Evaluation of De-O-acetylated meningococcal C polysaccharide-tetanus toxoid conjugate vaccine in infancy: reactogenicity, immunogenicity, immunologic priming, and bactericidal activity against O-acetylated and De-O-acetylated serogroup C strains

Development in the Concept of Bacterial Polysaccharide Repeating Unit-Based Antibacterial Conjugate Vaccines

The surface of cells is coated with a dense layer of glycans, known as the cell glycocalyx. The complex glycans in the glycocalyx are involved in various biological events, such as bacterial pathogenesis, protection of bacteria from environmental stresses, etc. Polysaccharides on the bacterial cell surface are highly conserved and accessible molecules, and thus they are excellent immunological targets. Consequently, bacterial polysaccharides and their repeating units have been extensively studied as antigens for the development of antibacterial vaccines. This Review surveys the recent developments in the synthetic and immunological investigations of bacterial polysaccharide repeating unit-based conjugate vaccines against several human pathogenic bacteria. The major challenges associated with the development of functional carbohydrate-based antibacterial conjugate vaccines are also considered.

Glycoconjugates: Synthesis, Functional Studies, and Therapeutic Developments

Glycoconjugates are major constituents of mammalian cells that are formed via covalent conjugation of carbohydrates to other biomolecules like proteins and lipids and often expressed on the cell surfaces. Among the three major classes of glycoconjugates, proteoglycans and glycoproteins contain glycans linked to the protein backbone via amino acid residues such as Asn for N-linked glycans and Ser/Thr for O-linked glycans. In glycolipids, glycans are linked to a lipid component such as glycerol, polyisoprenyl pyrophosphate, fatty acid ester, or sphingolipid. Recently, glycoconjugates have become better structurally defined and biosynthetically understood, especially those associated with human diseases, and are accessible to new drug, diagnostic, and therapeutic developments. This review describes the status and new advances in the biological study and therapeutic applications of natural and synthetic glycoconjugates, including proteoglycans, glycoproteins, and glycolipids. The scope, limitations, and novel methodologies in the synthesis and clinical development of glycoconjugates including vaccines, glyco-remodeled antibodies, glycan-based adjuvants, glycan-specific receptor-mediated drug delivery platforms, etc., and their future prospectus are discussed.

The Host-Pathogen Interactions and Epicellular Lifestyle of Neisseria meningitidis

Neisseria meningitidis is a gram-negative diplococcus and a transient commensal of the human nasopharynx. It shares and competes for this niche with a number of other Neisseria species including N. lactamica, N. cinerea and N. mucosa. Unlike these other members of the genus, N. meningitidis may become invasive, crossing the epithelium of the nasopharynx and entering the bloodstream, where it rapidly proliferates causing a syndrome known as Invasive Meningococcal Disease (IMD). IMD progresses rapidly to cause septic shock and meningitis and is often fatal despite aggressive antibiotic therapy. While many of the ways in which meningococci survive in the host environment have been well studied, recent insights into the interactions between N. meningitidis and the epithelial, serum, and endothelial environments have expanded our understanding of how IMD develops. This review seeks to incorporate recent work into the established model of pathogenesis. In particular, we focus on the competition that N. meningitidis faces in the nasopharynx from other Neisseria species, and how the genetic diversity of the meningococcus contributes to the wide range of inflammatory and pathogenic potentials observed among different lineages.

Preclinical development of the quadrivalent meningococcal (ACYW) tetanus toxoid conjugate vaccine, MenQuadfi®

Bacterial capsular polysaccharide vaccines are generally poorly immunogenic in infants and older adults. The immunogenicity of capsular polysaccharide vaccines can be improved by conjugating them to immunogenic carrier proteins. One of the most recently licensed conjugate vaccines is the quadrivalent meningococcal vaccine with serogroups A, C, Y, and W conjugated to a tetanus toxoid protein carrier (MenACYW-TT; MenQuadfi, Sanofi Pasteur, Swiftwater, PA, USA). MenACYW-TT was developed to induce optimal immune responses against each of the meningococcal serogroups A, C, W, and Y, and across all age groups, especially infants and older adults (those aged ≥ 50 years). Here, we detail the early iterative vaccine development approach taken, whereby many different ‘small-scale’ conjugate vaccine candidates were prepared and examined for immunogenicity in a mouse model to identify the most immunogenic vaccine. Additional insights from phase I clinical studies informed further optimization of the vaccine candidates by tailoring their conjugation parameter attributes for the optimal immune response in humans. The parameters studied included: different carrier proteins [PR]; polysaccharide [PS] sizes; conjugation chemistries [linker vs. no-linker; lattice vs. neoglycoprotein; activation/derivatization levels]; conjugate size; PS:PR loading ratio; percent free PS; percent free PR; and O-acetylation content. The lead quadrivalent conjugate vaccine (polysaccharides of > 50 kDa size conjugated to TT at a high PS:PR ratio via reductive amination for serogroups C, W and Y, and carbonyldiimidazole/adipic acid dihydrazide linker chemistry for serogroup A) empirically identified from the extensive preclinical studies, was ultimately confirmed by the robust antibody responses observed in all age groups in the various clinical studies, including in the most challenging infant and older adult age groups, and subsequently led to the licensed formulation.

Correlates of protection for meningococcal surface protein vaccines: lessons from the past

INTRODUCTION

Recombinant surface protein meningococcal serogroup B (MenB) vaccines are available but with different antigen compositions, leading to differences between vaccines in their immunogenicity and likely breadth of coverage. The serology and breadth of coverage assessment for MenB vaccines are multifaceted areas, and a comprehensive understanding of these complexities is required to appropriately compare licensed vaccines and those under development.

AREAS COVERED

In the first of two companion papers that comprehensively review the serology and breadth of coverage assessment for MenB vaccines, the history of early meningococcal vaccines is considered in this narrative review to identify transferable lessons applicable to the currently licensed MenB vaccines and those under development, as well as their serology.

EXPERT OPINION

Understanding correlates of protection and the breadth of coverage assessment for meningococcal surface protein vaccines is significantly more complex than that for capsular polysaccharide vaccines. Determination and understanding of the breadth of coverage of surface protein vaccines are clinically important and unique to each vaccine formulation. It is essential to estimate the proportion of MenB cases that are preventable by a specific vaccine to assess its overall potential impact and to compare the benefits and limitations of different vaccines in preventing invasive meningococcal disease.

