Current state of pneumococcal vaccines

A mathematical model of protein subunits COVID-19 vaccines

We consider a general mathematical model for protein subunit vaccine with a focus on the MF59-adjuvanted spike glycoprotein-clamp vaccine for SARS-CoV-2, and use the model to study immunological outcomes in the humoral and cell-mediated arms of the immune response from vaccination. The mathematical model is fit to vaccine clinical trial data. We elucidate the role of Interferon-γ and Interleukin-4 in stimulating the immune response of the host. Model results, and results from a sensitivity analysis, show that a balance between the T_H1 and T_H2 arms of the immune response is struck, with the T_H1 response being dominant. The model predicts that two-doses of the vaccine at 28 days apart will result in approximately 85% humoral immunity loss relative to peak immunity approximately 6 months post dose 1.

A cost-effectiveness analysis of PHiD-CV compared to PCV13 in a national immunization program setting in Tunisia

Background

In response to the substantial clinical and economic burden of diseases caused by Streptococcus pneumoniae and non-typeable Haemophilus influenzae (NTHi) in Tunisia, the 10-valent pneumococcal non-typeable Haemophilus influenzae protein D conjugate vaccine (PHiD-CV) was recently introduced into the national immunization program. However, there has yet to be a full-scale health economic analysis comparing currently available pneumococcal conjugate vaccines (PCVs) in Tunisia.

Methods

A Markov model that simulated the disease processes of invasive pneumococcal disease (IPD), pneumonia, and acute otitis media (AOM) over a newborn cohort lifetime was used to evaluate the cost-effectiveness/utility of PHiD-CV and the 13-valent pneumococcal conjugate vaccine (PCV13) from payer’s perspective, using 3% discounting. Vaccine effects were considered for up to 9 years of age.

Results

Vaccination with PHiD-CV or PCV13 was estimated to avert approximately 700 cases of IPD (200 meningitis, 500 bacteremia), and around 5,000 cases of all-cause pneumonia. However, PHiD-CV vaccination was estimated to avert around 4,000 additional AOM cases (18,000) versus PCV13 (14,000). Both PCVs were demonstrated to be cost-effective interventions, but PHiD-CV was estimated to generate additional cost savings of almost $1 million US dollars (USD) with similar levels of clinical benefits. An additional scenario which incorporated serotype-specific vaccine efficacy found no significant change in overall results.

Conclusion

PCVs are a cost-effective strategy to relieve the burden associated with diseases caused by S.pneumoniae and NTHi in Tunisia. PHiD-CV is more cost-effective than PCV13, generating similar health benefits, at a reduced net cost of almost $1 million USD per vaccinated cohort.

Polysaccharide Chemistry in Drug Delivery, Endocrinology, and Vaccines

Polysaccharides, due to their outstanding properties, have attracted the attention of researchers, working in the biomedical field and especially of those working in drug delivery. Modified/functionalized polysaccharides further increase the importance for various applications. Delivery of therapeutics for diverse ailments in different endocrine glands and hormones safely, is a focal point of researchers working in the field. Among the routes followed, the transdermal route is preferred due to non-exposure of active moieties to the harsh gastric environment and first-pass metabolism. This review starts with the overview of polysaccharides used for the delivery of various therapeutic agents. Advantages of polysaccharides used in the transdermal route are addressed in detail. Types of polysaccharides will be elaborated through examples, and in this context, special emphasis will be on the polysaccharides being used for synthesis of the membranes/films. Techniques employed for their modification to design novel carriers for therapeutics delivery will also be discussed. The review will end with a brief discussion on recent developments and future perspectives for delivery of therapeutic agents, and vaccine development.

LT-K63 Enhances B Cell Activation and Survival Factors in Neonatal Mice That Translates Into Long-Lived Humoral Immunity

Adjuvants enhance magnitude and duration of immune responses induced by vaccines. In this study we assessed in neonatal mice if and how the adjuvant LT-K63 given with a pneumococcal conjugate vaccine, Pnc1-TT, could affect the expression of tumor necrosis factor receptor (TNF-R) superfamily members, known to be involved in the initiation and maintenance of antibody responses; B cell activating factor receptor (BAFF-R) and B cell maturation antigen (BCMA) and their ligands, BAFF, and a proliferation inducing ligand (APRIL). Initially we assessed the maturation status of different B cell populations and their expression of BAFF-R and BCMA. Neonatal mice had dramatically fewer B cells than adult mice and the composition of different subsets within the B cell pool differed greatly. Proportionally newly formed B cells were most abundant, but they had diminished BAFF-R expression which could explain low proportions of marginal zone and follicular B cells observed. Limited BCMA expression was also detected in neonatal pre-plasmablasts/plasmablasts. LT-K63 enhanced vaccine-induced BAFF-R expression in splenic marginal zone, follicular and newly formed B cells, leading to increased plasmablast/plasma cells, and their enhanced expression of BCMA in spleen and bone marrow. Additionally, the induction of BAFF and APRIL expression occurred early in neonatal mice immunized with Pnc1-TT either with or without LT-K63. However, BAFF⁺ and APRIL⁺ cells in spleens were maintained at a higher level in mice that received the adjuvant. Furthermore, the early increase of APRIL⁺ cells in bone marrow was more profound in mice immunized with vaccine and adjuvant. Finally, we assessed, for the first time in neonatal mice, accessory cells of the plasma cell niche in bone marrow and their secretion of APRIL. We found that LT-K63 enhanced the frequency and APRIL expression of eosinophils, macrophages, and megakaryocytes, which likely contributed to plasma cell survival, even though APRIL⁺ cells showed a fast decline. All this was associated with enhanced, sustained vaccine-specific antibody-secreting cells in bone marrow and persisting vaccine-specific serum antibodies. Our study sheds light on the mechanisms behind the adjuvanticity of LT-K63 and identifies molecular pathways that should be triggered by vaccine adjuvants to induce sustained humoral immunity in early life.

Serotype-Independent Protection Against Invasive Pneumococcal Infections Conferred by Live Vaccine With lgt Deletion

Streptococcus pneumoniae is the most common respiratory bacterial pathogen among cases of community-acquired infection in young children, older adults, and individuals with underlying medical conditions. Although capsular polysaccharide-based pneumococcal vaccines have contributed to significant decrease in invasive pneumococcal infections, these vaccines have some limitations, including limited serotype coverage, lack of effective mucosal antibody responses, and high costs. In this study, we investigated the safety and immunogenicity of a live, whole-cell pneumococcal vaccine constructed by deleting the gene for prolipoprotein diacylglyceryl transferase (lgt) from the encapsulated pneumococcal strain TIGR4 (TIGR4Δlgt) for protection against heterologous pneumococcal strains. Pneumococcal strain TIGR4 was successfully attenuated by deletion of lgt, resulting in the loss of inflammatory activity and virulence. TIGR4Δlgt colonized the nasopharynx long enough to induce strong mucosal IgA and IgG2b-dominant systemic antibody responses that were cross-reactive to heterologous pneumococcal serotypes. Finally, intranasal immunization with TIGR4Δlgt provided serotype-independent protection against pneumococcal challenge in mice. Taken together, our results suggest that TIGR4Δlgt is an avirulent and attractive broad-spectrum pneumococcal vaccine candidate. More broadly, we assert that modulation of such "master" metabolic genes represents an emerging strategy for developing more effective vaccines against numerous infectious agents.

