Germie van den Dobbelsteen

Immunogenicity and safety of a hexavalent meningococcal outer-membrane-vesicle vaccine in children of 2-3 and 7-8 years of age.

To study the reactogenicity and immunogenicity of a hexavalent meningococcal outer-membrane-vesicle vaccine (OMV), two different dosages of this vaccine (7.5 and 15 microg of individual PorA proteins) consisting of vesicles expressing class 1 outer-membrane proteins (OMPs) of subtypes P1.7,16; P1.5,2; P1.19,15 and P1.5(c), 10; P1.12,13; P1.7(h),4 were administered to a group of 7-8 year (n=165) and a group of 2-3 year old children (n=172). Control groups of children with similar ages were vaccinated against hepatitis B. All participants received three injections. Pre- and postimmunisation sera were tested for bactericidal antibodies against six isogenic meningococcal vaccine strains expressing different PorA proteins. Antibody titres against OMP of the two different vesicles (PL16215 and PL10124) were measured by ELISA. The meningococcal hexavalent OMV vaccine was well tolerated. No statistically significant differences were seen between the high and low dose of hexavalent meningococcal OMV vaccine. The percentage of children showing a fourfold increase of bactericidal antibody titres against the specific serosubtype varied in toddlers from 28 to 98% and in older children from 16 to 100%. Both ELISA antibody titres and bactericidal activity showed the highest level in the youngest age-group.

Long-Term Effects of Pneumococcal Conjugate Vaccine on Nasopharyngeal Carriage of S. pneumoniae, S. aureus, H. influenzae and M. catarrhalis

Background Shifts in pneumococcal serotypes following introduction of 7-valent pneumococcal conjugate vaccine (PCV-7) may alter the presence of other bacterial pathogens co-inhabiting the same nasopharyngeal niche. Methodology/Principal Findings Nasopharyngeal prevalence rates of S. pneumoniae, S. aureus, H. influenzae and M. catarrhalis were investigated before, 3 and 4.5 years after introduction of PCV-7 in the national immunisation program in children at 11 and 24 months of age, and parents of 24-month-old children (n≈330/group) using conventional culture methods. Despite a virtual disappearance of PCV-7 serotypes over time, similar overall pneumococcal rates were observed in all age groups, except for a significant reduction in the 11-month-old group (adjusted Odds Ratio after 4.5 years 0.48, 95% Confidence Interval 0.34–0.67). Before, 3 and 4.5 years after PCV-7 implementation, prevalence rates of S. aureus were 5%, 9% and 14% at 11 months of age (3.59, 1.90–6.79) and 20%, 32% and 34% in parents (1.96, 1.36–2.83), but remained similar at 24 months of age, respectively. Prevalence rates of H. influenzae were 46%, 65% and 65% at 11 months (2.22, 1.58–3.13), 52%, 73% and 76% at 24 months of age (2.68, 1.88–3.82) and 23%, 30% and 40% in parents (2.26, 1.58–3.33), respectively. No consistent changes in M. catarrhalis carriage rates were observed over time. Conclusions/Significance In addition to large shifts in pneumococcal serotypes, persistently higher nasopharyngeal prevalence rates of S. aureus and H. influenzae were observed among young children and their parents after PCV-7 implementation. These findings may have implications for disease incidence and antibiotic treatment in the post-PCV era.

Serum bactericidal activity and isotype distribution of antibodies in toddlers and schoolchildren after vaccination with RIVM hexavalent PorA vesicle vaccine

A clinical phase II trial with the RIVM hexavalent OMV vaccine containing six different PorAs was carried out in toddlers (2-3 years) and schoolchildren (7-8 years) in The Netherlands. Children were vaccinated three times (0, 2, 8 months). Sera after two and three vaccinations were analysed for serum bactericidal activity (SBA) and isotype distribution in whole cell enzyme linked immunosorbent assay (ELISA). The SBA after vaccination against the six PorAs was significantly different. We investigated whether the age specific and PorA specific differences in SBA titers correlated with differences in PorA specific IgG isotype distribution. The SBA titers were higher in toddlers compared with schoolchildren. After vaccination, IgG1 antibodies dominated the response followed by IgG3 antibodies. IgG2 levels were low, whereas IgG4 was not detected. Irrespective of PorA, IgG total and isotype specific titers after two and three vaccinations were significantly higher in toddlers than in schoolchildren. A weak correlation was found between IgG total or IgG1 and SBA. Although the immunogenicity of the six PorAs is very different, the isotype distribution was similar for all six tested PorAs. We conclude that the RIVM hexavalent PorA vesicle vaccine induces bactericidal antibodies mainly of the IgG1 and IgG3 isotypes that are considered to be most important for protection against disease. The isotype distribution of the response is not age-dependent.