Safety and immunogenicity of meningococcal (Groups A and C) polysaccharide vaccine in children 2 to 6 y of age in China: a randomized, active-controlled, non-inferiority study

Meningococcal serogroups A and C cause significant numbers of cases in China. The Sanofi Pasteur meningococcal polysaccharide A + C vaccine (Men-AC) was licensed in China in 1995. Immunogenicity and safety of a single dose of Men-AC against a similar marketed vaccine, the Lanzhou Institute serogroups A and C vaccine (Lanzhou-AC), were evaluated in children 2 to 6 y of age. Antibody titers were determined before and on Day 30 after vaccination using a serum bactericidal assay using baby rabbit complement (SBA-BR). Immunogenicity endpoints included rates of seroconversion (postvaccination antibody titers ≥4-fold higher) and seroprotection (postvaccination titers ≥1:8). Unsolicited systemic adverse events (AEs) within 30 minutes after vaccination, solicited injection site and systemic reactions between Days 0 and 7, unsolicited non-serious AEs within 30 d, and serious adverse events (SAEs) throughout were recorded. Seroconversion rates against serogroups A and C were 97.0% (95% confidence interval [CI], 94.5-98.6) and 94.7% (95% CI, 91.6-97.0), respectively, in the Men-AC group and 97.7% (95% CI, 95.4-99.1) and 94.8% (95% CI, 91.7-97.0), respectively, in the Lanzhou-AC group, while seroprotection rates were 98.0% (95% CI, 95.8-99.3) and 97.0% (95% CI, 94.5-98.6), respectively, in the Men-AC group and 99.0% (95% CI, 97.2-99.8) and 96.8% (95% CI, 94.1-98.4), respectively, in the Lanzhou-AC group. Non-inferiority of Men-AC with regard to immunogenicity was demonstrated since the lower bounds of the 95% CIs of the differences in rates between the two groups were > -5% for both serogroups. Both vaccines were well tolerated.

Synthetic carbohydrate-based vaccines: challenges and opportunities

Glycoconjugate vaccines based on bacterial capsular polysaccharides (CPS) have been extremely successful in preventing bacterial infections. The glycan antigens for the preparation of CPS based glycoconjugate vaccines are mainly obtained from bacterial fermentation, the quality and length of glycans are always inconsistent. Such kind of situation make the CMC of glycoconjugate vaccines are difficult to well control. Thanks to the advantage of synthetic methods for carbohydrates syntheses. The well controlled glycan antigens are more easily to obtain, and them are conjugated to carrier protein to from the so-call homogeneous fully synthetic glycoconjugate vaccines. Several fully glycoconjugate vaccines are in different phases of clinical trial for bacteria or cancers. The review will introduce the recent development of fully synthetic glycoconjugate vaccine.

Stability of Vaccines

Vaccines are considered the most economical and effective preventive measure against most deadly infectious diseases. Vaccines help protect around three million lives every year, but hundreds of thousands of lives are lost due to the instability of vaccines. This review discusses the various types of instability observed, while manufacturing, storing, and distributing vaccines. It describes the specific stability problems associated with each type of vaccine. This review also discusses the various measures adopted to overcome these instability problems. Vaccines are classified based on their components, and this review discusses how these preventive measures relate to each type of vaccine. This review also includes certain case studies that illustrate various approaches to improve vaccine stability. Last, this review provides insight on prospective methods for developing more stable vaccines.

Recent Advances in the Synthesis of Glycoconjugates for Vaccine Development

During the last decade there has been a growing interest in glycoimmunology, a relatively new research field dealing with the specific interactions of carbohydrates with the immune system. Pathogens’ cell surfaces are covered by a thick layer of oligo- and polysaccharides that are crucial virulence factors, as they mediate receptors binding on host cells for initial adhesion and organism invasion. Since in most cases these saccharide structures are uniquely exposed on the pathogen surface, they represent attractive targets for vaccine design. Polysaccharides isolated from cell walls of microorganisms and chemically conjugated to immunogenic proteins have been used as antigens for vaccine development for a range of infectious diseases. However, several challenges are associated with carbohydrate antigens purified from natural sources, such as their difficult characterization and heterogeneous composition. Consequently, glycoconjugates with chemically well-defined structures, that are able to confer highly reproducible biological properties and a better safety profile, are at the forefront of vaccine development. Following on from our previous review on the subject, in the present account we specifically focus on the most recent advances in the synthesis and preliminary immunological evaluation of next generation glycoconjugate vaccines designed to target bacterial and fungal infections that have been reported in the literature since 2011.

Spontaneous point mutations in the capsule synthesis locus leading to structural and functional changes of the capsule in serogroup A meningococcal populations

Whole genome sequencing analysis of 100 Neisseria meningitidis serogroup A isolates has revealed that the csaABCD-ctrABCD-ctrEF capsule polysaccharide synthesis locus represents a spontaneous point mutation hotspot. Structural and functional properties of the capsule of 11 carriage and two disease isolates with non-synonymous point mutations or stop codons in capsule synthesis genes were analyzed for their capsular polysaccharide expression, recognition by antibodies and sensitivity to bactericidal killing. Eight of eleven carriage isolates presenting capsule locus mutations expressed no or reduced amounts of capsule. One isolate with a stop codon in the O-acetyltransferase gene expressed non-O-acetylated polysaccharide, and was not recognized by anti-capsule antibodies. Capsule and O-acetylation deficient mutants were resistant to complement deposition and killing mediated by anti-capsular antibodies, but not by anti-lipopolysaccharide antibodies. Two capsule polymerase mutants, one carriage and one case isolate, showed capsule over-expression and increased resistance against bactericidal activity of both capsule- and lipopolysaccharide-specific antibodies. Meningococci have developed multiple strategies for changing capsule expression and structure, which is relevant both for colonization and virulence. Here we show that point mutations in the capsule synthesis genes substantially contribute to the repertoire of genetic mechanisms in natural populations leading to variability in capsule expression.

Meningococcal serogroup C immunogenicity, antibody persistence and memory B-cells induced by the monovalent meningococcal serogroup C versus quadrivalent meningococcal serogroup ACWY conjugate booster vaccine: A randomized controlled trial

BACKGROUND

Adolescents are considered the key transmitters of meningococci in the population. Meningococcal serogroup C (MenC) antibody levels wane rapidly after MenC conjugate vaccination in young children, leaving adolescents with low antibody levels. In this study, we compared MenC immune responses after booster vaccination in adolescence with either tetanus toxoid conjugated MenC (MenC-TT) or MenACWY (MenACWY-TT) vaccine, and aimed to establish an optimal age for this booster.

METHODS

Healthy 10-, 12-, and 15-year-olds, who received a single dose of MenC-TT vaccine in early childhood, were randomized to receive MenC-TT or MenACWY-TT vaccine. MenC serum bactericidal antibody (rSBA) titers, MenC polysaccharide (PS) specific IgG, IgG1 and IgG2 and MenC-specific IgG and IgA memory B-cells were determined before, one month and one year after the booster. Non-inferiority was tested by comparing geometric mean titers (GMTs) between vaccinees at one year.