Safety and immunogenicity of a candidate bioconjugate vaccine against Shigella dysenteriae type 1 administered to healthy adults: A single blind, partially randomized Phase I study

BACKGROUND

Shigellae cause severe disease in endemic countries, especially in children. Several efficacy trials have been conducted with candidate vaccines against Shigellae, but the lack of protection, the safety concerns, or manufacturing challenges hindered successful market approval. Conjugated vaccines have been shown to be safe and effective for different pathogens (i.e., Neisseria meningitidis, Shigella pneumonia, Haemophilus influenzae). The bio-conjugation technology, exploited here for the Shigella dysenteriae candidate vaccine, offers a novel and potentially simpler way to develop and produce vaccines against one of the major causes of morbidity and mortality in developing countries.

METHODS

A novel S. dysenteriae bioconjugate vaccine (GVXN SD133) made of the polysaccharide component of the Shigella O1 lipopolysaccharide, conjugated to the exotoxin protein A of Pseudomonas aeruginosa (EPA), was evaluated for immunogenicity and safety in healthy adults in a single blind, partially randomized Phase I study. Forty subjects (10 in each dose group; 2 μg or 10 μg with or without aluminium adjuvant) received two injections 60 days apart and were followed-up for 150 days.

RESULTS

Both doses and formulations were well tolerated; the safety and reactogenicity profiles were consistent with that of other conjugated vaccines, adjuvanted or not, independent of the dose and the number of injections. The GVXN SD133 vaccine elicited statistically significant O1 specific humoral responses at all time points in all vaccination groups. Between-group comparisons did not show statistically significant differences in geometric mean titers of immunoglobulin G and A at any post-vaccination time point.

CONCLUSIONS

This study demonstrated that the GVXN SD133 vaccine has a satisfactory safety profile. It elicited a significant humoral response to Shigella O1 polysaccharides at all doses tested. The protein carrier also elicited functional antibodies, showing the technology's advantages in preserving both sugar and conjugated protein epitopes. This trial is registered at ClinicalTrials.gov (NCT01069471).

Pneumococcemia in children--a retrospective study before universal pneumococcal vaccinations

AIM

To evaluate the incidence and characteristics of blood culture-positive occult pneumococcemia compared with blood culture-positive pneumococcal pneumonia in children.

METHODS

In years 2001-2010, 105 children with positive blood cultures for Streptococcus pneumoniae were identified from hospital electronic files. The patient cards were retrospectively charted for clinical and laboratory data, and 38 patients had and 67 had not pneumonia.

RESULTS

The annual incidence of pneumococcemia was, on average, 29.0/10 000 at 0-12 months, 5.3/10 000 at 13-24 months and 1.9/10 000 at 2-4 years of ages, with no increasing or decreasing trend. The incidence of bacteraemic pneumococcal pneumonia increased (p = 0.022) during the study period. The duration of fever before hospitalization (<24 h 73.9% vs. 25.0%, p = 0.022) and the duration of intravenous antibiotics, usually G-penicillin (median 72 vs. 96 h, p = 0.021) was shorter in pneumococcemia patients. On admission, blood leucocyte count was higher in pneumococcemia (mean 26.6 vs. 21.9 × 10E9/L, p = 0.012), but serum CRP was higher in pneumonia (median 160 vs. 67.4 mg/L, p < 0.001). The serotypes 6B and 14 caused 53.2% of pneumococcemia cases.

CONCLUSION

The incidence of pneumococcemia was highest in 1-2-year-old children, and typical for pneumococcemia was rapid onset of fever, high blood leucocyte count and a modestly elevated CRP on admission.

The Spr1875 protein confers resistance to the microglia-mediated killing of Streptococcus pneumoniae

By screening a whole-genome λ-display library of Streptococcus pneumoniae, we have previously identified a novel surface protein, named Spr1875, that exhibited immunogenic properties and was closely related to pneumococcal virulence. In the present study, we investigated the role of the Spr1875 antigen in the interaction of S. pneumoniae with microglia, the resident brain macrophages. By using an in vitro infection model, the BV2 microglial cell line was challenged with the S. pneumoniae strain DP1004 and its isogenic spr1875-deleted mutant (Δspr1875). Both strains were phagocytosed by microglia efficiently and to a similar extent; however, the DP1004 strain was more resistant than the Δspr1875 mutant to the intracellular killing, as assessed by antibiotic protection and phagosome maturation assays. Moreover, significant differences between the two strains were also observed in terms of susceptibility to microglia-mediated killing. Taken together, these results indicate that S. pneumoniae-microglial cell interplay is influenced by the presence of Spr1875, suggesting that this protein may play a role in the pathogenesis of pneumococcal meningitis.

Human pathogenic streptococcal proteomics and vaccine development

Gram-positive streptococci are non-motile, chain-forming bacteria commonly found in the normal oral and bowel flora of warm-blooded animals. Over the past decade, a proteomic approach combining 2-DE and MS has been used to systematically map the cellular, surface-associated and secreted proteins of human pathogenic streptococcal species. The public availability of complete streptococcal genomic sequences and the amalgamation of proteomic, genomic and bioinformatic technologies have recently facilitated the identification of novel streptococcal vaccine candidate antigens and therapeutic agents. The objective of this review is to examine the constituents of the streptococcal cell wall and secreted proteome, the mechanisms of transport of surface and secreted proteins, and describe the current methodologies employed for the identification of novel surface-displayed proteins and potential vaccine antigens.

