Pneumococcal pneumonia and bacteremia model in mice for the analysis of protective antibodies

Promoting Fc-Fc interactions between anti-capsular antibodies provides strong immune protection against Streptococcus pneumoniae

Streptococcus pneumoniae is the leading cause of community-acquired pneumonia and an important cause of childhood mortality. Despite the introduction of successful vaccines, the global spread of both non-vaccine serotypes and antibiotic-resistant strains reinforces the development of alternative therapies against this pathogen. One possible route is the development of monoclonal antibodies (mAbs) that induce killing of bacteria via the immune system. Here, we investigate whether mAbs can be used to induce killing of pneumococcal serotypes for which the current vaccines show unsuccessful protection. Our study demonstrates that when human mAbs against pneumococcal capsule polysaccharides (CPS) have a poor capacity to induce complement activation, a critical process for immune protection against pneumococci, their activity can be strongly improved by hexamerization-enhancing mutations. Our data indicate that anti-capsular antibodies may have a low capacity to form higher-order oligomers (IgG hexamers) that are needed to recruit complement component C1. Indeed, specific point mutations in the IgG-Fc domain that strengthen hexamerization strongly enhance C1 recruitment and downstream complement activation on encapsulated pneumococci. Specifically, hexamerization-enhancing mutations E430G or E345K in CPS6-IgG strongly potentiate complement activation on S. pneumoniae strains that express capsular serotype 6 (CPS6), and the highly invasive serotype 19A strain. Furthermore, these mutations improve complement activation via mAbs recognizing CPS3 and CPS8 strains. Importantly, hexamer-enhancing mutations enable mAbs to induce strong opsonophagocytic killing by human neutrophils. Finally, passive immunization with CPS6-IgG1-E345K protected mice from developing severe pneumonia. Altogether, this work provides an important proof of concept for future optimization of antibody therapies against encapsulated bacteria.

Rhizodegradation of Pyrene by a Non-pathogenic Klebsiella pneumoniae Isolate Applied With Tagetes erecta L. and Changes in the Rhizobacterial Community

The non-clinical Klebsiella pneumoniae variants, isolated from different environments, are now well acknowledged for their role in plant-growth promotion and biodegradation of pollutants. In the present study, a non-clinical environmental isolate K. pneumoniae AWD5 is being described for rhizoremediation of pyrene, applied through the rhizosphere of an ornamental plant, Tagetes erecta L (marigold). The non-pathogenic nature of AWD5 was established using an in vivo mouse model experiment, where AWD5 was unable to cause lung infection in tested mice. Degradation of pyrene, in the presence of succinate as co-substrate, was observed to be 87.5% by AWD5, after 21 days of incubation in minimal (Bushnell–Hass) medium in vitro conditions. Consequently, the bacterial inoculation through the rhizosphere of T. erecta L. plants resulted in 68.61% degradation of pyrene, which was significantly higher than control soil. Inoculation of AWD5 also improved plant growth and exhibited an increase in root length (14.64%), dry root weight (80.56%), shoot length (3.26%), and dry shoot weight (45.35%) after 60 days of incubation. T. erecta L., an ornamental plant, was also found to be suitable for bioremediation of pyrene. The effect of AWD5 application, and rhizoremediation process, on rhizosphere bacterial diversity and community structure has been studied using the metagenomic analysis of the 16S (V3–V4) region of rRNA. 37 bacterial phyla constituted the core microbiome, which was dominated by Proteobacteria followed by Actinobacteria, Actinobacteria, and Planctomycetes for all the treatments. AWD5 inoculation enhanced the relative abundance of Firmicutes and Acidobacteria as compared with other treatments. Genus Kaistobacter and Verrucomicrobia were found to be an abundant indigenous population in pyrene-spiked soils. Bacterial richness and diversity were analyzed using the Shannon–Wiener (H) index. A lower diversity index was observed in pyrene-spiked soils. Canonical correspondence analysis (CCA) showed a possible linkage with plant growth attributes and available nitrogen content that influences diversity and abundance of the bacterial community.

Comparative evaluation of a newly developed 13-valent pneumococcal conjugate vaccine in a mouse model

Animal models facilitate evaluation of vaccine efficacy at relatively low cost. This study was a comparative evaluation of the immunogenicity and protective efficacy of a new 13-valent pneumococcal conjugate vaccine (PCV13) with a control vaccine in a mouse model.