RESULTS

Of 501 participants, 464 (92.6%) were included in the 'according to protocol' cohort analysis. At one month, all participants developed high MenC rSBA titers (>24,000 in all groups) and MenC-PS-specific IgG levels. Non-inferiority was not demonstrated one year after the booster with higher MenC GMTs after the monovalent vaccine, but 462/464 (99.6%) participants maintained protective MenC rSBA titers. IgG levels mainly consisted of IgG1, but similar levels of increase were observed for IgG1 and IgG2. Both vaccines induced a clear increase in the number of circulating MenC-PS specific IgG and IgA memory B-cells. Between one month and one year, the highest antibody decay rate was observed in the 10-year-olds.

CONCLUSION

Both MenC-TT and MenACWY-TT vaccines induced robust protective MenC immune responses after the booster vaccination, although non-inferiority could not be demonstrated for the MenACWY-TT vaccine after one year. Our results underline the importance of optimal timing of a meningococcal booster vaccination to protect against MenC disease in the long-term.

An Overview of Structural Features of Antibacterial Glycoconjugate Vaccines That Influence Their Immunogenicity

Bacterial cell-surface-derived or mimicked carbohydrate moieties that act as protective antigens are used in the development of antibacterial glycoconjugate vaccines. The carbohydrate antigen must have a minimum length or size to maintain the conformational structure of the antigenic epitope(s). The presence or absence of O-acetate, phosphate, glycerol phosphate and pyruvate ketal plays a vital role in defining the immunogenicity of the carbohydrate antigen. The nature of the carrier protein, spacer and conjugation pattern used to develop the glycoconjugate vaccine also defines its overall spatial orientation which in turn affects its avidity and selectivity of interaction with the desired target(s). In addition, the ratio of carbohydrate to protein in glycoconjugate vaccines also makes an important contribution in determining the optimum immunological response. This Review article presents the importance of these variables in the development of antibacterial glycoconjugate vaccines and their effects on immune efficacy.

Do Dose Numbers Matter?: Evaluation of Differing Infant and Toddler Meningococcal C Conjugate Vaccine Programs in Canadian Children

BACKGROUND

The diversity of Canadian infant meningococcal C conjugate (MenC) vaccine programs is unique among countries providing MenC vaccines and offers a valuable opportunity to determine the optimal vaccine program. This longitudinal study assessed differences in seroprotection by 3 different vaccine schedules in children two years after receiving either 1 toddler MenC vaccine dose (1 dose), 1 infant and 1 toddler dose (2 doses), or 2 infant and 1 toddler MenC vaccine dose (3 doses).

METHODS

Three similar cohorts of healthy infants from 1, 2 and 3 dose program areas were enrolled before to their 12 month toddler dose and vaccinated with MenC-tetanus toxoid (MenC-TT) conjugate vaccine. Sera obtained 2 years later were assayed for serogroup C bactericidal activity using standardized procedures with rabbit as the exogenous complement source. Serum bactericidal activity titers ≥1:8 were considered protective.

RESULTS

Results were available for 384 children. Rates of seroprotection at 36 months of age were significantly different between the 1 and 3 dose programs, but confidence intervals overlapped between the 1 and 2 dose programs and between the 2 and 3 dose programs: 1 dose 92% (95% confidence interval: 86%-96%) versus 99% (95%-100%) with 2 doses and 100% (97%-100%) with 3 doses. Geometric mean titers were significantly different at 12.1 (10.8-13.5), 32.4 (28.9-36.2) and 50.6 (45.7-55.9) in the 1, 2 and 3 dose programs, respectively.

CONCLUSIONS

At 36 months of age, evidence of seroprotection remained for greater than 90% of participants. Our results indicate that 1 toddler dose or 1 infant plus 1 toddler dose with MenC-TT vaccine provides seroprotection against MenC disease in early childhood.

Regulation of capsule in Neisseria meningitidis

Neisseria meningitidis, a devastating pathogen exclusive to humans, expresses capsular polysaccharides that are the major meningococcal virulence determinants and the basis for successful meningococcal vaccines. With rare exceptions, the expression of capsule (serogroups A, B, C, W, X, Y) is required for systemic invasive meningococcal disease. Changes in capsule expression or structure (e.g. hypo- or hyper-encapsulation, capsule "switching", acetylation) can influence immunologic diagnostic assays or lead to immune escape. The loss or down-regulation of capsule is also critical in meningococcal biology facilitating meningococcal attachment, microcolony formation and the carriage state at human mucosal surfaces. Encapsulated meningococci contain a cps locus with promoters located in an intergenic region between the biosynthesis and the conserved capsule transport operons. The cps intergenic region is transcriptionally regulated (and thus the amount of capsule expressed) by IS element insertion, by a two-component system, MisR/MisS and through sequence changes that result in post-transcriptional RNA thermoregulation. Reversible on-off phase variation of capsule expression is controlled by slipped strand mispairing of homo-polymeric tracts and by precise insertion and excision of IS elements (e.g. IS1301) in the biosynthesis operon. Capsule structure can be altered by phase-variable expression of capsular polymer modification enzymes or "switched" through transformation and homologous recombination of different polymerases. Understanding the complex regulation of meningococcal capsule has important implications for meningococcal biology, pathogenesis, diagnostics, current and future vaccine development and vaccine strategies.

Meningococcal disease epidemiology in Australia 10 years after implementation of a national conjugate meningococcal C immunization programme

Australia implemented conjugate meningococcal C immunization in 2003 with a single scheduled dose at age 12 months and catch-up for individuals aged 2–19 years. Several countries have recently added one or more booster doses to their programmes to maintain disease control. Australian disease surveillance and vaccine coverage data were used to assess longer term vaccine coverage and impact on invasive serogroup C disease incidence and mortality, and review vaccine failures. Coverage was 93% in 1-year-olds and 70% for catch-up cohorts. In 10 years, after adjusting for changes in diagnostic practices, population invasive serogroup C incidence declined 96% (95% confidence interval 94–98) to 0·4 and 0·6 cases/million in vaccinated and unvaccinated cohorts, respectively. Only three serogroup C deaths occurred in 2010–2012vs.68 in 2000–2002. Four (<1/million doses) confirmed vaccine failures were identified in 10 years with no increasing trend. Despite published evidence of waning antibody over time, an ongoing single dose of meningococcal C conjugate vaccine in the second year of life following widespread catch-up has resulted in near elimination of serogroup C disease in all age groups without evidence of vaccine failures in the first decade since introduction. Concurrently, serogroup B incidence declined independently by 55%.

Rapid processes for purification of capsular polysaccharides from Neisseria meningitidis serogroups A and C

The glycoconjugate vaccines against Neisseria meningitidis are highly effective, however most of these vaccines are expensive and still out of reach in the developing world as well as the technical know-how and the set-up required for the consistent production of pure polysaccharide is limited. Our laboratory has developed rapid, efficient and scalable processes for the downstream purification of N. meningitidis serogroup A (MenA) and serogroup C (MenC) capsular polysaccharides (PS). The MenC-PS was purified with a novel 2-step procedure including de-O-acetylation and hydrophobic interaction chromatography whereas, MenA-PS was purified using a rapid method as compared to the prior art. The purified PSs were analyzed by various analytical tests including nuclear magnetic resonance, molecular weight, composition and purity analyses to meet desired specifications. Our results provide a proof of principle for the purification of MenA-PS and MenC-PS with reduced timelines.