Programmed cell death 1 suppresses B-1b cell expansion and long-lived IgG production in response to T cell-independent type 2 antigens

B-1b cells play a key role in producing Abs against T cell-independent type 2 Ags. However, the factors regulating Ab production by this unique B cell subset are not well understood. In this study, a detailed analysis of the B cell response to 2,4,6-trinitrophenol (TNP)-Ficoll was performed using normal mice. TNP-Ficoll delivered i.p. or i.v. induced rapid Ag-specific B-1b cell activation, expansion, isotype switching, and plasmablast/plasma cell differentiation. Ag-specific B-1b cell numbers peaked at day 5 and then gradually declined in the spleen but remained elevated in the peritoneal cavity beyond 40 d postimmunization. In addition to expressing CD43, CD44, and CD86, Ag-activated B-1b cells transiently expressed programmed cell death 1 (PD-1), which functionally suppressed BCR-induced B-1b cell in vitro proliferation when additional costimulatory signals were lacking. Inhibiting PD-1:PD-1 ligand interactions during TNP-Ficoll immunization significantly enhanced Ag-specific B-1b cell expansion and the frequency of IgG isotype switching and plasmablast/plasma cell differentiation. Remarkably, PD-1 mAb blockade during the first week following immunization resulted in significantly increased numbers of both splenic and bone marrow Ag-specific IgG3-secreting cells, but not IgM-secreting cells, at both early (day 5) and late (week 6) time points. Moreover, Ag-specific serum IgG3 levels, as well as IgG2c, IgG2b, and IgA levels, remained significantly elevated in PD-1 mAb-treated mice relative to control Ab-treated mice for ≥6 wk postimmunization. Thus, PD-1:PD-1 ligand interactions occurring shortly after initial T cell-independent type 2 Ag encounter play a critical role in suppressing Ag-specific B-1b cell expansion and the development of long-term IgG-producing bone marrow and spleen cells.

Therapeutic targeting of B cells for rheumatic autoimmune diseases

Autoreactive B cells are characterized by their ability to secrete autoantibodies directed against self-peptides. During the last decade, it has become increasingly apparent that B lymphocytes not only produce autoantibodies but also exert important regulatory roles independent of their function as antibody-producing cells. This is especially relevant in the context of autoimmunity, because autoreactive B cells have been shown to possess the ability to activate pathogenic T cells, to produce pro-inflammatory cytokines, and to promote the formation of tertiary lymphoid tissue in target organs. The production of monoclonal antibodies against B-cell-surface molecules has facilitated the characterization of several distinct B lymphocyte subsets. These cell-surface molecules have not only served as useful cell differentiation markers but have also helped to unravel the important biological functions of these cells. Some of these molecules, all of which are expressed on the cell surface, have proven to be effective therapeutic targets. In both animal models and in clinical assays, the efficient elimination of B lymphocytes has been shown to be useful in the treatment of rheumatoid arthritis and other autoimmune diseases. The treatment of most rheumatic autoimmune diseases relies mainly on the use of cytotoxic immunosuppressants and corticosteroids. Although this has resulted in improved disease survival, patients may nonetheless suffer severe adverse events and, in some cases, their relapse rate remains high. The increasing need for safer and more effective drugs along with burgeoning new insights into the pathogenesis of these disorders has fueled interest in biological agents; clinical trials involving the B-cell depletion agent rituximab have been especially promising. This article reviews the current knowledge of B-cell biology and pathogenesis as well as the modern therapeutic approaches for rheumatic autoimmune diseases focusing in particular on the targeting of B-cell-specific surface molecules and on the blocking of B-cell activation and survival.

Synthesis, conjugation, and immunological evaluation of the serogroup 6 pneumococcal oligosaccharides

The first synthesis of the newly discovered oligosaccharide of pneumococcal serotype 6C and its spacer-containing analogue is reported. Conjugation of the spacer-containing oligosaccharides of pneumococcal saccharides 6A, 6B, 6C and derivatives thereof with bovine serum albumin (BSA) protein carrier was carried out by using squaric-acid approach to obtain the oligosaccharide-protein conjugates in excellent yields. The conjugates have been tested with a rabbit antiserum pool (Pool B) used for pneumococcal serotyping. The results showed that synthetic carbohydrate conjugates express epitopes found in native capsular polysaccharides of serotypes 6A, 6B, and 6C.

CD21/35 promotes protective immunity to Streptococcus pneumoniae through a complement-independent but CD19-dependent pathway that regulates PD-1 expression

Humoral immunity to T cell-independent type 2 Ags (TI-2 Ag) is critical for protection against encapsulated bacteria such as Streptococcus pneumoniae. The CD21/35 receptor is thought to promote protective humoral immunity to encapsulated bacteria by enabling complement-decorated capsular polysaccharides to coligate the CD21/35-CD19 signaling complex with the B cell Ag receptor (BCR), thereby enhancing Ag-specific B cell activation. However, Ab responses to S. pneumoniae type 3 capsular polysaccharide (PPS-3) and other strong TI-2 Ags were significantly impaired in CD21/35(-/-) but not C3(-/-) or C4(-/-) mice. B cells from CD21/35(-/-) mice expressed significantly higher levels of cell surface CD19. CD21/35(-/-) B cells exhibited enhanced BCR-induced calcium responses and significantly higher expression of the inhibitory programmed death-1 (PD-1) receptor following immunization with a TI-2 Ag or BCR crosslinking. Reducing CD19 expression in CD21/35(-/-) mice normalized BCR-induced calcium responses, PD-1 induction, and PPS-3-specific IgG3 responses and restored protection during S. pneumoniae infection. PD-1 blockade also selectively rescued PPS-3-specific IgG3 responses in CD21/35(-/-) mice. Thereby, CD21/35 promotes protective humoral immunity to S. pneumoniae and other strong TI-2 Ags through a complement-independent pathway by negatively regulating CD19 expression and PD-1 induction.

IgM in microbial infections: taken for granted?

Much has been learned about the structure, function, and production of IgM, since the antibody's initial characterization. It is widely accepted that IgM provides a first line of defense during microbial infections, prior to the generation of adaptive, high-affinity IgG responses that are important for long-lived immunity and immunological memory. Although IgM responses are commonly used as a measure of exposure to infectious diseases, it is perhaps surprising that the role of and requirement for IgM in many microbial infections has not been well explored in vivo. This is in part due to the lack of capabilities, until relatively recently, to evaluate the requirement for IgM in the absence of coincident IgG responses. Such evaluations are now possible, using gene-targeted mouse strains that produce only IgM, or isotype-switched IgG. A number of studies have revealed that IgM, produced either innately, or in response to antigen challenge, plays an important and perhaps under appreciated role in many microbial infections. Moreover, the characterization of the roles of various B cell subsets, in the production of IgM, and in host defense, has revealed important and divergent roles for B-1a and B-1b cells. This review will highlight studies in which IgM, in its own right, has been found to play an important role, not only in early immunity, but also in long-term protection, against a variety of microbial pathogens. Observations that long-lived IgM responses can be generated in vivo suggest that it may be feasible to target IgM production as part of vaccination strategies.

Synthesis of spacer-containing analogs of serogroup 6 pneumococcal oligosaccharides

An efficient convergent strategy for the synthesis of a range of spacer-containing pneumococcal oligosaccharides of serogroup 6 and derivatives thereof has been developed. The spacer-containing oligosaccharides were deprotected and are available for subsequent conjugation and immunological studies, which are underway in our laboratory.