After vaccination, anti-capsular antibody levels were evaluated by pneumococcal polysaccharide (PnP) enzyme-linked immunosorbent assay (ELISA) and opsonophagocytic killing assay (OPA). Also, mice were challenged intraperitoneally with 100-fold of the 50% lethal dose of Streptococcus pneumoniae.

The anti-capsular IgG levels against serotypes 1, 4, 7F, 14, 18C, 19A, and 19F were high (quartile 2 >1,600), while those against the other serotypes were low (Q2 ≤ 800). Also, the OPA titres were similar to those determined by PnP ELISA. Comparative analysis between new PCV13 and control vaccination group in a mouse model exhibited significant differences in serological immunity of a few serotypes and the range of anti-capsular IgG in the population. Challenge of wild-type or neutropenic mice with serotypes 3, 5, 6A, 6B, and 9V showed protective immunity despite of induced relatively low levels of anti-capsular antibodies. With comparison analysis, a mouse model should be adequate for evaluating serological efficacy and difference in the population level as preclinical trial.

Competition for FcRn-mediated transport gives rise to short half-life of human IgG3 and offers therapeutic potential

Human IgG3 displays the strongest effector functions of all IgG subclasses but has a short half-life for unresolved reasons. Here we show that IgG3 binds to IgG-salvage receptor (FcRn), but that FcRn-mediated transport and rescue of IgG3 is inhibited in the presence of IgG1 due to intracellular competition between IgG1 and IgG3. We reveal that this occurs because of a single amino acid difference at position 435, where IgG3 has an arginine instead of the histidine found in all other IgG subclasses. While the presence of R435 in IgG increases binding to FcRn at neutral pH, it decreases binding at acidic pH, affecting the rescue efficiency-but only in the presence of H435-IgG. Importantly, we show that in humans the half-life of the H435-containing IgG3 allotype is comparable to IgG1. H435-IgG3 also gave enhanced protection against a pneumococcal challenge in mice, demonstrating H435-IgG3 to be a candidate for monoclonal antibody therapies.

Identification of a conserved chromosomal region encoding Klebsiella pneumoniae type 1 and type 3 fimbriae and assessment of the role of fimbriae in pathogenicity

Type 3 fimbriae are expressed by most clinical Klebsiella pneumoniae isolates and mediate adhesion to host structures in vitro. However, the role of type 3 fimbriae in K. pneumoniae virulence has not been evaluated by use of in vivo infection models. In this study, the type 3 fimbrial gene cluster (mrk) of the clinical isolate C3091 is described in detail. The mrk gene cluster was revealed to be localized in close proximity to the type 1 fimbrial gene cluster. Thus, a 20.4-kb fimbria-encoding region was identified and found to be highly conserved among different K. pneumoniae isolates. Interestingly, a homologue to PecS, known as a global regulator of virulence in Erwinia chrysanthemi, was identified in the fimbria-encoding region. Comparison to the previously characterized plasmid encoded mrk gene cluster revealed significant differences, and it is established here that the putative regulatory gene mrkE is not a part of the chromosomally encoded type 3 fimbrial gene cluster. To evaluate the role of type 3 fimbriae in virulence, a type 3 fimbria mutant and a type 1 and type 3 fimbria double mutant was constructed. Type 3 fimbria expression was found to strongly promote biofilm formation. However, the fimbria mutants were as effective at colonizing the intestine as the wild type, and their virulence was not attenuated in a lung infection model. Also, in a urinary tract infection model, type 3 fimbriae did not influence the virulence, whereas type 1 fimbriae were verified as an essential virulence factor. Thus, type 3 fimbriae were established not to be a virulence factor in uncomplicated K. pneumoniae infections. However, since type 3 fimbriae promote biofilm formation, their role in development of infections in catheterized patients needs to be elucidated.

