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

Meningococcal serogroup C serum and salivary antibody responses to meningococcal quadrivalent conjugate vaccine in Saudi Arabian adolescents previously vaccinated with bivalent and quadrivalent meningococcal polysaccharide vaccine

Following repeated polysaccharide vaccination, reduced immune responses have been reported, but there are limited data on the mucosal response of meningococcal polysaccharide vaccine (PSV) or meningococcal conjugate vaccination. Saudi Arabian adolescents (aged 16-19 years) who had previously been vaccinated with ≥1 dose of bivalent meningococcal polysaccharide vaccine and 1 dose of quadrivalent meningococcal polysaccharide (MPSV4) were enrolled in a controlled, randomised, and modified observer-blind study (collectively termed the PSV-exposed group). The PSV-exposed group was randomised to receive either quadrivalent meningococcal conjugate vaccine (MCV4) (PSV-exposed/MCV4 group) or MPSV4 (PSV-exposed/MPSV4 group), and a PSV-naïve group received MCV4. Serum and saliva samples were collected pre-vaccination and 28 days post-vaccination. Serum serogroup-specific A, C, W and Y IgG were quantified as were salivary serogroup-specific C IgG and IgA together with total salivary IgG and IgA. For each serogroup, the post-vaccination serum geometric mean concentrations (GMCs) were significantly higher in the PSV-naïve and the PSV-exposed/MCV4 group than in the PSV-exposed/PSV4 group. For serogroup C, serum serogroup-specific IgG for the PSV-naïve group was significantly higher than both the PSV exposed groups. Higher levels of salivary serogroup C-specific IgG were found in the PSV-naïve group than those who had received two doses of polysaccharide but no significant differences were noted with regards to serogroup-specific IgA.

Evaluation of the safety and immunogenicity in United Kingdom laboratory workers of a combined Haemophilus influenzae type b and meningococcal capsular group C conjugate vaccine

Background

Although a combined Haemophilus influenzae type b (Hib)/meningococcal capsular group C (MenC) conjugate vaccine with a tetanus toxoid carrier protein (Hib/MenC-TT) is not licensed for use in those above 2 years of age due to lack of data on safety and efficacy, certain patient groups at high risk of MenC and/or Hib disease are recommended to receive it. Laboratory workers working with Hib and/or MenC cultures may be at a potentially increased risk of acquiring infectious diseases and vaccination is therefore an important safety consideration. We undertook a clinical trial to investigate the safety and immunogenicity of Hib/MenC-TT vaccine in this cohort.

Methods

A total of 33 subjects were recruited to the trial, all of whom were vaccinated. Serology was completed on samples taken at baseline and four weeks following vaccination to determine MenC specific IgG, MenC serum bactericidal antibody (SBA), anti-Hib polyribosylribitol phosphate (PRP) IgG and anti-tetanus toxoid IgG responses.

Results

At baseline, high proportions of subjects had protective antibody concentrations against MenC, Hib and tetanus due to previous vaccination and/or natural exposure. Vaccination induced > 3, 10 and 220 fold increases in geometric mean concentrations for MenC SBA, anti-tetanus toxoid IgG and anti-Hib PRP IgG, respectively. Following vaccination, 97% of subjects had putative protective SBA titres ≥ 8, 100% had short term protective anti-Hib PRP IgG concentrations ≥ 0.15 μg/mL and 97% had protective anti-tetanus toxoid concentrations ≥ 0.1 IU/mL. No safety concerns were reported with minor local reactions being reported by 21% of subjects.

Conclusions

Immunological responses determined in this trial are likely a combination of primary and secondary responses due to previous vaccination and natural exposure. Subjects were a representative cross-section of laboratory workers, enabling us to conclude that a single dose of Hib/MenC-TT was safe and immunogenic in healthy adults providing the evidence that this vaccine may be used for providing protection in an occupational setting.

Review of meningococcal vaccines with updates on immunization in adults

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

Orthotopic bladder substitution (Neobladder): part II: postoperative complications, management, and long-term follow-up

Bladder replacement following radical cystectomy is widely practiced and in some centers has become the standard method of urinary diversion when possible, rather than the traditional ileal conduit. To minimize the impact of cystectomy and bladder replacement on quality of life and to obtain optimal functional results, postoperative care must be comprehensive and multidisciplinary. Critical team members include the surgeon, urologic nurses, WOC nurses, and allied health care providers such as physiotherapists. This article highlights postoperative considerations for patients undergoing radical cystectomy with orthotopic neobladder construction. The common issues and complications that arise are discussed with a focus on strategies to optimize outcomes.