Are the enzyme immunoassays for antibodies to pneumococcal capsular polysaccharides serotype specific

ABSTRACT The specificity of antibody binding to pneumococcal capsular polysaccharides (Pnc PSs) measured by enzyme immunoassay (EIA) was studied by inhibition of antibody binding by homologous and heterologous PSs. We found extensive cross-reactivity of antibody binding to type 6B, 19F, and 23F PSs but not to type 14 PS, even after treatment with cell wall PS (CPS). The cross-reactive antibody was highly prevalent in sera of infants and adults with naturally acquired antibody, but not in sera of infants and adults immunized with pneumococcal vaccines. However, a type 11A antibody response was seen after vaccination with heterologous PSs. Monoclonal antibodies prepared against a type 6B PS-tetanus toxoid conjugate recognized also other than the specific type of PS in the EIA, implying the possible existence of a cross-reactive epitope. Remarkable differences in specificity among type 6B PS preparations from different manufacturers were found. Moreover, different lots of type 11A PS from the same manufacturer showed differences in specificity. The results suggest that some Pnc PS preparations may contain cross-reactive epitopes or impurities, other than CPS, that are common to many types of Pnc PS. The specificity of antibodies, especially in sera from nonimmunized subjects, measured by EIA can be questioned.

Pneumococcal Conjugate Vaccines Overcome Splenic Dependency of Antibody Response to Pneumococcal Polysaccharides

ABSTRACT Protection against infections with Streptococcus pneumoniae depends on the presence of antibodies against capsular polysaccharides that facilitate phagocytosis. Asplenic patients are at increased risk for pneumococcal infections, since both phagocytosis and the initiation of the antibody response to polysaccharides take place in the spleen. Therefore, vaccination with pneumococcal polysaccharide vaccines is recommended prior to splenectomy, which, as in the case of trauma, is not always feasible. We show that in rats, vaccination with a pneumococcal conjugate vaccine can induce good antibody responses even after splenectomy, particularly after a second dose. The spleen remains necessary for a fast, primary response to (blood-borne) polysaccharides, even when they are presented in a conjugated form. Coadministration of a conjugate vaccine with additional nonconjugated polysaccharides of other serotypes did not improve the response to the nonconjugated polysaccharides. We conclude that pneumococcal conjugate vaccines can be of value in protecting asplenic or hyposplenic patients against pneumococcal infections.

Immunogenicity of Streptococcus pneumoniae type 6B and 14 polysaccharide-tetanus toxoid conjugates and the effect of uncoupled polysaccharide on the antigen-specific immune response

The immunogenicity of two types of Streptococcus pneumoniae capsular polysaccharide-tetanus toxoid conjugates (PS6BTT and PS14TT) was evaluated in mice. Both conjugates induced high titres of high avidity type-specific anti-PS IgG, which include all IgG isotypes except IgG2a. Repeated immunization resulted in booster responses in both cases. The antibodies induced exhibited opsonic activity, as measured in an in vitro opsonophagocytosis assay, using the mouse macrophage cell line RAW-264. Furthermore, the influence of spiking PS6BTT with free PS6B of either 1000 kDa (native) or 37 kDa was investigated. The results indicate that not only the amount but also the molecular weight of the free PS6B present in the conjugate vaccine affect the anti-PS6B immune response. Large amounts of free PS6B of both molecular weights decrease each anti-PS6B IgG isotype response. However, unlike admixture of the low molecular weight PS6B, addition of the high molecular weight PS6B leads to a rather persistent state of unresponsiveness.

CC and CXC chemokine levels in children with meningococcal sepsis accurately predict mortality and disease severity.

IntroductionChemokines are a superfamily of small peptides involved in leukocyte chemotaxis and in the induction of cytokines in a wide range of infectious diseases. Little is known about their role in meningococcal sepsis in children and their relationship with disease severity and outcome.MethodsMonocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP) 1α, growth-related gene product (GRO)-α and interleukin (IL)-8 were measured in 58 children with meningococcal sepsis or septic shock on admission and 24 hours thereafter. Nine patients died. Serum chemokine levels of survivors and nonsurvivors were compared, and the chemokine levels were correlated with prognostic disease severity scores and various laboratory parameters.ResultsExtremely high levels of all chemokines were measured in the childrens acute-phase sera. These levels were significantly higher in nonsurvivors compared with survivors and in patients with septic shock compared with patients with sepsis (P < 0.0001). The cutoff values of 65,407 pg/ml, 85,427 pg/ml and 460 pg/ml for monocyte chemoattractant protein, for IL-8 and for macrophage inflammatory protein 1α, respectively, all had 100% sensitivity and 94–98% specificity for nonsurvival. Chemokine levels correlated better with disease outcome and severity than tumor necrosis factor (TNF)-α and correlated similarly to interleukin (IL)-6. In available samples 24 hours after admission, a dramatic decrease of chemokine levels was seen.ConclusionInitial-phase serum levels of chemokines in patients with meningococcal sepsis can predict mortality and can correlate strongly with disease severity. Chemokines may play a key role in the pathophysiology of meningococcal disease and are potentially new targets for therapeutic approaches.