IC31, a two-component novel adjuvant mixed with a conjugate vaccine enhances protective immunity against pneumococcal disease in neonatal mice

IC31 is a novel adjuvant which combines the immunostimulatory effects of an 11-mer antibacterial peptide (KLKL(5)KLK) and a synthetic oligodeoxynucleotide (ODN1a) which is a Toll-like receptor 9 agonist without containing cytosine phosphate guanine (CpG) motifs. The effects of IC31 on neonatal immune response to vaccination have not been reported. Neonatal mice were immunized once or twice with a Streptococcus pneumoniae serotype 1 polysaccharide conjugate containing Tetanus Toxoid (Pnc1-TT) carrier protein, with or without IC31 or CpG-ODN. IC31 significantly enhanced IgG1, IgG2a and IgG2b antibodies (Ab) to the serotype 1 polysaccharide. One dose of Pnc1-TT and low dose IC31 elicited high Ab levels that protected the neonatal mice completely from bacteraemia and significantly reduced lung infection following i.n. challenge with serotype 1 pneumococcal strain. One-sixth of an adult murine dose of IC31 was sufficient and optimal for induction of protective immunity in neonatal mice. Two doses of Pnc1-TT with or without adjuvants protected the neonatal mice completely, but more rapid Ab response was observed when IC31 was given with the Pnc1-TT. IC31 is a promising new adjuvant for neonatal vaccinations, rapidly enhancing protective humoral responses when combined with Pnc1-TT.

Efficacy of opsonic and nonopsonic serotype 3 pneumococcal capsular polysaccharide-specific monoclonal antibodies against intranasal challenge with Streptococcus pneumoniae in mice

Serotype-specific antibodies to pneumococcal capsular polysaccharide (PPS) are a critical component of vaccine-mediated immunity to Streptococcus pneumoniae. In this study, we investigated the in vitro opsonophagocytic activities of three PPS-specific mouse immunoglobulin G1 monoclonal antibodies (MAbs), 1E2, 5F6, and 7A9, and determined their in vivo efficacies against intranasal challenge with WU2, a serotype 3 pneumococcal strain, in normal and immunodeficient mice. The MAbs had different in vitro activities in a pneumococcal killing assay: 7A9 enhanced killing by mouse neutrophils and J774 cells in the presence of a complement source, whereas 5F6 promoted killing in the absence, but not the presence, of complement, and 1E2 did not promote killing under any conditions. Nonetheless, all three MAbs protected normal and complement component 3-deficient mice from a lethal intranasal challenge with WU2 in passive-immunization experiments in which 10 mug of the MAbs were administered intraperitoneally before intranasal challenge. In contrast, only 1E2 protected Fcgamma receptor IIB knockout (FcgammaRIIB KO) mice and mice that were depleted of neutrophils with the MAb RB6, whereas 7A9 and 5F6 required neutrophils and FcgammaRIIB to mediate protection. Conversely, 7A9 and 5F6 protected FcgammaR KO mice, but 1E2 did not. Hence, the efficacy of 1E2 required an activating FcgammaR(s), whereas 5F6 and 7A9 required the inhibitory FcgammaR (FcgammaRIIB). Taken together, our data demonstrate that both MAbs that do and do not promote pneumococcal killing in vitro can mediate protection in vivo, although their efficacies depend on different host receptors and/or components.

Complete genome sequence of the N2-fixing broad host range endophyte Klebsiella pneumoniae 342 and virulence predictions verified in mice

We report here the sequencing and analysis of the genome of the nitrogen-fixing endophyte, Klebsiella pneumoniae 342. Although K. pneumoniae 342 is a member of the enteric bacteria, it serves as a model for studies of endophytic, plant-bacterial associations due to its efficient colonization of plant tissues (including maize and wheat, two of the most important crops in the world), while maintaining a mutualistic relationship that encompasses supplying organic nitrogen to the host plant. Genomic analysis examined K. pneumoniae 342 for the presence of previously identified genes from other bacteria involved in colonization of, or growth in, plants. From this set, approximately one-third were identified in K. pneumoniae 342, suggesting additional factors most likely contribute to its endophytic lifestyle. Comparative genome analyses were used to provide new insights into this question. Results included the identification of metabolic pathways and other features devoted to processing plant-derived cellulosic and aromatic compounds, and a robust complement of transport genes (15.4%), one of the highest percentages in bacterial genomes sequenced. Although virulence and antibiotic resistance genes were predicted, experiments conducted using mouse models showed pathogenicity to be attenuated in this strain. Comparative genomic analyses with the presumed human pathogen K. pneumoniae MGH78578 revealed that MGH78578 apparently cannot fix nitrogen, and the distribution of genes essential to surface attachment, secretion, transport, and regulation and signaling varied between each genome, which may indicate critical divergences between the strains that influence their preferred host ranges and lifestyles (endophytic plant associations for K. pneumoniae 342 and presumably human pathogenesis for MGH78578). Little genome information is available concerning endophytic bacteria. The K. pneumoniae 342 genome will drive new research into this less-understood, but important category of bacterial-plant host relationships, which could ultimately enhance growth and nutrition of important agricultural crops and development of plant-derived products and biofuels.