Orthotopic bladder substitution (neobladder): part I: indications, patient selection, preoperative education, and counseling

Bladder substitution following radical cystectomy for urothelial cancer (transitional cell carcinoma) has become increasingly common and in many centers has evolved to become the standard method of urinary diversion. In determining the best type of urinary diversion for a specific patient, consideration must be given to both the morbidity associated with surgery and the potential positive impact on the patient's quality of life. Decision-making and perioperative care is ideally multidisciplinary, involving physicians and nurse specialists in urology, continence, and ostomy therapy. Physiotherapists may also be involved for pelvic floor muscle retraining. This article highlights preoperative considerations for patients undergoing radical cystectomy with a focus on issues specific to orthotopic bladder substitution as the method of urinary diversion. The second article in this 2-part series will outline postoperative strategies to manage these patients.

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.

Immunogenicity and safety of a meningococcal serogroup A, C, Y and W glycoconjugate vaccine, ACWY-TT

A quadrivalent meningococcal serogroup A, C, W and Y conjugate vaccine (ACWY), utilising tetanus toxoid (TT) as its carrier protein (ACWY-TT; Nimenrix™, GlaxoSmithKline Vaccines, Rixensart, Belgium) has been demonstrated to be safe and immunogenic when administered to young children from 12 months of age, older children, adolescents, and adults. Administration of a single dose of ACWY-TT induces protective serum bactericidal antibodies against all four serogroups as well as good antibody persistence. Coadministration studies have demonstrated that ACWY-TT can be administered with diphtheria, tetanus, three-component acellular pertussis, hepatitis B, inactivated polio virus and Haemophilus influenzae type b conjugate vaccine (DTaP3-IPV-HBV/Hib, Infanrix™ hexa; GlaxoSmithKline Vaccines, Rixensart, Belgium); measles, mumps, rubella, varicella vaccine (Priorix-Tetra™; GlaxoSmithKline Vaccines, Rixensart, Belgium); 10-valent pneumococcal conjugate vaccine (Synflorix(®); GlaxoSmithKline Vaccines, Rixensart, Belgium); hepatitis A and B vaccine (Twinrix(®); GlaxoSmithKline Vaccines, Rixensart, Belgium); and seasonal influenza vaccine (Fluarix™; GlaxoSmithKline Vaccines, Rixensart, Belgium). Studies in young infants from 2 months of age have now commenced but immunisation with a single dose of ACWY-TT from 12 months of age is a safe and immunogenic option in the prevention of meningococcal disease.

Use and interpretation of diagnostic vaccination in primary immunodeficiency: a working group report of the Basic and Clinical Immunology Interest Section of the American Academy of Allergy, Asthma & Immunology

A major diagnostic intervention in the consideration of many patients suspected to have primary immunodeficiency diseases (PIDDs) is the application and interpretation of vaccination. Specifically, the antibody response to antigenic challenge with vaccines can provide substantive insight into the status of human immune function. There are numerous vaccines that are commonly used in healthy individuals, as well as others that are available for specialized applications. Both can potentially be used to facilitate consideration of PIDD. However, the application of vaccines and interpretation of antibody responses in this context are complex. These rely on consideration of numerous existing specific studies, interpolation of data from healthy populations, current diagnostic guidelines, and expert subspecialist practice. This document represents an attempt of a working group of the American Academy of Allergy, Asthma & Immunology to provide further guidance and synthesis in this use of vaccination for diagnostic purposes in consideration of PIDD, as well as to identify key areas for further research.

The tetravalent meningococcal serogroups A, C, W-135, and Y tetanus toxoid conjugate vaccine is immunogenic with a clinically acceptable safety profile in subjects previously vaccinated with a tetravalent polysaccharide vaccine

OBJECTIVES

The immunogenicity and safety of the tetravalent meningococcal serogroups A, C, W-135, and Y tetanus toxoid conjugate vaccine (MenACWY-TT) were evaluated in subjects previously vaccinated with a tetravalent meningococcal polysaccharide vaccine and in subjects without previous meningococcal vaccination.