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.

Control and lot release of meningococcal group C conjugate vaccines

Meningococcal group C conjugate vaccines were first introduced to the UK in 1999. To date, the vaccines have been demonstrated to have an efficacy of approximately 90% and have since been adopted by other countries worldwide. The development of control tests used for lot release of meningococcal group C vaccines has been based on those used for Haemophilus influenzae type b conjugates, the key criteria being measurement of free saccharide and conjugate integrity by physicochemical means. In future, meningococcal group C vaccines are likely to be replaced by multivalent formulations containing different components in combination. This will present a new challenge for regulatory authorities and more extensive testing will be required to ensure vaccine safety and efficacy.

Long-term protection in children with meningococcal C conjugate vaccination: lessons learned

Owing to an increase in group C disease, extensive prelicensure studies have been funded by both the UK Department of Health and vaccine manufacturers. These demonstrated the safety and immunogenicity of three candidate meningococcal group C conjugate (MCC) vaccines (two conjugated to CRM(197) and one to tetanus toxoid) in the targeted age groups. Induction of immunological memory in infants and young children was also demonstrated by either a low dose of polysaccharide challenge following primary immunization with MCC or by an increase in avidity indices post-primary to pre-challenge. Immune memory after infant immunization persisted to at least 4 years of age, although antibody persistence in this age group was poor. MCC vaccine was introduced into the UK routine immunization schedule at 2, 3 and 4 months of age in 1999, with a catch-up as a single dose to all children aged 1-18 years with two doses for infants aged 5-11 months. The number of group C cases fell rapidly in the targeted age groups and early analyzes showed high vaccine effectiveness in all age groups together with significant herd immunity. However, when effectiveness was measured again more than 1 year after vaccination, there was a significant decline in all age groups, most marked in infants vaccinated in the routine infant immunization program, for whom there was no demonstrable efficacy after only 1 year and then in toddlers for whom efficacy declined to 61% (95% confidence interval: -327-94) from 88% (95% confidence interval: 65-96) in the first year. However, good disease control was maintained in the UK with only low numbers of vaccine failures. The assumption that immune memory was predictive of long-term protection is incorrect, at least after vaccination in infancy. Persistence of antibody and herd immunity may be more relevant for long-term disease control.

First evidence for a covalent linkage between enterobacterial common antigen and lipopolysaccharide in Shigella sonnei phase II ECALPS

Enterobacterial common antigen (ECA) is expressed by Gram-negative bacteria belonging to Enterobacteriaceae, including emerging drug-resistant pathogens such as Escherichia coli, Klebsiella pneumoniae, and Proteus spp. Recent studies have indicated the importance of ECA for cell envelope integrity, flagellum expression, and resistance of enteric bacteria to acetic acid and bile salts. ECA, a heteropolysaccharide built from the trisaccharide repeating unit, →3)-α-D-Fucp4NAc-(1→4)-β-D-ManpNAcA-(1→4)-α-D-GlcpNAc-(1→, occurs as a cyclic form (ECA(CYC)), a phosphatidylglycerol (PG)-linked form (ECA(PG)), and an endotoxin/lipopolysaccharide (LPS)-associated form (ECA(LPS)). Since the discovery of ECA in 1962, the structures of ECA(PG) and ECA(CYC) have been completely elucidated. However, no direct evidence has been presented to support a covalent linkage between ECA and LPS; only serological indications of co-association have been reported. This is paradoxical, given that ECA was first identified based on the capacity of immunogenic ECA(LPS) to elicit antibodies cross-reactive with enterobacteria. Using a simple isolation protocol supported by serological tracking of ECA epitopes and NMR spectroscopy and mass spectrometry, we have succeeded in the first detection, isolation, and complete structural analysis of poly- and oligosaccharides of Shigella sonnei phase II ECA(LPS). ECA(LPS) consists of the core oligosaccharide substituted with one to four repeating units of ECA at the position occupied by the O-antigen in the case of smooth S. sonnei phase I. These data represent the first structural evidence for the existence of ECA(LPS) in the half-century since it was first discovered and provide insights that could prove helpful in further structural analyses and screening of ECA(LPS) among Enterobacteriaceae species.

Effectiveness of meningococcal serogroup C vaccine programmes

Since the introduction of monovalent meningococcal serogroup C (MenC) glycoconjugate (MCC) vaccines and the implementation of national vaccination programmes, the incidence of MenC disease has declined markedly as a result of effective short-term vaccination and reduction in acquisition of MenC carriage leading to herd protection. Monovalent and quadrivalent conjugate vaccines are commonly used vaccines to provide protection against MenC disease worldwide. Studies have demonstrated that MCC vaccination confers protection in infancy (0-12 months) from the first dose but this is only short-term. NeisVac-C(®) has the greatest longevity of the currently licensed MCC vaccines in terms of antibody persistence, however antibody levels have been found to fall rapidly after early infant vaccination with two doses of all MCC vaccines - necessitating a booster at ∼12 months. In toddlers, only one dose of the MCC vaccine is required for routine immunization. If herd protection wanes following catch-up campaigns, many children may become vulnerable to infection. This has led many to question whether an adolescent booster is also required.

Characterization of size, structure and purity of serogroup X Neisseria meningitidis polysaccharide, and development of an assay for quantification of human antibodies

Serogroup X Neisseria meningitidis (MenX) has recently emerged as a cause of localized disease outbreaks in sub-Saharan Africa. In order to prepare for vaccine development, MenX polysaccharide (MenX PS) was purified by standard methods and analyzed for identity and structure by NMR spectroscopy. This study presents the first full assignment of the structure of the MenX PS using (13)C, (1)H and (31)P NMR spectroscopy and total correlation spectroscopy (TOCSY) and (1)H-(13)C heteronuclear single quantum coherence (HSQC). Molecular size distribution analysis using HPLC-SEC with multi-angle laser light scattering (MALLS) found the single peak of MenX PS to have a weight-average molar mass of 247,000g/mol, slightly higher than a reference preparation of purified serogroup C meningococcal polysaccharide. MenX PS tended to be more thermostable than serogroup A PS. A method for the quantification of MenX PS was developed by use of high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). A novel and specific ELISA assay for quantification of human anti-MenX PS IgG based on covalent linkage of the MenX PS to functionally modified microtitre plates was developed and found valid for the assessment of the specific antibody concentrations produced in response to MenX vaccination or natural infection. The current work thus provides the necessary background for the development of a MenX PS-based vaccine to prevent meningococcal infection caused by bacteria bearing this capsule.