Characterization of Klebsiella pneumoniae type 1 fimbriae by detection of phase variation during colonization and infection and impact on virulence

Klebsiella pneumoniae is recognized as an important gram-negative opportunistic pathogen. The ability of bacteria to adhere to host structures is considered essential for the development of infections; however, few studies have examined the influence of adhesion factors on K. pneumoniae virulence. In this study, we cloned and characterized the type 1 fimbria gene cluster of a clinical K. pneumoniae isolate. Although this cluster was not identical to the Escherichia coli type 1 fimbria gene cluster, an overall high degree of structural resemblance was demonstrated. Unique to the K. pneumoniae fim gene cluster is the fimK gene, whose product contains an EAL domain, suggesting that it has a role in regulation of fimbrial expression. Like expression of type 1 fimbriae in E. coli, expression of type 1 fimbriae in K. pneumoniae was found to be phase variable, and an invertible DNA element (fim switch) was characterized. An isogenic type 1 fimbria mutant was constructed and used to evaluate the influence of type 1 fimbriae in different infection models. Type 1 fimbriae did not influence the ability of K. pneumoniae to colonize the intestine or infect the lungs, but they were determined to be a significant virulence factor in K. pneumoniae urinary tract infection. By use of a PCR-based assay, the orientation of the fim switch during colonization and infection was investigated and was found to be all "off" in the intestine and lungs but all "on" in the urinary tract. Our results suggest that during colonization and infection, there is pronounced selective pressure in different host environments for selection of either the type 1 fimbriated or nonfimbriated phenotype of K. pneumoniae.

Functional antibodies elicited by two heptavalent pneumococcal conjugate vaccines in the Finnish Otitis Media Vaccine Trial

In the Finnish Otitis Media Vaccine Trial, the now-licensed pneumococcal conjugate vaccine containing polysaccharides conjugated to protein CRM(197) (PncCRM) and the experimental pneumococcal polysaccharide-meningococcal outer membrane protein complex conjugate vaccine (PncOMPC), showed similar efficacy profiles against acute otitis media despite different antibody concentrations in sera. We now report the opsonophagocytic activities (OPA) in these sera. OPA, antibody concentration, and avidity for serotypes 6B, 19F, and 23F were determined in sera of infants who received either pneumococcal conjugate (PCV) or control vaccine at 2, 4, and 6 months of age and either the homologous or pneumococcal polysaccharide vaccine at 12 months of age. OPA varied by vaccine and serotype. The majority of PCV recipients had positive OPA after the fourth dose, while OPA was undetectable in the control group. Coinciding with the efficacy data, the concentration of antibodies required for 50% killing was low for 6B and high for 19F for both PCVs. Contradictory to the efficacy data, PncOMPC induced lower functional capacity to 23F than PncCRM. OPA correlated with antibody concentration, while avidity and functional capacity of antibodies showed no correlation. The OPA data provide valuable additional information for serotype-specific differences in protection and when evaluating serotype-specific immunogenicity and should thus be considered when defining serological correlates of protection.

