Preclinical evidence for the potential of a bivalent fHBP vaccine to prevent Neisseria meningitidis Serogroup C Disease

Vertebrate and Invertebrate Animal and New In Vitro Models for Studying Neisseria Biology

The history of Neisseria research has involved the use of a wide variety of vertebrate and invertebrate animal models, from insects to humans. In this review, we itemise these models and describe how they have made significant contributions to understanding the pathophysiology of Neisseria infections and to the development and testing of vaccines and antimicrobials. We also look ahead, briefly, to their potential replacement by complex in vitro cellular models.

Translating meningococcal serogroup B vaccines for healthcare professionals

INTRODUCTION

Vaccination is an effective strategy to combat invasive meningococcal disease (IMD). Vaccines against the major disease-causing meningococcal serogroups are available; however, development of vaccines against serogroup B faced particular challenges, including the inability to target traditional meningococcal antigens (i.e. polysaccharide capsule) and limited alternative antigens due to serogroup B strain diversity. Two different recombinant, protein-based, serogroup B (MenB) vaccines that may address these challenges are currently available. These vaccines have been extensively evaluated in pre-licensure safety and immunogenicity trials, and recently in real-world studies on effectiveness, safety, and impact on disease burden.

AREAS COVERED

This review provides healthcare professionals, particularly pediatricians, an overview of currently available MenB vaccines, including development strategies and evaluation of coverage.

EXPERT OPINION

Overall, recombinant MenB vaccines are valuable tools for healthcare professionals to protect patients against IMD. Their development required innovative design approaches that overcame challenging hurdles and identified novel protein antigen targets; however, important distinctions in the approaches used in their development, evaluation, and administration exist and many unanswered questions remain. Healthcare providers frequently prescribing MenB vaccines are challenged to keep abreast of these differences to ensure patient protection against this serious disease.

4CMenB Immunization Induces Serum Bactericidal Antibodies Against Non-Serogroup B Meningococcal Strains in Adolescents

Introduction

Invasive meningococcal disease (IMD) is an important public health concern. In developed countries, most IMD is caused by meningococcal serogroup B (MenB) and two protein-based MenB vaccines are currently available: the four-component vaccine 4CMenB (Bexsero, GSK) and the bivalent vaccine MenB-FHbp (Trumenba, Pfizer). Genes encoding the 4CMenB vaccine antigens are also present in strains belonging to other meningococcal serogroups.

Methods

To evaluate the potential of 4CMenB vaccination to protect adolescents against non-MenB IMD, we tested the bactericidal activity of sera from immunized adolescents on 147 (127 European and 20 Brazilian) non-MenB IMD isolates, with a serum bactericidal antibody assay using human complement (hSBA). Serum pools were prepared using samples from randomly selected participants in various clinical trials, pre- and post-vaccination: 12 adolescents who received two doses of 4CMenB 2 months apart, and 10 adolescents who received a single dose of a MenACWY conjugate vaccine (as positive control).

Results

4CMenB pre-immune sera killed 7.5% of the 147 non-MenB isolates at hSBA titers ≥ 1:4. In total, 91 (61.9%) tested isolates were killed by post-dose 2 pooled sera at hSBA titers ≥ 1:4, corresponding to 44/80 (55.0%) MenC, 26/35 (74.3%) MenW, and 21/32 (65.6%) MenY isolates killed.

Conclusion

4CMenB vaccination in adolescents induces bactericidal killing of non-MenB isolates, suggesting that mass vaccination could impact IMD due to serogroups other than MenB.

WGS analysis of a penicillin-resistant Neisseria meningitidis strain containing a chromosomal ROB-1 β-lactamase gene

Objectives

Neisseria meningitidis is rarely penicillin resistant. We describe WGS analysis of a penicillin-resistant N. meningitidis collected from a case of invasive meningococcal disease.

Methods

Serogrouping, serotyping and serosubtyping were performed with specific antibodies. β-Lactamase was detected by nitrocefin. MICs were determined by Etest and agar dilution. Sequencing of N. meningitidis genomes was done on the Illumina MiSeq platform and genome data were analysed using the Bacterial Isolate Genome Sequence Database (BIGSdb) on the PubMLST Neisseria website (https://pubmlst.org/neisseria/). Transformation was used to confirm the genetic basis of the penicillin resistance.