Immunogenicity of a single dose of meningococcal group C conjugate vaccine given at 3 months of age to healthy infants in the United kingdom

BACKGROUND

From 1999, in the United Kingdom, meningococcal C conjugate (MCC) vaccines from 3 manufacturers were introduced to the infant immunization schedule at 2, 3 and 4 months of age. In 2006, the schedule was refined to a 2-dose primary schedule at 3 and 4 months of age, with a combined MCC/Haemophilus influenzae type b (MCC/Hib-TT) booster at 12 months of age. Recent data have demonstrated that 2 of the 3 MCC vaccines showed potential for use as a single priming dose in infancy.

METHODS

A randomized trial was undertaken with 2 MCC vaccines; one using tetanus toxoid carrier protein (MCC-TT) and one using CRM197 carrier protein (MCC-CRM197). Infants were immunized with MCC at 3 months of age followed by an MCC/Hib-TT booster at 12 months of age.

RESULTS

The serum bactericidal antibody geometric mean titers 1 month after a single dose of MCC-TT or MCC-CRM 197 were 223.3 (95% confidence interval [CI]: 162.9-306.1) and 95.8 (95% CI: 66.4-138.2) with 100% and 95.5% of infants having serum bactericidal antibody titers ≥ 8, respectively. Before boosting, antibody titers had declined, and 1 month after the MCC/Hib-TT booster, serum bactericidal antibody geometric mean titers rose to 2251.0 (95% CI: 1535.3-3300.3) and 355.9 (95% CI: 235.4-538.1) for children primed with MCC-TT and MCC-CRM 197, respectively.

CONCLUSIONS

In conclusion, a single priming dose of either MCC-TT or MCC-CRM197 administered at 3 months of age can be used together with the Hib/MCC-TT booster in the second year of life.

Immunogenicity and reactogenicity of a 13-valent-pneumococcal conjugate vaccine administered at 2, 4, and 12 months of age: a double-blind randomized active-controlled trial

BACKGROUND

A 2-, 4-, and 12-month schedule of a novel 13-valent-pneumococcal conjugate vaccine (PCV13), containing serotype 1, 3, 4, 5, 6A, 6B 7F, 9V, 14, 18C, 19A, 19F, and 23F polysaccharides individually conjugated to CRM197 was evaluated in a randomized, double-blind, controlled infant study.

METHODS

Two hundred eighty-six healthy infants received PCV13 or the 7-valent-pneumococcal conjugate vaccine (PCV7) at 2, 4, and 12 months of age, alongside a serogroup C meningococcal (MenC) vaccine (2 and 4 months of age), DTaP-IPV-Hib (2, 3, and 4 months), and a Hib-MenC vaccine (12 months). Specific antibody responses were assessed at age 5, 12, and 13 months.

RESULTS

At 13 months of age, >97% of PCV13 recipients had pneumococcal serotype-specific serum IgG concentrations ≥0.35 µg/mL for each vaccine serotype except serotype 3 (88.2%), and at least 93% of PCV13 recipients had OPA titers ≥1:8 for each serotype. At 5 months, 110/114 (96.5%) of PCV13 recipients and 100/102 (98.0%) of PCV7 recipients had serum anti-PRP (Hib) IgG concentration ≥0.15 µg/mL (difference, 1.5%; CI, -7.1%–3.7%), while 119/120 (99.2%) and 117/118 (99.2%), respectively, had MenC serum bactericidal assay titers of ≥1:8. All PCV13 recipients and 110/113 (97.3%) of PCV7 recipients had IgG concentrations against fimbrial agglutinogens of ≥2.2 EU/mL; IgG concentrations for the remaining pertussis antigens were ≥5 EU/mL for all participants. Local reactions and systemic events were similar in the PCV13 and PCV7 groups.

CONCLUSIONS

A 2-, 4-, and 12-month course of PCV13 was immunogenic for all 13 vaccine serotypes and was well tolerated.

Demonstration of immunologic memory using serogroup C meningococcal glycoconjugate vaccine

BACKGROUND

Studies of glycoconjugate vaccines have traditionally used an immune challenge with a plain polysaccharide vaccine to demonstrate immunologic memory. Plain polysaccharide vaccines are poorly immunogenic in children and can induce subsequent immunologic hyporesponsiveness. We therefore assessed the use of glycoconjugate vaccines as an alternative method of demonstrating immunologic memory.

METHODS

Children immunized with hepatitis B vaccine or serogroup C meningococcal glycoconjugate vaccine (MenCC) at age 2, 3, 4 months received a plain polysaccharide meningococcal serogroup A/C vaccine (MenACP) or MenCC at age 12 months. A post hoc analysis of serum bactericidal activity responses to MenCC assessed whether this differed in MenCC primed and MenCC naive infants.

RESULTS

MenCC primed children displayed higher geometric mean serum bactericidal titers than MenCC naive children following MenACP (1518 compared with 30; P = 0.003). A similar difference was seen after a dose of MenCC to toddlers (MenCC primed: 8663, MenCC naive: 710; P < 0.001). The latter comparison became a borderline significance after adjusting for higher pretoddler immunization serum bactericidal geometric mean titers in the MenCC primed group (P = 0.068).

CONCLUSIONS

Administration of glycoconjugate vaccines provides an important alternative method of demonstrating immunologic memory, avoiding the use of plain polysaccharide vaccines that are potentially deleterious in children. This has implications for the design of all future clinical trials of glycoconjugate vaccines.

Immunogenicity of a reduced schedule of meningococcal group C conjugate vaccine given concomitantly with the Prevenar and Pediacel vaccines in healthy infants in the United Kingdom

This study investigated the use of two doses of three different meningococcal group C conjugate (MCC) vaccines when given for primary immunization with a seven-valent pneumococcal conjugate vaccine (PCV7) and Pediacel, a combination product containing five acellular pertussis components, diphtheria and tetanus toxoids, Haemophilus influenzae type b (Hib) conjugate, and inactivated-poliovirus vaccine. The immune response after a single dose of MCC is also presented. Infants were randomized to receive two doses of one of the MCC vaccines and PCV7 at 2 and 3 months or at 2 and 4 months of age. Meningococcal group C serum bactericidal antibody (SBA) geometric mean titers, Hib-polyribosylribitol phosphate (PRP) immunoglobulin G (IgG) geometric mean concentrations (GMCs), and diphtheria and tetanus antitoxin GMCs, together with the proportions of infants achieving putative protective levels, were determined. A total of 393 infants were recruited. Following the first dose of NeisVac-C (MCC conjugated to tetanus toxoid), 97% of infants achieved protective levels (SBA titer of >or=8), compared with 80% and 53%, respectively, for Menjugate and Meningitec (both of which are conjugated to CRM(197)). SBA responses to MCC vaccines were not significantly different when administered at 2 and 3 or 2 and 4 months of age. Following two doses of each MCC, 98 to 100% of infants achieved protective levels. Both PRP IgG and tetanus responses were significantly enhanced when Pediacel was coadministered with NeisVac-C. This study demonstrates that NeisVac-C and Menjugate generate good immunogenicity after the first dose at 2 months of age when coadministered with PCV7 and Pediacel and merit further investigation in single-dose priming strategies.