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

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

Type-specific antibodies to pneumococcal capsular polysaccharide acquired either naturally or after vaccination with Prevenar in children with underlying chronic or recurrent lung diseases

The antibody response to capsular polysaccharides of pneumococcal serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F elicited either naturally or after vaccination with Prevenar was investigated in a cohort of children (n = 163) with underlying chronic or recurrent lung diseases at risk of developing pneumococcal pneumonia and ultimately invasive disease. Serum concentrations of serotype-specific antibodies, as measured by enzyme-linked immunosorbent assay, in unvaccinated children (n = 88) were higher in nasopharyngeal carriers (n = 10) than in noncarriers (n = 78) both at baseline and during follow-up. However, the antibody levels depended on the serotype and age of the children. During the study period, 35% of unvaccinated noncarriers and 60% of unvaccinated carriers displayed serum antibodies to all serotypes above the reported WHO working group putative protective serum concentration against invasive disease (0.2 mug/ml). Overall, children vaccinated with Prevenar before enrollment (n = 61), irrespective of their carrier status, displayed significantly higher serum levels of antibodies to all serotypes than unvaccinated children. More than 85% of the vaccinated children had protective serum antibody concentrations at baseline; although antibody titers tended to decrease over time, the above-mentioned figure remained without change at the end of follow-up. The vaccine Prevenar elicited a significant rise in serum antibody concentrations against all serotypes in 14 children vaccinated at entry. All of these children acquired and maintained serum antibody levels of >0.2 microg/ml throughout the study (a mean of 13 months of follow-up). These data support the systematic use of the vaccine Prevenar in children with underlying chronic or recurrent lung diseases and stress the fact that a percentage of vaccinated children may need to be revaccinated in order to achieve protection against pneumococcal disease.

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.

Modulation of the lung inflammatory response to serotype 8 pneumococcal infection by a human immunoglobulin m monoclonal antibody to serotype 8 capsular polysaccharide

The human monoclonal antibody to serotype 8 pneumococcal capsular polysaccharide D11 [immunoglobulin M(kappa)] protects wild-type and complement component 4 knockout (C4 KO) mice against lethal intratracheal challenge with serotype 8 pneumococcus, but it does not promote polymorphonuclear leukocyte (PMN)-mediated pneumococcal killing in vitro. In this study, we investigated the effect of D11 on the blood and lung bacterial burdens and the serum and lung expression of inflammatory chemokines and cytokines in an intratracheal challenge model with serotype 8 pneumococcus in C4 KO mice. Pneumococcus was not detected in the blood of D11-treated mice, whereas control mice had high-grade bacteremia with >10(7) CFU. Control mice had a >5-log increase in lung CFU and D11-treated mice manifested a nearly 3-log increase in lung CFU compared to the original inoculum 24 h after infection. Serum and lung levels of soluble macrophage inflammatory protein 2 (MIP-2) and interleulin-6 (IL-6) as measured by an enzyme-linked immunosorbent assay were lower in D11-treated mice than in control mice 24 h after infection. Real-time PCR was performed to examine lung mRNA chemokine and cytokine expression. The results showed that D11-treated mice had significantly less gamma interferon, MIP-2, IL-12, monocyte chemoattractant protein 1/JE, and tumor necrosis factor alpha expression than control mice 24 h after infection. Histopathology and immunohistochemical staining of lung tissues revealed that D11-treated mice had less inflammation, fewer PMNs, and less myeloperoxidase staining than control mice 24 h after infection. These findings suggest that the efficacy of certain serotype-specific antibodies against pneumococcal pneumonia could be associated with modulation of the lung inflammatory response and a reduction in host damage.

Protective levels of polysaccharide-specific maternal antibodies may enhance the immune response elicited by pneumococcal conjugates in neonatal and infant mice

Maternal antibodies (MatAbs) may protect the offspring against infections but may also interfere with their immune responses to vaccination. We have previously shown that maternal immunization with pneumococcal polysaccharides (PPS) conjugated to tetanus protein (Pnc-TT) protected the offspring against infections caused by three important pediatric serotypes. To study the influence of MatAb on the immune response to Pnc-TT early in life, adult female mice were immunized twice with Pnc-TT of serotype 1 (Pnc1-TT), and their offspring received Pnc1-TT subcutaneously three times at 3-week intervals starting at 1 week (neonatal) or 3 weeks (infant) of age. High levels of PPS-1-specific MatAb (>3 log) in offspring of Pnc1-TT-immunized dams completely inhibited their anti-PPS-1 response elicited by Pnc1-TT. In contrast, low or moderate ( approximately 1 to 2 log) levels of MatAb did not interfere with and even enhanced the immune response of the offspring, and a booster response to a second Pnc1-TT dose was observed. Carrier-specific MatAbs had little effect on the response of offspring to the conjugate. All Pnc1-TT-immunized offspring were protected against pneumococcal bacteremia and had reduced lung infection. These results demonstrate that in the presence of MatAb, Pnc1-TT may elicit a protective PPS-1-specific antibody response and prime for PPS-1-specific memory in young offspring. Importantly, low or moderate levels of PPS-1-specific MatAb not only provided protection against pneumococcal infections but also enhanced the immune response elicited by Pnc1-TT in neonatal and infant mice. This murine model will be used to develop novel strategies combining maternal and neonatal immunization to protect against infections caused by encapsulated bacteria in early life.