Results

An N. meningitidis blood isolate from a female patient in her mid-50s with a painful and septic left shoulder was found to have penicillin MIC values of 3–12 mg/L. The isolate was typed as Y: 14, 19: P1.– and ST3587, and was weakly β-lactamase positive. WGS analysis identified a full-length copy of the β-lactamase gene bla_ROB-1, which was contained on a 1719 bp insert with a G + C content of 41.7% (versus a G + C content of N. meningitidis of 51.7%), suggesting that the bla_ROB-1 gene came from a different bacterial species. A GenBank analysis of the bla_ROB-1 gene insert found 99.77% identity with a DNA segment found in plasmid pB1000′ from Haemophilus influenzae. Transformation of a penicillin-susceptible strain with the bla_ROB-1 gene conferred β-lactamase activity and penicillin resistance.

Conclusions

N. meningitidis serogroup Y, ST3587 can carry and express the bla_ROB-1 gene, leading to penicillin resistance. It is highly likely that the N. meningitidis isolate acquired the bla_ROB-1 gene from H. influenzae.

Incidence and Prevention of Invasive Meningococcal Disease in Global Mass Gathering Events

INTRODUCTION

Mass gathering events involve close contact among large numbers of people in a specific location at the same time, an environment conducive to transmission of respiratory tract illnesses including invasive meningococcal disease (IMD). This report describes IMD incidence at mass gatherings over the past 10 years and discusses strategies to prevent IMD at such events.

METHODS

A PubMed search was conducted in December 2018 using a search string intended to identify articles describing IMD at mass gatherings, including religious pilgrimages, sports events, jamborees, and refugee camps. The search was limited to articles in English published from 2008 to 2018. Articles were included if they described IMD incidence at a mass gathering event.

RESULTS

A total of 127 articles were retrieved, of which 7 reported on IMD incidence at mass gatherings in the past 10 years. Specifically, in Saudi Arabia between 2002 and 2011, IMD occurred in 16 Hajj pilgrims and 1 Umrah pilgrim; serotypes involved were not reported. At a youth sports festival in Spain in 2008, 1 case of serogroup B IMD was reported among 1500 attendees. At the 2015 World Scout Jamboree in Japan, an outbreak of serogroup W IMD was identified in five scouts and one parent. At a refugee camp in Turkey, one case of serogroup B IMD was reported in a Syrian girl; four cases of serogroup X IMD occurred in an Italian refugee camp among refugees from Africa and Bangladesh. In 2017, a funeral in Liberia resulted in 13 identified cases of serogroup C IMD. Requiring meningococcal vaccination for mass gathering attendees and vaccinating refugees might have prevented these IMD cases.

CONCLUSIONS

Mass gathering events increase IMD risk among attendees and their close contacts. Vaccines preventing IMD caused by serogroups ACWY and B are available and should be recommended for mass gathering attendees.

FUNDING

Pfizer.

Distribution of Neisseria meningitidis serogroup b (NmB) vaccine antigens in meningococcal disease causing isolates in the United States during 2009-2014, prior to NmB vaccine licensure

OBJECTIVES

Two Neisseria meningitidis serogroup B (NmB) vaccines are licensed in the United States. To estimate their potential coverage, we examined the vaccine antigen diversity among meningococcal isolates prior to vaccine licensure.

METHODS

NmB vaccine antigen genes of invasive isolates collected in the U.S. from 2009 to 2014 were characterized by Sanger or whole-genome sequencing.

RESULTS

During 2009-2014, the predominant antigen types have remained similar to those reported in 2000-2008 for NmB and 2006-2008 for NmC, NmY, with the emergence of a few new types. FHbp of subfamily B or variant 1 (B/v1) remained prevalent among NmB whereas FHbp of subfamily A or variant 2 and 3 (A/v2-3) were more prevalent among non-NmB. FHbp peptide 1 (B24/1.1) remains the most prevalent type in NmB. Full-length NadA peptide was detected in 26% of isolates, primarily in NmB and NmW. The greatest diversity of NhbA peptides was detected among NmB, with p0005 as the most prevalent type.