METHODS

In this phase II, open, controlled study (NCT00661557), healthy subjects aged 4.5-34 years received one dose of MenACWY-TT at month 0. Subjects in the MPS group (n=192) had received polysaccharide vaccine in a study conducted 30-42 months earlier; age-matched subjects in the noMPS control group (n=79) had received no meningococcal vaccination within the past 10 years. Serum bactericidal activity using rabbit complement (rSBA) was measured at month 0 and month 1.

RESULTS

At month 1, ≥97.0% of subjects had rSBA titers ≥1:128. Post-vaccination rSBA geometric mean titers (GMTs) were ≥3.9-fold higher than pre-vaccination in both treatment groups. Exploratory analyses showed no statistically significant differences between groups in percentages of subjects with rSBA titers ≥1:8 and ≥1:128, but significantly lower rSBA GMTs and vaccine response rates for each serogroup in the MPS versus the noMPS group. MenACWY-TT had an acceptable safety profile in both groups.

CONCLUSIONS

These results suggest that MenACWY-TT could be used in vaccination programs irrespective of the pre-vaccination status with polysaccharide vaccine.

Meningococcal disease serogroup C

Despite current advances in antibiotic therapy and vaccines, meningococcal disease serogroup C (MDC) remains a serious threat to global health, particularly in countries in North and Latin America, Europe, and Asia. MDC is a leading cause of morbidity, mortality, and neurological sequelae and it is a heavy economic burden. At the individual level, despite advances in antibiotics and supportive therapies, case fatality rate remains nearly 10% and severe neurological sequelae are frequent. At the population level, prevention and control of infection is more challenging. The main approaches include health education, providing information to the public, specific treatment, chemoprophylaxis, and the use of vaccines. Plain and conjugate meningococcal C polysaccharide vaccines are considered safe, are well tolerated, and have been used successfully for over 30 years. Most high-income countries use vaccination as a part of public health strategies, and different meningococcal C vaccination schedules have proven to be effective in reducing incidence. This is particularly so with conjugate vaccines, which have been found to induce immunogenicity in infants (the age group with the highest incidence rates of disease), stimulate immunologic memory, have longer effects, not lead to hyporesponsiveness with repeated dosing, and decrease acquisition of nasopharyngeal carriage, inducing herd immunity. Antibiotics are considered a cornerstone of MDC treatment and must be administered empirically as soon as possible. The choice of which antibiotic to use should be made based on local antibiotic resistance, availability, and circulating strains. Excellent options for a 7-day course are penicillin, ampicillin, chloramphenicol, and third-generation cephalosporins (ceftriaxone and cefotaxime) intravenously, although the latter are considerably more expensive than the others. The use of steroids as adjunctive therapy for MDC is still controversial and remains a topic of debate. A combination of all of the aforementioned approaches is useful in the prevention and control of MDC, and each country should tailor its public health policy to its own particular needs and knowledge of disease burden.

Hyporesponsiveness following booster immunization with bacterial polysaccharides is caused by apoptosis of memory B cells

BACKGROUND

Repeated immunizations with polysaccharide (PS) vaccines cause hyporesponsiveness through undefined mechanisms. We assessed the effects of a PS booster on immune responses, frequency, and survival of PS-specific B-cell subpopulations in spleen and bone marrow.

METHODS

Neonatal mice were primed with meningococcus serotype C (MenC) conjugate MenC-CRM(197)+CpG1826, boosted with MenC-CRM(197), MenC-PS, or saline; subsequently, bromodeoxyuridine (BrdU) was injected daily intraperitoneally. MenC-PS-specific cells were labeled with fluorescent MenC-PS and phenotyped by flow cytometry.

RESULTS

After MenC-PS booster, proliferating (BrdU(+)) MenC-PS-specific naive B cells (CD138(-)/B220(+); P = .0003) and plasma cells (CD138(+)/B220(-); P = .0002) in spleen were fewer than after saline booster. BrdU(+) MenC-PS-specific plasma cells were also reduced in bone marrow (P = .0308). Compared to saline, MenC-PS booster reduced BrdU(+) IgG(+) MenC-PS-specific B cells in spleen (P = .0002). Twelve hours after the MenC-PS booster, an increased frequency of apoptotic (AnnexinV(+)) MenC-PS-specific B cells in spleen was observed compared with MenC-CRM(197) (P = .0286) or saline (P = .001) boosters.

CONCLUSIONS

We demonstrated that the MenC-PS booster significantly reduced the frequency of newly activated MenC-PS-specific B cells-mostly switched IgG(+) memory cells-by driving them into apoptosis. It shows directly that apoptosis of PS-specific memory cells is the cause of PS-induced hyporesponsiveness. These results should be taken into account prior to consideration of the use of PS vaccines.