A rapid pneumococcal serotyping system based on monoclonal antibodies and PCR

Streptococcus pneumoniae expresses at least 91 different polysaccharide (PS) capsules and the currently available serotyping methods are tedious to perform. We have been developing a rapid pneumococcal serotyping assay (named the 'multibead assay') based on the capacity of pneumococcal lysates to inhibit the ability of 24 different anti-capsule antibodies to bind to latex beads coated with 24 different PSs (serotypes 1, 3, 4, 5, 6A, 6B, 7F, 9N, 9V, 14, 18C, 19A, 19F, 23F, 2, 8, 10A, 11A, 12F, 15B, 17F, 20, 22F and 33F). Because the polyclonal antibodies used for 10 serotypes (2, 8, 10A, 11A, 12F, 15B, 17F, 20, 22F and 33F) had limited serotype specificity, we replaced them with monoclonal antibodies for the 10 serotypes. To extend the serotype coverage beyond the 24 serotypes, we have adapted multiplexed PCR for five additional serotypes (15A, 15C, 16F, 35B and 38) to be useful with the pneumococcal lysates prepared for the multibead assay. We then validated the combined assay with 157 clinical isolates from the Centers for Disease Control and Prevention and found that the new combined assay produced results that are concordant with the quellung reaction. The combined assay is robust and could be used to rapidly identify the serotypes of the majority of pneumococci ( approximately 90 %). In addition, the assay validation study suggests the presence of serological subtypes within serotype 11A.

Maturation of Mucosal Immune Responses and Influence of Maternal Antibodies

The mucosae represent the primary point of contact between the major respiratory and enteric pathogens and the innate and adaptive immune response. The microanatomy and function of the mucosal immune system is now well-characterized, in particular the major effector mechanism that involves the production and translocation of secretory immunoglobulin A (IgA). Mucosal delivery of antigen has the potential to induce potent local and systemic immunity, although such responses may differ between neonatal, infant and adult mice. In younger animals mucosal immune responses are Th2 biased, whereas in adults there is a broader Th1 and Th2 responsiveness. There is much interest in the development of mucosally delivered vaccines which can be tailored to enhance Th1 immunity or to avoid potential interference from maternally derived antibodies (MDA). Accordingly, a range of mucosal adjuvants (particularly those derived from bacteria) has been tested, and live recombinant vectored vaccines may also be effectively delivered by this route.

Vaccines in the era of genomics: the pneumococcal challenge

In this review we aim to provide the reader with an understanding of the capsular-based complexity of Streptococcus pneumoniae, one of the main limitations to current vaccine development. We then discuss the need for a new vaccine strategy based on proteic antigen candidates discovered in silico. Describing specifically how reverse vaccinology coupled to conventional vaccinology has led to a new paradigm of vaccine development. Finally, we conclude with the importance of defining the pan-genome of the pneumococcus, that is, the sequencing and analysis of multiple genomes from the same species. A critical factor in determining conserved proteins in a group of epidemiologically relevant circulating S. pneumoniae strains, in order to achieve the greatest coverage. Ultimately, the identification of immunogenic surface antigens and assessment of their efficacy will be imperative in the development of a vaccine with the ability to protect against invasive disease independent of serotype.

Validation of a multiplex pneumococcal serotyping assay with clinical samples

We have recently developed a rapid pneumococcal serotyping method called "multibead assay" (J. Yu et al., J. Clin. Microbiol. 43:156-162, 2005) based on a multiplexed immunoassay for capsular polysaccharides in lysates of pneumococcal cultures. The multibead assay can identify 36 serotypes (1, 2, 3, 4, 5, 6A, 6B, 7A/7F, 8, 9L/9N, 9V, 10A/10B/39/33C, 11A/11D/11F, 12A/12B/12F, 14, 15B/5C, 17F, 18C, 19A, 19F, 20, 22A/22F, 23F, and 33A/33F). More than 90% of the U.S. isolates express one of these serotypes (J. B. Robbins et al., J. Infect. Dis. 148:1136-1159, 1983). To validate the new assay, we examined 495 clinical isolates of pneumococci obtained in Brazil, Denmark, and Mexico. Pneumococci were serotyped by the Neufeld test in their countries of origin, and lysates of each strain were coded and mailed to the United States for the multibead assay at ambient temperature without any thermal protection. After breaking the code, 54 discrepancies (11% of samples) were noted, but 46 were due to nonreproducible technical problems or insufficient growth of the pneumococci. All of the isolates grew well for a second test, and therefore, the culture medium used for the multibead assay is adequate. The discrepancies persisted for eight isolates, involving the 6A, 11A, and 18C serotypes. Additional studies of the eight isolates showed that the discrepancies were due to differences in the reagents used in the multibead or Neufeld tests for these three serotypes. For instance, five isolates were typed as 6A with the Neufeld test but as nontypeable by the multibead assay. Selection of another new monoclonal antibody (Hyp6AG1) for the multibead assay resulted in all five discrepant isolates typing as 6A. This finding indicates the validity of the multibead assay and emphasizes the need to validate any new pneumococcal serotyping assay with a large number of clinical isolates from different locations. It also suggests the presence of serological subtypes among isolates expressing the 6A serotype.

Early life T cell responses to pneumococcal conjugates increase with age and determine the polysaccharide-specific antibody response and protective efficacy

Immunization with a tetanus-protein (TT) pneumococcal polysaccharide (PPS) conjugate vaccine (Pnc1-TT) induces protective immunity against lethal pneumococcal infections in neonatal and infant mice, but anti-PPS IgG response and protective efficacy is lower than in adult mice. Here, we show that reduced antibody (Ab) response and protection against infections is directly related to impaired T cell response to the carrier. Whereas spleen cells from adult mice immunized with Pnc1-TT responded with proliferation and IFN-gamma secretion to in vitro stimulation with TT, spleen cells from neonatal and infant mice did not. However, significant, but age dependent, Th2-cytokine responses were observed in mice immunized with Pnc1-TT. Impaired IFN-gamma production upon TT-stimulation in vitro was also reflected in reduced IFN-gamma/IL-5 ratio. The IL--5 response correlated with IgG anti-PPS titers, and the lack of PPS Ab in the majority of neonatal mice was clearly associated with absence of carrier-specific IL-5 production. These results show that immunization with Pnc1-TT induces carrier-specific T cell responses that increase with age and determine the levels of PPS-specific Ab elicited. Whereas a weak and Th2-biased response was observed in neonatal mice, infant mice showed a mixed Th1-Th2 response as observed in adults.