CONCLUSIONS

The prevalence and diversity of the NmB vaccine antigens have remained stable with common antigen types persisting over time. The data collected prior to NmB vaccine licensure provide the baseline to understand the potential impact of NmB vaccines on antigen diversity and strain coverage.

MenB-FHbp Meningococcal Group B Vaccine (Trumenba®): A Review in Active Immunization in Individuals Aged ≥ 10 Years

MenB-FHbp (bivalent rLP2086; Trumenba^®) is a recombinant protein-based vaccine targeting Neisseria meningitidis serogroup B (MenB), which has recently been licensed in the EU for active immunization to prevent invasive disease caused by MenB in individuals ≥ 10 years of age. The vaccine, which contains a variant from each of the two identified subfamilies of the meningococcal surface protein factor H-binding protein (fHBP), has been licensed in the USA for active immunization in individuals 10-25 years of age since 2014. This article reviews the immunogenicity, reactogenicity and tolerability of MenB-FHbp, with a focus on the EU label and the European setting. As demonstrated in an extensive program of clinical trials in adolescents and young adults, a two-dose or three-dose series of MenB-FHbp elicits a strong immune response against a range of MenB test strains selected to be representative of strains prevalent in Europe and the USA. Follow-up studies investigating the persistence of the MenB-FHbp immune response and the effect of a booster dose of the vaccine indicate that a booster dose should be considered (following a primary vaccine series) in individuals at continued risk of invasive meningococcal disease. MenB-FHbp vaccine appears to be moderately reactogenic but, overall, is generally well tolerated, with most adverse reactions being mild to moderate in severity. Although post-marketing, population-based data will be required to establish the true effectiveness of the vaccine, currently available data indicate that MenB-FHbp, in a two-dose or three-dose series, is likely to provide broad protection against MenB strains circulating in Europe.

Bacterial Vaccine Antigen Discovery in the Reverse Vaccinology 2.0 Era: Progress and Challenges

The ongoing, and very serious, threat from antimicrobial resistance necessitates the development and use of preventative measures, predominantly vaccination. Polysaccharide-based vaccines have provided a degree of success in limiting morbidity from disseminated bacterial infections, including those caused by the major human obligate pathogens, Neisseria meningitidis, and Streptococcus pneumoniae. Limitations of these polysaccharide vaccines, such as partial coverage and induced escape leading to persistence of disease, provide a compelling argument for the development of protein vaccines. In this review, we briefly chronicle approaches that have yielded licensed vaccines before highlighting reverse vaccinology 2.0 and its potential application in the discovery of novel bacterial protein vaccine candidates. Technical challenges and research gaps are also discussed.

Clinical data supporting a 2-dose schedule of MenB-FHbp, a bivalent meningococcal serogroup B vaccine, in adolescents and young adults

Invasive meningococcal disease (IMD) caused by Neisseria meningitidis is a potentially devastating condition that can result in death and is associated with serious long-term sequelae in survivors. Vaccination is the preferred preventative strategy. Quadrivalent polysaccharide-based vaccines that protect against infection caused by meningococcal serogroups A, C, W, and Y are not effective against meningococcal serogroup B (MenB), which was responsible for approximately 60% and 35% of confirmed IMD cases in the European Union and the United States in 2016, respectively. A recombinant protein MenB vaccine (MenB-FHbp [bivalent rLP2086; Trumenba®]) has been approved for protection against MenB infection in persons 10-25 years of age in the United States and Canada and for individuals ≥10 years of age in the European Union and Australia. In these regions, MenB-FHbp is approved as a 2- or 3-dose primary vaccination schedule. This report will review the current evidence supporting administration of MenB-FHbp as a 2-dose primary vaccination schedule. Different contexts in which a 2- or 3-dose primary vaccination schedule might be preferred (eg, routine prospective vaccination vs outbreak control) are reviewed.