Hyporesponsiveness and its clinical implications after vaccination with polysaccharide or glycoconjugate vaccines

Hyporesponsiveness (immune tolerance) follows vaccination with meningococcal polysaccharide and many pneumococcal polysaccharide serotypes. Hyporesponsiveness after Haemophilus influenzae type b polysaccharide vaccination has not been directly observed, but may follow exposure during disease in some individuals. Use of currently licensed conjugate vaccines has not been associated with hyporesponsiveness to date, with the possible exception of pneumococcal serotype 3. Introduction of polysaccharide vaccines anywhere into a conjugate vaccination schedule may result in reduced immune responses on subsequent exposure. This review of vaccine-induced hyporesponsiveness and its potential clinical implications considers recent evidence suggesting that hyporesponsiveness may occur for specific components of combined conjugate vaccines, such as pneumococcal serotype 3. These data have implications for the development of new multivalent vaccines.

Meningococcal group C and w135 immunological hyporesponsiveness in african toddlers

A phase II clinical study was conducted in African toddlers (aged 12 to 23 months), with subjects receiving either investigational meningococcal group A conjugate (PsA-TT), meningococcal ACWY polysaccharide (PsACWY), or Haemophilus influenzae type b (Hib-TT) vaccine. Ten months following vaccination, the 3 study groups were further randomized to receive a dose of PsA-TT, a 1/5 dose of PsACWY, or a dose of Hib-TT vaccine. Group A serum bactericidal antibody (SBA) results have been reported previously, with PsA-TT demonstrating superior immunogenicity versus PsACWY vaccine. Immunogenicity for serogroups W135 and C was assessed by SBA assay to investigate the impact of multiple doses in this age group. Blood samples were taken prior to vaccination, 28 days and 40 weeks post-primary vaccination, and 7 and 28 days post-booster vaccination with a 1/5 dose of PsACWY. Subjects who had previously received a full dose of PsACWY had W135 SBA geometric mean titers (GMTs) of 26.1 and 4.4 at 7 and 28 days post-booster vaccination with a 1/5 PsACWY dose, respectively, whereas the W135 SBA GMTs of naïve subjects at these time points following vaccination with a 1/5 dose of PsACWY were 861.1 and 14.6, respectively. Similar differences were observed for serogroup C, with SBA GMTs of 99 and 5.9 at 7 and 28 days post-booster vaccination with a 1/5 dose of PsACWY, respectively, for naïve subjects, compared to 4.1 and 3.2 for previously vaccinated subjects. Immunologic hyporesponsiveness for groups C and W135 was observed following a full dose of PsACWY vaccine at 12 to 23 months of age and a 1/5 dose of PsACWY 10 months later compared to the case for PsACWY-naïve subjects receiving a 1/5 dose of PsACWY vaccine.

Impaired antibody response to conjugated meningococcal serogroup C vaccine in asplenic patients

The purpose of this study was to determine the quantity and quality of antibodies against the meningococcal serogroup C (MenC) conjugated vaccine in asplenic patients. In 116 asplenic patients, antibody concentrations (IgG) were measured against meningococcal serogroup C before and after immunisation. Of MenC-specific IgG, both antibody avidity and subclasses of IgG1 and IgG2 were determined. The mean MenC IgG concentration rose from 0.16 μg/mL prior to vaccination to 3.69 μg/mL 3 weeks post-vaccination, with 67% of patients reaching the threshold of ≥ 2.0 μg/mL. The mean IgG concentration at 35 weeks post-vaccination was 3.10 μg/mL. IgG2 concentrations increased more than IgG1. Marginal avidity maturation was seen. Hypo-responders to the first MenC vaccine (IgG anti-MenC ≤ 2.0 μg/mL) were offered a booster dose. After revaccination, 59% reached the chosen IgG threshold. The IgG concentration rose from 0.29 to 1.12 μg/mL, with an increase in the IgG1/IgG2 ratio. Avidity indices remained below 33%. In asplenic patients, the quantity and quality of antibodies produced after one dose of conjugated MenC vaccination is lower than that observed in previous studies in healthy adults. Booster vaccination does, indeed, lead to a rise in IgG geometric mean concentrations (GMCs), but does not lead to higher avidity of antibodies.