B-1a and B-1b Cells Exhibit Distinct Developmental Requirements and Have Unique Functional Roles in Innate and Adaptive Immunity to S. pneumoniae

B-1a and B-1b lymphocytes were found to exhibit specialized roles in providing immunity to Streptococcus pneumoniae and differ dramatically in their developmental requirements. Transgenic mice overexpressing CD19 (hCD19Tg) generated B-1a cells and natural antibodies that provided protection during infection, while CD19-deficient (CD19(-/-)) mice lacked B-1a cells, lacked natural antibodies, and were more susceptible to infection. By contrast, pneumococcal polysaccharide (PPS) immunization protected CD19(-/-) mice during lethal challenge, whereas hCD19Tg mice remained unprotected. This resulted from differences in the B-1b subset: the key population found to produce protective PPS-specific antibody in both wild-type and CD19(-/-) mice. Thus, CD19(-/-) mice generated B-1b cells and protective adaptive PPS-specific antibody responses, whereas hCD19Tg mice lacked B-1b cells and adaptive PPS-specific antibody responses. This reciprocal contribution of B-1a and B-1b subsets to innate and acquired immunity reveals an unexpected division of labor within the B-1 compartment that is normally balanced by their coordinated development.

The advantage of mucosal immunization for polysaccharide-specific memory responses in early life

The aim of vaccination is to rapidly elicit protective immunity and generate memory for sustained protection. We studied the induction and persistence of polysaccharide (PS)-specific memory in neonatal and infant mice primed with pneumococcal conjugate (Pnc1-TT) by assessing the response to native pneumococcal PS (PPS-1), the kinetics of the PPS-1-specific IgG response to a second Pnc1-TT dose and affinity maturation. A subcutaneous (s.c.) Pnc1-TT booster induced a rapid increase in PPS-1-specific IgG, indicating efficient priming for memory by a single dose of Pnc1-TT already at 1 week of age. High levels were maintained for >12 weeks. However, a PPS-1 booster induced no response in neonatal or infant mice. The adjuvant LT-K63 significantly enhanced the IgG response and affinity to Pnc1-TT by both the s.c. and the intranasal (i.n.) route in all age groups. In neonatal and infant mice, PPS-1 and LT-K63 induced a booster response only when given i.n. following either s.c. or i.n. priming with Pnc1-TT and LT-K63. In contrast, PPS-1 with or without LT-K63 administered s.c. compromised the ongoing PPS-1-specific response elicited in neonatal mice by either s.c. or i.n. priming with Pnc1-TT and LT-K63. These results demonstrate the advantage of the mucosal route for elicitation of PS-specific memory responses in early life.

The lack of Pneumococcal surface protein C (PspC) increases the susceptibility of Streptococcus pneumoniae to the killing by microglia

Microglial cells, the resident phagocytes in the brain, share many phenotypical and functional characteristics with peripheral macrophages, suggesting that they may participate in an innate immune response against microorganisms invading the central nervous system (CNS). In this study, we demonstrate that the microglial cells constitutively exhibit antibacterial activity in vitro against Streptococcus pneumoniae. By using a Pneumococcal surface protein C (PspC)-deleted strain and its wild-type counterpart, we found that the extent of such an activity is significantly influenced by the presence of a PspC molecule on the bacterial surface. The PspC- mutant FP20 is indeed more susceptible than the PspC+ strain HB565 to microglial killing. Interestingly, this phenomenon is observed when using a medium supplemented with heat-inactivated foetal bovine serum (FBS). Electron microscopy studies indicate that the microglial cells interact more efficiently with PspC- than with PspC+ pneumococci. Moreover, upon infection with the PspC- mutant, microglial cells produce levels of TNF-alpha, MIP-2, IL-10 and nitric oxide, significantly higher than those observed with PspC+ bacteria. These findings indicate that the lack of PspC significantly enhances the susceptibility of S. pneumoniae to both bactericidal activity and secretory response by the microglial cells, suggesting that this molecule may play an important role in the invasion of CNS by pneumococcus.

Assignment of weight-based antibody units for 13 serotypes to a human antipneumococcal standard reference serum, lot 89-S(f)

Weight-based immunoglobulin G (IgG), IgM, IgA, and total Ig antibody assignments were made to human antipneumococcal standard reference serum lot 89-S, also known as lot 89-SF, for Streptococcus pneumoniae capsular polysaccharide (PnPs) serotypes 2, 6A, 8, 9N, 10A, 11A, 12F, 15B, 19A, 17F, 20, 22F, and 33F, as well as for C-polysaccharide (C-Ps), extending the standard's usefulness for pneumococcal vaccine evaluation beyond the original serotype 1, 3, 4, 5, 6B, 7F, 9V, 14, 18C, 19F, and 23F assignments (S. A. Quataert, C. S. Kirch, L. J. Quackenbush Wiedl, D. C. Phipps, S. Strohmeyer, C. O. Cimino, J. Skuse, and D. V. Madore, Clin. Diagn. Lab. Immunol. 2:590-597, 1995). The additional 14 assignments were determined using an equivalence of absorbance method with an anti-PnPs serotype 6B reference enzyme-linked immunosorbent assay (EIA). To assure accuracy, anti-PnPs EIA for serotype 14 antibodies, a previously assigned serotype, was performed concurrently. This method assures consistency of the new microgram-per-microliter assignments with previous antiserotype assignments to lot 89-S. The sum of the experimentally derived isotype assignments for anti-PnPs serotypes in lot 89-S agrees well with the separately determined total Ig assignment for each serotype. The lot 89-S assignments for serotypes 1, 5, 6B, 14, 18C, 19F, and 23F were used for pneumococcal conjugate vaccine clinical trial evaluation and to generate data in efficacy trials where serological correlates for protection have been proposed. The assignment of antibody concentrations to additional pneumococcal serotypes in this reference reagent facilitates the consistent and accurate comparison of serum antibody concentrations across clinical trials.

Effect of the seven-valent conjugate pneumococcal vaccine on carriage and drug resistance of Streptococcus pneumoniae in healthy children attending day-care centers in Lisbon

AIMS

Prospective study to evaluate the impact of the 7-valent pneumococcal conjugate vaccine (Prevenar) on the nasopharyngeal (NP) carriage of drug-resistant Streptococcus pneumoniae (DRPn), by healthy children attending day-care centers (ages 6 months-6 years).

METHODS

Vaccinees (238 children) who received vaccine and controls (457 children) were followed for carriage of total S. pneumoniae and DRPn and for the serotypes and genetic backgrounds of DRPn during 6 consecutive sampling periods between May 2001 and February 2003.

RESULTS

We detected no significant differences between vaccinees and the control group in the total carriage rate of Pn (average, 68%) or in the frequency of carriage of DRPn (average, 38%), including the frequency of penicillin-nonsusceptible strains (average, 24%). In contrast, there was a decline in the carriage of DRPn with vaccine serotypes which was compensated by the appearance and gradual increase in the frequency of DRPn expressing unusual serotypes (6A, 10A, 15A and 15C, 19A, 23A, 33F) which were not present in the vaccine as well as an increase in nontypable strains. The majority of the DRPn with unusual serotypes showed different pulsed field gel electrophoresis patterns indicating replacement of the original resistant flora by other clonal types of drug-resistant bacteria. Antibiotic consumption and the frequency of respiratory tract infections were similar among the vaccinees and controls.