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.

Immunogenicity and efficacy of Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan peptide mimotope-protein conjugates in human immunoglobulin transgenic mice

Peptide mimotopes of capsular polysaccharides have been proposed as antigens for vaccines against encapsulated pathogens. In this study, we determined the antibody response to and efficacy of P13, a peptide mimetic of the Cryptococcus neoformans capsular polysaccharide glucuronoxylomannan (GXM), in mice that produce human antibodies. P13 was conjugated to tetanus toxoid (TT) or diphtheria toxoid (DT) and administered subcutaneously in Alhydrogel with or without CpG to mice transgenic for human immunoglobulin loci (XenoMouse mice) and expressing either immunoglobulin G2 (IgG2) (G2 mice) or IgG4 (G4 mice). Mice were vaccinated and revaccinated two or three times. The serum antibody responses of the mice to GXM and P13 and antibody idiotype expression were analyzed by an enzyme-linked immunosorbent assay. The results showed that both P13-TT and P13-DT were antigenic, inducing a mimetic response to P13 in both G2 and G4 mice, and immunogenic, inducing a mimotope response including VH3 (idiotype)-positive antibodies to GXM in G2 but not G4 mice. CpG led to higher titers of IgG to P13 and GXM in P13-TT-vaccinated G2 mice. C. neoformans challenge of P13-protein conjugate-vaccinated and control G2 mice induced anamnestic IgG- and VH3-positive responses to GXM and was associated with a significantly decreased risk of death and a prolongation of survival in P13-DT-vaccinated mice compared to phosphate-buffered saline-treated or protein carrier-vaccinated mice. These findings reveal that P13 elicited a human antibody response with VH3 expression in human immunoglobulin transgenic mice that has been observed for human antibodies to GXM and support the concept that peptide mimotope-based vaccines may hold promise for the treatment of C. neoformans infections.

Immunization of female mice with glycoconjugates protects their offspring against encapsulated bacteria

The immune system of the newborn is immature, and therefore it is difficult to induce protective immunity by vaccination in the neonatal period. Immunization of mothers during pregnancy against infections caused by encapsulated bacteria could thus be particularly attractive, as infants do not respond to polysaccharide (PS) antigens. Transmission of maternal vaccine-specific antibodies and protection of offspring against pneumococcal bacteremia and/or lung infection were studied in a neonatal murine model of pneumococcal immunization and infections. Adult female mice were immunized with native pneumococcal PS (PPS) of serotypes 1, 6B, and 19F or PPS conjugated to tetanus protein (Pnc-TT), and PPS-specific antibodies were measured in sera of mothers and their offspring. Effective transmission of maternal antibodies was observed, as PPS-specific immunoglobulin G levels in 3-week-old offspring of immunized mothers were 37 to 322% of maternal titers, and a significant correlation between maternal and offspring antibody levels was observed. The PPS-specific antibodies persisted for several weeks but slowly decreased over time. Offspring of Pnc-TT-immunized mothers were protected against pneumococcal infections with homologous serotypes, whereas PPS immunization of mothers did not protect their offspring, in agreement with the low titer of maternal PPS specific antibodies. When adult female mice were immunized with a meningococcal serogroup C conjugate vaccine (MenC-CRM), antibody response and transmission were similar to those observed for pneumococcal antibodies. Importantly, bactericidal activity was demonstrated in offspring of MenC-CRM-immunized mothers. These results demonstrate that this murine model of pneumococcal immunization and infections is suitable to study maternal immunization strategies for protection of offspring against encapsulated bacteria.

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.