Neutralizing Antibodies Elicited by a Novel Detoxified Pneumolysin Derivative, PlyD1, Provide Protection against Both Pneumococcal Infection and Lung Injury

ABSTRACT Streptococcus pneumoniae pneumolysin (PLY) is a virulence factor that causes toxic effects contributing to pneumococcal pneumonia. To date, deriving a PLY candidate vaccine with the appropriate detoxification and immune profile has been challenging. A pneumolysin protein that is appropriately detoxified and that retains its immunogenicity is a desirable vaccine candidate. In this study, we assessed the protective efficacy of our novel PlyD1 detoxified PLY variant and investigated its underlying mechanism of protection. Results have shown that PlyD1 immunization protected mice against lethal intranasal (i.n.) challenge with pneumococci and lung injury mediated by PLY challenge. Protection was associated with PlyD1-specific IgG titers and in vitro neutralization titers. Pretreatment of PLY with PlyD1-specific rat polyclonal antiserum prior to i.n. delivery of toxin reduced PLY-mediated lung lesions, interleukin-6 (IL-6) production, and neutrophil infiltration into lungs, indicating that protection from lung lesions induced by PLY is antibody mediated. Preincubation of PLY with a neutralizing monoclonal PLY antibody also specifically reduced the cytotoxic effects of PLY after i.n. inoculation in comparison to nonneutralizing monoclonal antibodies. These results indicate that the induction of neutralizing antibodies against PLY can contribute to protection against bacterial pneumonia by preventing the development of PLY-induced lung lesions and inflammation. Our detoxified PlyD1 antigen elicits such PLY neutralizing antibodies, thus serving as a candidate vaccine antigen for the prevention of pneumococcal pneumonia.

Is a single dose of meningococcal serogroup C conjugate vaccine sufficient for protection? experience from the Netherlands

BackgroundThe first meningococcal serogroup C (MenC) conjugate vaccine was licensed in 1999 and introduced in the United Kingdom. Countries that have implemented the MenC vaccine since then in their national immunisation programmes use different schedules. Nevertheless, all involved countries seem to experience substantial declines in the incidence of MenC disease.DiscussionSince 2001, the MenC conjugate vaccine has been implemented in the Netherlands by offering a single dose to all children aged 14 months. Prior to the introduction of the vaccine into the national immunisation programme, a catch-up vaccination campaign was initiated in which a single dose of the MenC conjugate vaccine was offered to all children aged from 14 months up to and including 18 years. Since then, there has been no report of any case of MenC disease among immunocompetent vaccinees. Administration of a single dose of MenC conjugate vaccine after infancy could be beneficial considering the already complex immunisation schedules with large numbers of vaccinations in the first year of life. The present paper deals with the advantages and critical aspects of a single dose of the MenC conjugate vaccine.SummaryA single dose of MenC conjugate vaccine at the age of 14 months in combination with a catch up vaccine campaign appeared to be a successful strategy to prevent MenC disease in the Netherlands, thereby confirming that a single dose of the vaccine could sufficiently protect against disease. Nevertheless, this approach can only be justified in countries with a relatively low incidence of serogroup C meningococcal disease in the first year of life. Furthermore, a good surveillance programme is recommended for timely detection of vaccine breakthroughs and outbreaks among non-vaccinees, since long-term protection after a single dose in the second year of life cannot currently be guaranteed.

In vivo antibody response and in vitro CTL activation induced by selected measles vaccine candidates, prepared with purified Quil A components.

Semipurified Quil A and purified Quil A were used to prepare well-characterized subunit vaccine candidates against measles. Variation in the relative amounts of the measles virus (MV) fusion (F) protein, Quil A-components and lipids did not influence induction of antibody responses in mice, but had a pronounced effect on the capacity to induce cytotoxic T cell (CTL) activity of a CD8(+) MV F-protein specific human T cell clone in vitro. A characteristic MV iscom preparation based on the combined use of HPLC-purified Quil A-components QA-3 and QA-22 (QA-3/22) efficiently induced CTL activity in vitro. Comparable results were obtained by mixing beta-propiolactone inactivated MV with iscom-matrix QA-3/22 or free QA-22. On the basis of the data presented it was concluded that these three preparations are interesting MV vaccine candidates for further evaluation in pre-clinical experiments in a primate model.