CONCLUSIONS

Pneumococcal vaccination did not change the frequency of carriage of drug-resistant strains being the initially dominant vaccine serotypes replaced by others expressing nonvaccine serotypes. Reduction in the carriage of DRPn may require a combination of the conjugate vaccine and a decrease in antibiotic pressure.

Rapid multiplex assay for serotyping pneumococci with monoclonal and polyclonal antibodies

We have developed and characterized a rapid semiautomated pneumococcal serotyping system incorporating a pneumococcal lysate preparation protocol and a multiplex serotyping assay. The lysate preparation incorporates a bile solubility test to confirm pneumococcal identification that also enhances assay specificity. The multiplex serotyping assay consists of 24 assays specific for 36 serotypes: serotypes 1, 2, 3, 4, 5, 6A, 6B, 7A/7F, 8, 9L/9N, 9V, 10A/10B/39/(33C), 11A/11D/11F, 12A/12B/12F, 14, 15B/(15C), 17F, 18C, 19A, 19F, 20, 22A/22F, 23F, and 33A/33F. The multiplex assay requires a flow cytometer, two sets of latex particles coated with pneumococcal polysaccharides, and serotype-specific antibodies. Fourteen newly developed monoclonal antibodies specific for common serotypes and a pool of polyclonal rabbit sera for some of the less-common serotypes are used. The two monoclonal antibodies specific for serotypes 18C and 23F recognize serotype-specific epitopes that have not been previously described. These monoclonal antibodies make the identification of the 14 common serotypes invariant. The specificity of the serotyping assay is fully characterized with pneumococci of all known (i.e., 90) serotypes. The assay is sensitive enough to use bacterial lysates diluted 20 fold. Our serotyping system can identify not only all the serotypes in pneumococcal vaccines but also most (>90%) of clinical isolates. This system should be very useful in serotyping clinical isolates for evaluating pneumococcal vaccine efficacy.

Immunogenicity and safety of the eleven valent pneumococcal polysaccharide-protein D conjugate vaccine in infants

BACKGROUND

Development is ongoing to increase the serotype coverage of pneumococcal conjugate vaccines. We report here the immunogenicity and safety of a new 11-valent pneumococcal conjugate vaccine (Pn-PD) in infants.

METHODS

In a randomized, single blind study, 154 Finnish infants received 1 of 3 regimens: 4 doses of Pn-PD at 2, 4, 6 and 12-15 months; 3 doses of the Pn-PD at 2, 4 and 6 months and 1 dose of 23-valent polysaccharide vaccine (PncPS) at 12-15 months; or 3 doses of the hepatitis B vaccine at 2, 4 and 6 months and Pn-PD at 12-15 months. Serum IgG antibodies to vaccine serotypes 1, 3, 4, 5, 6B, 7F, 9V, 14, 18C, 19F and 23F were measured with an enzyme immunoassay at the ages of 2, 7 and 12-15 months and at 4 or 28 days after the last vaccination. Local and systemic reactions were recorded by parents during 8 days after each dose. Serious adverse reactions were recorded during the entire study period.

RESULTS

There was a significant increase in the IgG concentrations to vaccine serotypes after 3 doses of Pn-PD. Antibody concentrations after the primary series varied between 1.26 and 4.92 microg/ml depending on the serotype and study group. PncPS vaccine induced a better booster response than the Pn-PD, measured at 28 days after the fourth dose. IgG concentrations after the Pn-PD booster ranged between 1.60 and 9.63 microg/ml and after the PncPS booster between 4.24 and 40.54 microg/ml, depending on the serotype. The antibody concentrations after the first dose of Pn-PD administered at 12-15 months increased significantly but were lower than after the fourth dose at the same age. No significant antibody increase was measured 4 days after the vaccinations at 12-15 months. The safety profile of the vaccine was acceptable.

CONCLUSIONS

The Pn-PD we tested was immunogenic and safe in infants.

Glycolytic enzymes associated with the cell surface of Streptococcus pneumoniae are antigenic in humans and elicit protective immune responses in the mouse

Streptococcus pneumoniae is a leading cause of otitis media, sinusitis, pneumonia, bacteraemia and meningitis worldwide. The drawbacks associated with the limited number of various capsular polysaccharides that can be included in the polysaccharide-based vaccines focuses much attention on pneumococcal proteins as vaccine candidates. We extracted an enriched cell wall fraction from S. pneumoniae WU2. Approximately 150 soluble proteins could be identified by 2D gel electrophoresis. The proteins were screened by 2D-Western blotting using sera that were obtained longitudinally from children attending day-care centres at 18, 30 and 42 months of age and sera from healthy adult volunteers. The proteins were further identified using matrix-assisted laser desorption ionization-time of flight mass spectrometry. Seventeen proteins were antigenic in children and adults, of which 13 showed an increasing antibody response with age in all eight children analysed. Two immunogenic proteins, fructose-bisphosphate aldolase (FBA) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and a control protein with known low immunogenicity, heat shock protein 70 (DnaK), were expressed in Escherichia coli, purified and used to immunize mice. Mouse antibodies elicited to the recombinant (r) FBA and rGAPDH were cross-reactive with several genetically unrelated strains of different serotypes and conferred protection to respiratory challenge with virulent pneumococci. In addition, the FBA used in this study (NP_345117) does not have a human ortholog and warrants further investigation as a candidate for a pneumococcal vaccine. In conclusion, the immunoproteomics based approach utilized in the present study appears to be a suitable tool for identification of novel S. pneumoniae vaccine candidates.

Pneumococcal conjugate vaccines for preventing vaccine-type invasive pneumococcal disease and pneumonia with consolidation on x-ray in children under two years of age

BACKGROUND

Pneumonia, most commonly caused by Streptococcus pneumoniae (Pnc), is a major cause of morbidity and mortality among young children especially in developing countries. Recently, the prevalence of antibiotic-resistant Pnc has increased worldwide such that the effectiveness of preventive strategies, like the new pneumococcal conjugate vaccines (PCV) on rates of invasive pneumococcal disease (IPD) and pneumonia, needs to be evaluated.

OBJECTIVES

To determine the efficacy of PCV in reducing the incidence of IPD due to vaccine serotypes (VT) and x-ray confirmed pneumonia with consolidation of unspecified etiology in children who received PCV before 12 months of age.

SEARCH STRATEGY

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, Issue 1 2004), MEDLINE (1990 to March 2004) and EMBASE (1990 to December 2003). Reference list of articles, and books of abstracts of relevant symposia, were hand searched. Researchers in the field were also contacted.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing PCV with placebo, or another vaccine, among children below two years with IPD and clinical/radiographic pneumonia as outcomes.

DATA COLLECTION AND ANALYSIS

Two reviewers independently identified eligible studies, assessed trial quality, and extracted data. Differences were resolved by discussion. The inverse variance method was used to pool effect sizes.