Central role of complement in passive protection by human IgG1 and IgG2 anti-pneumococcal antibodies in mice

Streptococcus pneumoniae is an important cause of morbitity and mortality worldwide. Capsule-specific IgG1 and IgG2 Abs are induced upon vaccination with polysaccharide-based vaccines that mediate host protection. We compared the protective capacity of human recombinant serogroup 6-specific IgG1 and IgG2 Abs in mice deficient for either leukocyte FcR or complement factors. Human IgG1 was found to interact with mouse leukocyte FcR in vitro, whereas human IgG2 did not. Both subclasses induced complement activation, resulting in C3c deposition on pneumococcal surfaces. Passive immunization of C57BL/6 mice with either subclass before intranasal challenge with serotype 6A induced similar degrees of protection. FcgammaRI- and III-deficient mice, as well as the combined FcgammaRI, II, and III knockout mice, were protected by passive immunization, indicating FcR not to be essential for protection. C1q or C2/factor B knockout mice, however, were not protected by passive immunization. Passively immunized C2/factor B(-/-) mice displayed higher bacteremic load than C1q(-/-) mice, supporting an important protective role of the alternative complement pathway. Spleens from wild-type and C1q(-/-) mice showed hyperemia and thrombotic vessel occlusion, as a result of septicemic shock. Notably, thrombus formation was absent in spleens of C2/factor B(-/-) mice, suggesting that the alternative complement pathway contributes to shock-induced intravascular coagulation. These studies demonstrate complement to play a central role in Ab-mediated protection against pneumococcal infection in vivo, as well as in bacteremia-associated thrombotic complications.

Pneumococcal serotype 19F conjugate vaccine induces cross-protective immunity to serotype 19A in a murine pneumococcal pneumonia model

Immunization with a pneumococcal conjugate vaccine (PNC) containing serotype 19F induces cross-reactive antibodies to 19A in mice and human infants. Active immunization with PNC and passive immunization with serum samples from infants vaccinated with PNC containing serotype 19F, but not serotype 19A, protected against lung infection caused by both serotypes in a murine model.

Population-based surveillance for hospitalized and ambulatory pediatric invasive pneumococcal disease in Santiago, Chile

BACKGROUND

Nine- and 11-valent pneumococcal conjugate vaccines under development may control pediatric pneumococcal disease in nonindustrialized countries. Because these vaccines are expensive, population-based surveillance of pneumococcal disease in children <36 months of age was undertaken in Santiago, Chile to provide health authorities with reliable data on the burden of invasive pneumococcal disease and causative serotypes, including those in outpatients with high fever.

METHODS

Automated blood culture machines were introduced into 9 hospitals that admit 85% of all hospitalized children in Santiago. Acutely ill pediatric febrile ambulatory patients are attended at 8 emergency rooms (ERs) and 36 urgent primary care services. After a 12-month pilot study in 3 ERs, health authorities collected blood cultures from children <36 months of age with high fever seen in the ER as standard practice. isolates were serotyped.

RESULTS

Blood cultures of 18 (1.2%) of 1,503 outpatients 6 to 35 months of age with high fever in the pilot study yielded S. In the ensuing 24 months 236 children <36 months old were hospitalized with invasive pneumococcal disease (incidence, 33.9 cases/10(5) children), and 188 bacteremias were detected among ambulatory ER patients with high fever (incidence, 27.0 cases/10(5) children). Although serotypes were similar among hospitalized and ambulatory cases (except 18C, which was more common in the latter), case fatality was 9.5% in hospitalized (21 of 236) 0% in ambulatory cases (0 of 188) (P = <0.0001). High level resistance to penicillin (25.8% vs 10.1%) and cefotaxime (19.5% vs 6.2%) was observed more often among pneumococcal isolates from hospitalized than among ambulatory cases (P < 0.001).

CONCLUSIONS

ER surveillance detected approximately one case of pneumococcal bacteremia among febrile ambulatory patients for each hospitalized invasive case. Because 71% of cases were caused by vaccine serotypes (and 87% by vaccine serogroups), 9- and 11-valent pneumococcal conjugate vaccines could prevent most invasive pediatric pneumococcal disease in Chile.

Effectiveness of heptavalent pneumococcal conjugate vaccine in children younger than five years of age for prevention of pneumonia

OBJECTIVE

To determine the effectiveness of the Wyeth heptavalent pneumococcal conjugate vaccine against clinical and radiograph-confirmed pneumonia in children.