Quadrivalent meningococcal vaccines: hyporesponsiveness as an important consideration when choosing between the use of conjugate vaccine or polysaccharide vaccine

Regional variations in the incidence and the distribution of serogroups which are responsible of meningococcal disease necessitate multivalent vaccines to ensure broad coverage for travelers. For almost 30 years, this has been provided by quadrivalent polysaccharide vaccine to protect against serogroups A, C, W-135 and Y, but with the advent of quadrivalent conjugate vaccines is there still a case to use the polysaccharide? The well documented hyporesponsiveness induced by polysaccharide vaccines after repeated administration, most clearly observed against serogroup C, suggest that, where available, conjugate vaccines should always be considered ahead of polysaccharide vaccine.

Purified capsular polysaccharide of Neisseria meningitidis serogroup A as immune potentiator for antibody production

The development of new immune potentiators for human vaccines is an important and expanding field of research. In the present study, the ability of the capsular polysaccharide from Neisseria meningitidis serogroup A (CPS-A), a mannose-containing carbohydrate, to enhance the antibody production against a co-administered model vaccine antigen, is examined. A protein-meningococcal serogroup C capsular polysaccharide (CPS-C) conjugate was selected as the model antigen for this study. After subcutaneous immunization of Balb/C mice, the conjugate mixed with CPS-A induced higher anti-CPS-C IgG and IgG(2a) antibody levels and higher anti-meningococcal serogroup C bactericidal titers than the conjugate alone or mixed with CPS-C. The immuno-stimulatory properties exhibited by CPS-A and the fact that vaccines based on purified CPS-A has been safely used during decades to fight the serogroup A meningococcal disease, support the proposal to use CPS-A as immune potentiator for human vaccination studies.

The 23-valent pneumococcal polysaccharide vaccine does not provide additional serotype antibody protection in children who have been primed with two doses of heptavalent pneumococcal conjugate vaccine

Current guidelines recommend up to two doses of the pneumococcal conjugate heptavalent vaccine (PCV-7) in children up to 5 years old followed by and a dose of the polysaccharide vaccine (PPV-23) for patients over 2 years old to broaden serotype immunity. We assessed the serotype responses to two doses of PCV-7 and a dose of PPV-23 in a cohort of children in the 2-16-year age range in order to determine whether PPV-23 induced effective immunity to non-PCV-7 serotypes. Pneumococcal antibody concentrations to the seven serotypes covered by PCV-7 and five additional serotypes covered by PPV-23 but not PCV-7 were measured in 60 children aged 2-16 years. None of the children had a primary antibody immunodeficiency. Vaccinated children had 7-30-fold higher antibody concentrations than unvaccinated children to all serotypes contained in the PCV-7 (P<0.001). In contrast, serotypes covered by the PPV-23 but not PCV-7 were only one- to two-fold higher and there was no significant increase in the number of children who had protective concentrations of antibody (> or =0.35 mcg/ml) against these serotypes. In this cohort of children, PPV-23 vaccine did not broaden the protection in vitro against potentially pathogenic strains of Streptococcus pneumoniae. We call into question the recommendation to use the PPV-23 in children.

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.

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.

Anti-pneumococcal antibody titre measurement: what useful information does it yield?

Measuring and interpretation of the immune response to pneumococcal polysaccharides is a complex field, owing to the diversity of the pneumococcal polysaccharide capsular types, different vaccine formulations including both polysaccharide and conjugate vaccines, diverse pneumococcal serological assays, lack of immunogenicity data for the conjugate in a number of at-risk groups and complex vaccine schedules. Even the reasons for performing pneumococcal serology can be complex, as assays may be performed for one of two reasons: either to assess an individual's immune status to the pneumococcus or to discriminate between normal and abnormal humoral immunity. This review details a history of the pneumococcal serological assays and provides some insight into when serology can prove useful, including vaccination data for certain at-risk groups.

Immunogenicity of varying dosages of 7-valent pneumococcal polysaccharide-protein conjugate vaccine in seniors previously vaccinated with 23-valent pneumococcal polysaccharide vaccine

In this dose-ranging study 220 seniors who had received the 23-valent pneumococcal polysaccharide (PnPS) vaccine at least 5 years prior to enrollment were assigned to receive one of four volumes (0.1, 0.5, 1 or 2 ml) of 7-valent pneumococcal conjugate (PnC) vaccine or a 0.5 ml dose of 23-valent PnPS vaccine. All participants received a reduced challenge dose of 0.1 ml of PnPS vaccine 1 year after enrollment. There was evidence of a dose response to PnC vaccine and antibody levels in the 1 ml PnC group tended to be significantly higher than in the PnPS group. A booster response to the challenge vaccination was not observed. Administration of a 1 ml dose of PnC vaccine is more immunogenic than 0.5 ml of PnPS vaccine in elderly adults previously vaccinated with PnPS vaccine.