MAIN RESULTS

We identified four trials assessing the efficacy of PCV in reducing the incidence of IPD, two on x-ray confirmed pneumonia as outcome, and one on clinical pneumonia, with or without x-ray confirmation. Results from pooling HIV-1 negative children from the South African study with the other studies were as follows: the pooled vaccine efficacy (VE) for vaccine-type IPD was 88% (95% confidence interval (CI) 73% to 94%; fixed effect and random effects models), the effect measure was statistically significant (p <0.00001) and there was no heterogeneity (p = 0.77I2 0%); the pooled VE for all-serotype IPD was 66% (95% CI 46% to 79%; fixed effect model), the effect measure was statistically significant (p <0.00001) and there was no statistical heterogeneity (p = 0.09, I2 51%); the pooled VE for x-ray confirmed pneumonia was 22% (95% CI 11% to 31%; both fixed effect and random effects models) and there was no statistical heterogeneity (p = 0.80, I2 0%). Analyses that included all the children in the South African study (HIV-1 negative and HIV-1 positive children) and pooled with data from the other studies gave very similar results.

REVIEWERS' CONCLUSIONS

PCV is effective in reducing the incidence of IPD from all serotypes but exerts a greater effect in reducing VT IPD. Although PCV is also effective in reducing the incidence of x-ray confirmed pneumonia, there are still uncertainties about the definition of this outcome. Additional randomised controlled trials are currently in progress.

Pneumococcal conjugate vaccines—a European perspective

Streptococcus pneumoniae is a leading cause of bacterial pneumonia, meningitis, and acute otitis media in children and adults worldwide. In the age group of < 2 years the incidence of invasive pneumococcal disease ranges from approximately 14 cases per 100,000 in Germany and the Netherlands and more than 90 per 100,000 children in Spain. The vulnerability of children to S. pneumoniae can also be demonstrated by the high rate of sequelae (> 20% in Germany) and the high mortality (7.5%) in pneumococcal meningitis. Furthermore, antibiotic resistance of S. pneumoniae is increasing in Europe, particularly in France, Spain, and Eastern European countries, whereas Germany and Northern Europe are only marginally affected. A 7-valent pneumococcal conjugate vaccine (7vPCV) that was shown to be highly efficacious in preventing invasive pneumococcal disease in infants in the USA was licensed in Europe in 2001. It is expected that broad usage of the vaccine would reduce the incidence of invasive pneumococcal disease and the levels of pneumococcal resistance significantly. Important questions have been raised regarding the effectiveness of this vaccine in high-risk populations, serotype replacement, the efficacy of this vaccine in otitis media, and the co-administration of the new vaccine with other standard childhood vaccines used in various European countries. France and Spain currently have the most-wide ranging guidelines recommending pneumococcal vaccination for children. Overall, the development of pneumococcal conjugate vaccines is a significant step in the control of pneumococcal disease in children in Europe. Further progress in pneumococcal vaccine development can be expected from conjugate vaccines including more than seven serotypes (9-valent, 11-valent).

Protection against pneumococcal pneumonia in mice by monoclonal antibodies to pneumolysin

Pneumolysin (PLY) is an important virulence factor of Streptococcus pneumoniae. We examined the ability of three murine monoclonal antibodies (MAbs) to PLY (PLY-4, PLY-5, and PLY-7) to affect the course of pneumococcal pneumonia in mice. The intravenous administration of antibodies PLY-4 and PLY-7 protected the mice from the lethal effect of the purified toxin. Mice treated with PLY-4 before intranasal inoculation of S. pneumoniae type 2 survived longer (median survival time, 100 h) than did untreated animals (median survival time, 60 h) (P < 0.0001). The median survival time for mice treated with a combination of PLY-4 and PLY-7 was 130 h, significantly longer than that for mice given isotype-matched indifferent MAbs (P = 0.0288) or nontreated mice (P = 0.0002). The median survival time for mice treated with a combination of three MAbs was significantly longer (>480 h) than that for mice treated with PLY-5 (48 h; P < 0.0001), PLY-7 (78 h; P = 0.0007), or PLY-4 (100 h; P = 0.0443) alone. Similarly, the survival rate for mice treated with three MAbs (10 of 20 mice) was significantly higher than the survival rate obtained with PLY-5 (1 of 20; P = 0.0033), PLY-4 (2 of 20; P = 0.0138), or PLY-7 (3 of 20; P = 0.0407) alone. These results suggest that anti-PLY MAbs act with a synergistic effect. Furthermore, MAb administration was associated with a significant decrease in bacterial lung colonization and lower frequencies of bacteremia and tissue injury with respect to the results for the control groups.

N19 polyepitope as a carrier for enhanced immunogenicity and protective efficacy of meningococcal conjugate vaccines

N19, a string of human universal CD4 T-cell epitopes from various pathogen-derived antigens, was shown to exert a stronger carrier effect than CRM197 for the induction of anti-group C Neisseria meningitidis capsular polysaccharide (MenC), after immunization of mice with various dosages of N19-MenC or CRM-MenC conjugate vaccines. After two immunizations, the N19-based construct induced anti-MenC antibody and protective bactericidal antibody titers higher than those induced by three doses of the CRM-MenC conjugate and required lower amounts of conjugate. N19-based conjugates are superior to CRM-based conjugates to induce protective immune responses to MenC conjugates.

Development of experimental carbohydrate-conjugate vaccines composed of Streptococcus pneumoniae capsular polysaccharides and the universal helper T-lymphocyte epitope (PADRE®)

Experimental carbohydrate-conjugate vaccines composed of the 13 amino acid universal Pan HLA-DR Epitope (PADRE) and Streptococcus pneumoniae capsular polysaccharides from serotypes 14, 6B and 9V were produced. Simple carbodiimide-mediated condensation chemistry was used to conjugate the PADRE synthetic peptide to the three chemically different capsular polysaccharides in a 1:1 molar ratio. The immunogenicity of the PADRE peptide component of the conjugate vaccines was confirmed by the induction of PADRE-specific CD4+ helper T cell (HTL) responses following immunization of C57BL/6 mice. High titer antibody responses specific for polysaccharides of S. pneumoniae serotypes 14, 6B and 9V were induced using Complete Freund's Adjuvant (CFA) and alhydrogel Al(OH)3 formulations. The HTL, or carrier, effect of the PADRE synthetic peptide was only evident using the PADRE-polysaccharide conjugates; simple mixtures of the PADRE peptide and polysaccharides were essentially nonimmunogenic. The functional or potential protective value of the polysaccharide-specific antibodies was measured as a function of opsonophagocytic activity for the 6B serotype. High titers of opsonophagocytic activity were measured in sera from mice immunized with formulations containing both adjuvants. These data demonstrate that the PADRE synthetic peptide can induce the HTL responses needed to support the development of antibodies specific for bacterial carbohydrates used in conjugate vaccines.