METHODS

The heptavalent CRM(197) pneumococcal conjugate vaccine (PCV) was given to infants at 2, 4, 6 and 12 to 15 months of age in a randomized, double blind trial. Children were randomized to receive either the CRM(197) PCV (vaccine group) or the meningococcal type C CRM(197) conjugate vaccine (control group). The primary outcome of this trial was invasive pneumococcal disease. In addition children with the clinical diagnosis of pneumonia in the study population were identified through review of automated inpatient, emergency and outpatient databases. The subset of the cohort of these children who had chest radiographs obtained at the time of diagnosis was identified, and the original reading of their radiographs by the radiologist was obtained from automated databases. Rates of clinically diagnosed pneumonia, of pneumonia with a radiograph obtained regardless of result, of pneumonia with positive radiograph (consolidation, empyema or parenchymal infiltrate) and of pneumonia with only perihilar infiltrates were compared between vaccinated and nonvaccinated groups. In addition risk of disease pneumonia was evaluated by race and ethnicity.

RESULTS

The incidence of a first pneumonia episode in the control group was 55.9 per 1000 person-years. A radiograph was obtained in 61% of episodes, a positive radiograph in 21% and perihilar findings in an additional 5%. In per protocol follow-up of children given PCV, first episodes of all clinically diagnosed pneumonia were reduced by 4.3% [95% confidence interval (CI), -3.5, 11.5%, = 0.27], episodes with a radiograph were reduced by 9.8% (CI 0.1, 18.5%, < 0.05) and episodes with a positive radiograph were reduced by 20.5% (CI 4.4, 34.0, = 0.02). In the intent to treat analysis including all episodes after randomization, episodes with a positive radiograph were reduced by 17.7%, =.01). The greatest impact was in the first year of life with a 32.2% reduction and a 23.4% reduction in the first 2 years, but only a 9.1% reduction in children >2 years of age. Asians, blacks and Hispanics were at higher risk of pneumonia than were whites, but there was no evidence of ethnic variation in PCV effectiveness. Ten of the 11 cases of pneumococcal pneumonia with a positive blood culture were in the control group.

CONCLUSION

The pneumococcal conjugate vaccine tested was effective in reducing the risk of pneumonia in young children.

Intranasal immunization with pneumococcal conjugate vaccines with LT-K63, a nontoxic mutant of heat-Labile enterotoxin, as adjuvant rapidly induces protective immunity against lethal pneumococcal infections in neonatal mice

Immunization with pneumococcal polysaccharides (PPS) conjugated to tetanus toxoid (TT) (Pnc-TT) elicits protective immunity in an adult murine pneumococcal infection model. To assess immunogenicity and protective immunity in early life, neonatal (1 week old) and infant (3 weeks old) mice were immunized intranasally (i.n.) or subcutaneously (s.c.) with Pnc-TT of serotype 1 (Pnc1-TT). Anti-PPS-1 and anti-TT immunoglobulin G (IgG) and IgM antibodies were measured in serum and saliva, and vaccine-induced protection was evaluated by i.n. challenge with serotype 1 pneumococci. Pnc1-TT was immunogenic in neonatal and infant mice when administered s.c. without adjuvant: a majority of the young mice were protected from bacteremia and a reduction of pneumococcal density in the lungs was observed, although antibody responses and protective efficacy remained lower than in adults. The addition of LT-K63, a nontoxic mutant of heat-labile enterotoxin, as adjuvant significantly enhanced PPS-1-specific IgG responses and protective efficacy following either s.c. or i.n. Pnc1-TT immunization. Mucosal immunization was particularly efficient in neonates, as a single i.n. dose of Pnc1-TT and LT-K63 induced significantly higher PPS-1-specific IgG responses than s.c. immunization and was sufficient to protect neonatal mice against pneumococcal infections, whereas two s.c. doses were required to induce complete protection. In addition, i.n. immunization with Pnc1-TT and LT-K63 induced a vigorous salivary IgA response. This suggests that mucosal immunization with pneumococcal conjugate vaccines and LT-K63 may be able to circumvent some of the limitations of neonatal antibody responses, which are required for protective immunity in early life.