The next chapter for group B meningococcal vaccines

The majority of invasive meningococcal disease (IMD) in the developed world is caused by capsular group B Neisseria meningitidis, however success with vaccination against organisms bearing this capsule has previously been restricted to control of geographically limited clonal outbreaks. As we enter a new era, with the first routine program underway to control endemic group B meningococcal disease for infants in the UK, it is timely to review the key landmarks in group B vaccine development, and discuss the issues determining whether control of endemic group B disease will be achieved. Evidence of a reduction in carriage acquisition of invasive group B meningococcal strains, after vaccination among adolescents, is imperative if routine immunization is to drive population control of disease beyond those who are vaccinated (i.e. through herd immunity). The need for multiple doses to generate a sufficiently protective response and reactogenicity remain significant problems with the new generation of vaccines. Despite these limitations, early data from the UK indicate that new group B meningococcal vaccines have the potential to have a major impact on meningococcal disease, and to provide new insight into how we might do better in the future.

Prevalence of factor H Binding Protein sub-variants among Neisseria meningitidis in China

OBJECTIVE

To study the prevalence of the fHbp genes in Neisseria meningitidis (N. meningitidis) isolates for further evaluation and development of serogroup B meningococcal vaccines in China.

METHODS

A panel of 1012 N. meningitidis strains was selected from the national culture collection from 1956 to 2016, according to the years of isolation, locations, and strain sources. These were tested by FHbp variant typing. Multi-locus sequence typing (MLST) was performed on 822 of these samples, including 242 strains from clinical strains and 580 carrier-derived strains. Analysis based on sequence types, serogroups, and FHbp variations were used to summarize the prevalence and characteristics of N. meningitidis.

RESULTS

There were 8 serogroups of N. meningitidis as well as a collection of nongroupable strains in this study. 1008 of 1012 N. meningitidis strains tested were positive for the fHbp gene. Serogroup A N. meningitidis (MenA) strains belonging to ST-1 and ST-5 clonal complexes harbored genes only encoding variant 1 (v1) FHbp. All MenW strains encoded v2 FHbp. 61.9% of clinical MenB strains were positive for v2 FHbp vs. 32.1% that were positive for v1. Among fHbp-positive carrier-derived MenB strains, v2 FHbp accounted for 90.8%. 79.7% of clinical MenC strains were positive for v1 FHbp and 20.3% were positive for v2 FHbp. Among carrier-derived MenC strains, v2 FHbp predominated. The number of major serogroups of N. meningitidis analyzed by MLST was 822, and the encoded FHbp showed CC- or ST-specific characteristics.

CONCLUSION

fHbp genes were detected in almost all N. meningitidis strains in this study. Therefore, it is possible that a vaccine against MenB or meningococci irrespective of serogroups, which includes FHbp, could be developed. Meningococcal vaccine development for China is a complex issue and these findings warrant further attention with respect to vaccine development.

Bivalent rLP2086 Vaccine (Trumenba(®)): A Review in Active Immunization Against Invasive Meningococcal Group B Disease in Individuals Aged 10-25 Years

Bivalent rLP2086 vaccine (Trumenba(®)) [hereafter referred to as rLP2086] is a Neisseria meningitidis serogroup B (MenB) vaccine recently licensed in the USA for active immunization to prevent invasive disease caused by MenB in individuals 10-25 years of age. rLP2086, which contains two variants of the meningococcal surface protein factor H-binding protein (fHBP), was approved by the FDA under the accelerated approval pathway after the immunogenicity of the vaccine was demonstrated in several phase II trials. This article reviews the immunogenicity and reactogenicity of rLP2086 as demonstrated in the trials with a focus on the US setting and on use of the vaccine as per FDA-approved labeling. rLP2086 is approved in the USA as a three-dose series administered in a 0-, 2-, and 6-month schedule. In the phase II trials, rLP2086 elicited a robust immune response against a panel of MenB test strains. A strong immune response was evident in a marked proportion of subjects after two vaccine doses, with a further increase after a third dose. The four primary test strains used were selected to be representative of MenB strains prevalent in the USA, with each expressing an fHBP variant heterologous to the vaccine antigens. rLP2086 was generally well tolerated in the trials, with most adverse reactions being mild to moderate in severity. Although some questions remain, including the duration of the protective response, rLP2086 vaccine has the potential to be a valuable tool for the prevention of invasive MenB disease.