Avidity of the immunoglobulin G response to a Neisseria meningitidis group C polysaccharide conjugate vaccine as measured by inhibition and chaotropic enzyme-linked immunosorbent assays

Antibody avidity, the strength of the multivalent interaction between antibodies and their antigens, is an important characteristic of protective immune responses. We have developed an inhibition enzyme-linked immunosorbent assay (ELISA) to measure antibody avidity for the capsular polysaccharide (PS) of Neisseria meningitidis group C (MnC) and determined the avidity constants (K(D)s) for 100 sera from children immunized with an MnC PS conjugate vaccine. The avidity constants were compared to the avidity indices (AI) obtained for the same sera using a chaotropic ELISA protocol. After the primary immunization series, the geometric mean (GM) K(D) was 674 nM and did not change in the months following immunization. However, the GM avidity did increase after the booster dose (GM K(D), 414 nM 1 month after booster immunization). In contrast, the GM AI increased from an initial value of 118 after the primary immunization series to 147 6 months after the completion of the primary immunization series and then further increased to 178 after booster immunization. At the individual subject level, the avidity constant and AI correlated after the primary immunization series and after booster immunization but not prior to boosting. This work suggests that the AI, as measured by the chaotropic ELISA, in contrast to the K(D), reflects changes that render antibody populations less susceptible to disruption by chaotropic agents without directly affecting the strength of the binding interactions.

Early appearance of bactericidal antibodies after polysaccharide challenge of toddlers primed with a group C meningococcal conjugate vaccine: what is its role in the maintenance of protection?

The contribution of memory responses after meningococcal vaccination to protection may depend on the rapidity of the response. Toddlers were challenged with a licensed polysaccharide (PS) vaccine 1 year after vaccination with a single dose of meningococcal group C-CRM(197) conjugate (MCC) vaccine at the age of 12 to 15 months. Bactericidal antibodies and immunoglobulin G (IgG) antibodies detected by an enzyme-linked immunosorbent assay (ELISA) were measured before challenge and 4, 7, 14, or 21 Days later ("Days" refer to treatment groups, "days" to sampling days). Among 281 subjects in the intent-to-treat population, 173 per-protocol (PP) subjects were challenged with 10 microg PS antigen and 103 others with a 50-microg PS vaccinating dose. Capsular PS-specific ELISA IgG titers were negligible in baseline samples and increased only twofold within 4 days of PS administration. In contrast, the proportion of PP subjects with serum bactericidal antibody (SBA) titers of >or=1:8 or >or=1:128 increased, respectively, from 41% and 16% before challenge to 84% and 74% at Day 4 and to 100% and 97% at Day 7. Recipients of 50 microg PS responded with similar kinetics but showed a trend toward higher antibody levels. Unexpectedly, 69% of subjects bled on days 2 to 3 already had achieved SBA titers of >or=1:8. The majority of toddlers previously immunized with MCC and challenged 1 year later with PS antigen mounted protective levels of bactericidal antibody within 2 to 4 days.

B cell mediated priming following pneumococcal colonization

The primary reservoir for Streptococcus pneumoniae is the human nasopharynx, and colonization is often the initial step in pathogenesis. Recently we have demonstrated that pneumococcal colonization primes the immune response to subsequent vaccination with the pneumococcal conjugate vaccine (CPV). In this study we wished to determine if colonization stimulates the production of B cell memory that is activated following vaccination with CPV. To test this hypothesis, we colonized mice with S. pneumoniae serotype 14, adoptively transferred their B cells and CD4+ T cells into naïve recipients, and vaccinated the recipients with CPV. Our results indicate that pneumococcal colonization stimulates the production of memory B cells which are responsible for enhancing the immune response to CPV vaccination.