Immunogenicity and reactogenicity of a booster dose of a novel combined Haemophilus influenzae type b-Neisseria meningitidis serogroup C-tetanus toxoid conjugate vaccine given to toddlers of 13-14 months of age with antibody persistence up to 31 months of age

BACKGROUND

A combined Haemophilus influenzae type b and Neisseria meningitidis serogroup C tetanus toxoid conjugate vaccine (Hib-MenC-TT) may be a convenient alternative to separate Hib and MenC conjugate vaccines.

METHODS

Healthy infants randomized in a previous study for priming at 2, 4, and 6 months: Hib-MenC-TT primed group, 3 doses of Hib-MenC-TT + DTPa-HBV-IPV (N = 87); MenC-TT primed group, 2 doses of MenC-TT (NeisVac-C; Baxter Healthcare SA, Zuürich, Switzerland) + 3 doses of DTPa/Hib containing vaccines (N = 178); MenC-CRM primed group, 3 doses of MenC-CRM197(Meningitec; Wyeth Corporation Delaware, Madison, NJ) + DTPa-HBV-IPV/Hib (N = 93). At 13-14 months of age, Hib-MenC-TT and MenC-TT primed groups received a Hib-MenC-TT booster dose and the MenC-CRM primed group a booster dose of DTPa-HBV-IPV/Hib. Blood samples were taken before and at 1 and 18 months postbooster.

RESULTS

Before the booster dose, persistence of anti-polyribosyl ribitol phosphate (PRP) antibody concentration > or =0.15 microg/mL in the Hib-MenC-TT (96.4%) and MenC-TT (96.1%) primed groups and of MenC bactericidal titers > or =1:8 in the Hib-MenC-TT primed group (96.3%) was statistically significantly higher than in the MenC-CRM primed group (86.4% and 85.4%, respectively). One month after the Hib-MenC-TT booster, 99.2% subjects in the Hib-MenC-TT primed + MenC-TT primed pooled groups had anti-PRP levels > or =1 microg/mL, and 99.6% had SBA-MenC titers > or =1:128. The Hib-MenC-TT booster tended to be less reactogenic than the DTPa-HBV-IPV/Hib control and no serious adverse events related to vaccination were reported. Eighteen months after boosting with Hib-MenC-TT, SBA-MenC titers > or =1:8 persisted in 92.7% subjects and anti-PRP > or =0.15 microg/mL persisted in 99.4%.

CONCLUSIONS

Primary immunization with 3 doses of Hib-MenC-TT coadministered with DTPa-HBV-IPV induced antibodies that persisted up to the second year of life. The Hib-MenC-TT booster administered to primed toddlers induced robust and persistent antibody responses to both the Hib and MenC components and had an acceptable safety profile.

A phase II, randomized study on an investigational DTPw-HBV/Hib-MenAC conjugate vaccine administered to infants in Northern Ghana

BACKGROUND

Combining meningococcal vaccination with routine immunization in infancy may reduce the burden of meningococcal meningitis, especially in the meningitis belt of Africa. We have evaluated the immunogenicity, persistence of immune response, immune memory and safety of an investigational DTPw-HBV/Hib-MenAC conjugate vaccine given to infants in Northern Ghana.

METHODS AND FINDINGS

In this phase II, double blind, randomized, controlled study, 280 infants were primed with DTPw-HBV/Hib-MenAC or DTPw-HBV/Hib vaccines at 6, 10 and 14 weeks of age. At 12 months of age, children in each group received a challenge dose of serogroup A+C polysaccharides. Antibody responses were assessed pre, and one month-post dose 3 of the priming schedule and pre and 1 month after administration of the challenge dose. One month post-dose 3, 87.8% and 88.2% of subjects in the study group had bactericidal meningococcal serogroup A (SBA-MenA) and meningococcal serogroup C (SBA-MenC) antibody titres > or = 1:8 respectively. Seroprotection/seropositivity rates to the 5 antigens administered in the routine EPI schedule were non-inferior in children in the study group compared to those in the control group. The percentages of subjects in the study group with persisting SBA-MenA titres > or = 1:8 or SBA-MenC titres > or = 1:8 at the age of 12 months prior to challenge were significantly higher than in control group (47.7% vs 25.7% and 56.4% vs 5.1% respectively). The administration of 10 microg of serogroup A polysaccharide increased the SBA-MenA GMT by 14.0-fold in the DTPW-HBV/HibMenAC-group compared to a 3.8 fold increase in the control-group. Corresponding fold-increases in SBA-MenC titres following challenge with 10 microg of group C polysaccharide were 18.8 and 1.9 respectively. Reactogenicity following primary vaccination or the administration of the challenge dose was similar in both groups, except for swelling (Grade 3) after primary vaccination which was more frequent in children in the vaccine than in the control group (23.7%; 95%CI [19.6-28.1] of doses vs 14.1%; 95% CI [10.9-17.8] of doses). Fifty-nine SAEs (including 8 deaths), none of them related to vaccination, were reported during the entire study.

CONCLUSIONS

Three dose primary vaccination with DTPw-HBV/Hib-MenAC was non-inferior to DTPw-HBV/Hib for the 5 common antigens used in the routine EPI schedule and induced bactericidal antibodies against Neisseria meningitidis of serogroups A and C in the majority of infants. Serogroup A and C bactericidal antibody levels had fallen below titres associated with protection in nearly half of the infants by the age of 12 months confirming that a booster dose is required at about that age. An enhanced memory response was shown after polysaccharide challenge. This vaccine could provide protection against 7 important childhood diseases (including meningococcal A and C) and be of particular value in countries of the African meningitis belt.

TRIAL REGISTRATION

Controlled-Trials.com ISRCTN35754083.

A novel combined Haemophilus influenzae type b-Neisseria meningitidis serogroups C and Y-tetanus-toxoid conjugate vaccine is immunogenic and induces immune memory when co-administered with DTPa-HBV-IPV and conjugate pneumococcal vaccines in infants

Immunogenicity and safety of a novel combined Haemophilus influenzae type b-Neisseria meningitidis serogroups C and Y-tetanus-toxoid conjugate vaccine (Hib-MenCY-TT) candidate was evaluated when co-administered with DTPa-HBV-IPV(Pediarix)+PCV7(Prevnar) at 2-4-6 months of age. Anti-PRP concentrations >or= 1.0 microg/mL were observed in 92.9-98.7%, rSBA-MenC/Y titres >or= 1:8 in >98%, rSBA-MenC/Y titres >or= 1:128 in >95.8 and >89.9% subjects. PRP and MenC responses were similar to respective controls (ActHIB and Menjugate) including for antibody persistence. Response to co-administered vaccines was not impaired. Polysaccharide challenge (PRP, PSC, PSY at 11-14 months of age) evidenced immune memory was induced for Hib, MenC/Y conjugate components. The safety profile of Hib-MenCY-TT was similar to controls. Hib-MenCY-TT administered according to the current US Hib vaccine schedule has the potential to induce protective antibodies against Hib and meningococcal-CY disease in infants and toddlers.