How the Knowledge of Interactions between Meningococcus and the Human Immune System Has Been Used to Prepare Effective Neisseria meningitidis Vaccines

In the last decades, tremendous advancement in dissecting the mechanisms of pathogenicity of Neisseria meningitidis at a molecular level has been achieved, exploiting converging approaches of different disciplines, ranging from pathology to microbiology, immunology, and omics sciences (such as genomics and proteomics). Here, we review the molecular biology of the infectious agent and, in particular, its interactions with the immune system, focusing on both the innate and the adaptive responses. Meningococci exploit different mechanisms and complex machineries in order to subvert the immune system and to avoid being killed. Capsular polysaccharide and lipooligosaccharide glycan composition, in particular, play a major role in circumventing immune response. The understanding of these mechanisms has opened new horizons in the field of vaccinology. Nowadays different licensed meningococcal vaccines are available and used: conjugate meningococcal C vaccines, tetravalent conjugate vaccines, an affordable conjugate vaccine against the N. menigitidis serogroup A, and universal vaccines based on multiple antigens each one with a different and peculiar function against meningococcal group B strains.

Meningococcal Antigen Typing System Development and Application to the Evaluation of Effectiveness of Meningococcal B Vaccine and Possible Use for Other Purposes

Development of the 4-component meningococcal serogroup B vaccine (4CMenB) has required new assays for the reliable evaluation of the expression and cross-reactivity of those specific antigen variants that are predicted to be targeted by bactericidal antibodies elicited by the vaccine in different isolates. Existing laboratory techniques, such as multilocus sequence typing, are poorly suited to this purpose, since they do not provide information on the contribution of single vaccine components and therefore cannot be applied to estimate the potential coverage of the multicomponent vaccine. The hSBA, the only correlate of protection against invasive meningococcal disease accepted thus far, cannot conveniently be used to test large number of strains. To overcome these issues, the meningococcal antigen typing system (MATS) has been specifically developed in order to predict 4CMenB coverage of individual meningococcus serogroup B strains. To date, MATS has proved advantageous for several reasons, including its ability to assess both qualitative and quantitative aspects of surface antigens of single strains in a highly reproducible, rapid, and resource-saving manner, while its shortcomings include a possible underestimation of 4CMenB coverage and the use of pooled sera to calculate the positive bactericidal threshold. This paper provides an overview of MATS development and its field application.

Optimization of Molecular Approaches to Genogroup Neisseria meningitidis Carriage Isolates and Implications for Monitoring the Impact of New Serogroup B Vaccines

The reservoir for Neisseria meningitidis (Nm) is the human oropharynx. Implementation of Nm serogroup C (NmC) glycoconjugate vaccines directly reduced NmC carriage. Prophylactic vaccines are now available to prevent disease caused by the five major Nm disease causing serogroups (ABCWY). Nm serogroup B (NmB) vaccines are composed of antigens that are conserved across Nm serogroups and therefore have the potential to impact all Nm carriage. To assess the effect of these vaccines on carriage, standardized approaches to identify and group Nm are required. Real-time PCR (rt-PCR) capsule grouping assays that were internally controlled to confirm Nm species were developed for eight serogroups associated with carriage (A, B, C, E, W, X, Y and Z). The grouping scheme was validated using diverse bacterial species associated with carriage and then used to evaluate a collection of diverse Nm carriage isolates (n=234). A scheme that also included porA and ctrA probes was able to speciate the isolates, while ctrA also provided insights on the integrity of the polysaccharide loci. Isolates were typed for the Nm vaccine antigen factor H binding protein (fHbp), and were found to represent the known diversity of this antigen. The porA rt-PCR yielded positive results with all 234 of the Nm carriage isolates. Genogrouping assays classified 76.5% (179/234) of these isolates to a group, categorized 53 as nongenogroupable (NGG) and two as mixed results. Thirty seven NGG isolates evidenced a disrupted capsular polysaccharide operon judged by a ctrA negative result. Only 28.6% (67/234) of the isolates were serogrouped by slide agglutination (SASG), highlighting the reduced capability of carriage strains to express capsular polysaccharide. These rt-PCR assays provide a comprehensive means to identify and genogroup N. meningitidis in carriage studies used to guide vaccination strategies and to assess the impact of novel fHbp containing vaccines on meningococcal carriage.

