Meningococcal Disease in Italy, 2008/09-2012/13

BACKGROUND

Following the introduction of meningococcal serogroup C conjugate vaccine in Italy in 2005, changes in the epidemiology of Invasive Meningococcal Disease (IMD) were expected. The study aims were to describe the epidemiological trend and to characterize the isolates collected during the period 2008/09-2012/13 by multilocus sequence typing (MLST). Data on laboratory confirmed meningococcal diseases from National Surveillance System of IMD were reported.

METHODS

Poisson regression models were used to estimate the incidence rate over time. Serogrouping and MLST were performed following published methods.

RESULTS

The incidence rate of laboratory confirmed meningococcal disease decreased from 0.33 per 100,000 population in 2008/09 to 0.25 per 100,000 population in 2012/13. The serogroup B incidence rate was significantly higher (p<0.01) than that of other serogroups, among all age groups. The significant decrease of the IMD incidence rate (p = 0.01) reflects the decrease of serogroup B and C, in particular among individuals aged 15-24 years old (p<0.01). On the other hand, serogroup Y incidence increased during the period (from 0.01/100,000 in 2008/09 to 0.02/100,000 in 2012/13, p = 0.05). Molecular characterizations revealed that ST-41/44 cc and ST-11 cc were the main clonal complexes identified among serogroup B and C isolates, respectively. In particular, ST-41/44 cc was predominant in all age groups, whereas ST-11 cc was not identified in infants less than 1 year of age.

CONCLUSIONS

IMD incidence declined in Italy and serogroup B caused most of the IMD cases, with infants having the highest risk of disease. Continued surveillance is needed to provide information concerning further changes in circulating meningococci with special regard to serogroup distribution. Moreover, knowledge of meningococcal genotypes is essential to detect hyper-invasive strains.

Host-pathogen interaction during bacterial vaccination

Vaccines have been developed and deployed against several important bacterial pathogens of humans, including Neisseria meningitidis, Bordetella pertussis, Streptococcus pneumoniae and Mycobacterium tuberculosis. These vaccines are generally considered a successful public health measure and are effective at controlling disease symptoms and/or burden. However, a troubling consequence of recent vaccination programs has been the selection of vaccine escape mutants, whereby the pathogen displays a different repertoire of immune targets than those represented in the vaccine formulation. To address these issues of antigenic variation and bacterial evolution, continued and sustained efforts in epidemiological surveillance, vaccine development/formulation research, and understanding of the host-pathogen interaction are required.

Review of meningococcal vaccines with updates on immunization in adults

Meningococcal disease is a serious and global life-threatening disease. Six serogroups (A, B, C, W-135, X, and Y) account for the majority of meningococcal disease worldwide. Meningococcal polysaccharide vaccines were introduced several decades ago and have led to the decline in the burden of disease. However, polysaccharide vaccines have several limitations, including poor immunogenicity in infants and toddlers, short-lived protection, lack of immunologic memory, negligible impact on nasopharyngeal carriage, and presence of hyporesponsiveness after repeated doses. The chemical conjugation of plain polysaccharide vaccines has the potential to overcome these drawbacks. Meningococcal conjugate vaccines include the quadrivalent vaccines (MenACWY-DT, MenACWY-CRM, and MenACWY-TT) as well as the monovalent A and C vaccines. These conjugate vaccines were shown to elicit strong immune response in adults. This review addresses the various aspects of meningococcal disease, the limitations posed by polysaccharide vaccines, the different conjugate vaccines with their immunogenicity and reactogenicity in adults, and the current recommendations in adults.

Towards the endgame and beyond: complexities and challenges for the elimination of infectious diseases

Successful control measures have interrupted the local transmission of human infectious diseases such as measles, malaria and polio, and saved and improved billions of lives. Similarly, control efforts have massively reduced the incidence of many infectious diseases of animals, such as rabies and rinderpest, with positive benefits for human health and livelihoods across the globe. However, disease elimination has proven an elusive goal, with only one human and one animal pathogen globally eradicated. As elimination targets expand to regional and even global levels, hurdles may emerge within the endgame when infections are circulating at very low levels, turning the last mile of these public health marathons into the longest mile. In this theme issue, we bring together recurring challenges that emerge as we move towards elimination, highlighting the unanticipated consequences of particular ecologies and pathologies of infection, and approaches to their management.