Issues surrounding standardization of meningococcal group W135 serology

Group W135 polysaccharide vaccines were licensed without efficacy trials using the serum bactericidal antibody (SBA) assay as a surrogate of protection. Standardization of group A and C SBA assays has been largely achieved. However, no such efforts have been focussed on W135. Although W135 strains have been recommended by WHO for polysaccharide production, no such recommendation are in place for use in immunoassays. Strain characterization is of importance as W135 strains may possess either an O-acetylated or de-O-acetylated polysaccharide capsule and the human immune response can vary according to the O-acetylation of the target antigen. Following conjugate or polysaccharide vaccination, few data are published with respect to complement source comparisons although both human and baby rabbit sera have been utilized with similar end points. In studies of natural immunity subcapsular antigens are primarily the target antigens and thus strain choice for use in the SBA assay is important. International standardization of assays is necessary to allow for comparisons of data over time and place.

Reconsideration of the use of meningococcal polysaccharide vaccine

In 2005, a quadrivalent meningococcal conjugate vaccine was licensed in the United States for persons aged 11-55 years of age. For children aged 2-10 years with underlying diseases associated with increased risk of meningococcal disease, unconjugated meningococcal polysaccharide (MPS) vaccination is still recommended. This article reviews the increasing evidence that MPS vaccination impairs serum anticapsular antibody responses to subsequent injections of MPS or meningococcal conjugate vaccines (antibody hyporesponsiveness). Administering MPS as a probe to assess conjugate vaccine-induced immunologic memory also can extinguish subsequent memory anticapsular antibody responses, whereas conjugate vaccination regenerates memory B cells. Whether induction of antibody hyporesponsiveness or loss of immunologic memory increase the risk of acquiring meningococcal disease remains speculative. However, for children at increased risk of meningococcal disease, immunization with meningococcal quadrivalent conjugate vaccine off-label instead of MPS vaccine should be considered. Requirements for licensure of new glycoconjugate vaccines that include performing comparative clinical trials to demonstrate noninferiority with MPS vaccine, or use of a MPS challenge to assess conjugate-induced immunologic memory also should be modified because there are safer approaches for obtaining the same information.

Immunogenicity, safety and tolerability of meningococcal C CRM197 conjugate vaccine administered 3, 5 and 11 months post-natally to pre- and full-term infants

A total of 79 pre-term infants with a gestational age > or =32 weeks and 74 full-term infants were studied in order to evaluate the immunogenicity, safety and tolerability of meningococcal C (MenC)-CRM(197) conjugate vaccine administered 3, 5 and 11 months post-natally. The evoked immune response seemed to be substantially similar in the pre- and full-term infants, and there were only clinically marginal differences in safety and tolerability between the groups. The results support the use of two doses of MenC-CRM(197) vaccine at 3 and 5 months of age for primary immunisation, with a booster dose being given at about 1 year. In addition to reducing costs, this scheme seems to assure global immunogenicity and potential efficacy that is better than that offered by the accelerated scheme of administration with only three doses of vaccine in the first months of life, and similar to that observed with a fourth dose used as booster after the first year.

A new approach to the definition of seroconversion following vaccination in a population with high background antibody concentrations

Licensure of meningitis vaccines is increasingly being made on the basis of safety and immunogenicity. For meningococcal vaccines, a measure of immunogenicity is seroconversion, usually defined as a four-fold increase in rSBA titre. However, this definition is likely to underestimate seroconversion in settings with high background immunity. Using data from a study of the immunogenicity of meningococcal polysaccharide vaccines undertaken in Ghana, a logistic regression model to estimate the probability of seroconversion as a function of pre-vaccination titre has been developed. The seroconversion rate (91%) based on a variable-fold increase in rSBA titre derived from the model was a more plausible estimate of immunogenicity than the seroconversion rate (32%) based on the fixed four-fold increase in rSBA.

Protective meningococcal capsular polysaccharide epitopes and the role of O acetylation

Previous studies with group C meningococcal polysaccharide-tetanus toxoid (GCMP-TT) conjugates had suggested that the GCMP O-acetyl group masked the protective epitope for group C meningococci through steric hindrance or altered conformations. For this report, we confirmed this phenomenon and performed comparative studies with group Y meningococcal polysaccharide (GYMP)-TT to determine whether it might extend to other serogroups. The de-O-acetylated (dOA) polysaccharides (PSs) resulted in higher serum bactericidal activities (SBA) towards the O-acetylated (OA) meningococcal strains from the respective serogroups. High-resolution H-nuclear magnetic resonance spectroscopy at 500 MHz and competitive inhibition serum bactericidal assays were used to characterize the nature of the protective epitope. In head-to-head comparisons with OA PSs as SBA inhibitors, the dOA PSs provided 10 to 1,000 times better inhibition for GCMP in human and mouse antisera and 6 to 13 times better inhibition for GYMP in mouse antisera, using OA strains in all assays. In addition, the SBA for OA strains was highly correlated with dOA PS-specific immunoglobulin G (r=0.72 to 0.98) for both GCMP and GYMP. The results suggest that there may be a generalized role for the O-acetyl group to provide an epitope of misdirected immunogenicity for meningococcal PS capsules, enabling escape from immune surveillance. In addition to greater chemical consistency, the dOA forms of GCMP and GYMP conjugate vaccines endow greater immunologic competence to the PSs, rendering them capable of eliciting higher levels of functional antibodies toward the protective epitopes.

Antibody responses induced by long-term vaccination with an octovalent conjugate Pseudomonas aeruginosa vaccine in children with cystic fibrosis

We assessed the serological responses over 10 years to repeated immunization of cystic fibrosis (CF) patients with an O-polysaccharide (OPS)-toxin A conjugate vaccine against Pseudomonas aeruginosa. A retrospective analysis was performed with sera from 25 vaccinated and 25 unvaccinated children treated at the same CF centre and matched for clinical management, age and gender. Yearly immunization led to sustained elevations of serum immunoglobulin G (IgG) antibody levels to all vaccine components. Eighteen unvaccinated patients but only eight vaccinated ones developed chronic pseudomonal lung infections. Infection rapidly caused further marked elevations of polysaccharide- but not toxin A-specific serum IgG in both immunized and nonimmunized patients, indicating that protection did not depend on the quantity of IgG present. However, qualitative analyses revealed that the protective capacity of specific serum IgG antibodies was linked to high affinity and to specificity for OPS serotypes rather than for lipopolysaccharide core epitopes.