Identification and therapeutic potential of a vitronectin binding region of meningococcal msf

The human pathogen Neisseria meningitides (Nm) attains serum resistance via a number of mechanisms, one of which involves binding to the host complement regulator protein vitronectin. We have shown previously that the Meningococcal surface fibril (Msf), a trimeric autotransporter, binds to the activated form of vitronectin (aVn) to increase Nm survival in human serum. In this study, we aimed to identify the aVn-binding region of Msf to assess its potential as an antigen which can elicit antibodies that block aVn binding and/or possess bactericidal properties. Using several recombinant Msf fragments spanning its surface-exposed region, the smallest aVn-binding recombinants were found to span residues 1-86 and 39-124. The use of further deletion constructs and overlapping recombinant Msf fragments suggested that a region of Msf comprising residues 39-82 may be primarily important for aVn binding and that other regions may also be involved but to a lesser extent. Molecular modelling implicated K66 and K68, conserved in all available Msf sequences, to be involved in the interaction. Recombinant fragments which bound to aVn were able to reduce the survival advantage conveyed by aVn-interaction in serum bactericidal assays. Antibodies raised against one such fragment inhibited aVn binding to Msf. In addition, the antibodies enhanced specific killing of Msf-expressing Nm in a dose-dependent manner. Overall, this study identifies an aVn-binding region of Msf, an adhesin known to impart serum resistance properties to the pathogen; and shows that this region of Msf can elicit antibodies with dual properties which reduce pathogen survival within the host and thus has potential as a vaccine antigen.

Role of factor H binding protein in Neisseria meningitidis virulence and its potential as a vaccine candidate to broadly protect against meningococcal disease

Neisseria meningitidis is a Gram-negative microorganism that exists exclusively in humans and can cause devastating invasive disease. Although capsular polysaccharide-based vaccines against serogroups A, C, Y, and W135 are widely available, the pathway to a broadly protective vaccine against serogroup B has been more complex. The last 11 years has seen the discovery and development of the N. meningitidis serogroup B (MnB) outer membrane protein factor H binding protein (fHBP) as a vaccine component. Since the initial discovery of fHBP, a tremendous amount of work has accumulated on the diversity, structure, and regulation of this important protein. fHBP has proved to be a virulence factor for N. meningitidis and a target for functional bactericidal antibodies. fHBP is critical for survival of meningococci in the human host, as it is responsible for the primary interaction with human factor H (fH). Binding of hfH by the meningococcus serves to downregulate the host alternative complement pathway and helps the organism evade host innate immunity. Preclinical studies have shown that an fHBP-based vaccine can elicit serum bactericidal antibodies capable of killing MnB, and the vaccine has shown very encouraging results in human clinical trials. This report reviews our current knowledge of fHBP. In particular, we discuss the recent advances in our understanding of fHBP, its importance to N. meningitidis, and its potential role as a vaccine for preventing MnB disease.

Neisseria meningitidis B vaccines: recent advances and possible immunization policies

Since the development of the first-generation vaccines based on outer membrane vesicles (OMV), which were able to contain strain-specific epidemics, but were not suitable for universal use, enormous steps forward in the prevention of Neisseria meningitidis B have been made. The first multicomponent vaccine, Bexsero(®), has recently been authorized for use; other vaccines, bivalent rLP2086 and next-generation OMV vaccines, are under development. The new vaccines may substantially contribute to reducing invasive bacterial infections as they could cover most Neisseria meningitidis B strains. Moreover, other potentially effective serogroup B vaccine candidates are being studied in preclinical settings. It is therefore appropriate to review what has recently been achieved in the prevention of disease caused by serogroup B.

New versus old meningococcal group B vaccines: how the new ones may benefit infants & toddlers