FcgammaRIIb balances efficient pathogen clearance and the cytokine-mediated consequences of sepsis

The immune response to infection must be controlled to ensure it is optimal for defense while avoiding the consequences of excessive inflammation, which include fatal septic shock. Mice deficient in FcgammaRIIb, an inhibitory immunoglobulin G Fc receptor, have enhanced immune responses. Therefore, we examined whether FcgammaRIIb controls the response to Streptococcus pneumoniae. Macrophages from FcgammaRIIb-deficient mice showed increased antibody-dependent phagocytosis of pneumococci in vitro, and consistent with this infected FcgammaRIIb-deficient mice demonstrated increased bacterial clearance and survival. In contrast, previously immunized FcgammaRIIb-deficient mice challenged with large inocula showed reduced survival. This correlated with increased production of the sepsis-associated cytokines tumor necrosis factor alpha and interleukin 6. We propose that FcgammaRIIb controls the balance between efficient pathogen clearance and the cytokine-mediated consequences of sepsis, with potential therapeutic implications.

Safety and immunogenicity of three doses of an eleven-valent diphtheria toxoid and tetanus protein--conjugated pneumococcal vaccine in Filipino infants

BACKGROUND

An 11-valent pneumococcal conjugate vaccine could provide significantly larger reduction in pneumococcal disease burden than the currently available 7-valent vaccine formulation in many countries.

METHODS

In total, 50 infants were enrolled to this open, uncontrolled study, which evaluated the safety and immunogenicity of an aluminium adjuvanted 11-valent mixed-carrier diphtheria toxoid or tetanus protein-conjugated vaccine (11-PncTD) when administered in three doses at 6, 10 and 14 weeks of age simultaneously with DTwP//PRP-T and OPV vaccines in Filipino infants.

RESULTS

The rates of local reactions between the two injection sites, those associated with the 11-PncTD vaccine and those with the DTwP//PRP-T were almost of equal frequency for all three vaccine doses except for induration, which was significantly more common in the DTP//PRP-T injection site. Fever was present in 39%, 22% and 21% of infants following each of the three doses. Antibody responses were determined by an enzyme immunoassay method before the first vaccination and after the three doses. The vaccine elicited a significant anti-pneumococcal polysaccharide antibody response against all serotypes included in the vaccine, except for type 14, for which the pre-vaccination geometric mean antibody concentration (GMC) was high (1.61 microg/ml). The GMCs one month after the vaccination series ranged from 1.1 micrograms/ml for type 6B to 23.4 microg/ml for type 4.

CONCLUSION

The 11-PncTD vaccine is safe, well-tolerated and immunogenic. The effectiveness of the non-adjuvanted formulation of the vaccine in preventing pneumonia is currently being evaluated in the Philippines.

Mucosal vaccination against encapsulated respiratory bacteria--new potentials for conjugate vaccines?

Polysaccharide (PS)-encapsulated bacteria such as Haemophilus influenzae type b (Hib), Streptococcus pneumoniae (pneumococcus), Neisseria meningitides (meningococcus) and group B streptococcus (GBS), cause a major proportion of disease in early childhood. Native PS vaccines are immunogenic and provide protection against disease in healthy adults but do not induce immunological memory. PSs are T-cell-independent antigens and do not elicit antibodies in infants and young children, but by conjugating PS to proteins they become T-cell dependent and immunogenic at an early age. Despite excellent efficacy of PS-protein conjugate vaccines against invasive disease, protection against mucosal infections such as pneumococcal otitis media has been less efficacious. Circulating PS-specific antibodies may protect against infections at mucosal sites, but mucosal immunoglobulin A antibodies may also contribute significantly to protection against mucosal infections. Mucosal immunization of experimental animals with conjugate vaccines against Hib, pneumococcus, meningococcus and GBS induces systemic and mucosal immune responses, which provide protection against carriage, otitis media and invasive disease in a variety of challenge models, providing new means for protection against encapsulated bacteria. In addition, mucosal immunization of neonatal mice with a pneumococcal conjugate and the nontoxic adjuvant LT-K63 has been superior to parenteral immunization in eliciting protective antibodies and PS-specific memory, and thus circumventing the limitations of antibody responses to PS that are responsible for enhanced susceptibility of neonates and infants to infections caused by encapsulated bacteria. Through T-cell dependent enhanced immunogenicity of PS-protein conjugate vaccines, mucosal immunization could be an attractive approach for early life immunization against encapsulated bacteria.

Contribution of a response regulator to the virulence of Streptococcus pneumoniae is strain dependent

Bacterial two-component signal transduction systems (TCS) enable bacteria to respond to environmental changes and regulate a range of genes accordingly. They have a crucial role in regulating many cellular responses and have excellent potential as antibacterial-drug targets. We have constructed mutations in a TCS response regulator gene for two different strains of the human pathogen Streptococcus pneumoniae. These mutants have been analyzed in our murine model of infection. Data suggest that in a D39 background the response regulator gene is essential for virulence; an isogenic mutant is avirulent via intraperitoneal, intranasal, and intravenous routes of infection. This mutant, which does not show impaired growth in vitro, is unable to grow in the lung tissue or in blood. Mutation of the response regulator in a 0100993 background results in a strain that is fully virulent intraperitoneally and intravenously but shows decreased levels of bacteremia and increased murine survival following intranasal infection. The ability to grow in the lung tissue is not impaired in this mutant, suggesting that it has an impaired ability to disseminate from the lungs to the systemic circulation. Our data highlight the importance of assessing the contribution of putative virulence factors to the infection process at different sites of infection and provide evidence that virulence determinants can behave very differently based on the genetic background of the bacterial strain. These important findings may be relevant to other bacterial pathogens.

Safety and efficacy of meningococcal group C conjugate vaccines

The UK was the first country to implement a universal vaccination programme with conjugate polysaccharide vaccines against Neisseria meningitidis group C. This article reviews the pre- and postlicensure data on their efficacy and safety 3 years after the introduction of the programme. Local reactogenicity data compare favourably with other routine vaccinations and no specific increase in adverse reactions has been associated with their use in infant vaccination programmes. Self-limiting systemic reactions such as fever, myalgia, headaches and irritability have commonly been observed in prelicensure studies. Passive postlicensure safety monitoring of suspected adverse reactions has identified a large number of reports, generally of reactions deemed non-serious and reversible. An Expert Working Group has concluded the balance of benefits and risks to be overwhelmingly favourable. Further safety data are expected from large data-linkage studies. Present efficacy estimates, based on active surveillance of case numbers, vaccine failures and coverage rates, are approximately 90% for all age groups. A significant fall in the number of cases attributable to meningococcal group C infection has been observed in the age group of < 20 years. The annual number of fatalities from confirmed meningococcal C disease in the same population has fallen from 67 to 5 cases within a 2-year period.