Immunization strategies for the control of serogroup C meningococcal disease in developed countries

In developed countries, the epidemiology of serogroup C meningococcal disease is characterized by unpredictable outbreaks and a bimodal distribution of cases, with the highest incidence rate among those below 1 year of age and a second peak in teenagers. Serogroup C meningococcal conjugate vaccines elicit a thymus-dependent immunological response that is already present in young infants and is characterized by the production of protective antibodies and the development of memory. Results from immunogenicity and effectiveness studies indicate that waning of immunity occurs over time, and the protection conferred by vaccination before 1 year of age seems to be shortlived. Very different control strategies have been implemented throughout the world and existing vaccination schedules may not be optimal. A schedule consisting of a first dose around 1 year of age and a second dose around 12 years of age seems to be a very cost-effective option in most epidemiological scenarios.

Safety and preliminary immunogenicity of MenC/P64k, a meningococcal serogroup C conjugate vaccine with a new recombinant carrier

This study reports the preliminary assessment of the safety and immunogenicity of the first serogroup C conjugate vaccine candidate that includes meningococcal P64k recombinant protein as the carrier (MenC/P64k). Twenty volunteers were recruited for a double-blind, randomized, controlled phase I clinical trial, receiving a single dose of MenC/P64k (study group) and a single dose of the commercial polysaccharide vaccine AC (control group). Only mild reactions were observed. No statistical differences were detected between the antipolysaccharide C IgG responses of both groups as well as between bactericidal serum titre (P > 0.05). The MenC/P64k vaccine was found to have a good safety profile, to be well tolerated and immunogenic.

Novel lipopolysaccharide biosynthetic genes containing tetranucleotide repeats in Haemophilus influenzae, identification of a gene for adding O-acetyl groups

Many of the genes for lipopolysaccharide (LPS) biosynthesis in Haemophilus influenzae are phase variable. The mechanism of this variable expression involves slippage of tetranucleotide repeats located within the reading frame of these genes. Based on this, we hypothesized that tetranucleotide repeat sequences might be used to identify as yet unrecognized LPS biosynthetic genes. Synthetic oligonucleotides (20 bases), representing all previously reported LPS-related tetranucleotide repeat sequences in H. influenzae, were used to probe a collection of 25 genetically and epidemiologically diverse strains of non-typeable H. influenzae. A novel gene identified through this strategy was a homologue of oafA, a putative O-antigen LPS acetylase of Salmonella typhimurium, that was present in all 25 non-typeable H. influenzae, 19 of which contained multiple copies of the tetranucleotide 5'-GCAA. Using lacZ fusions, we showed that these tetranucleotide repeats could mediate phase variation of this gene. Structural analysis of LPS showed that a major site of acetylation was the distal heptose (HepIII) of the LPS inner-core. An oafA deletion mutant showed absence of O-acetylation of HepIII. When compared with wild type, oafA mutants displayed increased susceptibility to complement-mediated killing by human serum, evidence that O-acetylation of LPS facilitates resistance to host immune clearance mechanisms. These results provide genetic and structural evidence that H. influenzae oafA is required for phase variable O-acetylation of LPS and functional evidence to support the role of O-acetylation of LPS in pathogenesis.

Immunogenicity of one, two or three doses of a meningococcal C conjugate vaccine conjugated to tetanus toxoid, given as a three-dose primary vaccination course in UK infants at 2, 3 and 4 months of age with acellular pertussis-containing DTP/Hib vaccine

Reduction of the number of injections necessary to confer protection in the infant schedule would reduce discomfort, improve cost-effectiveness and create space for the addition of new vaccinations in the future. This study assessed the immunogenicity of one, two or three doses of meningococcal C conjugate vaccine conjugated to tetanus toxoid (MCC-TT) [Neis-VacC] given concomitantly with a combined diphtheria/tetanus/acellular pertussis/Haemophilus influenzae type b -TT conjugate (DTaP-Hib-TT) [Infanrix-Hib] vaccine at 2, 3 and 4 months of age. A total of 106 healthy UK infants were enrolled and randomised into two groups, one in which blood was taken after the first and third dose and the other after the second and third dose. The meningococcal serogroup C serum bactericidal antibody (SBA) geometric mean titre (GMT) rose significantly from post-first dose (491, 95% CI 275, 877) to post-second dose (1052, 95% CI 774, 1433) (p=0.03), with no significant change after the third dose (1024, 95% CI 768, 1366). An SBA titre of >or=8 was achieved by 92% after the first dose and 100% after the second and third doses. The Hib IgG geometric mean concentration (GMC) rose significantly after each dose: post-first (0.14 microg/ml 95% CI 0.10, 0.18), post-second (0.54 microg/ml, 95% CI 0.33, 0.90), post-third (2.04 microg/ml, 95% CI 1.52, 2.74). The Hib GMC after the third dose was higher than reported previously when this DTaP/Hib was given either on its own or concomitantly with a MCC-CRM conjugate vaccine according to the UK 2, 3 and 4 month schedule. This suggests some enhancement of the response to a Hib-TT vaccine by concomitant administration of MCC-TT. These results suggest that a reduced number of doses of MCC-TT would be adequate in infancy if given concomitantly with an acellular pertussis-containing vaccine.

Effects of prior polysaccharide vaccination on magnitude, duration, and quality of immune responses to and safety profile of a meningococcal serogroup C tetanus toxoid conjugate vaccination in adults

Extensive use of meningococcal AC polysaccharide (MACP) vaccines has raised concerns about induction of immunologic hyporesponsiveness to C polysaccharide. We investigated the immunogenicity and safety of a meningococcal C-tetanus conjugate (MCC-TT) vaccine in naive adults and prior MACP vaccinees. Laboratory staff (n = 113) were recruited; 73 were naive to meningococcal vaccination, and 40 had previously received > or =1 dose of MACP vaccine. Blood was taken prior to MCC-TT vaccination and 1 week, 1 month, and 6 months later. At each time point, proportions of subjects with serum bactericidal antibody (SBA) titers of > or =8 or > or =128 were similar (P > 0.46); >94% of subjects achieved titers of > or =128 at 1 month. However, the geometric mean titer (GMT) of SBA at 1 month was higher in the naive (1,757; 95% confidence interval [95% CI], 1,102 to 2,803) than in the previously vaccinated (662; 95% CI, 363 to 1,207) group (P = 0.02), and similarly at 6 months (P < 0.001). Conversely, geometric mean concentrations (GMCs) of serogroup C-specific immunoglobulin G (IgG) were significantly higher in the previously vaccinated group pre-MCC-TT and at 1 week; the groups were similar at 1 month, and there was some evidence that the GMC for the previously vaccinated group was higher at 6 months. Qualitative differences in antibodies between groups were demonstrated by using the SBA/IgG ratio, though avidity measures were similar for the two groups throughout the study. MCC-TT was well tolerated, with similar safety profiles in the two groups. Pain in the arm and headache were the most frequently reported events following vaccination. The study shows that MCC-TT is safe and immunogenic in naive and previously MACP-vaccinated adults, though the magnitude and persistence of postvaccination SBA responses in the latter group were lower.

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.