Invasive disease caused by Neisseria meningitidis is associated with high mortality and high disability rates and mainly affects children under one year of age. Vaccination is the best way to prevent meningococcal disease, especially in infants and toddlers. The introduction of massive meningococcal serogroup C vaccination has drastically reduced the incidence of disease caused by this serogroup, and serogroup B has now become the main causative agent in several industrialized countries. The first serogroup B vaccines, which were used for more than two decades, were based on outer membrane vesicles and proved to be protective only against specific epidemic strains in Cuba, Norway, Brazil and New Zealand. Moreover, these often elicited a scant immune response in young children. Innovative genomics-based reverse vaccinology subsequently enabled researchers to identify genes encoding for surface proteins that are able to elicit a strong immune response against several B strains. This important discovery led to the development and recent approval in Europe of the four-component meningococcal serogroup B (4CMenB) vaccine. Large clinical trials have shown high immunogenicity and tolerability and acceptable safety levels of 4CMenB in infants and toddlers. This vaccine is expected to cover a large number of circulating invasive strains and may also be efficacious against other serogroups. Young children are particularly vulnerable to the devastating consequences of meningococcal disease. Given the high performance of 4CMenB and its non-interference with routine vaccinations, this age-group will be the first to benefit from the introduction of this vaccine.

A multi-country evaluation of Neisseria meningitidis serogroup B factor H-binding proteins and implications for vaccine coverage in different age groups

BACKGROUND

Recombinant vaccines containing factor H-binding protein (fHBP) have been developed for the purpose of protection from invasive meningococcal serogroup B disease. Neisseria meningitidis fHBP sequences can be divided into 2 genetically and immunologically distinct subfamilies (A and B); thus, cross protection is conferred within but not between subfamilies. A comprehensive understanding of fHBP epidemiology is required to accurately assess the potential vaccine impact when considering different vaccination implementation strategies.

METHODS

Systematically collected invasive meningococcal serogroup B isolates from England, Wales, Northern Ireland, the United States, Norway, France and the Czech Republic were previously characterized for fHBP sequence. This study expanded the evaluation with additional meningococcal serogroup B disease isolates from Spain (n = 346) and Germany (n = 205). This expanded set (n = 1841), collected over a 6-year period (2001 to 2006), was evaluated for fHBP sequence and fHBP subfamily relative to patient age.

RESULTS

All 1841 isolates contained fhbp. fHBP sequences from Spain and Germany fell within the previously described subfamilies, with 69% of isolates belonging to subfamily B and 31% to subfamily A; prevalent sequence variants were also similar. Stratification of data by age indicated that disease in infants <1 year of age was caused by a significantly higher proportion of isolates with fHBP subfamily A variants than that seen in adolescents and young adults 11-25 years (47.7% versus 19.5%, P < 0.0001, respectively).

CONCLUSIONS

These observations highlight a difference in epidemiology of fHBP subfamilies in different age groups, with fHBP subfamily A strains causing more disease in vulnerable populations, such as infants, than in adolescents.

Conservation of meningococcal antigens in the genus Neisseria

Neisseria meningitidis, one of the major causes of bacterial meningitis and sepsis, is a member of the genus Neisseria, which includes species that colonize the mucosae of many animals. Three meningococcal proteins, factor H-binding protein (fHbp), neisserial heparin-binding antigen (NHBA), and N. meningitidis adhesin A (NadA), have been described as antigens protective against N. meningitidis of serogroup B, and they have been employed as vaccine components in preclinical and clinical studies. In the vaccine formulation, fHbp and NHBA were fused to the GNA2091 and GNA1030 proteins, respectively, to enhance protein stability and immunogenicity. To determine the possible impact of vaccination on commensal neisseriae, we determined the presence, distribution, and conservation of these antigens in the available genome sequences of the genus Neisseria, finding that fHbp, NHBA, and NadA were conserved only in species colonizing humans, while GNA1030 and GNA2091 were conserved in many human and nonhuman neisseriae. Sequence analysis showed that homologous recombination contributed to shape the evolution and distribution of both NHBA and fHbp, three major variants of which have been defined. fHbp variant 3 was probably the ancestral form of meningococcal fHbp, while fHbp variant 1 from N. cinerea was introduced into N. meningitidis by a recombination event. fHbp variant 2 was the result of a recombination event inserting a stretch of 483 bp from variant 1 into the variant 3 background. These data indicate that a high rate of exchange of genetic material between neisseriae that colonize the human upper respiratory tract exists.