Experience with MCV-4, a meningococcal, diphtheria toxoid conjugate vaccine against serogroups A, C, Y and W-135

Invasive disease due to Neisseria meningitidis continues to cause debility and death worldwide in otherwise healthy individuals. Disease epidemiology varies globally, but most cases are due to serogroups A, B, C, W-135 or Y. MenactraTM (MCV-4), a quadrivalent, meningococcal diphtheria-conjugate vaccine against serogroups A, C, Y, and W-135, was licensed in the USA for individuals 11-55 years of age. Published results of clinical trials demonstrated robust immune responses that correlate with indicators of protection. MCV-4-induced antibody persist for up to 3 years after administration and anamnestic responses to revaccination. The vaccine was well tolerated; the most common reactions were transient, mild injection-site reactions and headache. MCV-4 should provide significant clinical benefits in the future.

Priming for immunologic memory in adults by meningococcal group C conjugate vaccination

Meningococcal group C polysaccharide-protein conjugate vaccines (MCV) prime infants and children for memory anticapsular responses upon subsequent exposure to unconjugated polysaccharide. The objective of this study was to determine whether MCV primes vaccine-naïve adults and adults previously vaccinated with meningococcal polysaccharide vaccine (MPSV) for memory antibody responses. Meningococcal vaccine-naïve adults were randomized to receive either MCV (MCV/naïve group) (n = 35) or pneumococcal conjugate vaccine (PCV) (PCV/naïve group) (n = 34). Participants with a history of receiving MPSV were given MCV (MCV/MPSV group) (n = 26). All subjects were challenged 10 months later with one-fifth of the usual dose of MPSV (10 mug of each polysaccharide). Sera were obtained before the conjugate vaccination and before and 7 days after the MPSV challenge and assayed for immunoglobulin G (IgG) anticapsular antibody concentrations and bactericidal titers. The MCV/naïve group had 7- to 10-fold-higher serum IgG and bactericidal responses after the MPSV challenge than the PCV/naïve group (P < 0.001). The increases (n-fold) in anticapsular antibody concentrations in the MCV/naïve group were greatest in subjects with antibody concentrations of <or=2 microg/ml before the challenge (geometric mean increase [n-fold] of 8.3 versus 1.1 in subjects with concentrations of >2 microg/ml before the challenge; P < 0.0001). Only 3 of 11 MCV-vaccinated subjects who had received MPSV before enrollment and who had antibody concentrations of <or=2 microg/ml before the polysaccharide challenge showed more-than-twofold increases in anticapsular antibody concentration or bactericidal titer after the challenge. MCV vaccination of meningococcal vaccine-naïve adults primes for robust memory antibody responses. There was no evidence of induction of memory by MCV in adults previously vaccinated with MPSV.

Total and serotype-specific pneumococcal antibody titres in children with normal and abnormal humoral immunity

A heptavalent pneumococcal conjugate vaccine (PCV-7) protects children against invasive pneumococcal disease. The aim of this study was to evaluate immunoglobulin subclass and serotype-specific pneumococcal antibody responses to vaccination in children with a history of recurrent or severe bacterial infections. Pneumococcal IgG, IgG1, IgG2 titres were assayed by ELISA, and nine serotype concentrations measured using a nonaplex bead assay in 145 children investigated for recurrent or severe infections. Children mounted an exclusively IgG1 response after vaccination with two doses of PCV-7 and a dose of 23 valent pneumococcal polysaccharide vaccine (PPV-23), with pneumococcal IgG2 antibody titres remaining low to negligible. Measurement of serotype-specific responses demonstrated that although PCV-7 specific serotype responses increased significantly post-vaccination, specific IgG against two of the serotypes not covered by PCV-7 but only by PPV-23 remained low. We conclude that in contrast to antibody response to natural infection with Pneumococcus or pneumococcal polysaccharide vaccines which are often of a IgG2 subclass, responses in children after PCV-7 are of IgG1 subclass. Serotype-specific IgG were useful in determining the protection against specific pneumococcal strains, and showed that the PPV-23 did not broaden protection against non-PCV-7 serotypes.

The effect of T cell independent and cross-reactive antigen on the immune response to pneumococcal conjugate vaccination

The effect of priming with various antigens on subsequent vaccination with the pneumococcal conjugate vaccine (CPV) was determined using BALB/c mice. Priming with pneumococcal polysaccharide or cross-reactive polysaccharide did not inhibit the IgG response to CPV immunization. Additionally, live intranasal colonization by Streptococcus pneumoniae or cross-reactive organism resulted in higher IgG responses to CPV. These results suggest that colonization elicits immunological memory capable of boosting the immune response to CPV.