The upper respiratory tract of healthy individuals is a complex ecosystem colonized by many bacterial species. Among these, there are representatives of the genus Neisseria, including Neisseria meningitidis, a major cause of bacterial meningitis and sepsis. Given the close relationship between commensal and pathogenic species, a protein-based vaccine against N. meningitidis has the potential to impact the other commensal species of Neisseria. For this reason, we have studied the distribution and evolutionary history of the antigen components of a recombinant vaccine, 4CMenB, that recently received approval in Europe under the commercial name of Bexsero®. We found that fHbp, NHBA, and NadA can be found in some of the human commensal species and that the evolution of these antigens has been essentially shaped by the high rate of genetic exchange that occurs between strains of neisseriae that cocolonize the same environment.

Prospects for eradication of meningococcal disease

Meningococcal meningitis and septicaemia remain a serious global health threat. This review focuses on the epidemiology of meningococcal disease following the recent implementation of effective vaccines and the potential utility of a vaccine against serogroup B meningococcus.

Design of meningococcal factor H binding protein mutant vaccines that do not bind human complement factor H

Meningococcal factor H binding protein (fHbp) is a human species-specific ligand for the complement regulator, factor H (fH). In recent studies, fHbp vaccines in which arginine at position 41 was replaced by serine (R41S) had impaired fH binding. The mutant vaccines elicited bactericidal responses in human fH transgenic mice superior to those elicited by control fHbp vaccines that bound human fH. Based on sequence similarity, fHbp has been classified into three variant groups. Here we report that although R41 is present in fHbp from variant groups 1 and 2, the R41S substitution eliminated fH binding only in variant group 1 proteins. To identify mutants in variant group 2 with impaired fH binding, we generated fHbp structural models and predicted 63 residues influencing fH binding. From these, we created 11 mutants with one or two amino acid substitutions in a variant group 2 protein and identified six that decreased fH binding. Three of these six mutants retained conformational epitopes recognized by all six anti-fHbp monoclonal antibodies (MAbs) tested and elicited serum complement-mediated bactericidal antibody titers in wild-type mice that were not significantly different from those obtained with the control vaccine. Thus, fHbp amino acid residues that affect human fH binding differ across variant groups. This result suggests that fHbp sequence variation induced by immune selection also affects fH binding motifs via coevolution. The three new fHbp mutants from variant group 2, which do not bind human fH, retained important epitopes for eliciting bactericidal antibodies and may be promising vaccine candidates.

Epidemiology and prevention of meningococcal disease: a critical appraisal of vaccine policies

Meningococcal disease is characterized by a marked variation in incidence and serogroup distribution by region and over time. In several European countries, Canada and Australia, immunization programs, including universal vaccination of infants or toddlers with catch-up campaigns in children and adolescents, aimed at controlling disease caused by meningococcal serogroup C have been successful in reducing disease incidence through direct and indirect protection. More recently, meningococcal conjugate vaccines targeting disease caused by serogroups A, C, W-135 and Y have been licensed and are being used in adolescent programs in the USA and Canada while a mass immunization campaign against serogroup A disease has been implemented in Africa. Positive results from clinical trials using vaccines against serogroup B disease in various age groups suggest the possibility of providing broader protection against serogroup B disease than is provided by the currently used outer membrane vesicle vaccines. The purpose of our review of meningococcal epidemiology and assessment of existing policies is to set the stage for future policy decisions. Vaccination policies to prevent meningococcal disease in different regions of the world should be based on quality information from enhanced surveillance systems.

Characterization of Neisseria meningitidis isolates that do not express the virulence factor and vaccine antigen factor H binding protein

Neisseria meningitidis remains a leading cause of bacterial sepsis and meningitis. Complement is a key component of natural immunity against this important human pathogen, which has evolved multiple mechanisms to evade complement-mediated lysis. One approach adopted by the meningococcus is to recruit a human negative regulator of the complement system, factor H (fH), to its surface via a lipoprotein, factor H binding protein (fHbp). Additionally, fHbp is a key antigen in vaccines currently being evaluated in clinical trials. Here we characterize strains of N. meningitidis from several distinct clonal complexes which do not express fHbp; all strains were recovered from patients with disseminated meningococcal disease. We demonstrate that these strains have either a frameshift mutation in the fHbp open reading frame or have entirely lost fHbp and some flanking sequences. No fH binding was detected to other ligands among the fHbp-negative strains. The implications of these findings for meningococcal pathogenesis and prevention are discussed.